Browsing by Subject "Replication gaps"

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    Replication gaps are a key determinant of PARP inhibitor synthetic lethality with BRCA deficiency
    (Cell Press, 2021) Cong, Ke; Peng, Min; Kousholt, Arne Nedergaard; Lee, Wei Ting C.; Lee, Silviana; Nayak, Sumeet; Krais, John; VanderVere-Carozza, Pamela S.; Pawelczak, Katherine S.; Calvo, Jennifer; Panzarino, Nicholas J.; Turchi, John J.; Johnson, Neil; Jonkers, Jos; Rothenberg, Eli; Cantor, Sharon B.; Medicine, School of Medicine
    Mutations in BRCA1 or BRCA2 (BRCA) is synthetic lethal with poly(ADP-ribose) polymerase inhibitors (PARPi). Lethality is thought to derive from DNA double-stranded breaks (DSBs) necessitating BRCA function in homologous recombination (HR) and/or fork protection (FP). Here, we report instead that toxicity derives from replication gaps. BRCA1- or FANCJ-deficient cells, with common repair defects but distinct PARPi responses, reveal gaps as a distinguishing factor. We further uncouple HR, FP, and fork speed from PARPi response. Instead, gaps characterize BRCA-deficient cells, are diminished upon resistance, restored upon resensitization, and, when exposed, augment PARPi toxicity. Unchallenged BRCA1-deficient cells have elevated poly(ADP-ribose) and chromatin-associated PARP1, but aberrantly low XRCC1 consistent with defects in backup Okazaki fragment processing (OFP). 53BP1 loss resuscitates OFP by restoring XRCC1-LIG3 that suppresses the sensitivity of BRCA1-deficient cells to drugs targeting OFP or generating gaps. We highlight gaps as a determinant of PARPi toxicity changing the paradigm for synthetic lethal interactions.