TY - JOUR T1 - Synergistically enhanced CYP2B6 Inducibility between a Polymorphic Mutation in CYP2B6 Promoter and PXR Activation JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.110.065185 SP - mol.110.065185 AU - Haishan Li AU - Stephen Ferguson AU - Hongbing Wang Y1 - 2010/07/12 UR - http://molpharm.aspetjournals.org/content/early/2010/07/12/mol.110.065185.abstract N2 - CYP2B6 is a highly inducible and polymorphic enzyme, involved in the metabolism of an increasing number of clinically important drugs. Significant interindividual variability in CYP2B6 expression has been attributed to either genetic polymorphisms or chemical-mediated induction through the activation of constitutive androstane receptor and/or pregnane X receptor (PXR). It was reported that the -82T>C substitution within the CYP2B6*22 allele creates a functional CCAAT/enhancer-binding protein (C/EBP) binding site and enhances the basal expression of the CYP2B6 gene. Here, we explored whether this polymorphic mutation could affect drug-mediated induction of CYP2B6. Cell-based promoter reporter assays demonstrated that CYP2B6 luciferase activity was synergistically enhanced in the presence of both -82T>C mutation and rifampicin (RIF) activated PXR. Conversely, this synergism was attenuated by disrupting the C/EBP binding site or knocking down C/EBPα expression. Mechanistic studies revealed that C/EBPα plays an important role in such synergism by directly interacting with PXR; enhancing RIF-mediated recruitment of PXR to the -82T>C harboring the CYP2B6 promoter; and looping the PXR-bound distal phenobarbital-responsive enhancer module towards the proximal C/EBP binding site. Furthermore, the genotype-phenotype association was evaluated in cultured human primary hepatocytes from 44 donors. Interestingly, RIF-mediated induction of CYP2B6 in four -82T/C carriers was higher compared to that in the reference -82T/T homozygotes. Collectively, our results demonstrate, for the first time, a synergistic interplay between a CYP2B6 polymorphism and PXR-mediated induction, which may contribute to the large individual variations and inducibility of CYP2B6 in humans. ER -