Hunt Clayton R, Pandita Raj K, Laszlo Andrei, Higashikubo Ryuji, Agarwal Manjula, Kitamura Tetsuya, Gupta Arun, Rief Nicole, Horikoshi Nobuo, Baskaran Rajeskaran, Lee Ji-Hoon, Löbrich Markus, Paull Tanya T, Roti Roti Joseph L, Pandita Tej K
Department of Radiation Oncology, Washington University School of Medicine, St Louis, Missouri, USA.
Cancer Res. 2007 Apr 1;67(7):3010-7. doi: 10.1158/0008-5472.CAN-06-4328.
All cells have intricately coupled sensing and signaling mechanisms that regulate the cellular outcome following exposure to genotoxic agents such as ionizing radiation (IR). In the IR-induced signaling pathway, specific protein events, such as ataxia-telangiectasia mutated protein (ATM) activation and histone H2AX phosphorylation (gamma-H2AX), are mechanistically well characterized. How these mechanisms can be altered, especially by clinically relevant agents, is not clear. Here we show that hyperthermia, an effective radiosensitizer, can induce several steps associated with IR signaling in cells. Hyperthermia induces gamma-H2AX foci formation similar to foci formed in response to IR exposure, and heat-induced gamma-H2AX foci formation is dependent on ATM but independent of heat shock protein 70 expression. Hyperthermia also enhanced ATM kinase activity and increased cellular ATM autophosphorylation. The hyperthermia-induced increase in ATM phosphorylation was independent of Mre11 function. Similar to IR, hyperthermia also induced MDC1 foci formation; however, it did not induce all of the characteristic signals associated with irradiation because formation of 53BP1 and SMC1 foci was not observed in heated cells but occurred in irradiated cells. Additionally, induction of chromosomal DNA strand breaks was observed in IR-exposed but not in heated cells. These results indicate that hyperthermia activates signaling pathways that overlap with those activated by IR-induced DNA damage. Moreover, prior activation of ATM or other components of the IR-induced signaling pathway by heat may interfere with the normal IR-induced signaling required for chromosomal DNA double-strand break repair, thus resulting in increased cellular radiosensitivity.
所有细胞都具有复杂的传感和信号传导机制，这些机制在细胞暴露于诸如电离辐射（IR）等基因毒性剂后调节细胞结果。在IR诱导的信号通路中，特定的蛋白质事件，如共济失调毛细血管扩张突变蛋白（ATM）激活和组蛋白H2AX磷酸化（γ-H2AX），在机制上已得到充分表征。目前尚不清楚这些机制如何被改变，尤其是被临床相关药物改变。在此我们表明，热疗作为一种有效的放射增敏剂，可在细胞中诱导与IR信号传导相关的多个步骤。热疗诱导的γ-H2AX焦点形成类似于对IR暴露作出反应而形成的焦点，并且热诱导的γ-H2AX焦点形成依赖于ATM，但与热休克蛋白70的表达无关。热疗还增强了ATM激酶活性并增加了细胞ATM的自磷酸化。热疗诱导的ATM磷酸化增加与Mre11功能无关。与IR相似，热疗也诱导了MDC1焦点形成；然而，它并未诱导与辐射相关的所有特征性信号，因为在受热细胞中未观察到53BP1和SMC1焦点的形成，而在受辐照细胞中则会出现。此外，在IR暴露的细胞中观察到了染色体DNA链断裂的诱导，但在受热细胞中未观察到。这些结果表明，热疗激活的信号通路与IR诱导的DNA损伤激活的信号通路重叠。此外，热疗预先激活ATM或IR诱导信号通路的其他成分可能会干扰染色体DNA双链断裂修复所需的正常IR诱导信号，从而导致细胞放射敏感性增加。
