The significance of protein-phosphorylating function of DNA-PK in DNA double-strand break repair: XRCC4 as the genuine target

抄録

DNA-PK (DNA-dependent protein kinase) is considered one of, at least, the most important enzymes in the repair and signal transduction of DNA double-strand breaks (DSBs). Although DNA-PK is known to phosphorylate a number of proteins with supposed function in DNA repair, cell cycle checkpoint and apoptosis in vitro, the true substrate(s) in vivo and the significance of phosphorylation are presently unclear. We demonstrated XRCC4 protein, which is implicated in the DNA double-strand break repair and V(D)J recombination with DNA ligase IV, as the first example of in vivo substrates of DNA-PK. Now we identified three phosphorylation site(s) in vitro, two of which were phosphorylated also in vivo after X-irradiaiton. Furthermore, the analysis of mutant lacking these phosphorylation sites strongly suggested an important role of the phosphorylation in the repair of radiation-induced DSBs and cell proliferation probably via the recruitment of XRCC4 to the site of DSBs.