201
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Abstract
A conserved signalling cascade--termed the mitotic-exit network in budding yeast and the septation-initiation network in fission yeast--controls key events during exit from mitosis and cytokinesis. Although the components of these signalling networks are highly conserved between the two yeasts, the outputs seem quite different. How, then, do these two pathways function, and how are they regulated?
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Affiliation(s)
- A J Bardin
- Center for Cancer Research, Howard Hughes Medical, Massachusetts Institute of Technology, Cambridge 02139, USA
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202
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Shah R, Jensen S, Frenz LM, Johnson AL, Johnston LH. The Spo12 protein of Saccharomyces cerevisiae: a regulator of mitotic exit whose cell cycle-dependent degradation is mediated by the anaphase-promoting complex. Genetics 2001; 159:965-80. [PMID: 11729145 PMCID: PMC1461877 DOI: 10.1093/genetics/159.3.965] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Spo12 protein plays a regulatory role in two of the most fundamental processes of biology, mitosis and meiosis, and yet its biochemical function remains elusive. In this study we concentrate on the genetic and biochemical analysis of its mitotic function. Since high-copy SPO12 is able to suppress a wide variety of mitotic exit mutants, all of which arrest with high Clb-Cdc28 activity, we speculated whether SPO12 is able to facilitate exit from mitosis when overexpressed by antagonizing mitotic kinase activity. We show, however, that Spo12 is not a potent regulator of Clb-Cdc28 activity and can function independently of either the cyclin-dependent kinase inhibitor (CDKi), Sic1, or the anaphase-promoting complex (APC) regulator, Hct1. Spo12 protein level is regulated by the APC and the protein is degraded in G1 by an Hct1-dependent mechanism. We also demonstrate that in addition to localizing to the nucleus Spo12 is a nucleolar protein. We propose a model where overexpression of Spo12 may lead to the delocalization of a small amount of Cdc14 from the nucleolus, resulting in a sufficient lowering of mitotic kinase levels to facilitate mitotic exit. Finally, site-directed mutagenesis of highly conserved residues in the Spo12 protein sequence abolishes both its mitotic suppressor activity as well as its meiotic function. This result is the first indication that Spo12 may carry out the same biochemical function in mitosis as it does in meiosis.
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Affiliation(s)
- R Shah
- National Institute for Medical Research, Medical Research Council, London NW7 1AA, United Kingdom
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203
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Abstract
Otx2 is a member of a highly conserved family of homeodomain-containing transcription factors that function in early brain development. Recent studies have identified a significant number of target genes downstream of Otx2, allowing us to address the question of how it fulfils its diverse developmental roles. Interestingly, many of these target genes are not transcription factors or signaling molecules, and they probably have no direct affect on gene expression. Furthermore, there is evidence that Otx2 coordinates the activity of unrelated genes that have overlapping functions, and that it does so directly without intermediate transcriptional or signaling activity.
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Affiliation(s)
- E Boncinelli
- Molecular Biology of Development, DIBIT, Instituto Scientifico H San Raffaele, via Olgettina, 58, 20132, Milan, Italy
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204
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Alvarez B, Martínez-A C, Burgering BM, Carrera AC. Forkhead transcription factors contribute to execution of the mitotic programme in mammals. Nature 2001; 413:744-7. [PMID: 11607034 DOI: 10.1038/35099574] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Cell cycle progression is a process that is tightly controlled by internal and external signals. Environmental cues, such as those provided by growth factors, activate early signals that promote cell cycle entry. Cells that have progressed past the restriction point become independent of growth factors, and cell cycle progression is then controlled endogenously. The phosphatidylinositol 3OH kinase (PI(3)K)/protein kinase B (PKB) pathway must be activated in G1 to inactivate forkhead transcription factors (FKH-TFs) and allow cell cycle entry. Here we show that subsequent attenuation of the PI(3)K/PKB pathway is required to allow transcriptional activation of FKH-TF in G2. FKH-TF activity in G2 controls mammalian cell cycle termination, as interference with FKH transcriptional activation by disrupting PI(3)K/PKB downregulation, or by expressing a transcriptionally inactive FKH mutant, induces cell accumulation in G2/M, defective cytokinesis, and delayed transition from M to G1 of the cell cycle. We demonstrate that FKH-TFs regulate expression of mitotic genes such as cyclin B and polo-like kinase (Plk). Our results support the important role of forkhead in the control of mammalian cell cycle completion, and suggest that efficient execution of the mitotic programme depends on downregulation of PI(3)K/PKB and consequent induction of FKH transcriptional activity.
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Affiliation(s)
- B Alvarez
- Department of Immunology and Oncology, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Cantoblanco, Madrid E-28049, Spain
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205
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Nigg EA. Cell cycle regulation by protein kinases and phosphatases. ERNST SCHERING RESEARCH FOUNDATION WORKSHOP 2001:19-46. [PMID: 11394046 DOI: 10.1007/978-3-662-04645-6_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Affiliation(s)
- E A Nigg
- Max-Plack-Institute for Biochemistry, Department of Cell Biology, Am Klopferspitz 18a, 82151 Martinsried, Germany
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206
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Abstract
In budding yeast, the release of the protein phosphatase Cdc14 from its inhibitor Cfi1/Net1 in the nucleolus during anaphase triggers the inactivation of Clb CDKs that leads to exit from mitosis. The mitotic exit pathway controls the association between Cdc14 and Cfi1/Net1. It is comprised of the RAS-like GTP binding protein Tem1, the exchange factor Lte1, the GTPase activating protein complex Bub2-Bfa1/Byr4, and several protein kinases including Cdc15 and Dbf2. Here we investigate the regulation of the protein kinases Dbf2 and Cdc15. We find that Cdc15 is recruited to both spindle pole bodies (SPBs) during anaphase. This recruitment depends on TEM1 but not DBF2 or CDC14 and is inhibited by BUB2. Dbf2 also localizes to SPBs during anaphase, which coincides with activation of Dbf2 kinase activity. Both events depend on the mitotic exit pathway components TEM1 and CDC15. In cells lacking BUB2, Dbf2 localized to SPBs in cell cycle stages other than anaphase and telophase and Dbf2 kinase was prematurely active during metaphase. Our results suggest an order of function of mitotic exit pathway components with respect to SPB localization of Cdc15 and Dbf2 and activation of Dbf2 kinase. BUB2 negatively regulates all 3 events. Loading of Cdc15 on SPBs depends on TEM1, whereas loading of Dbf2 on SPBs and activation of Dbf2 kinase depend on TEM1 and CDC15.
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Affiliation(s)
- R Visintin
- Center for Cancer Research, Howard Hughes Medical Institute, Massachusetts Institute of Technology, E17-233, 40 Ames Street, Cambridge MA 02139, USA
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207
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Chang L, Morrell JL, Feoktistova A, Gould KL. Study of cyclin proteolysis in anaphase-promoting complex (APC) mutant cells reveals the requirement for APC function in the final steps of the fission yeast septation initiation network. Mol Cell Biol 2001; 21:6681-94. [PMID: 11533255 PMCID: PMC99813 DOI: 10.1128/mcb.21.19.6681-6694.2001] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Cytokinesis in eukaryotic cells requires the inactivation of mitotic cyclin-dependent kinase complexes. An apparent exception to this relationship is found in Schizosaccharomyces pombe mutants with mutations of the anaphase-promoting complex (APC). These conditional lethal mutants arrest with unsegregated chromosomes because they cannot degrade the securin, Cut2p. Although failing at nuclear division, these mutants septate and divide. Since septation requires Cdc2p inactivation in wild-type S. pombe, it has been suggested that Cdc2p inactivation occurs in these mutants by a mechanism independent of cyclin degradation. In contrast to this prediction, we show that Cdc2p kinase activity fluctuates in APC cut mutants due to Cdc13/cyclin B destruction. In APC-null mutants, however, septation and cutting do not occur and Cdc13p is stable. We conclude that APC cut mutants are hypomorphic with respect to Cdc13p degradation. Indeed, overproduction of nondestructible Cdc13p prevents septation in APC cut mutants and the normal reorganization of septation initiation network components during anaphase.
