Inhibition of CYP3A4 expression by ketoconazole is mediated by the disruption of pregnane X receptor, steroid receptor coactivator-1, and hepatocyte nuclear factor 4α interaction

Abstract

Background Earlier studies have shown that ketoconazole inhibits CYP3A4 expression through pregnane X receptor (PXR)-mediated transcription and coactivator interaction. The involvement of other nuclear receptors remains to be elucidated. It was recently reported that hepatocyte nuclear receptor 4α (HNF4α), a master regulator of several nuclear receptors, associates with PXR thus regulates the expression of CYP3A4 under rifampin treatment. We therefore focused on the role of PXR–HNF4α interaction in the transcriptional regulation of CYP3A4 under rifampin-mediated ketoconazole inhibition. Methods and results Several approaches were used to characterize this role and to investigate the relation between the regulatory function of the PXR–HNF4α complex and CYP3A4 expression, including a mammalian two-hybrid system, DNA affinity precipitation assay, co-immunoprecipitation, and HNF4α silencing by RNA interference. Here, we report that HNF4α plays a critical role in CYP3A4 promoter activation, and the interaction between PXR and HNF4α, which is closely related to the expression of CYP3A4, might be involved in ketoconazole-mediated inhibition of CYP3A4 gene expression. These observations indicate that the inhibition of the interaction of PXR with HNF4α is likely an important mechanism of drug–drug interaction.