Comparison Of Cell Killing Effects Between Low-dose Rate And High-dose-rate γ-rays And Repair Of γ-ray Induced DNA Damage

Objective:To investigate the effectiveness of the high-dose-rate (or acute) and low-dose-rate (or chronic)γ-ray irradiation in inducing cell killing and growth inhibition in cultured mammalian cells, and the mechanism of repair the DNA double-strand breaks(DSBs).Methods:(1)The protein expression of phosphorylated ATM, P53 and P21 afterγ-irradiation in three kinds mammalian cells was analyzed by western blot hybridization using well characterized monoclonal antibodies. (2) To determine the reduction of biological effects, which cell maintained not only in exponentially growing condition but also in density-inhibited plateau phase, using colony formation assay.(3) Using theγ-H2AX assay, which reflects the presence of DNA double-strand breaks, to detect the role of ATM and DNA-PKcs in repair of DSBs.Result:(1) The results of Western Blot suggested that phosphorylated ATM protein appeared in all three kinds of cells at different time points, and clear phosphorylated P53,P21 induction. (2) the growth of cells became slower in low dose rate irradiation, especially in human fibroblasts (3)Exposure with both high-dose-rate and low-dose-rate irradiation, all three kinds of cells shows significant dose rate effect in not only exponentially growing condition but also density-inhibited plateau phase, but the survival fractions in high-dose-rate irradiation are much lower than low-dose-rate irradiation; (4) After exposure to high dose rate irradiation, the survival fraction of all the three kinds cell maintaining in the confluent condition increased according to the incubation time; (5) incubated with ATM inhibitor and DNA-PKcs inhibitor shows more DSBs compared with control after exposure with both high-dose-rate and low-dose-rate irradiation.Conclusions:(1)The phosphorylated ATM protein appeared and phosphorylated P53,P21 inducted after irradiation in mammalian cells. (2) With low dose rate irradiation, the growth of cells decreased compared with no irradiated condition, especially in human fibroblasts. (3) Significant dose rate effect is showed after exposed toγ-irradiation; the survival fractions in high-dose-rate irradiation are much lower than low-dose-rate irradiation (4) cells which maintained in the confluent condition shows clear repair of PLD after high dose rate irradiation; (5) ATM plays important role not only in the high dose rate irradiation induced DSBs repair but also low dose rate irradiation induced DSBs repair.