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Affiliation(s)
- L Chang
- Howard Hughes Medical Institute and Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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208
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Herceg Z, Hulla W, Gell D, Cuenin C, Lleonart M, Jackson S, Wang ZQ. Disruption of Trrap causes early embryonic lethality and defects in cell cycle progression. Nat Genet 2001; 29:206-11. [PMID: 11544477 DOI: 10.1038/ng725] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The transactivation/transformation-domain associated protein (TRRAP) belongs to the Ataxia-telangiectasia mutated (ATM) super-family and has been identified as a cofactor for c-MYC-mediated oncogenic transformation. TRRAP and its yeast homolog (Tra1p) are components of histone acetyltransferase (HAT) complexes, SAGA (refs. 2,4,5), PCAF (ref. 3) and NuA4 (ref. 6), which are important for the regulation of transcription and cell cycle progression and also have a role in cell viability. Yet the biological function of this molecule and how it controls proliferation are still unclear. Here we show that null mutation of Trrap in mice results in peri-implantation lethality due to a blocked proliferation of blastocysts. We use an inducible Cre-loxP system to show that loss of Trrap blocks cell proliferation because of aberrant mitotic exit accompanied by cytokinesis failure and endoreduplication. Trrap-deficient cells fail to sustain mitotic arrest despite chromosome missegregation and disrupted spindles, and display compromised cdk1 activity. Trrap is therefore essential for early development and required for the mitotic checkpoint and normal cell cycle progression.
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Affiliation(s)
- Z Herceg
- International Agency for Research on Cancer (IARC), 150 Cours Albert Thomas, F-69008, Lyon, France
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209
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Luca FC, Mody M, Kurischko C, Roof DM, Giddings TH, Winey M. Saccharomyces cerevisiae Mob1p is required for cytokinesis and mitotic exit. Mol Cell Biol 2001; 21:6972-83. [PMID: 11564880 PMCID: PMC99873 DOI: 10.1128/mcb.21.20.6972-6983.2001] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The Saccharomyces cerevisiae mitotic exit network (MEN) is a conserved set of genes that mediate the transition from mitosis to G(1) by regulating mitotic cyclin degradation and the inactivation of cyclin-dependent kinase (CDK). Here, we demonstrate that, in addition to mitotic exit, S. cerevisiae MEN gene MOB1 is required for cytokinesis and cell separation. The cytokinesis defect was evident in mob1 mutants under conditions in which there was no mitotic-exit defect. Observation of live cells showed that yeast myosin II, Myo1p, was present in the contractile ring at the bud neck but that the ring failed to contract and disassemble. The cytokinesis defect persisted for several mitotic cycles, resulting in chains of cells with correctly segregated nuclei but with uncontracted actomyosin rings. The cytokinesis proteins Cdc3p (a septin), actin, and Iqg1p/ Cyk1p (an IQGAP-like protein) appeared to correctly localize in mob1 mutants, suggesting that MOB1 functions subsequent to actomyosin ring assembly. We also examined the subcellular distribution of Mob1p during the cell cycle and found that Mob1p first localized to the spindle pole bodies during mid-anaphase and then localized to a ring at the bud neck just before and during cytokinesis. Localization of Mob1p to the bud neck required CDC3, MEN genes CDC5, CDC14, CDC15, and DBF2, and spindle pole body gene NUD1 but was independent of MYO1. The localization of Mob1p to both spindle poles was abolished in cdc15 and nud1 mutants and was perturbed in cdc5 and cdc14 mutants. These results suggest that the MEN functions during the mitosis-to-G(1) transition to control cyclin-CDK inactivation and cytokinesis.
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Affiliation(s)
- F C Luca
- Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania 19104, USA.
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210
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Schwab M, Neutzner M, Möcker D, Seufert W. Yeast Hct1 recognizes the mitotic cyclin Clb2 and other substrates of the ubiquitin ligase APC. EMBO J 2001; 20:5165-75. [PMID: 11566880 PMCID: PMC125620 DOI: 10.1093/emboj/20.18.5165] [Citation(s) in RCA: 172] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ubiquitin-mediated proteolysis has emerged as a key mechanism of regulation in eukaryotic cells. During cell division, a multi-subunit ubiquitin ligase termed the anaphase promoting complex (APC) targets critical regulatory proteins such as securin and mitotic cyclins, and thereby triggers chromosome separation and exit from mitosis. Previous studies in the yeast Saccharomyces cerevisiae identified the conserved WD40 proteins Cdc20 and Hct1 (Cdh1) as substrate-specific activators of the APC, but their precise mechanism of action has remained unclear. This study provides evidence that Hct1 functions as a substrate receptor that recognizes target proteins and recruits them to the APC for ubiquitylation and subsequent proteolysis. By co-immunoprecipitation, we found that Hct1 interacted with the mitotic cyclins Clb2 and Clb3 and the polo-related kinase Cdc5, whereas Cdc20 interacted with the securin Pds1. Failure to interact with Hct1 resulted in stabilization of Clb2. Analysis of Hct1 derivatives identified the C-box, a motif required for APC association of Hct1 and conserved among Cdc20-related proteins. We propose that proteins of the Cdc20 family are substrate recognition subunits of the ubiquitin ligase APC.
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Affiliation(s)
- M Schwab
- Institute of Industrial Genetics, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany
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211
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Fellenberg K, Hauser NC, Brors B, Neutzner A, Hoheisel JD, Vingron M. Correspondence analysis applied to microarray data. Proc Natl Acad Sci U S A 2001; 98:10781-6. [PMID: 11535808 PMCID: PMC58552 DOI: 10.1073/pnas.181597298] [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: 11/18/2022] Open
Abstract
Correspondence analysis is an explorative computational method for the study of associations between variables. Much like principal component analysis, it displays a low-dimensional projection of the data, e.g., into a plane. It does this, though, for two variables simultaneously, thus revealing associations between them. Here, we demonstrate the applicability of correspondence analysis to and high value for the analysis of microarray data, displaying associations between genes and experiments. To introduce the method, we show its application to the well-known Saccharomyces cerevisiae cell-cycle synchronization data by Spellman et al. [Spellman, P. T., Sherlock, G., Zhang, M. Q., Iyer, V. R., Anders, K., Eisen, M. B., Brown, P. O., Botstein, D. & Futcher, B. (1998) Mol. Biol. Cell 9, 3273-3297], allowing for comparison with their visualization of this data set. Furthermore, we apply correspondence analysis to a non-time-series data set of our own, thus supporting its general applicability to microarray data of different complexity, underlying structure, and experimental strategy (both two-channel fluorescence-tag and radioactive labeling).
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Affiliation(s)
- K Fellenberg
- Department of Theoretical Bioinformatics, German Cancer Research Center, PO 101949, D-69009 Heidelberg, Germany
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212
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Scaërou F, Starr DA, Piano F, Papoulas O, Karess RE, Goldberg ML. The ZW10 and Rough Deal checkpoint proteins function together in a large, evolutionarily conserved complex targeted to the kinetochore. J Cell Sci 2001; 114:3103-14. [PMID: 11590237 DOI: 10.1242/jcs.114.17.3103] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The zeste-white 10 (zw10) and rough deal (rod) genes of Drosophila both encode kinetochore components, and mutations in either gene greatly increase the missegregation of sister chromatids during mitosis. Here, we present genetic, cytological and biochemical evidence for a close, evolutionarily conserved relationship between the ROD and ZW10 proteins. We show that the phenotypes caused by disruption of either gene’s function are similar in Drosophila and in C. elegans. No additive effects are observed in zw10; rod double null mutants. In flies, the two proteins always colocalize and, moreover, require each other for their recruitment to the mitotic apparatus. The human ROD and ZW10 homologs also colocalize on HeLa cell kinetochores or kinetochore microtubules throughout most but not all of mitosis. Finally, we show that in both Drosophila and human cells, ROD and ZW10 are in fact physically associated, and in Drosophila these proteins are together constituents of a large (700-900 kDa), soluble macromolecular complex.
