The molecular functions of hepatocyte nuclear factors - In and beyond the liver (original) (raw)
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Molecular and cellular biology, 2000
Liver-specific gene expression is controlled by a heterogeneous group of hepatocyte-enriched transcription factors. One of these, the winged helix transcription factor hepatocyte nuclear factor 3beta (HNF3beta or Foxa2) is essential for multiple stages of embryonic development. Recently, HNF3beta has been shown to be an important regulator of other hepatocyte-enriched transcription factors as well as the expression of liver-specific structural genes. We have addressed the role of HNF3beta in maintenance of the hepatocyte phenotype by inactivation of HNF3beta in the liver. Remarkably, adult mice lacking HNF3beta expression specifically in hepatocytes are viable, with histologically normal livers and normal liver function. Moreover, analysis of >8,000 mRNAs by array hybridization revealed that lack of HNF3beta affects the expression of only very few genes. Based on earlier work it appears that HNF3beta plays a critical role in early liver development; however, our studies demonstra...
2000
Liver-specific gene expression is controlled by a heterogeneous group of hepatocyte-enriched transcription factors. One of these, the winged helix transcription factor hepatocyte nuclear factor 3 (HNF3 or Foxa2) is essential for multiple stages of embryonic development. Recently, HNF3 has been shown to be an important regulator of other hepatocyte-enriched transcription factors as well as the expression of liver-specific structural genes. We have addressed the role of HNF3 in maintenance of the hepatocyte phenotype by inactivation of HNF3 in the liver. Remarkably, adult mice lacking HNF3 expression specifically in hepatocytes are viable, with histologically normal livers and normal liver function. Moreover, analysis of >8,000 mRNAs by array hybridization revealed that lack of HNF3 affects the expression of only very few genes. Based on earlier work it appears that HNF3 plays a critical role in early liver development; however, our studies demonstrate that HNF3 is not required for maintenance of the adult hepatocyte or for normal liver function. This is the first example of such functional dichotomy for a tissue specification transcription factor.
Genomics, 1992
The genes for rat hepatocyte nuclear factors 3 and 4 (HNF-3a, HNF-3/3, HNF-37, and HNF-4) have been mapped in mouse by analysis of restriction fragment length polymorphisms in interspecific backcross mice. These hepatocyteenriched transcription factors are positive-acting transcription factors with binding sites in regulatory regions of many genes expressed in hepatocytes. Both HNF-3a, /3, and y and HNF-4 are also expressed in intestine. They have recently been implicated as potential participants in endodermal development from early gut cells because of their close homology to Drosophila genes, which themselves are expressed in the developing gut. Despite having similar functional roles and highly conserved DNA binding domains, the three loci from the Hnf-3 family of genes mapped to three different mouse chromosomes, suggesting that the Hnf-3 family has become widely dispersed during evolution and implying the necessity for independent activation of each member of the HNF-3 family.
Structural Basis of Disease-Causing Mutations in Hepatocyte Nuclear Factor 1β
Biochemistry, 2007
HNF1β is an atypical POU transcription factor that participates in a hierarchical network of transcription factors controlling the development and proper function of vital organs such as liver, pancreas, and kidney. Many inheritable mutations on HNF1β are the monogenic causes of diabetes and several kidney diseases. To elucidate the molecular mechanism of its function and the structural basis of mutations, we have determined the crystal structure of human HNF1β DNA binding domain in complex with a high-affinity promoter. Disease-causing mutations have been mapped to our structure, and their predicted effects have been tested by a set of biochemical/ functional studies. These findings together with earlier findings with a homologous protein HNF1α, help us to understand the structural basis of promoter recognition by these atypical POU transcription factors and the site-specific functional disruption by disease-causing mutations. HNF1β (hepatocyte nuclear factor 1β; also known as vHNF1 or TCF2) is a widely distributed transcription factor that plays a critical role in early vertebrate development and embryonic survival (1-3). First identified as a key regulator in the liver, HNF1β is also expressed in the pancreas, kidney, lung, ovary, testis, and throughout the gastrointestinal tract. In pancreatic β-cells, HNF1β is known to form an integrated regulatory network with other transcription factors such as HNF1α, HNF4α, Pdx-1, Foxa2, and NeuroD1 for organ development and proper function (1,4). Thus, in humans, heterozygous mutations in the HNF1β gene have been linked to neonatal diabetes (5) and the autosomal dominant subtype of diabetes known as MODY (maturity-onset diabetes of the young) (6). Extrapancreatic diseases are also increasingly recognized in different organs, especially in the kidney, with a variety of renal developmental disorders such as renal cysts, familial hypoplastic glomerulocystic kidney disease, renal malformation, and atypical familial hyperuricaemic nephropathy (7-11).
