Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
EMBO J. 2010 Nov 3;29(21):3723-32. doi: 10.1038/emboj.2010.238. Epub 2010 Sep 24.
TopBP1 is a checkpoint protein that colocalizes with ATR at sites of DNA replication stress. In this study, we show that TopBP1 also colocalizes with 53BP1 at sites of DNA double-strand breaks (DSBs), but only in the G1-phase of the cell cycle. Recruitment of TopBP1 to sites of DNA replication stress was dependent on BRCT domains 1-2 and 7-8, whereas recruitment to sites of DNA DSBs was dependent on BRCT domains 1-2 and 4-5. The BRCT domains 4-5 interacted with 53BP1 and recruitment of TopBP1 to sites of DNA DSBs in G1 was dependent on 53BP1. As TopBP1 contains a domain important for ATR activation, we examined whether it contributes to the G1 cell cycle checkpoint. By monitoring the entry of irradiated G1 cells into S-phase, we observed a checkpoint defect after siRNA-mediated depletion of TopBP1, 53BP1 or ATM. Thus, TopBP1 may mediate the checkpoint function of 53BP1 in G1.
TopBP1 是一种检查点蛋白，它与 ATR 在 DNA 复制应激部位共定位。在这项研究中，我们表明 TopBP1 也与 53BP1 在 DNA 双链断裂 (DSBs) 部位共定位，但仅在细胞周期的 G1 期。TopBP1 向 DNA 复制应激部位的募集依赖于 BRCT 结构域 1-2 和 7-8，而向 DNA DSB 部位的募集依赖于 BRCT 结构域 1-2 和 4-5。BRCT 结构域 4-5 与 53BP1 相互作用，TopBP1 在 G1 期向 DNA DSB 部位的募集依赖于 53BP1。由于 TopBP1 含有一个对 ATR 激活很重要的结构域，我们研究了它是否有助于 G1 细胞周期检查点。通过监测经照射的 G1 细胞进入 S 期的情况，我们观察到在用 siRNA 耗尽 TopBP1、53BP1 或 ATM 后，出现了检查点缺陷。因此，TopBP1 可能介导了 53BP1 在 G1 期的检查点功能。