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Affiliation(s)
- F Scaërou
- CNRS, Centre de Génétique Moléculaire, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France
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213
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Abstract
Most current models of spindle assembly checkpoint signaling involve inhibition of the Cdc20-APC by Mad2 protein. Interestingly, a paper from Hongtao Yu and colleagues in this issue of Developmental Cell suggests that the Cdc20/APC can also be inhibited in a Mad2-independent manner by a complex of proteins that includes BubR1.
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Affiliation(s)
- E S Gillett
- Massachusetts Institute of Technology, Dept of Biology, Cambridge 02139, USA
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214
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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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215
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Shou W, Sakamoto KM, Keener J, Morimoto KW, Traverso EE, Azzam R, Hoppe GJ, Feldman RM, DeModena J, Moazed D, Charbonneau H, Nomura M, Deshaies RJ. Net1 stimulates RNA polymerase I transcription and regulates nucleolar structure independently of controlling mitotic exit. Mol Cell 2001; 8:45-55. [PMID: 11511359 DOI: 10.1016/s1097-2765(01)00291-x] [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: 11/17/2022]
Abstract
The budding yeast RENT complex, consisting of at least three proteins (Net1, Cdc14, Sir2), is anchored to the nucleolus by Net1. RENT controls mitotic exit, nucleolar silencing, and nucleolar localization of Nop1. Here, we report two new functions of Net1. First, Net1 directly binds Pol I and stimulates rRNA synthesis both in vitro and in vivo. Second, Net1 modulates nucleolar structure by regulating rDNA morphology and proper localization of multiple nucleolar antigens, including Pol I. Importantly, we show that the nucleolar and previously described cell cycle functions of the RENT complex can be uncoupled by a dominant mutant allele of CDC14. The independent functions of Net1 link a key event in the cell cycle to nucleolar processes that are fundamental to cell growth.
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Affiliation(s)
- W Shou
- Division of Biology, California Institute of Technology, Pasadena 91125, USA
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216
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Mah AS, Jang J, Deshaies RJ. Protein kinase Cdc15 activates the Dbf2-Mob1 kinase complex. Proc Natl Acad Sci U S A 2001; 98:7325-30. [PMID: 11404483 PMCID: PMC34667 DOI: 10.1073/pnas.141098998] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Exit from mitosis in budding yeast requires inactivation of cyclin-dependent kinases through mechanisms triggered by the protein phosphatase Cdc14. Cdc14 activity, in turn, is regulated by a group of proteins, the mitotic exit network (MEN), which includes Lte1, Tem1, Cdc5, Cdc15, Dbf2/Dbf20, and Mob1. The direct biochemical interactions between the components of the MEN remain largely unresolved. Here, we investigate the mechanisms that underlie activation of the protein kinase Dbf2. Dbf2 kinase activity depended on Tem1, Cdc15, and Mob1 in vivo. In vitro, recombinant protein kinase Cdc15 activated recombinant Dbf2, but only when Dbf2 was bound to Mob1. Conserved phosphorylation sites Ser-374 and Thr-544 (present in the human, Caenorhabditis elegans, and Drosophila melanogaster relatives of Dbf2) were required for DBF2 function in vivo, and activation of Dbf2-Mob1 by Cdc15 in vitro. Although Cdc15 phosphorylated Dbf2, Dbf2-Mob1, and Dbf2(S374A/T544A)-Mob1, the pattern of phosphate incorporation into Dbf2 was substantially altered by either the S374A T544A mutations or omission of Mob1. Thus, Cdc15 promotes the exit from mitosis by directly switching on the kinase activity of Dbf2. We propose that Mob1 promotes this activation process by enabling Cdc15 to phosphorylate the critical Ser-374 and Thr-544 phosphoacceptor sites of Dbf2.
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Affiliation(s)
- A S Mah
- Division of Biology and Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA
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217
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Traverso EE, Baskerville C, Liu Y, Shou W, James P, Deshaies RJ, Charbonneau H. Characterization of the Net1 cell cycle-dependent regulator of the Cdc14 phosphatase from budding yeast. J Biol Chem 2001; 276:21924-31. [PMID: 11274204 DOI: 10.1074/jbc.m011689200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the budding yeast Saccharomyces cerevisiae, the multifunctional protein Net1 is implicated in regulating the cell cycle function of the Cdc14 protein phosphatase. Genetic and cell biological data suggest that during interphase and early mitosis Net1 holds Cdc14 within the nucleolus where its activity is suppressed. Upon its transient release from Net1 at late anaphase, active Cdc14 promotes exit from mitosis by dephosphorylating targets in the nucleus and cytoplasm. In this paper we present evidence supporting the proposed role of Net1 in regulating Cdc14 and exit from mitosis. We show that the NH(2)-terminal fragment Net1(1-600) directly binds Cdc14 in vitro and is a highly specific competitive inhibitor of its activity (K(i) = 3 nm) with five different substrates including the physiologic targets Swi5 and Sic1. An analysis of truncation mutants indicates that the Cdc14 binding site is located within a segment of Net1 containing residues 1-341. We propose that Net1 inhibits by occluding the active site of Cdc14 because it acts as a competitive inhibitor, binds to a site located within the catalytic domain (residues 1-374), binds with reduced affinity to a Cdc14 C283S mutant in which an active site Cys is replaced, and is displaced by tungstate, a transition state analog known to bind in the catalytic site of protein-tyrosine phosphatases.
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Affiliation(s)
- E E Traverso
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA
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218
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Lee SE, Jensen S, Frenz LM, Johnson AL, Fesquet D, Johnston LH. The Bub2-dependent mitotic pathway in yeast acts every cell cycle and regulates cytokinesis. J Cell Sci 2001; 114:2345-54. [PMID: 11493673 DOI: 10.1242/jcs.114.12.2345] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In eukaryotes an abnormal spindle activates a conserved checkpoint consisting of the MAD and BUB genes that results in mitotic arrest at metaphase. Recently, we and others identified a novel Bub2-dependent branch to this checkpoint that blocks mitotic exit. This cell-cycle arrest depends upon inhibition of the G-protein Tem1 that appears to be regulated by Bfa1/Bub2, a two-component GTPase-activating protein, and the exchange factor Lte1. Here, we find that Bub2 and Bfa1 physically associate across the entire cell cycle and bind to Tem1 during mitosis and early G1. Bfa1 is multiply phosphorylated in a cell-cycle-dependent manner with the major phosphorylation occurring in mitosis. This Bfa1 phosphorylation is Bub2-dependent. Cdc5, but not Cdc15 or Dbf2, partly controls the phosphorylation of Bfa1 and also Lte1. Following spindle checkpoint activation, the cell cycle phosphorylation of Bfa1 and Lte1 is protracted and some species are accentuated. Thus, the Bub2-dependent pathway is active every cell cycle and the effect of spindle damage is simply to protract its normal function. Indeed, function of the Bub2 pathway is also prolonged during metaphase arrests imposed by means other than checkpoint activation. In metaphase cells Bub2 is crucial to restrain downstream events such as actin ring formation, emphasising the importance of the Bub2 pathway in the regulation of cytokinesis. Our data is consistent with Bub2/Bfa1 being a rate-limiting negative regulator of downstream events during metaphase.
