Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan, ROC.
Institute of Molecular Medicine, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan, ROC.
Free Radic Biol Med. 2017 Nov;112:12-23. doi: 10.1016/j.freeradbiomed.2017.07.006. Epub 2017 Jul 6.
Mismatch repair (MMR) corrects replicative errors and minimizes DNA damage that occurs frequently in microsatellites. MMR deficiency is manifested as microsatellite instability (MSI), which contributes to hypermutability and cancer pathogenesis. Genomic instability, including MSI and chromosomal instability, appears to be responsible for the carcinogenesis of arsenic and cadmium, common contaminants in our environment. However, few studies have addressed arsenic- or cadmium-induced MSI, especially its potential link with arsenic- or cadmium-generated oxidative stress, due to the lack of quantifiable MSI assays and cost-effective animal models. Here, using a dual-fluorescent reporter, we demonstrate that sub-lethal doses of cadmium or arsenite, but not arsenate, increased the MSI frequency in human colorectal cancer cells. Arsenite- and cadmium-induced MSI occurred concomitantly with increased levels of reactive species and oxidative DNA damage, and with decreased levels of MMR proteins. However, N-acetyl-l-cysteine (NAC) suppressed arsenite- and cadmium-induced MSI and oxidative stress while restoring the levels of MMR proteins in the cells. Similarly, MSI was induced separately by arsenite and cadmium, and suppressed by NAC, in zebrafish in a fluorescinated PCR-based assay with newly-developed microsatellite markers and inter-segmental comparisons. Of five selected antioxidants examined, differential effects were exerted on the MSI induction and cytotoxicity of both arsenite and cadmium. Compared to MMR-proficient cells, MMR-deficient cells were more resistant to arsenic-mediated and cadmium-mediated cytotoxicity. Our findings demonstrate a novel linkage between arsenite-generated and cadmium-generated oxidative stress and MSI induction. Our findings also caution that antioxidants must be individually validated before being used for preventing arsenite- and cadmium-induced MSI that is associated with cancer development.
错配修复（MMR）纠正复制错误，并将微卫星中频繁发生的 DNA 损伤降至最低。MMR 缺陷表现为微卫星不稳定性（MSI），这有助于增加突变率并促进癌症发生。基因组不稳定性，包括 MSI 和染色体不稳定性，似乎是砷和镉致癌的原因，砷和镉是我们环境中的常见污染物。然而，由于缺乏可量化的 MSI 检测方法和具有成本效益的动物模型，很少有研究涉及砷或镉诱导的 MSI，特别是其与砷或镉产生的氧化应激之间的潜在联系。在这里，我们使用双荧光报告基因，证明亚致死剂量的镉或亚砷酸盐而非砷酸盐会增加人结直肠癌细胞中的 MSI 频率。亚砷酸盐和镉诱导的 MSI 伴随着活性氧和氧化 DNA 损伤水平的增加以及 MMR 蛋白水平的降低而发生。然而，N-乙酰-L-半胱氨酸（NAC）抑制了亚砷酸盐和镉诱导的 MSI 和氧化应激，同时恢复了细胞中 MMR 蛋白的水平。同样，在用新开发的微卫星标记物和节段间比较的基于荧光 PCR 的检测方法中，亚砷酸盐和镉分别诱导了斑马鱼中的 MSI，并被 NAC 抑制。在五种被检查的抗氧化剂中，对亚砷酸盐和镉的 MSI 诱导和细胞毒性产生了不同的影响。与 MMR 功能正常的细胞相比，MMR 缺陷型细胞对砷介导的和镉介导的细胞毒性具有更强的抵抗力。我们的研究结果表明，砷酸盐和镉酸盐产生的氧化应激与 MSI 诱导之间存在新的联系。我们的研究结果还警告说，在用于预防与癌症发展相关的砷酸盐和镉酸盐诱导的 MSI 之前，必须单独验证抗氧化剂。
