HepG2 cells were transfected with hCAR1 expression vector along with the CYP2B6-PBREM/XREM reporter. (A) Transfected cells were treated with vehicle (0.1 % DMSO), CITCO (0.1, 1 and 5 µM), PK-11195 (0.1, 1 and 10 µM) or increasing doses of CITCO with a fixed PK-11195 dose (10 µM). (B) hCAR1-transfected cells were exposed to vehicle (0.1 % DMS0), MG-132 (0.1, 1 and 10 µM), or increasing doses of CITCO with a fixed MG-132 (MG) dose (either 5 µM or 10 µM). After 24 h treatments, luciferase activities were determined and expressed relative to vehicle control. Data are the means ± S.D. (n = 3). Significantly different from DMSO (*), MG-132 (0.1 and 1 µM, #), P < 0.05.