Extensive genetic polymorphism in the human CYP2B6 gene with impact on expression and function in human liver.

TLDR

CYP2B6 metabolizes many therapeutic drugs and environmental toxicants. The study systematically investigates CYP2B6 genetic polymorphism on chromosome 19. The authors sequenced all nine exons and exon–intron boundaries of CYP2B6 in 35 subjects and developed PCR‑RFLP assays to detect five nonsynonymous mutations. Nine novel point mutations were identified—five nonsynonymous and four silent—with five nonsynonymous mutations found in 215 subjects at frequencies from 0.5 % to 32.6 %; haplotype analysis defined six mutant alleles, and carriers of the C1459T (R487C) mutation showed significantly reduced CYP2B6 protein expression and activity, showing that genetic polymorphism contributes to interindividual variability.

Abstract

The human cytochrome P450, CYP2B6, is involved in the metabolism of several therapeutically important drugs and environmental or abused toxicants. In this study, we present the first systematic investigation of genetic polymorphism in the CYP2B6 gene on chromosome 19. A specific direct sequencing strategy was developed based on CYP2B6 and CYP2B7 genomic sequence information and DNA from 35 subjects was completely analysed for mutations throughout all nine exons and their exon–intron boundaries. A total of nine novel point mutations were identified, of which five result in amino acid substitutions in exon 1 (C64T, Arg22Cys), exon 4 (G516T, Gln172His), exon 5 (C777A, Ser259Arg and A785G, Lys262Arg) and exon 9 (C1459T, Arg487Cys) and four are silent mutations (C78T, G216C, G714A and C732T). Polymerase chain reaction-restriction fragment length polymorphism tests were developed to detect each of the five nonsynonymous mutations in genomic DNA. By screening a population of 215 subjects the C64T, G516T, C777A, A785G and C1459T mutations were found at frequencies of 5.3%, 28.6%, 0.5%, 32.6% and 14.0%, respectively. Haplotype analysis revealed six different mutant alleles termed CYP2B6*2 (C64T), *3 (C777A), *4 (A785G), *5 (C1459T), *6 (G516T and A785G) and *7 (G516T, A785G and C1459T). By analysing a large number of human liver samples, significantly reduced CYP2B6 protein expression and S-mephenytoin N-demethylase activity were found in carriers of the C1459T (R487C) mutation (alleles *5 and *7). These data demonstrate that the extensive interindividual variability of CYP2B6 expression and function is not only due to regulatory phenomena, but also caused by a common genetic polymorphism.