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1.  Epistasis of Transcriptomes Reveals Synergism between Transcriptional Activators Hnf1α and Hnf4α 
PLoS Genetics  2010;6(5):e1000970.
The transcription of individual genes is determined by combinatorial interactions between DNA–binding transcription factors. The current challenge is to understand how such combinatorial interactions regulate broad genetic programs that underlie cellular functions and disease. The transcription factors Hnf1α and Hnf4α control pancreatic islet β-cell function and growth, and mutations in their genes cause closely related forms of diabetes. We have now exploited genetic epistasis to examine how Hnf1α and Hnf4α functionally interact in pancreatic islets. Expression profiling in islets from either Hnf1a+/− or pancreas-specific Hnf4a mutant mice showed that the two transcription factors regulate a strikingly similar set of genes. We integrated expression and genomic binding studies and show that the shared transcriptional phenotype of these two mutant models is linked to common direct targets, rather than to known effects of Hnf1α on Hnf4a gene transcription. Epistasis analysis with transcriptomes of single- and double-mutant islets revealed that Hnf1α and Hnf4α regulate common targets synergistically. Hnf1α binding in Hnf4a-deficient islets was decreased in selected targets, but remained unaltered in others, thus suggesting that the mechanisms for synergistic regulation are gene-specific. These findings provide an in vivo strategy to study combinatorial gene regulation and reveal how Hnf1α and Hnf4α control a common islet-cell regulatory program that is defective in human monogenic diabetes.
Author Summary
The transcriptional activity of each gene is typically determined by multiple transcription factors. This concept has been well established in studies of single genes. However, transcription factors do not simply regulate single genes, they also control broad gene programs that underlie cellular function and disease. Understanding how combinations of transcription factors interact at the level of cellular regulatory programs remains a challenge. Humans with mutations in the genes encoding for the transcription factors Hnf1α and Hnf4α develop similar forms of diabetes that result from abnormal insulin secretion, suggesting that the two factors might have related functions in insulin-producing islet-cells. We now show that Hnf1α or Hnf4α bind to a common set of genes and that islet-cells from mice in which either Hnf1α or Hnf4α has been selectively disrupted show abnormal expression of similar genes. By comparing the gene expression defects of mice with mutations in either Hnf1a, Hnf4a, or both genes, we determined that Hnf1α and Hnf4α regulate common target genes through synergistic mechanisms. These results thus provide insight into a regulatory network that fails in human diabetes. Similar genetic strategies can also be employed to unravel how other transcription factors interact functionally in native cellular contexts.
doi:10.1371/journal.pgen.1000970
PMCID: PMC2877749  PMID: 20523905
2.  Macrosomia and Hyperinsulinaemic Hypoglycaemia in Patients with Heterozygous Mutations in the HNF4A Gene 
PLoS Medicine  2007;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-4α) and HNF1A/TCF1 (encoding HNF-1α), 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 β-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.
HNF4A mutations were found to be associated with a considerable increase in birthweight and macrosomia, and were a cause of neonatal hypoglycaemia.
Editors' Summary
Background.
MODY, or maturity-onset diabetes of the young, is a particular subtype of diabetes; only a few percent of people with diabetes are thought to have this subtype. The condition comes about as a result of a mutation in one of six genes. Generally, people with MODY have high glucose (sugar) levels in the blood, and the typical symptoms of diabetes, such as increased thirst and urination, typically develop when the person is below the age of 25 y. Two of the genes that are known to cause MODY are mutant forms of HNF4A and HNF1A. The proteins that are encoded by these two genes control insulin levels produced by the pancreas; when these genes are mutated, not enough insulin is produced. Without enough insulin to control blood sugar, levels rise, leading to the symptoms of diabetes. However, MODY can be managed by many of the same interventions as other types of diabetes, such as diet, exercise, drug treatments, and insulin injections.
Why Was This Study Done?
Although the evidence shows that individuals who carry mutations in HNF4A and HNF1A do not produce enough insulin and therefore have higher glucose levels in their blood, there were some tantalizing suggestions from mouse experiments that this might not be the whole story. Specifically, the researchers suspected that during embryonic development, mutations in HNF4A or HNF1A might actually cause higher insulin levels. Too much insulin during development of a fetus is known to cause it to gain weight, resulting in a baby that is larger than the average size for its age. Larger babies are risky for both the baby and the mother. The researchers doing this study wanted to understand more precisely what the links were between the forms of MODY caused by HNF4A and HNF1A mutations, and birth-weight and blood-sugar levels.
What Did the Researchers Do and Find?
In this study, the researchers examined 15 families in which some family members had MODY caused by a mutation in HNF4A. They compared the birthweight for family members carrying the mutation (54 people) against the birthweight for those who did not (54 people). A similar comparison was done for 38 families in which some members had a different form of MODY, this time caused by a mutation in HNF1A. The results showed that the birthweight of family members who carried a mutation in HNF4A was, on average, 790 g higher than the birthweight of family members who didn't carry the mutation. Low blood-sugar levels at birth were also more common in people carrying the HNF4A mutation as compared to people who did not. However, the HNF1A mutation did not seem to be associated with greater birthweight or low blood-sugar levels at birth. Finally, in order to understand these findings further, the researchers created embryonic mice carrying mutations in the mouse equivalent of HNF4A. These embryos produced more insulin than normal mouse embryos and, after birth, were more likely to have low blood-sugar levels.
What Do These Findings Mean?
These findings show that there is a link between mutations in HNF4A, but not in HNF1A, and increased birthweight. The increase found in this study is quite substantial (a median weight of 4,660 g in the affected babies; a birthweight of more than 4,000 g is generally considered large). The results suggest that in human embryos with a mutated form of HNF4A, too much insulin is produced during development, causing faster growth and a higher chance of the baby being born with low blood-sugar levels. This is an unexpected finding, because later in life the HNF4A mutation causes lower insulin levels. Therefore, the biochemical pathways causing this type of MODY seem to be quite complicated, and further research will need to be done to fully understand them. Crucially, the research also suggests that pregnant women carrying HNF4A mutations should be closely followed to check their baby's growth and minimize the chance of complications. Doctors and families should also consider doing a genetic test for HNF4A if a baby has low blood-sugar levels and if there is a family history of diabetes; this would increase the chance of diagnosing MODY early.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed 0040118.
