ATM regulates Mre11-dependent DNA end-degradation and microhomology-mediated end joining
ATM regulates Mre11-dependent DNA end-degradation and microhomology-mediated end joining
复制标题
DOI：
10.4161/cc.9.14.12363
复制
发表时间：
2010-07
期刊：
影响因子：
4.3
通讯作者：
Elias A. Rahal;Elias A. Rahal;L. A. Henricksen;Yuling Li;R. S. Williams;J. Tainer;K. Dixon
中科院分区：
文献类型：
--
作者：
Elias A. Rahal;Elias A. Rahal;L. A. Henricksen;Yuling Li;R. S. Williams;J. Tainer;K. Dixon
以遗传不稳定和神经退行性变为特征的人类共济失调毛细血管扩张症（AT）是由共济失调毛细血管扩张突变激酶（ATM）突变引起的。ATM的丢失导致细胞周期检查点缺陷和其他DNA损伤信号缺陷，这些缺陷并不能完全解释与A-T相关的所有病理，包括神经元丢失。为了解决这个谜题，我们发现ATM通过微同源介导的末端连接（MMEJ）抑制DNA双链断裂（DSB）修复。我们发现ATM对DNA末端降解的抑制依赖于它的激酶活性，Mre11是A-T中DNA末端降解和MMEJ修复增加的主要核酸酶。通过体内报告系统对MMEJ的评估显示，mre11基因敲除细胞和mre11核酸酶抑制剂mirin处理的细胞中，MMEJ修复水平降低。基于结构的Mre11二聚体接合DNA末端的建模表明，桥接DSB的5‘端并置，这样DNA解绕和3’-5‘外切酶活性可能协同促进MMEJ中延长的5’端同时配对和3'端外切酶降解。综上所述，我们的研究结果提供了对MMEJ中ATM和Mre11的综合理解：ATM在控制DNA末端稳定性和易出错的DSB修复中具有关键的调节功能，Mre11核酸酶在哺乳动物细胞中启动MMEJ中起主要作用。ATM和Mre11的这些功能在有丝分裂后的神经细胞中可能特别重要，因此依赖于姐妹染色单体之间同源重组以外的机制来修复dsb。
The human disorder ataxia telangiectasia (AT), which is characterized by genetic instability and neurodegeneration, results from mutation of the ataxia telangiectasia mutated (ATM) kinase. The loss of ATM leads to cell-cycle checkpoint deficiencies and other DNA damage signaling defects that do not fully explain all pathologies associated with A-T including neuronal loss. In addressing this enigma, we find here that ATM suppresses DNA double-strand break (DSB) repair by microhomology-mediated end joining (MMEJ). We show that ATM repression of DNA end-degradation is dependent on its kinase activities and that Mre11 is the major nuclease behind increased DNA end-degradation and MMEJ repair in A-T. Assessment of MMEJ by an in vivo reporter assay system reveals decreased levels of MMEJ repair in Mre11-knockdown cells and in cells treated with Mre11-nuclease inhibitor mirin. Structure-based modeling of Mre11 dimer engaging DNA ends suggests the 5' ends of a bridged DSB are juxtaposed such that DNA unwinding and 3'-5' exonuclease activities may collaborate to facilitate simultaneous pairing of extended 5' termini and exonucleolytic degradation of the 3' ends in MMEJ. Together our results provide an integrated understanding of ATM and Mre11 in MMEJ: ATM has a critical regulatory function in controlling DNA end-stability and error-prone DSB repair and Mre11 nuclease plays a major role in initiating MMEJ in mammalian cells. These functions of ATM and Mre11 could be particularly important in neuronal cells, which are post-mitotic and therefore depend on mechanisms other than homologous recombination between sister chromatids to repair DSBs.