O6-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo
O6-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo
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DOI：
10.1073/pnas.0811991106
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发表时间：
2009-01-13
影响因子：
11.1
通讯作者：
Samson, Leona D.
中科院分区：
文献类型：
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作者：
Klapacz, Joanna;Meira, Lisiane B.;Samson, Leona D.
烷基化诱导的O-6-甲基鸟嘌呤（O（6）MeG）DNA损伤如果不被O（6）MeG-DNA甲基转移酶（Mgmt）蛋白修复，则可能具有致突变性或细胞毒性。O（6）MeG在DNA复制过程中与T配对，如果O（6）MeG：T错配持续存在，则G：C到A：T的转换突变在下一个复制循环中被固定。通过MutS α和MutL α检测O（6）MeG：T错配导致凋亡性细胞死亡，但其发生机制尚不清楚。为了探索错配修复如何介导O（6）MeG依赖性细胞凋亡，我们使用了Mgmt缺失小鼠模型，该模型结合了Msh 6缺失突变体（错配识别缺陷）或Exo 1缺失突变体（错配修复切除步骤受损）。正如预期的那样，来自Mgmt缺失小鼠的小鼠胚胎成纤维细胞和骨髓细胞比野生型更加烷基化敏感。然而，Msh 6或Exo 1功能的消融使得这些Mgmt缺失细胞与野生型细胞一样对烷基化诱导的细胞毒性具有抗性。Mgmt基因敲除小鼠的快速增殖组织（骨髓、胸腺和脾脏）对O（6）MeG产生剂诱导的细胞凋亡极其敏感。在这里，我们表明，无论是Msh 6或Exo 1功能的Mgmt基因敲除小鼠呈现这些快速增殖的组织烷基化抗性。然而，尽管Msh 6缺陷赋予总的烷基化抗性，Exo 1缺陷导致可变的组织特异性烷基化抗性表型。我们的研究结果表明Exo 1在未修复的O（6）MeGs诱导细胞凋亡中起着重要作用。
Alkylation-induced O-6-methylguanine (O(6)MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by the O(6)MeG-DNA methyltransferase (Mgmt) protein. O(6)MeG pairs with T during DNA replication, and if the O(6)MeG: T mismatch persists, a G: C to A: T transition mutation is fixed at the next replication cycle. O(6)MeG: T mismatch detection by MutS alpha and MutL alpha leads to apoptotic cell death, but the mechanism by which this occurs has been elusive. To explore how mismatch repair mediates O(6)MeG-dependent apoptosis, we used an Mgmt-null mouse model combined with either the Msh6-null mutant (defective in mismatch recognition) or the Exo1-null mutant (impaired in the excision step of mismatch repair). Mouse embryonic fibroblasts and bone marrow cells derived from Mgmt-null mice were much more alkylation-sensitive than wild type, as expected. However, ablation of either Msh6 or Exo1 function rendered these Mgmt-null cells just as resistant to alkylation-induced cytotoxicity as wild-type cells. Rapidly proliferating tissues in Mgmt-null mice (bone marrow, thymus, and spleen) are extremely sensitive to apoptosis induced by O(6)MeG-producing agents. Here, we show that ablation of either Msh6 or Exo1 function in the Mgmt-null mouse renders these rapidly proliferating tissues alkylation-resistant. However, whereas the Msh6 defect confers total alkylation resistance, the Exo1 defect leads to a variable tissue-specific alkylation resistance phenotype. Our results indicate that Exo1 plays an important role in the induction of apoptosis by unrepaired O(6)MeGs.