摘要目的 观察A549细胞的低剂量辐射超敏感性现象,探讨其发生的机制.方法 A549细胞接受0～2 Gy的60Co γ射线照射后,流式细胞仪对其分选计数,克隆形成法检测细胞存活分数,Western blot法检测ATMl981Ser-P蛋白表达,Hoechst 33258荧光染色法、AnnexinV-FITC/PI双染流式细胞仪检测细胞凋亡,PI单染流式细胞仪检测细胞周期.结果 细胞在0～0.3 Gy表现出单位剂量杀伤增强,在0.3～0.5 Gy表现出一定的辐射抗性,0.5 Gy后的区域存活分数随辐射剂量的增加而降低.照射后1 h,ATM激酶在0.2 Gy时开始活化,0.5 Gy时活化达高峰(t=7.96,P＜0.05);与0.5 Gy相比1.0和2.0 Gy的活化水平无明显变化(t=0.69、0.55,P＞0.05).照射后24 h,部分细胞发生凋亡,其凋亡曲线与存活曲线相吻合.与未照射组相比,0.1和0.2 Gy组在各时间点(照射后6、12和24 h)的细胞周期无明显变化,而0.3、0.4和0.5 Gy组,照射后6和12 h细胞发生G2/M期阻滞(t=2.87、2.88、4.92和3.70、3.12、8.11,P＜0.05),照射后24 h G2/M期细胞比例下降(t=3.87、4.77、3.01,P＜0.05).结论 A549细胞存在HRS/IRR现象,其发生可能与ATM激酶、细胞周期变化有关,凋亡是细胞死亡的主要方式.

abstractsObjective To study the low dose hyper-radiosensitivity in human lung cancer cell line A549,and its possible mechanisms.Methods Exponentially growing A549 cells were irradiated with 60Co γ-rays at doses of 0-2 Gy.Together with flow cytometry for precise cell sorting,cell survival fraction was measured by mean of conventional colony-formation assay.ATM1981 Ser-P protein expression was examined by Western blot.Apoptosis was identified by Hoechst 33258 fluorescent staining,and Annexin V-FITC and propidium iodide staining flow cytometry.Cell cycle distribution was observed by flow cytometry.Results There was an excessive cell killing per unit dose when the doses were below about 0.3 Gy,and the cells exhibited more resistant response at the doses between 0.3 and 0.5 Gy,the cell survival fraction was decreased as the doses over 0.5 Gy.The expression of ATM1981Ser-P protein was first observed at 0.2 Gy,followed by an increase over 0.2 Gy,and reached the peak at 0.5 Gy(compared with 0.2 Gy group,t=7.96,P＜0.05),with no further increase as the doses at 1.0 and 2.0 Gy(t=0.69,0.55,P＞0.05).24 hours after irradiation,part cells presented the characteristic morpholos4cal change of apoptosis,and the apoptosis curve was coincident with the dose-survival curve.Compared with the control group,the cell cycle had no change post-irradiation to 0.1 and 0.2 Gy.G2/M phase arrest was manifested at 6 and 12 hours post-irradiation to 0.3,0.4 and 0.5 Gy(t=2.87,2.88,4.92 and 3.70,3.12,8.11,P＜0.05),and the ratio of G2/M phase was decreased at 24 hours post-irradiation(t=3.87,4.77,3.01,P＜0.05).Conclusions A549 cells displays the phenomenon of hyper-radiosensitivity(HRS)/induced radioresistance(IRR).The model of cell death induced by low dose irradiation is mainly apoptosis.The activity of ATM and cell cycle change might play an important role in HRS/IRR.