Silencing effect of CpG island hypermethylation and histone modifications on O6-methylguanine-DNA methyltransferase (MGMT) gene expression in human cancer

摘要: O6-methylguanine-DNA methyltransferase (MGMT) repairs the cytotoxic and mutagenic O6-alkylguanine produced by alkylating agents such as chemotherapeutic mutagens. Recent studies have shown that in a subset of tumors, MGMT expression is inversely linked to hypermethylation CpG island promoter region; however, how epigenetic silencing mechanism works, it relates hypermethylation, was still unclear. To understand mechanism, we examined detailed methylation status whole with bisulfite-sequencing 19 non-expressed cancer cell lines. We found two highly methylated regions island. One upstream exon 1, including minimal promoter, other downstream, enhancer. Reporter gene assay showed both downstream suppressed luciferase activity drastically. Chromatin immunoprecipitation revealed histone H3 lysine 9 hypermethylated throughout negative line, whereas acetylation on H4 4 were at significantly high levels outside MGMT-expressed line. Furthermore, MeCP2 preferentially bound CpG-methylated Given these results, propose model for dependent state cancer.