hepatocyte nuclear factor 4, alpha
|Classification||Homo sapiens » Zinc-coordinating Group » Hormone-nuclear Receptor Family » Subfamily 2 (HNF4, RXR, TR2/4, DHR78, TLL, COUP-TF and EAR2, NR2A2/3, and 19 individual genes)|
|Related TF(s)|| • Hnf4a |
|Homologs ||(none defined here)|
|Links||ENSG00000101076 (Ensembl) 3172 (Entrez Gene) Homologene 606391, 600281, 125853, 125850 (OMIM)|
|Synonyms||TCF14, TCF, NR2A21, NR2A1, MODY, MODY1, HNF4alpha, HNF4a9, HNF4a8, HNF4a7, HNF4, FLJ39654|
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- (2010) Bolotin E, Liao H, Ta TC, Yang C, Hwang-Verslues W, Evans JR, Jiang T, Sladek FM. Integrated approach for the identification of human hepatocyte nuclear factor 4alpha target genes using protein binding microarrays. Hepatology, 51(2):642-53.
Hepatocyte nuclear factor 4 alpha (HNF4alpha), a member of the nuclear receptor superfamily, is essential for liver function and is linked to several diseases including diabetes, hemophilia, atherosclerosis, and hepatitis. Although many DNA response elements and target genes have been identified for HNF4alpha, the complete repertoire of binding sites and target genes in the human genome is unknown. Here, we adapt protein binding microarrays (PBMs) to examine the DNA-binding characteristics of two HNF4alpha species (rat and human) and isoforms (HNF4alpha2 and HNF4alpha8) in a high-throughput fashion. We identified approximately 1400 new binding sequences and used this dataset to successfully train a Support Vector Machine (SVM) model that predicts an additional approximately 10,000 unique HNF4alpha-binding sequences; we also identify new rules for HNF4alpha DNA binding. We performed expression profiling of an HNF4alpha RNA interference knockdown in HepG2 cells and compared the results to a search of the promoters of all human genes with the PBM and SVM models, as well as published genome-wide location analysis. Using this integrated approach, we identified approximately 240 new direct HNF4alpha human target genes, including new functional categories of genes not typically associated with HNF4alpha, such as cell cycle, immune function, apoptosis, stress response, and other cancer-related genes. CONCLUSION: We report the first use of PBMs with a full-length liver-enriched transcription factor and greatly expand the repertoire of HNF4alpha-binding sequences and target genes, thereby identifying new functions for HNF4alpha. We also establish a web-based tool, HNF4 Motif Finder, that can be used to identify potential HNF4alpha-binding sites in any sequence.
- (2009) Yuan X, Ta TC, Lin M, Evans JR, Dong Y, Bolotin E, Sherman MA, Forman BM, Sladek FM. Identification of an endogenous ligand bound to a native orphan nuclear receptor. PLoS ONE, 4(5):e5609.
Orphan nuclear receptors have been instrumental in identifying novel signaling pathways and therapeutic targets. However, identification of ligands for these receptors has often been based on random compound screens or other biased approaches. As a result, it remains unclear in many cases if the reported ligands are the true endogenous ligands,--i.e., the ligand that is bound to the receptor in an unperturbed in vivo setting. Technical limitations have limited our ability to identify ligands based on this rigorous definition. The orphan receptor hepatocyte nuclear factor 4 alpha (HNF4alpha) is a key regulator of many metabolic pathways and linked to several diseases including diabetes, atherosclerosis, hemophilia and cancer. Here we utilize an affinity isolation/mass-spectrometry (AIMS) approach to demonstrate that HNF4alpha is selectively occupied by linoleic acid (LA, C18:2omega6) in mammalian cells and in the liver of fed mice. Receptor occupancy is dramatically reduced in the fasted state and in a receptor carrying a mutation derived from patients with Maturity Onset Diabetes of the Young 1 (MODY1). Interestingly, however, ligand occupancy does not appear to have a significant effect on HNF4alpha transcriptional activity, as evidenced by genome-wide expression profiling in cells derived from human colon. We also use AIMS to show that LA binding is reversible in intact cells, indicating that HNF4alpha could be a viable drug target. This study establishes a general method to identify true endogenous ligands for nuclear receptors (and other lipid binding proteins), independent of transcriptional function, and to track in vivo receptor occupancy under physiologically relevant conditions.
- (2004) Odom DT, Zizlsperger N, Gordon DB, Bell GW, Rinaldi NJ, Murray HL, Volkert TL, Schreiber J, Rolfe PA, Gifford DK, Fraenkel E, Bell GI, Young RA. Control of pancreas and liver gene expression by HNF transcription factors. Science, 303(5662):1378-81.
The transcriptional regulatory networks that specify and maintain human tissue diversity are largely uncharted. To gain insight into this circuitry, we used chromatin immunoprecipitation combined with promoter microarrays to identify systematically the genes occupied by the transcriptional regulators HNF1alpha, HNF4alpha, and HNF6, together with RNA polymerase II, in human liver and pancreatic islets. We identified tissue-specific regulatory circuits formed by HNF1alpha, HNF4alpha, and HNF6 with other transcription factors, revealing how these factors function as master regulators of hepatocyte and islet transcription. Our results suggest how misregulation of HNF4alpha can contribute to type 2 diabetes.
- (2001) Hayhurst GP, Lee YH, Lambert G, Ward JM, Gonzalez FJ. Hepatocyte nuclear factor 4alpha (nuclear receptor 2A1) is essential for maintenance of hepatic gene expression and lipid homeostasis. Mol. Cell. Biol., 21(4):1393-403.
The numerous functions of the liver are controlled primarily at the transcriptional level by the concerted actions of a limited number of hepatocyte-enriched transcription factors (hepatocyte nuclear factor 1alpha [HNF1alpha], -1beta, -3alpha, -3beta, -3gamma, -4alpha, and -6 and members of the c/ebp family). Of these, only HNF4alpha (nuclear receptor 2A1) and HNF1alpha appear to be correlated with the differentiated phenotype of cultured hepatoma cells. HNF1alpha-null mice are viable, indicating that this factor is not an absolute requirement for the formation of an active hepatic parenchyma. In contrast, HNF4alpha-null mice die during embryogenesis. Moreover, recent in vitro experiments using tetraploid aggregation suggest that HNF4alpha is indispensable for hepatocyte differentiation. However, the function of HNF4alpha in the maintenance of hepatocyte differentiation and function is less well understood. To address the function of HNF4alpha in the mature hepatocyte, a conditional gene knockout was produced using the Cre-loxP system. Mice lacking hepatic HNF4alpha expression accumulated lipid in the liver and exhibited greatly reduced serum cholesterol and triglyceride levels and increased serum bile acid concentrations. The observed phenotypes may be explained by (i) a selective disruption of very-low-density lipoprotein secretion due to decreased expression of genes encoding apolipoprotein B and microsomal triglyceride transfer protein, (ii) an increase in hepatic cholesterol uptake due to increased expression of the major high-density lipoprotein receptor, scavenger receptor BI, and (iii) a decrease in bile acid uptake to the liver due to down-regulation of the major basolateral bile acid transporters sodium taurocholate cotransporter protein and organic anion transporter protein 1. These data indicate that HNF4alpha is central to the maintenance of hepatocyte differentiation and is a major in vivo regulator of genes involved in the control of lipid homeostasis.
- (1996) Yamagata K, Furuta H, Oda N, Kaisaki PJ, Menzel S, Cox NJ, Fajans SS, Signorini S, Stoffel M, Bell GI. Mutations in the hepatocyte nuclear factor-4alpha gene in maturity-onset diabetes of the young (MODY1) Nature, 384(6608):458-60.
The disease maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic form of non-insulin-dependent (type 2) diabetes mellitus (NIDDM), characterized by early onset, usually before 25 years of age and often in adolescence or childhood, and by autosomal dominant inheritance. It has been estimated that 2-5% of patients with NIDDM may have this form of diabetes mellitus. Clinical studies have shown that prediabetic MODY subjects have normal insulin sensitivity but suffer from a defect in glucose-stimulated insulin secretion, suggesting that pancreatic beta-cell dysfunction rather than insulin resistance is the primary defect in this disorder. Linkage studies have localized the genes that are mutated in MODY on human chromosomes 20 (MODY1), 7 (MODY2) and 12 (MODY3), with MODY2 and MODY3 being allelic with the genes encoding glucokinase, a key regulator of insulin secretion, and hepatocyte nuclear factor-1alpha (HNF-1alpha), a transcription factor involved in tissue-specific regulation of liver genes but also expressed in pancreatic islets, insulinoma cells and other tissues. Here we show that MODY1 is the gene encoding HNF-4alpha (gene symbol, TCF14), a member of the steroid/thyroid hormone receptor superfamily and an upstream regulator of HNF-1alpha expression.
- (1990) Sladek FM, Zhong WM, Lai E, Darnell JE. Liver-enriched transcription factor HNF-4 is a novel member of the steroid hormone receptor superfamily. Genes Dev., 4(12B):2353-65.
HNF-4 (hepatocyte nuclear factor 4) is a protein enriched in liver extracts that binds to sites required for the transcription of the genes for transthyretin (TTR), the carrier protein in the serum for vitamin A and thyroid hormone, and for apolipoprotein CIII (apoCIII), a major constituent of chylomicrons and very low-density lipoproteins (VLDL). Synthetic oligonucleotides derived from amino acid sequence of affinity-purified HNF-4 protein (54 kD) were used in the polymerase chain reaction (PCR) to isolate a cDNA clone encoding the protein. HNF-4 is a member of the steroid hormone receptor superfamily with an unusual amino acid in the conserved "knuckle" of the first zinc finger (DGCKG). Studies with in vitro-translated HNF-4 protein show that it binds to its recognition site as a dimer, and cotransfection assays indicate that it activates transcription in a sequence-specific fashion in nonhepatic (HeLa) cells. Northern blot analysis reveals that HNF-4 mRNA is present in kidney and intestine, as well as liver, but is absent in other tissues. DNA-binding and antisera reactivity data suggest that HNF-4 could be identical to liver factor A1 (LF-A1), a DNA-binding activity implicated in the regulation of transcription of the alpha 1-antitrypsin, apolipoprotein A1, and pyruvate kinase genes. The similarity between HNF-4 and other ligand-dependent transcription factors raises the possibility that HNF-4 and the genes it regulates respond to an as yet unidentified ligand.
review article (2009) Waxman DJ, Holloway MG. Sex differences in the expression of hepatic drug metabolizing enzymes. Mol. Pharmacol., 76(2):215-28.
Sex differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Sex-based differences in drug metabolism are the primary cause of sex-dependent pharmacokinetics and reflect underlying sex differences in the expression of hepatic enzymes active in the metabolism of drugs, steroids, fatty acids and environmental chemicals, including cytochromes P450 (P450s), sulfotransferases, glutathione transferases, and UDP-glucuronosyltransferases. Studies in the rat and mouse liver models have identified more than 1000 genes whose expression is sex-dependent; together, these genes impart substantial sexual dimorphism to liver metabolic function and pathophysiology. Sex differences in drug metabolism and pharmacokinetics also occur in humans and are due in part to the female-predominant expression of CYP3A4, the most important P450 catalyst of drug metabolism in human liver. The sexually dimorphic expression of P450s and other liver-expressed genes is regulated by the temporal pattern of plasma growth hormone (GH) release by the pituitary gland, which shows significant sex differences. These differences are most pronounced in rats and mice, where plasma GH profiles are highly pulsatile (intermittent) in male animals versus more frequent (nearly continuous) in female animals. This review discusses key features of the cell signaling and molecular regulatory mechanisms by which these sex-dependent plasma GH patterns impart sex specificity to the liver. Moreover, the essential role proposed for the GH-activated transcription factor signal transducer and activator of transcription (STAT) 5b, and for hepatic nuclear factor (HNF) 4alpha, as mediators of the sex-dependent effects of GH on the liver, is evaluated. Together, these studies of the cellular, molecular, and gene regulatory mechanisms that underlie sex-based differences in liver gene expression have provided novel insights into the physiological regulation of both xenobiotic and endobiotic metabolism.
review article (2008) Gonzalez FJ. Regulation of hepatocyte nuclear factor 4 alpha-mediated transcription. Drug Metab. Pharmacokinet., 23(1):2-7.
Hepatocyte nuclear factor 4alpha (HNF4alpha, NR2A1) is required for development of the liver and for controlling the expression of many genes specifically expressed in the liver and associated with a number of critical metabolic pathways. Among the genes regulated by HNF4alpha are the xenobiotic-metabolizing cytochromes P450, UDP-glucuronosyltransferases and sulfotransferases thus making this transcription factor critical in the control of drug metabolism. HNF4alpha, a member of the nuclear receptor superfamily, binds as a homodimer to direct repeat elements upstream of target genes. However, in contrast to many other nuclear receptors, there is no convincing evidence that HNF4alpha is activated by exogenous ligands, at least in the classic mechanism used by other steroid and metabolic nuclear receptors. X-ray crystallographic studies revealed that HNF4alpha has a fatty acid embedded in its putative ligand binding site that may not be easily released or displaced by exogenous ligands. HNF4alpha, as a general rule, controls constitutive expression of many hepatic genes but under certain circumstances can be subjected to regulation by differential co-activator recruitment, by phosphorylation and by interaction with other nuclear receptors. The ability of HNF4alpha to be regulated offers hope that it could be a drug target.
- (2008) Harries LW, Locke JM, Shields B, Hanley NA, Hanley KP, Steele A, Njølstad PR, Ellard S, Hattersley AT. The diabetic phenotype in HNF4A mutation carriers is moderated by the expression of HNF4A isoforms from the P1 promoter during fetal development. Diabetes, 57(6):1745-52.
OBJECTIVE: Mutations in the alternatively spliced HNF4A gene cause maturity-onset diabetes of the young (MODY). We characterized the spatial and developmental expression patterns of HNF4A transcripts in human tissues and investigated their role as potential moderators of the MODY phenotype. RESEARCH DESIGN AND METHODS: We measured the expression of HNF4A isoforms in human adult tissues and gestationally staged fetal pancreas by isoform-specific real-time PCR. The correlation between mutation position and age of diagnosis or age-related penetrance was assessed in a cohort of 190 patients with HNF4A mutations. RESULTS: HNF4A was expressed exclusively from the P2 promoter in adult pancreas, but from 9 weeks until at least 26 weeks after conception, up to 23% of expression in fetal pancreas was of P1 origin. HNF4A4-6 transcripts were not detected in any tissue. In whole pancreas, HNF4A9 expression was greater than in islets isolated from the endocrine pancreas (relative level 22 vs. 7%). Patients with mutations in exons 9 and 10 (absent from HNF4A3, HNF4A6, and HNF4A9 isoforms) developed diabetes later than those with mutations in exons 2-8, where all isoforms were affected (40 vs. 24 years; P = 0.029). Exon 9/10 mutations were also associated with a reduced age-related penetrance (53 vs. 10% without diabetes at age 55 years; P < 0.00001). CONCLUSIONS: We conclude that isoforms derived from the HNF4A P1 promoter are expressed in human fetal, but not adult, pancreas, and that their presence during pancreatic development may moderate the diabetic phenotype in individuals with mutations in the HNF4A gene.
- (2007) Gupta RK, Gao N, Gorski RK, White P, Hardy OT, Rafiq K, Brestelli JE, Chen G, Stoeckert CJ, Kaestner KH. Expansion of adult beta-cell mass in response to increased metabolic demand is dependent on HNF-4alpha. Genes Dev., 21(7):756-69.
