Emi1 Is a Mitotic Regulator that Interacts with Cdc20 and Inhibits the Anaphase Promoting Complex

Department of Pathology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305, USA.
Cell (Impact Factor: 32.24). 07/2001; 105(5):645-55. DOI: 10.1016/S0092-8674(01)00361-0
Source: PubMed


We have discovered an early mitotic inhibitor, Emi1, which regulates mitosis by inhibiting the anaphase promoting complex/cyclosome (APC). Emi1 is a conserved F box protein containing a zinc binding region essential for APC inhibition. Emi1 accumulates before mitosis and is ubiquitylated and destroyed in mitosis, independent of the APC. Emi1 immunodepletion from cycling Xenopus extracts strongly delays cyclin B accumulation and mitotic entry, whereas nondestructible Emi1 stabilizes APC substrates and causes a mitotic block. Emi1 binds the APC activator Cdc20, and Cdc20 can rescue an Emi1-induced block to cyclin B destruction. Our results suggest that Emi1 regulates progression through early mitosis by preventing premature APC activation, and may help explain the well-known delay between cyclin B/Cdc2 activation and cyclin B destruction.

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Available from: Edgar Kramer, Oct 05, 2015
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    • "These observations suggest that either APC/C inactivation is not required for the normal execution of meiosis and spore formation or that this ubiquitin ligase is disabled by redundant systems. In support of the latter possibility, several mechanisms are known to control APC/C function including inhibitory phosphorylation [41-44], APC/C specific inhibitors [45-52], or removal of the activator from the APC/C complex [53]. The roles these mechanisms play as cells exit the meiotic program are not well understood. "
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    ABSTRACT: The execution of meiotic nuclear divisions in S. cerevisiae is regulated by protein degradation mediated by the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase. The correct timing of APC/C activity is essential for normal chromosome segregation. During meiosis, the APC/C is activated by the association of either Cdc20p or the meiosis-specific factor Ama1p. Both Ama1p and Cdc20p are targeted for degradation as cells exit meiosis II with Cdc20p being destroyed by APC/CAma1. In this study we investigated how Ama1p is down regulated at the completion of meiosis. Here we show that Ama1p is a substrate of APC/CCdc20 but not APC/CCdh1 in meiotic cells. Cdc20p binds Ama1p in vivo and APC/CCdc20 ubiquitylates Ama1p in vitro. Ama1p ubiquitylation requires one of two degradation motifs, a D-box and a "KEN-box" like motif called GxEN. Finally, Ama1p degradation does not require its association with the APC/C via its conserved APC/C binding motifs (C-box and IR) and occurs simultaneously with APC/CAma1-mediated Cdc20p degradation. Unlike the cyclical nature of mitotic cell division, meiosis is a linear pathway leading to the production of quiescent spores. This raises the question of how the APC/C is reset prior to spore germination. This and a previous study revealed that Cdc20p and Ama1p direct each others degradation via APC/C-dependent degradation. These findings suggest a model that the APC/C is inactivated by mutual degradation of the activators. In addition, these results support a model in which Ama1p and Cdc20p relocate to the substrate address within the APC/C cavity prior to degradation.
    Cell Division 07/2013; 8(1):9. DOI:10.1186/1747-1028-8-9 · 3.53 Impact Factor
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    • "Evi5 has also another implicated role in the earlier phases of the cell cycle – as a regulator of cyclin accumulation via its effects on the stability of Early mitotic inhibitor 1 (Emi1) accumulation [4]. Emi1 is an inhibitor of anaphase promoting complex/cyclosome (APC/C) complex, and together with either of its activators Cdc20 or Cdh1, sustain levels of APC/C's cyclin substrates [17] [18]. Even in the absence of transcription factor E2F activation and basal levels of cyclin A transcription, Emi1's overexpression is apparently sufficient to drive S phase by stabilizing cyclin A [18]. "
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    ABSTRACT: The Ecotropic viral integration site 5 (Evi5) and Evi5-like (Evi5L) belong to a small subfamily of the Tre-2/Bub2/Cdc16 (TBC) domain-containing proteins with enigmatically divergent roles as modulators of cell cycle progression, cytokinesis, and cellular membrane traffic. First recognized as a potential oncogene and a cell cycle regulator, Evi5 acts as a GTPase Activating Protein (GAP) for Rab11 in cytokinesis. On the other hand, its homologue Evi5L has Rab-GAP activity towards Rab10 as well as Rab23, and has been implicated in primary cilia formation. Recent genetic susceptibility analysis points to Evi5 as an important factor in susceptibility to multiple sclerosis. We discuss below the myriad of cellular functions exhibited by the Evi5 family members, and their associations with disease conditions.
    FEBS letters 05/2013; 587(12). DOI:10.1016/j.febslet.2013.04.036 · 3.17 Impact Factor
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    • "By showing that KEN1 occupies the KEN box bind­ ing pocket of Cdc20, the structure illustrates the proposal that BubR1/Mad3 is a pseudosubstrate inhibitor of the APC that directly competes with Cdc20 substrates (Burton and Solomon, 2007; King et al., 2007; Sczaniecka et al., 2008). Incidentally, this might not be an isolated example: additional APC/C inhibi­ tors, including Acm1, Mes1, and Emi1/Rca1 (Dong et al., 1997; Reimann et al., 2001; Miller et al., 2006), are also believed to inhibit Cdh1 or Cdc20 as pseudosubstrates (Choi et al., 2008; Enquist­Newman et al., 2008; Kimata et al., 2008b; Ostapenko et al., 2008; Chao et al., 2012). "
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    ABSTRACT: The anaphase-promoting complex or cyclosome (APC/C) is a conserved, multisubunit E3 ubiquitin (Ub) ligase that is active both in dividing and in postmitotic cells. Its contributions to life are especially well studied in the domain of cell division, in which the APC/C lies at the epicenter of a regulatory network that controls the directionality and timing of cell cycle events. Biochemical and structural work is shedding light on the overall organization of APC/C subunits and on the mechanism of substrate recognition and Ub chain initiation and extension as well as on the molecular mechanisms of a checkpoint that seizes control of APC/C activity during mitosis. Here, we review how these recent advancements are modifying our understanding of the APC/C.
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