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Salamango DJ, Harris RS. Dual Functionality of HIV-1 Vif in APOBEC3 Counteraction and Cell Cycle Arrest. Front Microbiol 2021; 11:622012. [PMID: 33510734 PMCID: PMC7835321 DOI: 10.3389/fmicb.2020.622012] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 12/11/2020] [Indexed: 01/02/2023] Open
Abstract
Accessory proteins are a key feature that distinguishes primate immunodeficiency viruses such as human immunodeficiency virus type I (HIV-1) from other retroviruses. A prime example is the virion infectivity factor, Vif, which hijacks a cellular co-transcription factor (CBF-β) to recruit a ubiquitin ligase complex (CRL5) to bind and degrade antiviral APOBEC3 enzymes including APOBEC3D (A3D), APOBEC3F (A3F), APOBEC3G (A3G), and APOBEC3H (A3H). Although APOBEC3 antagonism is essential for viral pathogenesis, and a more than sufficient functional justification for Vif’s evolution, most viral proteins have evolved multiple functions. Indeed, Vif has long been known to trigger cell cycle arrest and recent studies have shed light on the underlying molecular mechanism. Vif accomplishes this function using the same CBF-β/CRL5 ubiquitin ligase complex to degrade a family of PPP2R5 phospho-regulatory proteins. These advances have helped usher in a new era of accessory protein research and fresh opportunities for drug development.
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Affiliation(s)
- Daniel J Salamango
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, United States.,Masonic Cancer Center, University of Minnesota, Minneapolis, MN, United States.,Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, United States
| | - Reuben S Harris
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, United States.,Masonic Cancer Center, University of Minnesota, Minneapolis, MN, United States.,Institute for Molecular Virology, University of Minnesota, Minneapolis, MN, United States.,Howard Hughes Medical Institute, University of Minnesota, Minneapolis, MN, United States
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2
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HIV-1 Vif Triggers Cell Cycle Arrest by Degrading Cellular PPP2R5 Phospho-regulators. Cell Rep 2020; 29:1057-1065.e4. [PMID: 31665623 PMCID: PMC6903395 DOI: 10.1016/j.celrep.2019.09.057] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 07/10/2019] [Accepted: 09/18/2019] [Indexed: 02/07/2023] Open
Abstract
HIV-1 Vif hijacks a cellular ubiquitin ligase complex to degrade antiviral APOBEC3 enzymes and PP2A phosphatase regulators (PPP2R5A–E). APOBEC3 counteraction is essential for viral pathogenesis. However, Vif also functions through an unknown mechanism to induce G2 cell cycle arrest. Here, deep mutagenesis is used to define the Vif surface required for PPP2R5 degradation and isolate a panel of separation-of-function mutants (PPP2R5 degradation-deficient and APOBEC3G degradation-proficient). Functional studies with Vif and PPP2R5 mutants were combined to demonstrate that PPP2R5 is, in fact, the target Vif degrades to induce G2 arrest. Pharmacologic and genetic approaches show that direct modulation of PP2A function or depletion of specific PPP2R5 proteins causes an indistinguishable arrest phenotype. Vif function in the cell cycle checkpoint is present in common HIV-1 subtypes worldwide and likely advantageous for viral pathogenesis. Salamango et al. discovered that the HIV-1 accessory protein Vif degrades several PP2A phospho-regulators to induce G2 cell cycle arrest. This activity is prevalent among diverse HIV-1 subtypes and global viral populations, suggesting that virus-induced G2 arrest is advantageous for pathogenesis.
