title: Impaired 53BP1/RIF1 DSB mediated end-protection stimulates CtIP-dependent end resection and switches the repair to PARP1-dependent end joining in G1.
abstract: End processing at DNA double strand breaks (DSB) is a decisive step in repair pathway selection. Here, we investigated the role of 53BP1/RIF1 in limiting BRCA1/CtIP-mediated end resection to control DSB repair pathway choice. ATM orchestrates this process through 53BP1 phosphorylation to promote RIF1 recruitment. As cells enter S/G2-phase, end resection is activated, which displaces pATM from DSB sites and diminishes 53BP1 phosphorylation and RIF1 recruitment. Consistently, the kinetics of ATM and 53BP1 phosphorylation in S/G2-phase concur. We show that defective 53BP1/RIF1-mediated DSB end-protection in G1-phase stimulates CtIP/MRE11-dependent end-resection, which requires Polo-like kinase 3. This end resection activity in G1 was shown to produce only short tracks of ssDNA overhangs, as evidenced by the findings that in 53BP1 depleted cells, (i) RPA focus intensity was significantly lower in G1 compared to that in S/G2 phase, and (ii) EXO1 knockdown did not alter either number or intensity of RPA foci in G1 but significantly decreased the RPA focus intensity in S/G2 phase. Importantly, we report that the observed DSB end resection in G1 phase inhibits DNA-PK-dependent nonhomologous end joining but is not sufficient to stimulate HR. Instead, it switches the repair to the alternative PARP1-dependent end joining pathway.
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Ali
authors: A
authors: Bakr
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Sabrina
authors: S
authors: Köcher
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Jennifer
authors: J
authors: Volquardsen
authors: Department of Radiotherapy and Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Cordula
authors: C
authors: Petersen
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Kerstin
authors: K
authors: Borgmann
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Ekkehard
authors: E
authors: Dikomey
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors: Kai
authors: K
authors: Rothkamm
authors: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.|Tumor Biology Department, National Cancer Institute, Cairo University, Egypt.
authors: Wael Y
authors: WY
authors: Mansour
mesh_terms: D019313:BRCA1 Protein / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000235:genetics; D004706:Endodeoxyribonucleases; D016193:G1 Phase; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics*; D010766:Phosphorylation; D000071137:Poly (ADP-Ribose) Polymerase-1 / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D034501:Telomere-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D000071857:Tumor Suppressor p53-Binding Protein 1 / Q000235:genetics*; D000097868:Polo-like Kinases
chemical_list: D019313:BRCA1 Protein; D002352:Carrier Proteins; D004277:DNA, Single-Stranded; D004706:Endodeoxyribonucleases; D009687:Nuclear Proteins; D000071137:Poly (ADP-Ribose) Polymerase-1; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering; D034501:Telomere-Binding Proteins; D025521:Tumor Suppressor Proteins; D000071857:Tumor Suppressor p53-Binding Protein 1; C492913:BRCA1 protein, human; C492743:Rif1 protein, human; C498301:TP53BP1 protein, human; C499320:PARP1 protein, human; C486256:PLK3 protein, human; D000097868:Polo-like Kinases; C410741:RBBP8 protein, human
keywords: 53BP1; A-EJ; ATM; RIF1; double strand break ends processing