Abstract
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. On the other hand, 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 CYP2B6 promoter; and looping the PXR-bound distal phenobarbital-responsive enhancer module toward 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 with that in the reference −82T/T homozygotes. Together, 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.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the National Institute of Health National Institute of Diabetes and Digestive and Kidney Diseases [Grant DK061652].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.065185.
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ABBREVIATIONS:
- NR
- nuclear receptor
- CAR
- constitutive androstane receptor
- C/EBP
- CCAAT/enhancer-binding protein
- ChIP
- chromatin immunoprecipitation assay
- CoIP
- coimmunoprecipitation assay
- 3C
- chromosome conformation capture assay
- DMSO
- dimethyl sulfoxide
- PB
- phenobarbital
- PBREM
- phenobarbital-responsive enhancer module
- PXR
- pregnane X receptor
- RIF
- rifampicin
- XREM
- xenobiotic-responsive enhancer module
- SNP
- single nucleotide polymorphism
- kb
- kilobase
- bp
- base pair
- siRNA
- short interfering RNA
- PCR
- polymerase chain reaction
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- IP
- immunoprecipitation
- RT-PCR
- reverse transcriptase polymerase chain reaction
- CYP2B6-82C
- CYP2B6 −82T→C.
- Received March 30, 2010.
- Accepted July 12, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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