FIGURE 1.

C/EBPα, HNF4α, and CAR cooperate to synergistically activate human CYP2B6. HepG2 cells were infected with Ad-C/EBPα, Ad-HNF4α, and Ad-CAR either individually or combined. Twenty-four hours later, 500 nm CITCO or solvent (DMSO) was incorporated, and at 48 h postinfection, cells were harvested and processed. A, CYP2B6 mRNA concentration was measured by quantitative RT-PCR. In parallel, the mRNA concentration of the housekeeping porphobilinogen deaminase was also analyzed for normalization. Data represent the mean ± S.D. of 4–5 independent experiments, expressed as the -fold increase over the control HepG2 cells. B, CYP2B6 activity was measured by determining the bupropion hydroxylation rate in cultured cells by LC/MS/MS. Enzymatic activity was expressed as pmol of metabolite formed/h/mg of total protein. Each bar represents mean ± S.D.; n = 4. C, adenovirus-transduced and control HepG2 cells were incubated with prototypical CYP2B6 inducers (chlorpromazine (CPZ) and PB) and with CAR agonists (triphenyl phosphate (TPP) and CITCO) and inverse agonists (androstanol (ANDR) and clotrimazole (CLZ)). CYP2B6 mRNA levels were measured 24 h later. Data represent the mean ± S.D. of 3–4 independent experiments, expressed as the -fold increase over control cells.