The absence of Ku but not defects in classical non-homologous end-joining is required to trigger PARP1-dependent end-joining

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• 作者：Wael Y. Mansour ; K. Borgmann ; C. Petersen ; Ekkehard Dikomey ; Jochen Dahm-Daphi
• 关键词：DSB repair ; Non-homologous end-joining ; Alternative end-joining ; PARP1-dependent end-joining
• 刊名：DNA Repair
• 出版年：December, 2013
• 年：2013
• 卷：12
• 期：12
• 页码：1134-1142
• 全文大小：1871 K

文摘

Classical-non-homologous end-joining (C-NHEJ) is considered the main pathway for repairing DNA double strand breaks (DSB) in mammalian cells. When C-NHEJ is defective, cells may switch DSB repair to an alternative-end-joining, which depends on PARP1 and is more erroneous. This PARP1-EJ is suggested to be active especially in tumor cells contributing to their genomic instability. Here, we define conditions under which cells would switch the repair to PARP1-EJ. Using the end jining repair substrate pEJ, we revealed that PARP1-EJ is solely used when Ku is deficient but not when either DNA-PKcs or Xrcc4 is lacking. In the latter case, DSB repair, however, could be shuttled to PARP1-EJ after additional Ku80 down-regulation, which partly rescued the DSB repair in these mutants. We demonstrate here that PARP-EJ may work on DSB ends at high fidelity manner, as evident from the unchanged efficiency upon blocking end resection by either roscovitin or mirin. Furthermore, we demonstrate for that PARP-EJ is likewise involved in the repair of multiple DSBs (I-PpoI- and IR-induced). Importantly, we identified a chromatin signature associated with the switch to PARP1-EJ which is characterized by a strong enrichment of both PARP1 and LigIII at damaged chromatin. Together, these data indicate that Ku is the main regulator for the hierarchal organization between C-NHEJ and PARP1-EJ.