Laboratory of Molecular Genetics, Cancer Research Institute, Vlárska 7, 833 91 Bratislava, Slovak Republic.
Mutagenesis. 2010 Mar;25(2):155-62. doi: 10.1093/mutage/gep056. Epub 2009 Dec 2.
Selenium (Se) belongs to nutrients that are essential for human health. Biological activity of this compound, however, mainly depends on its dose, with a potential of Se to induce detrimental effects at high doses. Although mechanisms lying behind detrimental effects of Se are poorly understood yet, they involve DNA damage induction. Consequently, DNA damage response and repair pathways may play a crucial role in cellular response to Se. Using Saccharomyces cerevisiae we showed that sodium selenite (SeL), an inorganic form of Se, can be toxic and mutagenic in this organism due to its ability to induce DNA double-strand breaks (DSBs). Moreover, we reported that a spectrum of mutations induced by this compound in the stationary phase of growth is mainly represented by 1-4 bp deletions. Consequently, we proposed that SeL acts as an oxidizing agent in yeast producing oxidative damage to DNA. As short deletions could be anticipated to arise as a result of action of non-homologous end-joining (NHEJ) and oxidative damage to DNA is primarily coped with base excision repair (BER), a contribution of these two pathways towards survival, DSB induction, mutation frequency and types of mutations following SeL exposure was examined in present study. First, we show that while NHEJ plays no role in repairing toxic DNA lesions induced by SeL, cells with impairment in BER are sensitized towards this compound. Of BER activities examined, those responsible for processing of 3'-blocking DNA termini seem to be the most crucial for manifestation of the toxic effects of SeL in yeast. Second, an impact of NHEJ and BER on DSB induction after SeL exposure turned to be inappreciable, as no increase in DNA double-strand breakage in NHEJ and BER single or NHEJ BER double mutant upon SeL exposure was observed. Finally, we demonstrate that impairment in both these pathways does not importantly change mutation frequency after SeL exposure and that NHEJ is not responsible for generation of short deletions after SeL treatment, as these were comparably induced in the wild-type and NHEJ-defective cells.
硒（Se）属于对人体健康至关重要的营养素。然而，这种化合物的生物活性主要取决于其剂量，高剂量的硒可能会产生有害影响。尽管硒的有害影响的机制尚未完全了解，但它们涉及 DNA 损伤的诱导。因此，DNA 损伤反应和修复途径可能在细胞对硒的反应中发挥关键作用。我们使用酿酒酵母表明，亚硒酸钠（SeL），一种硒的无机形式，由于其诱导 DNA 双链断裂（DSB）的能力，在该生物体中可能具有毒性和致突变性。此外，我们报道了该化合物在生长静止期诱导的一系列突变主要代表 1-4 bp 缺失。因此，我们提出 SeL 在酵母中作为一种氧化剂，对 DNA 产生氧化损伤。由于短缺失可能是由于非同源末端连接（NHEJ）的作用以及 DNA 的氧化损伤主要通过碱基切除修复（BER）来应对，因此本研究检查了这两种途径对生存、DSB 诱导、突变频率和突变类型的贡献。首先，我们表明，虽然 NHEJ 在修复 SeL 诱导的毒性 DNA 损伤中不起作用，但 BER 受损的细胞对这种化合物敏感。在所检查的 BER 活性中，负责处理 3'-阻塞 DNA 末端的那些似乎对酵母中 SeL 毒性作用的表现最为关键。其次，NHEJ 和 BER 对 SeL 暴露后 DSB 诱导的影响微不足道，因为在 SeL 暴露后，NHEJ 和 BER 单突变体或 NHEJ BER 双突变体中未观察到 DNA 双链断裂增加。最后，我们证明这两种途径的损伤不会重要地改变 SeL 暴露后的突变频率，并且 NHEJ 不会负责 SeL 处理后短缺失的产生，因为在野生型和 NHEJ 缺陷细胞中都可比较地诱导了这些缺失。
