Metilação das regiões promotoras dos genes RASSF1A e MGMT na carcinogênese de cabeça e pescoço

Abstract

Introduction: DNA methylation plays an important role in regulating gene expression. During tumorigenesis, the hypermethylation of CpG-rich islands in promoter regions (Cytosine phosphodiester Guanine) is a mechanism that can inactivate tumor suppressor genes and contribute to the development of cancer. Objective: This study aimed to evaluate the methylation of promoter regions of tumor suppressor genes RASSF1A (Ras association domain family member 1) and MGMT (O-6-methylguanine-DNA methyltransferase) in squamous cell carcinoma of the head and neck. Methods: The methylation analysis of promoter regions of RASSF1A and MGMT genes was performed using the High Resolution Melting (HRM) in 42 and 37 tumor tissue samples, respectively. Samples of tissue adjacent to the tumor or peripheral blood were used as controls. Results: For the RASSF1A gene, 50% (21 of 42) of tumor tissue samples analyzed were methylated, whereas for MGMT of 37 tumor tissue samples analyzed, 17 (46%) showed methylation. Statistical analysis between pairs of tumor samples and controls (tissue adjacent to the site of tumor and peripheral blood) showed significant differences in the presence of methylation for the RASSF1A gene (P = 0.027, Chi-square test) and the MGMT gene (P = 0.002, Chi-square test). The evaluation of the presence of methylation between tumor tissue and surrounding tissue showed no significant difference for RASSF1A genes (P = 1.0) and MGMT (P = 0.38). For the subset of tumor tissue and peripheral blood statistic was significant for RASSF1A (P = 0.005) and MGMT (P = 0.002) genes. Analysis of the presence of methylation in tumors relative to non-tumor tissues (tissues adjacent to tumor or peripheral blood) in different anatomical sites of primary occurrence showed that in oral cavity and pharynx no statistically significant difference for the RASSF1A gene (P = 0.233) relative to non-tumor samples; MGMT gene statistical results were significant (P = 0.033). In the larynx, the statistical results were significant for the RASSF1A gene (P = 0.04) compared to non-tumor samples, while for the MGMT gene, the result was not statistically significant (P = 0.998). The presence of the methylation of the MGMT gene in both genes simultaneously, RASSF1A and MGMT, were associated with the category N (P = 0.045 and P = 0.035, respectively). For the RASSF1A gene was not observed this association (P = 0.093). The analysis by multiple logistic regression of the influence of epidemiological factors (gender and age), risk factors (smoking and drinking) and clinical parameters of the tumor for the presence of methylation showed no significant association for these variables. Conclusions: The prevalence presence of methylation in the promoter region of RASSF1A and MGMT genes in tumor tissue of the pairs of samples (tumor and non-tumor tissue) suggests the involvement of these genes in the process of squamous cells carcinoma of the head and neck, in particular of the MGMT gene in tumors of the oral cavity and pharynx and RASSF1A gene in larynx tumors. No was observed association between methylation of RASSF1A and MGMT genes and age, gender, the tobacco and alcohol consumption and clinical tumor parameters.