CK2 phosphorylation of XRCC1 facilitates dissociation from DNA and single-strand break formation during base excision repair

CK2 phosphorylates the scaffold protein XRCC1, which is required for efficient DNA single-strand break (SSB) repair. Here, we express an XRCC1 protein (XRCC1ckm) that cannot be phosphorylated by CK2 in XRCC1 mutated EM9 cells and show that the role of this post-translational modification gives distinct phenotypes in SSB repair and base excision repair (BER). Interestingly, we find that fewer SSBs are formed during BER after treatment with the alkylating agent dimethyl sulfate (DMS) in EM9 cells expressing XRCC1ckm (CKM cells) or following inhibition with the CK2 inhibitor 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole (DMAT). We also show that XRCC1ckm protein has a higher affinity for DNA than wild type XRCC1 protein and resides in an immobile fraction on DNA, in particular after damage. We propose a model whereby the increased affinity for DNA sequesters XRCC1ckm and the repair enzymes associated with it, at the repair site, which retards kinetics of BER. In conclusion, our results indicate that phosphorylation of XRCC1 by CK2 facilitates the BER incision step, likely by promoting dissociation from DNA.

► CK2 phosphorylates XRCC1, which is a key protein in both BER and repair of direct DNA single-strand breaks (SSB repair).
► We investigate CK2 phosphorylation of XRCC1 in BER by monitoring the repair of alkylation damages in the DNA.
► Our results indicate that CK2-phosphorylations of XRCC1 facilitate the BER incision step, likely by promoting dissociation from DNA.