Base excision repair intermediates induce p53-independent cytotoxic and genotoxic responses
Base excision repair intermediates induce p53-independent cytotoxic and genotoxic responses
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DOI：
10.1074/jbc.m306592200
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发表时间：
2003-10-10
影响因子：
4.8
通讯作者：
Wilson, SH
中科院分区：
文献类型：
--
作者：
Sobol, RW;Kartalou, M;Wilson, SH
DNA烷基化损伤主要通过哺乳动物细胞中的碱基切除修复（BER）机制来修复。例如，在N-烷基化嘌呤碱基损伤的修复中，烷基腺嘌呤DNA糖基化酶（Aag）识别并去除碱基，而DNA聚合酶β（β-pol）有助于差距剪裁和DNA合成步骤。正是β-pol介导的5 '-脱氧核糖磷酸去除的丧失使得小鼠成纤维细胞对烷基化过敏。在这里，我们报告，甲基磺酸甲酯诱导的烷基化损伤后的β-pol缺陷细胞的超敏反应完全依赖于糖基化酶介导的修复启动，这表明烷基化的基础病变本身是耐受在这些细胞中，并证明β-pol防止有毒BER中间体的积累。此外，我们发现，这些中间体最初耐受体内的第二个修复途径，同源重组，诱导增加姐妹染色单体交换事件。如果不解决，这些BER中间体会引发DNA合成和细胞毒性的快速阻断。令人惊讶的是，细胞毒性和遗传毒性信号都独立于p53应答和错配DNA修复途径，表明p53不是功能性BER途径所需的，观察到的损伤应答不是p53应答网络的一部分，BER中间体诱导的细胞毒性和遗传毒性效应与响应错配修复信号传导的机制不同。这些研究表明，虽然BER途径修复了碱基损伤，但不完整的BER中间体穿梭进入同源重组途径，表明BER和重组机制之间可能存在协调。
DNA alkylation damage is primarily repaired by the base excision repair (BER) machinery in mammalian cells. In repair of the N-alkylated purine base lesion, for example, alkyl adenine DNA glycosylase (Aag) recognizes and removes the base, and DNA polymerase beta (beta-pol) contributes the gap tailoring and DNA synthesis steps. It is the loss of beta-pol-mediated 5'-deoxyribose phosphate removal that renders mouse fibroblasts alkylation-hypersensitive. Here we report that the hypersensitivity of beta-pol-deficient cells after methyl methanesulfonate-induced alkylation damage is wholly dependent upon glycosylase-mediated initiation of repair, indicating that alkylated base lesions themselves are tolerated in these cells and demonstrate that beta-pol protects against accumulation of toxic BER intermediates. Further, we find that these intermediates are initially tolerated in vivo by a second repair pathway, homologous recombination, inducing an increase in sister chromatid exchange events. If left unresolved, these BER intermediates trigger a rapid block in DNA synthesis and cytotoxicity. Surprisingly, both the cytotoxic and genotoxic signals are independent of both the p53 response and mismatch DNA repair pathways, demonstrating that p53 is not required for a functional BER pathway, that the observed damage response is not part of the p53 response network, and that the BER intermediate-induced cytotoxic and genotoxic effects are distinct from the mechanism engaged in response to mismatch repair signaling. These studies demonstrate that, although base damage is repaired by the BER pathway, incomplete BER intermediates are shuttled into the homologous recombination pathway, suggesting possible coordination between BER and the recombination machinery.