ATM expression is attenuated by promoter hypermethylation in human ovarian endometriotic stromal cells

A number of genes involved in the pathogenesis of endometriosis are silenced by the hypermethylation of their promoter regions. We assessed the effect and mechanism of the DNA demethylating agent 5-aza-2'-deoxycytidine (5-aza-dC) (10 μM) on the cell cycle in human endometriotic cyst stromal cells (ECSCs) and normal endometrial stromal cells (NESCs) by flow cytometry. The DNA methylation status of G2/M checkpoint regulators were investigated by methylation-specific PCR. The expression of ataxia telangiectasia mutated (ATM) and the effect of 5-aza-dC on its expression were also evaluated by quantitative RT-PCR and western blotting analysis. 5-aza-dC treatment resulted in the cell cycle arrest of ECSCs at the G2/M phase. In contrast, 5-aza-dC did not affect the cell cycle of NESCs. The promoter region of the ATM gene was hypermethylated in ECSCs, but not in NESCs. ATM mRNA expression was attenuated in ECSCs compared to that in NESCs. Further, 5-aza-dC was found to restore ATM expression in ECSCs by its promoter demethylation. Our findings indicate that ATM promoter hypermethylation occurs in endometriosis, and that ATM silencing is involved in tumorigenesis during this disease; moreover, selective DNA demethylating agents and molecular target drugs against ATM silencing are promising for the treatment of endometriosis.