A Late Mitotic Regulatory Network Controlling Cyclin Destruction in Saccharomyces cerevisiae

Department of Physiology, University of California, San Francisco, California 94143-0444, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 11/1998; 9(10):2803-17. DOI: 10.1091/mbc.9.10.2803
Source: PubMed


Exit from mitosis requires the inactivation of mitotic cyclin-dependent kinase-cyclin complexes, primarily by ubiquitin-dependent cyclin proteolysis. Cyclin destruction is regulated by a ubiquitin ligase known as the anaphase-promoting complex (APC). In the budding yeast Saccharomyces cerevisiae, members of a large class of late mitotic mutants, including cdc15, cdc5, cdc14, dbf2, and tem1, arrest in anaphase with a phenotype similar to that of cells expressing nondegradable forms of mitotic cyclins. We addressed the possibility that the products of these genes are components of a regulatory network that governs cyclin proteolysis. We identified a complex array of genetic interactions among these mutants and found that the growth defect in most of the mutants is suppressed by overexpression of SPO12, YAK1, and SIC1 and is exacerbated by overproduction of the mitotic cyclin Clb2. When arrested in late mitosis, the mutants exhibit a defect in cyclin-specific APC activity that is accompanied by high Clb2 levels and low levels of the anaphase inhibitor Pds1. Mutant cells arrested in G1 contain normal APC activity. We conclude that Cdc15, Cdc5, Cdc14, Dbf2, and Tem1 cooperate in the activation of the APC in late mitosis but are not required for maintenance of that activity in G1.

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Available from: Sue Jaspersen, Feb 15, 2014
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    • "The MEN brings about exit from mitosis by inactivating the mitotic cyclin-dependent kinase 1 (Cdk1). Cdk1, or Cdc28-Clb2 in budding yeast, is inactivated during anaphase via two partially redundant methods: inhibition of its kinase activity by Sic1 and degradation of the mitotic cyclin Clb2 by the APC Cdh1 complex (Jaspersen et al., 1998; Visintin et al., 1998). Both Sic1 and Cdh1 become active once dephosphorylated by the MEN component Cdc14, leading to inhibition of Cdk1 activity (Visintin et al., 1998). "
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    ABSTRACT: Cytokinesis separates cells by contraction of a ring composed of filamentous actin (F-actin) and type II myosin. Iqg1, an IQGAP family member, is an essential protein in Saccharomyces cerevisiae required for assembly and contraction of the actomyosin ring. Localization of F-actin to the ring occurs only after anaphase, and is mediated by the calponin homology domain (CHD) of Iqg1, but the regulatory mechanisms that temporally restrict actin ring assembly are not well defined. We tested the hypothesis that dephosphorylation of four perfect cyclin-dependent kinase (Cdk) sites flanking the CHD promotes actin ring formation using site-specific alanine mutants. Cells expressing the non-phosphorylatable iqg1-4A allele formed actin rings prior to anaphase and exhibited defects in myosin contraction and cytokinesis. The Cdc14 phosphatase is required for normal cytokinesis and acts on specific Cdk phosphorylation sites. Overexpression of Cdc14 resulted in premature actin ring assembly, while inhibition of Cdc14 function prevented actin ring formation. Cdc14 associated with Iqg1, dependent on several CHD-flanking Cdk sites, and efficiently dephosphorylated these sites in vitro. Importantly, the iqg1-4A mutant rescued the inability of cdc14-1 cells to form actin rings. Our data support a model in which dephosphorylation of Cdk sites around the Iqg1 CHD by Cdc14 is both necessary and sufficient to promote actin ring formation. Temporal control of actin ring assembly by Cdk and Cdc14 may help ensure cytokinesis onset occurs after nuclear division is complete. © 2015 by The American Society for Cell Biology.
    Full-text · Article · Jun 2015 · Molecular biology of the cell
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    • "It is kept inactive for much of the cell cycle by sequestration in the nucleolus. In anaphase, activation of a signaling cascade, the mitotic exit network (MEN), results in Cdc14 activation and its release into the nucleus and the cytoplasm (Jaspersen et al, 1998; Shou et al, 1999; Visintin et al, 1999; Lee et al, 2001). Once released, Cdc14 dephosphorylates numerous Cdk targets and contributes to Cdk downregulation by transcriptional activation and stabilization of the Cdk inhibitor Sic1 (Visintin et al, 1998). "
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    ABSTRACT: The final event of the eukaryotic cell cycle is cytokinesis, when two new daughter cells are born. How the timing and execution of cytokinesis is controlled is poorly understood. Here, we show that downregulation of cyclin-dependent kinase (Cdk) activity, together with upregulation of its counteracting phosphatase Cdc14, controls each of the sequential steps of cytokinesis, including furrow ingression, membrane resolution and cell separation in budding yeast. We use phosphoproteome analysis of mitotic exit to identify Cdk targets that are dephosphorylated at the time of cytokinesis. We then apply a new and widely applicable tool to generate conditionally phosphorylated proteins to identify those whose dephosphorylation is required for cytokinesis. This approach identifies Aip1, Ede1 and Inn1 as cytokinetic regulators. Our results suggest that cytokinesis is coordinately controlled by the master cell cycle regulator Cdk together with its counteracting phosphatase and that it is executed by concerted dephosphorylation of Cdk targets involved in several cell biological processes.
    Preview · Article · Nov 2014 · The EMBO Journal
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    • "In addition, Cdc5 also triggers MEN activation by phosphorylating Bfa1, a negative regulator of the MEN pathway [16]. The nucleolar release of Cdc14 triggers activation of kinases (Cdc15 and Dbf2/Dbf20) that phosphorylate both Net1 and Cdc14 [17], [18] independently of CDK activity. This causes sustained release of Cdc14 and completes mitotic exit. "
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    ABSTRACT: Cyclin-dependent kinases (CDK) are master regulators of the cell cycle in eukaryotes. CDK activity is regulated by the presence, post-translational modification and spatial localization of its regulatory subunit cyclin. In budding yeast, the B-cyclin Clb1 is phosphorylated and localizes to the nucleus during meiosis I. However the functional significance of Clb1's phosphorylation and nuclear localization and their mutual dependency is unknown. In this paper, we demonstrate that meiosis-specific phosphorylation of Clb1 requires its import to the nucleus but not vice versa. While Clb1 phosphorylation is dependent on activity of both CDK and polo-like kinase Cdc5, its nuclear localization requires CDK but not Cdc5 activity. Furthermore we show that increased nuclear localization of Clb1 during meiosis enhances activation of FEAR (Cdc Fourteen Early Anaphase Release) pathway. We discuss the significance of our results in relation to regulation of exit from meiosis I.
    Full-text · Article · Nov 2013 · PLoS ONE
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