Cdk1 Negatively Regulates Midzone Localization of the Mitotic Kinesin Mklp2 and the Chromosomal Passenger Complex

The survival of eukaryotes depends on the accurate coordination of mitosis with cytokinesis. Key for the coordination of both processes is the chromosomal passenger complex (CPC) comprising Aurora-B, INCENP, survivin, and borealin [1-5]. The translocation of the CPC from centromeres to the spindle miclzone, a structure composed of antiparallel microtubules, at anaphase onset is critical for the completion of cytokinesis [6-12]. In mammalian cells, the mitotic kinesin Mklp2 is essential for recruitment of the CPC to the spindle miclzone [13]. However, the mechanism regulating the binding of Mklp2 to microtubules has remained unknown. Here, we demonstrate that Mklp2 and the CPC mutually depend on each other for miclzone localization; i.e., Mklp2 is mislocalized in INCENP-RNAi cells and vice versa. Remarkably, INCENP is required for localization of Mklp2 to the ends of stable microtubules in cells with low Cdk1 activity. In vitro assays revealed that the association between the CPC and Mklp2 is negatively regulated by Cdk1. Collectively, our data suggest that anaphase onset triggers the association between the CPC and Mklp2 and that this association targets the CPC-Mklp2 complex to the ends of stable microtubules in the spindle miclzone.