Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center, Heidelberg, Germany.
Radiother Oncol. 2011 Oct;101(1):116-21. doi: 10.1016/j.radonc.2011.05.048. Epub 2011 Jun 23.
Repeated exposure to ionizing radiation (IR) can result in adaptive reactions. While DNA methylation changes in adaption to repeated stress exposure are established for a variety of drugs, their role in fractioned ionizing radiation is largely unknown.
MCF7 breast cancer cells were treated 5 times a week with IR in fractions of 2 Gy, resulting in total doses of 10 and 20 Gy. Cells were harvested 48 and 72 h after the last irradiation, as well as after a recovery period of at least 14 d. To identify genes differentially methylated in irradiated versus non-irradiated cells, we used methyl-CpG immunoprecipitation (MCIp) followed by global methylation profiling on CpG island microarrays.
MCIp profiling revealed methylation changes in several CpG islands 48 h after FIR with 10 and 20 Gy. Cells receiving a total dose of 10 Gy started regrowing after 14 d and exhibited similar radioresistance as mock-treated cells. Differential methylation of the CpG units associated with FOXC1 (p<0.001) and TRAPPC9 (p<0.001) could be confirmed by time-of-flight mass spectrometry (Sequenom).
In summary, these data indicate that regrowth of MCF7 cells after 10 Gy FIR is associated with locus-specific alterations in DNA methylation.
反复暴露于电离辐射（IR）会导致适应性反应。虽然各种药物的应激暴露适应过程中的 DNA 甲基化变化已得到证实，但在分次电离辐射中其作用尚不清楚。
MCF7 乳腺癌细胞每周接受 5 次 IR 照射，每次 2 Gy，总剂量分别为 10 和 20 Gy。末次照射后 48 和 72 h 以及至少 14 d 的恢复期后收获细胞。为了鉴定在照射和非照射细胞中差异甲基化的基因，我们使用甲基化 CpG 免疫沉淀（MCIp），然后在 CpG 岛微阵列上进行全局甲基化谱分析。
MCIp 谱分析显示，10 和 20 Gy FIR 后 48 h 时几个 CpG 岛的甲基化发生了变化。接受 10 Gy 总剂量的细胞在 14 d 后开始重新生长，并表现出与 mock 处理细胞相似的放射抗性。FOXC1（p<0.001）和 TRAPPC9（p<0.001）相关的 CpG 单位的差异甲基化可以通过飞行时间质谱（Sequenom）得到证实。
综上所述，这些数据表明，10 Gy FIR 后 MCF7 细胞的重新生长与 DNA 甲基化的特定部位改变有关。