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Ganapathy S, Fagman JB, Shen L, Yu T, Zhou X, Dai W, Makriyannis A, Chen C. Ral A, via activating the mitotic checkpoint, sensitizes cells lacking a functional Nf1 to apoptosis in the absence of protein kinase C. Oncotarget 2016; 7:84326-84337. [PMID: 27741517 PMCID: PMC5356664 DOI: 10.18632/oncotarget.12607] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 10/04/2016] [Indexed: 01/08/2023] Open
Abstract
Nf1 mutations or deletions are suggested to underlie the tumor predisposition of NF1 (neurofibromatosis type 1) and few treatments are available for treating NF1 patients with advanced malignant tumors. Aberrant activation of Ras in Nf1-deficient conditions is responsible for the promotion of tumorigenesis in NF1. PKC is proven to be an important factor in supporting the viability of Nf1-defected cells, but the molecular mechanisms are not fully understood. In this study, we demonstrate that the inhibition of protein kinase C (PKC) by 1-O-Hexadecyl-2-O-methyl-rac-glycerol (HMG, a PKC inhibitor) preferentially sensitizes Nf1-defected cells to apoptosis, via triggering a persistent mitotic arrest. In this process, Ral A is activated. Subsequently, Chk1 is phosphorylated and translocated to the nucleus. Silencing Ral A significantly blocks Chk1 nuclear translocation and releases HMG-treated Nf1-deficient cells from mitotic arrest, resulting in the reduction of the magnitude of apoptosis. Thus, our study reveals that PKC is able to maintain the homeostasis or viability of Nf1-defected cells and may serve as a potential target for developing new therapeutic strategies.
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Affiliation(s)
| | - Johan B Fagman
- The Institute of Clinic Sciences, Sahlgrenska Academy, Gothenburg, SE
| | - Ling Shen
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
| | - Tianqi Yu
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
| | - Xiaodong Zhou
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
- The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Wei Dai
- Department of Environmental Medicine, New York University, Tuxedo, NY, USA
| | | | - Changyan Chen
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
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4
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Zhou X, Kim SH, Shen L, Lee HJ, Chen C. Induction of mitotic catastrophe by PKC inhibition in Nf1-deficient cells. Cell Cycle 2014; 13:2340-8. [PMID: 25483185 DOI: 10.4161/cc.29297] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Mutations of tumor suppressor Nf1 gene deregulate Ras-mediated signaling, which confers the predisposition for developing benign or malignant tumors. Inhibition of protein kinase C (PKC) was shown to be in synergy with aberrant Ras for the induction of apoptosis in various types of cancer cells. However, it has not been investigated whether loss of PKC is lethal for Nf1-deficient cells. In this study, using HMG (3-hydroxy-3-methylgutaryl, a PKC inhibitor), we demonstrate that the inhibition of PKC by HMG treatment triggered a persistently mitotic arrest, resulting in the occurrence of mitotic catastrophe in Nf1-deficient ST8814 cells. However, the introduction of the Nf1 effective domain gene into ST8814 cells abolished this mitotic crisis. In addition, HMG injection significantly attenuated the growth of the xenografted ST8814 tumors. Moreover, Chk1 was phosphorylated, accompanied with the persistent increase of cyclin B1 expression in HMG-treated ST8814 cells. The knockdown of Chk1 by the siRNA prevented the Nf1-deficient cells from undergoing HMG-mediated mitotic arrest as well as mitotic catastrophe. Thus, our data suggested that the suppression of PKC activates the Chk1-mediated mitotic exit checkpoint in Nf1-deficient cells, leading to the induction of apoptosis via mitotic catastrophe. Collectively, the study indicates that targeting PKC may be a potential option for developing new strategies to treat Nf1-deficiency-related diseases.
