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

King, A.; Reichl, P.; Metson, J. S.; Parker, R.; Munro, D.; Oliveira, C.; Becker, J. R.; Biggs, D.; Preece, C.; Davies, B.; Chapman, J. R.

doi:10.1101/2023.12.20.572534

bioRxiv · 10.1101/2023.12.20.572534

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

King, A.·Reichl, P.·Metson, J. S.·Parker, R.·Munro, D.·Oliveira, C.·Becker, J. R.·Biggs, D.·Preece, C.·Davies, B.·Chapman, J. R.

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Abstract

53BP1 regulates DNA end-joining in lymphocytes, diversifying immune antigen receptors. This involves nucleosome-bound 53BP1 at DNA double-stranded breaks (DSBs) recruiting 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 non-homologous end-joining (NHEJ). However, how this axis regulates DNA end-joining and HR suppression remains unresolved. We investigated shieldin and its interplay with CST, a complex recently implicated in 53BP1-dependent activities. Immunophenotypically, mice lacking shieldin or CST are equivalent, with class-switch recombination co-reliant on both complexes. ATM-dependent DNA damage signalling underpins this cooperation, inducing physical interactions between these complexes that reveal shieldin as a DSB-responsive CST adaptor. Furthermore, DNA polymerase {zeta} functions downstream of shieldin, establishing DNA fill-in synthesis as the physiological function of shieldin-CST. Lastly, 53BP1 suppresses HR and promotes NHEJ in BRCA1-deficient mice and cells independently of shieldin. These findings showcase the resilience of the 53BP1 pathway, achieved through the collaboration of chromatin-bound 53BP1 complexes and DNA end-processing effector proteins.

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King, A., Reichl, P., Metson, J. S., Parker, R., Munro, D., Oliveira, C., Becker, J. R., Biggs, D., Preece, C., Davies, B., Chapman, J. R.. 2023-12-21. Shieldin and CST co-orchestrate DNA polymerase-dependent tailed-end joining reactions independently of 53BP1-governed repair pathway choice. https://doi.org/10.1101/2023.12.20.572534

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