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

Abstract

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.