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Affiliation(s)
- S E Lee
- Division of Yeast Genetics, National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK
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219
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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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220
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Sørensen CS, Lukas C, Kramer ER, Peters JM, Bartek J, Lukas J. A conserved cyclin-binding domain determines functional interplay between anaphase-promoting complex-Cdh1 and cyclin A-Cdk2 during cell cycle progression. Mol Cell Biol 2001; 21:3692-703. [PMID: 11340163 PMCID: PMC87003 DOI: 10.1128/mcb.21.11.3692-3703.2001] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Periodic activity of the anaphase-promoting complex (APC) ubiquitin ligase determines progression through multiple cell cycle transitions by targeting cell cycle regulators for destruction. At the G(1)/S transition, phosphorylation-dependent dissociation of the Cdh1-activating subunit inhibits the APC, allowing stabilization of proteins required for subsequent cell cycle progression. Cyclin-dependent kinases (CDKs) that initiate and maintain Cdh1 phosphorylation have been identified. However, the issue of which cyclin-CDK complexes are involved has been a matter of debate, and the mechanism of how cyclin-CDKs interact with APC subunits remains unresolved. Here we substantiate the evidence that mammalian cyclin A-Cdk2 prevents unscheduled APC reactivation during S phase by demonstrating its periodic interaction with Cdh1 at the level of endogenous proteins. Moreover, we identified a conserved cyclin-binding motif within the Cdh1 WD-40 domain and show that its disruption abolished the Cdh1-cyclin A-Cdk2 interaction, eliminated Cdh1-associated histone H1 kinase activity, and impaired Cdh1 phosphorylation by cyclin A-Cdk2 in vitro and in vivo. Overexpression of cyclin binding-deficient Cdh1 stabilized the APC-Cdh1 interaction and induced prolonged cell cycle arrest at the G(1)/S transition. Conversely, cyclin binding-deficient Cdh1 lost its capability to support APC-dependent proteolysis of cyclin A but not that of other APC substrates such as cyclin B and securin Pds1. Collectively, these data provide a mechanistic explanation for the mutual functional interplay between cyclin A-Cdk2 and APC-Cdh1 and the first evidence that Cdh1 may activate the APC by binding specific substrates.
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Affiliation(s)
- C S Sørensen
- Institute of Cancer Biology, Danish Cancer Society, DK-2100 Copenhagen Ø, Denmark
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221
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Abstract
Tight regulation of cell cycle progression is essential for the maintenance of genomic integrity. The orderly progression from one cell cycle phase to the other is mediated by timed activation of distinct cyclin/cdk complexes. For example, onset of mitosis is regulated by the activation of cyclin B/cdc2 and this event is controlled by several cell cycle checkpoints. Such checkpoints ensure that chromosome segregation does not occur in the case of unreplicated or damaged DNA, or misaligned chromosomes. Recently, new insights into the targets of the DNA damage checkpoint help to unravel more of the complex mechanisms of cell cycle checkpoints. This review focuses on the factors controlling the transition from G(2) phase to mitosis. Also, the pathways contributing to the DNA damage checkpoints in these phases of the cell cycle will be discussed.
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Affiliation(s)
- V A Smits
- The Netherlands Cancer Institute, Division of Molecular Biology H8, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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222
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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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223
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Hanna JS, Kroll ES, Lundblad V, Spencer FA. Saccharomyces cerevisiae CTF18 and CTF4 are required for sister chromatid cohesion. Mol Cell Biol 2001; 21:3144-58. [PMID: 11287619 PMCID: PMC86942 DOI: 10.1128/mcb.21.9.3144-3158.2001] [Citation(s) in RCA: 260] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CTF4 and CTF18 are required for high-fidelity chromosome segregation. Both exhibit genetic and physical ties to replication fork constituents. We find that absence of either CTF4 or CTF18 causes sister chromatid cohesion failure and leads to a preanaphase accumulation of cells that depends on the spindle assembly checkpoint. The physical and genetic interactions between CTF4, CTF18, and core components of replication fork complexes observed in this study and others suggest that both gene products act in association with the replication fork to facilitate sister chromatid cohesion. We find that Ctf18p, an RFC1-like protein, directly interacts with Rfc2p, Rfc3p, Rfc4p, and Rfc5p. However, Ctf18p is not a component of biochemically purified proliferating cell nuclear antigen loading RF-C, suggesting the presence of a discrete complex containing Ctf18p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p. Recent identification and characterization of the budding yeast polymerase kappa, encoded by TRF4, strongly supports a hypothesis that the DNA replication machinery is required for proper sister chromatid cohesion. Analogous to the polymerase switching role of the bacterial and human RF-C complexes, we propose that budding yeast RF-C(CTF18) may be involved in a polymerase switch event that facilities sister chromatid cohesion. The requirement for CTF4 and CTF18 in robust cohesion identifies novel roles for replication accessory proteins in this process.
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Affiliation(s)
- J S Hanna
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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224
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Roy L, Coullin P, Vitrat N, Hellio R, Debili N, Weinstein J, Bernheim A, Vainchenker W. Asymmetrical segregation of chromosomes with a normal metaphase/anaphase checkpoint in polyploid megakaryocytes. Blood 2001; 97:2238-47. [PMID: 11290584 DOI: 10.1182/blood.v97.8.2238] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During differentiation, megakaryocytes increase ploidy through a process called endomitosis, whose mechanisms remain unknown. As it corresponds to abortive mitosis at anaphase and is associated with a multipolar spindle, investigation of chromosome segregation may help to better understand this cell-cycle abnormality. To examine this variation, a new method was developed to combine primed in situ labeling to label centromeres of one chromosome category and immunostaining of tubulin. Human megakaryocytes were obtained from normal bone marrow culture. By confocal microscopy, this study demonstrates an asymmetrical distribution of chromosomes (1 or 7) either between the spindle poles at anaphase stage of endomitosis and between the different lobes of interphase megakaryocyte nuclei. The metaphase/anaphase checkpoint appears normal on the evidence that under nocodazole treatment megakaryocytes progressively accumulate in pseudo-metaphase, without spontaneous escape from this blockage. Immunostaining of p55CDC/hCDC20 with similar kinetochore localization and dynamics as during normal mitosis confirms this result. HCdh1 was also expressed in megakaryocytes, and its main target, cyclin B1, was normally degraded at anaphase, suggesting that the hCdh1-anaphase-promoting complex checkpoint was also functional. This study found the explanation for these unexpected results of an asymmetrical segregation coupled to normal checkpoints by careful analysis of multipolar endomitotic spindles: whereas each aster is connected to more than one other aster, one chromosome may segregate symmetrically between 2 spindle poles and still show asymmetrical segregation when the entire complex spindle is considered.
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Affiliation(s)
- L Roy
- Institut National de la Santé et de la Recherche Médicale (INSERM) U362, France
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225
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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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226
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Yoshida S, Toh-e A. Regulation of the localization of Dbf2 and mob1 during cell division of saccharomyces cerevisiae. Genes Genet Syst 2001; 76:141-7. [PMID: 11434459 DOI: 10.1266/ggs.76.141] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The mitotic exit network (MEN) governs Cdk inactivation. In budding yeast, MEN consists of the protein phosphatase Cdc14, the ras-like GTPase Tem1, protein kinases Cdc15, Cdc5, Dbf2 and Dbf2-binding protein Mob1. Tem1, Dbf2, Cdc5 and Cdc15 have been reported to be localized at the spindle pole body (SPB). Here we report changes of the localization of Dbf2 and Mob1 during cell division. Dbf2 and Mob1 localize to the SPBs in anaphase and then moves to the bud neck, just prior to actin ring assembly, consistent with their role in cytokinesis. The neck localization, but not SPB localization, of Dbf2 was inhibited by the Bub2 spindle checkpoint. Cdc14 is the downstream target of Dbf2 in Cdk inactivation, but we found that the neck localization of DbP2 and Mob1 was dependent on the Cdc14 activity, suggesting that Dbf2 and Mob1 function in cytokinesis at the end of the mitotic signaling cascade.
