Department of Gynecology, University Hospital and University of Zurich, Wagistrasse 14, 8952 Schlieren, Switzerland.
Department of Oncology, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK; Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, University of Oxford, Oxford OX3 7DQ, UK.
Mol Cell. 2019 May 2;74(3):571-583.e8. doi: 10.1016/j.molcel.2019.02.014. Epub 2019 Mar 18.
In mitosis, cells inactivate DNA double-strand break (DSB) repair pathways to preserve genome stability. However, some early signaling events still occur, such as recruitment of the scaffold protein MDC1 to phosphorylated histone H2AX at DSBs. Yet, it remains unclear whether these events are important for maintaining genome stability during mitosis. Here, we identify a highly conserved protein-interaction surface in MDC1 that is phosphorylated by CK2 and recognized by the DNA-damage response mediator protein TOPBP1. Disruption of MDC1-TOPBP1 binding causes a specific loss of TOPBP1 recruitment to DSBs in mitotic but not interphase cells, accompanied by mitotic radiosensitivity, increased micronuclei, and chromosomal instability. Mechanistically, we find that TOPBP1 forms filamentous structures capable of bridging MDC1 foci in mitosis, indicating that MDC1-TOPBP1 complexes tether DSBs until repair is reactivated in the following G1 phase. Thus, we reveal an important, hitherto-unnoticed cooperation between MDC1 and TOPBP1 in maintaining genome stability during cell division.
在有丝分裂中，细胞会使 DNA 双链断裂（DSB）修复途径失活，以维持基因组稳定性。然而，仍有一些早期信号事件发生，例如支架蛋白 MDC1 募集到 DSB 处磷酸化的组蛋白 H2AX。然而，这些事件对于维持有丝分裂过程中的基因组稳定性是否重要仍不清楚。在这里，我们鉴定了 MDC1 中一个高度保守的蛋白相互作用表面，该表面可被 CK2 磷酸化，并被 DNA 损伤反应介质蛋白 TOPBP1 识别。破坏 MDC1-TOPBP1 结合会导致 TOPBP1 在有丝分裂而非间期中特异性地丧失对 DSB 的募集，同时伴有有丝分裂辐射敏感性增加、微核增加和染色体不稳定。从机制上讲，我们发现 TOPBP1 形成了丝状结构，能够在有丝分裂中桥接 MDC1 焦点，表明 MDC1-TOPBP1 复合物将 DSB 固定，直到在下一个 G1 期重新激活修复。因此，我们揭示了 MDC1 和 TOPBP1 在细胞分裂过程中维持基因组稳定性的一个重要的、迄今未被注意到的合作。
