Gou Qiheng, Xie Yuxin, Liu Lei, Xie Keqi, Wu Yanxia, Wang Qianqian, Wang Zhu, Li Ping
State Key Laboratory of Biotherapy/Collaborative Innovation Center of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
Cancer Center, West China Hospital, West China Medical School, Sichuan University, Chengdu, Sichuan 610041, P.R. China.
Oncol Rep. 2015 Jul;34(1):251-7. doi: 10.3892/or.2015.3980. Epub 2015 May 14.
DNA double-strand breaks (DSBs) induced by ionizing radiation (IR) are among the most cytotoxic types of DNA damage. The DNA damage response (DDR) may be a reason for the cancer cell resistance to radiotherapy using IR. Identified as critical upstream mediators of the phosphorylation of ataxia telangiectasia-mutated (ATM) pathway, mediator of DNA damage checkpoint 1 (MDC1) and p53-binding proteins 1 (53BP1) may affect the radiosensitivity of tumor cells. In the present study, we generated two HEP-2 cell lines with a stable knockdown of MDC1 or 53BP1 with short hairpin RNA (shRNA), respectively, and investigated the effect of MDC1 and 53BP1 on cell radiosensitivity, cell cycle distribution and the formation of cell foci. Downregulation of the two proteins reduced the number of clonogenic cells that treated with IR. Accumulation of G2/M phase cells was detected after the MDC1 and 53BP1 downregulation. These results indicated that the expression of MDC1 or 53BP1 limited tumor cell sensitivity to radiotherapy and may play an important role in the DNA repair progression. Furthermore, the MDC1 foci was identified and presented in the 53BP1-inhibited cells. By contrast, the 53BP1 foci was absent from the MDC1-inhibited cells. The results confirmed that the recruitment of 53BP1 into the foci occurred in an MDC1-dependent manner.
电离辐射（IR）诱导的DNA双链断裂（DSB）是最具细胞毒性的DNA损伤类型之一。DNA损伤反应（DDR）可能是癌细胞对使用IR的放射治疗产生抗性的原因。作为共济失调毛细血管扩张突变（ATM）途径磷酸化的关键上游介质，DNA损伤检查点1（MDC1）和p53结合蛋白1（53BP1）的介质可能影响肿瘤细胞的放射敏感性。在本研究中，我们分别用短发夹RNA（shRNA）构建了两个稳定敲低MDC1或53BP1的HEP-2细胞系，并研究了MDC1和53BP1对细胞放射敏感性、细胞周期分布和细胞病灶形成的影响。这两种蛋白的下调减少了经IR处理的克隆形成细胞的数量。在MDC1和53BP1下调后检测到G2/M期细胞的积累。这些结果表明，MDC1或53BP1的表达限制了肿瘤细胞对放射治疗的敏感性，并且可能在DNA修复进程中起重要作用。此外，在53BP1抑制的细胞中鉴定并呈现出MDC1病灶。相比之下，在MDC1抑制的细胞中不存在53BP1病灶。结果证实，53BP1募集到病灶中是以MDC1依赖的方式发生的。
