1
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Ng CT, Deng L, Chen C, Lim HH, Shi J, Surana U, Gan L. Electron cryotomography analysis of Dam1C/DASH at the kinetochore-spindle interface in situ. J Cell Biol 2018; 218:455-473. [PMID: 30504246 PMCID: PMC6363454 DOI: 10.1083/jcb.201809088] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 10/25/2018] [Accepted: 10/31/2018] [Indexed: 01/01/2023] Open
Abstract
In dividing cells, depolymerizing spindle microtubules move chromosomes by pulling at their kinetochores. While kinetochore subcomplexes have been studied extensively in vitro, little is known about their in vivo structure and interactions with microtubules or their response to spindle damage. Here we combine electron cryotomography of serial cryosections with genetic and pharmacological perturbation to study the yeast chromosome segregation machinery in vivo. Each kinetochore microtubule has one (rarely, two) Dam1C/DASH outer kinetochore assemblies. Dam1C/DASH contacts the microtubule walls and does so with its flexible "bridges"; there are no contacts with the protofilaments' curved tips. In metaphase, ∼40% of the Dam1C/DASH assemblies are complete rings; the rest are partial rings. Ring completeness and binding position along the microtubule are sensitive to kinetochore attachment and tension, respectively. Our study and those of others support a model in which each kinetochore must undergo cycles of conformational change to couple microtubule depolymerization to chromosome movement.
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Affiliation(s)
- Cai Tong Ng
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore
| | - Li Deng
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore
| | - Chen Chen
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore
| | - Hong Hwa Lim
- Institute of Molecular and Cell Biology Agency for Science Technology and Research, Singapore.,Bioprocessing Technology Institute, Agency for Science Technology and Research, Singapore
| | - Jian Shi
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore
| | - Uttam Surana
- Institute of Molecular and Cell Biology Agency for Science Technology and Research, Singapore.,Bioprocessing Technology Institute, Agency for Science Technology and Research, Singapore.,Department of Pharmacology, National University of Singapore, Singapore
| | - Lu Gan
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore
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2
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Skowyra A, Allan LA, Saurin AT, Clarke PR. USP9X Limits Mitotic Checkpoint Complex Turnover to Strengthen the Spindle Assembly Checkpoint and Guard against Chromosomal Instability. Cell Rep 2018; 23:852-865. [PMID: 29669289 PMCID: PMC5917450 DOI: 10.1016/j.celrep.2018.03.100] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 02/04/2018] [Accepted: 03/21/2018] [Indexed: 02/09/2023] Open
Abstract
Faithful chromosome segregation during mitosis depends on the spindle assembly checkpoint (SAC), which delays progression through mitosis until every chromosome has stably attached to spindle microtubules via the kinetochore. We show here that the deubiquitinase USP9X strengthens the SAC by antagonizing the turnover of the mitotic checkpoint complex produced at unattached kinetochores. USP9X thereby opposes activation of anaphase-promoting complex/cyclosome (APC/C) and specifically inhibits the mitotic degradation of SAC-controlled APC/C substrates. We demonstrate that depletion or loss of USP9X reduces the effectiveness of the SAC, elevates chromosome segregation defects, and enhances chromosomal instability (CIN). These findings provide a rationale to explain why loss of USP9X could be either pro- or anti-tumorigenic depending on the existing level of CIN.
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Affiliation(s)
- Agnieszka Skowyra
- Division of Cancer Research, School of Medicine, University of Dundee, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
| | - Lindsey A Allan
- Division of Cancer Research, School of Medicine, University of Dundee, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
| | - Adrian T Saurin
- Division of Cancer Research, School of Medicine, University of Dundee, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK.
| | - Paul R Clarke
- Division of Cancer Research, School of Medicine, University of Dundee, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK; The University of Queensland Diamantina Institute, Faculty of Medicine, Translational Research Institute, 37 Kent Street, Woolloongabba QLD 4102, Australia.
