Abstract
The DNA-dependent protein kinase (DNA-PK), composed of the KU heterodimer and the large catalytic subunit (DNA-PKcs), is a classical non-homologous end-joining (cNHEJ) factor. Naïve B cells undergo class switch recombination (CSR) to generate antibodies with different isotypes by joining two DNA double-strand breaks at different switching regions via the cNHEJ pathway. DNA-PK and the cNHEJ pathway play important roles in the DNA repair phase of CSR. To initiate cNHEJ, KU binds to DNA ends, and recruits and activates DNA-PK. DNA-PKcs is the best-characterized substrate of DNA-PK, which phosphorylates DNA-PKcs at both the S2056 and T2609 clusters. Loss of T2609 cluster phosphorylation increases radiation sensitivity, suggesting a role of T2609 phosphorylation in DNA repair. Using the DNA-PKcs5A mouse model carrying an alanine substitution at the T2609 cluster, here we show that loss of T2609 phosphorylation of DNA-PKcs does not affect the CSR efficiency. Yet, the CSR junctions recovered from DNA-PKcs5A/5A B cells reveal increased chromosomal translocation, excess end-resection, and preferential usage of micro-homology – all signs of the alternative end-joining pathway. Thus, these results uncover a role of DNA-PKcs T2609 phosphorylation in promoting cNHEJ repair pathway choice during CSR.
Key points Loss of T2069 cluster phosphorylation of DNA-PKcs promotes Alt-EJ-mediated CSR.
Competing Interest Statement
The authors have declared no competing interest.
3) Abbreviations
- Alt-EJ
- alternative end-joining
- cNHEJ
- classical non-homologous end-joining
- CSR
- class switch recombination
- DNA-PK
- DNA-dependent protein kinase
- DSB
- double-strand break
- HTGTS
- High throughput genomic translocation sequencing
- MH
- micro-homology
- SHM
- somatic hypermutation
