Ho Erick L Y, Parent Marianne, Satoh Masahiko S
Division of Health and Environmental Research, Laval University Medical Centre (CHUL) and Department of Anatomy and Physiology, Faculty of Medicine, Laval University, Quebec, Quebec, Canada.
J Biol Chem. 2007 Jul 27;282(30):21913-23. doi: 10.1074/jbc.M610651200. Epub 2007 May 31.
DNA repair is known as a defense mechanism against genotoxic insults. However, the most lethal type of DNA damages, double-strand DNA breaks (DSBs), can be produced by DNA repair. We have previously demonstrated that when long patch base excision repair attempts to repair a synthetic substrate containing two uracils, the repair produces DSBs (Vispe, S. and Satoh, M. S. (2000) J. Biol. Chem. 275, 27386-27392 and Vispe, S., Ho, E. L., Yung, T. M., and Satoh, M. S. (2003) J. Biol. Chem. 278, 35279-35285). In this synthetic substrate, the two uracils are located on the opposite DNA strands (separated by an intervening sequence stable at 37 degrees C) and represent a high risk site for DSB formation. It is not clear, however, whether similar high risk sites are also induced in genomic DNA by exposure to DNA damaging agents. Thus, to investigate the mechanisms of DSB formation, we have modified the DSB formation assay developed previously and demonstrated that high risk sites for DSB formation are indeed generated in genomic DNA by exposure of cells to alkylating agents. In fact, genomic DNA containing alkylated base damages, which could represent high risk sites, are converted into DSBs by enzymes present in extracts prepared from cells derived from clinically normal individuals. Furthermore, DSBs are also produced by extracts from cells derived from ataxia-telangiectasia patients who show cancer proneness due to an impaired response to DSBs. These results suggest the presence of a novel link between base damage formation and DSBs and between long patch base excision repair and human diseases that occur due to an impaired response to DSB.
DNA修复被认为是一种抵御基因毒性损伤的防御机制。然而，DNA修复可产生最致命的DNA损伤类型，即双链DNA断裂（DSB）。我们之前已经证明，当长片段碱基切除修复试图修复一个含有两个尿嘧啶的合成底物时，修复过程会产生DSB（维斯佩，S.和佐藤，M.S.（2000年）《生物化学杂志》275卷，27386 - 27392页；维斯佩，S.，何，E.L.，容，T.M.和佐藤，M.S.（2003年）《生物化学杂志》278卷，35279 - 35285页）。在这个合成底物中，两个尿嘧啶位于相反的DNA链上（由在37摄氏度稳定的间隔序列隔开），代表了DSB形成的高风险位点。然而，尚不清楚暴露于DNA损伤剂时，基因组DNA中是否也会诱导出类似的高风险位点。因此，为了研究DSB形成的机制，我们改进了之前开发的DSB形成检测方法，并证明细胞暴露于烷化剂会在基因组DNA中产生DSB形成的高风险位点。事实上，含有烷基化碱基损伤（可能代表高风险位点）的基因组DNA会被来自临床正常个体细胞制备的提取物中的酶转化为DSB。此外，共济失调 - 毛细血管扩张症患者细胞的提取物也会产生DSB，这些患者由于对DSB的反应受损而具有患癌倾向。这些结果表明碱基损伤形成与DSB之间以及长片段碱基切除修复与因对DSB反应受损而发生的人类疾病之间存在新的联系。
