A novel CYP2A6*20 allele found in African-American population produces a truncated protein lacking enzymatic activity.
Human CYP2A6 is a cytochrome P450 (CYP) isoform responsible for the metabolism of nicotine, coumarin, tegafur, and valproic acid, and metabolic activation of nitrosamines. Genetic polymorphisms of the CYP2A6 gene are a major causal factor of the large interindividual differences in nicotine metabolism. In the present study, we identified a novel allele, termed CYP2A6*20, in an African-American population. The allele possesses the deletion of two nucleotides in exon 4 resulting in a frame-shift from codon 196 and an early stop codon at 220 (exon 5) as well as three synonymous SNPs of G51A (G51A in cDNA), T5684C (T1191C), and C6692G (C1546G, 3'-untranslated region). The allele frequency in the African-American population (n=96) was 1.6% (95% confidence interval, 0.6-4.5%). In contrast, the CYP2A6*20 allele was not found in Caucasians (European-American) (n=185), Japanese (n=184) and Korean (n=209) populations. To investigate the effects of the polymorphism on the enzymatic activities, we expressed a wild type or variant (deletion of two nucleotides) CYP2A6 together with NADPH-CYP reductase in Escherichia coli. SDS-PAGE and immunoblot analyses demonstrated that truncated CYP2A6 protein was produced from the variant allele, although detected mRNA was the predicted size by reverse transcriptional-polymerase chain reaction. Coumarin 7-hydroxylation and nicotine C-oxidation, which are typical CYP2A6 activities, were completely abolished in the E. coli membrane expressing the variant allele. In vivo nicotine metabolism was evaluated using the cotinine/nicotine ratio 2 h after the chewing of one piece of nicotine gum. Two CYP2A6*1/CYP2A6*20 heterozygotes and a single CYP2A6*17/CYP2A6*20 heterozygote revealed lower cotinine/nicotine ratios compared with CYP2A6*1/CYP2A6*1 subjects (1.6 and 4.5, and 1.8 versus 9.5+/-5.4, n=52, respectively). We found a novel CYP2A6*20 allele in African-American subjects which codes a truncated protein lacking enzymatic activity.
Fukami
Tatsuki
T
Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
Nakajima
Miki
M
Higashi
Eriko
E
Yamanaka
Hiroyuki
H
McLeod
Howard L
HL
Yokoi
Tsuyoshi
T
D001741:Black or African American / Q000235:genetics*; D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D065637:Cytochrome P-450 CYP2A6; D004926:Escherichia coli / Q000235:genetics; D005787:Gene Frequency; D006801:Humans; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009538:Nicotine / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
D011994:Recombinant Proteins; D009538:Nicotine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6