Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses
Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses
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DOI：
10.1073/pnas.0830918100
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发表时间：
2003-04-29
影响因子：
11.1
通讯作者：
Löbrich, M
中科院分区：
文献类型：
--
作者：
Rothkamm, K;Löbrich, M
DNA双链断裂（DSB）是电离辐射引起癌症和遗传性疾病的最重要的生物学损伤。然而，没有关于生理相关辐射剂量后DSB的诱导和处理的信息。许多用于测量DSB修复的方法无意中引入了这种形式的损伤作为方法的一部分，因此其灵敏度有限。在这里，我们提出的证据表明，病灶的γ-H2 AX（磷酸化组蛋白），通过免疫荧光检测，是定量相同的DSB，并能够量化个别DSB的修复。这一发现允许在辐射剂量低至1 mGy后研究DSB修复，这比现有方法提高了几个数量级。令人惊讶的是，由非常低的辐射剂量（约1 mGy）在非分裂原代人成纤维细胞培养物中诱导的DSB在许多天内保持未修复，这与在较高剂量下观察到的有效DSB修复形成强烈对比。然而，DSB在辐照培养物中的水平降低到未辐照的细胞培养物，如果细胞被允许在辐照后增殖，我们提出的证据表明，这种影响可能是由消除携带未修复的DSB的细胞引起的。目前的风险评估模型假设细胞反应在低剂量和高剂量下同样有效，并提供了采用γ-H2 AX病灶形成作为人类暴露于低剂量电离辐射的直接生物标志物的机会。
DNA double-strand breaks (DSBs) are generally accepted to be the most biologically significant lesion by which ionizing radiation causes cancer and hereditary disease. However, no information on the induction and processing of DSBs after physiologically relevant radiation doses is available. Many of the methods used to measure DSB repair inadvertently introduce this form of damage as part of the methodology, and hence are limited in their sensitivity. Here we present evidence that foci of gamma-H2AX (a phosphorylated histone), detected by immunofluorescence, are quantitatively the same as DSBs and are capable of quantifying the repair of individual DSBs. This finding allows the investigation of DSB repair after radiation doses as low as 1 mGy, an improvement by several orders of magnitude over current methods. Surprisingly, DSBs induced in cultures of nondividing primary human fibroblasts by very low radiation doses (approximate to1 mGy) remain unrepaired for many days, in strong contrast to efficient DSB repair that is observed at higher doses. However, the level of DSBs in irradiated cultures decreases to that of unirradiated cell cultures if the cells are allowed to proliferate after irradiation, and we present evidence that this effect may be caused by an elimination of the cells carrying unrepaired DSBs. The results presented are in contrast to current models of risk assessment that assume that cellular responses are equally efficient at low and high doses, and provide the opportunity to employ gamma-H2AX foci formation as a direct biomarker for human exposure to low quantities of ionizing radiation.