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Affiliation(s)
- S Yoshida
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Japan
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227
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Gieffers C, Dube P, Harris JR, Stark H, Peters JM. Three-dimensional structure of the anaphase-promoting complex. Mol Cell 2001; 7:907-13. [PMID: 11336713 DOI: 10.1016/s1097-2765(01)00234-9] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The anaphase-promoting complex (APC) is a cell cycle-regulated ubiquitin-protein ligase, composed of at least 11 subunits, that controls progression through mitosis and G1. Using cryo-electron microscopy and angular reconstitution, we have obtained a three-dimensional model of the human APC at a resolution of 24 A. The APC has a complex asymmetric structure 140 A x 140 A x 135 A in size, in which an outer protein wall surrounds a large inner cavity. We discuss the possibility that this cavity represents a reaction chamber in which ubiquitination reactions take place, analogous to the inner cavities formed by other protein machines such as the 26S proteasome and chaperone complexes. This cage hypothesis could help to explain the great subunit complexity of the APC.
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Affiliation(s)
- C Gieffers
- Research Institute of Molecular Pathology (IMP), Dr. Bohr-Gasse 7, A-1030 Vienna, Austria
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228
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Asakawa K, Yoshida S, Otake F, Toh-e A. A novel functional domain of Cdc15 kinase is required for its interaction with Tem1 GTPase in Saccharomyces cerevisiae. Genetics 2001; 157:1437-50. [PMID: 11290702 PMCID: PMC1461593 DOI: 10.1093/genetics/157.4.1437] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Exit from mitosis requires the inactivation of cyclin-dependent kinase (CDK) activity. In the budding yeast Saccharomyces cerevisiae, a number of gene products have been identified as components of the signal transduction network regulating inactivation of CDK (called the MEN, for the mitotic exit network). Cdc15, one of such components of the MEN, is an essential protein kinase. By the two-hybrid screening, we identified Cdc15 as a binding protein of Tem1 GTPase, another essential regulator of the MEN. Coprecipitation experiments revealed that Tem1 binds to Cdc15 in vivo. By deletion analysis, we found that the Tem1-binding domain resides near the conserved kinase domain of Cdc15. The cdc15-LF mutation, which was introduced into the Tem1-binding domain, reduced the interaction with Cdc15 and Tem1 and caused temperature-sensitive growth. The kinase activity of Cdc15 was not so much affected by the cdc15-LF mutation. However, Cdc15-LF failed to localize to the SPB at the restrictive temperature. Our data show that the interaction with Tem1 is important for the function of Cdc15 and that Cdc15 and Tem1 function in a complex to direct the exit from mitosis.
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Affiliation(s)
- Kazuhide Asakawa
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
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229
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Romero F, Multon MC, Ramos-Morales F, Domínguez A, Bernal JA, Pintor-Toro JA, Tortolero M. Human securin, hPTTG, is associated with Ku heterodimer, the regulatory subunit of the DNA-dependent protein kinase. Nucleic Acids Res 2001; 29:1300-7. [PMID: 11238996 PMCID: PMC29753 DOI: 10.1093/nar/29.6.1300] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2000] [Revised: 01/29/2001] [Accepted: 01/29/2001] [Indexed: 11/13/2022] Open
Abstract
We have previously isolated the hpttg proto-oncogene, which is expressed in normal tissues containing proliferating cells and in several kinds of tumors. In fact, expression of hPTTG correlates with cell proliferation in a cell cycle-dependent manner. Recently it was reported that PTTG is a vertebrate analog of the yeast securins Pds1 and Cut2, which are involved in sister chromatid separation. Here we show that hPTTG binds to Ku, the regulatory subunit of the DNA-dependent protein kinase (DNA-PK). hPTTG and Ku associate both in vitro and in vivo and the DNA-PK catalytic subunit phosphorylates hPTTG in vitro. Furthermore, DNA double-strand breaks prevent hPTTG-Ku association and disrupt the hPTTG-Ku complexes, indicating that genome damaging events, which result in the induction of pathways that activate DNA repair mechanisms and halt cell cycle progression, might inhibit hPTTG-Ku interaction in vivo. We propose that hPTTG might connect DNA damage-response pathways with sister chromatid separation, delaying the onset of mitosis while DNA repair occurs.
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Affiliation(s)
- F Romero
- Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Apdo. 1095, 41080-Sevilla, Spain.
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230
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Chu T, Henrion G, Haegeli V, Strickland S. Cortex, a Drosophila gene required to complete oocyte meiosis, is a member of the Cdc20/fizzy protein family. Genesis 2001; 29:141-52. [PMID: 11252055 DOI: 10.1002/gene.1017] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mutations in cortex and grauzone cause abnormal arrest in Drosophila female meiosis. cortex was mapped to a 14 kb interval in 26F-27A by the male recombination mapping method. While these experiments mapped the gene accurately, they also illustrated some complexities of this method. Rescue results showed that a 2.8 kb genomic fragment from this interval was able to fully rescue the cortex phenotype. The 2.8 kb rescuing fragment contains a single open reading frame. The predicted amino acid sequence indicates that cortex encodes a WD-repeat protein and is a distant member of the Cdc20 protein family. Results from a developmental Northern analysis showed that the cortex transcript is expressed at high levels during oogenesis and early embryogenesis. Interestingly, the meiotic metaphase-anaphase II arrest defect in embryos laid by cortex homozygous females resembles the mitotic metaphase-anaphase defects observed in yeast cdc20 mutants. The predicted nature of the Cortex protein, together with the observed meiotic phenotype in cortex mutants, suggest that a similar pathway to the cdc20 dependent APC-mediated proteolysis pathway, which governs the metaphase-anaphase transition in mitosis, is also important in regulating oocyte meiosis.
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Affiliation(s)
- T Chu
- Department of Pharmacology, Program in Molecular Biology and Biochemistry, University at Stony Brook, Stony Brook, New York, USA
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231
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Josefsberg LB, Kaufman O, Galiani D, Kovo M, Dekel N. Inactivation of M-phase promoting factor at exit from first embryonic mitosis in the rat is independent of cyclin B1 degradation. Biol Reprod 2001; 64:871-8. [PMID: 11207203 DOI: 10.1095/biolreprod64.3.871] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Exit from M-phase and completion of cell division requires inactivation of M-phase promoting factor (MPF), a heterodimer composed of the regulatory cyclin B1 and the catalytic p34cdc2 kinase. Inactivation of MPF is associated with cyclin B1 degradation that is brought about by the ubiquitin-proteasome pathway. Our study examined the role of the proteasome in the first mitosis of rat embryos and its participation in the regulation of cyclin B1 degradation and MPF inactivation. We show that in the early zygote the proteasome is evenly distributed in the ooplasm and the nucleus, whereas during mitosis it accumulates on the spindle apparatus. We further demonstrate that inhibition of proteasomal catalytic activity prevents 1-cell embryos from undergoing mitosis. This mitotic arrest is associated with the presence of relatively high amounts of cyclin B1, which unexpectedly does not result in elevated MPF activity. Our findings strongly imply that completion of the first embryonic division depends on proteasomal degradation and that cyclin B1 is included among its target proteins. They also provide the first evidence that MPF inactivation at this stage of development is not solely dependent upon cyclin B1 degradation and is insufficient to allow the formation of the 2-cell embryo.
