XRCC5 and colorectal carcinoma: Some studies quantifying endogenous SUMO modifications have reported that Ku80 can undergo SUMOylation by SUMO2/3 at several sites, including K568.34–36 Recently, Dan Feng et al. reported that SUMO2/3-mediated Ku80 SUMOylation occurs at K307, K568, and K285 and that Ku80-K307 SUMOylation promotes oxaliplatin resistance in CRC cells.20 In our work, we also verified Ku80 K568 SUMOylation and revealed that Ku80 crotonylation antagonizes SUMOylation at the K568 residue in cells under normal growth conditions.