In a related Perspective in PLoS Medicine, Benjamin Glaser discusses causes of type 2 diabetes mellitus in the context of this study's findings
The US National Institute of Diabetes and Digestive and Kidney Diseases has pages of information on different types of diabetes
Wikipedia has an entry on Maturity Onset Diabetes of the Young (MODY) (note that Wikipedia is an internet encyclopedia that anyone can edit)
Diabetes Research Department, Peninsula Medical School, Exeter, UK provides information for patients and doctors on genetic types of diabetes; the website is maintained by the research group carrying out this study
Information from the Centers for Disease Control and Prevention on diabetes and pregnancy
doi:10.1371/journal.pmed.0040118
PMCID: PMC1845156  PMID: 17407387
3.  Effects of hepatocyte nuclear factor-1A and -4A on pancreatic stone protein/regenerating protein and C-reactive protein gene expression: implications for maturity-onset diabetes of the young 
Background
There is a significant clinical overlap between patients with hepatocyte nuclear factor (HNF)-1A and HNF4A maturity-onset diabetes of the young (MODY), two forms of monogenic diabetes. HNF1A and HNF4A are transcription factors that control common and partly overlapping sets of target genes. We have previously shown that elevated serum pancreatic stone protein / regenerating protein A (PSP/reg1A) levels can be detected in subjects with HNF1A-MODY. In this study, we investigated whether PSP/reg is differentially regulated by HNF1A and HNF4A.
Methods
Quantitative real-time PCR (qPCR) and Western blotting were used to validate gene and protein expression in cellular models of HNF1A- and HNF4A-MODY. Serum PSP/reg1A levels and high-sensitivity C-reactive protein (hsCRP) were measured by ELISA in 31 HNF1A- and 9 HNF4A-MODY subjects. The two groups were matched for age, body mass index, diabetes duration, blood pressure, lipid profile and aspirin and statin use.
Results
Inducible repression of HNF1A and HNF4A function in INS-1 cells suggested that PSP/reg induction required HNF4A, but not HNF1A. In contrast, crp gene expression was significantly reduced by repression of HNF1A, but not HNF4A function. PSP/reg levels were significantly lower in HNF4A subjects when compared to HNF1A subjects [9.25 (7.85-12.85) ng/ml vs. 12.5 (10.61-17.87) ng/ml, U-test P = 0.025]. hsCRP levels were significantly lower in HNF1A-MODY [0.22 (0.17-0.35) mg/L] compared to HNF4A-MODY group [0.81 (0.38-1.41) mg/L, U-test P = 0.002], Parallel measurements of serum PSP/reg1A and hsCRP levels were able to discriminate HNF1A- and HNF4A-MODY subjects.
Conclusion
Our study demonstrates that two distinct target genes, PSP/reg and crp, are differentially regulated by HNF1A and HNF4A, and provides clinical proof-of-concept that serum PSP/reg1A and hsCRP levels may distinguish HNF1A-MODY from HNF4A-MODY subjects.
doi:10.1186/1479-5876-11-156
PMCID: PMC3707779  PMID: 23803251
HNF1A; HNF4A; MODY; PSP/reg; HsCRP; Gene regulation
4.  Liver-Specific Reactivation of the Inactivated Hnf-1α Gene: Elimination of Liver Dysfunction To Establish a Mouse MODY3 Model 
Molecular and Cellular Biology  2003;23(3):923-932.
Mice deficient in hepatocyte nuclear factor 1 α (HNF-1α) develop dwarfism, liver dysfunction, and type 2 diabetes mellitus. Liver dysfunction in HNF-1α-null mice includes severe hepatic glycogen accumulation and dyslipidemia. The liver dysfunction may appear as soon as 2 weeks after birth. Since the HNF-1α-null mice become diabetic 2 weeks after birth, the early onset of the liver dysfunction is unlikely to be due to the diabetic status of the mice. More likely, it is due directly to the deficiency of HNF-1α in liver. Although the HNF-1α-null mice have an average life span of 1 year, the severe liver phenotype has thwarted attempts to study the pathogenesis of maturity-onset diabetes of the young type 3 (MODY3) and to examine therapeutic strategies for diabetes prevention and treatment in these mice. To circumvent this problem, we have generated a new Hnf-1α mutant mouse line, Hnf-1αkin/kin, using gene targeting to inactivate the Hnf-1α gene and at the same time, to incorporate the Cre-loxP DNA recombination system into the locus for later revival of the Hnf-1α gene in tissues by tissue-specifically expressed Cre recombinase. The Hnf-1αkin/kin mice in which the expression of HNF-1α was inactivated in germ line cells were indistinguishable from the HNF-1α-null mice with regard to both the diabetes and liver phenotypes. Intriguingly, when the inactivated Hnf-1α gene was revived in liver (hepatic Hnf-1α revived) by the Cre recombinase driven by an albumin promoter, the Hnf-1αkin/kin mice, although severely diabetic, grew normally and did not develop any of the liver dysfunctions. In addition, we showed that the expression of numerous genes in pancreas, including a marker gene for pancreas injury, was affected by liver dysfunction but not by the deficiency of HNF-1α in pancreas. Thus, our hepatic-Hnf-1α-revived mice may serve as a useful mouse model to study the human MODY3 disorder.
doi:10.1128/MCB.23.3.923-932.2003
PMCID: PMC140695  PMID: 12529398
5.  Hepatic Nuclear Factor 1-α Directs Nucleosomal Hyperacetylation to Its Tissue-Specific Transcriptional Targets 
Molecular and Cellular Biology  2001;21(9):3234-3243.
