title: The absence of Ku but not defects in classical non-homologous end-joining is required to trigger PARP1-dependent end-joining.
abstract: 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.
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, Medical Center, Hamburg 20246, Germany; Department of Tumor Biology, National Cancer Institute, Cairo University, Cairo, Egypt. Electronic address: wmansour@uke.uni-hamburg.de.
authors.forename: Wael Y
authors.initials: WY
authors.lastname: Mansour
authors.forename: K
authors.initials: K
authors.lastname: Borgmann
authors.forename: C
authors.initials: C
authors.lastname: Petersen
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Dikomey
authors.forename: Jochen
authors.initials: J
authors.lastname: Dahm-Daphi
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear / Q000276:immunology / Q000378:metabolism*; D016466:CHO Cells; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D003412:Cricetulus; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D004268:DNA-Binding Proteins / Q000276:immunology / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D000072200:Ku Autoantigen; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D011744:Pyrimidinones / Q000494:pharmacology; D000077546:Roscovitine; D013871:Thiones / Q000494:pharmacology
chemical_list: C526365:6-(4-hydroxyphenyl)-2-thioxo-2,3-dihydro-4(1H)-pyrimidinone; D034961:Antigens, Nuclear; D002843:Chromatin; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011687:Purines; D011744:Pyrimidinones; D013871:Thiones; C101467:XRCC4 protein, human; D000077546:Roscovitine; D011065:Poly(ADP-ribose) Polymerases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen
keywords: Alternative end-joining; DSB repair; Non-homologous end-joining; PARP1-dependent end-joining