Lim Yun-Ping, Kuo Sheng-Chun, Lai Ming-Liang, Huang Jin-Ding
Department of Pharmacology, Medical College, National Cheng Kung University, Tainan, Taiwan.
Pharmacogenet Genomics. 2009 Jan;19(1):11-24. doi: 10.1097/FPC.0b013e32831665ea.
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 4alpha (HNF4alpha), 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-HNF4alpha interaction in the transcriptional regulation of CYP3A4 under rifampin-mediated ketoconazole inhibition.
Several approaches were used to characterize this role and to investigate the relation between the regulatory function of the PXR-HNF4alpha complex and CYP3A4 expression, including a mammalian two-hybrid system, DNA affinity precipitation assay, co-immunoprecipitation, and HNF4alpha silencing by RNA interference. Here, we report that HNF4alpha plays a critical role in CYP3A4 promoter activation, and the interaction between PXR and HNF4alpha, 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 HNF4alpha is likely an important mechanism of drug-drug interaction.
早期研究表明酮康唑通过孕烷X受体（PXR）介导的转录和共激活因子相互作用抑制CYP3A4表达。其他核受体的参与情况仍有待阐明。最近有报道称，肝细胞核受体4α（HNF4α）作为几种核受体的主要调节因子，与PXR相关联，从而在利福平治疗下调节CYP3A4的表达。因此，我们重点研究了在利福平介导的酮康唑抑制作用下，PXR-HNF4α相互作用在CYP3A4转录调控中的作用。
我们采用了多种方法来表征这一作用，并研究PXR-HNF4α复合物的调节功能与CYP3A4表达之间的关系，包括哺乳动物双杂交系统、DNA亲和沉淀试验、免疫共沉淀以及通过RNA干扰沉默HNF4α。在此，我们报告HNF4α在CYP3A4启动子激活中起关键作用，且PXR与HNF4α之间的相互作用与CYP3A4的表达密切相关，可能参与酮康唑介导的CYP3A4基因表达抑制。这些观察结果表明，抑制PXR与HNF4α的相互作用可能是药物相互作用的重要机制。
