Chang In-Youb, Kim Soo-Hyun, Cho Hyun-Ju, Lee Do Young, Kim Mi-Hwa, Chung Myung-Hee, You Ho Jin
Research Center for Proteinous Materials, Chosun University, 375 Seusuk-dong, Gwangju 501-759, Korea.
Nucleic Acids Res. 2005 Sep 7;33(16):5073-81. doi: 10.1093/nar/gki829. Print 2005.
The multifunctional mammalian apurinic/apyrimidinic (AP) endonuclease (APE) participates in the repair of AP sites in the cellular DNA as well as participating in the redox regulation of the transcription factor function. The function of APE is considered as the rate-limiting step in DNA base excision repair. Paradoxically, an unbalanced increase in APE protein leads to genetic instability. Therefore, we investigated the mechanisms of genetic instability that are induced by APE. Here, we report that the overexpression of APE protein disrupts the repair of DNA mismatches, which results in microsatellite instability (MSI). We found that expression of APE protein led to the suppression of the repair of DNA mismatches in the normal human fibroblast cells. Western blot analysis revealed that hMSH6 protein was markedly reduced in the APE-expressing cells. Moreover, the addition of purified Mutalpha (MSH2 and MSH6 complex) to the extracts from the APE-expressing cells led to the restoration of mismatch repair (MMR) activity. By performing MMR activity assay and MSI analysis, we found that the co-expression of hMSH6 and APE exhibited the microsatellite stability, whereas the expression of APE alone generated the MSI-high phenotype. The APE-mediated decrease in MMR activity described here demonstrates the presence of a new and highly effective APE-mediated mechanism for MSI.
多功能哺乳动物脱嘌呤/脱嘧啶（AP）内切核酸酶（APE）参与细胞DNA中AP位点的修复，以及转录因子功能的氧化还原调节。APE的功能被认为是DNA碱基切除修复中的限速步骤。矛盾的是，APE蛋白的不平衡增加会导致基因不稳定。因此，我们研究了由APE诱导的基因不稳定机制。在此，我们报告APE蛋白的过表达会破坏DNA错配修复，从而导致微卫星不稳定（MSI）。我们发现APE蛋白的表达导致正常人成纤维细胞中DNA错配修复受到抑制。蛋白质免疫印迹分析显示，在表达APE的细胞中hMSH6蛋白明显减少。此外，向表达APE的细胞提取物中添加纯化的Mutalpha（MSH2和MSH6复合物）可恢复错配修复（MMR）活性。通过进行MMR活性测定和MSI分析，我们发现hMSH6和APE的共表达表现出微卫星稳定性，而单独表达APE则产生MSI高表型。此处描述的APE介导的MMR活性降低证明存在一种新的、高效的APE介导的MSI机制。
