Department of Food Chemistry and Toxicology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
Institute of Medical Radiation Biology, Medical School, University of Duisburg-Essen, 45122 Essen, Germany.
Int J Mol Sci. 2023 Jun 20;24(12):10392. doi: 10.3390/ijms241210392.
Manganese is an essential trace element; nevertheless, on conditions of overload, it becomes toxic, with neurotoxicity being the main concern. Chromate is a well-known human carcinogen. The underlying mechanisms seem to be oxidative stress as well as direct DNA damage in the case of chromate, but also interactions with DNA repair systems in both cases. However, the impact of manganese and chromate on DNA double-strand break (DSB) repair pathways is largely unknown. In the present study, we examined the induction of DSB as well as the effect on specific DNA DSB repair mechanisms, namely homologous recombination (HR), non-homologous end joining (NHEJ), single strand annealing (SSA), and microhomology-mediated end joining (MMEJ). We applied DSB repair pathway-specific reporter cell lines, pulsed field gel electrophoresis as well as gene expression analysis, and investigated the binding of specific DNA repair proteins via immunoflourescence. While manganese did not seem to induce DNA DSB and had no impact on NHEJ and MMEJ, HR and SSA were inhibited. In the case of chromate, the induction of DSB was further supported. Regarding DSB repair, no inhibition was seen in the case of NHEJ and SSA, but HR was diminished and MMEJ was activated in a pronounced manner. The results indicate a specific inhibition of error-free HR by manganese and chromate, with a shift towards error-prone DSB repair mechanisms in both cases. These observations suggest the induction of genomic instability and may explain the microsatellite instability involved in chromate-induced carcinogenicity.
锰是一种必需的微量元素；然而，在超载的情况下，它会变得有毒，其神经毒性是主要关注点。铬酸盐是一种已知的人类致癌物。其潜在机制似乎是氧化应激以及铬酸盐直接导致的 DNA 损伤，但在这两种情况下也与 DNA 修复系统相互作用。然而，锰和铬酸盐对 DNA 双链断裂 (DSB) 修复途径的影响在很大程度上尚不清楚。在本研究中，我们检查了 DSB 的诱导以及对特定 DNA DSB 修复机制的影响，即同源重组 (HR)、非同源末端连接 (NHEJ)、单链退火 (SSA) 和微同源介导的末端连接 (MMEJ)。我们应用了 DSB 修复途径特异性报告细胞系、脉冲场凝胶电泳以及基因表达分析，并通过免疫荧光法研究了特定 DNA 修复蛋白的结合。虽然锰似乎不会诱导 DNA DSB，并且对 NHEJ 和 MMEJ 没有影响，但 HR 和 SSA 受到抑制。对于铬酸盐，进一步支持了 DSB 的诱导。关于 DSB 修复，NHEJ 和 SSA 没有观察到抑制，但 HR 减少，MMEJ 明显激活。结果表明，锰和铬酸盐特异性抑制无差错的 HR，两种情况下均偏向易错的 DSB 修复机制。这些观察结果表明诱导基因组不稳定性，并可能解释铬酸盐诱导致癌性中涉及的微卫星不稳定性。
