RT Journal Article SR Electronic T1 Cell Cycle and Apoptosis Regulator 1, CCAR1, Regulates Enhancer-Dependent Nuclear Receptor CAR Transactivation JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 120 OP 126 DO 10.1124/mol.118.114272 VO 95 IS 1 A1 Yuichiro Kanno A1 Shuai Zhao A1 Naoya Yamashita A1 Nao Saito A1 Aoi Ujiie A1 Rie Iijima A1 Nami Kikawa A1 Kiyomitsu Nemoto A1 Yoshio Inouye YR 2019 UL http://molpharm.aspetjournals.org/content/95/1/120.abstract AB The constitutive active/androstane receptor (CAR) controls genes involved in xenochemical metabolism. Although numerous cofactors have been reported to be involved in CAR-mediated transactivation, unknown and poorly defined proteins recruited by CAR have yet to be characterized. In this study, a novel CAR-interacting protein, cell cycle and apoptosis regulator 1 (CCAR1), was identified by coimmunoprecipitation analysis using human hepatocarcinoma HepG2 cells expressing FLAG epitope–tagged CAR. We demonstrated that CCAR1 can act as an enhancer-dependent coactivator of CAR. First, we showed that overexpression of CCAR1 enhanced CAR-induced reporter gene activity with triplicate consensus direct repeat 4 motif (DR4-Luc), xenobiotic-responsive enhancer module (XREM)-enhancer of CYP3A4 (XREM-Luc), and phenobarbital-responsive enhancer module of UDP-glucuronosyltransferases 1A1 (UGT1A1) (gtPBREM)-enhancer of UGT1A1 (gtPBREM-Luc)-driven reporter plasmids but not PBREM-enhancer of CYP2B6 (PBREM-Luc)-driven reporter activity. Furthermore, we showed that knockdown of CCAR1 suppressed CAR-induced UGT1A1 mRNA expression but did not affect CAR-induced CYP2B6 mRNA expression in HepTR/CAR and HepaRG cells. Moreover, CCAR1 could be recruited to the gtPBREM of the UGT1A1 enhancer by CAR but not to the PBREM of the CYP2B6 enhancer. Moreover, we showed that CCAR1 can act as a secondary coactivator by cooperating with the p160 family of steroid receptor coactivators (SRCs). These findings demonstrated CCAR1 to be a novel transcriptional cofactor for CAR and provided insight regarding the mechanism of CAR-mediated gene-selective transactivation.