Shieldin and CST co-orchestrate DNA polymerase-dependent tailed-end joining reactions independently of 53BP1-governed repair pathway choice

Ashleigh King; Pia I Reichl; Jean S Metson; Robert Parker; Daniella Munro; Catarina Oliveira; Lucia Sommerova; Jordan R Becker; Daniel Biggs; Chris Preece; Benjamin Davies; J Ross Chapman

doi:10.1038/s41594-024-01381-9

Shieldin and CST co-orchestrate DNA polymerase-dependent tailed-end joining reactions independently of 53BP1-governed repair pathway choice

Nat Struct Mol Biol. 2024 Sep 3. doi: 10.1038/s41594-024-01381-9. Online ahead of print.

Authors

Affiliations

¹ Genome Integrity laboratory, Medical Research Council Molecular Haematology Unit, MRC Weatherall Institute of Molecular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
² Centre for Immuno-Oncology, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
³ Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.
⁴ Francis Crick Institute, London, UK.
⁵ Genome Integrity laboratory, Medical Research Council Molecular Haematology Unit, MRC Weatherall Institute of Molecular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, UK. [email protected].

PMID: 39227718
DOI: 10.1038/s41594-024-01381-9

Abstract

Tumor suppressor p53-binding protein 1 (53BP1) regulates DNA end joining in lymphocytes, diversifying immune antigen receptors. This involves nucleosome-bound 53BP1 at DNA double-stranded breaks (DSBs) recruiting Rap1-interacting factor 1 homolog (RIF1) and shieldin, a poorly understood DNA-binding complex. The 53BP1-RIF1-shieldin axis is pathological in BRCA1-mutated cancers, blocking homologous recombination (HR) and driving illegitimate nonhomologous end joining (NHEJ). However, how this axis regulates DNA end joining and HR suppression remains unresolved. We investigated shieldin and its interplay with the Ctc1-Stn1-Ten1 (CST) complex, which was recently implicated downstream of 53BP1. Immunophenotypically, mice lacking shieldin or CST are equivalent, with class-switch recombination coreliant on both complexes. Ataxia-telangiectasia mutated kinase-dependent DNA damage signaling underpins this cooperation, inducing physical interactions between these complexes that reveal shieldin as a DSB-responsive CST adaptor. Furthermore, DNA polymerase ζ functions downstream of shieldin, establishing DNA fill-in synthesis as the physiological function of shieldin-CST. Lastly, we demonstrate that 53BP1 suppresses HR and promotes NHEJ in BRCA1-deficient mice and cells independently of shieldin. These findings showcase the versatility of the 53BP1 pathway, achieved through the collaboration of chromatin-bound 53BP1 complexes and DNA end-processing effector proteins.