The failure to expand functional pancreatic beta-cell mass in response to increased metabolic demand is a hallmark of type 2 diabetes. Lineage tracing studies indicate that replication of existing beta-cells is the principle mechanism for beta-cell expansion in adult mice. Here we demonstrate that the proliferative response of beta-cells is dependent on the orphan nuclear receptor hepatocyte nuclear factor-4alpha (HNF-4alpha), the gene that is mutated in Maturity-Onset Diabetes of the Young 1 (MODY1). Computational analysis of microarray expression profiles from isolated islets of mice lacking HNF-4alpha in pancreatic beta-cells reveals that HNF-4alpha regulates selected genes in the beta-cell, many of which are involved in proliferation. Using a physiological model of beta-cell expansion, we show that HNF-4alpha is required for beta-cell replication and the activation of the Ras/ERK signaling cascade in islets. This phenotype correlates with the down-regulation of suppression of tumorigenicity 5 (ST5) in HNF-4alpha mutants, which we identify as a novel regulator of ERK phosphorylation in beta-cells and a direct transcriptional target of HNF-4alpha in vivo. Together, these results indicate that HNF-4alpha is essential for the physiological expansion of adult beta-cell mass in response to increased metabolic demand.
review article (2006) Ellard S, Colclough K. Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha (HNF1A) and 4 alpha (HNF4A) in maturity-onset diabetes of the young. Hum. Mutat., 27(9):854-69.
Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset (often <25 years of age), and pancreatic beta-cell dysfunction. MODY is both clinically and genetically heterogeneous, with six different genes identified to date; glucokinase (GCK), hepatocyte nuclear factor-1 alpha (HNF1A, or TCF1), hepatocyte nuclear factor-4 alpha (HNF4A), insulin promoter factor-1 (IPF1 or PDX1), hepatocyte nuclear factor-1 beta (HNF1B or TCF2), and neurogenic differentiation 1 (NEUROD1). Mutations in the HNF1A gene are a common cause of MODY in the majority of populations studied. A total of 193 different mutations have been described in 373 families. The most common mutation is Pro291fs (P291fsinsC) in the polycytosine (poly C) tract of exon 4, which has been reported in 65 families. HNF4A mutations are rarer; 31 mutations reported in 40 families. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The identification of an HNF1A or 4A gene mutation confirms a diagnosis of MODY and has important implications for clinical management.
- (2006) Briançon N, Weiss MC. In vivo role of the HNF4alpha AF-1 activation domain revealed by exon swapping. EMBO J., 25(6):1253-62.
The gene encoding the nuclear receptor hepatocyte nuclear factor 4alpha (HNF4alpha) generates isoforms HNF4alpha1 and HNF4alpha7 from usage of alternative promoters. In particular, HNF4alpha7 is expressed in the pancreas whereas HNF4alpha1 is found in liver, and mutations affecting HNF4alpha function cause impaired insulin secretion and/or hepatic defects in humans and in tissue-specific 'knockout' mice. HNF4alpha1 and alpha7 isoforms differ exclusively by amino acids encoded by the first exon which, in HNF4alpha1 but not in HNF4alpha7, includes the activating function (AF)-1 transactivation domain. To investigate the roles of HNF4alpha1 and HNF4alpha7 in vivo, we generated mice expressing only one isoform under control of both promoters, via reciprocal swapping of the isoform-specific first exons. Unlike Hnf4alpha gene disruption which causes embryonic lethality, these 'alpha7-only' and 'alpha1-only' mice are viable, indicating functional redundancy of the isoforms. However, the former show dyslipidemia and preliminary results indicate impaired glucose tolerance for the latter, revealing functional specificities of the isoforms. These 'knock-in' mice provide the first test in vivo of the HNF4alpha AF-1 function and have permitted identification of AF-1-dependent target genes.
- (2003) Parviz F, Matullo C, Garrison WD, Savatski L, Adamson JW, Ning G, Kaestner KH, Rossi JM, Zaret KS, Duncan SA. Hepatocyte nuclear factor 4alpha controls the development of a hepatic epithelium and liver morphogenesis. Nat. Genet., 34(3):292-6.
Although advances have been made in understanding cell differentiation, only rudimentary knowledge exists concerning how differentiated cells form tissues and organs. We studied liver organogenesis because the cell and tissue architecture of this organ is well defined. Approximately 60% of the adult liver consists of hepatocytes that are arranged as single-cell anastomosing plates extending from the portal region of the liver lobule toward the central vein. The basal surface of the hepatocytes is separated from adjacent sinusoidal endothelial cells by the space of Disse, where the exchange of substances between serum and hepatocytes takes place. The hepatocyte's apical surface forms bile canaliculi that transport bile to the hepatic ducts. Proper liver architecture is crucial for hepatic function and is commonly disrupted in disease states, including cirrhosis and hepatitis. Here we report that hepatocyte nuclear factor 4alpha (Hnf4alpha) is essential for morphological and functional differentiation of hepatocytes, accumulation of hepatic glycogen stores and generation of a hepatic epithelium. We show that Hnf4alpha is a dominant regulator of the epithelial phenotype because its ectopic expression in fibroblasts induces a mesenchymal-to-epithelial transition. Most importantly, the morphogenetic parameters controlled by Hnf4alpha in hepatocytes are essential for normal liver architecture, including the organization of the sinusoidal endothelium.
- (1995) Jiang G, Nepomuceno L, Hopkins K, Sladek FM. Exclusive homodimerization of the orphan receptor hepatocyte nuclear factor 4 defines a new subclass of nuclear receptors. Mol. Cell. Biol., 15(9):5131-43.
Hepatocyte nuclear factor 4 (HNF-4), a highly conserved member of the steroid hormone receptor superfamily critical for development and liver-specific gene expression, is very similar to another superfamily member, retinoid X receptor alpha (RXR alpha), in overall amino acid sequence and DNA binding specificity. Since RXR alpha is known to heterodimerize with many other nuclear receptors, the formation of heterodimers between HNF-4 and RXR alpha was examined. With the electrophoretic mobility shift assay, coimmunoprecipitation, and transient transfection assays, it is shown that, unlike other nuclear receptors, HNF-4 does not form heterodimers with RXR alpha either in the presence or in the absence of DNA. We also show that in vitro-translated HNF-4 does not form heterodimeric complexes on DNA with a number of other receptors, including RXR beta, RXR gamma, retinoic acid receptor alpha, or thyroid hormone receptor alpha. To investigate the hypothesis that the lack of heterodimerization between HNF-4 and RXR alpha is due to a strong homodimerization activity of HNF-4, glycerol gradient sedimentation and kinetic analysis were used to show that HNF-4 is in fact a stable homodimer in solution. Finally, immunohistochemistry is used to show that the HNF-4 protein is found exclusively in the nuclei in both HepG2 cells, which express endogenous HNF-4, and transfected COS cells, which overexpress HNF-4. These findings lead us to propose that HNF-4 defines a new subclass of nuclear receptors which reside primarily in the nucleus and which bind DNA and regulate transcription as homodimers.
- (1994) Chen WS, Manova K, Weinstein DC, Duncan SA, Plump AS, Prezioso VR, Bachvarova RF, Darnell JE. Disruption of the HNF-4 gene, expressed in visceral endoderm, leads to cell death in embryonic ectoderm and impaired gastrulation of mouse embryos. Genes Dev., 8(20):2466-77.
Expression of HNF-4, a transcription factor in the steroid hormone receptor superfamily, is detected only in the visceral endoderm of mouse embryos during gastrulation and is expressed in certain embryonic tissues from 8.5 days of gestation. To examine the role of HNF-4 during embryonic development, we disrupted the gene in embryonic stem cells and found that the homozygous loss of functional HNF-4 protein was an embryonic lethal. Cell death was evident in the embryonic ectoderm at 6.5 days when these cells normally initiate gastrulation. As assessed by expression of Brachyury and HNF-3 beta, primitive streak formation and initial differentiation of mesoderm do occur, but with a delay of approximately 24 h. Development of embryonic structures is severely impaired. These results demonstrate that the expression of HNF-4 in the visceral endoderm is essential for embryonic ectoderm survival and normal gastrulation.
- (2009) Han S, Chiang JY. Mechanism of vitamin D receptor inhibition of cholesterol 7alpha-hydroxylase gene transcription in human hepatocytes. Drug Metab. Dispos., 37(3):469-78.
Lithocholic acid (LCA) is a potent endogenous vitamin D receptor (VDR) ligand. In cholestasis, LCA levels increase in the liver and intestine. The objective of this study is to test the hypothesis that VDR plays a role in inhibiting cholesterol 7alpha-hydroxylase (CYP7A1) gene expression and bile acid synthesis in human hepatocytes. Immunoblot analysis has detected VDR proteins in the nucleus of the human hepatoma cell line HepG2 and human primary hepatocytes. 1alpha, 25-Dihydroxy-vitamin D(3) or LCA acetate-activated VDR inhibited CYP7A1 mRNA expression and bile acid synthesis, whereas small interfering RNA to VDR completely abrogated VDR inhibition of CYP7A1 mRNA expression in HepG2 cells. Electrophoretic mobility shift assay and mutagenesis analyses have identified the negative VDR response elements that bind VDR/retinoid X receptor alpha in the human CYP7A1 promoter. Mammalian two-hybrid, coimmunoprecipitation, glutathione S-transferase pull-down, and chromatin immunoprecipitation assays show that ligand-activated VDR specifically interacts with hepatocyte nuclear factor 4alpha (HNF4alpha) to block HNF4alpha interaction with coactivators or to compete with HNF4alpha for coactivators or to compete for binding to CYP7A1 chromatin, which results in the inhibition of CYP7A1 gene transcription. This study shows that VDR is expressed in human hepatocytes and may play a critical role in the inhibition of bile acid synthesis, thus protecting liver cells during cholestasis.
- (2009) Xie X, Liao H, Dang H, Pang W, Guan Y, Wang X, Shyy JY, Zhu Y, Sladek FM. Down-regulation of hepatic HNF4alpha gene expression during hyperinsulinemia via SREBPs. Mol. Endocrinol., 23(4):434-43.
Mutations in the coding region of hepatocyte nuclear factor 4alpha (HNF4alpha), and its upstream promoter (P2) that drives expression in the pancreas, are known to lead to maturity-onset diabetes of the young 1 (MODY1). HNF4alpha also controls gluconeogenesis and lipid metabolism in the liver, where the proximal promoter (P1) predominates. However, very little is known about the role of hepatic HNF4alpha in diabetes. Here, we examine the expression of hepatic HNF4alpha in two diabetic mouse models, db/db mice (type 2, insulin resistant) and streptozotocin-treated mice (type 1, insulin deficient). We found that the level of HNF4alpha protein and mRNA was decreased in the liver of db/db mice but increased in streptozotocin-treated mice. Because insulin increases the activity of sterol regulatory element-binding proteins (SREBP)-1c and -2, we also examined the effect of SREBPs on hepatic HNF4alpha gene expression and found that, like insulin, ectopic expression of SREBPs decreases the level of hepatic HNF4alpha protein and mRNA both in vitro in primary hepatocytes and in vivo in the liver of C57BL/6 mice. Finally, we use gel shift, chromatin immunoprecipitation, small interfering RNA, and reporter gene analysis to show that SREBP2 binds the human HNF4alpha P1 promoter and negatively regulates its expression. These data indicate that hyperinsulinemia down-regulates HNF4alpha in the liver through the up-regulation of SREBPs, thereby establishing a link between these two critical transcription factor pathways that regulate lipid and glucose metabolism in the liver. These findings also provide new insights into diabetes-associated complications such as fatty liver disease.
- (2009) Wallerman O, Motallebipour M, Enroth S, Patra K, Bysani MS, Komorowski J, Wadelius C. Molecular interactions between HNF4a, FOXA2 and GABP identified at regulatory DNA elements through ChIP-sequencing. Nucleic Acids Res., 37(22):7498-508.
Gene expression is regulated by combinations of transcription factors, which can be mapped to regulatory elements on a genome-wide scale using ChIP experiments. In a previous ChIP-chip study of USF1 and USF2 we found evidence also of binding of GABP, FOXA2 and HNF4a within the enriched regions. Here, we have applied ChIP-seq for these transcription factors and identified 3064 peaks of enrichment for GABP, 7266 for FOXA2 and 18783 for HNF4a. Distal elements with USF2 signal was frequently bound also by HNF4a and FOXA2. GABP peaks were found at transcription start sites, whereas 94% of FOXA2 and 90% of HNF4a peaks were located at other positions. We developed a method to accurately define TFBS within peaks, and found the predicted sites to have an elevated conservation level compared to peak centers; however the majority of bindings were not evolutionary conserved. An interaction between HNF4a and GABP was seen at TSS, with one-third of the HNF4a positive promoters being bound also by GABP, and this interaction was verified by co-immunoprecipitations.
- (2009) Tomaru Y, Nakanishi M, Miura H, Kimura Y, Ohkawa H, Ohta Y, Hayashizaki Y, Suzuki M. Identification of an inter-transcription factor regulatory network in human hepatoma cells by Matrix RNAi. Nucleic Acids Res., 37(4):1049-60.
Transcriptional regulation by transcriptional regulatory factors (TRFs) of their target TRF genes is central to the control of gene expression. To study a static multi-tiered inter-TRF regulatory network in the human hepatoma cells, we have applied a Matrix RNAi approach in which siRNA knockdown and quantitative RT-PCR are used in combination on the same set of TRFs to determine their interdependencies. This approach focusing on several liver-enriched TRF families, each of which consists of structurally homologous members, revealed many significant regulatory relationships. These include the cross-talks between hepatocyte nuclear factors (HNFs) and the other TRF groups such as CCAAT/enhancer-binding proteins (CEBPs), retinoic acid receptors (RARs), retinoid receptors (RXRs) and RAR-related orphan receptors (RORs), which play key regulatory functions in human hepatocytes and liver. In addition, various multi-component regulatory motifs, which make up the complex inter-TRF regulatory network, were identified. A large part of the regulatory edges identified by the Matrix RNAi approach could be confirmed by chromatin immunoprecipitation. The resultant significant edges enabled us to depict the inter-TRF TRN forming an apparent regulatory hierarchy of (FOXA1, RXRA) --> TCF1 --> (HNF4A, ONECUT1) --> (RORC, CEBPA) as the main streamline.
- (2009) Darsigny M, Babeu JP, Dupuis AA, Furth EE, Seidman EG, Lévy E, Verdu EF, Gendron FP, Boudreau F. Loss of hepatocyte-nuclear-factor-4alpha affects colonic ion transport and causes chronic inflammation resembling inflammatory bowel disease in mice. PLoS ONE, 4(10):e7609.
BACKGROUND: Hnf4alpha, an epithelial specific transcriptional regulator, is decreased in inflammatory bowel disease and protects against chemically-induced colitis in mice. However, the precise role of this factor in maintaining normal inflammatory homeostasis of the intestine remains unclear. The aim of this study was to evaluate the sole role of epithelial Hnf4alpha in the maintenance of gut inflammatory homeostasis in mice. METHODOLOGY/PRINCIPAL FINDINGS: We show here that specific epithelial deletion of Hnf4alpha in mice causes spontaneous chronic intestinal inflammation leading to focal areas of crypt dropout, increased cytokines and chemokines secretion, immune cell infiltrates and crypt hyperplasia. A gene profiling analysis in diseased Hnf4alpha null colon confirms profound genetic changes in cell death and proliferative behaviour related to cancer. Among the genes involved in the immune protection through epithelial barrier function, we identify the ion transporter claudin-15 to be down-modulated early in the colon of Hnf4alpha mutants. This coincides with a significant decrease of mucosal ion transport but not of barrier permeability in young animals prior to the manifestation of the disease. We confirm that claudin-15 is a direct Hnf4alpha gene target in the intestinal epithelial context and is down-modulated in mouse experimental colitis and inflammatory bowel disease. CONCLUSION: Our results highlight the critical role of Hnf4alpha to maintain intestinal inflammatory homeostasis during mouse adult life and uncover a novel function for Hnf4alpha in the regulation of claudin-15 expression. This establishes Hnf4alpha as a mediator of ion epithelial transport, an important process for the maintenance of gut inflammatory homeostasis.
- (2009) Le Guével R, Oger F, Lecorgne A, Dudasova Z, Chevance S, Bondon A, Barath P, Simonneaux G, Salbert G. Identification of small molecule regulators of the nuclear receptor HNF4alpha based on naphthofuran scaffolds. Bioorg. Med. Chem., 17(19):7021-30.
