Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences (K.N., Ma.N., C.I., T.F., Mi.N.), and WPI Nano Life Science Institute (Ma.N., T.F., Mi.N.), Kanazawa University, Kakuma-machi, Kanazawa, Japan.
Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences (K.N., Ma.N., C.I., T.F., Mi.N.), and WPI Nano Life Science Institute (Ma.N., T.F., Mi.N.), Kanazawa University, Kakuma-machi, Kanazawa, Japan
Drug Metab Dispos. 2019 Jun;47(6):639-647. doi: 10.1124/dmd.119.086702. Epub 2019 Apr 15.
A-to-I RNA editing, the most frequent type of RNA editing in mammals, is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes. Recently, we found that there is a large interindividual variation in the expression of ADAR1 protein in the human livers. In this study, we investigated the possibility that A-to-I RNA editing may modulate the expression of cytochrome P450 (P450), causing interindividual variations in drug metabolism potencies. We found that knockdown of ADAR1 or ADAR2 in HepaRG cells resulted in the decreased expression of CYP2B6 and CYP2C8 mRNA and protein. Knockdown of ADARs significantly decreased the stability of CYP2B6 mRNA but not CYP2C8 mRNA. Luciferase assays revealed that the 3'-untranslated region of CYP2B6 and the promoter region of CYP2C8 would be involved in the decrease in their expression by the knockdown of ADARs. We found that the decreased expression of the hepatocyte nuclear factor 4 (HNF4) protein by the knockdown of ADARs was one of the reasons for the decreased transactivity of CYP2C8. The mRNA levels of other P450 isoforms, such as CYP2A6, 2C9, 2C19, 2D6, and 2E1, which are known to be regulated by HNF4, were also decreased by ADAR1 or ADAR2 knockdown. Exceptionally, the CYP3A4 mRNA level was significantly increased by ADAR1 knockdown, suggesting the possibility that the change could be due to the change in the expression or function of other regulatory factors. In conclusion, this study revealed that the RNA editing enzymes ADAR1 and ADAR2 are novel regulatory factors of P450-mediated drug metabolism in the human liver.
A-to-I RNA 编辑是哺乳动物中最常见的 RNA 编辑类型，由腺苷脱氨酶作用于 RNA（ADAR）酶催化。最近，我们发现人类肝脏中 ADAR1 蛋白的表达存在很大的个体间差异。在这项研究中，我们研究了 A-to-I RNA 编辑是否可能调节细胞色素 P450（P450）的表达，从而导致药物代谢能力的个体间差异。我们发现 HepaRG 细胞中 ADAR1 或 ADAR2 的敲低导致 CYP2B6 和 CYP2C8 mRNA 和蛋白的表达降低。ADARs 的敲低显著降低了 CYP2B6 mRNA 的稳定性，但不影响 CYP2C8 mRNA。荧光素酶测定显示，CYP2B6 的 3'-非翻译区和 CYP2C8 的启动子区可能参与了 ADARs 敲低导致其表达降低。我们发现，ADARs 的敲低导致核因子 4（HNF4）蛋白表达的降低是 CYP2C8 转录活性降低的原因之一。其他 P450 同工酶（如 CYP2A6、2C9、2C19、2D6 和 2E1）的 mRNA 水平也因 ADAR1 或 ADAR2 的敲低而降低，这些同工酶已知受 HNF4 调节。例外的是，ADAR1 的敲低显著增加了 CYP3A4 mRNA 水平，这表明这种变化可能是由于其他调节因子的表达或功能发生变化。总之，本研究揭示了 RNA 编辑酶 ADAR1 和 ADAR2 是人类肝脏中 P450 介导的药物代谢的新型调节因子。