Mutations in the gene encoding hepatic nuclear factor 1-α (HNF1-α) cause a subtype of human diabetes resulting from selective pancreatic β-cell dysfunction. We have analyzed mice lacking HNF1-α to study how this protein controls β-cell-specific transcription in vivo. We show that HNF1-α is essential for the expression of glut2 glucose transporter and L-type pyruvate kinase (pklr) genes in pancreatic insulin-producing cells, whereas in liver, kidney, or duodenum tissue, glut2 and pklr expression is maintained in the absence of HNF1-α. HNF1-α nevertheless occupies the endogenous glut2 and pklr promoters in both pancreatic islet and liver cells. However, it is indispensable for hyperacetylation of histones in glut2 and pklr promoter nucleosomes in pancreatic islets but not in liver cells, where glut2 and pklr chromatin remains hyperacetylated in the absence of HNF1-α. In contrast, the phenylalanine hydroxylase promoter requires HNF1-α for transcriptional activity and localized histone hyperacetylation only in liver tissue. Thus, different HNF1-α target genes have distinct requirements for HNF1-α in either pancreatic β-cells or liver cells. The results indicate that HNF1-α occupies target gene promoters in diverse tissues but plays an obligate role in transcriptional activation only in cellular- and promoter-specific contexts in which it is required to recruit histone acetylase activity. These findings provide genetic evidence based on a live mammalian system to establish that a single activator can be essential to direct nucleosomal hyperacetylation to transcriptional targets.
doi:10.1128/MCB.21.9.3234-3243.2001
PMCID: PMC86965  PMID: 11287626
6.  The MODY1 Gene for Hepatocyte Nuclear Factor 4α and a Feedback Loop Control COUP-TFII Expression in Pancreatic Beta Cells▿  
Molecular and Cellular Biology  2008;28(14):4588-4597.
Pancreatic islet beta cell differentiation and function are dependent upon a group of transcription factors that maintain the expression of key genes and suppress others. Knockout mice with the heterozygous deletion of the gene for chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) or the complete disruption of the gene for hepatocyte nuclear factor 4α (HNF4α) in pancreatic beta cells have similar insulin secretion defects, leading us to hypothesize that there is transcriptional cross talk between these two nuclear receptors. Here, we demonstrate specific HNF4α activation of a reporter plasmid containing the COUP-TFII gene promoter region in transfected pancreatic beta cells. The stable association of the endogenous HNF4α with a region of the COUP-TFII gene promoter that contains a direct repeat 1 (DR-1) binding site was revealed by chromatin immunoprecipitation. Mutation experiments showed that this DR-1 site is essential for HNF4α transactivation of COUP-TFII. The dominant negative suppression of HNF4α function decreased endogenous COUP-TFII expression, and the specific inactivation of COUP-TFII by small interfering RNA caused HNF4α mRNA levels in 832/13 INS-1 cells to decrease. This positive regulation of HNF4α by COUP-TFII was confirmed by the adenovirus-mediated overexpression of human COUP-TFII (hCOUP-TFII), which increased HNF4α mRNA levels in 832/13 INS-1 cells and in mouse pancreatic islets. Finally, hCOUP-TFII overexpression showed that there is direct COUP-TFII autorepression, as COUP-TFII occupies the proximal DR-1 binding site of its own gene in vivo. Therefore, COUP-TFII may contribute to the control of insulin secretion through the complex HNF4α/maturity-onset diabetes of the young 1 (MODY1) transcription factor network operating in beta cells.
doi:10.1128/MCB.01191-07
PMCID: PMC2447131  PMID: 18474611
7.  Hepatic function in a family with a nonsense mutation (R154X) in the hepatocyte nuclear factor-4alpha/MODY1 gene. 
Journal of Clinical Investigation  1997;100(6):1400-1405.
Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic disorder characterized by autosomal dominant inheritance, onset usually before 25 yr of age, and abnormal pancreatic beta-cell function. Mutations in the hepatocyte nuclear factor(HNF)-4alpha/MODY1, glucokinase/MODY2, and HNF-1alpha/MODY3 genes can cause this form of diabetes. In contrast to the glucokinase and HNF-1alpha genes, mutations in the HNF-4alpha gene are a relatively uncommon cause of MODY, and our understanding of the MODY1 form of diabetes is based on studies of only a single family, the R-W pedigree. Here we report the identification of a second family with MODY1 and the first in which there has been a detailed characterization of hepatic function. The affected members of this family, Dresden-11, have inherited a nonsense mutation, R154X, in the HNF-4alpha gene, and are predicted to have reduced levels of this transcription factor in the tissues in which it is expressed, including pancreatic islets, liver, kidney, and intestine. Subjects with the R154X mutation exhibited a diminished insulin secretory response to oral glucose. HNF-4alpha plays a central role in tissue-specific regulation of gene expression in the liver, including the control of synthesis of proteins involved in cholesterol and lipoprotein metabolism and the coagulation cascade. Subjects with the R154X mutation, however, showed no abnormalities in lipid metabolism or coagulation except for a paradoxical 3.3-fold increase in serum lipoprotein(a) levels, nor was there any evidence of renal dysfunction in these subjects. The results suggest that MODY1 is primarily a disorder of beta-cell function.
PMCID: PMC508318  PMID: 9294105
8.  Genetic evidence that HNF-1α–dependent transcriptional control of HNF-4α is essential for human pancreatic β cell function 
Mutations in the genes encoding hepatocyte nuclear factor 4α (HNF-4α) and HNF-1α impair insulin secretion and cause maturity onset diabetes of the young (MODY). HNF-4α is known to be an essential positive regulator of HNF-1α. More recent data demonstrates that HNF-4α expression is dependent on HNF-1α in mouse pancreatic islets and exocrine cells. This effect is mediated by binding of HNF-1α to a tissue-specific promoter (P2) located 45.6 kb upstream from the previously characterized Hnf4α promoter (P1). Here we report that the expression of HNF-4α in human islets and exocrine cells is primarily mediated by the P2 promoter. Furthermore, we describe a G → A mutation in a conserved nucleotide position of the HNF-1α binding site of the P2 promoter, which cosegregates with MODY. The mutation results in decreased affinity for HNF-1α, and consequently in reduced HNF-1α–dependent activation. These findings provide genetic evidence that HNF-1α serves as an upstream regulator of HNF-4α and interacts directly with the P2 promoter in human pancreatic cells. Furthermore, they indicate that this regulation is essential to maintain normal pancreatic function.
doi:10.1172/JCI15085
PMCID: PMC151122  PMID: 12235114
9.  Targeted Deficiency of the Transcriptional Activator Hnf1α Alters Subnuclear Positioning of Its Genomic Targets 
PLoS Genetics  2008;4(5):e1000079.