Nuclear receptors are ligand-activated transcription factors involved in all major physiological functions of complex organisms. In this respect, they are often described as drugable targets for a number of pathological states including hypercholesterolemia and atherosclerosis. HNF4alpha (NR2A1) is a recently 'deorphanized' nuclear receptor which is bound in vivo by linoleic acid, although this natural ligand does not seem to promote transcriptional activation. In mouse, HNF4alpha is a major regulator of liver development and hepatic lipid metabolism and mutations in human have been linked to diabetes. Here, we have used a yeast one-hybrid system to identify small molecule activators of HNF4alpha in a library of synthetic compounds and found one hit bearing a methoxy group branched on a nitronaphthofuran backbone. A collection of molecules deriving from the discovered hit was generated and tested for activity toward HNF4alpha in yeast one-hybrid system. It was found that both the nitro group and a complete naphthofuran backbone were required for full activity of the compounds. Furthermore, adding a hydroxy group at position 7 of the minimal backbone led to the most active compound of the collection. Accordingly, a direct interaction of the hydroxylated compound with the ligand binding domain of HNF4alpha was detected by NMR and thermal denaturation assays. When used in mammalian cell culture systems, these compounds proved to be highly toxic, except when methylated on the furan ring. One such compound was able to modulate HNF4alpha-driven transcription in transfected HepG2C3A cells. These data indicate that HNF4alpha activity can be modulated by small molecules and suggest new routes for targeting the receptor in humans.
- (2009) Cattin AL, Le Beyec J, Barreau F, Saint-Just S, Houllier A, Gonzalez FJ, Robine S, Pinçon-Raymond M, Cardot P, Lacasa M, Ribeiro A. Hepatocyte nuclear factor 4alpha, a key factor for homeostasis, cell architecture, and barrier function of the adult intestinal epithelium. Mol. Cell. Biol., 29(23):6294-308.
Hepatocyte nuclear factor 4alpha (HNF-4alpha) is a transcription factor which is highly expressed in the intestinal epithelium from duodenum to colon and from crypt to villus. The homeostasis of this constantly renewing epithelium relies on an integrated control of proliferation, differentiation, and apoptosis, as well as on the functional architecture of the epithelial cells. In order to determine the consequences of HNF-4alpha loss in the adult intestinal epithelium, we used a tamoxifen-inducible Cre-loxP system to inactivate the Hnf-4a gene. In the intestines of adult mice, loss of HNF-4alpha led to an increased proliferation in crypts and to an increased expression of several genes controlled by the Wnt/beta-catenin system. This control of the Wnt/beta-catenin signaling pathway by HNF-4alpha was confirmed in vitro. Cell lineage was affected, as indicated by an increased number of goblet cells and an impairment of enterocyte and enteroendocrine cell maturation. In the absence of HNF-4alpha, cell-cell junctions were destabilized and paracellular intestinal permeability increased. Our results showed that HNF-4alpha modulates Wnt/beta-catenin signaling and controls intestinal epithelium homeostasis, cell function, and cell architecture. This study indicates that HNF-4alpha regulates the intestinal balance between proliferation and differentiation, and we hypothesize that it might act as a tumor suppressor.
- (2009) Badis G, Berger MF, Philippakis AA, Talukder S, Gehrke AR, Jaeger SA, Chan ET, Metzler G, Vedenko A, Chen X, Kuznetsov H, Wang CF, Coburn D, Newburger DE, Morris Q, Hughes TR, Bulyk ML. Diversity and complexity in DNA recognition by transcription factors. Science, 324(5935):1720-3.
Sequence preferences of DNA binding proteins are a primary mechanism by which cells interpret the genome. Despite the central importance of these proteins in physiology, development, and evolution, comprehensive DNA binding specificities have been determined experimentally for only a few proteins. Here, we used microarrays containing all 10-base pair sequences to examine the binding specificities of 104 distinct mouse DNA binding proteins representing 22 structural classes. Our results reveal a complex landscape of binding, with virtually every protein analyzed possessing unique preferences. Roughly half of the proteins each recognized multiple distinctly different sequence motifs, challenging our molecular understanding of how proteins interact with their DNA binding sites. This complexity in DNA recognition may be important in gene regulation and in the evolution of transcriptional regulatory networks.
- (2009) Babeu JP, Darsigny M, Lussier CR, Boudreau F. Hepatocyte nuclear factor 4alpha contributes to an intestinal epithelial phenotype in vitro and plays a partial role in mouse intestinal epithelium differentiation. Am. J. Physiol. Gastrointest. Liver Physiol., 297(1):G124-34.
Hepatocyte nuclear factor 4alpha (HNF4alpha) is a regulator of hepatocyte and pancreatic transcription. Hnf4alpha deletion in the mouse is embryonically lethal with severe defects in visceral endoderm formation. It has been concluded in the past that the role of Hnf4alpha in the developing colon was much less important than in the liver. However, the precise role of Hnf4alpha in the homeostasis of the small intestinal epithelium remains unclear. Our aim was to evaluate the potential of Hnf4alpha to support an intestinal epithelial phenotype. First, Hnf4alpha potential to dictate this phenotype was assessed in nonintestinal cell lines in vitro. Forced expression of Hnf4alpha in fibroblasts showed an induction of features normally restricted to epithelial cells. Combinatory expression of Hnf4alpha with specific transcriptional regulators of the intestine resulted in the induction of intestinal epithelial genes in this context. Second, the importance of Hnf4alpha in maintaining the homeostasis of the intestinal epithelium was investigated in mice. Mice conditionally deficient for intestinal Hnf4alpha developed normally throughout adulthood with an epithelium displaying normal morphological and functional structures with minor alterations. Subtle but statistical differences were observed at the proliferation and the cytodifferentiation levels. Hnf4alpha mutant mice displayed an increase in the number of goblet and enteroendocrine cells compared with controls. Given the fundamental role of this transcription factor in other tissues, these findings dispute the crucial role for this regulator in the maintenance of intestinal epithelial cell function at a period of time that follows cytodifferentiation but may suggest a functional role in instructing cells to become specific to the intestinal epithelium.
- (2009) Huang J, Levitsky LL, Rhoads DB. Novel P2 promoter-derived HNF4alpha isoforms with different N-terminus generated by alternate exon insertion. Exp. Cell Res., 315(7):1200-11.
Hepatocyte nuclear factor 4alpha (HNF4alpha) is a critical transcription factor for pancreas and liver development and functions in islet beta cells to maintain glucose homeostasis. Mutations in the human HNF4A gene lead to maturity onset diabetes of the young (MODY1) and polymorphisms are associated with increased risk for type 2 diabetes mellitus (T2DM). Expression of six HNF4alpha variants, three each from two developmentally regulated promoters, has been firmly established. We have now detected a new set of HNF4alpha variants designated HNF4alpha10-12 expressed from distal promoter P2. These variants, generated by inclusion of previously undetected exon 1E (human=222 nt, rodent=136 nt) following exon 1D have an altered N-terminus but identical remaining reading frame. HNF4alpha10-alpha12 are expressed in pancreatic islets (and liver) and exhibit transactivation potentials similar to the corresponding alpha7-alpha9 isoforms. DNA-binding analyses implied much higher protein levels of HNF4alpha10-alpha12 in liver than expected from the RT-PCR data. Our results provide evidence for a more complex expression pattern of HNF4alpha than previously appreciated. We recommend inclusion of exon 1E and nearby DNA sequences in screening for HNF4alpha mutations and polymorphisms in genetic analyses of MODY1 and T2DM.
review article (2008) Stanger BZ. HNF4A and diabetes: injury before insult? Diabetes, 57(6):1461-2.
- (2008) Lee SS, Cha EY, Jung HJ, Shon JH, Kim EY, Yeo CW, Shin JG. Genetic polymorphism of hepatocyte nuclear factor-4alpha influences human cytochrome P450 2D6 activity. Hepatology, 48(2):635-45.
Hepatocyte nuclear factor-4 alpha (HNF4A) is an essential transcriptional regulator for many genes that are expressed preferentially in the liver. Among the important functions of the liver is drug metabolism in response to xenobiotic exposure. Recent studies have suggested that HNF4A regulates the expression of cytochrome P450 (CYP), including CYP2D6 and CYP3A4, which show large individual variations in their activities. To understand the genetic factors that influence individual CYP activities, a genetic variant of HNF4A and the effects of genetic variants of HNF4A on CYP activity were investigated. Here, we report the identification of a novel coding variant of HNF4A that influences CYP2D6 activity in humans. After direct sequencing, a polymorphism search revealed the HNF4A G60D variant in Koreans. This variant was unable to bind to the recognition site in the CYP2D6 promoter and therefore lacked the regulatory function for this gene. Human liver specimens with the heterozygous HNF4A G60D genotype showed a tendency toward lower levels of CYP2D6 activity than the wild-type genotype in the same genetic background of CYP2D6. Furthermore, human subjects with the HNF4A G60D genotype tended to have lower CYP2D6 activity than those with the wild-type HNF4A. The HNF4A G60D variant was detected at low frequency in Asian populations, including Koreans, Chinese, and Vietnamese, and was not found in Africans or Caucasians. CONCLUSION: This is the first report to show that the genetic polymorphism of liver-enriched nuclear receptor HNF4A influences downstream CYP2D6 function in human subjects.
- (2008) Sugai M, Umezu H, Yamamoto T, Jiang S, Iwanari H, Tanaka T, Hamakubo T, Kodama T, Naito M. Expression of hepatocyte nuclear factor 4 alpha in primary ovarian mucinous tumors. Pathol. Int., 58(11):681-6.
Hepatocyte nuclear factor 4 alpha (HNF4 alpha) is a member of the nuclear receptor superfamily and is expressed in several endodermal tissues. The aim of the present study was to examine the expression of HNF4 alpha on ovarian epithelial tumors with immunocytochemistry and immunohistochemistry using mAbs recognizing P1 and P2 promoter-driven HNF4 alpha. Ovarian mucinous adenoma, mucinous tumors of borderline malignancy, and mucinous adenocarcinoma had positive nuclear staining for HNF4 alpha (41/45, 91%). One-third (34%) of mucinous tumors had P1-positive staining and most had P1/P2-positive staining (93%). MUC2- and MUC5AC-positive staining was observed in 34% and 95% of mucinous tumors, respectively. The histological subtype of these mucinous tumors was not correlated with HNF4 alpha expression. On cytology it was found that cancer cells in the ascites from ovarian mucinous adenocarcinomas were HNF4 alpha positive, but tumor cells in ascites from other types of ovarian carcinomas were negative for HNF4 alpha. Thus, HNF4 alpha is demonstrated to be a useful marker for histological and cytological diagnosis of ovarian mucinous tumors.
- (2008) Nammo T, Yamagata K, Tanaka T, Kodama T, Sladek FM, Fukui K, Katsube F, Sato Y, Miyagawa J, Shimomura I. Expression of HNF-4alpha (MODY1), HNF-1beta (MODY5), and HNF-1alpha (MODY3) proteins in the developing mouse pancreas. Gene Expr. Patterns, 8(2):96-106.
The type 1, 3, and 5 forms of maturity-onset diabetes of the young (MODY) are caused by mutations of the genes encoding hepatocyte nuclear factor (HNF)-4alpha, HNF-1alpha, and HNF-1beta, respectively [Yamagata, K., Oda, N., Kaisaki, P.J., Menzel, S., Furuta, H., Vaxillaire, M., et al., 1996a. Mutations in the hepatocyte nuclear factor-1alpha gene in maturity-onset diabetes of the young (MODY3). Nature 384, 455-458; Yamagata, K., Furuta, H., Oda, N., Kaisaki, P.J., Menzel, S., Cox, N.J., et al., 1996b. Mutations in the hepatocyte nuclear factor-4alpha gene in maturity-onset diabetes of the young (MODY1). Nature 384, 458-460; Horikawa, Y., Iwasaki, N., Hara, M., Furuta, H., Hinokio, Y., Cockburn, B.N. et al., 1997. Mutation in hepatocyte nuclear factor-1beta gene (TCF2) associated with MODY. Nat. Genet. 17, 384-385]. Among these transcription factors, the pattern of HNF-4alpha expression during pancreatic differentiation remains largely unknown. We performed an immunohistochemical study to investigate its expression in comparison with the expression of HNF-1alpha and HNF-1beta. We found considerable variation in the level of HNF-4alpha expression by the individual epithelial cells in the pancreatic buds on E9.5. HNF-4alpha and HNF-1beta were initially expressed by Pdx1(+) common progenitor cells and neurogenin3(+) (Ngn3(+)) endocrine precursor cells during the first transition, but expression of HNF-1beta and either HNF-4alpha or HNF-1alpha became complementary around the end of the second transition (E15.5). In the mature pancreas, HNF-4alpha was expressed by glucagon-positive alpha-cells, insulin-positive beta-cells, somatostatin-positive delta-cells, and pancreatic polypeptide-positive PP-cells, as well as by pancreatic exocrine cells and ductal cells. Most of the HNF-4alpha(+) cells were also positive for HNF-1alpha, but HNF-4alpha expression in some non-beta-cells was remarkably high, and this was not paralleled by high HNF-1alpha expression. These results indicate that the expression of MODY proteins in each of the pancreatic cell types is strictly regulated in accordance with the status of differentiation during pancreatic organogenesis.
- (2008) Lu P, Rha GB, Melikishvili M, Wu G, Adkins BC, Fried MG, Chi YI. Structural basis of natural promoter recognition by a unique nuclear receptor, HNF4alpha. Diabetes gene product. J. Biol. Chem., 283(48):33685-97.
HNF4alpha (hepatocyte nuclear factor 4alpha) plays an essential role in the development and function of vertebrate organs, including hepatocytes and pancreatic beta-cells by regulating expression of multiple genes involved in organ development, nutrient transport, and diverse metabolic pathways. As such, HNF4alpha is a culprit gene product for a monogenic and dominantly inherited form of diabetes, known as maturity onset diabetes of the young (MODY). As a unique member of the nuclear receptor superfamily, HNF4alpha recognizes target genes containing two hexanucleotide direct repeat DNA-response elements separated by one base pair (DR1) by exclusively forming a cooperative homodimer. We describe here the 2.0 angstroms crystal structure of human HNF4alpha DNA binding domain in complex with a high affinity promoter element of another MODY gene, HNF1alpha, which reveals the molecular basis of unique target gene selection/recognition, DNA binding cooperativity, and dysfunction caused by diabetes-causing mutations. The predicted effects of MODY mutations have been tested by a set of biochemical and functional studies, which show that, in contrast to other MODY gene products, the subtle disruption of HNF4alpha molecular function can cause significant effects in afflicted MODY patients.
- (2008) Ishikawa F, Nose K, Shibanuma M. Downregulation of hepatocyte nuclear factor-4alpha and its role in regulation of gene expression by TGF-beta in mammary epithelial cells. Exp. Cell Res., 314(10):2131-40.
We found that a specific isoform of hepatocyte nuclear factor 4alpha (HNF-4alpha), HNF-4alpha8, was expressed in mouse mammary epithelial NMuMG cells, and that its expression was repressed by TGF-beta. The repression was interfered by dominant negative forms of activin receptor-like kinase 5 (ALK5) and Smad3, and sensitive to cycloheximide, suggesting the involvement of additional protein(s) as well as ALK5 and Smad3 in the repression. Further study showed that high mobility group A2 (HMGA2), which is reported to be directly upregulated by Smads, repressed HNF-4alpha8 expression. Therefore, it is likely that HMGA2 mediates the downregulation of HNF-4alpha8 downstream of ALK5 and Smads To determine the significance of the downregulation of HNF-4alpha8 in TGF-beta signaling, we performed DNA microarray analysis and extracted a subgroup of TGF-beta1-regulated genes, including tenascin C and tissue inhibitor of metalloproteinase 3 (TIMP-3), whose regulation by TGF-beta1 was attenuated by forced expression of HNF-4alpha8. HMGA2 has recently emerged as a transcriptional organizer of TGF-beta signaling, regulating several key factors involved in epithelial-mesenchymal transition (EMT). In this study, we identified an isoform of HNF-4alpha as a new target downstream of HMGA2 and assigned a new role to HNF-4alpha in the TGF-beta signaling/transcriptional cascade driven by ALK5/Smad/HMGA2 and associated with the malignant transformation of cells.
