TY - JOUR T1 - The Molecular Mechanism Regulating Diurnal Rhythm of Flavin-containing Monooxygenase 5 in Mouse Liver JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.119.088450 SP - dmd.119.088450 AU - Min Chen AU - Bao Zhang Guan AU - Hai Man Xu AU - Fang Jun Yu AU - Tian Peng Zhang AU - Bao Jian Wu Y1 - 2019/01/01 UR - http://dmd.aspetjournals.org/content/early/2019/09/12/dmd.119.088450.abstract N2 - Flavin-containing monooxygenase 5 (FMO5) is a phase I enzyme that plays an important role in xenobiotic metabolism. Here, we aimed to characterize diurnal rhythms of Fmo5 expression and activity in mouse liver, and to investigate the potential roles of circadian clock genes (Bmal1, Rev-erbα and E4bp4) in generation of diurnal rhythms. Fmo5 mRNA and protein showed robust diurnal rhythms with peak values at ZT10/14 and trough values at ZT2/22 in mouse liver. Consistently, a diurnal rhythm was observed for in vitro microsomal metabolism of pentoxifylline (PTX), a specific substrate of Fmo5. Pharmacokinetic study revealed a more extensive metabolism of PTX at dosing time of ZT14 than at ZT2 consistent with the diurnal pattern of Fmo5 protein. Fmo5 expression was down-regulated and its rhythm was blunted in Bmal1-/- and Rev-erbα-/- mice. Positive regulation of Fmo5 by Bmal1 and Rev-erbα was confirmed in primary mouse hepatocytes and/or Hepa1-6 cells. Furthermore, Fmo5 expression was up-regulated and its rhythm was attenuated in E4bp4-/- mice. Negative regulation of Fmo5 by E4bp4 was validated using primary mouse hepatocytes. Combined luciferase reporter and chromatin immunoprecipitation assays demonstrated that Bmal1 (a known Rev-erbα activator) activated Fmo5 transcription via direct binding to an E-box (−1822/−1816 bp) in the promoter, whereas E4bp4 (a known Rev-erbα target gene) inhibited Fmo5 transcription by binding to two D-boxes (-1726/-1718 and -804/-796 bp). In conclusion, circadian clock genes control diurnal expression of Fmo5 through transcriptional actions on E-box and D-box cis-elements.SIGNIFICANCE STATEMENT Flavin-containing monooxygenase 5 (FMO5) is a phase I enzyme that plays an important role in xenobiotic metabolism. In this study, we reported diurnal expression and activity of Fmo5 in mouse liver. Moreover, we uncovered the molecular mechanism by which the rhythmic Fmo5 expression was generated. To be specific, Fmo5 promoter presents E-box and D-box binding elements for transcriptional actions from circadian clock proteins such as Bmal1, E4bp4 and Dbp. In addition to direct trans-activation, the E-box binding protein Bmal1 indirectly regulates the transcription of Fmo5 through Dbp and Rev-erbα/E4bp4 axis. Our study has significant implications for understanding of clock-controlled drug metabolism and for facilitating the practice of chronotherapeutics. ER -