DNA binding transcriptional activators play a central role in gene-selective regulation. In part, this is mediated by targeting local covalent modifications of histone tails. Transcriptional regulation has also been associated with the positioning of genes within the nucleus. We have now examined the role of a transcriptional activator in regulating the positioning of target genes. This was carried out with primary β-cells and hepatocytes freshly isolated from mice lacking Hnf1α, an activator encoded by the most frequently mutated gene in human monogenic diabetes (MODY3). We show that in Hnf1a−/− cells inactive endogenous Hnf1α-target genes exhibit increased trimethylated histone H3-Lys27 and reduced methylated H3-Lys4. Inactive Hnf1α-targets in Hnf1a−/− cells are also preferentially located in peripheral subnuclear domains enriched in trimethylated H3-Lys27, whereas active targets in wild-type cells are positioned in more central domains enriched in methylated H3-Lys4 and RNA polymerase II. We demonstrate that this differential positioning involves the decondensation of target chromatin, and show that it is spatially restricted rather than a reflection of non-specific changes in the nuclear organization of Hnf1a-deficient cells. This study, therefore, provides genetic evidence that a single transcriptional activator can influence the subnuclear location of its endogenous genomic targets in primary cells, and links activator-dependent changes in local chromatin structure to the spatial organization of the genome. We have also revealed a defect in subnuclear gene positioning in a model of a human transcription factor disease.
Author Summary
All cells in an organism share a common genome, yet distinct subsets of genes are transcribed in different cells. Selectivity of gene transcription is largely determined by transcription factors that bind to target genes and promote local changes in chromatin. Such changes are thought to be instrumental for transcription. Emerging evidence indicates that the position of genes in the 3-dimensional structure of the nucleus may also be important in transcriptional regulation. However, the role of transcription factors in gene positioning, and its possible relationship with chromatin modifications, is poorly understood. To examine this, we employed a genetic approach. We used mice lacking Hnf1α, a transcription factor gene that is mutated in an inherited form of diabetes. We studied genes that are directly bound by Hnf1α, as well as various control genomic regions, and determined their position in nuclear space in liver and insulin-producing β-cells. The results showed that the absence of Hnf1α causes local changes in the chromatin of target genes. At the same time, it modifies the position of target genes in nuclear space. The findings of this study lead us to propose a model whereby transcription factor dependent local chromatin modifications are linked to subnuclear gene positioning. They also revealed abnormal subnuclear positioning in a model of a human transcription factor disease.
doi:10.1371/journal.pgen.1000079
PMCID: PMC2375116  PMID: 18497863
10.  Expression and localization of P1 promoter-driven hepatocyte nuclear factor-4α (HNF4α) isoforms in human and rats 
Nuclear Receptor  2003;1:5.
Background
Hepatocyte nuclear factor-4α (HNF4α; NR2A1) is an orphan member of the nuclear receptor superfamily involved in various processes that could influence endoderm development, glucose and lipid metabolism. A loss-of-function mutation in human HNF4α causes one form of diabetes mellitus called maturity-onset diabetes of the young type 1 (MODY1) which is characterized in part by a diminished insulin secretory response to glucose. The expression of HNF4α in a variety of tissues has been examined predominantly at the mRNA level, and there is little information regarding the cellular localization of the endogenous HNF4α protein, due, in part, to the limited availability of human HNF4α-specific antibodies.
Results
Monoclonal antibodies have been produced using baculovirus particles displaying gp64-HNF4α fusion proteins as the immunizing agent. The mouse anti-human HNF4α monoclonal antibody (K9218) generated against human HNF4α1/α2/α3 amino acids 3–49 was shown to recognize not only the transfected and expressed P1 promoter-driven HNF4α proteins, but also endogenous proteins. Western blot analysis with whole cell extracts from Hep G2, Huh7 and Caco-2 showed the expression of HNF4α protein, but HEK293 showed no expression of HNF4α protein. Nuclear-specific localization of the HNF4α protein was observed in the hepatocytes of liver cells, proximal tubular epithelial cells of kidney, and mucosal epithelial cells of small intestine and colon, but no HNF4α protein was detected in the stomach, pancreas, glomerulus, and distal and collecting tubular epithelial cells of kidney. The same tissue distribution of HNF4α protein was observed in humans and rats. Electron microscopic immunohistochemistry showed a chromatin-like localization of HNF4α in the liver and kidney. As in the immunohistochemical investigation using K9218, HNF4α mRNA was found to be localized primarily to liver, kidney, small intestine and colon by RT-PCR and GeneChip analysis.
Conclusion
These results suggest that this method has the potential to produce valuable antibodies without the need for a protein purification step. Immunohistochemical studies indicate the tissue and subcellular specific localization of HNF4α and demonstrate the utility of K9218 for the detection of P1 promoter-driven HNF4α isoforms in humans and in several other mammalian species.
doi:10.1186/1478-1336-1-5
PMCID: PMC194242  PMID: 12952540
11.  Functional Targets of the Monogenic Diabetes Transcription Factors HNF-1α and HNF-4α Are Highly Conserved Between Mice and Humans 
Diabetes  2009;58(5):1245-1253.
OBJECTIVE
The evolutionary conservation of transcriptional mechanisms has been widely exploited to understand human biology and disease. Recent findings, however, unexpectedly showed that the transcriptional regulators hepatocyte nuclear factor (HNF)-1α and -4α rarely bind to the same genes in mice and humans, leading to the proposal that tissue-specific transcriptional regulation has undergone extensive divergence in the two species. Such observations have major implications for the use of mouse models to understand HNF-1α– and HNF-4α–deficient diabetes. However, the significance of studies that assess binding without considering regulatory function is poorly understood.
RESEARCH DESIGN AND METHODS
We compared previously reported mouse and human HNF-1α and HNF-4α binding studies with independent binding experiments. We also integrated binding studies with mouse and human loss-of-function gene expression datasets.
RESULTS
First, we confirmed the existence of species-specific HNF-1α and -4α binding, yet observed incomplete detection of binding in the different datasets, causing an underestimation of binding conservation. Second, only a minor fraction of HNF-1α– and HNF-4α–bound genes were downregulated in the absence of these regulators. This subset of functional targets did not show evidence for evolutionary divergence of binding or binding sequence motifs. Finally, we observed differences between conserved and species-specific binding properties. For example, conserved binding was more frequently located near transcriptional start sites and was more likely to involve multiple binding events in the same gene.