- (2008) Huang J, Karakucuk V, Levitsky LL, Rhoads DB. Expression of HNF4alpha variants in pancreatic islets and Ins-1 beta cells. Diabetes Metab. Res. Rev., 24(7):533-43.
BACKGROUND: Hepatocyte nuclear factor (HNF4alpha) is a nuclear receptor essential for endodermal differentiation and cell functions in the adult pancreas, liver, and other tissues. Mutations in the HNF4A gene cause MODY1. Up to nine protein variants arise from two developmentally regulated promoters. Because some variants lack the N-terminal activation function 1 (AF-1) and/or C-terminal inhibitory F domain, defining their tissue-specific regulation and function is important for understanding pancreatic beta cell behaviour. METHODS: Expression of HNF4alpha variants in islets, rat Ins-1 insulinoma cells, and human Hep3B hepatocellular carcinoma cells was assessed using a long-range reverse transcription-polymerase chain reaction (RT-PCR) strategy capable of recognizing each combination of mRNA termini. Protein expression was verified by immuno-blotting with terminus-specific antibodies and DNA-binding assays. RESULTS: Mouse islets and both cell lines express HNF4alpha9, which lacks both AF-1 and the F domain. Islets also expressed the HNF4alpha P1 promoter variants HNF4alpha1/alpha2, and Hep3B cells expressed HNF4alpha3. When ectopically expressed in COS-7 cells, HNF4alpha1, alpha3, alpha7, and alpha9 each stimulated an HNF4alpha-dependent promoter. Variants containing exon 1B (HNF4alpha4 - alpha6) were not detected. Lack of canonical splicing signals and species conservation argues against exon 1B usage. CONCLUSIONS: This is the first report of HNF4alpha9 expression in any tissue. Our findings extend our understanding of HNF4alpha gene transcription and function. This knowledge may be useful in efforts to recover or establish regulated insulin secretion.
- (2008) Ahn SH, Shah YM, Inoue J, Morimura K, Kim I, Yim S, Lambert G, Kurotani R, Nagashima K, Gonzalez FJ, Inoue Y. Hepatocyte nuclear factor 4alpha in the intestinal epithelial cells protects against inflammatory bowel disease. Inflamm. Bowel Dis., 14(7):908-20.
BACKGROUND: Hepatocyte nuclear factor 4alpha (HNF4alpha; NR2A1) is an orphan member of the nuclear receptor superfamily expressed in liver and intestine. While HNF4alpha expression is critical for liver function, its role in the gut and in the pathogenesis of inflammatory bowel disease (IBD) is unknown. METHODS: Human intestinal biopsies from control and IBD patients were examined for expression of mRNAs encoding HNF4alpha and other nuclear receptors. An intestine-specific HNF4alpha null mouse line (Hnf4alpha(DeltaIEpC)) was generated using an Hnf4alpha-floxed allele and villin-Cre transgene. These mice and their control floxed counterparts (Hnf4alpha(F/F)), were subjected to a dextran sulfate sodium (DSS)-induced IBD colitis protocol and their clinical symptoms and gene expression patterns determined. RESULTS: In human intestinal biopsies, HNF4alpha was significantly decreased in intestinal tissues from Crohn's disease and ulcerative colitis patients. HNF4alpha expression was also suppressed in the intestine of DSS-treated mice. In Hnf4alpha(DeltaIEpC) mice, disruption of HNF4alpha expression was observed in the epithelial cells throughout the intestine. In the DSS-induced colitis model Hnf4alpha(DeltaIEpC) mice showed markedly more severe changes in clinical symptoms and pathologies associated with IBD including loss of body weight, colon length, and histological morphology as compared with Hnf4alpha(F/F) mice. Furthermore, the Hnf4alpha(DeltaIEpC) mice demonstrate a significant alteration of mucin-associated genes and increased intestinal permeability, which may play an important role in the increased susceptibility to acute colitis following an inflammatory insult. CONCLUSIONS: While HNF4alpha does not have a major role in normal function of the intestine, it protects the gut against DSS-induced colitis.
- (2008) Kapoor RR, Locke J, Colclough K, Wales J, Conn JJ, Hattersley AT, Ellard S, Hussain K. Persistent hyperinsulinemic hypoglycemia and maturity-onset diabetes of the young due to heterozygous HNF4A mutations. Diabetes, 57(6):1659-63.
OBJECTIVE: Mutations in the human HNF4A gene encoding the hepatocyte nuclear factor (HNF)-4alpha are known to cause maturity-onset diabetes of the young (MODY), which is characterized by autosomal-dominant inheritance and impaired glucose-stimulated insulin secretion from pancreatic beta-cells. HNF-4alpha has a key role in regulating the multiple transcriptional factor networks in the islet. Recently, heterozygous mutations in the HNF4A gene were reported to cause transient hyperinsulinemic hypoglycemia associated with macrosomia. RESEARCH DESIGN AND METHODS: Three infants presented with macrosomia and severe hypoglycemia with a positive family history of MODY. The hypoglycemia was confirmed to be due to hyperinsulinism, and all three patients required diazoxide therapy to maintain normoglycemia. Two of the three infants are still requiring diazoxide therapy at 8 and 18 months, whereas one of them had resolution of hyperinsulinemic hypoglycemia at 32 months of age. RESULTS: Sequencing of the HNF4A gene identified heterozygous mutations in all three families. In family 1, a frameshift mutation L330fsdel17ins9 (c.987 1003del17ins9; p.Leu330fs) was present in the proband; a mutation affecting the conserved A nucleotide of the intron 2 branch site (c.264-21A>G) was identified in the proband of family 2; and finally a nonsense mutation, Y16X (c.48C>G, p.Tyr16X), was found in the proband of family 3. CONCLUSIONS: Heterozygous HNF4A mutations can therefore cause both transient and persistent hyperinsulinemic hypoglycemia associated with macrosomia. We recommend that macrosomic infants with transient or persistent hyperinsulinemic hypoglycemia should be screened for HNF4A mutations if there is a family history of youth-onset diabetes.
- (2007) Sun K, Montana V, Chellappa K, Brelivet Y, Moras D, Maeda Y, Parpura V, Paschal BM, Sladek FM. Phosphorylation of a conserved serine in the deoxyribonucleic acid binding domain of nuclear receptors alters intracellular localization. Mol. Endocrinol., 21(6):1297-311.
Nuclear receptors (NRs) are a superfamily of transcription factors whose genomic functions are known to be activated by lipophilic ligands, but little is known about how to deactivate them or how to turn on their nongenomic functions. One obvious mechanism is to alter the nuclear localization of the receptors. Here, we show that protein kinase C (PKC) phosphorylates a highly conserved serine (Ser) between the two zinc fingers of the DNA binding domain of orphan receptor hepatocyte nuclear factor 4alpha (HNF4alpha). This Ser (S78) is adjacent to several positively charged residues (Arg or Lys), which we show here are involved in nuclear localization of HNF4alpha and are conserved in nearly all other NRs, along with the Ser/threonine (Thr). A phosphomimetic mutant of HNF4alpha (S78D) reduced DNA binding, transactivation ability, and protein stability. It also impaired nuclear localization, an effect that was greatly enhanced in the MODY1 mutant Q268X. Treatment of the hepatocellular carcinoma cell line HepG2 with PKC activator phorbol 12-myristate 13-acetate also resulted in increased cytoplasmic localization of HNF4alpha as well as decreased endogenous HNF4alpha protein levels in a proteasome-dependent fashion. We also show that PKC phosphorylates the DNA binding domain of other NRs (retinoic acid receptor alpha, retinoid X receptor alpha, and thyroid hormone receptor beta) and that phosphomimetic mutants of the same Ser/Thr result in cytoplasmic localization of retinoid X receptor alpha and peroxisome proliferator-activated receptor alpha. Thus, phosphorylation of this conserved Ser between the two zinc fingers may be a common mechanism for regulating the function of NRs.
- (2007) Pearson ER, Boj SF, Steele AM, Barrett T, Stals K, Shield JP, Ellard S, Ferrer J, Hattersley AT. Macrosomia and hyperinsulinaemic hypoglycaemia in patients with heterozygous mutations in the HNF4A gene. PLoS Med., 4(4):e118.
BACKGROUND: Macrosomia is associated with considerable neonatal and maternal morbidity. Factors that predict macrosomia are poorly understood. The increased rate of macrosomia in the offspring of pregnant women with diabetes and in congenital hyperinsulinaemia is mediated by increased foetal insulin secretion. We assessed the in utero and neonatal role of two key regulators of pancreatic insulin secretion by studying birthweight and the incidence of neonatal hypoglycaemia in patients with heterozygous mutations in the maturity-onset diabetes of the young (MODY) genes HNF4A (encoding HNF-4alpha) and HNF1A/TCF1 (encoding HNF-1alpha), and the effect of pancreatic deletion of Hnf4a on foetal and neonatal insulin secretion in mice. METHODS AND FINDINGS: We examined birthweight and hypoglycaemia in 108 patients from families with diabetes due to HNF4A mutations, and 134 patients from families with HNF1A mutations. Birthweight was increased by a median of 790 g in HNF4A-mutation carriers compared to non-mutation family members (p < 0.001); 56% (30/54) of HNF4A-mutation carriers were macrosomic compared with 13% (7/54) of non-mutation family members (p < 0.001). Transient hypoglycaemia was reported in 8/54 infants with heterozygous HNF4A mutations, but was reported in none of 54 non-mutation carriers (p = 0.003). There was documented hyperinsulinaemia in three cases. Birthweight and prevalence of neonatal hypoglycaemia were not increased in HNF1A-mutation carriers. Mice with pancreatic beta-cell deletion of Hnf4a had hyperinsulinaemia in utero and hyperinsulinaemic hypoglycaemia at birth. CONCLUSIONS: HNF4A mutations are associated with a considerable increase in birthweight and macrosomia, and are a novel cause of neonatal hypoglycaemia. This study establishes a key role for HNF4A in determining foetal birthweight, and uncovers an unanticipated feature of the natural history of HNF4A-deficient diabetes, with hyperinsulinaemia at birth evolving to decreased insulin secretion and diabetes later in life.
- (2007) Erdmann S, Senkel S, Arndt T, Lucas B, Lausen J, Klein-Hitpass L, Ryffel GU, Thomas H. Tissue-specific transcription factor HNF4alpha inhibits cell proliferation and induces apoptosis in the pancreatic INS-1 beta-cell line. Biol. Chem., 388(1):91-106.
Hepatocyte nuclear factor 4alpha (HNF4alpha) is a tissue-specific transcription factor expressed in many cell types, including pancreatic beta-cells. Mutations in the HNF4alpha gene in humans give rise to maturity-onset diabetes of the young (MODY1) characterized by defective insulin secretion by beta-cells. To elucidate the mechanism underlying this disease, we introduced the splice form HNF4alpha2 or HNF4alpha8 into the rat beta-cell line INS-1. Upon tetracycline-induced expression, both HNF4alpha isoforms caused distinct changes in cell morphology and a massive loss of cell numbers that was correlated with reduced proliferation and induced apoptosis. This differential activity was reflected in oligonucleotide microarray analysis that identified more genes affected by HNF4alpha2 compared to HNF4alpha8, and suggests that both isoforms regulate largely the same set of genes, with HNF4alpha2 being a stronger transactivator. We verified the induction of selected transcripts by real-time RT-PCR, including KAI1 and AIF, both known to have apoptotic potential. By establishing cell lines with inducible expression of these target genes, we deduce that both factors are insufficient to induce apoptosis. We propose that the anti-proliferative and apoptotic properties of HNF4alpha may be an essential feature impaired in MODY1 and possibly also in type 2 diabetes.
- (2007) Wortham M, Czerwinski M, He L, Parkinson A, Wan YJ. Expression of constitutive androstane receptor, hepatic nuclear factor 4 alpha, and P450 oxidoreductase genes determines interindividual variability in basal expression and activity of a broad scope of xenobiotic metabolism genes in the human liver. Drug Metab. Dispos., 35(9):1700-10.
Identification of genetic variation predictive of clearance rate of a wide variety of prescription drugs could lead to cost-effective personalized medicine. Here we identify regulatory genes whose variable expression level among individuals may have widespread effects upon clearance rate of a variety of drugs. Twenty liver samples with variable CYP3A activity were profiled for expression level and activity of xenobiotic metabolism genes as well as genes involved in the regulation thereof. Regulatory genes whose expression level accounted for the highest degree of collinearity among expression levels of xenobiotic metabolism genes were identified as possible master regulators of drug clearance rate. Significant linear correlations (p < 0.05) were identified among mRNA levels of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, MRP2, OATP2, P450 oxidoreductase (POR), and UDP-glucuronosyltranferase 1A1, suggesting that these xenobiotic metabolism genes are coregulated at the transcriptional level. Using partial regression analysis, constitutive androstane receptor (CAR) and hepatic nuclear factor 4 alpha (HNF4 alpha) were identified as the nuclear receptors whose expression levels are most strongly associated with expression of coregulated xenobiotic metabolism genes. POR expression level, which is also associated with CAR and HNF4 alpha expression level, was found to be strongly associated with the activity of many cytochromes P450. Thus, interindividual variation in the expression level of CAR, HNF4 alpha, and POR probably determines variation in expression and activity of a broad scope of xenobiotic metabolism genes and, accordingly, clearance rate of a variety of xenobiotics. Identification of polymorphisms in these candidate master regulator genes that account for their variable expression among individuals may yield readily detectable biomarkers that could serve as predictors of xenobiotic clearance rate.
- (2007) Aueviriyavit S, Furihata T, Morimoto K, Kobayashi K, Chiba K. Hepatocyte nuclear factor 1 alpha and 4 alpha are factors involved in interindividual variability in the expression of UGT1A6 and UGT1A9 but not UGT1A1, UGT1A3 and UGT1A4 mRNA in human livers. Drug Metab. Pharmacokinet., 22(5):391-8.
UDP-glucuronosyltransferases (UGTs) catalyze phase-II biotransformation reaction of a variety of substances. Among the UGT1A isoforms, UGT1A1, UGT1A3, UGT1A4, UGT1A6 and UGT1A9 are predominantly expressed in the liver. Interindividual variability in expression of these isoforms would cause interindividual differences in drug response, toxicity and cancer susceptibility. In the present study, we investigated the interindividual variability in UGT1A mRNA expression and whether hepatocyte nuclear factor 1alpha (HNF1alpha) and HNF4alpha were factors responsible for their variability in human livers. The amounts of UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, HNF1alpha and HNF4alpha mRNA in 18 human livers were measured by quantitative real-time polymerase chain reaction. The largest and smallest interindividual differences in expression levels were observed in UGT1A1 (8.6-fold) and UGT1A4 (2.5-fold) mRNA, respectively. The amounts of HNF1alpha and HNF4alpha mRNA were strongly correlated with the amount of UGT1A9 mRNA and moderately correlated with that of UGT1A6 mRNA, whereas no significant correlation was found with the amounts of UGT1A1, UGT1A3 and UGT1A4 mRNA. Our results suggest that HNF1alpha and HNF4alpha are the factors involved in the interindividual variability of UGT1A6 and UGT1A9 mRNA expression. Further studies of other transcription factors are needed to clarify the factor(s) determining the interindividual variations in UGT1A1, UGT1A3 and UGT1A4 mRNA expression.
- (2006) Battle MA, Konopka G, Parviz F, Gaggl AL, Yang C, Sladek FM, Duncan SA. Hepatocyte nuclear factor 4alpha orchestrates expression of cell adhesion proteins during the epithelial transformation of the developing liver. Proc. Natl. Acad. Sci. U.S.A., 103(22):8419-24.
Epithelial formation is a central facet of organogenesis that relies on intercellular junction assembly to create functionally distinct apical and basal cell surfaces. How this process is regulated during embryonic development remains obscure. Previous studies using conditional knockout mice have shown that loss of hepatocyte nuclear factor 4alpha (HNF4alpha) blocks the epithelial transformation of the fetal liver, suggesting that HNF4alpha is a central regulator of epithelial morphogenesis. Although HNF4alpha-null hepatocytes do not express E-cadherin (also called CDH1), we show here that E-cadherin is dispensable for liver development, implying that HNF4alpha regulates additional aspects of epithelial formation. Microarray and molecular analyses reveal that HNF4alpha regulates the developmental expression of a myriad of proteins required for cell junction assembly and adhesion. Our findings define a fundamental mechanism through which generation of tissue epithelia during development is coordinated with the onset of organ function.