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Affiliation(s)
- Xiaodong Zhou
- a Center for Drug Discovery; Northeastern University; Boston, MA USA
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5
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Xu Y, Ching YP, Zhou Y, Chiu JF, Chen F, He QY. Multiple pathways were involved in tubeimoside-1-induced cytotoxicity of HeLa cells. J Proteomics 2011; 75:491-501. [DOI: 10.1016/j.jprot.2011.08.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 08/03/2011] [Accepted: 08/16/2011] [Indexed: 01/22/2023]
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6
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Sakai K, Barnitz RA, Chaigne-Delalande B, Bidère N, Lenardo MJ. Human immunodeficiency virus type 1 Vif causes dysfunction of Cdk1 and CyclinB1: implications for cell cycle arrest. Virol J 2011; 8:219. [PMID: 21569376 PMCID: PMC3113979 DOI: 10.1186/1743-422x-8-219] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Accepted: 05/11/2011] [Indexed: 12/16/2022] Open
Abstract
The two major cytopathic factors in human immunodeficiency virus type 1 (HIV-1), the accessory proteins viral infectivity factor (Vif) and viral protein R (Vpr), inhibit cell-cycle progression at the G2 phase of the cell cycle. Although Vpr-induced blockade and the associated T-cell death have been well studied, the molecular mechanism of G2 arrest by Vif remains undefined. To elucidate how Vif induces arrest, we infected synchronized Jurkat T-cells and examined the effect of Vif on the activation of Cdk1 and CyclinB1, the chief cell-cycle factors for the G2 to M phase transition. We found that the characteristic dephosphorylation of an inhibitory phosphate on Cdk1 did not occur in infected cells expressing Vif. In addition, the nuclear translocation of Cdk1 and CyclinB1 was disregulated. Finally, Vif-induced cell cycle arrest was correlated with proviral expression of Vif. Taken together, our results suggest that Vif impairs mitotic entry by interfering with Cdk1-CyclinB1 activation.
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Affiliation(s)
- Keiko Sakai
- Laboratory of Immunology, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
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7
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Quantitative reconstitution of mitotic CDK1 activation in somatic cell extracts. Mol Cell 2010; 37:753-67. [PMID: 20347419 DOI: 10.1016/j.molcel.2010.02.023] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 12/15/2009] [Accepted: 02/10/2010] [Indexed: 11/22/2022]
Abstract
The regulation of mitotic entry in somatic cells differs from embryonic cells, yet it is only for embryonic cells that we have a quantitative understanding of this process. To gain a similar insight into somatic cells, we developed a human cell extract system that recapitulates CDK1 activation and nuclear envelope breakdown in response to mitotic cyclins. As cyclin B concentrations increase, CDK1 activates in a three-stage nonlinear response, creating an ordering of substrate phosphorylations. This response is established by dual regulatory feedback loops involving WEE1/MYT1, which impose a cyclin B threshold, and CDC25, which allows CDK1 to escape the WEE1/MYT1 inhibition. This system also exhibits a complex response to cyclin A. Cyclin A promotes WEE1 phosphorylation to weaken the negative feedback loop and primes mitotic entry through cyclin B. This observation explains the requirement of both cyclin A and cyclin B to initiate mitosis in somatic cells.
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Iwao Y, Uchida Y, Ueno S, Yoshizaki N, Masui Y. Midblastula transition (MBT) of the cell cycles in the yolk and pigment granule-free translucent blastomeres obtained from centrifuged Xenopus embryos. Dev Growth Differ 2005; 47:283-94. [PMID: 16026537 DOI: 10.1111/j.1440-169x.2005.00802.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We obtained translucent blastomeres free of yolk and pigment granules from Xenopus embryos which had been centrifuged at the beginning of the 8-cell stage with cellular integrity. They divided synchronously regardless of their cell size until they had decreased to 37.5 microm in radius; those smaller than this critical size, however, divided asynchronously with cell cycle times inversely proportional to the square of the cell radius after midblastula transition (MBT). The length of the S phase was determined as the time during which nuclear DNA fluorescence increased in Hoechst-stained blastomeres. When the cell cycle time exceeded 45 min, S and M phases were lengthened; when the cell cycle times exceeded 70 min, the G2 phase appeared; and after cell cycle times became longer than 150 min, the G1 phase appeared. Lengths of G1, S and M phases increased linearly with increasing cell cycle time. Enhanced green fluorescent protein (EGFP)-tagged proliferating cell nuclear antigen (PCNA) expressed in the blastomeres appeared in the S phase nucleus, but suddenly dispersed into the cytoplasm at the M phase. The system developed in this study is useful for examining the cell cycle behavior of the cell cycle-regulating molecules in living Xenopus blastomeres by fluorescence microscopy in real time.
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Affiliation(s)
- Yasuhiro Iwao
- Department of Biological Science, Faculty of Science, Yamaguchi University, 753-8512 Yamaguchi, Japan.
