Shakeri Manesh Sara, Sangsuwan Traimate, Pour Khavari Ali, Fotouhi Asal, Emami S Noushin, Haghdoost Siamak
Centre for Radiation Protection Research, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, SE-10691 Stockholm, Sweden.
Mutagenesis. 2017 May 1;32(3):389-396. doi: 10.1093/mutage/gex003.
Our previous results showed that in addition to the immediate interaction of ionising radiation with DNA (direct and indirect effect), low-dose and chronic low-dose rate of irradiation induce endogenous oxidative stress. During oxidative stress, free radicals react with DNA, nucleoside triphosphates (dNTPs), proteins and lipids, and modify their structures. The MYH and MTH1 genes play important roles in preventing mutations induced by 8-hydroxy-guanine, which is an oxidised product of guanine. In this study, we used short-hairpin RNA to permanently knockdown MYH and MTH1 proteins in human lymphoblastoid TK6 cells. Knockdown and wild-type cells were chronically exposed to low dose rates of γ-radiation (between 1.4 and 30 mGy/h). The cells were also subjected to acute doses delivered at a high-dose rate. Growth rate, extracellular 8-hydroxy-2'-deoxyguanosine, clonogenic cell survival and mutant frequencies were analysed in all cell types. A reduced level of cell growth and survival as well as increased mutant frequencies were observed in cells lacking both MYH and MTH1 proteins as compared to cells lacking only MYH and wild-type cells. To sum up, our results suggest that low-dose rates elevate oxidative stress. MTH1 together with MYH plays an important role in protection against mutations induced by modified dNTPs during chronic oxidative stress. In addition, we found no dose-rate effect at the level of mutations in the wild-type TK6 and MYH-KD cells. Our data interestingly indicate a dose-rate threshold for mutation induction in MTH1/MYH double knockdown cells.
我们之前的研究结果表明，除了电离辐射与DNA的即时相互作用（直接和间接效应）外，低剂量和慢性低剂量率照射会诱导内源性氧化应激。在氧化应激期间，自由基与DNA、核苷三磷酸（dNTPs）、蛋白质和脂质发生反应，并改变它们的结构。MYH和MTH1基因在预防由鸟嘌呤的氧化产物8-羟基鸟嘌呤诱导的突变中起重要作用。在本研究中，我们使用短发夹RNA永久敲低人淋巴母细胞TK6细胞中的MYH和MTH1蛋白。敲低细胞和野生型细胞长期暴露于低剂量率的γ辐射（1.4至30 mGy/h之间）。细胞还接受了高剂量率的急性剂量照射。分析了所有细胞类型的生长速率、细胞外8-羟基-2'-脱氧鸟苷、克隆形成细胞存活率和突变频率。与仅缺乏MYH的细胞和野生型细胞相比，同时缺乏MYH和MTH1蛋白的细胞中观察到细胞生长和存活率降低以及突变频率增加。总之，我们的结果表明低剂量率会加剧氧化应激。在慢性氧化应激期间，MTH1与MYH一起在保护细胞免受修饰的dNTPs诱导的突变方面发挥重要作用。此外，我们发现在野生型TK6和MYH敲低细胞的突变水平上没有剂量率效应。我们的数据有趣地表明了MTH1/MYH双敲低细胞中突变诱导的剂量率阈值。