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Affiliation(s)
- L B Josefsberg
- Department of Biological Regulation, The Weizmann Institute of Science, Rehovot, 76100 Israel Faculty of Life Science, Bar-Ilan University, Ramat-Gan, Israel
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232
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Spruck C, Strohmaier H, Watson M, Smith AP, Ryan A, Krek TW, Reed SI. A CDK-independent function of mammalian Cks1: targeting of SCF(Skp2) to the CDK inhibitor p27Kip1. Mol Cell 2001; 7:639-50. [PMID: 11463388 DOI: 10.1016/s1097-2765(01)00210-6] [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: 12/30/2022]
Abstract
The Cks/Suc1 proteins associate with CDK/cyclin complexes, but their precise function(s) is not well defined. Here we demonstrate that Cks1 directs the ubiquitin-mediated proteolysis of the CDK-bound substrate p27Kip1 by the protein ubiquitin ligase (E3) SCF(Skp2). Cks1 associates with the F box protein Skp2 and is essential for recognition of the p27Kip1 substrate for ubiquitination in vivo and in vitro. Using purified recombinant proteins, we reconstituted p27Kip1 ubiquitination activity and show that it is dependent on Cks1. CKS1-/- mice are abnormally small, and cells derived from them proliferate poorly, particularly under limiting mitogen conditions, possibly due to elevated levels of p27Kip1.
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Affiliation(s)
- C Spruck
- The Scripps Research Institute, La Jolla, California 92037, USA
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233
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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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234
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Abstract
Oligosyndactylism (Os) is a radiation-induced mouse mutation associated with recessive lethality and a dominant effect on limb and kidney development. The lethal effect of the mutation is due to a cell-autonomous block in the transition from metaphase to anaphase. We have previously characterized two transgene-induced mutations, 94-A and 94-K, which are allelic with Os. These mutations facilitated the identification of genomic segments and transcribed sequences in the affected region. One of the transcripts in this region corresponds to the mouse homolog of the anaphase-promoting complex component APC10/DOC1. The disruption of this gene can explain the mitotic arrest phenotype of all three alleles of Os.
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Affiliation(s)
- D D Pravtcheva
- Department of Human Genetics, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, New York 10314, USA.
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235
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Abstract
Separation of chromosomes during mitosis is monitored by a checkpoint that leads to cell-cycle arrest if the chromosomes are not properly attached to the mitotic spindle. Molecular mechanisms controlling this checkpoint have been identified. In addition, loss of this checkpoint has been shown to result in chromosome missegregation in higher eukaryotes and may contribute to the genomic instability observed in human cancers.
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Affiliation(s)
- K Wassmann
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center and the Sloan-Kettering Division, Graduate School of Medical Sciences, Cornell University, Box 241, 1275 York Avenue, New York, New York 10021, USA
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236
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Yam CH, Siu WY, Kaganovich D, Ruderman JV, Poon RY. Cleavage of cyclin A at R70/R71 by the bacterial protease OmpT. Proc Natl Acad Sci U S A 2001; 98:497-501. [PMID: 11136238 PMCID: PMC14615 DOI: 10.1073/pnas.98.2.497] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Previous work has shown that cyclin A can be cleaved at Arg-70/Arg-71 by a proteolytic activity present in an in vitro-coupled transcription/translation system by using rabbit reticulocyte lysate programmed by plasmid DNA encoding p27(KIP1), a cyclin-dependent kinase inhibitor, but not by plasmid DNAs encoding other cyclin-dependent kinases inhibitors. Here we report that cyclin A is also cleaved by translation product programmed by plasmid DNA encoding cyclin B. Several findings indicate that the cleavage activity in this assay is provided by the bacterial protease OmpT, which cofractionates with cyclin B and p27(KIP1) plasmid DNAs and is thus carried over into the coupled in vitro transcription/translation reactions. (i) Cleavage activity appeared even when transcription or translation of the cyclin B or p27(KIP1) was blocked. (ii) Activity resembling OmpT, a serine protease that cleaves between dibasic residues, routinely copurifies with p27(KIP1) and cyclin B plasmid DNAs. (iii) Both cyclin A cleavage activity and OmpT activity are heat stable, resistant to denaturation, and inhibited by Zn(2+), Cu(2+), or benzamidine. (iv) Cyclin A cleavage activity is detected when using lysates or DNAs prepared from Escherichia coli strains that contained OmpT but not with strains lacking OmpT. (v) Purified OmpT enzyme itself cleaves cyclin A at R70/R71. These data indicate that OmpT can be present in certain DNA preparations obtained by using standard plasmid purification protocols, and its presence can potentially affect the outcome and interpretation of studies carried out using in vitro-translated proteins.
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Affiliation(s)
- C H Yam
- Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
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237
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Abstract
Previous work has shown that cyclin A can be cleaved at Arg-70/Arg-71 by a proteolytic activity present in an in vitro-coupled transcription/translation system by using rabbit reticulocyte lysate programmed by plasmid DNA encoding p27(KIP1), a cyclin-dependent kinase inhibitor, but not by plasmid DNAs encoding other cyclin-dependent kinases inhibitors. Here we report that cyclin A is also cleaved by translation product programmed by plasmid DNA encoding cyclin B. Several findings indicate that the cleavage activity in this assay is provided by the bacterial protease OmpT, which cofractionates with cyclin B and p27(KIP1) plasmid DNAs and is thus carried over into the coupled in vitro transcription/translation reactions. (i) Cleavage activity appeared even when transcription or translation of the cyclin B or p27(KIP1) was blocked. (ii) Activity resembling OmpT, a serine protease that cleaves between dibasic residues, routinely copurifies with p27(KIP1) and cyclin B plasmid DNAs. (iii) Both cyclin A cleavage activity and OmpT activity are heat stable, resistant to denaturation, and inhibited by Zn(2+), Cu(2+), or benzamidine. (iv) Cyclin A cleavage activity is detected when using lysates or DNAs prepared from Escherichia coli strains that contained OmpT but not with strains lacking OmpT. (v) Purified OmpT enzyme itself cleaves cyclin A at R70/R71. These data indicate that OmpT can be present in certain DNA preparations obtained by using standard plasmid purification protocols, and its presence can potentially affect the outcome and interpretation of studies carried out using in vitro-translated proteins.
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238
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Jörgensen PM, Gräslund S, Betz R, Ståhl S, Larsson C, Höög C. Characterisation of the human APC1, the largest subunit of the anaphase-promoting complex. Gene 2001; 262:51-9. [PMID: 11179667 DOI: 10.1016/s0378-1119(00)00511-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Accurate segregation of sister chromatids during mitosis is necessary to avoid the aneuploidy found in many cancers. The spindle checkpoint, which monitors the metaphase to anaphase transition, has been shown to be defective in cancers with chromosomal instability. This checkpoint regulates the anaphase-promoting complex or cyclosome (APC/C), a cell cycle ubiquitin ligase regulating among other things sister chromatid separation. We have previously investigated the mouse Apc1 protein (previously also called Tsg24), the largest subunit of the APC/C. We have now sequenced a full-length human APC1 cDNA, mapped its chromosomal location, and analysed its intron-exon boundaries. We have also investigated the RNA and protein expression of the Apc1 and other APC/C components in normal and cancer cells and the relative occurrence of expressed sequence tags (ESTs) representing APC subunits from different tissues. The different APC/C subunits are expressed in most tissues and cell types at fairly constant levels relative to each other, suggesting that they perform their functions as part of a complex. A difference from this pattern is however seen for the APC6, which in some cases is more strongly expressed, suggesting a special function for this protein in certain tissues and cell types.
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Affiliation(s)
- P M Jörgensen
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
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239
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Abstract
The process of cell division, or mitosis, has fascinated biologists since its discovery in the late 1870s. Progress through mitosis is traditionally divided into stages that were defined over 100 years ago from analyses of fixed material from higher plants and animals. However, this terminology often leads to ambiguity, especially when comparing different systems. We therefore suggest that mitosis can be re-staged to reflect more accurately the molecular pathways that underlie key transitions.
