351
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Pfleger CM, Lee E, Kirschner MW. Substrate recognition by the Cdc20 and Cdh1 components of the anaphase-promoting complex. Genes Dev 2001; 15:2396-407. [PMID: 11562349 PMCID: PMC312782 DOI: 10.1101/gad.918201] [Citation(s) in RCA: 194] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The specificity of ubiquitin-mediated protein degradation with regards to the selection of substrates to be polyubiquitinated has only been determined rather recently. Substrate targeting by the N-end rule and HECT (homology to E6AP carboxyl terminus) domain ubiquitin ligases occurs through substrate-specific binding domains. In contrast, the SCF complex recruits substrates through a substrate adaptor protein, the F-box subunit. Despite evidence showing that Cdc20 and Cdh1 bind and activate the anaphase-promoting complex (APC) in a substrate-specific manner, there is no evidence that the activating protein and substrate interact directly; hence, no clear model exists for the mechanism of APC activation or recruitment of substrates. We show here that the activators Cdc20 and Cdh1 can associate with substrates via their N termini. In the absence of APC, Cdc20 and Cdh1 bind substrates reflecting Cdc20-APC and Cdh1-APC specificity. The N termini of Cdc20 and Cdh1 provide specificity functionally, as demonstrated by the generation of active chimeras that display the specificity corresponding to their N termini. Thus, Cdc20 and Cdh1 act as both substrate recognition and activating modules for APC.
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Affiliation(s)
- C M Pfleger
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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352
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Burton JL, Solomon MJ. D box and KEN box motifs in budding yeast Hsl1p are required for APC-mediated degradation and direct binding to Cdc20p and Cdh1p. Genes Dev 2001; 15:2381-95. [PMID: 11562348 PMCID: PMC312781 DOI: 10.1101/gad.917901] [Citation(s) in RCA: 153] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The precise order of molecular events during cell cycle progression depends upon ubiquitin-mediated proteolysis of cell cycle regulators. We demonstrated previously that Hsl1p, a protein kinase that inhibits the Swe1p protein kinase in a bud morphogenesis checkpoint, is targeted for ubiquitin-mediated turnover by the anaphase-promoting complex (APC). Here, we investigate regions of Hsl1p that are critical both for binding to the APC machinery and for APC-mediated degradation. We demonstrate that Hsl1p contains both a destruction box (D box) and a KEN box motif that are necessary for Hsl1p turnover with either APC(Cdc20) or APC(Cdh1). In coimmunoprecipitation studies, the D box of full-length Hsl1p was critical for association with Cdc20p, whereas the KEN box was important for association with Cdh1p. Fusion of a 206-amino-acid fragment of Hsl1p containing these motifs to a heterologous protein resulted in APC-dependent degradation of the fusion protein that required intact D box and KEN box motifs. Finally, this bacterially expressed Hsl1p fusion protein interacted with Cdc20p and Cdh1p either translated in vitro or expressed in and purified from insect cells. Binding to Cdc20p and Cdh1p was disrupted completely by a D box/KEN box double mutant. These results indicate that D box and KEN box motifs are important for direct binding to the APC machinery, leading to ubiquitination and subsequent protein degradation.
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Affiliation(s)
- J L Burton
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA
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353
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Hilioti Z, Chung YS, Mochizuki Y, Hardy CF, Cohen-Fix O. The anaphase inhibitor Pds1 binds to the APC/C-associated protein Cdc20 in a destruction box-dependent manner. Curr Biol 2001; 11:1347-52. [PMID: 11553328 DOI: 10.1016/s0960-9822(01)00399-2] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
An essential aspect of progression through mitosis is the sequential degradation of key mitotic regulators in a process that is mediated by the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase [1]. In mitotic cells, two forms of the APC/C exist, APC/C(Cdc20) and APC/C(Cdh1), which differ in their associated WD-repeat proteins (Cdc20 and Cdh1, respectively), time of activation, and substrate specificity [2, 3]. How the WD-repeat proteins contribute to APC/C's activation and substrate specificity is not clear. Many APC/C substrates contain a destruction box element that is necessary for their ubiquitination [4-6]. One such APC/C substrate, the budding yeast anaphase inhibitor Pds1 (securin), is degraded prior to anaphase initiation in a destruction box and APC/C(Cdc20)-dependent manner [3, 7]. Here we find that Pds1 interacts directly with Cdc20 and that this interaction requires Pds1's destruction box. Our results suggest that Cdc20 provides a link between the substrate and the core APC/C and that the destruction box is essential for efficient Cdc20-substrate interaction. We also find that Pds1 does not interact with Cdh1. Finally, the effect of spindle assembly checkpoint activation, known to inhibit APC/C function [8], on the Pds1-Cdc20 interaction is examined.
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Affiliation(s)
- Z Hilioti
- The Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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354
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Abstract
Previous studies of the spindle checkpoint suggested that its ability to prevent entry into anaphase was mediated by the inhibition of the anaphase-promoting complex (APC) ubiquitin ligase by Mad2. Two new studies challenge that view by demonstrating that another checkpoint protein, BubR1, is a far more potent inhibitor of APC function.
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Affiliation(s)
- M A Hoyt
- Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA.
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355
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Sudakin V, Chan GK, Yen TJ. Checkpoint inhibition of the APC/C in HeLa cells is mediated by a complex of BUBR1, BUB3, CDC20, and MAD2. J Cell Biol 2001; 154:925-36. [PMID: 11535616 PMCID: PMC2196190 DOI: 10.1083/jcb.200102093] [Citation(s) in RCA: 649] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The mitotic checkpoint prevents cells with unaligned chromosomes from prematurely exiting mitosis by inhibiting the anaphase-promoting complex/cyclosome (APC/C) from targeting key proteins for ubiquitin-mediated proteolysis. We have examined the mechanism by which the checkpoint inhibits the APC/C by purifying an APC/C inhibitory factor from HeLa cells. We call this factor the mitotic checkpoint complex (MCC) as it consists of hBUBR1, hBUB3, CDC20, and MAD2 checkpoint proteins in near equal stoichiometry. MCC inhibitory activity is 3,000-fold greater than that of recombinant MAD2, which has also been shown to inhibit APC/C in vitro. Surprisingly, MCC is not generated from kinetochores, as it is also present and active in interphase cells. However, only APC/C isolated from mitotic cells was sensitive to inhibition by MCC. We found that the majority of the APC/C in mitotic lysates is associated with the MCC, and this likely contributes to the lag in ubiquitin ligase activity. Importantly, chromosomes can suppress the reactivation of APC/C. Chromosomes did not affect the inhibitory activity of MCC or the stimulatory activity of CDC20. We propose that the preformed interphase pool of MCC allows for rapid inhibition of APC/C when cells enter mitosis. Unattached kinetochores then target the APC/C for sustained inhibition by the MCC.
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Affiliation(s)
- V Sudakin
- Institute for Cancer Research, The Fox Chase Cancer Center, Philadelphia, PA 19111, USA
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356
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Bagby S, Tong KI, Ikura M. Optimization of protein solubility and stability for protein nuclear magnetic resonance. Methods Enzymol 2001; 339:20-41. [PMID: 11462812 DOI: 10.1016/s0076-6879(01)39307-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- S Bagby
- Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
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357
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Tang Z, Bharadwaj R, Li B, Yu H. Mad2-Independent inhibition of APCCdc20 by the mitotic checkpoint protein BubR1. Dev Cell 2001; 1:227-37. [PMID: 11702782 DOI: 10.1016/s1534-5807(01)00019-3] [Citation(s) in RCA: 324] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The mitotic checkpoint blocks the activation of the anaphase-promoting complex (APC) until all sister chromatids have achieved bipolar attachment to the spindle. A checkpoint complex containing BubR1 and Bub3 has been purified from mitotic human cells. Upon checkpoint activation, the BubR1-Bub3 complex interacts with Cdc20. In the absence of Mad2, BubR1 inhibits the activity of APC by blocking the binding of Cdc20 to APC. Surprisingly, the kinase activity of BubR1 is not required for the inhibition of APCCdc20. BubR1 also prevents the activation of APCCdc20 in Xenopus egg extracts, and restores the mitotic arrest in Cdc20-overexpressing cells treated with nocodazole. Because BubR1 also interacts with the mitotic motor CENP-E, the ability of BubR1 to inhibit APC may be regulated by kinetochore tension or occupancy.
