P02.08.A The relations of focal and total DNA methylation in gliomas

Abstract

Abstract Background The role of epigenetic events in gliomagenesis is undoubtful. However, the role of specific pathological events is not so clear. It was shown that loss in total DNA methylation correlates with higher tumor malignancy and oxidative DNA damage. But promoter methylation of many genes was reported to be significant for gliomas’ malignancy and predictive for the treatment outcome. In carcinogenesis in general global DNA hypomethylation and focal hypermethylation coexist. The aim of our project was to evaluate the correlation between total DNA methylation and promoter methylation of selected genes. Material and Methods We analysed glioma tissues from 60 patients. For total DNA methylation analysis we used the radiolabelling method with TLC separation of nucleotides and content estimation with phosphoimager. For promoter methylation analysis we have chosen: MGMT (O-6-Methylguanine-DNA Methyltransferase), MPG (DNA-3-methyladenine glycosylase), GJA1 (Gap junction alpha-1 protein / connexin 43). The promoter methylation level was evaluated with the methylation-sensitive high-resolution melting (MS-HRM) method. Results Total DNA methylation was reversely correlated with brain tumor grade, confirming that 5-methylcytosine loss is important step in gliomagenesis. From 3 genes only MPG promoter methylation showed clear low reverse correlation with tumor grade. Promoter methylation in GJA1 show low correlation with both, MGMT and MPG, but there was no link between MGMT and MPG. IDHwt presence was significantly correlated with higher tumor grade. Promoter methylations in MPG and GJA1 were better correlated with IDH status than in MGMT. Conclusion There is a clear correlation between total DNA methylation and tumor malignancy. Gene promoter methylation is not highly correlated with total DNA methylation and shows low significance in selected cases. Promoter methylation showed clear correlation with tumor grade only in MPG case. That suggests diverse mechanisms steering DNA methylation in general and local changes. It also shows that total DNA methylation is best predictor of tumor grade.