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3
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Bonaiuti P, Chiroli E, Gross F, Corno A, Vernieri C, Štefl M, Cosentino Lagomarsino M, Knop M, Ciliberto A. Cells Escape an Operational Mitotic Checkpoint through a Stochastic Process. Curr Biol 2017; 28:28-37.e7. [PMID: 29249657 DOI: 10.1016/j.cub.2017.11.031] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 10/23/2017] [Accepted: 11/13/2017] [Indexed: 11/18/2022]
Abstract
Improperly attached chromosomes activate the mitotic checkpoint that arrests cell division before anaphase. Cells can maintain an arrest for several hours but eventually will resume proliferation, a process we refer to as adaptation. Whether adapting cells bypass an active block or whether the block has to be removed to resume proliferation is not clear. Likewise, it is not known whether all cells of a genetically homogeneous population are equally capable to adapt. Here, we show that the mitotic checkpoint is operational when yeast cells adapt and that each cell has the same propensity to adapt. Our results are consistent with a model of the mitotic checkpoint where adaptation is driven by random fluctuations of APC/CCdc20, the molecular species inhibited by the checkpoint. Our data provide a quantitative framework for understanding how cells overcome a constant stimulus that halts cell cycle progression.
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Affiliation(s)
- Paolo Bonaiuti
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy
| | - Elena Chiroli
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy
| | - Fridolin Gross
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy
| | - Andrea Corno
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy
| | - Claudio Vernieri
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy; Medical Oncology Department, Fondazione IRCCS Istituto Nazionale Tumori, via Venezian 1, 20133 Milan, Italy
| | - Martin Štefl
- DKFZ-ZMBH Alliance, Centre for Molecular Biology (ZMBH), University of Heidelberg, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Marco Cosentino Lagomarsino
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy; Sorbonne Universités, UPMC Univ Paris 06, 5 Place Jussieu, 75005 Paris, France; CNRS, UMR 7238 "Biologie Computationnelle et Quantitative," UPMC, Institut de Biologie Paris Seine, 4 Place Jussieu, 75005 Paris, France
| | - Michael Knop
- DKFZ-ZMBH Alliance, Centre for Molecular Biology (ZMBH), University of Heidelberg, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany; DKFZ-ZMBH Alliance, Department of Cell and Tumour Biology, German Cancer Research Centre (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Andrea Ciliberto
- Istituto Firc di Oncologia Molecolare, IFOM, via Adamello 16, 20139 Milan, Italy; Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), via Abbiategrasso 207, 27100 Pavia, Italy.
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4
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Chen C, Lim HH, Shi J, Tamura S, Maeshima K, Surana U, Gan L. Budding yeast chromatin is dispersed in a crowded nucleoplasm in vivo. Mol Biol Cell 2016; 27:3357-3368. [PMID: 27605704 PMCID: PMC5170867 DOI: 10.1091/mbc.e16-07-0506] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Accepted: 09/01/2016] [Indexed: 11/11/2022] Open
Abstract
Chromatin organization has an important role in the regulation of eukaryotic systems. Although recent studies have refined the three-dimensional models of chromatin organization with high resolution at the genome sequence level, little is known about how the most fundamental units of chromatin-nucleosomes-are positioned in three dimensions in vivo. Here we use electron cryotomography to study chromatin organization in the budding yeast Saccharomyces cerevisiae Direct visualization of yeast nuclear densities shows no evidence of 30-nm fibers. Aside from preribosomes and spindle microtubules, few nuclear structures are larger than a tetranucleosome. Yeast chromatin does not form compact structures in interphase or mitosis and is consistent with being in an "open" configuration that is conducive to high levels of transcription. From our study and those of others, we propose that yeast can regulate its transcription using local nucleosome-nucleosome associations.
