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.