Department of Oncology, University of Alberta, Alberta, and the Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
J Biol Chem. 2010 Nov 26;285(48):37619-29. doi: 10.1074/jbc.M109.058719. Epub 2010 Sep 17.
XRCC4 plays a crucial role in the nonhomologous end joining (NHEJ) pathway of DNA double-strand break repair acting as a scaffold protein that recruits other NHEJ proteins to double-strand breaks. Phosphorylation of XRCC4 by protein kinase CK2 promotes a high affinity interaction with the forkhead-associated domain of the end-processing enzyme polynucleotide kinase/phosphatase (PNKP). Here we reveal that unphosphorylated XRCC4 also interacts with PNKP through a lower affinity interaction site within the catalytic domain and that this interaction stimulates the turnover of PNKP. Unexpectedly, CK2-phosphorylated XRCC4 inhibited PNKP activity. Moreover, the XRCC4·DNA ligase IV complex also stimulated PNKP enzyme turnover, and this effect was independent of the phosphorylation of XRCC4 at threonine 233. Our results reveal that CK2-mediated phosphorylation of XRCC4 can have different effects on PNKP activity, with implications for the roles of XRCC4 and PNKP in NHEJ.
XRCC4 在 DNA 双链断裂修复的非同源末端连接 (NHEJ) 途径中发挥着至关重要的作用，作为一种支架蛋白，它可以招募其他 NHEJ 蛋白到双链断裂处。蛋白激酶 CK2 对 XRCC4 的磷酸化促进了其与末端加工酶多核苷酸激酶/磷酸酶（PNKP）的叉头相关结构域的高亲和力相互作用。在这里，我们揭示了未磷酸化的 XRCC4 也通过催化结构域内的低亲和力相互作用位点与 PNKP 相互作用，并且这种相互作用刺激了 PNKP 的周转。出乎意料的是，CK2 磷酸化的 XRCC4 抑制了 PNKP 的活性。此外，XRCC4·DNA 连接酶 IV 复合物也刺激了 PNKP 酶的周转，并且这种效应与 XRCC4 丝氨酸 233 的磷酸化无关。我们的结果揭示了 CK2 介导的 XRCC4 磷酸化对 PNKP 活性可能产生不同的影响，这对 XRCC4 和 PNKP 在 NHEJ 中的作用具有重要意义。