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Affiliation(s)
- Chen Chen
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543, Singapore
| | - Hong Hwa Lim
- Institute of Molecular and Cell Biology, Agency for Science Technology and Research, Proteos, Singapore 138673, Singapore.,Bioprocessing Technology Institute, Singapore 138668, Singapore
| | - Jian Shi
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543, Singapore
| | - Sachiko Tamura
- National Institute of Genetics and Sokendai, Graduate University for Advanced Studies, Mishima, Shizuoka 411-8540, Japan
| | - Kazuhiro Maeshima
- National Institute of Genetics and Sokendai, Graduate University for Advanced Studies, Mishima, Shizuoka 411-8540, Japan
| | - Uttam Surana
- Institute of Molecular and Cell Biology, Agency for Science Technology and Research, Proteos, Singapore 138673, Singapore.,Bioprocessing Technology Institute, Singapore 138668, Singapore.,Department of Pharmacology, National University of Singapore, Singapore 117543, Singapore
| | - Lu Gan
- Department of Biological Sciences and Centre for BioImaging Sciences, National University of Singapore, Singapore 117543, Singapore
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5
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Ohta S, Kimura M, Takagi S, Toramoto I, Ishihama Y. Identification of Mitosis-Specific Phosphorylation in Mitotic Chromosome-Associated Proteins. J Proteome Res 2016; 15:3331-41. [PMID: 27504668 DOI: 10.1021/acs.jproteome.6b00512] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
During mitosis, phosphorylation of chromosome-associated proteins is a key regulatory mechanism. Mass spectrometry has been successfully applied to determine the complete protein composition of mitotic chromosomes, but not to identify post-translational modifications. Here, we quantitatively compared the phosphoproteome of isolated mitotic chromosomes with that of chromosomes in nonsynchronized cells. We identified 4274 total phosphorylation sites and 350 mitosis-specific phosphorylation sites in mitotic chromosome-associated proteins. Significant mitosis-specific phosphorylation in centromere/kinetochore proteins was detected, although the chromosomal association of these proteins did not change throughout the cell cycle. This mitosis-specific phosphorylation might play a key role in regulation of mitosis. Further analysis revealed strong dependency of phosphorylation dynamics on kinase consensus patterns, thus linking the identified phosphorylation sites to known key mitotic kinases. Remarkably, chromosomal axial proteins such as non-SMC subunits of condensin, TopoIIα, and Kif4A, together with the chromosomal periphery protein Ki67 involved in the establishment of the mitotic chromosomal structure, demonstrated high phosphorylation during mitosis. These findings suggest a novel mechanism for regulation of chromosome restructuring in mitosis via protein phosphorylation. Our study generated a large quantitative database on protein phosphorylation in mitotic and nonmitotic chromosomes, thus providing insights into the dynamics of chromatin protein phosphorylation at mitosis onset.
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Affiliation(s)
- Shinya Ohta
- Center for Innovative and Translational Medicine Medical School, Kochi University Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Michiko Kimura
- Graduate School of Pharmaceutical Sciences, Kyoto University 46-29 Yoshidashimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Shunsuke Takagi
- Graduate School of Pharmaceutical Sciences, Kyoto University 46-29 Yoshidashimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Iyo Toramoto
- Center for Innovative and Translational Medicine Medical School, Kochi University Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Yasushi Ishihama
- Graduate School of Pharmaceutical Sciences, Kyoto University 46-29 Yoshidashimoadachi-cho, Sakyo-ku, Kyoto 606-8501, Japan
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6
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Wengner AM, Siemeister G, Koppitz M, Schulze V, Kosemund D, Klar U, Stoeckigt D, Neuhaus R, Lienau P, Bader B, Prechtl S, Raschke M, Frisk AL, von Ahsen O, Michels M, Kreft B, von Nussbaum F, Brands M, Mumberg D, Ziegelbauer K. Novel Mps1 Kinase Inhibitors with Potent Antitumor Activity. Mol Cancer Ther 2016; 15:583-92. [PMID: 26832791 DOI: 10.1158/1535-7163.mct-15-0500] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 01/04/2016] [Indexed: 11/16/2022]
Abstract
Monopolar spindle 1 (Mps1) has been shown to function as the key kinase that activates the spindle assembly checkpoint (SAC) to secure proper distribution of chromosomes to daughter cells. Here, we report the structure and functional characterization of two novel selective Mps1 inhibitors, BAY 1161909 and BAY 1217389, derived from structurally distinct chemical classes. BAY 1161909 and BAY 1217389 inhibited Mps1 kinase activity with IC50 values below 10 nmol/L while showing an excellent selectivity profile. In cellular mechanistic assays, both Mps1 inhibitors abrogated nocodazole-induced SAC activity and induced premature exit from mitosis ("mitotic breakthrough"), resulting in multinuclearity and tumor cell death. Both compounds efficiently inhibited tumor cell proliferation in vitro (IC50 nmol/L range). In vivo, BAY 1161909 and BAY 1217389 achieved moderate efficacy in monotherapy in tumor xenograft studies. However, in line with its unique mode of action, when combined with paclitaxel, low doses of Mps1 inhibitor reduced paclitaxel-induced mitotic arrest by the weakening of SAC activity. As a result, combination therapy strongly improved efficacy over paclitaxel or Mps1 inhibitor monotreatment at the respective MTDs in a broad range of xenograft models, including those showing acquired or intrinsic paclitaxel resistance. Both Mps1 inhibitors showed good tolerability without adding toxicity to paclitaxel monotherapy. These preclinical findings validate the innovative concept of SAC abrogation for cancer therapy and justify clinical proof-of-concept studies evaluating the Mps1 inhibitors BAY 1161909 and BAY 1217389 in combination with antimitotic cancer drugs to enhance their efficacy and potentially overcome resistance. Mol Cancer Ther; 15(4); 583-92. ©2016 AACR.