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Affiliation(s)
- Z Tang
- Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 75390, USA
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358
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Zhang Y, Lees E. Identification of an overlapping binding domain on Cdc20 for Mad2 and anaphase-promoting complex: model for spindle checkpoint regulation. Mol Cell Biol 2001; 21:5190-9. [PMID: 11438673 PMCID: PMC87243 DOI: 10.1128/mcb.21.15.5190-5199.2001] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Activation of the anaphase-promoting complex (APC) is required for anaphase initiation and for exit from mitosis in mammalian cells. Cdc20, which specifically recognizes APC substrates involved in the metaphase-to-anaphase transition, plays a pivotal role in APC activation through direct interaction with the APC. The activation of the APC by Cdc20 is prevented by the interaction of Cdc20 with Mad2 when the spindle checkpoint is activated. Using deletion mutagenesis and peptide mapping, we have identified the sequences in Cdc20 that target it to Mad2 and the APC, respectively. These sequences are distinct but overlapping, providing a possible structural explanation for the internal modulation of the APC-Cdc20 complex by Mad2. In the course of these studies, a truncation mutant of Cdc20 (1-153) that constitutively binds Mad2 but fails to bind the APC was identified. Overexpression of this mutant induces the formation of multinucleated cells and increases their susceptibility to undergoing apoptosis when treated with microtubule-inhibiting drugs. Our experiments demonstrate that disruption of the Mad2-Cdc20 interaction perturbs the mitotic checkpoint, leading to premature activation of the APC, sensitizing the cells to the cytotoxic effects of microtubule-inhibiting drugs.
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Affiliation(s)
- Y Zhang
- Department of Oncology, DNAX Research Institute, Palo Alto, California 94304-1104, USA
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359
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Kornitzer D, Sharf R, Kleinberger T. Adenovirus E4orf4 protein induces PP2A-dependent growth arrest in Saccharomyces cerevisiae and interacts with the anaphase-promoting complex/cyclosome. J Cell Biol 2001; 154:331-44. [PMID: 11470822 PMCID: PMC2150760 DOI: 10.1083/jcb.200104104] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adenovirus early region 4 open reading frame 4 (E4orf4) protein has been reported to induce p53-independent, protein phosphatase 2A (PP2A)-dependent apoptosis in transformed mammalian cells. In this report, we show that E4orf4 induces an irreversible growth arrest in Saccharomyces cerevisiae at the G2/M phase of the cell cycle. Growth inhibition requires the presence of yeast PP2A-Cdc55, and is accompanied by accumulation of reactive oxygen species. E4orf4 expression is synthetically lethal with mutants defective in mitosis, including Cdc28/Cdk1 and anaphase-promoting complex/cyclosome (APC/C) mutants. Although APC/C activity is inhibited in the presence of E4orf4, Cdc28/Cdk1 is activated and partially counteracts the E4orf4-induced cell cycle arrest. The E4orf4-PP2A complex physically interacts with the APC/C, suggesting that E4orf4 functions by directly targeting PP2A to the APC/C, thereby leading to its inactivation. Finally, we show that E4orf4 can induce G2/M arrest in mammalian cells before apoptosis, indicating that E4orf4-induced events in yeast and mammalian cells are highly conserved.
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Affiliation(s)
- D Kornitzer
- The Gonda Center of Molecular Microbiology, The Bruce Rappaport Faculty of Medicine, Technion, Haifa 31096, Israel
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360
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Hernando E, Orlow I, Liberal V, Nohales G, Benezra R, Cordon-Cardo C. Molecular analyses of the mitotic checkpoint components hsMAD2, hBUB1 and hBUB3 in human cancer. Int J Cancer 2001; 95:223-7. [PMID: 11400114 DOI: 10.1002/1097-0215(20010720)95:4<223::aid-ijc1038>3.0.co;2-l] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
During the metaphase-anaphase transition, the spindle checkpoint prevents segregation of chromosomes if the spindle assembly is perturbed. Critical components of this checkpoint are the MAD and BUB families of proteins, which prevent the proteolysis of Pds1 and B cyclins, producing mitotic arrest. In the present study, we first intended to resolve the role of the hsMAD2 gene in human cancer by determining the potential presence of hsMAD2 mutations in 44 primary bladder tumors, 42 soft-tissue sarcomas and 10 hepatocellular carcinomas. The entire coding region of the hsMAD2 gene was analyzed using PCR-SSCP and sequencing. One of the bladder tumor samples showed a point mutation consisting of a transition, ATC-->GTC (Ile-->Val) in codon 190 of hsMAD2. However, no differences were found in the mitotic arrest between cells transfected with mutant and wild-type MAD2 cDNA. We also identified mobility shifts in hsMAD2 in both normal and tumor DNA in 3 bladder tumors, 3 soft-tissue sarcomas and 1 hepatocellular carcinoma, consistent with a polymorphism at codon 143, CCA-->CCG (Pro-->Pro). Another polymorphism was identified in a hepatocellular carcinoma case at codon 22, GAG-->GAA (Glu-->Glu). In addition, a subgroup of 67 primary tumors was analyzed by Southern blot hybridization. No deletion or visible re-arrangements were detected by comparing tumor and normal DNA band signals. Two other important components of the spindle mitotic checkpoint, hBUB1 and hBUB3, were also screened for mutations: hBUB1 in 43 bladder tumors and 9 bladder cell lines and hBUB3 only in the cell lines. Two polymorphisms were found in hBUB1 at positions 144, CAG-->CAA (Gln-->Gln) in 1 primary tumor and 1 bladder cell line, and 913 (ATC-->ATT, Ile-->Ile) in 1 primary tumor. We did not find sequence alterations in hBUB3. These results suggest that mutations of the hsMAD2, hBUB1 and hBUB3 genes are very rare in bladder tumors and that hsMAD2 alterations are also infrequent in soft-tissue sarcomas and hepatocellular carcinomas.
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Affiliation(s)
- E Hernando
- Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
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361
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Abstract
Anaphase-promoting complex (APC), a ubiquitin ligase, controls both sister chromatid separation and mitotic exit. The APC is activated in mitosis and G1 by CDC20 and CDH1, and inhibited by the checkpoint protein MAD2, a specific inhibitor of CDC20. We show here that a MAD2 homolog MAD2B also inhibits APC. In contrast to MAD2, MAD2B inhibits both CDH1-APC and CDC20-APC. This inhibition is targeted to CDH1 and CDC20, but not directly to APC. Unlike MAD2, whose interaction with MAD1 is required for mitotic checkpoint control, MAD2B does not interact with MAD1, suggesting that MAD2B may relay a different cellular signal to APC.
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Affiliation(s)
- J Chen
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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362
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Pfleger CM, Salic A, Lee E, Kirschner MW. Inhibition of Cdh1-APC by the MAD2-related protein MAD2L2: a novel mechanism for regulating Cdh1. Genes Dev 2001; 15:1759-64. [PMID: 11459825 PMCID: PMC312740 DOI: 10.1101/gad.897901] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Exit from mitosis requires the degradation of regulatory proteins including the mitotic cyclins and securin through ubiquitination by the anaphase promoting complex (APC) bound to Cdc20 or Cdh1. Cdc20-APC is regulated through inhibition by the spindle assembly checkpoint protein MAD2. Knowledge of Cdh1-APC regulation is limited to the phosphorylation-dependent dissociation of Cdh1 from APC. We report a novel means of regulating Cdh1 by the MAD2-related gene, MAD2L2. MAD2L2 specifically binds and inhibits Cdh1-APC, paralleling the effect of MAD2 on Cdc20. We suggest that MAD2L2 and MAD2 inhibit the release of substrates from APC and propose a mechanism of inhibition.
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Affiliation(s)
- C M Pfleger
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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363
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Abrieu A, Magnaghi-Jaulin L, Kahana JA, Peter M, Castro A, Vigneron S, Lorca T, Cleveland DW, Labbé JC. Mps1 is a kinetochore-associated kinase essential for the vertebrate mitotic checkpoint. Cell 2001; 106:83-93. [PMID: 11461704 DOI: 10.1016/s0092-8674(01)00410-x] [Citation(s) in RCA: 250] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The mitotic checkpoint acts to inhibit entry into anaphase until all chromosomes have successfully attached to spindle microtubules. Unattached kinetochores are believed to release an activated form of Mad2 that inhibits APC/C-dependent ubiquitination and subsequent proteolysis of components needed for anaphase onset. Using Xenopus egg extracts, a vertebrate homolog of yeast Mps1p is shown here to be a kinetochore-associated kinase, whose activity is necessary to establish and maintain the checkpoint. Since high levels of Mad2 overcome checkpoint loss in Mps1-depleted extracts, Mps1 acts upstream of Mad2-mediated inhibition of APC/C. Mps1 is essential for the checkpoint because it is required for recruitment and retention of active CENP-E at kinetochores, which in turn is necessary for kinetochore association of Mad1 and Mad2.
