Polo-like Kinase-1 Is Required for Bipolar Spindle Formation but Is Dispensable for Anaphase Promoting Complex/Cdc20 Activation and Initiation of Cytokinesis

Abstract

Polo-like kinase-1 (Plk1) performs multiple essential functions during the cell cycle. Here we show that human Plk1-deficient cells are unable to separate their centrosomes, fail to form a bipolar spindle, and undergo a Mad2/BubR1-dependent prometaphase arrest. However, electron microscopy demonstrates that kinetochore-microtubule interactions can be established in cells lacking Plk1. In addition, co-depletion of Plk1 and survivin allows mitotic exit. This indicates that Plk1 depletion does not prevent microtubule attachment, but specifically interferes with the generation of tension, as a consequence of a failure to form a bipolar spindle. Moreover, we find that after silencing of the spindle assembly checkpoint, degradation of cyclin B1 is unaffected in cells lacking Plk1. These data indicate that activation of the anaphase promoting complex or cyclosome (APC/C)-Cdc20 complex that is under control of the spindle assembly checkpoint does not require Plk1 activity. Finally, we find that translocation of chromosome passengers and initiation of cleavage furrow ingression is unaffected in cells depleted of Plk1. Thus, our data confirm an important role of Plk1 in bipolar spindle formation, and also demonstrate that Plk1 is dispensable for APC/C-Cdc20 activation and the initiation of cytokinesis.

Plk1 Regulates Activation of the Anaphase Promoting Complex by Phosphorylating and Triggering SCFβTrCP-dependent Destruction of the APC Inhibitor Emi1

“…The siRNAs used in their studies and in our studies are different and no direct comparison has been made, although the Plk1 siRNA we have used is very efficient (Figure 2). Another very recent article from Medema and coworkers suggests that Plk1 is not strictly required for APC activation in HeLa cells (van Vugt et al, 2004). Here, the authors cause Plk1 inactivation with a transfected pSUPER vector, a hairpin siRNA expression construct.…”

Getting in and out of mitosis with Polo-like kinase-1

“…Injection of anti-Plk1 antibodies in primary human cells or depletion of Plx1 from Xenopus extracts does result in G2 arrest and argues in favor of this idea (Lane and Nigg, 1996;Qian et al, 1998aQian et al, , 2001). However, injection of anti-Plk1 antibodies in transformed human cells, expression of dominant-negative Plk1 fragments and RNA interference of Plk1 in a range of human cells did not result in G2 arrest but rather caused a mitotic arrest with high Cyclin B-Cdk1 levels (Lane and Nigg, 1996;Liu and Erikson, 2002;Seong et al, 2002;SpankuchSchmitt et al, 2002;van Vugt et al, 2004b). Likely, mitotic entry requires multiple factors, and only in some cell types or situations does Plk1 become rate limiting for this process.…”

Quantitative Phospho-proteomics to Investigate the Polo-like Kinase 1-Dependent Phospho-proteome

“…During mitotic entry, PLK1 amplifies cyclin-dependent kinase 1 (CDK1) activation, enabling efficient onset of mitosis (4) and mediates centrosome maturation, the accumulation of ␥-tubulin complexes on centrosomes (5,6). In prometaphase, PLK1 is required for the generation of stable kinetochoremicrotubule attachments (7)(8)(9)(10). PLK1 also promotes dissociation of cohesin from chromosome arms in prophase and prometaphase by phosphorylating cohesin's STAG2 subunit (11)(12)(13)(14), as well as multiple aspects of cytokinesis by phosphorylating activators and effectors of RhoA (1,15).…”