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Affiliation(s)
| | | | | | | | | | - Ulrich Klar
- Bayer Pharma AG, Drug Discovery, Berlin, Germany
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7
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Palou G, Palou R, Zeng F, Vashisht AA, Wohlschlegel JA, Quintana DG. Three Different Pathways Prevent Chromosome Segregation in the Presence of DNA Damage or Replication Stress in Budding Yeast. PLoS Genet 2015; 11:e1005468. [PMID: 26332045 PMCID: PMC4558037 DOI: 10.1371/journal.pgen.1005468] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Accepted: 07/27/2015] [Indexed: 11/18/2022] Open
Abstract
A surveillance mechanism, the S phase checkpoint, blocks progression into mitosis in response to DNA damage and replication stress. Segregation of damaged or incompletely replicated chromosomes results in genomic instability. In humans, the S phase checkpoint has been shown to constitute an anti-cancer barrier. Inhibition of mitotic cyclin dependent kinase (M-CDK) activity by Wee1 kinases is critical to block mitosis in some organisms. However, such mechanism is dispensable in the response to genotoxic stress in the model eukaryotic organism Saccharomyces cerevisiae. We show here that the Wee1 ortholog Swe1 does indeed inhibit M-CDK activity and chromosome segregation in response to genotoxic insults. Swe1 dispensability in budding yeast is the result of a redundant control of M-CDK activity by the checkpoint kinase Rad53. In addition, our results indicate that Swe1 is an effector of the checkpoint central kinase Mec1. When checkpoint control on M-CDK and on Pds1/securin stabilization are abrogated, cells undergo aberrant chromosome segregation. Genetic inheritance during cell proliferation requires chromosome duplication (replication) and segregation of the replicated chromosomes to the two daughter cells. In response to the presence of DNA damage, cells block chromosome segregation to avoid the inheritance of damaged, incompletely replicated chromosomes. Failure to do so results in loss of genomic integrity. Here we show that three different, redundant pathways are responsible for such control in budding yeast, a model eukaryotic organism. One of the pathways had been described before and blocks the separation of the replicated chromosomes. We show now that two additional pathways inhibit the essential pro-mitotic Cyclin Dependent Kinase (M-CDK) activity. One of them involves the conserved inhibition of M-CDK through tyrosine phosphorylation, which was puzzlingly dispensable in the response to challenged replication in budding yeast. We show that the reason for such dispensability is the existence of redundant control of M-CDK activity by Rad53. Rad53 is part of a surveillance mechanism termed the S phase checkpoint that detects and responds to replication insults. Such control mechanism has been proposed to constitute an anti-cancer barrier in human cells.
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Affiliation(s)
- Gloria Palou
- Department of Biochemistry and Molecular Biology, Biophysics Unit, School of Medicine, Universitat Autonoma de Barcelona, Bellaterra, Catalonia, Spain
| | - Roger Palou
- Department of Biochemistry and Molecular Biology, Biophysics Unit, School of Medicine, Universitat Autonoma de Barcelona, Bellaterra, Catalonia, Spain
| | - Fanli Zeng
- Department of Biochemistry and Molecular Biology, Biophysics Unit, School of Medicine, Universitat Autonoma de Barcelona, Bellaterra, Catalonia, Spain
| | - Ajay A. Vashisht
- Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, California, United States of America
| | - James A. Wohlschlegel
- Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, California, United States of America
| | - David G. Quintana
- Department of Biochemistry and Molecular Biology, Biophysics Unit, School of Medicine, Universitat Autonoma de Barcelona, Bellaterra, Catalonia, Spain
- * E-mail:
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8
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Sivakumar S, Gorbsky GJ. Spatiotemporal regulation of the anaphase-promoting complex in mitosis. Nat Rev Mol Cell Biol 2015; 16:82-94. [PMID: 25604195 DOI: 10.1038/nrm3934] [Citation(s) in RCA: 201] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The appropriate timing of events that lead to chromosome segregation during mitosis and cytokinesis is essential to prevent aneuploidy, and defects in these processes can contribute to tumorigenesis. Key mitotic regulators are controlled through ubiquitylation and proteasome-mediated degradation. The APC/C (anaphase-promoting complex; also known as the cyclosome) is an E3 ubiquitin ligase that has a crucial function in the regulation of the mitotic cell cycle, particularly at the onset of anaphase and during mitotic exit. Co-activator proteins, inhibitor proteins, protein kinases and phosphatases interact with the APC/C to temporally and spatially control its activity and thus ensure accurate timing of mitotic events.