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Affiliation(s)
- A Abrieu
- Ludwig Institute for Cancer Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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364
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Jallepalli PV, Waizenegger IC, Bunz F, Langer S, Speicher MR, Peters JM, Kinzler KW, Vogelstein B, Lengauer C. Securin is required for chromosomal stability in human cells. Cell 2001; 105:445-57. [PMID: 11371342 DOI: 10.1016/s0092-8674(01)00340-3] [Citation(s) in RCA: 298] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Abnormalities of chromosome number are the most common genetic aberrations in cancer. The mechanisms regulating the fidelity of mitotic chromosome transmission in mammalian cells are therefore of great interest. Here we show that human cells without an hSecurin gene lose chromosomes at a high frequency. This loss was linked to abnormal anaphases during which cells underwent repetitive unsuccessful attempts to segregate their chromosomes. The abnormal mitoses were associated with biochemical defects in the activation of separin, the sister-separating protease, rendering it unable to cleave the cohesin subunit Scc1 efficiently. These results illuminate the function of mammalian securin and show that it is essential for the maintenance of euploidy.
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Affiliation(s)
- P V Jallepalli
- The Johns Hopkins Oncology Center, 1650 Orleans Street, Baltimore, MD 21231, USA
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365
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Sharp-Baker H, Chen RH. Spindle checkpoint protein Bub1 is required for kinetochore localization of Mad1, Mad2, Bub3, and CENP-E, independently of its kinase activity. J Cell Biol 2001; 153:1239-50. [PMID: 11402067 PMCID: PMC2192030 DOI: 10.1083/jcb.153.6.1239] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2000] [Accepted: 05/04/2001] [Indexed: 12/16/2022] Open
Abstract
The spindle checkpoint inhibits the metaphase to anaphase transition until all the chromosomes are properly attached to the mitotic spindle. We have isolated a Xenopus homologue of the spindle checkpoint component Bub1, and investigated its role in the spindle checkpoint in Xenopus egg extracts. Antibodies raised against Bub1 recognize a 150-kD phosphoprotein at both interphase and mitosis, but the molecular mass is reduced to 140 upon dephosphorylation in vitro. Bub1 is essential for the establishment and maintenance of the checkpoint and is localized to kinetochores, similar to the spindle checkpoint complex Mad1-Mad2. However, Bub1 differs from Mad1-Mad2 in that Bub1 remains on kinetochores that have attached to microtubules; the protein eventually dissociates from the kinetochore during anaphase. Immunodepletion of Bub1 abolishes the spindle checkpoint and the kinetochore binding of the checkpoint proteins Mad1, Mad2, Bub3, and CENP-E. Interestingly, reintroducing either wild-type or kinase-deficient Bub1 protein restores the checkpoint and the kinetochore localization of these proteins. Our studies demonstrate that Bub1 plays a central role in triggering the spindle checkpoint signal from the kinetochore, and that its kinase activity is not necessary for the spindle checkpoint in Xenopus egg extracts.
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Affiliation(s)
- Hilary Sharp-Baker
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Rey-Huei Chen
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
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366
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Reimann JD, Freed E, Hsu JY, Kramer ER, Peters JM, Jackson PK. Emi1 is a mitotic regulator that interacts with Cdc20 and inhibits the anaphase promoting complex. Cell 2001; 105:645-55. [PMID: 11389834 DOI: 10.1016/s0092-8674(01)00361-0] [Citation(s) in RCA: 297] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
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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Affiliation(s)
- J D Reimann
- Department of Pathology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305, USA
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367
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Wang H, Liu D, Wang Y, Qin J, Elledge SJ. Pds1 phosphorylation in response to DNA damage is essential for its DNA damage checkpoint function. Genes Dev 2001; 15:1361-72. [PMID: 11390356 PMCID: PMC312708 DOI: 10.1101/gad.893201] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In Saccharomyces cerevisiae, Pds1 is an anaphase inhibitor and plays an essential role in DNA damage and spindle checkpoint pathways. Pds1 is phosphorylated in response to DNA damage but not spindle disruption, indicating distinct mechanisms delaying anaphase entry. Phosphorylation of Pds1 is Mec1 and Chk1 dependent in vivo. Here, we show that Pds1 is phosphorylated at multiple sites in vivo in response to DNA damage by Chk1. Mutation of the Chk1 phosphorylation sites on Pds1 abolished most of its DNA damage-inducible phosphorylation and its checkpoint function, whereas its anaphase inhibitor functions and spindle checkpoint functions remain intact. Loss of Pds1 phosphorylation correlates with APC-dependent Pds1 destruction in response to DNA damage. We also show that APC(Cdc20) is active in preanaphase arrested cells after DNA damage. This suggests that Pds1 is stabilized by phosphorylation in response to DNA damage, but APC(Cdc20) activity is not altered. Our results indicate that phosphorylation of Pds1 by Chk1 is the key function of Chk1 required to prevent anaphase entry.
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Affiliation(s)
- H Wang
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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368
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Abstract
p55Cdc/Cdc20 is expressed in cycling mammalian cells and has been shown to be an activator of the mitotic spindle assembly checkpoint. We previously showed that overexpression of p55Cdc/Cdc20 in myeloid cells resulted in accelerated apoptosis and inhibition of granulocyte differentiation in the murine myeloid cell line 32Dcl3. p55Cdc/Cdc20 protein expression is detected in cells at late G1 phase of the cell cycle but is maximal during G2 phase. We report in this paper that inducible expression of p55Cdc/Cdc20 in 32Dcl3 cells results in premature transition from G1 to S phase. To characterize the mechanism of this early transition, we examined the expression of critical regulatory proteins during the cell cycle. Although expression of cyclin D, cyclin E, cdk2, and cdc2 did not change significantly between p55Cdc/Cdc20-overexpressing and control cells, p27Kip1 protein levels were lower and cdk2 activity higher during G1 to S transition in p55Cdc/Cdc20-overexpressing cells compared to control cells. Cyclin B1 levels were lower at early G1 phase in cells overexpressing p55Cdc/Cdc20. Our results suggest that p55Cdc/Cdc20 may play an important role in G1 to S transition during myelopoiesis.
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Affiliation(s)
- M L Lin
- Department of Pediatrics, UCLA School of Medicine, Los Angeles, California 90095-1752, USA
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369
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Kaspar M, Dienemann A, Schulze C, Sprenger F. Mitotic degradation of cyclin A is mediated by multiple and novel destruction signals. Curr Biol 2001; 11:685-90. [PMID: 11369231 DOI: 10.1016/s0960-9822(01)00205-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Exit from mitosis requires Cdk1 inactivation, with the most prominent mechanism of Cdk1 inactivation being proteolysis of mitotic cyclins [1]. In higher eukaryotes this involves sequential destruction of A- and B-type cyclins. CycA is destroyed first, and CycA/Cdk1 inactivation is required for the metaphase-to-anaphase transition [2]. The degradation of CycA is delayed in response to DNA damage but is not prevented when the spindle checkpoint is activated [3, 4]. Cyclin destruction is thought to be mediated by a conserved motif, the destruction box (D box). Like B-type cyclins, A-type cyclins contain putative destruction box sequences in their N termini [5]. However, no detailed in vivo analysis of the sequence requirements for CycA destruction has been described so far. Here we tested several mutations in the CycA coding region for destruction in Drosophila embryos. We show that D box sequences are not essential for mitotic destruction of CycA. Destruction is mediated by at least three different elements that act in an overlapping fashion to mediate its mitotic degradation.
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Affiliation(s)
- M Kaspar
- Institut für Genetik, Universität zu Köln, Weyertal 121, D-50931, Köln, Germany
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370
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Skoufias DA, Andreassen PR, Lacroix FB, Wilson L, Margolis RL. Mammalian mad2 and bub1/bubR1 recognize distinct spindle-attachment and kinetochore-tension checkpoints. Proc Natl Acad Sci U S A 2001; 98:4492-7. [PMID: 11274370 PMCID: PMC31862 DOI: 10.1073/pnas.081076898] [Citation(s) in RCA: 224] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Metaphase checkpoint controls sense abnormalities of chromosome alignment during mitosis and prevent progression to anaphase until proper alignment has been attained. A number of proteins, including mad2, bub1, and bubR1, have been implicated in the metaphase checkpoint control in mammalian cells. Metaphase checkpoints have been shown, in various systems, to read loss of either spindle tension or microtubule attachment at the kinetochore. Characteristically, HeLa cells arrest in metaphase in response to low levels of microtubule inhibitors that leave an intact spindle and a metaphase plate. Here we show that the arrest induced by nanomolar vinblastine correlates with loss of tension at the kinetochore, and that in response the checkpoint proteins bub1 and bubR1 are recruited to the kinetochore but mad2 is not. mad2 remains competent to respond and is recruited at higher drug doses that disrupt spindle association with the kinetochores. Further, although mad2 forms a complex with cdc20, it does not associate with bub1 or bubR1. We conclude that mammalian bub1/bubR1 and mad2 operate as elements of distinct pathways sensing tension and attachment, respectively.
