Article

Reddy, S. K. et al. Ubiquitination by the anaphase-promoting complex drives spindle checkpoint inactivation. Nature 446, 921-925

Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Nature (Impact Factor: 41.46). 05/2007; 446(7138):921-5. DOI: 10.1038/nature05734
Source: PubMed

ABSTRACT

Eukaryotic cells rely on a surveillance mechanism known as the spindle checkpoint to ensure accurate chromosome segregation. The spindle checkpoint prevents sister chromatids from separating until all kinetochores achieve bipolar attachments to the mitotic spindle. Checkpoint proteins tightly inhibit the anaphase-promoting complex (APC), a ubiquitin ligase required for chromosome segregation and progression to anaphase. Unattached kinetochores promote the binding of checkpoint proteins Mad2 and BubR1 to the APC-activator Cdc20, rendering it unable to activate APC. Once all kinetochores are properly attached, however, cells inactivate the checkpoint within minutes, allowing for the rapid and synchronous segregation of chromosomes. How cells switch from strong APC inhibition before kinetochore attachment to rapid APC activation once attachment is complete remains a mystery. Here we show that checkpoint inactivation is an energy-consuming process involving APC-dependent multi-ubiquitination. Multi-ubiquitination by APC leads to the dissociation of Mad2 and BubR1 from Cdc20, a process that is reversed by a Cdc20-directed de-ubiquitinating enzyme. The mutual regulation between checkpoint proteins and APC leaves the cell poised for rapid checkpoint inactivation and ensures that chromosome segregation promptly follows the completion of kinetochore attachment. In addition, our results suggest a mechanistic basis for how cancer cells can have a compromised spindle checkpoint without corresponding mutations in checkpoint genes.

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    • "p31 comet is a structurally unique HOR MA domain protein with a stable closed-like conformation (Fig. S1C) and forms a heterodimer specifically with C-Mad2 (Fig. 2Habu et al., 2002;Mapelli et al., 2006;Yang et al., 2007). Disruption of p31 comet in mammalian cells results in prolonged metaphase, implying it has a role in SAC inactivation (Habu et al., 2002;Xia et al., 2004;Hagan et al., 2011), and experiments in cell extracts have suggested that p31 comet functions by disassembling the MCC (Reddy et al., 2007;Westhorpe et al., 2011). Recently, p31 comet was found to interact with TRIP13, a hexameric AAA+ ATPase related to a large family of protein complex remodelers/unfoldases (Tipton et al., 2012; Figure 2. Structure and function of Mad2 and p31 comet in the spindle assembly checkpoint. "
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    ABSTRACT: The HORMA domain is a multifunctional protein-protein interaction module found in diverse eukaryotic signaling pathways including the spindle assembly checkpoint, numerous DNA recombination/repair pathways, and the initiation of autophagy. In all of these pathways, HORMA domain proteins occupy key signaling junctures and function through the controlled assembly and disassembly of signaling complexes using a stereotypical "safety belt" peptide interaction mechanism. A recent explosion of structural and functional work has shed new light on these proteins, illustrating how strikingly similar structural mechanisms give rise to radically different functional outcomes in each family of HORMA domain proteins.
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    • "Tetraploid cells have been shown to promote tumorigenesis in mice (Fujiwara et al. 2005) and can have multiple centrosomes, which increases the chance of forming merotelic attachments and developing aneuploidy (see below). Additionally , genes involved in SAC inactivation and mitotic progression, such as UBCH10 and CUEDC2, can lead to aneuploidy when overexpressed in cell lines and/or mouse models and are up-regulated in some human tumors (Reddy et al. 2007; van Ree et al. 2010; Gao et al. 2011; Xie et al. 2014). Taking into account these observations, it is likely that we are underestimating the frequency of alterations that impinge on the SAC in human tumors. "
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    ABSTRACT: Aneuploidy, defined as an abnormal number of chromosomes, is a hallmark of cancer. Paradoxically, aneuploidy generally has a negative impact on cell growth and fitness in nontransformed cells. In this work, we review recent progress in identifying how aneuploidy leads to genomic and chromosomal instability, how cells can adapt to the deleterious effects of aneuploidy, and how aneuploidy contributes to tumorigenesis in different genetic contexts. Finally, we also discuss how aneuploidy might be a target for anticancer therapies.
    Preview · Article · Sep 2014 · Cold Spring Harbor perspectives in biology
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    • "The Mad2 inhibitor p31 comet is required for cyclin B1 degradation and mitotic adaptation p31 comet prevents the conformational activation of Mad2 and promotes MCC disassembly and APC/C Cdc20 activation during checkpoint silencing (Habu et al, 2002; Xia et al, 2004; Mapelli et al, 2006; Reddy et al, 2007; Yang et al, 2007; Jia et al, 2011; Teichner et al, 2011; Westhorpe et al, 2011). Depletion of p31 comet sensitizes cancer cells to mitotic arrest and killing by spindle poisons (Xia et al, 2004; Ma et al, 2012). "
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    ABSTRACT: The antimitotic anti-cancer drugs, including taxol, perturb spindle dynamics, and induce prolonged, spindle checkpoint-dependent mitotic arrest in cancer cells. These cells then either undergo apoptosis triggered by the intrinsic mitochondrial pathway or exit mitosis without proper cell division in an adaptation pathway. Using a genome-wide small interfering RNA (siRNA) screen in taxol-treated HeLa cells, we systematically identify components of the mitotic apoptosis and adaptation pathways. We show that the Mad2 inhibitor p31comet actively promotes mitotic adaptation through cyclin B1 degradation and has a minor separate function in suppressing apoptosis. Conversely, the pro-apoptotic Bcl2 family member, Noxa, is a critical initiator of mitotic cell death. Unexpectedly, the upstream components of the mitochondrial apoptosis pathway and the mitochondrial fission protein Drp1 contribute to mitotic adaption. Our results reveal crosstalk between the apoptosis and adaptation pathways during mitotic arrest.
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