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Affiliation(s)
- Sushama Sivakumar
- Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, Oklahoma 73104, USA
| | - Gary J Gorbsky
- Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, Oklahoma 73104, USA
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9
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Surana U, Liang H, Lim HH. Staging a recovery from mitotic arrest: Unusual ways of Cdk1. BIOARCHITECTURE 2014; 2:33-37. [PMID: 22754627 PMCID: PMC3383719 DOI: 10.4161/bioa.20421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Checkpoint controls, the surveillance pathways that impose "an order of execution" on the major cell cycle events, are critical to the maintenance of genome stability. When cells fail to execute a cellular event or do so erroneously due to misregulation or exposure to genotoxic stresses, these evolutionarily conserved regulatory circuits prevent passage to the subsequent event, thus bringing the cell cycle to a halt. Once the checkpoint stimulus is removed, cells recover from the arrest and eventually resume cell cycle progression. While the activation, execution and maintenance, the three major aspects of the checkpoint controls, have been investigated in detail, the recovery process remains underexplored. It is not clear if cells recover passively upon dissipation of the checkpoint signals or require an active participation by specific effectors. A recent study in the yeast Saccharomyces cerevisiae uncovered two previously unsuspected functions of Cdk1 in efficient recovery from the spindle assembly checkpoint (SAC) imposed arrest. An inability to fulfil these requirements in the absence of Cdk1 makes it virtually impossible for cells to recover from the mitotic arrest. Given the conserved nature of the SAC, these findings may have implications for vertebrate cells.
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Affiliation(s)
- Uttam Surana
- Institute of Molecular and Cell Biology; Proteos, Singapore
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10
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Vernieri C, Chiroli E, Francia V, Gross F, Ciliberto A. Adaptation to the spindle checkpoint is regulated by the interplay between Cdc28/Clbs and PP2ACdc55. ACTA ACUST UNITED AC 2013; 202:765-78. [PMID: 23999167 PMCID: PMC3760609 DOI: 10.1083/jcb.201303033] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
PP2ACdc55 dephosphorylates APC/CCdc20 to prevent anaphase, an effect that is counteracted by Cdc28/Clbs to allow for spindle checkpoint adaptation. The spindle checkpoint arrests cells in metaphase until all chromosomes are properly attached to the chromosome segregation machinery. Thereafter, the anaphase promoting complex (APC/C) is activated and chromosome segregation can take place. Cells remain arrested in mitosis for hours in response to checkpoint activation, but not indefinitely. Eventually, they adapt to the checkpoint and proceed along the cell cycle. In yeast, adaptation requires the phosphorylation of APC/C. Here, we show that the protein phosphatase PP2ACdc55 dephosphorylates APC/C, thereby counteracting the activity of the mitotic kinase Cdc28. We also observe that the key regulator of Cdc28, the mitotic cyclin Clb2, increases before cells adapt and is then abruptly degraded at adaptation. Adaptation is highly asynchronous and takes place over a range of several hours. Our data suggest the presence of a double negative loop between PP2ACdc55 and APC/CCdc20 (i.e., a positive feedback loop) that controls APC/CCdc20 activity. The circuit could guarantee sustained APC/CCdc20 activity after Clb2 starts to be degraded.
