title: PARP-mediated repair, homologous recombination, and back-up non-homologous end joining-like repair of single-strand nicks.
abstract: Double-strand breaks (DSBs) in chromosomal DNA can induce both homologous recombination (HR) and non-homologous end-joining (NHEJ). Recently we showed that single-strand nicks induce HR with a significant reduction in toxicity and mutagenic effects associated with NHEJ. To further investigate the differences and similarities of DSB- and nick-induced repair, we used an integrated reporter system in human cells to measure HR and NHEJ produced by the homing endonuclease I-AniI and a designed 'nickase' variant that nicks the same target site, focusing on the PARP and HR repair pathways. PARP inhibitors, which block single-strand break repair, increased the rate of nick-induced HR up to 1.7-fold but did not affect DSB-induced HR or mutNHEJ. Additionally, expression of the PALB2 WD40 domain in trans acted as a dominant-negative inhibitor of both DSB- and nick-induced HR, sensitized cells to PARP inhibition, and revealed an alternative mutagenic repair pathway for nicks. Thus, while both DSB- and nick-induced HR use a common pathway, their substrates are differentially processed by cellular factors. These results also suggest that the synthetic lethality of PARP and BRCA may be due to repair of nicks through an error prone, NHEJ-like mechanism that is active when both PARP and HR pathways are blocked.
authors.affiliation: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N., Seattle, WA 98109, USA. mm4184@columbia.edu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Metzger
authors.forename: Barry L
authors.initials: BL
authors.lastname: Stoddard
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Monnat
mesh_terms: D024682:BRCA2 Protein / Q000235:genetics / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D053904:DNA Breaks, Single-Stranded; D059766:DNA End-Joining Repair; D015253:Deoxyribonucleases, Type I Site-Specific / Q000235:genetics / Q000378:metabolism; D000076164:Fanconi Anemia Complementation Group N Protein; D057809:HEK293 Cells; D006801:Humans; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D059767:Recombinational DNA Repair; D025521:Tumor Suppressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D024682:BRCA2 Protein; D000076164:Fanconi Anemia Complementation Group N Protein; D009687:Nuclear Proteins; C512790:PALB2 protein, human; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D025521:Tumor Suppressor Proteins; D011065:Poly(ADP-ribose) Polymerases; D015253:Deoxyribonucleases, Type I Site-Specific