Watrin Erwan, Peters Jan-Michael
Research Institute of Molecular Pathology (IMP), Vienna, Austria.
EMBO J. 2009 Sep 2;28(17):2625-35. doi: 10.1038/emboj.2009.202. Epub 2009 Jul 23.
Cohesin complexes mediate sister chromatid cohesion. Cohesin also becomes enriched at DNA double-strand break sites and facilitates recombinational DNA repair. Here, we report that cohesin is essential for the DNA damage-induced G2/M checkpoint. In contrast to cohesin's role in DNA repair, the checkpoint function of cohesin is independent of its ability to mediate cohesion. After RNAi-mediated depletion of cohesin, cells fail to properly activate the checkpoint kinase Chk2 and have defects in recruiting the mediator protein 53BP1 to DNA damage sites. Earlier work has shown that phosphorylation of the cohesin subunits Smc1 and Smc3 is required for the intra-S checkpoint, but Smc1/Smc3 are also subunits of a distinct recombination complex, RC-1. It was, therefore, unknown whether Smc1/Smc3 function in the intra-S checkpoint as part of cohesin. We show that Smc1/Smc3 are phosphorylated as part of cohesin and that cohesin is required for the intra-S checkpoint. We propose that accumulation of cohesin at DNA break sites is not only needed to mediate DNA repair, but also facilitates the recruitment of checkpoint proteins, which activate the intra-S and G2/M checkpoints.
黏连蛋白复合体介导姐妹染色单体黏连。黏连蛋白在DNA双链断裂位点也会富集，并促进重组性DNA修复。在此，我们报告黏连蛋白对于DNA损伤诱导的G2/M期检验点至关重要。与黏连蛋白在DNA修复中的作用相反，其检验点功能与其介导黏连的能力无关。在通过RNA干扰介导耗尽黏连蛋白后，细胞无法正常激活检验点激酶Chk2，并且在将介质蛋白53BP1募集到DNA损伤位点方面存在缺陷。早期研究表明，黏连蛋白亚基Smc1和Smc3的磷酸化对于S期内检验点是必需的，但Smc1/Smc3也是一种不同的重组复合体RC-1的亚基。因此，尚不清楚Smc1/Smc3在S期内检验点中是否作为黏连蛋白的一部分发挥作用。我们表明，Smc1/Smc3作为黏连蛋白的一部分被磷酸化，并且黏连蛋白对于S期内检验点是必需的。我们提出，黏连蛋白在DNA断裂位点的积累不仅是介导DNA修复所必需的，而且还促进了检验点蛋白的募集，从而激活S期内检验点和G2/M期检验点。
