Identification of rhythmic human CYPs and their circadian regulators using synchronized hepatoma cells.

Cytochromes P450 (CYPs) catalyze a great number of metabolic reactions that have profound effects on the biological activities of xenobiotics and endobiotics. In this study, we aimed to characterize rhythmic expressions of drug-metabolizing CYPs using synchronized hepatoma cells, and to investigate the potential roles of cis-elements of circadian clock system (E-box, D-box and RevRE or RORE) in generating the rhythms.Serum was used to synchronize circadian cycles and to induce circadian gene expression in cultured hepatoma cells (HepRG and HepG2 cells). Regulation of CYP genes by circadian clock components was investigated by performing luciferase reporter, overexpression and knockdown experiments. mRNA and protein expression were determined by qPCR and Western blotting assays, respectively.Of ten major drug-metabolizing CYP genes, six are rhythmically expressed (CYP1A2, 2B6, 2C8, 2D6, 2E1 and 3A4), whereas other four are non-rhythmic (CYP1B1, 2A6, 2C9 and 2C19).The E-box binding protein BMAL1 directly controls the rhythmic expression of CYP1A2. Rhythmic expressions of CYP2E1 and CYP3A4 are generated via both E-box and D-box elements. The RevRE binding protein REV-ERBα contributes to rhythmic oscillations in CYP2B6 and CYP2C8.In conclusion, rhythmic expressions of five human CYPs (CYP1A2, 2B6, 2C8, 2E1 and 3A4) are generated and regulated by E-box-, D-box-, and/or RevRE-acting clock components. Our findings may have implications for understanding chronopharmacokinetic events in humans.