Fig. 1.

TOPK activity and expression rises at the G2/M border to facilitate mitotic entry. Activation of TOPK is initiated by Cdk1-mediated dissociation of protein phosphatase 1 alpha (PP1α). TOPK activity is instrumental in the stabilisation of the Cdk1/Cyclin B complex between prophase and metaphase, which promotes spindle formation and correct chromosomal alignment. Rapid dephosphorylation of TOPK at the metaphase/anaphase border (mid-mitotic checkpoint) releases TOPK from Cdk1, enabling proteolytic degradation of Cyclin B by the anaphase promoting complex (APC). A drop in Cyclin B levels enables chromosomal migration to spindle poles and progression into anaphase