Protection of Centromeric Cohesion by Bub1 and Sgo1

描述（由申请人提供）：生物体的遗传稳定性取决于有丝分裂期间姐妹染色单体准确划分为两个子细胞，这反过来又需要维持姐妹染色单体之间的物理连接（内聚力），直到它们的双极附着到有丝分裂纺锤体上。从染色体上去除粘着蛋白（维持姐妹染色单体粘着的蛋白质复合物），然后导致姐妹染色单体分离。在脊椎动物细胞中，去除粘连蛋白分两步进行。在分裂前期，染色体臂上沿着的大部分粘着蛋白通过Polo样激酶（Plk 1）/Aurora B依赖性的粘着蛋白磷酸化而被去除。在中期，残留的着丝粒池内的粘连蛋白被分离酶切割，使姐妹染色单体分离。我实验室的长期目标是了解哺乳动物细胞染色体分离的分子机制。在这个建议中，我们将解决一个有趣的难题在这方面：如何从Plk 1/极光B在前期的行动的着丝粒粘附屏蔽？我们最近提供的证据表明，纺锤体检查点激酶Bub 1的目标和Sgo 1着丝粒蛋白和蛋白磷酸酶2A（PP 2A）的着丝粒，在那里他们抵消了磷酸化的凝聚素Plk 1和其他有丝分裂激酶。在具体目标1和2中，我们将进一步描述Bub 1，Sgo 1和PP 2A合作保护着丝粒凝聚力的机制。另一方面，我们的研究结果也指出了Sgo 1的PP 2A独立作用。事实上，我们在过去一年中取得了两项新颖而相关的发现。Sgo 1直接与称为ILF 2-ILF 3（白细胞介素增强子结合因子2和3）的RNA结合蛋白复合物相互作用。Sgo 1本身在体外与RNA结合。在目标3和4中计划进行实验，以确定这些发现的体内相关性。着丝粒姐妹染色单体凝聚力的过早丧失导致染色体错误分离和子细胞中染色体数目异常（非整倍性），这有助于癌症形成和出生缺陷。这项拟议的研究将揭示染色体分离的机制，并可能反过来导致更好地理解和预防人类癌症和出生缺陷（如唐氏综合症）中的染色体不稳定性和非整倍性。

DESCRIPTION (provided by applicant): The genetic stability of an organism depends on the accurate partition of sister chromatids into two daughter cells during mitosis, which in turn requires the maintenance of the physical linkage (cohesion) between sister chromatids until their bipolar attachment to the mitotic spindle. Removal of cohesin (the protein complex that maintains sister chromatid cohesion) from chromosomes then leads to sister chromatid separation. In vertebrate cells, removal of cohesin occurs in two steps. At prophase, most of cohesin along the chromosome arms is removed through Polo-like kinase (Plk1)/Aurora B-dependent phosphorylation of cohesin. At metaphase, the residual centromeric pool of cohesin is cleaved by separase to allow sister chromatid separation. The long-term goal of my lab is to understand the molecular mechanism of chromosome segregation in mammalian cells. In this proposal, we will address an interesting puzzle in this area: how is the centromeric cohesin shielded from the actions of Plk1 /Aurora B in prophase? We have recently provided evidence to suggest that the spindle checkpoint kinase Bub1 targets and the Sgo1 centromeric protein and protein phosphatase 2A (PP2A) to centromeres where they counteract the phosphorylation of cohesin by Plk1 and other mitotic kinases. In Specific Aims 1 and 2, we will further delineate the mechanisms by which Bub1, Sgo1, and PP2A collaborate to protect centromeric cohesion. On the other hand, our results also point to a PP2A-independent role of Sgo1. Indeed, we have made two novel and related findings in the past year. Sgo1 directly interacts with an RNA-binding protein complex called ILF2-ILF3 (interleukin enhancer binding factors 2 and 3). Sgo1 itself binds to RNA in vitro. Experiments are planned in Aims 3 and 4 to establish the in vivo relevance of these findings. Premature loss of centromeric sister chromatid cohesion leads to chromosome missegregation and abnormal numbers of chromosomes in daughter cells (aneuploidy), which contributes to cancer formation and birth defects. The proposed research will shed light on the mechanism of chromosome segregation and may in turn lead to better understanding and prevention of chromosomal instability and aneuploidy in human cancers and birth defects, such as Down Syndrome.