TY - JOUR T1 - Adenosine deaminases acting on RNA downregulate the expression of constitutive androstane receptor in the human liver-derived cells by attenuating splicing JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther DO - 10.1124/jpet.119.260109 SP - jpet.119.260109 AU - Masataka Nakano AU - Tatsuki Fukami AU - Miki Nakajima Y1 - 2019/01/01 UR - http://jpet.aspetjournals.org/content/early/2019/07/03/jpet.119.260109.abstract N2 - Adenosine deaminases acting on RNA (ADAR) enzymes-catalyzing A-to-I RNA editing possibly modulates gene expression and function. In this study, we investigated whether ADARs regulate the expression of human constitutive androstane receptor (CAR), which controls the expression of various drug-metabolizing enzymes. CAR mRNA and protein levels in human hepatocellular carcinoma-derived HepG2 cells were increased by knockdown of ADAR1, and slightly increased by ADAR2, indicating that ADARs negatively regulates CAR expression. Increased luciferase activity of a reporter plasmid containing the CYP3A4 promoter region by phenobarbital was augmented by transfection of siADAR1 but not by siADAR2. In addition, the knockdown of ADAR1 resulted in the enhanced induction of CYP2B6 and CYP3A4 mRNA by 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime (CITCO) and phenobarbital, respectively. These results suggest that ADAR1-mediated downregulation of CAR affects its downstream P450s expression. When the transcription was inhibited by α-amanitin, the degradation of CAR mRNA was attenuated by knockdown of ADAR1, suggesting that the increase in CAR mRNA level by ADAR1 knockdown is a posttranscriptional event. Finally, we found that ADAR1 knockdown promotes the splicing of CAR as a mechanism of the increased expression of CAR by ADAR1 knockdown. In conclusion, this study revealed that ADAR1 plays a role in modulating xenobiotic metabolism potency via regulation of CAR.SIGNIFICANCE STATEMENT This study revealed that ADAR1 and ADAR2, which catalyze A-to-I RNA editing, down-regulate the expression of CAR in human liver-derived cells by attenuating splicing. The down-regulation of CAR by ADARs affected its downstream P450s expression. ADARs would play a role in modulating xenobiotic metabolism potency via regulation of CAR. ER -