TRANSCRIPTIONAL REGULATION BY HNF-4 OF THE STEROID 15-ALPHA-HYDROXYLASE P450 (CYP2A-4) GENE IN MOUSE-LIVER

The mouse P450 gene Cyp2a-4 encodes the hepatic steroid 15 alpha-hydro xylase. We have defined in the 5'-flanking sequence of Cyp2a-4 gene, a composite regulatory element ((-61)AGACCAAAGTCCGGCCTTC(-42)) which co ntains a potential CpG methylation site at position -50. Gel-shift ass ay indicate that this element consists of overlapped binding sites for a hepatocyte-enriched transcription factor HNF-4 and a Sp1-like prote in. Moreover, transcription of the Cyp2a-4 gene is activated by coexpr ession of HNF-4 in HepG2 cells. A mutation (C at -50 to A) abolishes t he binding of HNF-4 to the element as well as the transcriptional acti vation by HNF-4. The methylated C at position -50, however, does not a ffect HNF-4 binding. Neither the mutation nor the methylation at posit ion -50 affect the binding of Spl-like protein to the element. It appe ars, therefore, that HNF-4 activates the hepatic transcription of Cyp2 a-4 gene through its direct binding to the regulatory element regardle ss of the methylation at position -50. Published by Elsevier Science L td.