Telomere shortening alters the kinetics of the DNA damage response after ionizing radiation in human cells.
Telomere shortening alters the kinetics of the DNA damage response after ionizing radiation in human cells.
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DOI：
10.1158/1940-6207.capr-11-0069
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发表时间：
2011-12
期刊：
影响因子：
--
通讯作者：
Dome JS
中科院分区：
文献类型：
--
作者：
Drissi R;Wu J;Hu Y;Bockhold C;Dome JS
对端粒酶缺陷小鼠和人类细胞系的研究表明，端粒缩短增强了对电离辐射（IR）的敏感性。这一观察结果的分子基础尚不清楚。为了更好地了解端粒缩短和辐射敏感性之间的联系，我们评估了正常人成纤维细胞中短端粒和长端粒的DNA损伤反应途径的组成部分。与较长端粒的早代细胞相比，端粒较短的晚代细胞对IR的敏感性增强。与早代细胞相比，晚代细胞IR前磷酸化H2AX蛋白（γH2AX）的基线水平较高，但IR后磷酸化H2AX的峰值水平降低，γH2AX灶的出现和消失均延迟，提示DNA修复延迟。与H2AX的情况相反，ATM和p53磷酸化动力学在早期和晚期传代细胞中相似，但染色质结合的ATM靶点SMC 1和NBS1的磷酸化在晚期传代细胞中延迟。由于与短端粒相关的受损磷酸化仅限于染色质结合的ATM靶，因此评估了染色质结构。来自具有短端粒的细胞的DNA对微球菌核酸酶的消化更具抗性，这表明染色质致密。此外，短端粒的细胞显示出与异染色质一致的组蛋白乙酰化和甲基化特征。总之，我们的数据表明，短端粒诱导染色质结构的变化，限制激活的ATM的访问其下游目标的染色质上的模型，从而提供了一个潜在的解释与端粒缩短所看到的辐射敏感性增加。
Studies of telomerase-deficient mice and human cell lines have demonstrated that telomere shortening enhances sensitivity to ionizing radiation (IR). The molecular basis for this observation remains unclear. To better understand the connection between telomere shortening and radiation sensitivity, we evaluated components of the DNA damage response pathway in normal human fibroblasts with short and long telomeres. Late-passage cells with short telomeres showed enhanced sensitivity to IR compared to early-passage cells with longer telomeres. Compared to early-passage cells, late-passage cells had a higher baseline level of phosphorylated H2AX protein (γH2AX) before IR, but diminished peak levels of H2AX phosphorylation after IR. Both the appearance and disappearance of γH2AX foci were delayed in late-passage cells, indicative of delayed DNA repair. In contrast to the situation with H2AX, ATM and p53 phosphorylation kinetics were similar in early and late-passage cells, but phosphorylation of the chromatin-bound ATM targets SMC1 and NBS1 was delayed in late-passage cells. Because impaired phosphorylation associated with short telomeres was restricted to chromatin-bound ATM targets, chromatin structure was assessed. DNA from cells with short telomeres was more resistant to digestion with micrococcal nuclease, indicative of compacted chromatin. Moreover, cells with short telomeres showed histone acetylation and methylation profiles consistent with heterochromatin. Together our data suggest a model in which short telomeres induce chromatin structure changes that limit access of activated ATM to its downstream targets on the chromatin, thereby providing a potential explanation for the increased radiation sensitivity seen with telomere shortening.