CONCLUSIONS
Despite evolutionary changes in binding, essential direct transcriptional functions of HNF-1α and -4α are largely conserved between mice and humans.
doi:10.2337/db08-0812
PMCID: PMC2671044  PMID: 19188435
12.  Hepatocyte Nuclear Factor 4α Contributes to Thyroid Hormone Homeostasis by Cooperatively Regulating the Type 1 Iodothyronine Deiodinase Gene with GATA4 and Krüppel-Like Transcription Factor 9▿ †  
Molecular and Cellular Biology  2008;28(12):3917-3931.
Type 1 iodothyronine deiodinase (Dio1), a selenoenzyme catalyzing the bioactivation of thyroid hormone, is highly expressed in the liver. Dio1 mRNA and enzyme activity levels are markedly reduced in the livers of hepatocyte nuclear factor 4α (HNF4α)-null mice, thus accounting for its liver-specific expression. Consistent with this deficiency, serum T4 and rT3 concentrations are elevated in these mice compared with those in HNF4α-floxed control littermates; however, serum T3 levels are unchanged. Promoter analysis of the mouse Dio1 gene demonstrated that HNF4α plays a key role in the transactivation of the mouse Dio1 gene. Deletion and substitution mutation analyses demonstrated that a proximal HNF4α site (direct repeat 1 [TGGACAAAGGTGC]; HNF4α-RE) is crucial for transactivation of the mouse Dio1 gene by HNF4α. Mouse Dio1 is also stimulated by thyroid hormone signaling, but a direct role for thyroid hormone receptor action has not been reported. We also showed that thyroid hormone-inducible Krüppel-like factor 9 (KLF9) stimulates the mouse Dio1 promoter very efficiently through two CACCC sequences that are located on either side of HNF4α-RE. Furthermore, KLF9 functions together with HNF4α and GATA4 to synergistically activate the mouse Dio1 promoter, suggesting that Dio1 is regulated by thyroid hormone in the mouse through an indirect mechanism requiring prior KLF9 induction. In addition, we showed that physical interactions between the C-terminal zinc finger domain (Cf) of GATA4 and activation function 2 of HNF4α and between the basic domain adjacent to Cf of GATA4 and a C-terminal domain of KLF9 are both required for this synergistic response. Taken together, these results suggest that HNF4α regulates thyroid hormone homeostasis through transcriptional regulation of the mouse Dio1 gene with GATA4 and KLF9.
doi:10.1128/MCB.02154-07
PMCID: PMC2423126  PMID: 18426912
13.  Genetic analysis of a transcriptional activation pathway by using hepatoma cell variants. 
Molecular and Cellular Biology  1994;14(11):7086-7094.
A hierarchy of liver-enriched transcription factors plays an important role in activating expression of many hepatic genes. In particular, hepatocyte nuclear factor 4 (HNF-4) is a major activator of the gene encoding HNF-1, and HNF-1 itself activates expression of more than 20 liver genes. To dissect this activation pathway genetically, we prepared somatic cell variants that were deficient in expression of the liver-specific alpha 1-antitrypsin (alpha 1AT) gene, which requires both HNF-1 and HNF-4 for high-level gene activity. This was accomplished in two steps. First, hepatoma transfectants that stably expressed two selectable markers under alpha 1AT promoter control were prepared; second, variant sublines that could no longer express either transgene were isolated by direct selection. In this report, we demonstrate that the variants contain defects in the HNF-4/HNF-1 activation pathway. These defects functioned in trans, as expression of many liver genes was affected, but the variant phenotypes were recessive to wild type in somatic cell hybrids. Three different variant classes could be discriminated by their phenotypic responses to ectopic expression of either HNF-4 or HNF-1. Two variant clones appeared specifically deficient in HNF-4 expression, as transfection with an HNF-4 expression cassette fully restored their hepatic phenotypes. Another line activated HNF-1 in response to forced HNF-4 expression, but activation of downstream genes failed to occur. One clone was unresponsive to either HNF-1 or HNF-4. Using the variants, we demonstrate further that the chromosomal genes encoding alpha 1AT, aldolase B, and alpha-fibrinogen display strict requirements for HNF-1 activation in vivo, while other liver genes were unaffected by the presence or absence of HNF-1 or HNF-4. We also provide evidence for the existence of an autoregulatory loop in which HNF-1 regulates its own expression through activation of HNF-4.
Images
PMCID: PMC359242  PMID: 7935424
14.  The transcriptional activator hepatocyte nuclear factor 6 regulates liver gene expression. 
Molecular and Cellular Biology  1996;16(11):6273-6284.
The hepatocyte nuclear factor 3(alpha) (HNF-3(alpha)), -3(beta), and -3(gamma) proteins share homology in the winged-helix/fork head DNA binding domain and mediate hepatocyte-enriched transcription of numerous genes whose expression is necessary for organ function. In this work, we identify a liver-enriched transcription factor, HNF-6, which recognizes the -138 to -126 region of the HNF-3(beta) promoter and binds the original HNF-3 site of the transthyretin promoter (-94 to -106). We show that HNF-6 and HNF-3 possess different DNA binding specificities by competition and methylation interference studies and are immunologically distinct. Site-directed mutagenesis of the HNF-6 sites in the HNF-3(beta) and transthyretin promoters diminishes reporter gene expression, suggesting that HNF-6 activates transcription of these promoters. Using the HNF-6 binding sequence DHWATTGAYTWWD (where W = A or T, Y = T or C, H is not G, and D is not C) determined by sequence comparison and methylation interference, we predicted that HNF-6 will bind to 22 additional hepatocyte-enriched genes. Of these potential target genes, we selected seven of the HNF-6 binding sequences and demonstrated that they bind the HNF-6 protein. These include promoter sequences from alpha-2 urinary globulin, alpha-1 antitrypsin, cytochrome P-450 2C13, L-type 6-phosphofructo-2-kinase, mouse major urinary protein, tryptophan oxygenase, and alpha-fetoprotein genes. HNF-6 binding activity was also found in the intestinal epithelial cell line HT29, and potential HNF-6 binding sites were present in intestinal sucrase isomaltase, cdx-2 homeodomain protein, and intestinal fatty acid binding protein promoter regions. These studies suggest that HNF-6 may regulate hepatocyte-specific genes and may play a role in epithelial cell differentiation of gut endoderm via regulation of HNF-3(beta).
PMCID: PMC231630  PMID: 8887657
15.  Differential Effects of HNF-1α Mutations Associated with Familial Young-Onset Diabetes on Target Gene Regulation 
Molecular Medicine  2010;17(3-4):256-265.
