RepoMan stimulates the chromosome-dependent pathway of microtubule assembly

RepoMan is a chromosome-associated scaffold protein that integrates signaling of multiple kinases and phosphatases to coordinate spindle-kinetochore interactions, chromosome (de)condensation and nuclear envelope (dis)assembly during mitosis. Another key mitotic event is the assembly of a microtubule-based spindle, which involves redundant pathways emanating from the centrosomes, microtubules and chromosomes. Here we describe a novel mitotic function of RepoMan in regulating chromosome-dependent microtubule assembly. At limiting concentrations of microtubule-destabilizing agents, RepoMan-depleted cells showed enhanced chromosome clustering. This clustering was completely dependent on the partial inhibition of microtubule growth originating from the chromosome-dependent pathway. We also demonstrated that RepoMan interacts with prime regulators of the chromosome-dependent spindle assembly such as NuSAP1, NuMA, and TPX2. In addition, RepoMan was required to enable or maintain phosphorylation of NuSAP1 at CDK sites, thereby enabling activation of NuSAP1 through dissociation of inhibitory importin β/7. Our data identify RepoMan as an enhancer of microtubule assembly at chromosomes.

RepoMan是一种染色体相关支架蛋白，可整合多种激酶与磷酸酶的信号通路，以协调有丝分裂过程中的纺锤体-动粒相互作用、染色体（去）浓缩以及核被膜（解）组装。另一关键有丝分裂事件是基于微管的纺锤体组装，该过程涉及源自中心体、微管与染色体的多条冗余通路。本文阐述了RepoMan在调控染色体依赖型微管组装方面的全新有丝分裂功能。当使用亚适浓度的微管解聚剂时，RepoMan敲低细胞中的染色体聚集现象显著增强；该聚集现象完全依赖于源自染色体依赖通路的微管生长受到部分抑制这一条件。本研究还证实，RepoMan可与染色体依赖型纺锤体组装的核心调控因子（如NuSAP1、NuMA及TPX2）发生相互作用。此外，RepoMan是介导或维持NuSAP1在细胞周期蛋白依赖性激酶（Cyclin-dependent kinase, CDK）位点磷酸化所必需的，进而通过解离抑制性importin β/7复合物激活NuSAP1。本研究数据证实，RepoMan是染色体处微管组装的增强因子。