Requirement for Parp-1 and DNA ligases 1 or 3 but not of Xrcc1 in chromosomal translocation formation by backup end joining

• Published in: Nucleic acids research Vol. 42; no. 10; pp. 6380 - 6392
• Main Authors: Soni, Aashish, Siemann, Maria, Grabos, Martha, Murmann, Tamara, Pantelias, Gabriel E, Iliakis, George
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 02.06.2014
• Subjects: Animals; Cells, Cultured; Cricetinae; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA Ligase ATP; DNA Ligases - physiology; DNA-Binding Proteins - physiology; G2 Phase - genetics; G2 Phase - radiation effects; G2 Phase Cell Cycle Checkpoints; Genome Integrity, Repair and; Humans; Mice; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases - physiology; Poly-ADP-Ribose Binding Proteins; Radiation, Ionizing; Recombinational DNA Repair; Translocation, Genetic; X-ray Repair Cross Complementing Protein 1; Xenopus Proteins
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gku298

In mammalian cells, ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) are repaired in all phases of the cell cycle predominantly by classical, DNA-PK-dependent nonhomologous end joining (D-NHEJ). Homologous recombination repair (HRR) is functional during the S- and G2-phases, when a sister chromatid becomes available. An error-prone, alternative form of end joining, operating as backup (B-NHEJ) functions robustly throughout the cell cycle and particularly in the G2-phase and is thought to backup predominantly D-NHEJ. Parp-1, DNA-ligases 1 (Lig1) and 3 (Lig3), and Xrcc1 are implicated in B-NHEJ. Chromosome and chromatid translocations are manifestations of erroneous DSB repair and are crucial culprits in malignant transformation and IR-induced cell lethality. We analyzed shifts in translocation formation deriving from defects in D-NHEJ or HRR in cells irradiated in the G2-phase and identify B-NHEJ as the main DSB repair pathway backing up both of these defects at the cost of a large increase in translocation formation. Our results identify Parp-1 and Lig1 and 3 as factors involved in translocation formation and show that Xrcc1 reinforces the function of Lig3 in the process without being required for it. Finally, we demonstrate intriguing connections between B-NHEJ and DNA end resection in translocation formation and show that, as for D-NHEJ and HRR, the function of B-NHEJ facilitates the recovery from the G2-checkpoint. These observations advance our understanding of chromosome aberration formation and have implications for the mechanism of action of Parp inhibitors.