Hepatocyte nuclear factor 1-α (HNF-1α) is a homeodomain transcription factor expressed in a variety of tissues (including liver and pancreas) that regulates a wide range of genes. Heterozygous mutations in the gene encoding HNF-1α (HNF1A) cause familial young-onset diabetes, also known as maturity-onset diabetes of the young, type 3 (MODY3). The variability of the MODY3 clinical phenotype can be due to environmental and genetic factors as well as to the type and position of mutations. Thus, functional characterization of HNF1A mutations might provide insight into the molecular defects explaining the variability of the MODY3 phenotype. We have functionally characterized six HNF1A mutations identified in diabetic patients: two novel ones, p.Glu235Gly and c-57-64delCACGCGGT;c-55G>C; and four previously described, p.Val133Met, p.Thr196Ala, p.Arg271Trp and p.Pro379Arg. The effects of mutations on transcriptional activity have been measured by reporter assays on a subset of HNF-1α target promoters in Cos7 and Min6 cells. Target DNA binding affinities have been quantified by electrophoretic mobility shift assay using bacterially expressed glutathione-S-transferase (GST)-HNF-1α fusion proteins and nuclear extracts of transfected Cos7 cells. Our functional studies revealed that mutation c-57-64delCACGCGGT;c-55G>C reduces HNF1A promoter activity in Min6 cells and that missense mutations have variable effects. Mutation p.Arg271Trp impairs HNF-1α activity in all conditions tested, whereas mutations p.Val133Met, p.Glu235Gly and p.Pro379Arg exert differential effects depending on the target promoter. In contrast, substitution p.Thr196Ala does not appear to alter HNF-1α function. Our results suggest that HNF1A mutations may have differential effects on the regulation of specific target genes, which could contribute to the variability of the MODY3 clinical phenotype.
doi:10.2119/molmed.2010.00097
PMCID: PMC3060974  PMID: 21170474
16.  An indirect negative autoregulatory mechanism involved in hepatocyte nuclear factor-1 gene expression. 
Nucleic Acids Research  1993;21(25):5882-5889.
Recent studies have revealed that hepatocyte nuclear factor 4 (HNF-4) is an essential positive regulator of another liver enriched transcription factor HNF-1, defining a transcriptional hierarchy between the two factors operating in hepatocytes. To assess the possible autoregulation of the HNF-1 gene we have examined the effect of HNF-1 on its own transcription. In transient transfection assays, HNF-1 strongly down-regulated transcription driven by its own promoter in HepG2 cells. In addition HNF-1 also repressed the activity of HNF-4 dependent ApoCIII and ApoAI promoters. The same effect was observed using vHNF-1, a distinct but highly related protein to HNF-1. Both HNF-1 and vHNF-1 downregulated HNF-4 activated transcription from intact and chimeric promoter constructs carrying various HNF-4 binding sites implying that they act by impeding HNF-4 binding or activity. DNA binding and cell free transcription experiments however failed to demonstrate any direct or indirect interaction of HNF-1 and vHNF-1 with the above regulatory regions. Both factors repressed HNF-4 induced transcription of the ApoCIII and HNF-1 genes in HeLa cells, arguing against the requirement of a hepatocyte specific function. These findings define an indirect negative autoregulatory mechanism involved in HNF-1 gene expression, which in turn may affect HNF-4 dependent transcription of other liver specific genes.
Images
PMCID: PMC310469  PMID: 8290348
17.  SRC-1 and GRIP1 Coactivate Transcription with Hepatocyte Nuclear Factor 4* 
The Journal of biological chemistry  1998;273(47):30847-30850.
Hepatocyte nuclear factor-4 (HNF4), a member of the nuclear receptor superfamily, plays an important role in tissue-specific gene expression, including genes involved in hepatic glucose metabolism. In this study, we show that SRC-1 and GRIP1, which act as coactivators for various nuclear receptors, associate with HNF4 in vivo and enhance its transactivation potential. The AF-2 domain of HNF4 is required for this interaction and for the potentiation of transcriptional activity by these co-activators. p300 can also serve as a coactivator with HNF4, and it synergizes with SRC-1 to further augment the activity of HNF4. HNF4 is also a key regulator of the expression of hepatocyte nuclear factor-1 (HNF1). The overexpression of SRC-1 or GRIP1 enhances expression from a HNF1 gene promoter-reporter in HepG2 hepatoma cells, and this requires an intact HNF4-binding site in the HNF1 gene promoter. Type 1 maturity onset diabetes of young (MODY), which is characterized by abnormal glucose-mediated insulin secretion, is caused by mutations of the HNF4 gene. A mutation of the HNF4-binding site in the HNF1 gene promoter has also been associated with MODY. Thus, HNF4 is involved in the regulation of glucose homeostasis at several levels and along with the SRC-1, GRIP1, and p300 may play an important role in the pathophysiology of non-insulin-dependent diabetes mellitus.
PMCID: PMC3968904  PMID: 9812974
18.  Species-Specific Differences in the Expression of the HNF1A, HNF1B and HNF4A Genes 
PLoS ONE  2009;4(11):e7855.
Background
The HNF1A, HNF1B and HNF4A genes are part of an autoregulatory network in mammalian pancreas, liver, kidney and gut. The layout of this network appears to be similar in rodents and humans, but inactivation of HNF1A, HNF1B or HNF4A genes in animal models cause divergent phenotypes to those seen in man. We hypothesised that some differences may arise from variation in the expression profile of alternatively processed isoforms between species.
Methodology/Principal Findings
We measured the expression of the major isoforms of the HNF1A, HNF1B and HNF4A genes in human and rodent pancreas, islet, liver and kidney by isoform-specific quantitative real-time PCR and compared their expression by the comparative Ct (ΔΔCt) method. We found major changes in the expression profiles of the HNF genes between humans and rodents. The principal difference lies in the expression of the HNF1A gene, which exists as three isoforms in man, but as a single isoform only in rodents. More subtle changes were to the balance of HNF1B and HNF4A isoforms between species; the repressor isoform HNF1B(C) comprised only 6% in human islets compared with 24–26% in rodents (p = 0.006) whereas HNF4A9 comprised 22% of HNF4A expression in human pancreas but only 11% in rodents (p = 0.001).