- (2006) Tanaka T, Jiang S, Hotta H, Takano K, Iwanari H, Sumi K, Daigo K, Ohashi R, Sugai M, Ikegame C, Umezu H, Hirayama Y, Midorikawa Y, Hippo Y, Watanabe A, Uchiyama Y, Hasegawa G, Reid P, Aburatani H, Hamakubo T, Sakai J, Naito M, Kodama T. Dysregulated expression of P1 and P2 promoter-driven hepatocyte nuclear factor-4alpha in the pathogenesis of human cancer. J. Pathol., 208(5):662-72.
Hepatocyte nuclear factor-4alpha (HNF4alpha) exists in multiple isoforms that are generated by alternative promoter (P1 and P2) usage and splicing. Here we establish monoclonal antibodies (mAbs) for detecting P1 and P2 promoter-driven HNF4alpha, and evaluate their expression in normal adult human tissues and surgically resected carcinomas of different origins. Using immunohistochemical analysis, we demonstrate that, while P1 promoter-driven HNF4alpha is expressed in hepatocytes, small intestine, colon, kidney and epididymis, P2 promoter-driven HNF4alpha is expressed in bile duct, pancreas, stomach, small intestine, colon and epididymis. Altered expression patterns of P1 and P2 promoter-driven HNF4alpha were observed in gastric, hepatocellular and colorectal carcinomas. HNF4alpha was expressed in lung metastases from renal cell, hepatocellular and colorectal carcinoma but was not observed in lung tumours. The P1 and P2 promoter-driven HNF4alpha expression pattern of tumour metastases correlated with the primary site of origin. P1 promoter-driven HNF4alpha was also found in intestinal metaplasia of the stomach. These data provide evidence for the tissue distribution of P1 and P2 promoter-driven HNF4alpha at the protein level and suggest that HNF4alpha may be a novel diagnostic marker for metastases of unknown primary. We propose that the dysregulation of alternative promoter usage of HNF4alpha is associated with the pathogenesis of certain cancers.
- (2006) Guo H, Gao C, Mi Z, Wai PY, Kuo PC. Phosphorylation of Ser158 regulates inflammatory redox-dependent hepatocyte nuclear factor-4alpha transcriptional activity. Biochem. J., 394(Pt 2):379-87.
In IL-1beta (interleukin 1beta)-stimulated rat hepatocytes exposed to superoxide, we have previously identified an IRX (inflammatory redox)-sensitive DR1 [direct repeat of RG(G/T)TCA with one base spacing] cis-acting activator element (nt -1327 to -1315) in the iNOS (inducible nitric oxide synthase) promoter: AGGTCAGGGGACA. The corresponding transcription factor was identified to be HNF4alpha (hepatocyte nuclear factor-4alpha). HNF4alpha DNA binding activity and transactivation potential are tightly regulated by its state of phosphorylation. However, the functional consequences of IRX-mediated post-translational phosphorylation of HNF4alpha have not been well characterized. In the setting of IL-1beta+H2O2, HNF4alpha functional activity is associated with a unique serine/threonine phosphorylation pattern. This indicates that an IRX-sensitive serine/threonine kinase pathway targets HNF4alpha to augment hepatocyte iNOS transcription. In the present study, following identification of phosphorylated residues in HNF4alpha, serial mutations were performed to render the target residues phosphorylation-resistant. Electrophoretic mobility-shift assays and transient transfection studies utilizing the iNOS promoter showed that the S158A mutation ablates IRX-mediated HNF4alpha DNA binding and transactivation. Gain-of-function mutation with the S158D phosphomimetic HNF4alpha vector supports a critical role for Ser158 phosphorylation. In vitro phosphorylation and kinase inhibitor studies implicate p38 kinase activity. Our results indicate that p38 kinase-mediated Ser158 phosphorylation is essential for augmentation of the DNA binding and transactivation potential of HNF4alpha in the presence of IL-1beta+H2O2. This pathway results in enhanced iNOS expression in hepatocytes exposed to pro-inflammatory cytokines and oxidative stress.
- (2006) Weissglas-Volkov D, Huertas-Vazquez A, Suviolahti E, Lee J, Plaisier C, Canizales-Quinteros S, Tusie-Luna T, Aguilar-Salinas C, Taskinen MR, Pajukanta P. Common hepatic nuclear factor-4alpha variants are associated with high serum lipid levels and the metabolic syndrome. Diabetes, 55(7):1970-7.
Hepatic nuclear factor-4alpha (HNF-4alpha), a transcription factor involved in the regulation of serum lipid and glucose levels, has recently been associated with type 2 diabetes. The HNF-4alpha gene (HNF4A) resides on chromosome 20q12-q13.1, which, in addition to type 2 diabetes, has also previously been linked to high triglycerides in Finnish familial combined hyperlipidemia (FCHL) families. FCHL, characterized by elevated levels of serum total cholesterol, triglycerides, or both, is a common dyslipidemia observed in up to 20% of patients with premature coronary heart disease. Considering the clear phenotypic overlap between type 2 diabetes and FCHL, both predisposing to high serum triglycerides and glucose intolerance, we tested this gene for association in dyslipidemic families originating from two distinct populations, Finnish and Mexican, and comprising 1,447 subjects. Our data show that common HNF4A variants and haplotypes are associated with elevated serum lipid levels and the metabolic syndrome (P = 0.008-0.04), as well as with elevated glucose parameters (P = 0.008-0.03), using family-based association analysis. Importantly, both Finnish and Mexican families shared two common lipid-associated HNF4A haplotypes (P = 0.005 for total cholesterol and 0.006 for triglycerides). In conclusion, we show for the first time that common HNF4A variants are associated with high serum lipid levels and the metabolic syndrome.
- (2006) Barrero MJ, Malik S. Two functional modes of a nuclear receptor-recruited arginine methyltransferase in transcriptional activation. Mol. Cell, 24(2):233-43.
Nuclear receptors, like other transcriptional activators, switch on gene transcription by recruiting a complex network of coregulatory proteins. Here, we have identified the arginine methyltransferase PRMT1 as a coactivator for HNF4, an orphan nuclear receptor that regulates the expression of genes involved in diverse metabolic pathways. Remarkably, PRMT1, whose methylation activity on histone H4 strongly correlates with induction of HNF4 target genes in differentiating enterocytes, regulates HNF4 activity through a bipartite mechanism. First, PRMT1 binds and methylates the HNF4 DNA-binding domain (DBD), thereby enhancing the affinity of HNF4 for its binding site. Second, PRMT1 is recruited to the HNF4 ligand-binding domain (LBD) through a mechanism that involves the p160 family of coactivators and methylates histone H4 at arginine 3. This, together with recruitment of the histone acetyltransferase p300, leads to nucleosomal alterations and subsequent RNA polymerase II preinitiation complex formation.
- (2006) Garrison WD, Battle MA, Yang C, Kaestner KH, Sladek FM, Duncan SA. Hepatocyte nuclear factor 4alpha is essential for embryonic development of the mouse colon. Gastroenterology, 130(4):1207-20.
BACKGROUND & AIMS: Hepatocyte nuclear factor 4 alpha (HNF4alpha) is a transcription factor that has been shown to be required for hepatocyte differentiation and development of the liver. It has also been implicated in regulating expression of genes that act in the epithelium of the lower gastrointestinal tract. This implied that HNF4alpha might be required for development of the gut. METHODS: Mouse embryos were generated in which Hnf4a was ablated in the epithelial cells of the fetal colon by using Cre-loxP technology. Embryos were examined by using a combination of histology, immunohistochemistry, DNA microarray, reverse-transcription polymerase chain reaction, electrophoretic mobility shift assays, and chromatin immunoprecipitation analyses to define the consequences of loss of HNF4alpha on colon development. RESULTS: Embryos were recovered at E18.5 that lacked HNF4alpha in their colons. Although early stages of colonic development occurred, HNF4alpha-null colons failed to form normal crypts. In addition, goblet-cell maturation was perturbed and expression of an array of genes that encode proteins with diverse roles in colon function was disrupted. Several genes whose expression in the colon was dependent on HNF4alpha contained HNF4alpha-binding sites within putative transcriptional regulatory regions and a subset of these sites were occupied by HNF4alpha in vivo. CONCLUSIONS: HNF4alpha is a transcription factor that is essential for development of the mammalian colon, regulates goblet-cell maturation, and is required for expression of genes that control normal colon function and epithelial cell differentiation.
- (2006) Miura A, Yamagata K, Kakei M, Hatakeyama H, Takahashi N, Fukui K, Nammo T, Yoneda K, Inoue Y, Sladek FM, Magnuson MA, Kasai H, Miyagawa J, Gonzalez FJ, Shimomura I. Hepatocyte nuclear factor-4alpha is essential for glucose-stimulated insulin secretion by pancreatic beta-cells. J. Biol. Chem., 281(8):5246-57.
Mutations in the hepatocyte nuclear factor (HNF)-4alpha gene cause a form of maturity-onset diabetes of the young (MODY1) that is characterized by impairment of glucose-stimulated insulin secretion by pancreatic beta-cells. HNF-4alpha, a transcription factor belonging to the nuclear receptor superfamily, is expressed in pancreatic islets as well as in the liver, kidney, and intestine. However, the role of HNF-4alpha in pancreatic beta-cell is unclear. To clarify the role of HNF-4alpha in beta-cells, we generated beta-cell-specific HNF-4alpha knock-out (betaHNF-4alphaKO) mice using the Cre-LoxP system. The betaHNF-4alphaKO mice exhibited impairment of glucose-stimulated insulin secretion, which is a characteristic of MODY1. Pancreatic islet morphology, beta-cell mass, and insulin content were normal in the HNF-4alpha mutant mice. Insulin secretion by betaHNF-4alphaKO islets and the intracellular calcium response were impaired after stimulation by glucose or sulfonylurea but were normal after stimulation with KCl or arginine. Both NAD(P)H generation and ATP content at high glucose concentrations were normal in the betaHNF-4alphaKO mice. Expression levels of Kir6.2 and SUR1 proteins in the betaHNF-4alphaKO mice were unchanged as compared with control mice. Patch clamp experiments revealed that the current density was significantly increased in betaHNF-4alphaKO mice compared with control mice. These results are suggestive of the dysfunction of K(ATP) channel activity in the pancreatic beta-cells of HNF-4alpha-deficient mice. Because the K(ATP) channel is important for proper insulin secretion in beta-cells, altered K(ATP) channel activity could be related to the impaired insulin secretion in the betaHNF-4alphaKO mice.
- (2006) Kyrmizi I, Hatzis P, Katrakili N, Tronche F, Gonzalez FJ, Talianidis I. Plasticity and expanding complexity of the hepatic transcription factor network during liver development. Genes Dev., 20(16):2293-305.
Cross-regulatory cascades between hepatic transcription factors have been implicated in the determination of the hepatic phenotype. Analysis of recruitments to regulatory regions and the temporal and spatial expression pattern of the main hepatic regulators during liver development revealed a gradual increase in complexity of autoregulatory and cross-regulatory circuits. Within these circuits we identified a core group of six transcription factors, which regulate the expression of each other and the expression of other downstream hepatic regulators. Changes in the promoter occupancy patterns during development included new recruitments, release, and exchange of specific factors. We also identified promoter and developmental stage-specific dual regulatory functions of certain factors as an important feature of the network. Inactivation of HNF-4alpha in embryonic, but not in adult, liver resulted in the diminished expression of most hepatic factors, demonstrating that the stability of the network correlates with its complexity. The results illustrate the remarkable flexibility of a self-sustaining transcription factor network, built up by complex dominant and redundant regulatory motifs in developing hepatocytes.
- (2005) Ihara A, Yamagata K, Nammo T, Miura A, Yuan M, Tanaka T, Sladek FM, Matsuzawa Y, Miyagawa J, Shimomura I. Functional characterization of the HNF4alpha isoform (HNF4alpha8) expressed in pancreatic beta-cells. Biochem. Biophys. Res. Commun., 329(3):984-90.
Mutations in the hepatocyte nuclear factor (HNF) 4alpha gene cause a form of maturity-onset diabetes of the young (MODY1), which is a monogenic form of type 2 diabetes characterized by impaired insulin secretion by pancreatic beta-cells. HNF4alpha is a transcription factor expressed in the liver, kidney, intestine, and pancreatic islet. Multiple splice variants of the HNF4alpha gene have been identified and an isoform of HNF4alpha8, an N-terminal splice variant, is expressed in pancreatic beta-cells. However, expression levels of HNF4alpha protein in pancreatic beta-cells and the transcriptional activity of HNF4alpha8 are not yet understood. In the present study, we investigated the expression of HNF4alpha in beta-cells and examined its functional properties. Western blotting and immunohistochemical analysis revealed that the expression of HNF4alpha protein in pancreatic islets and INS-1 cells was much lower than in the liver. A reporter gene assay showed that the transactivation potential of HNF4alpha8 was significantly weaker than that of HNF4alpha2, which is a major isoform in the liver, suggesting that the total level of HNF4alpha activity is very weak in pancreatic beta-cells. We also showed that the N-terminal A/B region of HNF4alpha8 possessed no activation function and C-terminal F region negatively regulated the transcriptional activity of HNF4alpha8. The information presented here would be helpful for the better understanding of MODY1/HNF4alpha diabetes.
- (2005) Gupta RK, Vatamaniuk MZ, Lee CS, Flaschen RC, Fulmer JT, Matschinsky FM, Duncan SA, Kaestner KH. The MODY1 gene HNF-4alpha regulates selected genes involved in insulin secretion. J. Clin. Invest., 115(4):1006-15.
Mutations in the gene encoding hepatocyte nuclear factor-4alpha (HNF-4alpha) result in maturity-onset diabetes of the young (MODY). To determine the contribution of HNF-4alpha to the maintenance of glucose homeostasis by the beta cell in vivo, we derived a conditional knockout of HNF-4alpha using the Cre-loxP system. Surprisingly, deletion of HNF-4alpha in beta cells resulted in hyperinsulinemia in fasted and fed mice but paradoxically also in impaired glucose tolerance. Islet perifusion and calcium-imaging studies showed abnormal responses of the mutant beta cells to stimulation by glucose and sulfonylureas. These phenotypes can be explained in part by a 60% reduction in expression of the potassium channel subunit Kir6.2. We demonstrate using cotransfection assays that the Kir6.2 gene is a transcriptional target of HNF-4alpha. Our data provide genetic evidence that HNF-4alpha is required in the pancreatic beta cell for regulation of the pathway of insulin secretion dependent on the ATP-dependent potassium channel.
- (2005) Schroeder F, Huang H, Hostetler HA, Petrescu AD, Hertz R, Bar-Tana J, Kier AB. Stability of fatty acyl-coenzyme A thioester ligands of hepatocyte nuclear factor-4alpha and peroxisome proliferator-activated receptor-alpha. Lipids, 40(6):559-68.
Although long-chain fatty acyl-coenzyme A (LCFA-CoA) thioesters are specific high-affinity ligands for hepatocyte nuclear factor-4alpha (HNF-4alpha) and peroxisome proliferator-activated receptor-alpha (PPARalpha), X-ray crystals of the respective purified recombinant ligand-binding domains (LBD) do not contain LCFA-CoA, but instead exhibit bound LCFA or have lost all ligands during the purification process, respectively. As shown herein: (i) The acyl chain composition of LCFA bound to recombinant HNF-4alpha reflected that of the bacterial LCFA-CoA pool, rather than the bacterial LCFA pool. (ii) Bacteria used to produce the respective HNF-4alpha and PPARalpha contained nearly 100-fold less LCFA-CoA than LCFA. (iii) Under conditions used to crystallize LBD (at least 3 wk at room temperature in aqueous buffer), 16:1-CoA was very unstable in buffer alone. (iv) In the presence of the respective nuclear receptor (i.e., HNF-4alpha and PPARalpha), LBD 70-75% of 16:1-CoA was degraded after 1 d at room temperature in the crystallization buffer, whereas as much as 94-97% of 16:1-CoA was degraded by 3 wk. (v) Cytoplasmic LCFA-CoA binding proteins such as acyl-CoA binding protein, sterol carrier protein-2, and liver-FA binding protein slowed the process of 16:1-CoA degradation proportional to their respective affinities for this ligand. Taken together, these data for the first time indicated that the absence of LCFA-CoA in the crystallized HNF-4alpha and PPARalpha was due to the paucity of LCFA-CoA in bacteria as well as to the instability of LCFA-CoA in aqueous buffers and the conditions used for LBD crystallization. Furthermore, instead of protecting bound LCFA-CoA from autohydrolysis like several cytoplasmic LCFA-CoA binding proteins, these nuclear receptors facilitated LCFA-CoA degradation.
review article (2005) Kaestner KH. The making of the liver: developmental competence in foregut endoderm and induction of the hepatogenic program. Cell Cycle, 4(9):1146-8.
