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

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Chiang, Ting-Wei Will 
Lescale, Chloe 
de Krijger, Inge 
Martin, Alistair G 

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.

Description

Keywords

Animals, BRCA1 Protein, Bone Neoplasms, Breast Neoplasms, Cell Cycle Proteins, Cell Line, Tumor, Cisplatin, DNA Breaks, Double-Stranded, DNA End-Joining Repair, DNA-Binding Proteins, Dose-Response Relationship, Drug, Drug Resistance, Neoplasm, Female, HEK293 Cells, Humans, Mad2 Proteins, Mice, Multiprotein Complexes, Osteosarcoma, Ovarian Neoplasms, Poly(ADP-ribose) Polymerase Inhibitors, Proteins, Recombinational DNA Repair, Telomere-Binding Proteins, Tumor Suppressor p53-Binding Protein 1, Xenograft Model Antitumor Assays

Journal Title

Nat Cell Biol

Conference Name

Journal ISSN

1465-7392
1476-4679

Volume Title

20

Publisher

Springer Science and Business Media LLC
Sponsorship
Cancer Research UK (18796)
Cancer Research UK (C6/A21454)
Wellcome Trust (206388/Z/17/Z)
Wellcome Trust (104641/Z/14/Z)
National Institute for Health Research (NIHR) (unknown)
Cambridge University Hospitals NHS Foundation Trust (CUH) (BRC 2012-2017)
Wellcome Trust (206721/Z/17/Z)
Cancer Research UK (unknown)
Cancer Research UK (unknown)
Cancer Research UK (unknown)
Cancer Research UK (unknown)
Cancer Research UK (unknown)
Cancer Research Uk (None)
Cancer Research UK (unknown)
Cancer Research UK (60098573)
Cancer Research UK (unknown)
Cancer Research UK (CB4140)
Cancer Research UK (20544)
Cancer Research Uk (None)
Cambridge University Hospitals NHS Foundation Trust (CUH) (RG51913)
Department of Health (via National Institute for Health Research (NIHR)) (unknown)
Department of Health (via National Institute for Health Research (NIHR)) (NF-SI-0515-10090)
Wellcome Trust (200814/Z/16/Z)
Medical Research Council (MR/N000161/1)
Cancer Research UK (C6946/A24843)
Wellcome Trust (203144/Z/16/Z)