Bora and the Kinase Aurora A Cooperatively Activate the Kinase Plk1 and Control Mitotic Entry (original) (raw)
Related papers
Cell Cycle, 2014
Cdk1 and plk1/plx1 activation leads to their inactivation through negative feedback loops. Cdk1 deactivates itself by activating the ApC/C, consequently generating embryonic cell cycle oscillations. ApC/C inhibition by the mitotic checkpoint in somatic cells and the cytostatic factor (CSF) in oocytes sustain the mitotic state. plk1/plx1 targets its co-activator Bora for degradation, but it remains unclear how embryonic oscillations in plx1 activity are generated, and how plk1/plx1 activity is sustained during mitosis. We show that plx1-mediated degradation of Bora in interphase generates oscillations in plx1 activity and is essential for development. In CSF extracts, phosphorylation of Bora on the Cdk consensus site t52 blocks Bora degradation. Upon fertilization, Calcineurin dephosphorylates t52, triggering plx1 oscillations. Similarly, we find that GFp-Bora is degraded when plk1 activity spreads to somatic cell cytoplasm before mitosis. Interestingly, GFp-Bora degradation stops upon mitotic entry when Cdk1 activity is high. We hypothesize that Cdk1 controls Bora through an incoherent feedforward loop synchronizing the activities of mitotic kinases.
Cdk1 Activity Is Required for Mitotic Activation of Aurora A during G2/M Transition of Human Cells
Journal of Biological Chemistry, 2010
In mammalian cells entry into and progression through mitosis are regulated by multiple mitotic kinases. How mitotic kinases interact with each other and coordinately regulate mitosis remains to be fully understood. Here we employed a chemical biology approach using selective small molecule kinase inhibitors to dissect the relationship between Cdk1 and Aurora A kinases during G 2 /M transition. We find that activation of Aurora A first occurs at centrosomes at late G 2 and is required for centrosome separation independently of Cdk1 activity. Upon entry into mitosis, Aurora A then becomes fully activated downstream of Cdk1 activation. Inactivation of Aurora A or Plk1 individually during a synchronized cell cycle shows no significant effect on Cdk1 activation and entry into mitosis. However, simultaneous inactivation of both Aurora A and Plk1 markedly delays Cdk1 activation and entry into mitosis, suggesting that Aurora A and Plk1 have redundant functions in the feedback activation of Cdk1. Together, our data suggest that Cdk1, Aurora A, and Plk1 mitotic kinases participate in a feedback activation loop and that activation of Cdk1 initiates the feedback loop activity, leading to rapid and timely entry into mitosis in human cells. In addition, live cell imaging reveals that the nuclear cycle of cells becomes uncoupled from cytokinesis upon inactivation of both Aurora A and Aurora B kinases and continues to oscillate in a Cdk1-dependent manner in the absence of cytokinesis, resulting in multinucleated, polyploidy cells.
Plk1- and β-TrCP–dependent degradation of Bora controls mitotic progression
The Journal of Cell Biology, 2008
Through a convergence of functional genomic and proteomic studies, we identify Bora as a previously unknown cell cycle protein that interacts with the Plk1 kinase and the SCF–β-TrCP ubiquitin ligase. We show that the Bora protein peaks in G2 and is degraded by proteasomes in mitosis. Proteolysis of Bora requires the Plk1 kinase activity and is mediated by SCF–β-TrCP. Plk1 phosphorylates a conserved DSGxxT degron in Bora and promotes its interaction with β-TrCP. Mutations in this degron stabilize Bora. Expression of a nondegradable Bora variant prolongs the metaphase and delays anaphase onset, indicating a physiological requirement of Bora degradation. Interestingly, the activity of Bora is also required for normal mitotic progression, as knockdown of Bora activates the spindle checkpoint and delays sister chromatid segregation. Mechanistically, Bora regulates spindle stability and microtubule polymerization and promotes tension across sister kinetochores during mitosis. We conclude ...
