Laboratory for Experimental Oncology and Radiobiology (LEXOR), Center for Experimental Molecular Medicine, Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands.
DNA Repair (Amst). 2013 Jan 1;12(1):38-45. doi: 10.1016/j.dnarep.2012.10.008. Epub 2012 Dec 11.
In S and G2 phase mammalian cells DNA double strand breaks (DSBs) can potentially be repaired by homologous recombination (HR) or non-homologous end-joining (NHEJ). Results of several studies suggest that these two mechanistically distinct repair pathways can compete for DNA ends. Because HR and NHEJ differ with respect to error susceptibility, generation of chromosome rearrangements, which are potentially carcinogenic products of DSB repair, may depend on the pathway choice. To investigate this hypothesis, the influence of HR and NHEJ inhibition on the frequencies of chromosome aberrations in G2 phase cells was investigated. SW-1573 and RKO cells were treated with mild (41 °C) hyperthermia in order to disable HR and/or NU7441/cisplatin to inactivate NHEJ and frequencies of chromosomal fragments (resulting from unrepaired DSBs) and translocations (products of erroneous DSB rejoining) were studied using premature chromosome condensation (PCC) combined with fluorescence in situ hybridization (FISH). It is shown here that temporary inhibition of HR by hyperthermia results in increased frequency of ionizing-radiation (IR)-induced chromosomal translocations and that this effect is abrogated by NU7441- or cisplatin-mediated inhibition of NHEJ. The results suggest that in the absence of HR, DSB repair is shifted to the error-prone NHEJ pathway resulting in increased frequencies of chromosomal rearrangements. These results might be of consequence for clinical cancer treatment approaches that aim at inhibition of one or more DSB repair pathways.
在 S 和 G2 期哺乳动物细胞中，DNA 双链断裂（DSBs）可以通过同源重组（HR）或非同源末端连接（NHEJ）来修复。多项研究的结果表明，这两种机制不同的修复途径可以竞争 DNA 末端。由于 HR 和 NHEJ 在易出错性、染色体重排的产生方面存在差异，而染色体重排是 DSB 修复的潜在致癌产物，因此可能取决于途径的选择。为了验证这一假说，研究了 HR 和 NHEJ 抑制对 G2 期细胞染色体畸变频率的影响。SW-1573 和 RKO 细胞用温和（41°C）热疗处理以失活 HR，并用 NU7441/顺铂处理以失活 NHEJ，并用早熟染色体凝聚（PCC）结合荧光原位杂交（FISH）研究未修复的 DSBs 产生的染色体片段（源自未修复的 DSBs）和易位（错误的 DSB 重连产物）的频率。结果表明，HR 的短暂抑制导致电离辐射（IR）诱导的染色体易位频率增加，而 NU7441 或顺铂介导的 NHEJ 抑制可消除这种效应。结果表明，在没有 HR 的情况下，DSB 修复转向易错的 NHEJ 途径，导致染色体重排频率增加。这些结果可能对旨在抑制一种或多种 DSB 修复途径的临床癌症治疗方法具有重要意义。
