Rifampicin induction of CYP3A4 requires PXR crosstalk with HNF4α and co‐activators, and suppression of SHP gene expression

Abstract

Bile acids and drugs activate PXR to induce CYP3A4, which is the predominant cytochrome P450 enzymes in the liver and intestine and plays a critical role in detoxifying bile acids and drugs. Induction of CYP3A4 by PXR may protect against bile acid and drug induced-cholestasis. The aim of this study is to investigate the molecular mechanism of PXR regulation of human CYP3A4 gene transcription. Rifampicin induced the CYP3A4 but inhibited small heterodimer partner (SHP) mRNA expressions in primary human hepatocytes. The human CYP3A4 promoter contains two PXR binding sites in the xenobiotic response element module (XREM) and a HNF4α binding site is adjacent to the XREM. Rifampicin induced HNF4α and PXR interaction and synergistically stimulated CYP3A4 reporter activity. However, HNF4α alone or mutation of the HNF4α site did not affect CYP3A4 reporter activity. SHP inhibited CYP3A4 reporter activity stimulated by PXR and HNF4α. Adenovirus-mediated overexpression of SHP in human primary hepatocytes inhibited both basal and rifampicin-induced CYP3A4 mRNA levels. Chromatin immunoprecipitation assays revealed that rifampicin enhanced PXR recruitment of HNF4α and SRC-1 to the CYP3A4 chromatin, but SHP reduced PXR recruitment of these coactivators to chromatin. The human SHP promoter activity was stimulated by HNF4α and PGC-1α but inhibited by PXR. These results suggest that PXR strongly induces CYP3A4 gene transcription by interacting with HNF4α, SRC-1 and PGC-1α. PXR concomitantly inhibits SHP gene transcription to maximize the induction of the CYP3A4 gene in human livers. Drugs targeted to PXR may be developed for treating cholestatic liver diseases.