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Affiliation(s)
- J Pines
- Wellcome/CRC Institute, Tennis Court Road, Cambridge, CB2 1QR, UK.
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240
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Abstract
Mitosis and cytokinesis are undoubtedly the most spectacular parts of the cell cycle. Errors in the choreography of these processes can lead to aneuploidy or genetic instability, fostering cell death or disease. Here, I give an overview of the many mitotic kinases that regulate cell division and the fidelity of chromosome transmission.
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Affiliation(s)
- E A Nigg
- Max-Planck-Institute for Biochemistry, Department of Cell Biology, Am Klopferspitz 18a, D-82152 Martinsried, Germany.
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241
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Golden A, Sadler PL, Wallenfang MR, Schumacher JM, Hamill DR, Bates G, Bowerman B, Seydoux G, Shakes DC. Metaphase to anaphase (mat) transition-defective mutants in Caenorhabditis elegans. J Cell Biol 2000; 151:1469-82. [PMID: 11134076 PMCID: PMC2150685 DOI: 10.1083/jcb.151.7.1469] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The metaphase to anaphase transition is a critical stage of the eukaryotic cell cycle, and, thus, it is highly regulated. Errors during this transition can lead to chromosome segregation defects and death of the organism. In genetic screens for temperature-sensitive maternal effect embryonic lethal (Mel) mutants, we have identified 32 mutants in the nematode Caenorhabditis elegans in which fertilized embryos arrest as one-cell embryos. In these mutant embryos, the oocyte chromosomes arrest in metaphase of meiosis I without transitioning to anaphase or producing polar bodies. An additional block in M phase exit is evidenced by the failure to form pronuclei and the persistence of phosphohistone H3 and MPM-2 antibody staining. Spermatocyte meiosis is also perturbed; primary spermatocytes arrest in metaphase of meiosis I and fail to produce secondary spermatocytes. Analogous mitotic defects cause M phase delays in mitotic germline proliferation. We have named this class of mutants "mat" for metaphase to anaphase transition defective. These mutants, representing six different complementation groups, all map near genes that encode subunits of the anaphase promoting complex or cyclosome, and, here, we show that one of the genes, emb-27, encodes the C. elegans CDC16 ortholog.
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Affiliation(s)
- Andy Golden
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
| | - Penny L. Sadler
- Department of Biology, University of Houston, Houston, Texas 77204
- Department of Biology, College of William and Mary, Williamsburg, Virginia 23187
| | - Matthew R. Wallenfang
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Jill M. Schumacher
- Department of Molecular Genetics, University of Texas, M.D. Anderson Cancer Center, Houston, Texas 77030
| | - Danielle R. Hamill
- Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403
| | - Gayle Bates
- Department of Biology, College of William and Mary, Williamsburg, Virginia 23187
| | - Bruce Bowerman
- Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403
| | - Geraldine Seydoux
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Diane C. Shakes
- Department of Biology, College of William and Mary, Williamsburg, Virginia 23187
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242
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Bäumer M, Künzler M, Steigemann P, Braus GH, Irniger S. Yeast Ran-binding protein Yrb1p is required for efficient proteolysis of cell cycle regulatory proteins Pds1p and Sic1p. J Biol Chem 2000; 275:38929-37. [PMID: 10991951 DOI: 10.1074/jbc.m007925200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ubiquitin-dependent proteolysis of specific target proteins is required for several important steps during the cell cycle. Degradation of such proteins is strictly cell cycle-regulated and triggered by two large ubiquitin ligases, termed anaphase-promoting complex (APC) and Skp1/Cullin/F-box complex (SCF). Here we show that yeast Ran-binding protein 1 (Yrb1p), a predominantly cytoplasmic protein implicated in nucleocytoplasmic transport, is required for cell cycle regulated protein degradation. Depletion of Yrb1p results in the accumulation of unbudded G(1) cells and of cells arrested in mitosis implying a function of Yrb1p in the G(1)/S transition and in the progression through mitosis. Temperature-sensitive yrb1-51 mutants are defective in APC-mediated degradation of the anaphase inhibitor protein Pds1p and in degradation of the cyclin-dependent kinase inhibitor Sic1p, a target of SCF. Thus, Yrb1p is crucial for efficient APC- and SCF-mediated proteolysis of important cell cycle regulatory proteins. We have identified the UBS1 gene as a multicopy suppressor of yrb1-51 mutants. Ubs1p is a nuclear protein, and its deletion is synthetic lethal with a yrb1-51 mutation. Interestingly, UBS1 was previously identified as a multicopy suppressor of cdc34-2 mutants, which are defective in SCF activity. We suggest that Ubs1p may represent a link between nucleocytoplasmic transport and ubiquitin ligase activity.
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Affiliation(s)
- M Bäumer
- Institute of Microbiology and Genetics, Georg-August-University, Grisebachstrasse 8, D-37077 Göttingen, Germany
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243
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Criqui MC, Parmentier Y, Derevier A, Shen WH, Dong A, Genschik P. Cell cycle-dependent proteolysis and ectopic overexpression of cyclin B1 in tobacco BY2 cells. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2000; 24:763-73. [PMID: 11135110 DOI: 10.1111/j.1365-313x.2000.t01-1-.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Activation of cyclin B/Cdc2 kinase complex triggers entry into mitosis in all eukaryotic cells. Although cyclin gene expression has been extensively studied in plants, not much is known at the level of the protein stability and function. Here, we demonstrated by using the highly synchronizable tobacco BY2 cell culture, that endogenous cyclin B1 protein undergoes cell cycle-dependent proteolysis and is stabilized when the spindle checkpoint has been activated. Furthermore, we established transgenic tobacco BY2 cell cultures expressing under the control of an inducible promoter, cyclin B1 protein as well as its non-degradable form as fusion proteins with GFP and found that the ectopic expression of these proteins did not dramatically disturb the cell cycle progression. These results indicate that, to a certain extent, cell cycle exit is possible without cyclin B1 proteolysis.
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Affiliation(s)
- M C Criqui
- Institut de Biologie Moléculaire des Plantes du CNRS, 12, rue du Général Zimmer, 67084 Strasbourg Cédex, France
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244
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Sumara I, Vorlaufer E, Gieffers C, Peters BH, Peters JM. Characterization of vertebrate cohesin complexes and their regulation in prophase. J Cell Biol 2000; 151:749-62. [PMID: 11076961 PMCID: PMC2169443 DOI: 10.1083/jcb.151.4.749] [Citation(s) in RCA: 325] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2000] [Accepted: 09/14/2000] [Indexed: 11/22/2022] Open
Abstract
In eukaryotes, sister chromatids remain connected from the time of their synthesis until they are separated in anaphase. This cohesion depends on a complex of proteins called cohesins. In budding yeast, the anaphase-promoting complex (APC) pathway initiates anaphase by removing cohesins from chromosomes. In vertebrates, cohesins dissociate from chromosomes already in prophase. To study their mitotic regulation we have purified two 14S cohesin complexes from human cells. Both complexes contain SMC1, SMC3, SCC1, and either one of the yeast Scc3p orthologs SA1 and SA2. SA1 is also a subunit of 14S cohesin in Xenopus. These complexes interact with PDS5, a protein whose fungal orthologs have been implicated in chromosome cohesion, condensation, and recombination. The bulk of SA1- and SA2-containing complexes and PDS5 are chromatin-associated until they become soluble from prophase to telophase. Reconstitution of this process in mitotic Xenopus extracts shows that cohesin dissociation does neither depend on cyclin B proteolysis nor on the presence of the APC. Cohesins can also dissociate from chromatin in the absence of cyclin-dependent kinase 1 activity. These results suggest that vertebrate cohesins are regulated by a novel prophase pathway which is distinct from the APC pathway that controls cohesins in yeast.
