CEA, INAC, SCIB, UJF & CNRS, LCIB (UMR_E 3 CEA-UJF and FRE 3200), Laboratoire Lésions des Acides Nucléiques, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France.
Mutat Res. 2010 Dec 10;694(1-2):53-9. doi: 10.1016/j.mrfmmm.2010.10.001. Epub 2010 Oct 20.
The well established toxicity of cadmium and cadmium compounds results from their additive effects on several key cellular processes, including DNA repair. Mammalian cells have evolved several biochemical pathways to repair DNA lesions and maintain genomic integrity. By interfering with the homeostasis of redox metals and antioxidant systems, cadmium promotes the development of an intracellular environment that results in oxidative DNA damage which can be mutagenic if unrepaired. Small base lesions are recognised by specialized glycosylases and excised from the DNA molecule. The resulting abasic sites are incised, and the correct sequences restored by DNA polymerases using the opposite strands as template. Bulky lesions are recognised by a different set of proteins and excised from DNA as part of an oligonucleotide. As in base repair, the resulting gaps are filled by DNA polymerases using the opposite strands as template. Thus, these two repair pathways consist in excision of the lesion followed by DNA synthesis. In this study, we analysed in vitro the direct effects of cadmium exposure on the functionality of base and nucleotide DNA repair pathways. To this end, we used recently described dedicated microarrays that allow the parallel monitoring in cell extracts of the repair activities directed against several model base and/or nucleotide lesions. Both base and nucleotide excision/repair pathways are inhibited by CdCl₂, with different sensitivities. The inhibitory effects of cadmium affect mainly the recognition and excision stages of these processes. Furthermore, our data indicate that the repair activities directed against different damaged bases also exhibit distinct sensitivities, and the direct comparison of cadmium effects on the excision of uracile in different sequences even allows us to propose a hierarchy of cadmium sensibility within the glycosylases removing U from DNA. These results indicate that, in our experimental conditions, cadmium is a very potent DNA repair poison.
镉和镉化合物的毒性是众所周知的，这是由于它们对几种关键细胞过程具有加性效应，包括 DNA 修复。哺乳动物细胞已经进化出几种生化途径来修复 DNA 损伤并维持基因组完整性。通过干扰氧化还原金属和抗氧化系统的动态平衡，镉促进了细胞内环境的发展，导致氧化 DNA 损伤，如果不修复，可能会导致突变。小碱基损伤被专门的糖苷酶识别，并从 DNA 分子中切除。由此产生的无碱基位点被内切酶切割，正确的序列由 DNA 聚合酶使用互补链作为模板进行修复。大体积损伤被另一组蛋白质识别并从 DNA 中切除作为寡核苷酸的一部分。与碱基修复一样，产生的缺口由 DNA 聚合酶使用互补链作为模板进行填充。因此，这两种修复途径都包括切除损伤，然后进行 DNA 合成。在这项研究中，我们分析了镉暴露对碱基和核苷酸 DNA 修复途径功能的直接影响。为此，我们使用了最近描述的专用微阵列，允许在细胞提取物中平行监测针对几种模型碱基和/或核苷酸损伤的修复活性。碱基和核苷酸切除/修复途径都被 CdCl₂抑制，敏感性不同。镉的抑制作用主要影响这些过程的识别和切除阶段。此外，我们的数据表明，针对不同受损碱基的修复活性也表现出不同的敏感性，并且直接比较镉对不同序列中尿嘧啶的切除效果甚至使我们能够在从 DNA 中去除 U 的糖苷酶中提出镉敏感性的等级顺序。这些结果表明，在我们的实验条件下，镉是一种非常有效的 DNA 修复毒物。