Conclusions/Significance
The differences we note in the isoform-specific expression of the human and rodent HNF1A, HNF1B and HNF4A genes may impact on the absolute activity of these genes, and therefore on the activity of the pancreatic transcription factor network as a whole. We conclude that alterations to expression of HNF isoforms may underlie some of the phenotypic variation caused by mutations in these genes.
doi:10.1371/journal.pone.0007855
PMCID: PMC2773013  PMID: 19924231
19.  Association between Hepatocyte Nuclear Factor 6 (HNF-6) and FoxA2 DNA Binding Domains Stimulates FoxA2 Transcriptional Activity but Inhibits HNF-6 DNA Binding 
Molecular and Cellular Biology  2003;23(2):437-449.
In previous studies we used transgenic mice or recombinant adenovirus infection to increase hepatic expression of forkhead box A2 (FoxA2, previously called hepatocyte nuclear factor 3β [HNF-3β]), which caused diminished hepatocyte glycogen levels and reduced expression of glucose homeostasis genes. Because this diminished expression of FoxA2 target genes was associated with reduced levels of the Cut-Homeodomain HNF-6 transcription factor, we conducted the present study to determine whether there is a functional interaction between HNF-6 and FoxA2. Human hepatoma (HepG2) cotransfection assays demonstrated that HNF-6 synergistically stimulated FoxA2 but not FoxA1 or FoxA3 transcriptional activity, and protein-binding assays showed that this protein interaction required the HNF-6 Cut-Homeodomain and FoxA2 winged-helix DNA binding domains. Furthermore, we show that the HNF-6 Cut-Homeodomain sequences were sufficient to synergistically stimulate FoxA2 transcriptional activation by recruiting the p300/CBP coactivator proteins. This was supported by the fact that FoxA2 transcriptional synergy with HNF-6 was dependent on retention of the HNF-6 Cut domain LXXLL sequence, which mediated recruitment of the p300/CBP proteins. Moreover, cotransfection and DNA binding assays demonstrated that increased FoxA2 levels caused a decrease in HNF-6 transcriptional activation of the glucose transporter 2 (Glut-2) promoter by interfering with the binding of HNF-6 to its target DNA sequence. These data suggest that at a FoxA-specific site, HNF-6 serves as a coactivator protein to enhance FoxA2 transcription, whereas at an HNF-6-specific site, FoxA2 represses HNF-6 transcription by inhibiting HNF-6 DNA binding activity. This is the first reported example of a liver-enriched transcription factor (HNF-6) functioning as a coactivator protein to potentiate the transcriptional activity of another liver factor, FoxA2.
doi:10.1128/MCB.23.2.437-449.2003
PMCID: PMC151533  PMID: 12509444
20.  Inhibitor of the Tissue-Specific Transcription Factor HNF4, a Potential Regulator in Early Xenopus Development 
Molecular and Cellular Biology  2000;20(23):8676-8683.
Hepatocyte nuclear factor 4α (HNF4α) is an orphan receptor of the nuclear receptor superfamily and expressed in vertebrates as a tissue-specific transcription factor in liver, kidney, intestine, stomach, and pancreas. It also plays a crucial role in early embryonic development and has been identified as a maternal component in the Xenopus egg. We now report on an activity present in Xenopus embryos that inhibits the DNA binding of HNF4. This HNF4 inhibitor copurifies with a 25-kDa protein under nondenaturing conditions but can be separated from this protein by sodium dodecyl sulfate treatment. Protease treatment of the inhibitor results in a core fragment of about 5 kDa that retains full inhibitory activity. The activity of the HNF4 inhibitor can also be monitored in the absence of DNA, as it alters the mobility of the HNF4 protein in native polyacrylamide gels and the accessibility of antibodies. Comparing the activity of the HNF4 inhibitor with acyl coenzyme A's, recently proposed to be ligands of HNF4, we observe a more stringent specificity for the HNF4 inhibitor activity. Using deletion constructs of the HNF4 protein, we could show that the potential ligand-binding domain of HNF4 is not required, and thus the HNF4 inhibitor does not represent a classical ligand as defined for the nuclear receptor superfamily. Based on our previous finding that maternal HNF4 is abundantly present in Xenopus embryos but the target gene HNF1α is only marginally expressed, we propose that the HNF4 inhibitor functions in the embryo to restrict the activity of the maternal HNF4 proteins.
PMCID: PMC86478  PMID: 11073969
21.  Regulation of HSulf-1 expression by variant hepatic nuclear factor 1 (vHNF1) in ovarian cancer 
Cancer research  2009;69(11):4843-4850.
We recently identified HSulf-1 as a downregulated gene in ovarian carcinomas. Our previous analysis indicated that HSulf-1 inactivation in ovarian cancers is partly mediated by loss of heterozygosity (LOH) and epigenetic silencing. Here we demonstrate that variant hepatic nuclear factor 1 (vHNF1), encoded by transcription factor 2 gene (TCF2, HNF-1β) negatively regulates HSulf-1 expression in ovarian cancer. Immunoblot assay revealed that vHNF1 is highly expressed in HSulf-1 deficient OV207, SKOV3 and TOV-21G cell lines but not in HSulf-1 expressing OSE, OV167 and OV202 cells. By shRNA-mediated downregulation of vHNF1 in TOV21-G cells and transient enhanced vHNF1 expression in OV202 cells, we showed that vHNF1 suppresses HSulf-1 expression in ovarian cancer cell lines. Reporter assay and chromatin immunoprecipitation (ChIP) experiments showed that vHNF1 is specifically recruited to HSulf-1 promoter at two different vHNF1 responsive elements in OV207 and TOV-21G cells. Additionally, downregulation of vHNF1 expression in OV207 and TOV-21G cells increased cisplatin- or paclitaxel-mediated cytotoxicity as determined by both MTT and clonogenic assays and this effect was reversed by downregulation of HSulf-1. Moreover, nude mice bearing TOV-21G cell xenografts with stably downregulated vHNF1 were more sensitive to cisplatin-or paclitaxel-induced cytotoxicity compared to xenografts of TOV-21G clonal lines with nontargeted control shRNA. Finally, immunohistochemical analysis of 501 ovarian tumors including 140 clear cell tumors on tissue microarrays showed that vHNF1 inversely correlates to HSulf-1 expression. Collectively, these results indicate that vHNF1 acts as a repressor of HSulf-1 expression and might be a molecular target for ovarian cancer therapy.
doi:10.1158/0008-5472.CAN-08-3065
PMCID: PMC2713066  PMID: 19487294
vHNF1; HSulf-1; ovarian cancer
22.  INS-1 Cells Undergoing Caspase-Dependent Apoptosis Enhance the Regenerative Capacity of Neighboring Cells 
Diabetes  2010;59(11):2799-2808.