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Affiliation(s)
- D A Skoufias
- Institut de Biologie Structurale J.-P. Ebel (Commissariat à l'Energie Atomique-Centre National de la Recherche Scientifique), 41 Rue Jules Horowitz, 38027 Grenoble Cedex 1, France
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371
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Geley S, Kramer E, Gieffers C, Gannon J, Peters JM, Hunt T. Anaphase-promoting complex/cyclosome-dependent proteolysis of human cyclin A starts at the beginning of mitosis and is not subject to the spindle assembly checkpoint. J Cell Biol 2001; 153:137-48. [PMID: 11285280 PMCID: PMC2185534 DOI: 10.1083/jcb.153.1.137] [Citation(s) in RCA: 334] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2000] [Accepted: 02/07/2001] [Indexed: 11/22/2022] Open
Abstract
Cyclin A is a stable protein in S and G2 phases, but is destabilized when cells enter mitosis and is almost completely degraded before the metaphase to anaphase transition. Microinjection of antibodies against subunits of the anaphase-promoting complex/cyclosome (APC/C) or against human Cdc20 (fizzy) arrested cells at metaphase and stabilized both cyclins A and B1. Cyclin A was efficiently polyubiquitylated by Cdc20 or Cdh1-activated APC/C in vitro, but in contrast to cyclin B1, the proteolysis of cyclin A was not delayed by the spindle assembly checkpoint. The degradation of cyclin B1 was accelerated by inhibition of the spindle assembly checkpoint. These data suggest that the APC/C is activated as cells enter mitosis and immediately targets cyclin A for degradation, whereas the spindle assembly checkpoint delays the degradation of cyclin B1 until the metaphase to anaphase transition. The "destruction box" (D-box) of cyclin A is 10-20 residues longer than that of cyclin B. Overexpression of wild-type cyclin A delayed the metaphase to anaphase transition, whereas expression of cyclin A mutants lacking a D-box arrested cells in anaphase.
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Affiliation(s)
- Stephan Geley
- Imperial Cancer Research Fund Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom
| | - Edgar Kramer
- Institute for Molecular Pathology, A-1030 Vienna, Austria
| | | | - Julian Gannon
- Imperial Cancer Research Fund Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom
| | | | - Tim Hunt
- Imperial Cancer Research Fund Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom
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372
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Abstract
Mitosis is controlled by the specific and timely degradation of key regulatory proteins, notably the mitotic cyclins that bind and activate the cyclin-dependent kinases (Cdks). In animal cells, cyclin A is always degraded before cyclin B, but the exact timing and the mechanism underlying this are not known. Here we use live cell imaging to show that cyclin A begins to be degraded just after nuclear envelope breakdown. This degradation requires the 26S proteasome, but is not affected by the spindle checkpoint. Neither deletion of its destruction box nor disrupting Cdk binding prevents cyclin A proteolysis, but Cdk binding is necessary for degradation at the correct time. We also show that increasing the levels of cyclin A delays chromosome alignment and sister chromatid segregation. This delay depends on the proteolysis of cyclin A and is not caused by a lag in the bipolar attachment of chromosomes to the mitotic spindle, nor is it mediated via the spindle checkpoint. Thus, proteolysis that is not under the control of the spindle checkpoint is required for chromosome alignment and anaphase.
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Affiliation(s)
- Nicole den Elzen
- Wellcome/Cancer Research Campaign Institute, Cambridge CB2 1QR, United Kingdom
| | - Jonathon Pines
- Wellcome/Cancer Research Campaign Institute, Cambridge CB2 1QR, United Kingdom
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373
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Huang TS, Shu CH, Chao Y, Chen LT. Evaluation of GL331 in combination with paclitaxel: GL331's interference with paclitaxel-induced cell cycle perturbation and apoptosis. Anticancer Drugs 2001; 12:259-66. [PMID: 11290873 DOI: 10.1097/00001813-200103000-00011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Combination of selecting agents that act on different cellular mechanisms is a common strategy in cancer chemotherapy. GL331 is a new potent topoisomerase II (Topo II) poison; distinctly, paclitaxel is a microtubule-interfering cancer chemotherapeutic agent. In this study, we intended to evaluate the efficacy of combining GL331 with paclitaxel in cell killing and apoptotic induction in nasopharyngeal carcinoma NPC-TW01 cells. By MTT and internucleosomal DNA cleavage assays, we found that pretreatment or simultaneous treatment of NPC-TW01 cells with GL331 could significantly interfere with paclitaxel's cell killing and apoptosis-inducing activity. When the administration schedule was reversed, the cytotoxicity of GL331 was attenuated by paclitaxel pretreatment. The anti-cancer activity produced by combining GL331 with paclitaxel was obviously lower than the addition of the activities of two individual agents. NPC-TW01 cells were treated with GL331 and 3H-labeled paclitaxel simultaneously or with GL331 before 3H-labeled paclitaxel. In both conditions, GL331 did not reduce the [3H]paclitaxel level in the cells, suggesting that GL331's interference with paclitaxel's cell-killing and apoptosis-inducing efficacy did not result from any inhibition of cellular uptake or retention of paclitaxel. In addition, we found that GL331-induced perturbation of cell cycle progression dramatically over-rode the patterns of mitotic arrest induced by paclitaxel, and the mechanism could be the inhibition of cyclin B1/CDC2 kinase and MAD2 checkprotein activities.
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Affiliation(s)
- T S Huang
- Cooperative Laboratory, Cancer Research Division, National Health Research Institutes; Taipei, Taiwan, ROC.
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374
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Zur A, Brandeis M. Securin degradation is mediated by fzy and fzr, and is required for complete chromatid separation but not for cytokinesis. EMBO J 2001; 20:792-801. [PMID: 11179223 PMCID: PMC145417 DOI: 10.1093/emboj/20.4.792] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
We have studied the ubiquitination and degradation patterns of the human securin/PTTG protein. We show that, in contrast to budding yeast pds1, securin degradation is catalyzed by both fzy (fizzy/cdc20) and fzr (fizzy-related/cdh1/hct1). Both fzy and fzr also induce the APC/C to ubiquitinate securin in vitro. Securin degradation is mediated by an RXXL destruction box and a KEN box, and is inhibited only when both sequences are mutated. Interestingly, the non-degradable securin mutant is also partially ubiquitinated by fzy and fzr in vitro. Expressing the non-degradable securin mutant in cells frequently resulted in incomplete chromatid separation and gave rise to daughter cells connected by a thin chromatin fiber, presumably of chromosomes that failed to split completely. Strikingly, the mutant securin did not prevent the majority of sister chromatids from separating completely, nor did it prevent mitotic cyclin degradation and cytokinesis. This phenotype, reminiscent of the fission yeast cut (cells untimely torn) phenotype, is reported here for the first time in mammals.
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Affiliation(s)
| | - Michael Brandeis
- Department of Genetics, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Corresponding author e-mail:
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375
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Schwab MS, Roberts BT, Gross SD, Tunquist BJ, Taieb FE, Lewellyn AL, Maller JL. Bub1 is activated by the protein kinase p90(Rsk) during Xenopus oocyte maturation. Curr Biol 2001; 11:141-50. [PMID: 11231148 DOI: 10.1016/s0960-9822(01)00045-8] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND The kinetochore attachment (spindle assembly) checkpoint arrests cells in metaphase to prevent exit from mitosis until all the chromosomes are aligned properly at the metaphase plate. The checkpoint operates by preventing activation of the anaphase-promoting complex (APC), which triggers anaphase by degrading mitotic cyclins and other proteins. This checkpoint is active during normal mitosis and upon experimental disruption of the mitotic spindle. In yeast, the serine/threonine protein kinase Bub1 and the WD-repeat protein Bub3 are elements of a signal transduction cascade that regulates the kinetochore attachment checkpoint. In mammalian cells, activated MAPK is present on kinetochores during mitosis and activity is upregulated by the spindle assembly checkpoint. In vertebrate unfertilized eggs, a special form of meiotic metaphase arrest by cytostatic factor (CSF) is mediated by MAPK activation of the protein kinase p90(Rsk), which leads to inhibition of the APC. However, it is not known whether CSF-dependent metaphase arrest caused by p90(Rsk) involves components of the spindle assembly checkpoint. RESULTS xBub1 is present in resting oocytes and its protein level increases slightly during oocyte maturation and early embryogenesis. In Xenopus oocytes, Bub1 is localized to kinetochores during both meiosis I and meiosis II, and the electrophoretic mobility of Bub1 upon SDS-PAGE decreases during meiosis I, reflecting phosphorylation and activation of the enzyme. The activation of Bub1 can be induced in interphase egg extracts by selective stimulation of the MAPK pathway by c-Mos, a MAPKKK. In oocytes treated with the MEK1 inhibitor U0126, the MAPK pathway does not become activated, and Bub1 remains in its low-activity, unshifted form. Injection of a constitutively active target of MAPK, the protein kinase p90(Rsk), restores the activation of Bub1 in the presence of U0126. Moreover, purified p90(Rsk) phosphorylates Bub1 in vitro and increases its protein kinase activity. CONCLUSIONS Bub1, an upstream component of the kinetochore attachment checkpoint, is activated during meiosis in Xenopus in a MAPK-dependent manner. Moreover, a single substrate of MAPK, p90(Rsk), is sufficient to activate Bub1 in vitro and in vivo. These results indicate that in vertebrate eggs, kinetochore attachment/spindle assembly checkpoint proteins, including Bub1, are downstream of p90(Rsk) and may be effectors of APC inhibition and CSF-dependent metaphase arrest by p90(Rsk).