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Affiliation(s)
- I Sumara
- Research Institute of Molecular Pathology (IMP), A-1030 Vienna, Austria
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245
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Wang Y, Hu F, Elledge SJ. The Bfa1/Bub2 GAP complex comprises a universal checkpoint required to prevent mitotic exit. Curr Biol 2000; 10:1379-82. [PMID: 11084339 DOI: 10.1016/s0960-9822(00)00779-x] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
At the end of the cell cycle, cyclin-dependent kinase (CDK) activity is inactivated to allow mitotic exit [1]. A protein phosphatase, Cdc14, plays a key role during mitotic exit in budding yeast by activating the Cdh1 component of the anaphase-promoting complex to degrade cyclin B (Clb) and inducing the CDK inhibitor Sic1 to inactivate Cdk1 [2]. To prevent mitotic exit when the cell cycle is arrested at G2/M, cells must prevent CDK inactivation. In the spindle checkpoint pathway, this is accomplished through Bfa1/Bub2, a heteromeric GTPase-activating protein (GAP) that inhibits Clb degradation by keeping the G protein Tem1 inactive [3-5]. Tem1 is required for Cdc14 activation. Here we show that in budding yeast, BUB2 and BFA1 are also required for the maintenance of G2/M arrest in response to DNA damage and to spindle misorientation. cdc13-1 bub2 and cdc13-1 bfa1 but not cdc13-1 mad2 double mutants rebud and reduplicate their DNA at the restrictive temperature. We also found that the delay in mitotic exit in mutants with misoriented spindles depended on BUB2 and BFA1, but not on MAD2. We propose that Bfa1/Bub2 checkpoint pathway functions as a universal checkpoint in G2/M that prevents CDK inactivation in response to cell-cycle delay in G2/M.
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Affiliation(s)
- Y Wang
- Verna and Mars McLean Department of Biochemistry and Molecular Biology, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030, USA
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246
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Abstract
Yeast cells must segregate sister chromosomes to the opposite sides of the bud neck during mitosis. A pathway has been identified, involving a small GTPase, which prevents the onset of cytokinesis until one of the spindle poles has migrated into the bud.
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Affiliation(s)
- R Li
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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247
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Simbulan-Rosenthal CM, Ly DH, Rosenthal DS, Konopka G, Luo R, Wang ZQ, Schultz PG, Smulson ME. Misregulation of gene expression in primary fibroblasts lacking poly(ADP-ribose) polymerase. Proc Natl Acad Sci U S A 2000; 97:11274-9. [PMID: 11016956 PMCID: PMC17190 DOI: 10.1073/pnas.200285797] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Poly(ADP-ribose) polymerase (PARP) is implicated in the maintenance of genomic integrity, given that inhibition or depletion of this enzyme increases genomic instability in cells exposed to genotoxic agents. We previously showed that immortalized fibroblasts derived from PARP(-/-) mice exhibit an unstable tetraploid population, and partial chromosomal gains and losses in PARP(-/-) mice and immortalized fibroblasts are accompanied by changes in the expression of p53, Rb, and c-Jun, as well as other proteins. A tetraploid population has also now been detected in primary fibroblasts derived from PARP(-/-) mice. Oligonucleotide microarray analysis was applied to characterize more comprehensively the differences in gene expression between asynchronously dividing primary fibroblasts derived from PARP(-/-) mice and their wild-type littermates. Of the 11,000 genes monitored, 91 differentially expressed genes were identified. The loss of PARP results in down-regulation of the expression of several genes involved in regulation of cell cycle progression or mitosis, DNA replication, or chromosomal processing or assembly. PARP deficiency also up-regulates genes that encode extracellular matrix or cytoskeletal proteins that are implicated in cancer initiation or progression or in normal or premature aging. These results provide insight into the mechanism by which PARP deficiency impairs mitotic function, thereby resulting in the genomic alterations and chromosomal abnormalities as well as in altered expression of genes that may contribute to genomic instability, cancer, and aging.
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Affiliation(s)
- C M Simbulan-Rosenthal
- Department of Biochemistry and Molecular Biology, Georgetown University School of Medicine, 3900 Reservoir Road NW, Washington, DC 20007, USA
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248
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Walter AO, Seghezzi W, Korver W, Sheung J, Lees E. The mitotic serine/threonine kinase Aurora2/AIK is regulated by phosphorylation and degradation. Oncogene 2000; 19:4906-16. [PMID: 11039908 DOI: 10.1038/sj.onc.1203847] [Citation(s) in RCA: 226] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Aurora2 is a cell cycle regulated serine/threonine protein kinase which is overexpressed in many tumor cell lines. We demonstrate that Aurora2 is regulated by phosphorylation in a cell cycle dependent manner. This phosphorylation occurs on a conserved residue, Threonine 288, within the activation loop of the catalytic domain of the kinase and results in a significant increase in the enzymatic activity. Threonine 288 resides within a consensus motif for the cAMP dependent kinase and can be phosphorylated by PKA in vitro. The protein phosphatase 1 is shown to dephosphorylate this site in vitro, and in vivo the phosphorylation of T288 is induced by okadaic acid treatment. Furthermore, we show that the Aurora2 kinase is regulated by proteasome dependent degradation and that Aurora2 phosphorylated on T288 may be targeted for degradation during mitosis. Our experiments suggest that phosphorylation of T288 is important for regulation of the Aurora2 kinase both for its activity and its stability.
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Affiliation(s)
- A O Walter
- DNAX Research Institute, Palo Alto, California 94304, USA
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249
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Sorensen CS, Lukas C, Kramer ER, Peters JM, Bartek J, Lukas J. Nonperiodic activity of the human anaphase-promoting complex-Cdh1 ubiquitin ligase results in continuous DNA synthesis uncoupled from mitosis. Mol Cell Biol 2000; 20:7613-23. [PMID: 11003657 PMCID: PMC86321 DOI: 10.1128/mcb.20.20.7613-7623.2000] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2000] [Accepted: 07/21/2000] [Indexed: 12/29/2022] Open
Abstract
Ubiquitin-proteasome-mediated destruction of rate-limiting proteins is required for timely progression through the main cell cycle transitions. The anaphase-promoting complex (APC), periodically activated by the Cdh1 subunit, represents one of the major cellular ubiquitin ligases which, in Saccharomyces cerevisiae and Drosophila spp., triggers exit from mitosis and during G(1) prevents unscheduled DNA replication. In this study we investigated the importance of periodic oscillation of the APC-Cdh1 activity for the cell cycle progression in human cells. We show that conditional interference with the APC-Cdh1 dissociation at the G(1)/S transition resulted in an inability to accumulate a surprisingly broad range of critical mitotic regulators including cyclin B1, cyclin A, Plk1, Pds1, mitosin (CENP-F), Aim1, and Cdc20. Unexpectedly, although constitutively assembled APC-Cdh1 also delayed G(1)/S transition and lowered the rate of DNA synthesis during S phase, some of the activities essential for DNA replication became markedly amplified, mainly due to a progressive increase of E2F-dependent cyclin E transcription and a rapid turnover of the p27(Kip1) cyclin-dependent kinase inhibitor. Consequently, failure to inactivate APC-Cdh1 beyond the G(1)/S transition not only inhibited productive cell division but also supported slow but uninterrupted DNA replication, precluding S-phase exit and causing massive overreplication of the genome. Our data suggest that timely oscillation of the APC-Cdh1 ubiquitin ligase activity represents an essential step in coordinating DNA replication with cell division and that failure of mechanisms regulating association of APC with the Cdh1 activating subunit can undermine genomic stability in mammalian cells.
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Affiliation(s)
- C S Sorensen
- Danish Cancer Society, Institute of Cancer Biology, DK-2100 Copenhagen O, Denmark
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250
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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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