The transcriptional activator hepatocyte nuclear factor 6 regulates liver gene expression.
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).
Samadani
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Department of Biochemistry, University of Illinois at Chicago, 60612-7334, USA.
Costa
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RH
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D016384:Consensus Sequence; D019175:DNA Methylation; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011228:Prealbumin / Q000096:biosynthesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism*; D015533:Transcriptional Activation
D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins; C496606:Onecut1 protein, mouse; D011228:Prealbumin; D011994:Recombinant Proteins; D015534:Trans-Activators