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9
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Terasaki M, Okumura EI, Hinkle B, Kishimoto T. Localization and dynamics of Cdc2-cyclin B during meiotic reinitiation in starfish oocytes. Mol Biol Cell 2003; 14:4685-94. [PMID: 14551249 PMCID: PMC266783 DOI: 10.1091/mbc.e03-04-0249] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Cdc2-cyclin B kinase has a central role in regulating the onset of M phase. In starfish oocytes, Cdc2-cyclin B begins to be activated approximately 10 min after application of maturation hormone, followed by accumulation in the nucleus then nuclear envelope breakdown. By immunofluorescence and by expressing a green fluorescent (GFP) chimera of cyclin B, we find that cyclin B is present in aggregates in the cytoplasm of immature oocytes. The aggregates disperse at approximately 10 min, suggesting that the dispersal is closely related to the activation of the kinase. Using cyclin B-GFP, the dispersion begins from the region containing the centrosomes. Extractability of Cdc2-cyclin B changes with similar kinetics during maturation. Active Cdc25 phosphatase released Cdc2-cyclin B from the detergent-insoluble fraction independently of its phosphatase activity. Live cell imaging also showed that Cdc2-cyclin B begins to accumulate in the nucleus before changes in nuclear pore permeability, consistent with Cdc2-cyclin B-induced disassembly of the pores.
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Affiliation(s)
- Mark Terasaki
- Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
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Robert C, Hue I, McGraw S, Gagné D, Sirard MA. Quantification of cyclin B1 and p34(cdc2) in bovine cumulus-oocyte complexes and expression mapping of genes involved in the cell cycle by complementary DNA macroarrays. Biol Reprod 2002; 67:1456-64. [PMID: 12390876 DOI: 10.1095/biolreprod.102.002147] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Although high amounts of cyclin B1 mRNA are present in bovine oocytes arrested at the germinal vesicle (GV) stage, the protein is not detectable. Furthermore, there is a depletion of the stored cyclin B1 mRNA in the oocyte as follicular growth progresses. To assess the effect of follicular growth on the accumulation of M-phase promoting factor (MPF) components, mRNA and protein levels of cyclin B1 and p34(cdc2) were measured in GV oocytes collected from diverse follicle size groups (<2 mm, 3-5 mm, and >6 mm). Because oocytes collected from very small follicles have high levels of cyclin B1 mRNA, the onset of its accumulation in the oocytes was evaluated by in situ hybridization of fetal ovaries. Also, a comparative expression map of cell cycle-related genes expressed in the oocyte and cumulus cells was established using nylon-based cDNA arrays, which allowed the detection of 35 different genes transcribed mostly in oocytes. Both components of the pre-MPF complex were expressed at the mRNA level in GV oocytes, whereas p34(cdc2) was the only pre-MPF protein detected at that stage, thus indicating that meiosis resumption in bovine oocytes is differentially regulated as compared with other mammals, and meiosis resumption seems to be regulated by the translation of cyclin B1 mRNA.
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Affiliation(s)
- Claude Robert
- Department of Animal Sciences, Centre de Recherche en Biologie de la Reproduction, Laval University, Québec, Canada G1K 7P4
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11
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Peter M, Le Peuch C, Labbé JC, Meyer AN, Donoghue DJ, Dorée M. Initial activation of cyclin-B1-cdc2 kinase requires phosphorylation of cyclin B1. EMBO Rep 2002; 3:551-6. [PMID: 12034754 PMCID: PMC1084145 DOI: 10.1093/embo-reports/kvf111] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2001] [Revised: 03/21/2002] [Accepted: 04/04/2002] [Indexed: 11/14/2022] Open
Abstract
At the G(2)/M transition of the cell cycle, the cdc25c phosphatase dephosphorylates inhibitory residues of cdc2, and cyclin-B-cdc2 kinase (MPF) is activated. Phosphorylation of cyclin B1 induces its nuclear accumulation, and, since cdc25c is also believed to accumulate and activate shortly before G(2)/M in the nucleus, it has been proposed that this induces cyclin-B1-cdc2 kinase activation. We demonstrate that cyclin B1 phosphorylation has another essential function in vivo: it is required for cdc25c and MPF activation, which does not require nuclear accumulation of cyclin B1, and occurs in the cytoplasm.