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11
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Lianga N, Williams EC, Kennedy EK, Doré C, Pilon S, Girard SL, Deneault JS, Rudner AD. A Wee1 checkpoint inhibits anaphase onset. ACTA ACUST UNITED AC 2013; 201:843-62. [PMID: 23751495 PMCID: PMC3678162 DOI: 10.1083/jcb.201212038] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The budding yeast Wee1 kinase Swe1 restrains the metaphase-to-anaphase transition by preventing the Cdk1-dependent phosphorylation and activation of APCCdc20. Cdk1 drives both mitotic entry and the metaphase-to-anaphase transition. Past work has shown that Wee1 inhibition of Cdk1 blocks mitotic entry. Here we show that the budding yeast Wee1 kinase, Swe1, also restrains the metaphase-to-anaphase transition by preventing Cdk1 phosphorylation and activation of the mitotic form of the anaphase-promoting complex/cyclosome (APCCdc20). Deletion of SWE1 or its opposing phosphatase MIH1 (the budding yeast cdc25+) altered the timing of anaphase onset, and activation of the Swe1-dependent morphogenesis checkpoint or overexpression of Swe1 blocked cells in metaphase with reduced APC activity in vivo and in vitro. The morphogenesis checkpoint also depended on Cdc55, a regulatory subunit of protein phosphatase 2A (PP2A). cdc55Δ checkpoint defects were rescued by mutating 12 Cdk1 phosphorylation sites on the APC, demonstrating that the APC is a target of this checkpoint. These data suggest a model in which stepwise activation of Cdk1 and inhibition of PP2ACdc55 triggers anaphase onset.
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Affiliation(s)
- Noel Lianga
- Ottawa Institute of Systems Biology and Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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12
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Characterization of novel MPS1 inhibitors with preclinical anticancer activity. Cell Death Differ 2013; 20:1532-45. [PMID: 23933817 DOI: 10.1038/cdd.2013.105] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Revised: 06/10/2013] [Accepted: 07/08/2013] [Indexed: 11/08/2022] Open
Abstract
Monopolar spindle 1 (MPS1), a mitotic kinase that is overexpressed in several human cancers, contributes to the alignment of chromosomes to the metaphase plate as well as to the execution of the spindle assembly checkpoint (SAC). Here, we report the identification and functional characterization of three novel inhibitors of MPS1 of two independent structural classes, N-(4-{2-[(2-cyanophenyl)amino][1,2,4]triazolo[1,5-a]pyridin-6-yl}phenyl)-2-phenylacetamide (Mps-BAY1) (a triazolopyridine), N-cyclopropyl-4-{8-[(2-methylpropyl)amino]-6-(quinolin-5-yl)imidazo[1,2-a]pyrazin-3-yl}benzamide (Mps-BAY2a) and N-cyclopropyl-4-{8-(isobutylamino)imidazo[1,2-a]pyrazin-3-yl}benzamide (Mps-BAY2b) (two imidazopyrazines). By selectively inactivating MPS1, these small inhibitors can arrest the proliferation of cancer cells, causing their polyploidization and/or their demise. Cancer cells treated with Mps-BAY1 or Mps-BAY2a manifested multiple signs of mitotic perturbation including inefficient chromosomal congression during metaphase, unscheduled SAC inactivation and severe anaphase defects. Videomicroscopic cell fate profiling of histone 2B-green fluorescent protein-expressing cells revealed the capacity of MPS1 inhibitors to subvert the correct timing of mitosis as they induce a premature anaphase entry in the context of misaligned metaphase plates. Hence, in the presence of MPS1 inhibitors, cells either divided in a bipolar (but often asymmetric) manner or entered one or more rounds of abortive mitoses, generating gross aneuploidy and polyploidy, respectively. In both cases, cells ultimately succumbed to the mitotic catastrophe-induced activation of the mitochondrial pathway of apoptosis. Of note, low doses of MPS1 inhibitors and paclitaxel (a microtubular poison) synergized at increasing the frequency of chromosome misalignments and missegregations in the context of SAC inactivation. This resulted in massive polyploidization followed by the activation of mitotic catastrophe. A synergistic interaction between paclitaxel and MPS1 inhibitors could also be demonstrated in vivo, as the combination of these agents efficiently reduced the growth of tumor xenografts and exerted superior antineoplastic effects compared with either compound employed alone. Altogether, these results suggest that MPS1 inhibitors may exert robust anticancer activity, either as standalone therapeutic interventions or combined with microtubule-targeting chemicals.
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13
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The spindle-assembly checkpoint and the beauty of self-destruction. Nat Struct Mol Biol 2013; 19:1059-61. [PMID: 23132380 DOI: 10.1038/nsmb.2429] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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