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Affiliation(s)
- M S Schwab
- Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado, School of Medicine, 4200 East Ninth Ave., Denver, CO 80262, USA
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376
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Michel LS, Liberal V, Chatterjee A, Kirchwegger R, Pasche B, Gerald W, Dobles M, Sorger PK, Murty VV, Benezra R. MAD2 haplo-insufficiency causes premature anaphase and chromosome instability in mammalian cells. Nature 2001; 409:355-9. [PMID: 11201745 DOI: 10.1038/35053094] [Citation(s) in RCA: 561] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The mitotic checkpoint protein hsMad2 is required to arrest cells in mitosis when chromosomes are unattached to the mitotic spindle. The presence of a single, lagging chromosome is sufficient to activate the checkpoint, producing a delay at the metaphase-anaphase transition until the last spindle attachment is made. Complete loss of the mitotic checkpoint results in embryonic lethality owing to chromosome mis-segregation in various organisms. Whether partial loss of checkpoint control leads to more subtle rates of chromosome instability compatible with cell viability remains unknown. Here we report that deletion of one MAD2 allele results in a defective mitotic checkpoint in both human cancer cells and murine primary embryonic fibroblasts. Checkpoint-defective cells show premature sister-chromatid separation in the presence of spindle inhibitors and an elevated rate of chromosome mis-segregation events in the absence of these agents. Furthermore, Mad2+/- mice develop lung tumours at high rates after long latencies, implicating defects in the mitotic checkpoint in tumorigenesis.
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Affiliation(s)
- L S Michel
- Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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377
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Peter M, Castro A, Lorca T, Le Peuch C, Magnaghi-Jaulin L, Dorée M, Labbé JC. The APC is dispensable for first meiotic anaphase in Xenopus oocytes. Nat Cell Biol 2001; 3:83-7. [PMID: 11146630 DOI: 10.1038/35050607] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Here we show that segregation of homologous chromosomes and that of sister chromatids are differentially regulated in Xenopus and possibly in other higher eukaryotes. Upon hormonal stimulation, Xenopus oocytes microinjected with antibodies against the anaphase-promoting complex (APC) activator Fizzy or the APC core subunit Cdc27, or with the checkpoint protein Mad2, a destruction-box peptide or methylated ubiquitin, readily progress through the first meiotic cell cycle and arrest at second meiotic metaphase. However, they fail to segregate sister chromatids and remain arrested at second meiotic metaphase when electrically stimulated or when treated with ionophore A34187, two treatments that mimic fertilization and readily induce chromatid segregation in control oocytes. Thus, APC is required for second meiotic anaphase but not for first meiotic anaphase.
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Affiliation(s)
- M Peter
- CRBM, UPR 1086 CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France
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378
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Affiliation(s)
- J V Shah
- Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA 92093, USA
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379
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Percy MJ, Myrie KA, Neeley CK, Azim JN, Ethier SP, Petty EM. Expression and mutational analyses of the human MAD2L1 gene in breast cancer cells. Genes Chromosomes Cancer 2000; 29:356-62. [PMID: 11066082 DOI: 10.1002/1098-2264(2000)9999:9999<::aid-gcc1044>3.0.co;2-n] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Breast cancer is a heterogeneous disorder in which most tumors display some degree of aneuploidy, especially those at later stages of the disease. Aneuploidy and associated chromosome instability may be important in the progression of mammary tumorigenesis. Aneuploidy is prevented during normal cell division in part through regulation of a mitotic spindle checkpoint where mitotic arrest prevents segregation of misaligned chromosomes into daughter cells at anaphase. Mitotic arrest genes, including the MAD family, which was originally characterized in yeast, help regulate normal function of the mitotic spindle checkpoint. Decreased expression of the human gene MAD2L1 was previously reported in a breast cancer cell line exhibiting chromosome instability and aneuploidy. To explore further the potential role of MAD2L1 in breast cancer, we analyzed MAD2L1 gene expression in 13 minimally to grossly aneuploid human breast cancer cell lines and found significant differences of expression in three lines. Sequence analysis of MAD2L1 cDNA in these as well as nine additional aneuploid breast cancer and five immortalized normal human mammary epithelial cell lines revealed one heterozygous frameshift (572 del A) mutation in a cancer cell line that demonstrated a high level of transcript expression. In addition, two 3'UTR sequence variants were noted in breast cancer cell lines. The 572 del A mutation creates a truncated MAD2 protein product. Further functional studies in primary breast tumors are therefore warranted to determine the potential role MAD2L1 may play in breast cancer.
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Affiliation(s)
- M J Percy
- Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA
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380
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Daum JR, Tugendreich S, Topper LM, Jorgensen PM, Hoog C, Hieter P, Gorbsky GJ. The 3F3/2 anti-phosphoepitope antibody binds the mitotically phosphorylated anaphase-promoting complex/cyclosome. Curr Biol 2000; 10:R850-2. [PMID: 11114529 DOI: 10.1016/s0960-9822(00)00836-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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381
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Yamada HY, Matsumoto S, Matsumoto T. High dosage expression of a zinc finger protein, Grt1, suppresses a mutant of fission yeast slp1(+), a homolog of CDC20/p55CDC/Fizzy. J Cell Sci 2000; 113 ( Pt 22):3989-99. [PMID: 11058086 DOI: 10.1242/jcs.113.22.3989] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Selective proteolysis at and after the onset of anaphase is a key cell cycle event required for sister chromatid separation as well as for exit from mitosis. It requires ubiquitination of substrates by Anaphase Promoting Complex(APC)/Cyclosome. Slp1, a WD-repeat protein, is a putative activator for APC in fission yeast. With another WD- repeat protein, Ste9/Srw1, it is thought to promote the proteolysis in a substrate-specific manner. We report here characterization of a temperature-sensitive (ts) slp1 mutant and its high-dosage suppressor, grt1(+). In cells arrested in metaphase, wild-type Slp1 was preferentially found in a complex with hyperphosphorylated Cut9 (subunit of APC), whereas the ts Slp1 protein, lacking the last 113 amino acids, failed to interact with Cut9. The temperature sensitivity was suppressed by high dosage expression of a zinc finger protein, Grt1. The ts slp1 mutant was unable to maintain the normal level of Grt1 protein. The reduction in the Grt1 level may be a primary defect since high dosage expression of grt1(+) rescues the slp1 mutant. The grt1-suppression had an additive effect to ste9 and wee1-50, both of which partially suppress the ts slp1 mutant. Therefore, grt1(+) would define an independent pathway that facilitates the function of Slp1.
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Affiliation(s)
- H Y Yamada
- Departments of Radiation Oncology and Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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382
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Krishnan R, Pangilinan F, Lee C, Spencer F. Saccharomyces cerevisiae BUB2 prevents mitotic exit in response to both spindle and kinetochore damage. Genetics 2000; 156:489-500. [PMID: 11014800 PMCID: PMC1461296 DOI: 10.1093/genetics/156.2.489] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The spindle assembly checkpoint-mediated mitotic arrest depends on proteins that signal the presence of one or more unattached kinetochores and prevents the onset of anaphase in the presence of kinetochore or spindle damage. In the presence of either damage, bub2 cells initiate a preanaphase delay but do not maintain it. Inappropriate sister chromatid separation in nocodazole-treated bub2 cells is prevented when mitotic exit is blocked using a conditional tem1(c) mutant, indicating that the preanaphase failure in bub2 cells is a consequence of events downstream of TEM1 in the mitotic exit pathway. Using a conditional bub2(tsd) mutant, we demonstrate that the continuous presence of Bub2 protein is required for maintaining spindle damage-induced arrest. BUB2 is not required to maintain a DNA damage checkpoint arrest, revealing a specificity for spindle assembly checkpoint function. In a yeast two-hybrid assay and in vitro, Bub2 protein interacts with the septin protein Cdc3, which is essential for cytokinesis. These data support the view that the spindle assembly checkpoint encompasses regulation of distinct mitotic steps, including a MAD2-directed block to anaphase initiation and a BUB2-directed block to TEM1-dependent exit.