The making of the vertebrate liver occurs in a two step process, beginning with the establishment of competence in the foregut endoderm to respond to signals from cardiac mesoderm, followed by the induction of liver-specific gene expression. Two winged helix transcription factors, Foxa1 and Foxa2, act in concert in hepatic specification. In a mouse model engineered to lack both of these genes in the foregut endoderm, no liver bud is formed and expression of even the earliest known hepatoblast markers does not occur. Furthermore, foregut endoderm derived from double mutant embryos is not responsive to inductive signals in vitro. The Foxa1/Foxa2 model is the first of a completely "liver-less mouse" and provides strong evidence for the competence model of hepatic induction.
review article (2004) Lemaigre F, Zaret KS. Liver development update: new embryo models, cell lineage control, and morphogenesis. Curr. Opin. Genet. Dev., 14(5):582-90.
The three phases of liver development that are the focus of this review are: the specification of hepatoblasts within the endoderm, the lineage split of hepatoblasts into hepatocytes and biliary cells, and the interaction of these cells with different mesodermal cell derivatives during liver morphogenesis. Advances in these areas include new genes and experimental models for studying liver development, the role of HNF6 and HNF1beta transcription factors and notch signaling in the hepatocyte-biliary cell lineage decision, the identification of genomic targets for HNF4, and HNF4's role in controlling hepatic epithelial structure and the sinusoidal organization of the liver.
- (2004) Briançon N, Bailly A, Clotman F, Jacquemin P, Lemaigre FP, Weiss MC. Expression of the alpha7 isoform of hepatocyte nuclear factor (HNF) 4 is activated by HNF6/OC-2 and HNF1 and repressed by HNF4alpha1 in the liver. J. Biol. Chem., 279(32):33398-408.
The hepatocyte nuclear factor (HNF) 4alpha gene possesses two promoters, proximal P1 and distal P2, whose use results in HNF4alpha1 and HNF4alpha7 transcripts, respectively. Both isoforms are expressed in the embryonic liver, whereas HNF4alpha1 is almost exclusively in the adult liver. A 516-bp fragment, encompassing a DNase I-hypersensitive site associated with P2 activity that is still retained in adult liver, contains functional HNF1 and HNF6 binding sites and confers full promoter activity in transient transfections. We demonstrate a critical role of the Onecut factors in P2 regulation using site-directed mutagenesis and embryos doubly deficient for HNF6 and OC-2 that show reduced hepatic HNF4alpha7 transcript levels. Transient transgenesis showed that a 4-kb promoter region is sufficient to drive expression of a reporter gene in the stomach, intestine, and pancreas, but not the liver, for which additional activating sequences may be required. Quantitative PCR analysis revealed that throughout liver development HNF4alpha7 transcripts are lower than those of HNF4alpha1. HNF4alpha1 represses P2 activity in transfection assays and as deduced from an increase in P2-derived transcript levels in recombinant mice in which HNF4alpha1 has been deleted and replaced by HNF4alpha7. We conclude that although HNF6/OC-2 and perhaps HNF1 activate the P2 promoter in the embryo, increasing HNF4alpha1 expression throughout development causes a switch to essentially exclusive P1 promoter activity in the adult liver.
- (2004) Duda K, Chi YI, Shoelson SE. Structural basis for HNF-4alpha activation by ligand and coactivator binding. J. Biol. Chem., 279(22):23311-6.
In addition to suggesting that fatty acids are endogenous ligands, our recent crystal structure of HNF-4alpha showed an unusual degree of structural flexibility in the AF-2 domain (helix alpha12). Although every molecule contained a fatty acid within its ligand binding domain, one molecule in each homodimer was in an open inactive conformation with alpha12 fully extended and colinear with alpha10. By contrast, the second molecule in each homodimer was in a closed conformation with alpha12 folded against the body of the domain in what is widely considered to be the active state. This indicates that although ligand binding is necessary, it is not sufficient to induce an activating structural transition in HNF-4alpha as is commonly suggested to occur for nuclear receptors. To further assess potential mechanisms of activation, we have solved a structure of human HNF-4alpha bound to both fatty acid ligand and a coactivator sequence derived from SRC-1. The mode of coactivator binding is similar to that observed for other nuclear receptors, and in this case, all of the molecules adopt the closed active conformation. We conclude that for HNF-4alpha, coactivator rather than ligand binding locks the active conformation.
- (2003) Hong YH, Varanasi US, Yang W, Leff T. AMP-activated protein kinase regulates HNF4alpha transcriptional activity by inhibiting dimer formation and decreasing protein stability. J. Biol. Chem., 278(30):27495-501.
AMP-activated protein kinase (AMPK) is the central component of a cellular signaling system that regulates multiple metabolic enzymes and pathways in response to reduced intracellular energy levels. The transcription factor hepatic nuclear factor 4alpha (HNF4alpha) is an orphan nuclear receptor that regulates the expression of genes involved in energy metabolism in the liver, intestine, and endocrine pancreas. Inheritance of a single null allele of HNF4alpha causes diabetes in humans. Here we demonstrate that AMPK directly phosphorylates HNF4alpha and represses its transcriptional activity. AMPK-mediated phosphorylation of HNF4alpha on serine 304 had a 2-fold effect, reducing the ability of the transcription factor to form homodimers and bind DNA and increasing its degradation rate in vivo. These results demonstrate that HNF4alpha is a downstream target of AMPK and raise the possibility that one of the effects of AMPK activation is reduced expression of HNF4alpha target genes.
- (2003) Watt AJ, Garrison WD, Duncan SA. HNF4: a central regulator of hepatocyte differentiation and function. Hepatology, 37(6):1249-53.
- (2002) Ellrott K, Yang C, Sladek FM, Jiang T. Identifying transcription factor binding sites through Markov chain optimization. Bioinformatics, 18 Suppl 2:S100-9.
Even though every cell in an organism contains the same genetic material, each cell does not express the same cohort of genes. Therefore, one of the major problems facing genomic research today is to determine not only which genes are differentially expressed and under what conditions, but also how the expression of those genes is regulated. The first step in determining differential gene expression is the binding of sequence-specific DNA binding proteins (i.e. transcription factors) to regulatory regions of the genes (i.e. promoters and enhancers). An important aspect to understanding how a given transcription factor functions is to know the entire gamut of binding sites and subsequently potential target genes that the factor may bind/regulate. In this study, we have developed a computer algorithm to scan genomic databases for transcription factor binding sites, based on a novel Markov chain optimization method, and used it to scan the human genome for sites that bind to hepatocyte nuclear factor 4 alpha (HNF4alpha). A list of 71 known HNF4alpha binding sites from the literature were used to train our Markov chain model. By looking at the window of 600 nucleotides around the transcription start site of each confirmed gene on the human genome, we identified 849 sites with varying binding potential and experimentally tested 109 of those sites for binding to HNF4alpha. Our results show that the program was very successful in identifying 77 new HNF4alpha binding sites with varying binding affinities (i.e. a 71% success rate). Therefore, this computational method for searching genomic databases for potential transcription factor binding sites is a powerful tool for investigating mechanisms of differential gene regulation.
- (2002) Wisely GB, Miller AB, Davis RG, Thornquest AD, Johnson R, Spitzer T, Sefler A, Shearer B, Moore JT, Miller AB, Willson TM, Williams SP. Hepatocyte nuclear factor 4 is a transcription factor that constitutively binds fatty acids. Structure, 10(9):1225-34.
The 2.7 A X-ray crystal structure of the HNF4gamma ligand binding domain (LBD) revealed the presence of a fatty acid within the pocket, with the AF2 helix in a conformation characteristic of a transcriptionally active nuclear receptor. GC/MS and NMR analysis of chloroform/methanol extracts from purified HNF4alpha and HNF4gamma LBDs identified mixtures of saturated and cis-monounsaturated C14-18 fatty acids. The purified HNF4 LBDs interacted with nuclear receptor coactivators, and both HNF4 subtypes show high constitutive activity in transient transfection assays, which was reduced by mutations designed to interfere with fatty acid binding. The endogenous fatty acids did not readily exchange with radiolabeled palmitic acid, and all attempts to displace them without denaturing the protein failed. Our results suggest that the HNF4s may be transcription factors that are constitutively bound to fatty acids.
review article (2002) Zaret KS. Regulatory phases of early liver development: paradigms of organogenesis. Nat. Rev. Genet., 3(7):499-512.
Genetic analysis, embryonic tissue explantation and in vivo chromatin studies have together identified the distinct regulatory steps that are necessary for the development of endoderm into a bud of liver tissue and, subsequently, into an organ. In this review, I discuss the acquisition of competence to express liver-specific genes by the endoderm, the control of early hepatic growth, the coordination of hepatic and vascular development and the cell differentiation that is necessary to generate a functioning liver. The regulatory mechanisms that underlie these phases are common to the development of many organ systems and might be recapitulated or disrupted during stem-cell differentiation and adult tissue pathogenesis.
- (2002) Dhe-Paganon S, Duda K, Iwamoto M, Chi YI, Shoelson SE. Crystal structure of the HNF4 alpha ligand binding domain in complex with endogenous fatty acid ligand. J. Biol. Chem., 277(41):37973-6.
HNF4 alpha is an orphan member of the nuclear receptor family with prominent functions in liver, gut, kidney and pancreatic beta cells. We have solved the x-ray crystal structure of the HNF4 alpha ligand binding domain, which adopts a canonical fold. Two conformational states are present within each homodimer: an open form with alpha helix 12 (alpha 12) extended and collinear with alpha 10 and a closed form with alpha 12 folded against the body of the domain. Although the protein was crystallized without added ligands, the ligand binding pockets of both closed and open forms contain fatty acids. The carboxylic acid headgroup of the fatty acid ion pairs with the guanidinium group of Arg(226) at one end of the ligand binding pocket, while the aliphatic chain fills a long, narrow channel that is lined with hydrophobic residues. These findings suggest that fatty acids are endogenous ligands for HNF4 alpha and establish a framework for understanding how HNF4 alpha activity is enhanced by ligand binding and diminished by MODY1 mutations.
- (2002) Torres-Padilla ME, Sladek FM, Weiss MC. Developmentally regulated N-terminal variants of the nuclear receptor hepatocyte nuclear factor 4alpha mediate multiple interactions through coactivator and corepressor-histone deacetylase complexes. J. Biol. Chem., 277(47):44677-87.
To understand the mechanisms governing the regulation of nuclear receptor (NR) function, we compared the parameters of activation and repression of two isoforms of the orphan receptor hepatocyte nuclear factor (HNF) 4alpha. HNF4alpha7 and HNF4alpha1 differ only in their N-terminal domains, and their expression in the liver is regulated developmentally. We show that the N-terminal activation function (AF)-1 of HNF4alpha1 possesses significant activity that can be enhanced through interaction with glucocorticoid receptor-interacting protein 1 (GRIP-1) and cAMP response element-binding protein-binding protein (CBP). In striking contrast, HNF4alpha7 possesses no measurable AF-1, implying major functional differences between the isoforms. Indeed, although HNF4alpha1 and HNF4alpha7 are able to interact via AF-2 with GRIP-1, p300, and silencing mediator for retinoid and thyroid receptors (SMRT), only HNF4alpha1 interacts in a synergistic fashion with GRIP-1 and p300. Although both isoforms interact physically and functionally with SMRT, the repression of HNF4alpha7 is less robust than that of HNF4alpha1, which may be caused by an increased ability of the latter to recruit histone deacetylase (HDAC) activity to target promoters. Moreover, association of SMRT with HDACs enhanced recruitment of HNF4alpha1 but not of HNF4alpha7. These observations suggest that NR isoform-specific association with SMRT could affect activity of the SMRT complex, implying that selection of HDAC partners is a novel point of regulation for NR activity. Possible physiological consequences of the multiple interactions with these coregulators are discussed.
- (2001) Hatzis P, Talianidis I. Regulatory mechanisms controlling human hepatocyte nuclear factor 4alpha gene expression. Mol. Cell. Biol., 21(21):7320-30.
Hepatocyte nuclear factor 4alpha (HNF-4alpha) (nuclear receptor 2A1) is an essential regulator of hepatocyte differentiation and function. Genetic and molecular evidence suggests that the tissue-restricted expression of HNF-4alpha is regulated mainly at the transcriptional level. As a step toward understanding the molecular mechanism involved in the transcriptional regulation of the human HNF-4alpha gene, we cloned and analyzed a 12.1-kb fragment of its upstream region. Major DNase I-hypersensitive sites were found at the proximal promoter, the first intron, and the more-upstream region comprising kb -6.5, -8.0, and -8.8. By the use of reporter constructs, we found that the proximal-promoter region was sufficient to drive high levels of hepatocyte-specific transcription in transient-transfection assays. DNase I footprint analysis and electrophoretic mobility shift experiments revealed binding sites for HNF-1alpha and -beta, Sp-1, GATA-6, and HNF-6. High levels of HNF-4alpha promoter activity were dependent on the synergism between either HNF-1alpha and HNF-6 or HNF-1beta and GATA-6, which implies that at least two alternative mechanisms may activate HNF-4alpha gene transcription. Chromatin immunoprecipitation experiments with human hepatoma cells showed stable association of HNF-1alpha, HNF-6, Sp-1, and COUP-TFII with the promoter. The last factor acts as a repressor via binding to a newly identified direct repeat 1 (DR-1) sequence of the human promoter, which is absent in the mouse homologue. We present evidence that this sequence is a bona fide retinoic acid response element and that HNF-4alpha expression is upregulated in vivo upon retinoic acid signaling.
review article (2001) Ryffel GU. Mutations in the human genes encoding the transcription factors of the hepatocyte nuclear factor (HNF)1 and HNF4 families: functional and pathological consequences. J. Mol. Endocrinol., 27(1):11-29.
Mutations in the human genes encoding the tissue-specific transcription factors hepatocyte nuclear factor (HNF)1alpha, HNF1beta and HNF4alpha are responsible for maturity onset diabetes of the young (MODY), a monogenic dominant inherited form of diabetes mellitus characterized by defective insulin secretion of the pancreatic beta-cells. In addition, the mutated HNF1beta gene causes defective development of the kidney and genital malformation. This review summarizes the main features of these transcription factors and discusses potential events leading to the specific disease phenotypes.
- (2001) Bailly A, Torres-Padilla ME, Tinel AP, Weiss MC. An enhancer element 6 kb upstream of the mouse HNF4alpha1 promoter is activated by glucocorticoids and liver-enriched transcription factors. Nucleic Acids Res., 29(17):3495-505.
We have characterized a 700 bp enhancer element around -6 kb relative to the HNF4alpha1 transcription start. This element increases activity and confers glucocorticoid induction to a heterologous as well as the homologous promoters in differentiated hepatoma cells and is transactivated by HNF4alpha1, HNF4alpha7, HNF1alpha and HNF1beta in dedifferentiated hepatoma cells. A 240 bp sub-region conserves basal and hormone-induced enhancer activity. It contains HNF1, HNF4, HNF3 and C/EBP binding sites as shown by DNase I footprinting and electrophoretic mobility shift assays using nuclear extracts and/or recombinant HNF1alpha and HNF4alpha1. Mutation analyses showed that the HNF1 site is essential for HNF1alpha transactivation and is required for full basal enhancer activity, as is the C/EBP site. Glucocorticoid response element consensus sites which overlap the C/EBP, HNF4 and HNF3 sites are crucial for optimal hormonal induction. We present a model that accounts for weak expression of HNF4alpha1 in the embryonic liver and strong expression in the newborn/adult liver via the binding sites identified in the enhancer.
