Screening methylation of DNA repair genes in the oral mucosa of chronic smokers

Abstract

Objective: The aim of this study was to evaluate the epigenetic changes in the process of oral carcinogenesis by screening the methylation of repair genes in chronic smokers. Design: Two groups were formed: Group 1: 16 smokers with consumption of 20 cigarettes/day for at least 10 years; and Group 2: 10 non-smoking. Exfoliative cytology of the tongue was performed, and the extracted DNA was treated by enzymes. The PCR Array System performed methylation screening to evaluate 22 DNA repair genes, and the results were validated by RT-qPCR for each gene with methylation levels ≥10%. Results: Highest percentages of methylation were observed for MLH3 and XRCC1 genes (11–20% methylation) and in one case for MRE11A and PMS2 (>50% methylation). Statistical analysis showed significant differences in the expression of the genes MRE11A (p = 0.0002), PMS2(p = 0.0068), XRCC1 (p = 0.0080) and MLH3 (0.0057) between the two groups. Conclusion: The effects of chronic smoking on oral mucosa led to the methylation of genes MRE11A PMS2, XRCC1 and MLH3, but resulted in a reduction of gene expression of MRE11A and PMS2, which showed ≥50% methylation. These results provide evidence that smoking cause methylation and reduced expression of repair genes.