Differential control of Eg5-dependent centrosome separation by Plk1 and Cdk1Mammalian centrosomes separate prior to mitosis in a process involving Cdk1 and the kinesin Eg5. Dissection by chemical genetics reveals a Cdk1-independent alternative mechanism, in which Plk1 counteracts both centrosomal cohesion factors and Eg5-opposing cytoskeletal forces.

Entry into mitosis is triggered by activation of Cdk1 and inactivation of its counteracting phosphatase PP2A/B55. Greatwall kinase inactivates PP2A/B55 via its substrates Ensa and ARPP19. Both Greatwall and Ensa/ARPP19 are regulated by phosphorylation, but the dynamic regulation of Greatwall activity and the phosphatases that control Greatwall kinase and its substrates are poorly understood. To address these questions we applied a combination of mathematical modelling and experiments using phospho-specific antibodies to monitor Greatwall, Ensa/ARPP19 and Cdk substrate phosphorylation during mitotic entry and exit. We demonstrate that PP2A/B55 is required for Gwl dephosphorylation at the essential Cdk site Thr194. Ensa/ARPP19 dephosphorylation is mediated by the RNA Polymerase II carboxy terminal domain phosphatase Fcp1. Surprisingly, inhibition or depletion of neither Fcp1 nor PP2A appears to block dephosphorylation of the bulk of mitotic Cdk1 substrates during mitotic exit. Taken together our results suggest a hierarchy of phosphatases coordinating Greatwall, Ensa/ARPP19 and Cdk substrate dephosphorylation during mitotic exit.

Richard (2018) Type II kinase inhibitors targeting Cys-gatekeeper kinases display orthogonality with wild type and Ala/Gly-gatekeeper kinases.