Work

CST Is Epistatic With Shieldin to Limit DNA Double‐Strand Break End Resection and Promote Repair During Igh Class Switch Recombination

Year: 2025

Type: article

Abstract: ABSTRACT Downstream of 53BP1‐RIF1 lies the Shieldin (SHLD) protein complex, which comprises MAD2L2/REV7, SHLD3, SHLD2, and SHLD1, and the CTC1‐STN1‐TEN1 (CST) complex. During immunoglobulin heavy‐chain ( Igh ) class switch recombination (CSR), 53BP1‐RIF1‐SHLD promotes productive end‐joining by limiting resection of activation‐induced cytidine deaminase (AID)‐generated DNA double‐strand break (DSB) ends. The precise role of the CST complex and its interplay with SHLD during CSR is however elusive. Here, we established AID‐inducible B cell lines deficient for CTC1, SHLD1, or both and analyzed CSR in these cells. We show that stimulated CTC1‐deficient B cells are defective for IgM‐to‐IgA class switching, accumulate Igh chromosome breaks and translocations, and display increased end‐resection and micro‐homology usage at switching sites, demonstrating that CTC1 is essential to suppress alternative end‐joining during CSR. We show that CTC1 and SHLD1 are epistatic in preventing exacerbated DNA end resection and genetic instability during CSR. Moreover, using a complementation approach in Shld1 knockout splenic B cells, we show that a SHLD1 mutant defective in CST binding (SHLD1 ΔLDLP ) is fully proficient for IgM‐to‐IgG1, IgG2b, IgG3, and IgA class switching, thus demonstrating that the SHLD1‐CTC1 interaction through this motif is dispensable for CST and SHLD functions in promoting CSR.

Source: European Journal of Immunology

DOI: 10.1002/eji.202451585