Abstract
Variability in hepatic CYP3A4 cannot be explained by common CYP3A4 coding variants. We previously identified polymorphisms in pregnane X receptor (PXR) and ATP-binding cassette subfamily B member 1 (ABCB1) associated with CYP3A4 mRNA levels in small cohorts of human livers. However, the relative contributions of these genetic variations or of polymorphisms in other CYP3A4 regulators to variable CYP3A4 expression were not known. We phenotyped livers from white donors (n = 128) by quantitative real-time polymerase chain reaction for expression of CYP3A4, CYP3A5, and CYP3A7 and nine transcriptional regulators, coactivators, and corepressors. We resequenced hepatic nuclear factor-3-β (HNF3β, FoxA2), HNF4α, HNF3γ (FoxA3), nuclear receptor corepressor 2 (NCoR2), and regions of the CYP3A4 promoter and genotyped informative single-nucleotide polymorphisms in PXR and ABCB1 in the same livers. CYP3A4 mRNA was positively correlated with PXR and FoxA2 and negatively correlated with NCoR2 mRNA. A common silent polymorphism and a polymorphic trinucleotide (CCT) repeat in FoxA2 were associated with CYP3A4 expression. The transcriptional activity of the FoxA2 polymorphic CCT repeat alleles (wild-type, n = 14 and variant, n = 13, 15, and 19) when assayed by luciferase reporter transactivation assays was greatest for the wild-type repeat, with deviations from this number having decreased transcriptional activity. This corresponded with higher expression of FoxA2 mRNA and its targets PXR and CYP3A4 in human livers with (CCT) n = 14 genotypes. Multiple linear regression analysis was used to quantify the contributions of selected genetic polymorphisms to variable CYP3A4 expression. This approach identified sex and polymorphisms in FoxA2, HNF4α, FoxA3, PXR, ABCB1, and the CYP3A4 promoter that together explained as much as 24.6% of the variation in hepatic CYP3A4 expression.
Footnotes
This work was supported in part by the National Institutes of Health [Grant GM60346]; National Institutes of Health National Institute of General Medical Sciences Pharmacogenetics Research Network and Database [Grants U01-GM61374, U01-GM61393]; the National Institutes of Health Cancer Center Support [Grant P30-CA21765]; and by the American Lebanese Syrian Associated Charities.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.109.160804.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- LETF
- liver enriched transcription factor
- PXR
- pregnane X receptor
- FoxA2, HNF3β
- hepatic nuclear factor-3-β
- FoxA3, HNF3γ
- hepatic nuclear factor-3-γ
- C/EBP
- CCAAT/enhancer binding protein
- SMRT
- silencing mediator for retenoid or thyroid hormone receptor
- Ncor2
- nuclear receptor corepressor 2
- SNP
- single-nucleotide polymorphism
- MDR1/ABCB1
- multidrug resistance protein 1/ATP-binding cassette subfamily B member 1
- MLR
- multiple linear regression
- PCR
- polymerase chain reaction
- UTR
- untranslated region
- LD
- linkage disequilibrium.
- Received August 19, 2009.
- Accepted November 23, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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