title: Enhanced non-homologous end joining contributes toward synthetic lethality of pathological RAD51C mutants with poly (ADP-ribose) polymerase.
abstract: Poly (ADP-ribose) polymerase 1 (PARP1) inhibitors are actively under clinical trials for the treatment of breast and ovarian cancers that arise due to mutations in BRCA1 and BRCA2. The RAD51 paralog RAD51C has been identified as a breast and ovarian cancer susceptibility gene. The pathological RAD51C mutants that were identified in cancer patients are hypomorphic with partial repair function. However, targeting cancer cells that express hypomorphic mutants of RAD51C is highly challenging. Here, we report that RAD51C-deficient cells can be targeted by a 'synthetic lethal' approach using PARP inhibitor and this sensitivity was attributed to accumulation of cells in the G2/M and chromosomal aberrations. In addition, spontaneous hyperactivation of PARP1 was evident in RAD51C-deficient cells. Interestingly, RAD51C-negative cells exhibited enhanced recruitment of non-homologous end joining (NHEJ) proteins onto chromatin and this accumulation correlated with increased activity of error-prone NHEJ as well as genome instability leading to cell death. Notably, inhibition of DNA-PKcs or depletion of KU70 or Ligase IV rescued this phenotype. Strikingly, stimulation of NHEJ by low dose of ionizing radiation (IR) in the PARP inhibitor-treated RAD51C-deficient cells and cells expressing pathological RAD51C mutants induced enhanced toxicity 'synergistically'. These results demonstrate that cancer cells arising due to hypomorphic mutations in RAD51C can be specifically targeted by a 'synergistic approach' and imply that this strategy can be potentially applied to cancers with hypomorphic mutations in other homologous recombination pathway genes.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India.
authors.forename: Kumar
authors.initials: K
authors.lastname: Somyajit
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India.
authors.forename: Anup
authors.initials: A
authors.lastname: Mishra
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India.
authors.forename: Aida
authors.initials: A
authors.lastname: Jameei
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, Karnataka 560012, India nganesh@biochem.iisc.ernet.in.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Nagaraju
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D002453:Cell Cycle; D049109:Cell Proliferation; D002843:Chromatin / Q000235:genetics; D002869:Chromosome Aberrations; D004249:DNA Damage; D059766:DNA End-Joining Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005455:Fluorescent Antibody Technique; D042822:Genomic Instability; D006367:HeLa Cells; D006801:Humans; D009154:Mutation / Q000235:genetics*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics* / Q000378:metabolism; D011995:Recombination, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D002843:Chromatin; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C448305:RAD51C protein, human; D011065:Poly(ADP-ribose) Polymerases