- (2001) Torres-Padilla ME, Fougère-Deschatrette C, Weiss MC. Expression of HNF4alpha isoforms in mouse liver development is regulated by sequential promoter usage and constitutive 3' end splicing. Mech. Dev., 109(2):183-93.
Hepatocyte nuclear factor 4alpha (HNF4alpha) is essential for the establishment and maintenance of liver-specific gene expression. The HNF4alpha gene codes for several isoforms whose developmental and physiological relevance has not yet been explored. HNF4alpha1 and HNF4alpha7 originate from different promoters, while alternative splicing in 3' leads to HNF4alpha2 and HNF4alpha8, respectively. HNF4alpha7/alpha8 were abundantly expressed in embryonic liver and fetal-like hepatoma cells. HNF4alpha1/alpha2 transcripts were up-regulated at birth and represented the only isoforms in adult-like hepatoma cells. In line with its expression profile, HNF4alpha7 activated more avidly than HNF4alpha1 reporter plasmids for genes that are expressed early. The expression patterns of both isoforms together with the differences observed in their transcriptional activities provide elements accounting for fine-tuning of the activity of HNF4alpha. The sequential expression of HNF4alpha7/alpha8 and HNF4alpha1/alpha2 during mouse liver development is the only modification in liver-enriched transcription factors thus far recorded, which parallels the transition from the fetal to the adult hepatic phenotype.
- (2000) Bogan AA, Dallas-Yang Q, Ruse MD, Maeda Y, Jiang G, Nepomuceno L, Scanlan TS, Cohen FE, Sladek FM. Analysis of protein dimerization and ligand binding of orphan receptor HNF4alpha. J. Mol. Biol., 302(4):831-51.
Hepatocyte nuclear factor 4alpha (HNF4alpha) (NR2A1), an orphan member of the nuclear receptor superfamily, binds DNA exclusively as a homodimer even though it is very similar in amino acid sequence to retinoid X receptor alpha (RXRalpha), which heterodimerizes readily with other receptors. Here, experimental analysis of residues involved in protein dimerization and studies on a reported ligand for HNF4alpha are combined with a structural model of the HNF4alpha ligand-binding domain (LBD) (residues 137 to 384). When K300 (in helix 9) and E327 (in helix 10) of HNF4alpha1 were converted to the analogous residues in RXRalpha (E390 and K417, respectively) the resulting construct did not heterodimerize with the wild-type HNF4alpha, although it was still able to form homodimers and bind DNA. Furthermore, the double mutant did not heterodimerize with RXR or RAR but was still able to dimerize in solution with an HNF4alpha construct truncated at amino acid residue 268. This suggests that the charge compatibility between helices 9 and 10 is necessary, but not sufficient, to determine dimerization partners, and that additional residues in the HNF4alpha LBD are also important in dimerization. The structural model of the HNF4alpha LBD and an amino acid sequence alignment of helices 9 and 10 in various HNF4 and other receptor genes indicates that a K(X)(26)E motif can be used to identify HNF4 genes from other organisms and that a (E/D(X)(26-29)K/R) motif can be used to predict heterodimerization of many, but not all, receptors with RXR. In vitro analysis of another HNF4alpha mutant construct indicates that helix 10 also plays a structural role in the conformational integrity of HNF4alpha. The structural model and experimental analysis indicate that fatty acyl CoA thioesters, the proposed HNF4alpha ligands, are not good candidates for a traditional ligand for HNF4alpha. Finally, these results provide insight into the mechanism of action of naturally occurring mutations in the human HNF4alpha gene found in patients with maturity onset diabetes of the young 1 (MODY1).
- (2000) Soutoglou E, Katrakili N, Talianidis I. Acetylation regulates transcription factor activity at multiple levels. Mol. Cell, 5(4):745-51.
CREB-binding protein (CBP) possesses an intrinsic acetyltransferase activity capable of acetylating nucleosomal histones as well as several nonhistone proteins. Here, it is shown that CBP can acetylate hepatocyte nuclear factor-4 (HNF-4), a member of the nuclear hormone receptor family, at lysine residues within the nuclear localization sequence. CBP-mediated acetylation is crucial for the proper nuclear retention of HNF-4, which is otherwise transported out to the cytoplasm via the CRM1 pathway. Acetylation also increases HNF-4 DNA binding activity and its affinity of interaction with CBP itself and is required for target gene activation. The results show that acetylation is a key posttranslational modification that may affect several properties of a transcription factor critical for the execution of its biological functions.
review article (2000) Winter WE, Silverstein JH. Molecular and genetic bases for maturity onset diabetes of youth. Curr. Opin. Pediatr., 12(4):388-93.
Maturity onset diabetes of youth (MODY) occurs in children, adolescents and young adults as a non-insulin-requiring form of diabetes mellitus that is inherited as an autosomal dominant trait. Maturity onset diabetes of youth in whites presents subtly similar to type 2 diabetes in adults. In contrast, a MODY variant that occurs in young blacks, termed atypical diabetes mellitus, presents as an acute-onset form of diabetes. Months to years after diagnosis, atypical diabetes mellitus reverts to a noninsulin requiring course similar to MODY in whites. Five molecular causes for MODY have been identified: mutations in four transcription factors and mutations in one enzyme (glucokinase). Transcription factors regulate gene expression within cells. Mutations in hepatocyte nuclear factor-4alpha, hepatocyte nuclear factor-1alpha, insulin promoter factor-1 and hepatocyte nuclear factor-1beta, respectively, cause MODY1, MODY3, MODY4, and MODY5. Glucokinase is the glucosensor of the beta cell. MODY2 is caused by glucokinase mutations. Although testing for MODY mutations is only available in research laboratories, a careful history and review of the patient's clinical course can often allow the clinician to diagnose MODY. The diagnosis of MODY has implications for the clinical management of the patient's diabetes.
- (1999) Sladek FM, Ruse MD, Nepomuceno L, Huang SM, Stallcup MR. Modulation of transcriptional activation and coactivator interaction by a splicing variation in the F domain of nuclear receptor hepatocyte nuclear factor 4alpha1. Mol. Cell. Biol., 19(10):6509-22.
Transcription factors, such as nuclear receptors, often exist in various forms that are generated by highly conserved splicing events. Whereas the functional significance of these splicing variants is often not known, it is known that nuclear receptors activate transcription through interaction with coactivators. The parameters, other than ligands, that might modulate those interactions, however, are not well characterized, nor is the role of splicing variants. In this study, transient transfection, yeast two-hybrid, and GST pulldown assays are used to show not only that nuclear receptor hepatocyte nuclear factor 4 alpha1 (HNF4alpha1, NR2A1) interacts with GRIP1, and other coactivators, in the absence of ligand but also that the uncommonly large F domain in the C terminus of the receptor inhibits that interaction. In vitro, the F domain was found to obscure an AF-2-independent binding site for GRIP1 that did not map to nuclear receptor boxes II or III. The results also show that a natural splicing variant containing a 10-amino-acid insert in the middle of the F domain (HNF4alpha2) abrogates that inhibition in vivo and in vitro. A series of protease digestion assays indicates that there may be structural differences between HNF4alpha1 and HNF4alpha2 in the F domain as well as in the ligand binding domain (LBD). The data also suggest that there is a direct physical contact between the F domain and the LBD of HNF4alpha1 and -alpha2 and that that contact is different in the HNF4alpha1 and HNF4alpha2 isoforms. Finally, we propose a model in which the F domain of HNF4alpha1 acts as a negative regulatory region for transactivation and in which the alpha2 insert ameliorates the negative effect of the F domain. A conserved repressor sequence in the F domains of HNF4alpha1 and -alpha2 suggests that this model may be relevant to other nuclear receptors as well.
- (1998) Nakshatri H, Bhat-Nakshatri P. Multiple parameters determine the specificity of transcriptional response by nuclear receptors HNF-4, ARP-1, PPAR, RAR and RXR through common response elements. Nucleic Acids Res., 26(10):2491-9.
A number of nuclear receptors, including retinoic acid receptors (RARs), retinoid-X receptors (RXRs), hepatocyte nuclear factor 4 (HNF-4), chicken ovalbumin upstream promoter transcription factor I (COUP-TFI), apolipoprotein regulatory protein 1 (ARP-1) and peroxisome proliferator-activated receptor (PPAR), bind to response elements comprised of two core motifs, 5'-RG(G/T)TCA, or a closely related sequence separated by 1 nt (DR1 elements). The potential role of the precise sequence of the core motif as well as the spacer nucleotide in determining specificity and promiscuity of receptor-response element interactions was investigated. We show here that nucleotides at base positions 1, 2 and 4 of the core motif as well as the spacer nucleotide determine the binding preference of HNF-4 and ARP-1 homodimers and RAR:RXR and PPAR:RXR heterodimers. In transfection experiments transcriptional activation by HNF-4 and PPAR:RXR and repression by ARP-1 correlated with the relative in vitro binding affinity provided the element was located within the proper promoter context. Furthermore, promoter context also determined whether an element that binds to HNF-4 and PPAR:RXR with equal affinity functions as an HNF-4 response element or PPAR response element. Thus, apart from the element-specific differences in affinity for the receptors, additional promoter-specific transcription factors that interact with HNF-4 and PPAR:RXR determine the specificity of transcriptional response through DR1-type elements.
- (1998) Green VJ, Kokkotou E, Ladias JA. Critical structural elements and multitarget protein interactions of the transcriptional activator AF-1 of hepatocyte nuclear factor 4. J. Biol. Chem., 273(45):29950-7.
The nuclear receptor hepatocyte nuclear factor 4 (HNF-4) is an important regulator of several genes involved in diverse metabolic and developmental pathways. Mutations in the HNF-4A gene are responsible for the maturity-onset diabetes of the young type 1. Recently, we showed that the 24 N-terminal residues of HNF-4 function as an acidic transcriptional activator, termed AF-1 (Hadzopoulou-Cladaras, M., Kistanova, E., Evagelopoulou, C., Zeng, S. , Cladaras C., and Ladias, J. A. A. (1997) J. Biol. Chem. 272, 539-550). To identify the critical residues for this activator, we performed an extensive genetic analysis using site-directed mutagenesis. We showed that the aromatic and bulky hydrophobic residues Tyr6, Tyr14, Phe19, Lys10, and Lys17 are essential for AF-1 function. To a lesser degree, five acidic residues are also important for optimal activity. Positional changes of Tyr6 and Tyr14 reduced AF-1 activity, underscoring the importance of primary structure for this activator. Our analysis also indicated that AF-1 is bipartite, consisting of two modules that synergize to activate transcription. More important, AF-1 shares common structural motifs and molecular targets with the activators of the tumor suppressor protein p53 and NF-kappaB-p65, suggesting similar mechanisms of action. Remarkably, AF-1 interacted specifically with multiple transcriptional targets, including the TATA-binding protein; the TATA-binding protein-associated factors TAFII31 and TAFII80; transcription factor IIB; transcription factor IIH-p62; and the coactivators cAMP-responsive element-binding protein-binding protein, ADA2, and PC4. The interaction of AF-1 with proteins that regulate distinct steps of transcription may provide a mechanism for synergistic activation of gene expression by AF-1.
- (1998) Hertz R, Magenheim J, Berman I, Bar-Tana J. Fatty acyl-CoA thioesters are ligands of hepatic nuclear factor-4alpha. Nature, 392(6675):512-6.
Dietary fatty acids specifically modulate the onset and progression of various diseases, including cancer, atherogenesis, hyperlipidaemia, insulin resistances and hypertension, as well as blood coagulability and fibrinolytic defects; their effects depend on their chain length and degree of saturation. Hepatocyte nuclear factor-4alpha (HNF-4alpha) is an orphan transcription factor of the superfamily of nuclear receptors and controls the expression of genes that govern the pathogenesis and course of some of these diseases. Here we show that long-chain fatty acids directly modulate the transcriptional activity of HNF-4alpha by binding as their acyl-CoA thioesters to the ligand-binding domain of HNF-4alpha. This binding may shift the oligomeric-dimeric equilibrium of HNF-4alpha or may modulate the affinity of HNF-4alpha for its cognate promoter element, resulting in either activation or inhibition of HNF-4alpha transcriptional activity as a function of chain length and the degree of saturation of the fatty acyl-CoA ligands. In addition to their roles as substrates to yield energy, as an energy store, or as constituents of membrane phospholipids, dietary fatty acids may affect the course of a disease by modulating the expression of HNF-4alpha-controlled genes.
- (1997) Jiang G, Nepomuceno L, Yang Q, Sladek FM. Serine/threonine phosphorylation of orphan receptor hepatocyte nuclear factor 4. Arch. Biochem. Biophys., 340(1):1-9.
We showed previously that hepatocyte nuclear factor 4 (HNF-4) defines a new subclass, Group IV, of nuclear receptors. In order to determine whether members of this subclass are phosphorylated, HNF-4 was overexpressed to high levels in insect cells using a baculovirus expression system. The baculovirus-expressed HNF-4 (HNF4.BV) was characterized and compared to HNF-4 overexpressed in transiently transfected mammalian (COS-7) cells (HNF4.COS). The results indicate that both HNF4.BV and HNF4.COS are phosphorylated although HNF4.BV was hypophosphorylated relative to HNF4.COS. Phosphoamino acid analysis showed that HNF-4 is phosphorylated mainly on serine and to a lesser extent on threonine residues. Phosphopeptide mapping revealed 13 phosphopeptides for HNF4.COS, only 9 of which were present in the HNF4.BV sample. DNA-binding studies also showed that HNF4.BV binds DNA with a lower specificity and affinity, as measured by the equilibrium dissociation constant (Kd), than does HNF4.COS. Partial proteolytic digestion experiments also revealed that HNF4.BV and HNF4.COS adopt somewhat different three-dimensional conformations. Since glycosylation of HNF4.BV was ruled out by a number of methods and since HNF-4 expressed in bacteria exhibited an even lower DNA-binding affinity than HNF4.BV, we propose that serine/theronine phosphorylation may play a role in the DNA-binding activity of HNF-4 and, therefore, possibly of other Group IV receptors as well.
- (1997) Jiang G, Sladek FM. The DNA binding domain of hepatocyte nuclear factor 4 mediates cooperative, specific binding to DNA and heterodimerization with the retinoid X receptor alpha. J. Biol. Chem., 272(2):1218-25.
We recently showed that hepatocyte nuclear factor 4 (HNF-4) defines a unique subclass of nuclear receptors that exist in solution and bind DNA elements as homodimers (Jiang, G., Nepomuceno, L., Hopkins, K., and Sladek, F. M. (1995) Mol. Cell. Biol. 15, 5131-5143). In this study, we show that the dimerization domains of HNF-4 map to both the DNA binding and the ligand binding domain. Whereas the latter is critical for dimerization in solution, the DNA binding domain mediates cooperative, specific binding to direct repeats of AGGTCA separated by one or two nucleotides. Whereas amino acid residues 117-125 (the T-box/third helix region) are insufficient for cooperative homodimerization and high affinity DNA binding, residues 126-142 (encompassing the A-box region) are required. Finally, in contrast to the full-length receptor, the DNA binding domain of HNF-4 is capable of heterodimerizing with that of the retinoid X receptor alpha but not with that of other receptors. These results indicate that the HNF-4 DNA binding domain is distinct from that of other receptors and that the determinants that prevent HNF-4 from heterodimerizing with RXR lie outside the DNA binding domain, presumably in the ligand binding domain.
- (1997) Viollet B, Kahn A, Raymondjean M. Protein kinase A-dependent phosphorylation modulates DNA-binding activity of hepatocyte nuclear factor 4. Mol. Cell. Biol., 17(8):4208-19.
