Loss of nonhomologous end joining confers camptothecin resistance in DT40 cells - Implications for the repair of topoisomerase I-mediated DNA damage
Loss of nonhomologous end joining confers camptothecin resistance in DT40 cells - Implications for the repair of topoisomerase I-mediated DNA damage
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DOI：
10.1074/jbc.m313910200
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发表时间：
2004-09-03
影响因子：
4.8
通讯作者：
Koyama, H
中科院分区：
文献类型：
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作者：
Adachi, N;So, SR;Koyama, H
DNA拓扑异构酶I（Top1）通过形成切割复合物产生瞬时DNA单链断裂，其中酶与切割链的3 '-磷酸连接。抗癌药物喜树碱（CPT）通过捕获切割复合物来毒害Top1，从而诱导Top1连接的单链断裂。这种DNA损伤在与复制叉碰撞时转化为DNA双链断裂（DSB），这意味着DSB修复途径可能参与Top1介导的DNA损伤的处理/修复。在这里，我们报告Top1介导的DNA损伤主要通过同源重组来修复，这是DSB修复的主要途径。然而，出乎意料的是，我们发现，非同源末端连接（NHEJ），另一种DSB修复途径，在相关的修复中没有积极的作用;值得注意的是，DT 40细胞突变体缺乏任何NHEJ因子（即Ku 70，DNA依赖性蛋白激酶催化亚基，和DNA连接酶IV）是耐杀伤CPT。此外，我们还发现，NHEJ的缺失使得CPT诱导的DNA损伤修复需要同源重组。我们的研究结果表明，NHEJ可以在CPT的存在下，细胞毒性途径，脱落的新的光的分子机制的形成和修复的Top1介导的DNA损伤的脊椎动物。因此，我们的数据对涉及Top1抑制剂的癌症化疗具有重要意义。
DNA topoisomerase I (Top1) generates transient DNA single-strand breaks via the formation of cleavage complexes in which the enzyme is linked to the 3'-phosphate of the cleavage strand. The anticancer drug camptothecin (CPT) poisons Top1 by trapping cleavage complexes, thereby inducing Top1-linked single-strand breaks. Such DNA lesions are converted into DNA double-strand breaks (DSBs) upon collision with replication forks, implying that DSB repair pathways could be involved in the processing/repair of Top1-mediated DNA damage. Here we report that Top1-mediated DNA damage is repaired primarily by homologous recombination, a major pathway of DSB repair. Unexpectedly, however, we found that nonhomologous end joining (NHEJ), another DSB repair pathway, has no positive role in the relevant repair; notably, DT40 cell mutants lacking either of the NHEJ factors ( namely, Ku70, DNA-dependent protein kinase catalytic subunit, and DNA ligase IV) were resistant to killing by CPT. In addition, we showed that the absence of NHEJ alleviates the requirement of homologous recombination in the repair of CPT-induced DNA damage. Our results indicate that NHEJ can be a cytotoxic pathway in the presence of CPT, shedding new light on the molecular mechanisms for the formation and repair of Top1-mediated DNA damage in vertebrates. Thus, our data have significant implications for cancer chemotherapy involving Top1 inhibitors.