Plk1 regulates mitotic Aurora A function through βTrCP-dependent degradation of hBora
Chromosoma, 2008
Polo-like kinase 1 (Plk1) and Aurora A play key roles in centrosome maturation, spindle assembly, and chromosome segregation during cell division. Here we show that the functions of these kinases during early mitosis are coordinated through Bora, a partner of Aurora A first identified in Drosophila. Depletion of human Bora (hBora) results in spindle defects, accompanied by increased spindle recruitment of Aurora A and its partner TPX2. Conversely, hBora overexpression induces mislocalization of Aurora A and monopolar spindle formation, reminiscent of the phenotype seen in Plk1-depleted cells. Indeed, Plk1 regulates hBora. Following Cdk1-dependent recruitment, Plk1 triggers hBora destruction by phosphorylating a recognition site for SCF "ÀTrCP. Plk1 depletion or inhibition results in a massive accumulation of hBora, concomitant with displacement of Aurora A from spindle poles and impaired centrosome maturation, but remarkably, co-depletion of hBora partially restores Aurora A localization and bipolar spindle formation. This suggests that Plk1 controls Aurora A localization and function by regulating cellular levels of hBora. 1 (Plk1), and Aurora A (Barr et al. 2004; Blagden and Glover 2003; Nigg 2001; Vagnarelli and Earnshaw 2004). Cdk1 is initially activated at the centrosome (Jackman et al. 2003) and required for centrosome separation (Blangy et al. 1995; Sawin and Mitchison 1995). Likewise, Plk1 and Aurora A localize to centrosomes and are activated at the G2/M transition, but the coordination of their activities is not presently understood. When Plk1 activity is impaired by antibody injection (Lane and Nigg 1996), RNAimediated Plk1 depletion (
Mitotic requirement for aurora A kinase is bypassed in the absence of aurora B kinase
FEBS Letters, 2005
We investigated why treatment of cells with dual aurora A and B kinase inhibitors produces phenotypes identical to inactivation of aurora B. We found that dual aurora kinase inhibitors in fact potently inhibit cellular activities of both kinases, indicating that inactivation of aurora B bypasses aurora A in mitosis. RNAi experiments further established that inactivation of aurora B indeed bypasses the requirement for aurora A and leads to polyploidy. Inactivation of aurora A activates checkpoint kinase BubR1 in an aurora B-dependent manner. Our results thus show that aurora B is responsible for mitotic arrest in the absence of aurora A.
A dimerization-dependent mechanism regulates enzymatic activation and nuclear entry of PLK1
Oncogene, 2021
Polo-like kinase 1 (PLK1) is a crucial regulator of cell cycle progression. It is established that the activation of PLK1 depends on the coordinated action of Aurora-A and Bora. Nevertheless, very little is known about the spatiotemporal regulation of PLK1 during G2, specifically, the mechanisms that keep cytoplasmic PLK1 inactive until shortly before mitosis onset. Here, we describe PLK1 dimerization as a new mechanism that controls PLK1 activation. During the early G2 phase, Bora supports transient PLK1 dimerization, thus fine-tuning the timely regulated activation of PLK1 and modulating its nuclear entry. At late G2, the phosphorylation of T210 by Aurora-A triggers dimer dissociation and generates active PLK1 monomers that support entry into mitosis. Interfering with this critical PLK1 dimer/monomer switch prevents the association of PLK1 with importins, limiting its nuclear shuttling, and causes nuclear PLK1 mislocalization during the G2-M transition. Our results suggest a novel...
Functional Interaction of Aurora-A and PP2A during Mitosis
Molecular Biology of the Cell, 2007
Entry into mitosis is a highly regulated process, promoted by the activated Cyclin B1/Cdk1 complex. Activation of this complex is controlled, in part, by the protein kinase Aurora-A, which is a member of a multigenic serine/threonine kinase family. In normal cells, Aurora-A activity is regulated, at least in part, by degradation through the APC-ubiquitinproteasome pathway. It has recently been proposed that, in Xenopus, Aurora-A degradation can be inhibited by phosphorylation. It would thus be expected that a phosphatase activity would release this blockade at the end of mitosis.