Gene promoter hypermethylation in leukoplakia of the oral mucosa

Abstract

Gene promoter hypermethylation in leukoplakia of the oral mucosa Mingli Liu1, Lei Feng2, Ximing Tang3, Shanchun Guo41Department of Physics, Tufts University School of Medicine, Boston, Massachussetts; 2Department of Thoracic/Head and Neck Medical Oncology, 3Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, Texas; 4Sylvester Cancer Center, University of Miami School of Medicine, Florida, USAAbstract: To examine whether aberrant DNA methylation in the promoter region might occur earlier in tumorigenesis, particularly in premalignant lesions, we examined biopsies from 111 participants in a chemoprevention trial aimed at reversal of oral leukoplakia, using methylation-specific polymerase chain reaction for the promoter regions of the tumor suppressor gene CDKN2A (p16), the putative metastasis suppressor gene for death-associated protein kinase (DAP-K), the DNA repair gene O6-methyguanine-DNA-methyltransferase (MGMT), and the detoxification gene glutathione S-transferase p1(GSTP1). p16 promoter hypermethylation was detected in 21 of 82 (25.6%), DAP-K hypermethylation in 28 of 87 (32.2%), and MGMT hypermethylation in 32 of 106 (30.2%) oral leukoplakia lesions analyzed. No aberrant methylation was found at the GSTP1 gene in 110 lesions examined. Among 68 biopsies analyzed for all three genes (p16, DAP-K, MGMT), 17 biopsies were detected with an abnormal methylation pattern at only one gene, 15 at two genes, and 8 at all three genes. Among clinical characteristics and their correlation with methylation, only alcohol consumption was correlated with DAP-K methylation (P = 0.027), while MGMT methylation was more frequent in females (P = 0.003) and nonsmokers (P = 0.0005). A significant correlation was found between p16 and DAP-K hypermethylation; p16 promoter was methylated in 14 (56%) of 25 lesions with DAP-K methylation, and only 5 (11.1%) of 45 DAP-K methylation-negative lesions (P = 0.0001). DAP-K aberrant methylation was also significantly correlated with MGMT methylation (16 of 31 in MGMT methylation-positive lesions versus 12 of 52 MGMT methylation-negative lesions, P = 0.0016). Our results suggest that epigenetic mechanisms of inactivation, such as aberrant methylation of p16, DAP-K, and MGMT genes, occur early in head and neck tumorigenesis, and might play a role in the progression of these lesions.Keywords: p16, DAP-K, MGMT, GSTP1 genes, methylation, leukoplakia