Uncoupling the DSB End-Protecting and CSR-Promoting Functions of 53BP1

Fernandez, Keith Conrad; Chaudhuri, Jayanta

doi:10.1016/j.celrep.2019.07.076

Cited by 1 publication

(1 citation statement)

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“…On the other hand, in 53bp1 −/− cells the requirement for CtIP to exclude 53BP1/Rif1 becomes minimal as resection suppression by Rif1 has been canceled out. Consistent with the minimal effect of resection on CSR efficiency we observed in 53bp1 −/− cells, a recent report revealed that resection can be largely uncoupled with CSR ( Sundaravinayagam et al, 2019 ) and suggested that higher order chromatin structure by 53BP1 oligomerization is essential to enforce the 3-D architecture of IgH locus for efficient class switching ( Dong et al, 2015 ; Fernandez and Chaudhuri, 2019 ). In this context, resection inhibition in 53bp1 −/− cells by either Mre11/CtIP silencing or ATM ablation did not change A-EJ efficiency, as the requisite IgH loops for efficient CSR has already greatly collapsed ( Wuerffel et al, 2007 ; Feldman et al, 2017 ; Zhang et al, 2019 ) ( Cortizas et al, 2013 ).…”

Section: Discussionsupporting

confidence: 89%

Multiple DSB Resection Activities Redundantly Promote Alternative End Joining-Mediated Class Switch Recombination

Sun

Bai

et al. 2021

Front. Cell Dev. Biol.

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Alternative end joining (A-EJ) catalyzes substantial level of antibody class switch recombination (CSR) in B cells deficient for classical non-homologous end joining, featuring increased switch (S) region DSB resection and junctional microhomology (MH). While resection has been suggested to initiate A-EJ in model DSB repair systems using engineered endonucleases, the contribution of resection factors to A-EJ-mediated CSR remains unclear. In this study, we systematically dissected the requirement for individual DSB resection factors in A-EJ-mediated class switching with a cell-based assay system and high-throughput sequencing. We show that while CtIP and Mre11 both are mildly required for CSR in WT cells, they play more critical roles in mediating A-EJ CSR, which depend on the exonuclease activity of Mre11. While DNA2 and the helicase/HRDC domain of BLM are required for A-EJ by mediating long S region DSB resection, in contrast, Exo1’s resection-related function does not play any obvious roles for class switching in either c-NHEJ or A-EJ cells, or mediated in an AID-independent manner by joining of Cas9 breaks. Furthermore, ATM and its kinase activity functions at least in part independent of CtIP/Mre11 to mediate A-EJ switching in Lig4-deficient cells. In stark contrast to Lig4 deficiency, 53BP1-deficient cells do not depend on ATM/Mre11/CtIP for residual joining. We discuss the roles for each resection factor in A-EJ-mediated CSR and suggest that the extent of requirements for resection is context dependent.

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