A transcriptional regulatory element common to a large family of hepatic cytochrome P450 genes is a functional binding site of the orphan receptor HNF-4.
Hepatic cytochrome P450 (CYP) genes, including members of CYP1 to CYP4 families, comprise the majority of the CYP gene superfamily. Previous study has demonstrated that HepG2-specific transcriptional activation of two CYP2C genes was dependent on a common element that bound a HepG2 nuclear protein designated HPF-1 (Venepally, P., Chen, D., and Kemper, B. (1992) J. Biol. Chem. 267, 17333-17338). This cis-acting element is highly homologous to the hepatocyte nuclear factor 4 (HNF-4) binding motif and is present in the promoters of more than 20 other CYP2 genes. To investigate the relationship between HPF-1 and HNF-4, we have compared their tissue distribution, DNA binding, and immunochemical characteristics, as well as transcriptional activity of their recognition elements. DNase I footprint analyses and gel-shift assays indicated that HPF-1, like HNF-4, was present in liver and kidney, but not brain and spleen. Both factors bound to either the HPF-1 site in the CYP2C2 promoter or an HNF-4 site in the human apolipoprotein CIII promoter. These complexes could be "supershifted" by an antiserum specific for HNF-4. When the sequence of the HPF-1 site in the CYP2C2 promoter was changed to that of the apolipoprotein CIII HNF-4 site, comparable transcriptional activities were obtained with the wild-type promoter and the HNF-4 mutant in transfected HepG2 cells. Cotransfection of HNF-4 with CYP2C2 promoter-luciferase constructs in COS-1 cells indicated that HNF-4 could trans-activate the promoters containing the HPF-1 site. These results indicate that the HPF-1 motif is a functional HNF-4-binding site, and the common immunological properties indicate that HPF-1 and HNF-4 are closely related and possibly identical. HNF-4, therefore, may act as a common regulator for the liver-specific expression of many CYP2 genes.
Chen
D
D
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
Lepar
G
G
Kemper
B
B
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D007527:Isoenzymes / Q000235:genetics*; D008099:Liver / Q000201:enzymology*; D008113:Liver Neoplasms; D008297:Male; D008969:Molecular Sequence Data; D005810:Multigene Family; D010750:Phosphoproteins; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D007527:Isoenzymes; C403128:MLX protein, human; D010750:Phosphoproteins; C501970:Tcfl4 protein, mouse; D014157:Transcription Factors; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase