Mechanism of rifampicin and pregnane X receptor inhibition of human cholesterol 7α-hydroxylase gene transcription
Mechanism of rifampicin and pregnane X receptor inhibition of human cholesterol 7α-hydroxylase gene transcription
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DOI：
10.1152/ajpgi.00258.2004
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发表时间：
2005-01-01
影响因子：
4.5
通讯作者：
Chiang, JYL
中科院分区：
文献类型：
--
作者：
Li, TG;Chiang, JYL
胆汁酸、类固醇和药物激活类固醇和异源受体孕烷X受体(PXR；NR1I2)，从而诱导药物代谢中的人细胞色素P4503A4(CYP3A4)和肝脏胆汁酸合成中的胆固醇7α-羟基酶(CYP7A1)。利福平是一种人类PXR激动剂，可抑制胆汁酸的合成，已被用于治疗胆汁淤积性疾病。本研究旨在阐明PXR抑制细胞色素P7A1基因转录的机制。采用实时定量聚合酶链式反应(Q-PCR)技术检测人原代肝细胞中细胞色素P7A1和几种已知的核受体的表达水平。利福平降低细胞色素P7A1和小二聚体伴侣(SHP；NR02B)的mRNA表达，提示SHP不参与PXR对细胞色素P7A1的抑制作用。利福平抑制CYP7A1报告活性，PXR结合位点定位于胆汁酸反应元件-I。哺乳动物双杂交实验表明，PXR与肝细胞核因子4α(HNF4α，NR2A1)相互作用，需要利福平。免疫共沉淀实验证实了PXR与HNF4α的相互作用。PXR还与PGC-1α相互作用，PGC-1α与HNF4α相互作用，诱导细胞色素P7A1基因转录。利福平增强PXR与HNF4α的相互作用，降低PGC-1α与HNF4α的相互作用。染色质免疫沉淀分析表明，PXR、HNF4α和PGC-1α与细胞色素PYP7A1染色质结合，利福平使PGC-1α从染色质上解离。这些结果表明，利福平激活PXR促进了PXR与HNF4α的相互作用，阻断了PGC-1α与HNF4α的激活，从而抑制了CYP7A1基因的转录。利福平抑制胆汁酸的合成可能是其对抗药物和胆汁酸所致胆汁淤积的机制之一。
Bile acids, steroids, and drugs activate steroid and xenobiotic receptor pregnane X receptor (PXR; NR1I2), which induces human cytochrome P4503A4 (CYP3A4) in drug metabolism and cholesterol 7alpha-hydroxylase (CYP7A1) in bile acid synthesis in the liver. Rifampicin, a human PXR agonist, inhibits bile acid synthesis and has been used to treat cholestatic diseases. The objective of this study is to elucidate the mechanism by which PXR inhibits CYP7A1 gene transcription. The mRNA expression levels of CYP7A1 and several nuclear receptors known to regulate the CYP7A1 gene were assayed in human primary hepatocytes by quantitative real-time PCR (Q-PCR). Rifampicin reduced CYP7A1 and small heterodimer partner (SHP; NR02B) mRNA expression suggesting that SHP was not involved in PXR inhibition of CYP7A1. Rifampicin inhibited CYP7A1 reporter activity and a PXR binding site was localized to the bile acid response element-I. Mammalian two-hybrid assays revealed that PXR interacted with hepatic nuclear factor 4alpha (HNF4alpha, NR2A1) and rifampicin was required. Coimmunoprecipitation assay confirmed PXR interaction with HNF4alpha. PXR also interacted with peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha), which interacted with HNF4alpha and induced CYP7A1 gene transcription. Rifampicin enhanced PXR interaction with HNF4alpha and reduced PGC-1alpha interaction with HNF4alpha. Chromatin immunoprecipitation assay showed that PXR, HNF4alpha, and PGC-1alpha bound to CYP7A1 chromatin, and rifampicin dissociated PGC-1alpha from chromatin. These results suggest that activation of PXR by rifampicin promotes PXR interaction with HNF4alpha and blocks PGC-1alpha activation with HNF4alpha and results in inhibition of CYP7A1 gene transcription. Rifampicin inhibition of bile acid synthesis may be a protective mechanism against drug and bile acid-induced cholestasis.