Roles of Bub1 and BubR1 in human checkpoint signalling

遗传物质准确而平等地分离到子代细胞需要姐妹染色单体从相反的纺锤体极连接到动态的纺锤体微管。这是通过着丝粒发生的，它不仅提供了微管和染色体之间的机械连接，而且还作为监测系统的平台，称为纺锤体组装检查点(SAC)，该系统确保姐妹染色单体在所有染色体正确双向之前不会分离。该检查点的组成包括Mad1、Mad2、Bub3蛋白和Bub1、BubR1、Mps1(Mph1)和Aurora B蛋白。当单个动点没有与纺锤体微管结合或不处于张力状态时，SAC组件就会结合动点并启动信号传递。最近发现，Mps1蛋白激酶对动粒蛋白KNL1中多个重复基序(熔融)的磷酸化，为Bub3-Bub1复合体创建了一个结合位点。Mps1进一步磷酸化Bub1的中心非催化区，促进Mad1-MAD2复合体与Bub1的结合。MAD1-MAD2复合体一旦与动点结合，就会催化可溶性MAD2(O-MAD2)转化为C-MAD2，从而与CDC20和Bub3-BubR1结合，形成有丝分裂检查点复合体(MCC)，这是一种重要的E3泛素连接酶，是后期促进复合体(APC/C)的有效抑制因子。当检查点被满足时，主轴检查点信号被静音，并且CDC20-APC/C被激活。这触发了Securin和Cyclin的多泛素化，从而分别允许姐妹染色单体凝聚力和有丝分裂进程的溶解。在人类细胞中，酵母中不存在的Rod-Zw10-Zwilch(RZZ)复合体为Mad1-MAD2复合体在动点提供了第二个结合位点。这个PHD项目旨在阐明在正常和转化的人类细胞中，Bub1和BubR1激酶在检查点信号传递中的作用。

The accurate and equal segregation of genetic material to daughter cells requires attachment of sister chromatids to dynamic spindle microtubules from opposite spindle poles. This occurs through the kinetochore, which not only provides the mechanical linkage between microtubules and chromosomes, but which also acts as the platform for a surveillance system, known as the spindle assembly checkpoint (SAC), that ensures sister chromatids do not separate until all chromosomes are correctly bi-oriented. Components of the checkpoint include the Mad1, Mad2, Bub3 proteins and the Bub1, BubR1, Mps1(Mph1) and Aurora B kinases. SAC components bind kinetochores and initiate signalling when individual kinetochores are either not bound to spindle microtubules or not under tension. It has recently been found that phosphorylation of multiple repetitive motifs (MELT) in the kinetochore protein KNL1 by the Mps1 protein kinase, creates a binding site for the Bub3-Bub1 complex. Further phosphorylation of the central non-catalytic region of Bub1 by Mps1 promotes the association of Mad1-Mad2 complex to Bub1. The Mad1-Mad2 complex, once bound to kinetochores, catalyses the conversion of soluble Mad2 (O-Mad2) into a form (C-Mad2), which binds both Cdc20 and Bub3-BubR1, to form the mitotic checkpoint complex (MCC), a potent inhibitor of the anaphase promoting complex (APC/C), an essential E3 ubiquitin ligase. When the checkpoint is satisfied the spindle checkpoint signal is silenced and the Cdc20-APC/C is activated. This triggers the poly-ubiquitination of securin and cyclin, which allows the dissolution of sister chromatid cohesion and mitotic progression, respectively. In human cells the Rod-Zw10-Zwilch (RZZ) complex, which is absent in yeast, provides a second binding site for the Mad1-Mad2 complex at kinetochores. This PhD project is designed to elucidate the roles of the Bub1 and BubR1 kinases in checkpoint signalling in both normal and transformed human cells.