Role of ATM kinase in the effect of CpG ODN7909 on X-ray-induced G₂/M phase arrest and apoptosis in A549 cells

Objective: To investigate the relationship between the effect of unmethylated cytosine phosphate-guanine oligodeoxynucleotide (CpG ODN) 7909 on X-ray-induced G₂/M phase arrest and apoptosis and the phosphorylation of ATM kinase. Methods: Human lung adenocarcinoma A549 cells were randomly classified into five groups, control, CpG group, irradiation group, CpG + irradiation group and ATM siRNA + CpG + irradiation group. Cell survival fraction was evaluated by clonogenic assay. Cell cycle and apoptosis were analyzed by flow cytometry. The expressions of ATM, checkpoint kinase-2 (Chk2) and p53 were detected with Western blot. Results: Compared to the situation under X-ray irradiation alone, decreased cell clonogenic survival, prolonged G₂/M arrest, and increased cell apoptosis were observed after the combination treatment with CpG ODN7909 and X-rays (t=13.41, 17.32 and 7.71, P<0.05). Moreover, the phosphorylations on ATM, Chk2, and p53 were increased in the irradiated A549 cells that had been pre-treated with CpG ODN7909. After ATM siRNA interfering, abrogation of G₂/M arrest, reduction of apoptosis, and decrease of Chk2 and p53 phosphorylation were found in A549 cells treated with CpG ODN7909 and X-rays (t=26.84, 2.98, 47.24 and 67.47, P<0.05). Conclusions: CpG ODN7909 can enhance the X-ray-induced phosphorylation of ATM kinase in human lung adenocarcinoma cells in vitro, which might be involved in regulating G₂/M phase arrest and apoptosis. (authors)