The mismatch repair (MMR) complex is composed of MutSα (MSH2-MSH6) and MutLα (MLH1-PMS2) and specifically recognizes mismatched bases during DNA replication. O 6-Methylguanine is produced by treatment with alkylating agents, such as N-methyl-N-nitrosourea (MNU), and during DNA replication forms a DNA mismatch (i.e. an O 6-methylguanine/thymine pair) and induces a G/C to A/T transition mutation. To prevent this outcome, cells carrying this DNA mismatch are eliminated by MMR-dependent apoptosis, but the underlying molecular mechanism is unclear. In this study, we provide evidence that the chromatin-regulatory and ATP-dependent nucleosome-remodeling protein SMARCAD1 is involved in the induction of MMR-dependent apoptosis in human cells. Unlike control cells, SMARCAD1-knockout cells (ΔSMARCAD1) were MNU-resistant, and the appearance of a sub-G1 population and caspase-9 activation were significantly suppressed in the ΔSMARCAD1 cells. Furthermore, the MNU-induced mutation frequencies were increased in these cells. Immunoprecipitation analyses revealed that the recruitment of MutLα to chromatin-bound MutSα, observed in SMARCAD1-proficient cells, is suppressed in ΔSMARCAD1 cells. Of note, the effect of SMARCAD1 on the recruitment of MutLα exclusively depended on the ATPase activity of the protein. On the basis of these findings, we propose that SMARCAD1 induces apoptosis via its chromatin-remodeling activity, which helps recruit MutLα to MutSα on damaged chromatin.

中文翻译：

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SMARCAD1介导的DNA错配修复蛋白MutLα募集到受损染色质上的MutSα诱导人细胞凋亡。

错配修复（MMR）复合体由MutSα（MSH2-MSH6）和MutLα（MLH1-PMS2）组成，可在DNA复制过程中特异性识别错配的碱基。O 6-甲基鸟嘌呤是通过用烷基化剂（例如N-甲基-N-亚硝基脲（MNU））处理而产生的，在DNA复制过程中会形成DNA错配（即O 6-甲基鸟嘌呤/胸腺嘧啶对）并诱导G / C到A / T转换突变。为了防止这种结果，携带这种DNA错配的细胞会被MMR依赖性细胞凋亡所消除，但是其潜在的分子机制尚不清楚。在这项研究中，我们提供的证据表明，染色质调节和ATP依赖性核小体重塑蛋白SMARCAD1参与了人类细胞MMR依赖性细胞凋亡的诱导。与对照细胞不同，SMARCAD1基因敲除细胞（ΔSMARCAD1）具有MNU抵抗力，并在ΔSMARCAD1细胞中显着抑制了sub-G1群体的出现和caspase-9激活。此外，在这些细胞中，MNU诱导的突变频率增加。免疫沉淀分析表明，在精通SMARCAD1的细胞中观察到MutLα向染色质结合的MutSα的募集在ΔSMARCAD1细胞中受到抑制。值得注意的是，SMARCAD1对MutLα募集的作用完全取决于蛋白质的ATPase活性。根据这些发现，我们建议SMARCAD1通过其染色质重塑活性诱导凋亡，这有助于将MutLα募集到受损染色质上的MutSα。免疫沉淀分析表明，在精通SMARCAD1的细胞中观察到MutLα向染色质结合的MutSα的募集在ΔSMARCAD1细胞中受到抑制。值得注意的是，SMARCAD1对MutLα募集的作用完全取决于蛋白质的ATPase活性。根据这些发现，我们建议SMARCAD1通过其染色质重塑活性诱导凋亡，这有助于在受损的染色质上将MutLα募集到MutSα。免疫沉淀分析表明，在精通SMARCAD1的细胞中观察到MutLα向染色质结合的MutSα的募集在ΔSMARCAD1细胞中受到抑制。值得注意的是，SMARCAD1对MutLα募集的作用完全取决于蛋白质的ATPase活性。根据这些发现，我们建议SMARCAD1通过其染色质重塑活性诱导凋亡，这有助于在受损的染色质上将MutLα募集到MutSα。