Specific site methylation in the 5 '-flanking region of CYP1A2 - Interindividual differences in human livers

Human cytochrome P450 1A2 (CYP1A2) is involved in the metabolism of a large number of common drugs and is responsible for the metabolic activation of numerous promutagens and procarcinogens. Large interindividual differences exist in the expression of this enzyme. This variability has important impl ications for drug efficacy and cancer susceptibility. In this sudy, the met hylation status of the CCGG site (bp -2759) located adjacent to an AP-1 sit e in the 5 ' -flanking region of the CYP1A2 gene was assessed in liver samp les from a pool of 55 human donors. DNA methylation is an important epigene tic mechanism controlling gene expression and may be one of the molecular m echanisms underlying the interindividual variation. Analysis was conducted using Hpa II digestion and PCR. Results showed that individual samples vari ed in the methylation status at this site. The site was found to be hyperme thylated in similar to 60% of the samples. To compare methylation status wi th level of CYP1A2 expression, results were analyzed by median test. In 44% of the samples with expression levels above the median the CCGG site was h ypermethylated. However, for those samples with levels below the median hyp ermethylation of the site was found in 73% of the samples. The difference w as statistically significant (p <0.05), These findings indicate that CpG me thylation may be involved in controlling the expression of CYP1A2, with hyp ermethylation reducing expression. Moreover, this approach can be useful in assessing the role of site-specific DNA methylation in interindividual var iation of CYP1A2. Analysis of other CpG sites in potentially important regu latory elements of the CYP1A2 gene will continue, (C) 2001 Elsevier Science . All rights reserved.