Hepatocyte nuclear factor 4 (HNF4), a liver-enriched transcription factor of the nuclear receptor superfamily, is critical for development and liver-specific gene expression. Here, we demonstrate that its DNA-binding activity is modulated posttranslationally by phosphorylation in vivo, ex vivo, and in vitro. In vivo, HNF4 DNA-binding activity is reduced by fasting and by inducers of intracellular cyclic AMP (cAMP) accumulation. A consensus protein kinase A (PKA) phosphorylation site located within the A box of its DNA-binding domain has been identified, and its role in phosphorylation-dependent inhibition of HNF4 DNA-binding activity has been investigated. Mutants of HNF4 in which two potentially phosphorylatable serines have been replaced by either neutral or charged amino acids were able to bind DNA in vitro with affinity similar to that of the wild-type protein. However, phosphorylation by PKA strongly repressed the binding affinity of the wild-type factor but not that of HNF4 mutants. Accordingly, in transfection assays, expression vectors for the mutated HNF4 proteins activated transcription more efficiently than that for the wild-type protein-when cotransfected with the PKA catalytic subunit expression vector. Therefore, HNF4 is a direct target of PKA which might be involved in the transcriptional inhibition of liver genes by cAMP inducers.
- (1997) Furuta H, Iwasaki N, Oda N, Hinokio Y, Horikawa Y, Yamagata K, Yano N, Sugahiro J, Ogata M, Ohgawara H, Omori Y, Iwamoto Y, Bell GI. Organization and partial sequence of the hepatocyte nuclear factor-4 alpha/MODY1 gene and identification of a missense mutation, R127W, in a Japanese family with MODY. Diabetes, 46(10):1652-7.
Hepatocyte nuclear factor-4 alpha (HNF-4 alpha) is a member of the nuclear receptor superfamily, a class of ligand-activated transcription factors. A nonsense mutation in the gene encoding this transcription factor was recently found in a white family with one form of maturity-onset diabetes of the young, MODY1. Here, we report the exon-intron organization and partial sequence of the human HNF-4 alpha gene. In addition, we have screened the 12 exons, flanking introns and minimal promoter region for mutations in a group of 57 unrelated Japanese subjects with early-onset NIDDM/MODY of unknown cause. Eight nucleotide substitutions were noted, of which one resulted in the mutation of a conserved arginine residue, Arg127 (CGG)-->Trp (TGG) (designated R127W), located in the T-box, a region of the protein that may play a role in HNF-4 alpha dimerization and DNA binding. This mutation was not found in 214 unrelated nondiabetic subjects (53 Japanese, 53 Chinese, 51 white, and 57 African-American). The R127W mutation was only present in three of five diabetic members in this family, indicating that it is not the only cause of diabetes in this family. The remaining seven nucleotide substitutions were located in the proximal promoter region and introns. They are not predicted to affect the transcription of the gene or mRNA processing and represent polymorphisms and rare variants. The results suggest that mutations in the HNF-4 alpha gene may cause early-onset NIDDM/MODY in Japanese but they are less common than mutations in the HNF-1 alpha/MODY3 gene. The information on the sequence of the HNF-4 alpha gene and its promoter region will facilitate the search for mutations in other populations and studies of the role of this gene in determining normal pancreatic beta-cell function.
- (1997) Hadzopoulou-Cladaras M, Kistanova E, Evagelopoulou C, Zeng S, Cladaras C, Ladias JA. Functional domains of the nuclear receptor hepatocyte nuclear factor 4. J. Biol. Chem., 272(1):539-50.
The hepatocyte nuclear factor 4 (HNF-4) is a member of the nuclear receptor superfamily and participates in the regulation of several genes involved in diverse metabolic pathways and developmental processes. To date, the functional domains of this nuclear receptor have not been identified, and it is not known whether its transcriptional activity is regulated by a ligand or other signals. In this report, we show that HNF-4 contains two transactivation domains, designated AF-1 and AF-2, which activate transcription in a cell type-independent manner. AF-1 consists of the extreme N-terminal 24 amino acids and functions as a constitutive autonomous activator of transcription. This short transactivator belongs to the class of acidic activators, and it is predicted to adopt an amphipathic alpha-helical structure. In contrast, the AF-2 transactivator is complex, spanning the 128-366 region of HNF-4, and it cannot be further dissected without impairing activity. The 360-366 region of HNF-4 contains a motif that is highly conserved among transcriptionally active nuclear receptors, and it is essential for AF-2 activity, but it is not necessary for dimerization and DNA binding of HNF-4. Thus, HNF-4 deletion mutants lacking the 361-465 region bind efficiently to DNA as homo- and heterodimers and behave as dominant negative mutants. Remarkably, the full transactivation potential of AF-2 is inhibited by the region spanning residues 371-465 (region F). The inhibitory effect of region F on the HNF-4 AF-2 activity is a unique feature among members of the nuclear receptor superfamily, and we propose that it defines a distinct regulatory mechanism of transcriptional activation by HNF-4.
- (1997) Jiang G, Lee U, Sladek FM. Proposed mechanism for the stabilization of nuclear receptor DNA binding via protein dimerization. Mol. Cell. Biol., 17(11):6546-54.
Hepatocyte nuclear factor 4 (HNF-4) defines a new subgroup of nuclear receptors that exist in solution and bind DNA exclusively as homodimers. We recently showed that the putative ligand binding domain (LBD) of HNF-4 is responsible for dimerization in solution and prevents heterodimerization with other receptors. In this report, the role of the LBD in DNA binding by HNF-4 is further investigated by using electrophoretic mobility shift analysis. A comparison of constructs containing either the DNA binding domain (DBD) alone or the DBD plus the LBD of HNF-4 showed that dimerization via the DBD was sufficient to provide nearly the full DNA binding affinity of the full-length HNF-4. In contrast, dimerization via the DBD was not sufficient to produce a stable protein-DNA complex, whereas dimerization via the LBD increased the half-life of the complex by at least 100-fold. Circular permutation analysis showed that full-length HNF-4 bent DNA by approximately 80 degrees while the DBD bent DNA by only 24 degrees. Nonetheless, analysis of other constructs indicated that the increase in stability afforded by the LBD could be explained only partially by an increased ability to bend DNA. Coimmunoprecipitation studies, on the other hand, showed that dimerization via the LBD produced a protein-protein complex that was much more stable than the corresponding protein-DNA complex. These results led us to propose a model in which dimerization via the LBD stabilizes the receptor on DNA by converting an energetically favorable two-step dissociation event into an energetically unfavorable single-step event. Implications of this one-step model for other nuclear receptors are discussed.
- (1996) Drewes T, Senkel S, Holewa B, Ryffel GU. Human hepatocyte nuclear factor 4 isoforms are encoded by distinct and differentially expressed genes. Mol. Cell. Biol., 16(3):925-31.
Hepatocyte nuclear factor 4 (HNF4) was first identified as a DNA binding activity in rat liver nuclear extracts. Protein purification had then led to the cDNA cloning of rat HNF4, which was found to be an orphan member of the nuclear receptor superfamily. Binding sites for this factor were identified in many tissue-specifically expressed genes, and the protein was found to be essential for early embryonic development in the mouse. We have now isolated cDNAs encoding the human homolog of the rat and mouse HNF4 splice variant HNF4 alpha 2, as well as a previously unknown splice variant of this protein, which we called HNF alpha 4. More importantly, we also cloned a novel HNF4 subtype (HNF4 gamma) derived from a different gene and showed that the genes encoding HNF 4 alpha and HNF4 gamma are located on human chromosomes 20 and 8, respectively. Northern (RNA) blot analysis revealed that HNF4 GAMMA is expressed in the kidney, pancreas, small intestine, testis, and colon but not in the liver, while HNF4 alpha RNA was found in all of these tissues. By cotransfection experiments in C2 and HeLa cells, we showed that HNF4 gamma is significantly less active than HNF4 alpha 2 and that the novel HNF4 alpha splice variant HNF4 alpha 4 has no detectable transactivation potential. Therefore, the differential expression of distinct HNF4 proteins may play a key role in the differential transcriptional regulation of HNF4-dependent genes.
- (1995) Ktistaki E, Ktistakis NT, Papadogeorgaki E, Talianidis I. Recruitment of hepatocyte nuclear factor 4 into specific intranuclear compartments depends on tyrosine phosphorylation that affects its DNA-binding and transactivation potential. Proc. Natl. Acad. Sci. U.S.A., 92(21):9876-80.
Hepatocyte nuclear factor 4 (HNF-4) is a prominent member of the family of liver-enriched transcription factors, playing a role in the expression of a large number of liver-specific genes. We report here that HNF-4 is a phosphoprotein and that phosphorylation at tyrosine residue(s) is important for its DNA-binding activity and, consequently, for its transactivation potential both in cell-free systems and in cultured cells. Tyrosine phosphorylation did not affect the transport of HNF-4 from the cytoplasm to the nucleus but had a dramatic effect on its subnuclear localization. HNF-4 was concentrated in distinct nuclear compartments, as evidenced by in situ immunofluorescence and electron microscopy. This compartmentalization disappeared when tyrosine phosphorylation was inhibited by genistein. The correlation between the intranuclear distribution of HNF-4 and its ability to activate endogenous target genes demonstrates a phosphorylation signal-dependent pathway in the regulation of transcription factor activity.
- (1994) Duncan SA, Manova K, Chen WS, Hoodless P, Weinstein DC, Bachvarova RF, Darnell JE. Expression of transcription factor HNF-4 in the extraembryonic endoderm, gut, and nephrogenic tissue of the developing mouse embryo: HNF-4 is a marker for primary endoderm in the implanting blastocyst. Proc. Natl. Acad. Sci. U.S.A., 91(16):7598-602.
The expression of HNF-4 (hepatocyte nuclear factor 4) mRNA in postimplantation mouse embryos was analyzed by in situ hybridization. Expression was found in the primary endoderm at embryonic day 4.5 and was restricted to the columnar visceral endoderm cells of the yolk sac from day 5.5 to day 8.5. HNF-4 mRNA was first detected in embryonic tissues at day 8.5, in the liver diverticulum and the hindgut. At later times HNF-4 transcripts were observed in the mesonephric tubules, pancreas, stomach, and intestine and, still later, in the metanephric tubules of the developing kidney. This expression pattern suggests that HNF-4 has a role in the earliest stages of murine postimplantation development as well as in organogenesis.
- (1992) Mietus-Snyder M, Sladek FM, Ginsburg GS, Kuo CF, Ladias JA, Darnell JE, Karathanasis SK. Antagonism between apolipoprotein AI regulatory protein 1, Ear3/COUP-TF, and hepatocyte nuclear factor 4 modulates apolipoprotein CIII gene expression in liver and intestinal cells. Mol. Cell. Biol., 12(4):1708-18.
Apolipoprotein CIII (apoCIII), a lipid-binding protein involved in the transport of triglycerides and cholesterol in the plasma, is synthesized primarily in the liver and the intestine. A cis-acting regulatory element, C3P, located at -90 to -66 upstream from the apoCIII gene transcriptional start site (+1), is necessary for maximal expression of the apoCIII gene in human hepatoma (HepG2) and intestinal carcinoma (Caco2) cells. This report shows that three members of the steroid receptor superfamily of transcription factors, hepatocyte nuclear factor 4 (HNF-4), apolipoprotein AI regulatory protein 1 (ARP-1), and Ear3/COUP-TF, act at the C3P site. HNF-4 activates apoCIII gene expression in HepG2 and Caco2 cells, while ARP-1 and Ear3/COUP-TF repress its expression in the same cells. HNF-4 activation is abolished by increasing amounts of ARP-1 or Ear3/COUP-TF, and repression by ARP-1 or Ear3/COUP-TF is alleviated by increasing amounts of HNF-4. HNF-4 and ARP-1 bind with similar affinities to the C3P site, suggesting that their opposing transcriptional effects may be mediated by direct competition for DNA binding. HNF-4 and ARP-1 mRNAs are present within the same cells in the liver and intestine, and protein extracts from hepatic tissue, HepG2, and Caco2 cells contain significantly more HNF-4 than ARP-1 or Ear3/COUP-TF binding activities. These findings suggest that the transcription of the apoCIII gene in vivo is dependent, at least in part, upon the intracellular balance of these positive and negative regulatory factors.
- (1992) Ladias JA, Hadzopoulou-Cladaras M, Kardassis D, Cardot P, Cheng J, Zannis V, Cladaras C. Transcriptional regulation of human apolipoprotein genes ApoB, ApoCIII, and ApoAII by members of the steroid hormone receptor superfamily HNF-4, ARP-1, EAR-2, and EAR-3. J. Biol. Chem., 267(22):15849-60.
Apolipoproteins B, CIII, and AII are synthesized primarily in the liver and intestine and play an important role in lipid and cholesterol metabolism. It was previously shown that the cis-acting elements (BA1 (-79 to -63), CIIIB (-87 to -63), and AIIJ (-740 to -719) present in the regulatory regions of the human apoB, apoCIII, and apoAII genes, respectively, are recognized by common transcription factors present in hepatic nuclear extracts. This report shows that four members of the steroid receptor superfamily, ARP-1, EAR-2, EAR-3, and HNF-4, bind specifically to the regulatory elements BA1, CIIIB, and AIIJ. Dissociation constant measurements showed that ARP-1, EAR-2, and HNF-4 bind to elements BA1 and CIIIB with similar affinities (Kd 1-3 nM). Cotransfection experiments in HepG2 cells revealed that ARP-1, EAR-2, and EAR-3 repressed the BA1, CIIIB, and AIIJ element-dependent transcription of the reporter gene constructs and the transcription driven by homopolymeric promoters containing either five BA1 or two CIIIB elements. In contrast, HNF-4 activated transcription of reporter genes containing the elements BA1, CIIIB, and AIIJ and reversed the ARP-1-mediated repression of the apoB and apoCIII genes. These results suggested that the opposing transcription effects observed between HNF-4 and ARP-1 may be due to competition for binding to the same regulatory element. Mutations which affected the binding of HNF-4 to elements BA1 and CIIIB affected its ability to activate transcription of the apoB and apoCIII reporter genes, respectively. Transcriptional activation by HNF-4 depended on the presence of elements II (-112 to -94) and III (-86 to -62) of the apoB and H (-705 to -690), I (-766 to -726), and J (-792 to -779) of the apoCIII promoters, indicating that transcriptional activation of apoB and apoCIII genes by HNF-4 requires the synergistic interaction of factors binding to these elements. The finding that HNF-4, ARP-1, EAR-2 and EAR-3 can regulate the expression of the apoB, apoCIII, and apoAII genes suggest that these nuclear hormone receptors may be an important part of the signal transduction pathways modulating lipid metabolism and cholesterol homeostasis.
- (1992) Reijnen MJ, Sladek FM, Bertina RM, Reitsma PH. Disruption of a binding site for hepatocyte nuclear factor 4 results in hemophilia B Leyden. Proc. Natl. Acad. Sci. U.S.A., 89(14):6300-3.
Hemophilia B Leyden is an X chromosome-linked bleeding disorder characterized by very low plasma levels of blood coagulation factor IX (fIX) during childhood. After puberty, plasma fIX levels gradually rise to a maximum of 60% of normal, probably under the influence of testosterone. Single point mutations in the fIX promoter region of hemophilia B Leyden patients have been reported at -20, -6, -5, +8 and +13. In addition, one promoter mutation (G----C at -26) has been detected that abolishes fIX expression throughout life (M. Ludwig, personal communication). We examined how one of the hemophilia B Leyden mutations (T----A at -20) and the G----C mutation at -26 interfere with fIX gene transcription. We report that the wild-type promoter of the human fIX gene contains a binding site (at nucleotides -34 to -10) for hepatocyte nuclear factor 4 (HNF-4), a member of the steroid hormone receptor superfamily of transcription factors. The binding of HNF-4 is disrupted by both the T----A mutation at -20 and the G----C mutation at -26. Whereas HNF-4 transactivates the wild-type promoter sequence in liver (HepG2) and non-liver (HeLa) cell types quite well, it transactivates the -20 mutated promoter to only a limited extent and the -26 mutated promoter not at all. These data suggest that HNF-4 is a major factor controlling fIX expression in the normal individual and that its inability to bind efficiently to the -20 T----A and the -26 G----C mutated promoter sequence results in hemophilia. Further, the severity of the hemophilia phenotype appears to be directly related to the degree of disruption of HNF-4 binding and transactivation.
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