2005
A complex network of hepatocyte nuclear transcription factors, including HNF6 and Foxa2, regulates the expression of liver-specific genes. The current model, based on in vitro studies, suggests that HNF6 and Foxa2 interact physically. This interaction is thought to synergistically stimulate Foxa2-dependent transcription through the recruitment of p300/CBP by HNF6 and to inhibit HNF6-mediated transcription due to the interference of Foxa2 with DNA binding by HNF6. To test this model in vivo, we utilized hepatocyte-specific gene ablation to study the binding of HNF6 to its targets in the absence of Foxa2. Chromatin immunoprecipitation using anti-HNF6 antibodies was performed on chromatin isolated from Foxa2 loxP/loxP Alfp.Cre and control mouse livers, and HNF6 binding to its target, Glut2, was determined by quantitative PCR. In contrast to the current model, we found no significant difference in HNF6 occupancy at the Glut2 promoter between Foxa2-deficient and control livers. In order to evaluate the Foxa2/HNF6 interaction model on a global scale, we performed a location analysis using a microarray with 7,000 mouse promoter fragments. Again, we found no evidence that HNF6 binding to its targets in chromatin is reduced in the presence of Foxa2. We also examined the mRNA levels of HNF6 targets in the liver using a cDNA array and found that their expression was similar in Foxa2-deficient and control mice. Overall, our studies demonstrate that HNF6 binds to and regulates its target promoters in vivo in the presence and absence of Foxa2.
Genes & Development, 1991
Hepatocyte nuclear factor 1 (HNF-1) is a transcriptional regulatory protein possibly involved in the activation of many liver-specifically expressed genes. HNF-1 mRNA is restricted to a small number of tissues, suggesting that the HNF-1 gene itself is regulated at the transcriptional level. We have isolated and characterized the promoter region of this gene and have determined its transcriptional potential in several cell types by cell-free transcription and transient transfection experiments. In in vitro transcription assays, an HNF-1 promoter is active in nuclear extracts from liver and kidney, two tissues that contain HNF-1, but silent in nuclear extracts from spleen and lung, which are devoid of this transcription factor. Likewise, in transfection experiments, HNF-1 promoter-chloramphenicol acetyltransferase (CAT) fusion genes are expressed in Hep G2 cells, which express HNF-1, but not in mouse L cells or Hela cells, which do not express HNF-1. In both cell-free transcription and transient transfection assays, a relatively short promoter segment located between positions -82 and -40 is necessary and sufficient to direct cell type-specific HNF-1 transcription. This region contains a single site for a DNA-binding protein that has been tentatively identified as hepatocyte nuclear factor 4, a member of the steroid hormone receptor family. Cold Spring Harbor Laboratory Press on July 15, 2016 -Published by genesdev.cshlp.org Downloaded from 2226 GENES & DEVELOPMENT Cold Spring Harbor Laboratory Press on July 15, 2016 -Published by genesdev.cshlp.org Downloaded from 2230 GENES & DEVELOPMENT Cold Spring Harbor Laboratory Press on July 15, 2016 -Published by genesdev.cshlp.org Downloaded from Tissue-specific HNF-1 transcription Discussion Access the most recent version at doi: 1991 5: 2225-2234 Genes Dev. J M Tian and U Schibler factor 1 may involve hepatocyte nuclear factor 4. Tissue-specific expression of the gene encoding hepatocyte nuclear References http://genesdev.cshlp.org/content/5/12a/2225.full.html#ref-list-1
Nucleic Acids Research, 1993
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 downregulated transcription driven by its own promoter in HepG2 cells. In addition HNF-1 also repressed the activity of HNF-4 dependent ApoCill and ApoAl 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 ApoCill 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.
Structure of the gene enconding hepatocyte nuclear factor 1 (HNF1)
Nucleic Acids Research, 1992
Genomic clones have been isolated that cover the entire gene for the transcription factor HNF1 (hepatocyte nuclear factor 1). This protein governs the expression of many genes, synthesized in the liver in a tissue-specific manner. We have determined the intron/exon structure of the HNF1 gene, which is strictly conserved between rat and mouse and estimate that it spans not more than 40kb in the rat genome. Whereas most homeoprotein genes do not contain introns within the homeodomain, HNF1 displays an intron between the regions encoding the second and the third helices. We discuss possible evolutionary mechanisms leading to this homeobox intron/exon pattern.
Hepatology, 2004
A network of liver-enriched transcription factors controls differentiation and morphogenesis of the liver. These factors interact via direct, feedback, and autoregulatory loops. Previous work has suggested that hepatocyte nuclear factor (HNF)-6/OC-1 and HNF-3␣/FoxA1 participate coordinately in this hepatic network. We investigated how HNF-6 controls the expression of Foxa1. We observed that Foxa1 expression was upregulated in the liver of Hnf6 ؊/؊ mouse embryos and in bipotential mouse embryonic liver (BMEL) cell lines derived from embryonic Hnf6 ؊/؊ liver, suggesting that HNF-6 inhibits the expression of Foxa1. Because no evidence for a direct repression of Foxa1 by HNF-6 was found, we postulated the existence of an indirect mechanism. We found that the expression of a mediator and targets of the transforming growth factor beta (TGF-) signaling was increased both in Hnf6 ؊/؊ liver and in Hnf6 ؊/؊ BMEL cell lines. Using these cell lines, we demonstrated that TGF- signaling was increased in the absence of HNF-6, and that this resulted from upregulation of TGF- receptor II expression. We also found that TGF- can stimulate the expression of Foxa1 in Hnf6 ؉/؉ cells and that inhibition of TGF- signaling in Hnf6 ؊/؊ cells downregulates the expression of Foxa1. In conclusion, we propose that Foxa1 upregulation in the absence of HNF-6 results from increased TGF- signaling via increased expression of the TGF- receptor II. We further conclude that HNF-6 inhibits Foxa1 by inhibiting the activity of the TGF- signaling pathway. This identifies a new mechanism of interaction between liver-enriched transcription factors whereby one factor indirectly controls another by modulating the activity of a signaling pathway. (HEPATOLOGY 2004;40:1266 -1274