Identification of a single nucleotide polymorphism in the TATA box of the CYP2A6 gene: Impairment of its promoter activity

Human cytochrome P450 2A6 (CYP2A6) constitutes the major nicotine oxidase, and large interindividual differences are seen in the levels of this enzyme , to a great extent caused by the distribution of several different polymor phic gene variants mainly located in the open reading frame (ORF). In the p resent study, we report a common polymorphism located in the 5 ' flanking r egion of CYP2A6 affecting its expression. DHPLC analysis and complete seque nce of the open reading frame of the gene from a Turkish individual reveale d a -48T > G substitution disrupting the TATA box. Using dynamic allele-spe cific hybridization (DASH), genotyping of this novel variant (named CYP2A6* 9) was carried out in 116 Swedish, 132 Turkish, and 102 Chinese subjects, a nd the allele frequencies were found to be 5.2, 7.2, and 15.7%, respectivel y. The significance of the polymorphism was investigated by the constructio n of luciferase reporter plasmids containing 135 or 500 bp of the 5 ' -upst ream region of the gene transfected into human hepatoma B16A2 cells. The co nstructs carrying the -48T > G mutation were only expressed at about 50% of the wild-type alleles. It is concluded that the CYP2A6*9 allele might be o ne of the most common CYP2A6 variants in Caucasians that alters the levels of enzyme expression. (C) 2001 Academic Press.