Increased expression of hepatic DNA methyltransferase in smokers.

The DNA methyltransferase enzyme (DNA MTase) catalyzes DNA methylation at cytosines in CpG dinucleotides. 5-Methylcytosine modification of DNA is important in gene regulation, DNA replication, chromatin organization and disease. Increased levels of DNA MTase have been associated with the initiation and promotion of cancer. This study was conducted to assess whether cigarette smoking and other factors, such as age and gender, influence DNA MTase expression in nontumorous tissue. DNA MTase was significantly (p<0.05) higher in samples from cigarette smokers; the mean level of DNA MTase mRNA was almost 2-fold higher in these samples than in those from nonsmokers. Levels of DNA MTase mRNA were higher in samples from females than in those from males, but the difference was not statistically significant. Age was not associated with DNA MTase levels. Increased levels of DNA MTase in individuals who smoke may indicate a greater susceptibility to the risk of cancer since increased levels of this enzyme are found in cancer cell lines and human tumors. The results of this study suggest that further investigations of increased expression of this enzyme as a predisposing factor for cancer susceptibility are needed.