ABSTRACT
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 polymorphic gene variants mainly located in the open reading frame (ORF). In the present study, we report a common polymorphism located in the 5' flanking region of CYP2A6 affecting its expression. DHPLC analysis and complete sequence of the open reading frame of the gene from a Turkish individual revealed a -48T > G substitution disrupting the TATA box. Using dynamic allele-specific hybridization (DASH), genotyping of this novel variant (named CYP2A6*9) was carried out in 116 Swedish, 132 Turkish, and 102 Chinese subjects, and the allele frequencies were found to be 5.2, 7.2, and 15.7%, respectively. The significance of the polymorphism was investigated by the construction of luciferase reporter plasmids containing 135 or 500 bp of the 5'-upstream region of the gene transfected into human hepatoma B16A2 cells. The constructs 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 one of the most common CYP2A6 variants in Caucasians that alters the levels of enzyme expression.
Subject(s)
Aryl Hydrocarbon Hydroxylases , Cytochrome P-450 Enzyme System/genetics , Mixed Function Oxygenases/genetics , Oxidoreductases/genetics , Polymorphism, Single Nucleotide/genetics , Promoter Regions, Genetic/physiology , TATA Box/genetics , Alleles , Asian People/genetics , Cell Line , China/ethnology , Chromatography, High Pressure Liquid , Cytochrome P-450 CYP2A6 , DNA Mutational Analysis , Gene Expression/physiology , Genes, Reporter , Genetic Testing , Genetic Variation , Genotype , Humans , Nucleic Acid Denaturation , Nucleic Acid Heteroduplexes/analysis , Nucleic Acid Heteroduplexes/genetics , Nucleic Acid Hybridization/methods , Sweden/ethnology , Transfection , Turkey/ethnology , White People/geneticsABSTRACT
In humans, glutathione-S-transferases (GSTs) are involved in the detoxification of xenobiotics. A deletion polymorphism in the glutathione S-transferase Theta 1 gene (GSTT1 null genotype) is associated with an increased risk of certain forms of cancer. The distribution of this polymorphism in 240 healthy individuals has been examined, using a polymerase chain reaction (PCR)-based method. The GSTT1 null genotype frequency was 20% in a Turkish Population.