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Affiliation(s)
- R Krishnan
- Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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383
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Jackson PK, Eldridge AG, Freed E, Furstenthal L, Hsu JY, Kaiser BK, Reimann JD. The lore of the RINGs: substrate recognition and catalysis by ubiquitin ligases. Trends Cell Biol 2000; 10:429-39. [PMID: 10998601 DOI: 10.1016/s0962-8924(00)01834-1] [Citation(s) in RCA: 475] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Recently, many new examples of E3 ubiquitin ligases or E3 enzymes have been found to regulate a host of cellular processes. These E3 enzymes direct the formation of multiubiquitin chains on specific protein substrates, and - typically - the subsequent destruction of those proteins. We discuss how the modular architecture of E3 enzymes connects one of two distinct classes of catalytic domains to a wide range of substrate-binding domains. In one catalytic class, a HECT domain transfers ubiquitin directly to substrate bound to a non-catalytic domain. Members of the other catalytic class, found in the SCF, VBC and APC complexes, use a RING finger domain to facilitate ubiquitylation. The separable substrate-recognition domains of E3 enzymes provides a flexible means of linking a conserved ubiquitylation function to potentially thousands of ubiquitylated substrates in eukaryotic cells.
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Affiliation(s)
- P K Jackson
- Dept of Pathology, The Stanford University School of Medicine, Stanford, CA 94305-5324, USA.
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384
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Howell BJ, Hoffman DB, Fang G, Murray AW, Salmon ED. Visualization of Mad2 dynamics at kinetochores, along spindle fibers, and at spindle poles in living cells. J Cell Biol 2000; 150:1233-50. [PMID: 10995431 PMCID: PMC2150717 DOI: 10.1083/jcb.150.6.1233] [Citation(s) in RCA: 267] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The spindle checkpoint prevents errors in chromosome segregation by inhibiting anaphase onset until all chromosomes have aligned at the spindle equator through attachment of their sister kinetochores to microtubules from opposite spindle poles. A key checkpoint component is the mitotic arrest-deficient protein 2 (Mad2), which localizes to unattached kinetochores and inhibits activation of the anaphase-promoting complex (APC) through an interaction with Cdc20. Recent studies have suggested a catalytic model for kinetochore function where unattached kinetochores provide sites for assembling and releasing Mad2-Cdc20 complexes, which sequester Cdc20 and prevent it from activating the APC. To test this model, we examined Mad2 dynamics in living PtK1 cells that were either injected with fluorescently labeled Alexa 488-XMad2 or transfected with GFP-hMAD2. Real-time, digital imaging revealed fluorescent Mad2 localized to unattached kinetochores, spindle poles, and spindle fibers depending on the stage of mitosis. FRAP measurements showed that Mad2 is a transient component of unattached kinetochores, as predicted by the catalytic model, with a t(1/2) of approximately 24-28 s. Cells entered anaphase approximately 10 min after Mad2 was no longer detectable on the kinetochores of the last chromosome to congress to the metaphase plate. Several observations indicate that Mad2 binding sites are translocated from kinetochores to spindle poles along microtubules. First, Mad2 that bound to sites on a kinetochore was dynamically stretched in both directions upon microtubule interactions, and Mad2 particles moved from kinetochores toward the poles. Second, spindle fiber and pole fluorescence disappeared upon Mad2 disappearance at the kinetochores. Third, ATP depletion resulted in microtubule-dependent depletion of Mad2 fluorescence at kinetochores and increased fluorescence at spindle poles. Finally, in normal cells, the half-life of Mad2 turnover at poles, 23 s, was similar to kinetochores. Thus, kinetochore-derived sites along spindle fibers and at spindle poles may also catalyze Mad2 inhibitory complex formation.
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Affiliation(s)
- B J Howell
- Department of Biology, CB#3280, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
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385
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Abrieu A, Kahana JA, Wood KW, Cleveland DW. CENP-E as an essential component of the mitotic checkpoint in vitro. Cell 2000; 102:817-26. [PMID: 11030625 DOI: 10.1016/s0092-8674(00)00070-2] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Accurate chromatid separation is monitored by a checkpoint mechanism that delays anaphase onset until all centromeres are correctly attached to the mitotic spindle. Using Xenopus egg extracts, the kinetochore-associated microtubule motor protein CENP-E is now found to be required for establishing and maintaining this checkpoint. When CENP-E function is disrupted by immunodepletion or antibody addition, extracts fail to arrest in response to spindle damage. Mitotic arrest can be restored by addition of high levels of soluble MAD2, demonstrating that the absence of CENP-E eliminates kinetochore-dependent signaling but not the downstream steps in checkpoint signal transduction. Because it directly binds both to spindle microtubules and to the kinetochore-associated checkpoint kinase BUBR1, CENP-E is a central component in the vertebrate checkpoint that modulates signaling activity in a microtubule-dependent manner.
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Affiliation(s)
- A Abrieu
- Ludwig Institute for Cancer Research, University of California San Diego, La Jolla 92093-0660, USA
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386
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Leismann O, Herzig A, Heidmann S, Lehner CF. Degradation of Drosophila PIM regulates sister chromatid separation during mitosis. Genes Dev 2000; 14:2192-205. [PMID: 10970883 PMCID: PMC316890 DOI: 10.1101/gad.176700] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2000] [Accepted: 07/05/2000] [Indexed: 11/25/2022]
Abstract
Drosophila Pimples (PIM) and Three rows (THR) are required for sister chromatid separation in mitosis. PIM accumulates during interphase and is degraded rapidly during mitosis. This degradation is dependent on a destruction box similar to that of B-type cyclins. Nondegradable PIM with a mutant destruction box can rescue sister chromatid separation in pim mutants but only when expressed at low levels. Higher levels of nondegradable PIM, as well as overexpression of wild-type PIM, inhibit sister chromatid separation. Moreover, cells arrested in mitosis before sister chromatid separation (by colcemid or by mutations in fizzy/CDC20) fail to degrade PIM. Thus, although not related by primary sequence, PIM has intriguing functional similarities to the securin proteins of budding yeast, fission yeast, and vertebrates. Whereas these securins are known to form a complex with separins, we show that PIM associates in vivo with THR, which does not contain the conserved separin domain.
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Affiliation(s)
- O Leismann
- Department of Genetics, University of Bayreuth, 95440 Bayreuth, Germany
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387
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Ishida N, Kitagawa M, Hatakeyama S, Nakayama K. Phosphorylation at serine 10, a major phosphorylation site of p27(Kip1), increases its protein stability. J Biol Chem 2000; 275:25146-54. [PMID: 10831586 DOI: 10.1074/jbc.m001144200] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The association of the p27(Kip1) protein with cyclin and cyclin-dependent kinase complexes inhibits their kinase activities and contributes to the control of cell proliferation. The p27(Kip1) protein has now been shown to be phosphorylated in vivo, and this phosphorylation reduces the electrophoretic mobility of the protein. Substitution of Ser(10) with Ala (S10A) markedly reduced the extent of p27(Kip1) phosphorylation and prevented the shift in electrophoretic mobility. Phosphopeptide mapping and phosphoamino acid analysis revealed that phosphorylation at Ser(10) accounted for approximately 70% of the total phosphorylation of p27(Kip1), and the extent of phosphorylation at this site was approximately 25- and 75-fold greater than that at Ser(178) and Thr(187), respectively. The phosphorylation of p27(Kip1) was markedly reduced when the positions of Ser(10) and Pro(11) were reversed, suggesting that a proline-directed kinase is responsible for the phosphorylation of Ser(10). The extent of Ser(10) phosphorylation was markedly increased in cells in the G(0)-G(1) phase of the cell cycle compared with that apparent for cells in S or M phase. The p27(Kip1) protein phosphorylated at Ser(10) was significantly more stable than the unphosphorylated form. Furthermore, a mutant p27(Kip1) in which Ser(10) was replaced with glutamic acid in order to mimic the effect of Ser(10) phosphorylation exhibited a marked increase in stability both in vivo and in vitro compared with the wild-type or S10A mutant proteins. These results suggest that Ser(10) is the major site of phosphorylation of p27(Kip1) and that phosphorylation at this site, like that at Thr(187), contributes to regulation of p27(Kip1) stability.
