Li Weiwei, Gu Xueyan, Zhang Xiaoning, Kong Jinxin, Ding Nan, Qi Yongmei, Zhang Yingmei, Wang Jufang, Huang Dejun
Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University, Lanzhou 730000, China.
Gansu Key laboratory of Space Radiobiology, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
Mutat Res. 2015 Sep;779:112-23. doi: 10.1016/j.mrfmmm.2015.07.002. Epub 2015 Jul 9.
Although studies have shown that cadmium (Cd) interfered with DNA damage repair (DDR), whether Cd could affect non-homologous end joining (NHEJ) repair remains elusive. To further understand the effect of Cd on DDR, we used X-ray irradiation of Hela cells as an in vitro model system, along with γH2AX and 53BP1 as markers for DNA damage. Results showed that X-ray significantly increased γH2AX and 53BP1 foci in Hela cells (p < 0.01), all of which are characteristic of accrued DNA damage. The number of foci declined rapidly over time (1-8h postirradiation), indicating an initiation of NHEJ process. However, the disappearance of γH2AX and 53BP1 foci was remarkably slowed by Cd pretreatment (p < 0.01), suggesting that Cd reduced the efficiency of NHEJ. To further elucidate the mechanisms of Cd toxicity, several markers of NHEJ pathway including Ku70, DNA-PKcs, XRCC4 and Ligase IV were examined. Our data showed that Cd altered the phosphorylation of DNA-PKcs, and reduced the expression of both XRCC4 and Ligase IV in irradiated cells. These observations are indicative of the impairment of NHEJ-dependent DNA repair pathways. In addition, zinc (Zn) mitigated the effects of Cd on NHEJ, suggesting that the Cd-induced NHEJ alteration may partly result from the displacement of Zn or from an interference with the normal function of Zn-containing proteins by Cd. Our findings provide a new insight into the toxicity of Cd on NHEJ repair and its underlying mechanisms in human cells.
尽管研究表明镉（Cd）会干扰DNA损伤修复（DDR），但Cd是否会影响非同源末端连接（NHEJ）修复仍不清楚。为了进一步了解Cd对DDR的影响，我们使用X射线照射Hela细胞作为体外模型系统，并使用γH2AX和53BP1作为DNA损伤的标志物。结果表明，X射线显著增加了Hela细胞中的γH2AX和53BP1焦点（p < 0.01），所有这些都是累积DNA损伤的特征。随着时间的推移（照射后1 - 8小时），焦点数量迅速下降，表明NHEJ过程开始。然而，Cd预处理显著减缓了γH2AX和53BP1焦点的消失（p < 0.01），表明Cd降低了NHEJ的效率。为了进一步阐明Cd毒性的机制，我们检测了NHEJ途径的几个标志物，包括Ku70、DNA-PKcs、XRCC4和连接酶IV。我们的数据表明，Cd改变了DNA-PKcs的磷酸化，并降低了照射细胞中XRCC4和连接酶IV的表达。这些观察结果表明NHEJ依赖性DNA修复途径受到损害。此外，锌（Zn）减轻了Cd对NHEJ的影响，表明Cd诱导的NHEJ改变可能部分是由于Zn的置换或Cd对含Zn蛋白质正常功能的干扰。我们的研究结果为Cd对人类细胞中NHEJ修复的毒性及其潜在机制提供了新的见解。
