Radiation induced DNA double-strand breaks (DSB) are the major initial lesions whose misrejoining may lead to exchange aberrations. However, the role of glutathione (GSH), a major cellular thiol, in regulating cell's sensitivity to DNA damaging agents is not well understood. Influence of endogenous GSH on the efficiency of X-rays and bleomycin (Blem) induced DNA DSBs end-joining has been tested here cytogenetically, in human lymphocytes and Hct116 cells. In another approach, oligomeric DNA (75bp) containing 5'-compatible and non-compatible overhangs mimicking the endogenous DSB were for rejoining in presence of cell-free extracts from cells having different endogenous GSH levels. Frequency of aberrations, particularly exchange aberrations, was significantly increased when Blem was combined with radiation. The exchange aberration frequency was further enhanced when combined treatment was given at 4 degrees C since DNA lesions are poorly repaired at 4 degrees C so that a higher number of DNA breaks persist and interact when shifted from 4 degrees C to 37 degrees C. The exchange aberrations increased further when the combined treatment was given to Glutathione-ester (GE) pre-treated cells, indicating more frequent rejoining of DNA lesions in presence of higher cellular GSH. This is further supported by the drastic reduction in frequency of exchange aberrations but significant increase in incidences of deletions when combined treatment was given to GSH-depleted cells. End-joining efficiency of DNA DSBs with compatible ends was better than for non-compatible ends. End-joining efficiency of testicular and MCF7 cell extracts was better than that of lungs and Hct116 cells. Cell extract made from GE-treated MCF-7 cells provided more efficient end-joining than from untreated and GSH-depleted cells. However, direct addition of GSH to the cell-free extracts showed considerable reduction in end-joining efficiency. Present data indicate that higher endogenous GSH favours rejoining of DNA DSBs (both restitution and illegitimate reunion) which in turn produce more exchange aberrations.

中文翻译：

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还原型谷胱甘肽对DNA双链断裂末端连接的影响：细胞遗传学和分子方法。

辐射诱导的DNA双链断裂（DSB）是主要的初始病变，其错误结合可能导致交换像差。然而，人们还不了解谷胱甘肽（GSH）（一种主要的细胞硫醇）在调节细胞对DNA破坏剂的敏感性方面的作用。内源性谷胱甘肽对X射线和博莱霉素（Blem）诱导的DNA DSB末端连接的效率的影响已在此处进行了细胞遗传学测试，涉及人淋巴细胞和Hct116细胞。在另一种方法中，含有模仿内源DSB的5'-相容和非相容突出端的寡聚DNA（75bp）用于在来自具有不同内源GSH水平的细胞的无细胞提取物的存在下重新结合。当Blem与放射线结合使用时，畸变的频率（尤其是交换像差）会显着增加。当在4摄氏度下进行联合治疗时，交换畸变频率会进一步提高，因为在4摄氏度下DNA损伤修复不良，因此当从4摄氏度转变为37摄氏度时，更多的DNA断裂持续存在并相互作用。当对谷胱甘肽-酯（GE）预处理的细胞进行联合治疗时，畸变进一步增加，这表明在存在较高细胞GSH的情况下，DNA损伤的重新结合更为频繁。交换畸变频率的显着降低进一步支持了这一点，但是当对GSH耗尽的细胞进行联合治疗时，其缺失发生率显着增加。具有相容性末端的DNA DSB的末端连接效率要优于非相容性末端。睾丸和MCF7细胞提取物的末端连接效率要好于肺和Hct116细胞。由GE处理的MCF-7细胞制成的细胞提取物比未处理的和GSH耗尽的细胞具有更高的末端连接效率。但是，直接向无细胞提取物中添加GSH会显着降低末端连接效率。目前的数据表明，较高的内源性GSH有助于DNA DSB的重新结合（恢复原状和非法团聚），这反过来又会产生更多的交换像差。