title: Poly(ADP-ribose) polymerase is hyperactivated in homologous recombination-defective cells.
abstract: Poly(ADP-ribose) (PAR) polymerase 1 (PARP1) is activated by DNA single-strand breaks (SSB) or at stalled replication forks to facilitate DNA repair. Inhibitors of PARP efficiently kill breast, ovarian, or prostate tumors in patients carrying hereditary mutations in the homologous recombination (HR) genes BRCA1 or BRCA2 through synthetic lethality. Here, we surprisingly show that PARP1 is hyperactivated in replicating BRCA2-defective cells. PARP1 hyperactivation is explained by the defect in HR as shRNA depletion of RAD54, RAD52, BLM, WRN, and XRCC3 proteins, which we here show are all essential for efficient HR and also caused PARP hyperactivation and correlated with an increased sensitivity to PARP inhibitors. BRCA2-defective cells were not found to have increased levels of SSBs, and PAR polymers formed in HR-defective cells do not colocalize to replication protein A or gammaH2AX, excluding the possibility that PARP hyperactivity is due to increased SSB repair or PARP induced at damaged replication forks. Resistance to PARP inhibitors can occur through genetic reversion in the BRCA2 gene. Here, we report that PARP inhibitor-resistant BRCA2-mutant cells revert back to normal levels of PARP activity. We speculate that the reason for the sensitivity of HR-defective cells to PARP inhibitors is related to the hyperactivated PARP1 in these cells. Furthermore, the presence of PAR polymers can be used to identify HR-defective cells that are sensitive to PARP inhibitors, which may be potential biomarkers.
authors.affiliation: Cancer Research UK-Medical Research Council, Gray Institute for Radiation Oncology and Biology, University of Oxford, Oxford, United Kingdom.
authors.forename: Ponnari
authors.initials: P
authors.lastname: Gottipati
authors.forename: Barbara
authors.initials: B
authors.lastname: Vischioni
authors.forename: Niklas
authors.initials: N
authors.lastname: Schultz
authors.forename: Joyce
authors.initials: J
authors.lastname: Solomons
authors.forename: Helen E
authors.initials: HE
authors.lastname: Bryant
authors.forename: Tatjana
authors.initials: T
authors.lastname: Djureinovic
authors.forename: Natalia
authors.initials: N
authors.lastname: Issaeva
authors.forename: Kate
authors.initials: K
authors.lastname: Sleeth
authors.forename: Ricky A
authors.initials: RA
authors.lastname: Sharma
authors.forename: Thomas
authors.initials: T
authors.lastname: Helleday
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D006224:Cricetinae; D004249:DNA Damage; D004261:DNA Replication; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D055786:Gene Knockout Techniques; D019398:Genes, BRCA1; D024522:Genes, BRCA2; D006801:Humans; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology* / Q000235:genetics*; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D011995:Recombination, Genetic
chemical_list: D004273:DNA, Neoplasm; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases