[Potentials of DNA-PKcs, Ku80, and ATM in enhancing radiosensitivity of cervical carcinoma cells]

DNA double strand break (DSB) is the lethal damage of cells after irradiation. DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Ku80, and ataxia-telangiectasia mutated (ATM) are the most important repair proteins of DSB. Cervical carcinoma is mainly treated by radiotherapy; however, the tumor cells display different radiosensitivity. This study tried to explore the correlations of DNA-PKcs, Ku80, and ATM expression to radiosensitivity of cervical cancer cells, and to probe their potentials in enhancing the radiosensitivity of cervical carcinoma.The expression of DNA-PKcs, Ku80, and ATM in 41 specimens of cervical carcinoma was detected by immunohistochemistry. Their expression in 8 tumor cell lines (including 4 cervical carcinoma cell lines) was measured by Western blot; the survival fraction at 2 Gy (SF2) and alpha value were measured by colony formation test; the correlations of protein expression to SF2 and alpha values were analyzed by Pearson linear correlation analysis. The small hairpin RNA (shRNA) targeting DNA-PKcs and a competitive DNA-PKcs inhibitor LY294002 were used to inhibit DNA-PKcs expression and activity in cervical carcinoma cell line HeLa. The SF2 and alpha values of HeLa cells after X-ray irradiation were measured by colony formation test; cell apoptosis was analyzed by flow cytometry.The positive rates of Ku80, DNA-PKcs, and ATM in the 41 specimens of cervical carcinoma were 70.73%, 68.29%, and 19.51%, respectively. The expression of DNA-PKcs was positively related to the SF2 values of the 8 tumor cell lines (r = 0.72, P = 0.04); the expression of Ku80 and ATM had no correlation to SF2 and alpha values. The SF2 value was lower in DNA-PKcs shRNA-transfected HeLa cells than in control HeLa cells (0.37 vs. 0.53, P0.05). When treated with 50 mumol/L LY294002 for 1 h, the apoptosis rate of HeLa cells had no significant change ( P0.05); when irradiated by 6 Gy X-ray for 48 h and 72 h, the apoptosis rate was significantly higher in LY294002-pretreated HeLa cells than in control HeLa cells (t = 3.25, P = 0.03; t = 3.01, P = 0.04).DNA-PKcs protein is highly expressed in cervical carcinoma, and its expression level could prognosticate the radiosensitivity of tumor cells. Inhibiting DNA-PKcs expression or activity may sensitize HeLa cells to X-ray.