Academy of Integrated Science, Virginia Polytechnic Institute & State University, Blacksburg, VA 24601.
Cell & Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109.
Mol Biol Cell. 2022 Sep 1;33(10):br16. doi: 10.1091/mbc.E22-03-0085. Epub 2022 Jun 29.
During mitosis, unattached kinetochores in a dividing cell activate the spindle assembly checkpoint (SAC) and delay anaphase onset by generating the anaphase-inhibitory mitotic checkpoint complex (MCC). These kinetochores generate the MCC by recruiting its constituent proteins, including BubR1. In principle, BubR1 recruitment to signaling kinetochores should increase its local concentration and promote MCC formation. However, in human cells BubR1 is mainly thought to sensitize the SAC to silencing. Whether BubR1 localization to signaling kinetochores by itself enhances SAC signaling remains unknown. Therefore, we used ectopic SAC activation (eSAC) systems to isolate two molecules that recruit BubR1 to the kinetochore, the checkpoint protein Bub1 and the KI and MELT motifs in the kinetochore protein KNL1, and observed their contribution to eSAC signaling. Our quantitative analyses and mathematical modeling show that Bub1-mediated BubR1 recruitment to the human kinetochore promotes SAC signaling and highlight BubR1's dual role of strengthening the SAC directly and silencing it indirectly.
在有丝分裂过程中，分裂细胞中未附着的动粒会激活纺锤体组装检查点（SAC），并通过产生有丝分裂检查点复合物（MCC）来延迟后期起始。这些动粒通过招募其组成蛋白，包括 BubR1，来产生 MCC。原则上，BubR1 向信号动粒的募集应该增加其局部浓度并促进 MCC 的形成。然而，在人类细胞中，BubR1 主要被认为能使 SAC 对沉默敏感。BubR1 自身定位到信号动粒是否能增强 SAC 信号仍然未知。因此，我们使用异位 SAC 激活（eSAC）系统来分离两种将 BubR1 招募到动粒的分子，即检查点蛋白 Bub1 和动粒蛋白 KNL1 中的 KI 和 MELT 基序，并观察它们对 eSAC 信号的贡献。我们的定量分析和数学建模表明，Bub1 介导的 BubR1 向人动粒的募集促进了 SAC 信号，并突出了 BubR1 直接增强 SAC 和间接使其沉默的双重作用。
