1. Shieldin complex promotes DNA end-joining and counters homologous recombination in BRCA1-null cells
- Author
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Dev, Harveer, Chiang, Ting-Wei Will, Lescale, Chloe, De Krijger, Inge, Martin, Alistair G, Pilger, Domenic, Coates, Julia, Sczaniecka-Clift, Matylda, Wei, Wenming, Ostermaier, Matthias, Herzog, Mareike, Lam, Jonathan, Shea, Abigail, Demir, Mukerrem, Wu, Qian, Yang, Fengtang, Fu, Beiyuan, Lai, Zhongwu, Balmus, Gabriel, Belotserkovskaya, Rimma, Serra, Violeta, O'Connor, Mark J, Bruna, Alejandra, Beli, Petra, Pellegrini, Luca, Caldas, Carlos, Deriano, Ludovic, Jacobs, Jacqueline JL, Galanty, Yaron, and Jackson, Stephen P
- Subjects
DNA End-Joining Repair ,Telomere-Binding Proteins ,Bone Neoplasms ,Breast Neoplasms ,Cell Cycle Proteins ,Poly(ADP-ribose) Polymerase Inhibitors ,Mice ,Cell Line, Tumor ,Animals ,Humans ,DNA Breaks, Double-Stranded ,skin and connective tissue diseases ,Ovarian Neoplasms ,Osteosarcoma ,Dose-Response Relationship, Drug ,BRCA1 Protein ,Proteins ,Recombinational DNA Repair ,Xenograft Model Antitumor Assays ,3. Good health ,DNA-Binding Proteins ,HEK293 Cells ,Drug Resistance, Neoplasm ,Multiprotein Complexes ,Mad2 Proteins ,Female ,Cisplatin ,Tumor Suppressor p53-Binding Protein 1 - Abstract
BRCA1 deficiencies cause breast, ovarian, prostate and other cancers, and render tumours hypersensitive to poly(ADP-ribose) polymerase (PARP) inhibitors. To understand the resistance mechanisms, we conducted whole-genome CRISPR-Cas9 synthetic-viability/resistance screens in BRCA1-deficient breast cancer cells treated with PARP inhibitors. We identified two previously uncharacterized proteins, C20orf196 and FAM35A, whose inactivation confers strong PARP-inhibitor resistance. Mechanistically, we show that C20orf196 and FAM35A form a complex, 'Shieldin' (SHLD1/2), with FAM35A interacting with single-stranded DNA through its C-terminal oligonucleotide/oligosaccharide-binding fold region. We establish that Shieldin acts as the downstream effector of 53BP1/RIF1/MAD2L2 to promote DNA double-strand break (DSB) end-joining by restricting DSB resection and to counteract homologous recombination by antagonizing BRCA2/RAD51 loading in BRCA1-deficient cells. Notably, Shieldin inactivation further sensitizes BRCA1-deficient cells to cisplatin, suggesting how defining the SHLD1/2 status of BRCA1-deficient tumours might aid patient stratification and yield new treatment opportunities. Highlighting this potential, we document reduced SHLD1/2 expression in human breast cancers displaying intrinsic or acquired PARP-inhibitor resistance.