Transcriptional regulation by HNF-4 of the steroid 15α-hydroxylase P450 ( Cyp2a-4) gene in mouse liver

The mouse P450 gene Cyp2a-4 encodes the hepatic steroid 15α-hydroxylase. We have defined in the 5′-flanking sequence of Cyp2a-4 gene, a composite regulatory element ( −61AGACCAAAGTC CG GCCTTC −42) which contains a potential CpG methylation site at position −50. Gel-shift assays indicate that this element consists of overlapped binding sites for a hepatocyte-enriched transcription factor HNF-4 and a Sp1-like protein. Moreover, transcription of the Cyp2a-4 gene is activated by coexpression of HNF-4 in HepG2 cells. A mutation (C at −50 to A) abolishes the binding of HNF-4 to the element as well as the transcriptional activation by HNF-4. The methylated C at position −50, however, does not affect HNF-4 binding. Neither the mutation nor the methylation at position −50 affect the binding of Sp1-like protein to the element. It appears, therefore, that HNF-4 activates the hepatic transcription of Cyp2a-4 gene through its direct binding to the regulatory element regardless of the methylation at position −50.