Farnesoid X receptor regulates CYP1A1 and CYP1B1 and estradiol metabolism in mouse and human cell lines

Human CYP1A1 and CYP1B1 are two important enzymes for the hydroxylation of estrogens. In this study, we aimed to investigate the potential role for FXR receptor in the regulation of CYP1A1 and CYP1B1 expressions and activities. First, pharmacokinetic analysis was conducted in male wild-type and Fxr^−/− mice after intraperitoneal dosing of exogenous estradiol. In vitro microsomal Cyp1a1 and Cyp1b1 activities were probed using their substrates estradiol, phenacetin, and melatonin. The regulatory effects of FXR on these two enzymes were explored using female Fxr^−/− mice, mouse 4T1 and human MCF-7 cell lines. As a result, Fxr-deficiency significantly changed the plasma concentration-time curve and exposure (AUC_0–2 h) of estradiol, and the metabolism ratios of its hydroxylated metabolites. Global deletion of Fxr led to significant down-regulation of Cyp1a1 and Cyp1b1 mRNA and protein in major organs (liver, lung, kidney, stomach, small intestine). Overexpression of Fxr in mouse 4T1 cells resulted in increased levels of Cyp1a1 and Cyp1b1 mRNA and protein, whereas Fxr knockdown caused down-regulation of Cyp1a1 and Cyp1b1 expression. In human MCF-7 cells, there was a similar regulatory trend of FXR towards CYP1A1 and CYP1B1 as well as those in mouse 4T1 cells. In vitro incubation assays also supported these results. Based on luciferase reporter and electrophoretic mobility shift assays, Fxr directly activated Cyp1a1 and Cyp1b1 via their specific binding to (−488 ∼ −477 bp) and (−1475 ∼ −1460 bp) regions in their promoters, respectively. Therefore, FXR transcriptionally regulates the expression of CYP1A1 and CYP1B1, impacting the in vitro metabolism and pharmacokinetics of their substrates.