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Affiliation(s)
- N Ishida
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan
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388
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Yao X, Abrieu A, Zheng Y, Sullivan KF, Cleveland DW. CENP-E forms a link between attachment of spindle microtubules to kinetochores and the mitotic checkpoint. Nat Cell Biol 2000; 2:484-91. [PMID: 10934468 DOI: 10.1038/35019518] [Citation(s) in RCA: 287] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Here we show that suppression of synthesis of the microtubule motor CENP-E (centromere-associated protein E), a component of the kinetochore corona fibres of mammalian centromeres, yields chromosomes that are chronically mono-orientated, with spindles that are flattened along the plane of the substrate. Despite apparently normal microtubule numbers and the continued presence at kinetochores of other microtubule motors, spindle poles fragment in the absence of CENP-E, which implicates this protein in delivery of components from kinetochores to poles. CENP-E represents a link between attachment of spindle microtubules and the mitotic checkpoint signalling cascade, as depletion of this motor leads to profound checkpoint activation, whereas immunoprecipitation reveals a nearly stoichiometric association of CENP-E with the checkpoint kinase BubR1 during mitosis.
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Affiliation(s)
- X Yao
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706, USA
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389
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Tanaka T, Fuchs J, Loidl J, Nasmyth K. Cohesin ensures bipolar attachment of microtubules to sister centromeres and resists their precocious separation. Nat Cell Biol 2000; 2:492-9. [PMID: 10934469 DOI: 10.1038/35019529] [Citation(s) in RCA: 255] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The multisubunit protein complex cohesin is required to establish cohesion between sister chromatids during S phase and to maintain it during G2 and M phases. Cohesin is essential for mitosis, and even partial defects cause very high rates of chromosome loss. In budding yeast, cohesin associates with specific sites which are distributed along the entire length of a chromosome but are more dense in the vicinity of the centromere. Real-time imaging of individual centromeres tagged with green fluorescent protein suggests that cohesin bound to centromeres is important for bipolar attachment to microtubules. This cohesin is, however, incapable of resisting the consequent force, which leads to sister centromere splitting and chromosome stretching. Meanwhile, cohesin bound to sequences flanking the centromeres prevents sister chromatids from completely unzipping and is required to pull back together sister centromeres that have already split. Cohesin therefore has a central role in generating a dynamic tension between microtubules and sister chromatid cohesion at centromeres, which lasts until chromosome segregation is finally promoted by separin-dependent cleavage of the cohesin subunit Scc1p.
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Affiliation(s)
- T Tanaka
- Research Institute of Molecular Pathology, Dr Bohr-Gasse 7, A-1030 Vienna, Austria
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390
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Yamanaka A, Hatakeyama S, Kominami K, Kitagawa M, Matsumoto M, Nakayama K. Cell cycle-dependent expression of mammalian E2-C regulated by the anaphase-promoting complex/cyclosome. Mol Biol Cell 2000; 11:2821-31. [PMID: 10930472 PMCID: PMC14958 DOI: 10.1091/mbc.11.8.2821] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Progression through mitosis requires the precisely timed ubiquitin-dependent degradation of specific substrates. E2-C is a ubiquitin-conjugating enzyme that plays a critical role with anaphase-promoting complex/cyclosome (APC/C) in progression of and exit from M phase. Here we report that mammalian E2-C is expressed in late G(2)/M phase and is degraded as cells exit from M phase. The mammalian E2-C shows an autoubiquitinating activity leading to covalent conjugation to itself with several ubiquitins. The ubiquitination of E2-C is strongly enhanced by APC/C, resulting in the formation of a polyubiquitin chain. The polyubiquitination of mammalian E2-C occurs only when cells exit from M phase. Furthermore, mammalian E2-C contains two putative destruction boxes that are believed to act as recognition motifs for APC/C. The mutation of this motif reduced the polyubiquitination of mammalian E2-C, resulting in its stabilization. These results suggest that mammalian E2-C is itself a substrate of the APC/C-dependent proteolysis machinery, and that the periodic expression of mammalian E2-C may be a novel autoregulatory system for the control of the APC/C activity and its substrate specificity.
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Affiliation(s)
- A Yamanaka
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan
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391
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Flatt PM, Pietenpol JA. Mechanisms of cell-cycle checkpoints: at the crossroads of carcinogenesis and drug discovery. Drug Metab Rev 2000; 32:283-305. [PMID: 11139130 DOI: 10.1081/dmr-100102335] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Human tumors arise from multiple genetic changes that gradually transform growth-limited cells into highly invasive cells that are unresponsive to growth controls. The genetic evolution of normal cells into cancer cells is largely determined by the fidelity of DNA replication, repair, and division. Cell-cycle arrest in response to stress is integral to the maintenance of genomic integrity. The control mechanisms that restrain cell-cycle transition or induce apoptotic signaling pathways after cell stress are known as cell-cycle checkpoints. This review will focus on the mechanisms of cell-cycle checkpoint pathways and how different components of these pathways are frequently altered in the genesis of human tumors. As our knowledge of cell-cycle regulation and checkpoints increases, so will our understanding of how xenobiotic agents can affect these processes to either initiate or inhibit tumorigenesis.
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Affiliation(s)
- P M Flatt
- Department of Biochemistry, Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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392
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Blanco MA, Sánchez-Díaz A, de Prada JM, Moreno S. APC(ste9/srw1) promotes degradation of mitotic cyclins in G(1) and is inhibited by cdc2 phosphorylation. EMBO J 2000; 19:3945-55. [PMID: 10921876 PMCID: PMC306614 DOI: 10.1093/emboj/19.15.3945] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Fission yeast ste9/srw1 is a WD-repeat protein highly homologous to budding yeast Hct1/Cdh1 and Drosophila Fizzy-related that are involved in activating APC/C (anaphase-promoting complex/cyclosome). We show that APC(ste9/srw1) specifically promotes the degradation of mitotic cyclins cdc13 and cig1 but not the S-phase cyclin cig2. APC(ste9/srw1) is not necessary for the proteolysis of cdc13 and cig1 that occurs at the metaphase-anaphase transition but it is absolutely required for their degradation in G(1). Therefore, we propose that the main role of APC(ste9/srw1) is to promote degradation of mitotic cyclins when cells need to delay or arrest the cell cycle in G(1). We also show that ste9/srw1 is negatively regulated by cdc2-dependent protein phosphorylation. In G(1), when cdc2-cyclin kinase activity is low, unphosphorylated ste9/srw1 interacts with APC/C. In the rest of the cell cycle, phosphorylation of ste9/srw1 by cdc2-cyclin complexes both triggers proteolysis of ste9/srw1 and causes its dissociation from the APC/C. This mechanism provides a molecular switch to prevent inactivation of cdc2 in G(2) and early mitosis and to allow its inactivation in G(1).
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Affiliation(s)
- M A Blanco
- Instituto de Microbiología Bioquímica, Departamento de Microbiología y Genética, CSIC/Universidad de Salamanca, Edificio Departamental, Campus Miguel de Unamuno, 37007 Salamanca, Spain
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393
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Yamaguchi S, Okayama H, Nurse P. Fission yeast Fizzy-related protein srw1p is a G(1)-specific promoter of mitotic cyclin B degradation. EMBO J 2000; 19:3968-77. [PMID: 10921878 PMCID: PMC306604 DOI: 10.1093/emboj/19.15.3968] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Downregulation of cyclin-dependent kinase (Cdk)-mitotic cyclin complexes is important during cell cycle progression and in G(1) arrested cells undergoing differentiation. srw1p, a member of the Fizzy-related protein family in fission yeast, is required for the degradation of cdc13p mitotic cyclin B during G(1) arrest. Here we show that srw1p is not required for the degradation of cdc13p during mitotic exit demonstrating that there are two systems operative at different stages of the cell cycle for cdc13p degradation, and that srw1p is phosphorylated by Cdk-cdc13p only becoming dephosphorylated during G(1) arrest. We propose that this phosphorylation targets srw1p for proteolysis and inhibits its activity to promote cdc13p turnover.
