Influence of ATM on DNA methyltransferase inhibitor-iduced radioensitization

Abstract

Background: Preclinical studies have demonstrated that inhibition of DNA methyltrasferase (DMNT) induces radiosensitization in human cancer cells. The current study is to investigate the role of ATM in DNMT inhibitor-mediated radiosensitization. Methods: A pair of isogenic cell lines was constructed from AT fibroblasts: one without ATM and the other expressing functional ATM. The effects of DNMT inhibitor treatment on radiosensitivity were evaluated in these cell lines using two DNMT inhibitors: psammaplin A (PSA) and 5-aza-2-deoxycytidine (DAC). DNA damage repair was analyzed using γH2AX foci. Western blot of DNA damage foci proteins was done. Results: DNMT inhibition induced radiosensitization of ATM-expressing cells, but had no effect in ATM-null cells. DNMT inhibitor treatment prolonged expression of both γH2AX foci and phospho-BRCA1 after irradiation in cells with ATM, whereas neither was observed in ATM-null cells treated with DNMT inhibitors. Expression of MRN complex subunits (MRE11, Rad50, NBS1) was not altered by either of DNMT inhibition or irradiation. DNMT inhibitor treatment or irradiation induced MRE11 phosphorylation in both ATM-null and ATM-expressing cell lines. Conclusion: DNMT inhibitors enhance radiosensitivity by delaying DNA damage repairs. Radiosensitization by DNMT inhibition requires functional ATM.