OBJECTIVE
In diabetes, β-cell mass is not static but in a constant process of cell death and renewal. Inactivating mutations in transcription factor 1 (tcf-1)/hepatocyte nuclear factor1a (hnf1a) result in decreased β-cell mass and HNF1A–maturity onset diabetes of the young (HNF1A-MODY). Here, we investigated the effect of a dominant-negative HNF1A mutant (DN-HNF1A) induced apoptosis on the regenerative capacity of INS-1 cells.
RESEARCH DESIGN AND METHODS
DN-HNF1A was expressed in INS-1 cells using a reverse tetracycline-dependent transactivator system. Gene(s)/protein(s) involved in β-cell regeneration were investigated by real-time quantitative RT-PCR, Western blotting, and immunohistochemistry. Pancreatic stone protein/regenerating protein (PSP/reg) serum levels in human subjects were detected by enzyme-linked immunosorbent assay.
RESULTS
We detected a prominent induction of PSP/reg at the gene and protein level during DN-HNF1A–induced apoptosis. Elevated PSP/reg levels were also detected in islets of transgenic HNF1A-MODY mice and in the serum of HNF1A-MODY patients. The induction of PSP/reg was glucose dependent and mediated by caspase activation during apoptosis. Interestingly, the supernatant from DN-HNF1A–expressing cells, but not DN-HNF1A–expressing cells treated with zVAD.fmk, was sufficient to induce PSP/reg gene expression and increase cell proliferation in naïve, untreated INS-1 cells. Further experiments demonstrated that annexin-V–positive microparticles originating from apoptosing INS-1 cells mediated the induction of PSP/reg. Treatment with recombinant PSP/reg reversed the phenotype of DN-HNF1A–induced cells by stimulating cell proliferation and increasing insulin gene expression.
CONCLUSIONS
Our results suggest that apoptosing INS-1 cells shed microparticles that may stimulate PSP/reg induction in neighboring cells, a mechanism that may facilitate the recovery of β-cell mass in HNF1A-MODY.
doi:10.2337/db09-1478
PMCID: PMC2963538  PMID: 20682686
23.  HNF4beta, a new gene of the HNF4 family with distinct activation and expression profiles in oogenesis and embryogenesis of Xenopus laevis. 
Molecular and Cellular Biology  1997;17(2):687-694.
The transcription factor hepatocyte nuclear factor 4 (HNF4) is an orphan member of the nuclear receptor superfamily expressed in mammals in liver, kidney, and the digestive tract. Recently, we isolated the Xenopus homolog of mammalian HNF4 and revealed that it is not only a tissue-specific transcription factor but also a maternal component of the Xenopus egg and distributed within an animal-to-vegetal gradient. We speculate that this gradient cooperates with the vegetally localized embryonic induction factor activin A to activate expression of HNF1alpha, a tissue-specific transcription factor with an expression pattern overlapping that of HNF4. We have now identified a second Xenopus HNF4 gene, which is more distantly related to mammalian HNF4 than the previously isolated gene. This new gene was named HNF4beta to distinguish it from the known HNF4 gene, which is now called HNF4alpha. By reverse transcription-PCR, we detected within the 5' untranslated region of HNF4beta two splice variants (HNF4beta2 and HNF4beta3) with additional exons, which seem to affect RNA stability. HNF4beta is a functional transcription factor acting sequence specifically on HNF4 binding sites known for HNF4alpha, but it seems to have a lower DNA binding activity and is a weaker transactivator than the alpha isoform. Furthermore, the two factors differ with respect to tissue distribution in adult frogs: whereas HNF4alpha is expressed in liver and kidney, HNF4beta is expressed in addition in stomach, intestine, lung, ovary, and testis. Both factors are maternal proteins and present at constant levels throughout embryogenesis. However, using reverse transcription-PCR, we found the RNA levels to change substantially: whereas HNF4alpha is expressed early during oogenesis and is absent in the egg, HNF4beta is first detected in the latest stage of oogenesis, and transcripts are present in the egg and early cleavage stages. Furthermore, zygotic HNF4alpha transcripts appear in early gastrula and accumulate during further embryogenesis, whereas HNF4beta mRNA transiently appears during gastrulation before it accumulates again at the tail bud stage. All of these distinct characteristics of the newly identified HNF4 protein imply that the alpha and beta isoform have different functions in development and in adult tissues.
PMCID: PMC231794  PMID: 9001222
24.  Hepatocyte Nuclear Factor 4α enhances the Hepatocyte Nuclear Factor 1α-mediated activation of transcription 
Nucleic Acids Research  2004;32(8):2586-2593.
Hepatocyte Nuclear Factor 1α (HNF1α) and Hepatocyte Nuclear Factor 4α (HNF4α) are two liver-enriched transcription factors coexpressed in specific tissues where they play a crucial role through their involvement in a complex cross-regulatory network. HNF1α down regulates HNF4α-mediated activation of transcription via a direct protein–protein interaction. Here we show that HNF4α enhances the transcriptional activity of HNF1α in a DNA binding independent manner, thus indicating that it behaves as a HNF1α coactivator. Using mutations in the ligand binding domain (LBD) of HNF4α, we confirmed the involvement of the Activation Function 2 module and demonstrated the requirement of the integrity of the LBD for the interaction with HNF1α. Moreover, we show that HNF4α cooperates with p300 to achieve the highest HNF1α-mediated transcription rates. Our findings highlight a new way by which HNF4α can regulate gene expression and extend our knowledge of the complexity of the transcriptional network involving HNF4α and HNF1α.
doi:10.1093/nar/gkh581
PMCID: PMC419469  PMID: 15141028
25.  Human hepatocyte nuclear factor 4 isoforms are encoded by distinct and differentially expressed genes. 
Molecular and Cellular Biology  1996;16(3):925-931.
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.
PMCID: PMC231074  PMID: 8622695

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