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

Department of Pathology, Stanford University School of Medicine, Palo Alto, CA 94305, USA.
Molecular Biology of the Cell (Impact Factor: 4.55). 01/2005; 15(12):5623-34. DOI: 10.1091/mbc.E04-07-0598
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ABSTRACT Progression through mitosis requires activation of cyclin B/Cdk1 and its downstream targets, including Polo-like kinase and the anaphase-promoting complex (APC), the ubiquitin ligase directing degradation of cyclins A and B. Recent evidence shows that APC activation requires destruction of the APC inhibitor Emi1. In prophase, phosphorylation of Emi1 generates a D-pS-G-X-X-pS degron to recruit the SCF(betaTrCP) ubiquitin ligase, causing Emi1 destruction and allowing progression beyond prometaphase, but the kinases directing this phosphorylation remain undefined. We show here that the polo-like kinase Plk1 is strictly required for Emi1 destruction and that overexpression of Plk1 is sufficient to trigger Emi1 destruction. Plk1 stimulates Emi1 phosphorylation, betaTrCP binding, and ubiquitination in vitro and cyclin B/Cdk1 enhances these effects. Plk1 binds to Emi1 in mitosis and the two proteins colocalize on the mitotic spindle poles, suggesting that Plk1 may spatially control Emi1 destruction. These data support the hypothesis that Plk1 activates the APC by directing the SCF-dependent destruction of Emi1 in prophase.

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    • "By knocking down Cdh1 or inhibiting Plk1 activity during G2 we wanted to test whether Plk1 and APC/ C activities can independently promote centriole disengagement in this phase of the cell cycle. Although centriole disengagement/ reduplication are reported to occur in a Plk1 activity dependent fashion in G2 (Lončarek et al., 2010), we re-examined this issue because that Plk1 phosphorylates Emi1 to target it for SCF-Trcp1 mediated destruction (Guardavaccaro et al., 2003; Margottin- Goguet et al., 2003; Hansen et al., 2004; Moshe et al., 2004). Thus, inhibition of Plk1 activity starting before cells reach G2 (Lončarek et al., 2010) should also block Emi1 destruction thereby inhibiting APC/C activity; the resulting lack of centriole disengagement in the absence of Plk1 and APC/C activity would thus be expected (Tsou et al., 2009). "
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    • "Entry and progression of mitosis is tightly regulated by multiple kinases including Aurora-A (Marumoto et al., 2005). Mitotic entry is controlled by the activation of cyclin-dependent kinase 1 (Cdk1), whose activity is regulated directly by mitotic cyclins and phosphatase Cdc25, (Murray, 2004) and indirectly by polo-like kinase 1 (Plk1) (Hansen et al., 2004; Lenart et al., 2007). Plk1, Cdc25, and Cdk1 form a feedback loop and positively regulate each other's activity (Murray, 2004). "
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    • "At the G1/S transition, Emi1 functions as a pseudo-substrate inhibitor of the APC/C (Miller et al., 2006), allowing substrates to accumulate (Guardavaccaro et al., 2003; Miller et al., 2006). In early mitosis , Emi1 is phosphorylated by Plk1 (Hansen et al., 2004), which triggers SCF βTrCP -dependent ubiquitination and destruction, thus inducing APC/C activation and mitotic progression (Margottin- Goguet et al., 2003). Emi1 overexpression leads to unscheduled cell proliferation, tetraploidy, and chromosomal instability in p53- deficient cells (Lehman et al., 2006; Figure 2). "
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