Shieldin complex promotes DNA end-joining and counters homologous recombination in BRCA1-null cells

Harveer Dev (1, 2, 3) , Ting-Wei Will Chiang (1, 2) , Chloé Lescale (4) , Inge de Krijger (5) , Alistair Martin (6) , Domenic Pilger (1, 2) , Julia Coates (1, 2) , Matylda Sczaniecka-Clift (1, 2) , Wenming Wei (4) , Matthias Ostermaier (7) , Mareike Herzog (1, 2) , Jonathan Lam (1, 2) , Abigail Shea (6) , Mukerrem Demir (1, 2) , Qian Wu (2) , Fengtang Yang (8) , Beiyuan Fu (8) , Zhongwu Lai (9) , Gabriel Balmus (10, 2, 8) , Rimma Belotserkovskaya (10, 2) , Violeta Serra (11) , Mark O’connor (12) , Alejandra Bruna (6) , Petra Beli (7) , Luca Pellegrini (13, 2) , Carlos Caldas (6) , Ludovic Deriano (4) , Jacqueline Jacobs (5) , Yaron Galanty (1, 2) , Stephen T. Jackson (1, 2)

1 Wellcome Trust/Cancer Research UK Gurdon Institute
2 Department of Biochemistry [Cambridge]
3 CUH - Cambridge University Hospitals - NHS
4 Intégrité du génome, immunité et cancer - Genome integrity, Immunity and Cancer
5 NKI - Netherlands Cancer Institute
6 CRUK - Cancer Research UK Cambridge Institute [Cambridge, Royaume-Uni]
7 IMB - Institute of Molecular Biology
8 Wellcome Trust Sanger Institute [Hinxton, UK]
9 AstraZeneca US [Waltham, USA]
10 The Wellcome Trust Sanger Institute [Cambridge]
11 VHIO - Vall d'Hebron Institute of Oncology [Barcelone]
12 AstraZeneca [Cambridge, UK]
13 CAM - University of Cambridge [UK]

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.

Keywords: DNA damage and repair; Cancer

Domains: Cancer; Cellular Biology; Genetics; Molecular biology

Harveer Dev, Ting-Wei Will Chiang, Chloé Lescale, Inge de Krijger, Alistair Martin, et al.. Shieldin complex promotes DNA end-joining and counters homologous recombination in BRCA1-null cells. Nature Cell Biology, 2018, 20 (8), pp.954-965. ⟨10.1038/s41556-018-0140-1⟩. ⟨pasteur-02757608⟩