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Mol. Cell. Biol., Nov 1996, 6273-6284, Vol 16, No. 11
U Samadani and RH Costa
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).
Copyright © 1996, American Society for Microbiology
The transcriptional activator hepatocyte nuclear factor 6 regulates liver gene expression
Department of Biochemistry, University of Illinois at Chicago, 60612- 7334, USA.
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