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Affiliation(s)
- S Yamaguchi
- Cell Cycle Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK
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394
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Abstract
Ubiquitin-mediated proteolysis of cell cycle regulators is a crucial process during the cell cycle. The anaphase-promoting complex (APC) is a large, multiprotein complex whose E3-ubiquitin ligase activity is required for the ubiquitination of mitotic cyclins and other regulatory proteins that are targeted for destruction during cell division. The recent identification of new APC subunits and regulatory proteins has begun to reveal some of the intricate mechanisms that govern APC regulation. One mechanism is the use of specificity factors to impose temporal control over substrate degradation. A second mechanism is the APC-mediated proteolysis of specific APC regulators. Finally, components of both the APC and the SCF E3 ubiquitin-ligase complex contain several conserved sequence motifs, including WD-40 repeats and cullin homology domains, which suggest that both complexes may use a similar mechanism for substrate ubiquitination.
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Affiliation(s)
- A M Page
- Center for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada.
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395
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Yucel JK, Marszalek JD, McIntosh JR, Goldstein LS, Cleveland DW, Philp AV. CENP-meta, an essential kinetochore kinesin required for the maintenance of metaphase chromosome alignment in Drosophila. J Cell Biol 2000; 150:1-11. [PMID: 10893249 PMCID: PMC2185570 DOI: 10.1083/jcb.150.1.1] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2000] [Accepted: 06/02/2000] [Indexed: 11/22/2022] Open
Abstract
CENP-meta has been identified as an essential, kinesin-like motor protein in Drosophila. The 257-kD CENP-meta protein is most similar to the vertebrate kinetochore-associated kinesin-like protein CENP-E, and like CENP-E, is shown to be a component of centromeric/kinetochore regions of Drosophila chromosomes. However, unlike CENP-E, which leaves the centromere/kinetochore region at the end of anaphase A, the CENP-meta protein remains associated with the centromeric/kinetochore region of the chromosome during all stages of the Drosophila cell cycle. P-element-mediated disruption of the CENP-meta gene leads to late larval/pupal stage lethality with incomplete chromosome alignment at metaphase. Complete removal of CENP-meta from the female germline leads to lethality in early embryos resulting from defects in metaphase chromosome alignment. Real-time imaging of these mutants with GFP-labeled chromosomes demonstrates that CENP-meta is required for the maintenance of chromosomes at the metaphase plate, demonstrating that the functions required to establish and maintain chromosome congression have distinguishable requirements.
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Affiliation(s)
- Jennifer K. Yucel
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Janet D. Marszalek
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
| | - J. Richard McIntosh
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Lawrence S.B. Goldstein
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Pharmacology, University of California, San Diego, La Jolla, California 92093
| | - Don W. Cleveland
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Medicine, University of California, San Diego, La Jolla, California 92093
| | - Alastair Valentine Philp
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
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396
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Yucel JK, Marszalek JD, McIntosh JR, Goldstein LS, Cleveland DW, Philp AV. CENP-meta, an Essential Kinetochore Kinesin Required for the Maintenance of Metaphase Chromosome Alignment in Drosophila. J Cell Biol 2000. [DOI: 10.1083/jcb.150.1.1a] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
CENP-meta has been identified as an essential, kinesin-like motor protein in Drosophila. The 257-kD CENP-meta protein is most similar to the vertebrate kinetochore-associated kinesin-like protein CENP-E, and like CENP-E, is shown to be a component of centromeric/kinetochore regions of Drosophila chromosomes. However, unlike CENP-E, which leaves the centromere/kinetochore region at the end of anaphase A, the CENP-meta protein remains associated with the centromeric/kinetochore region of the chromosome during all stages of the Drosophila cell cycle. P-element–mediated disruption of the CENP-meta gene leads to late larval/pupal stage lethality with incomplete chromosome alignment at metaphase. Complete removal of CENP-meta from the female germline leads to lethality in early embryos resulting from defects in metaphase chromosome alignment. Real-time imaging of these mutants with GFP-labeled chromosomes demonstrates that CENP-meta is required for the maintenance of chromosomes at the metaphase plate, demonstrating that the functions required to establish and maintain chromosome congression have distinguishable requirements.
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Affiliation(s)
- Jennifer K. Yucel
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Janet D. Marszalek
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
| | - J. Richard McIntosh
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Lawrence S.B. Goldstein
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Pharmacology, University of California, San Diego, La Jolla, California 92093
| | - Don W. Cleveland
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Medicine, University of California, San Diego, La Jolla, California 92093
| | - Alastair Valentine Philp
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California 92093
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397
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Overexpression of murine fizzy-related (fzr) increases natural killer cell–mediated cell death and suppresses tumor growth. Blood 2000. [DOI: 10.1182/blood.v96.1.259.013k36_259_263] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fizzy-related (fzr) is a recently identified 7WD domain family member implicated in cell cycle regulation of Drosophila and yeast. In this study, the murine homologue of fzr was isolated by suppression subtractive hybridization as a gene with decreased expression during malignant progression of a murine B-lymphoma cell line. Retroviral overexpression of fzr in B-lymphoma cells reduced tumor formation. Those tumors that did arise had diminished or extinguished retroviral Fzr. Surprisingly, fzr overexpression dramatically increased B-lymphoma cell susceptibility to natural killer cell (NK) cytotoxicity, a host-resistant mechanism for tumor formation in this model system. These findings implicate fzr as a new category of genes suppressing B-cell tumorigenesis and suggest a novel role for fzr in the target cell interaction with NK cells.
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398
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Overexpression of murine fizzy-related (fzr) increases natural killer cell–mediated cell death and suppresses tumor growth. Blood 2000. [DOI: 10.1182/blood.v96.1.259] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstract
Fizzy-related (fzr) is a recently identified 7WD domain family member implicated in cell cycle regulation of Drosophila and yeast. In this study, the murine homologue of fzr was isolated by suppression subtractive hybridization as a gene with decreased expression during malignant progression of a murine B-lymphoma cell line. Retroviral overexpression of fzr in B-lymphoma cells reduced tumor formation. Those tumors that did arise had diminished or extinguished retroviral Fzr. Surprisingly, fzr overexpression dramatically increased B-lymphoma cell susceptibility to natural killer cell (NK) cytotoxicity, a host-resistant mechanism for tumor formation in this model system. These findings implicate fzr as a new category of genes suppressing B-cell tumorigenesis and suggest a novel role for fzr in the target cell interaction with NK cells.
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399
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Southern SA, Herrington CS. Disruption of cell cycle control by human papillomaviruses with special reference to cervical carcinoma. Int J Gynecol Cancer 2000; 10:263-274. [PMID: 11240685 DOI: 10.1046/j.1525-1438.2000.010004263.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Human papillomaviruses (HPVs) play a major role in neoplastic transformation of squamous epithelial cells. The viral genome is small in size and only encodes a limited number of proteins, so one of the major functions of the viral proteins is to modulate the function of key cellular proteins involved in cell cycle control and DNA replication. During this process important host cell cycle checkpoints are lost which may lead to the accumulation of genetic abnormalities and eventual malignant transformation. This review briefly describes the normal cell cycle and also the mechanisms by which HPVs interfere with cell cycle control both as part of their productive life cycle and in the process of neoplastic transformation.
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Affiliation(s)
- S. A. Southern
- Department of Pathology, University of Liverpool, Royal Liverpool University Hospital, Liverpool, England, United Kingdom
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400
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Leverson JD, Joazeiro CA, Page AM, Huang HK, Hieter P, Hunter T. The APC11 RING-H2 finger mediates E2-dependent ubiquitination. Mol Biol Cell 2000; 11:2315-25. [PMID: 10888670 PMCID: PMC14921 DOI: 10.1091/mbc.11.7.2315] [Citation(s) in RCA: 146] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Polyubiquitination marks proteins for degradation by the 26S proteasome and is carried out by a cascade of enzymes that includes ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), and ubiquitin ligases (E3s). The anaphase-promoting complex or cyclosome (APC/C) comprises a multisubunit ubiquitin ligase that mediates mitotic progression. Here, we provide evidence that the Saccharomyces cerevisiae RING-H2 finger protein Apc11 defines the minimal ubiquitin ligase activity of the APC. We found that the integrity of the Apc11p RING-H2 finger was essential for budding yeast cell viability, Using purified, recombinant proteins we showed that Apc11p interacted directly with the Ubc4 ubiquitin conjugating enzyme (E2). Furthermore, purified Apc11p was capable of mediating E1- and E2-dependent ubiquitination of protein substrates, including Clb2p, in vitro. The ability of Apc11p to act as an E3 was dependent on the integrity of the RING-H2 finger, but did not require the presence of the cullin-like APC subunit Apc2p. We suggest that Apc11p is responsible for recruiting E2s to the APC and for mediating the subsequent transfer of ubiquitin to APC substrates in vivo.
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Affiliation(s)
- J D Leverson
- Molecular Biology and Virology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, California 92037, USA
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