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Affiliation(s)
- Marion Peter
- Centre de Recherches de Biochimie Macromoléculaire, CNRS UPR 1086, 1919 route de Mende, F-34293 Montpellier cedex 5, France
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12
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Faivre J, Frank-Vaillant M, Poulhe R, Mouly H, Bréchot C, Sobczak-Thépot J, Jessus C. Membrane-anchored cyclin A2 triggers Cdc2 activation in Xenopus oocyte. FEBS Lett 2001; 506:243-8. [PMID: 11602254 DOI: 10.1016/s0014-5793(01)02920-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In Xenopus oocyte, the formation of complexes between neosynthesized cyclins and Cdc2 contributes to Cdc2 kinase activation that triggers meiotic divisions. It has been proposed that cytoplasmic membranes could be involved in this process. To investigate this possibility, we have injected in the oocyte two undegradable human cyclin A2 mutants anchored to the endoplasmic reticulum (ER) membrane. They encode fusion proteins between the truncated cyclin A2-Delta152 and a viral or cellular ER-targeting domain. We show that both mutants are fully functional as mitotic cyclins when expressed in Xenopus oocytes, bind Cdc2 and activate M-phase promoting factor.
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Affiliation(s)
- J Faivre
- INSERM U370, Institut Pasteur/Necker, Faculté de Médecine Necker, Paris, France
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13
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Wang P, Hayden S, Masui Y. Transition of the blastomere cell cycle from cell size-independent to size-dependent control at the midblastula stage in Xenopus laevis. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2000; 287:128-44. [PMID: 10900432 DOI: 10.1002/1097-010x(20000701)287:2<128::aid-jez3>3.0.co;2-g] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Dissociated animal cap blastomeres of Xenopus laevis blastulae were cultured at a low Ca level (1 microM) from 9th to 18th cell cycle at 22 +/- 1 degrees C and observed by a time-lapse video recorder. Blastomeres cleaved unequally to increase variability in cell size as cell cycles progressed, but synchronously at a constant cell cycle time of about 30 min up to the 12th cleavage in diploid cells, and up to the 13th cleavage in haploid cells, regardless of their cell sizes. Thereafter, blastomeres cleaved asynchronously at varying cell cycle times in proportion to the inverse square of their radii. The transition from the cell size-independent to -dependent cell cycles occurred at the critical cell radius, 37.5 microm for the diploid and 27.9 microm for the haploid. While the protein synthesis inhibitor, cycloheximide (CHX) lengthened cell cycle times two- to six-fold, epidermal growth factor (EGF) had no significant effect on the cell cycle. CHX-treated blastomeres synchronously cleaved at a constant cell cycle time of 60 min up to the 12th cleavage. Thereafter, cell cycle times became variable in proportion to the inverse square of radii in the presence of CHX at 0.10-0.14 microg/ml, but to the inverse cube of radii at 0.18 microg/ml. The critical cell size of CHX-treated blastomeres for the transition from cell size-independent to -dependent cell cycles remained the same as that of untreated blastomeres. Frequency distributions of cell cycle times of synchronous cell cycles were monomodal with the peak at 30 min, except for CHX-treated blastomeres with the peak at 60 min. In contrast, frequency distributions of asynchronous cell cycles were polymodal with peaks at multiples of a unit time of 30-35 min. To explain these results, we propose that blastomere cytoplasm has 30-min cycles that repeatedly produce mitosis promoting factor (MPF) in a quantity proportional to the cell surface area. MPF is neutralized when it titrates a nuclear inhibitor present in a quantity proportional to the genome size, and sequestered in the nucleus. When the total amount of MPF produced exceeds the threshold required to titrate all of the inhibitor, mitosis is initiated.
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Affiliation(s)
- P Wang
- Department of Zoology, University of Toronto, Ontario, Canada
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14
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Palmer A, Nebreda AR. The activation of MAP kinase and p34cdc2/cyclin B during the meiotic maturation of Xenopus oocytes. PROGRESS IN CELL CYCLE RESEARCH 2000; 4:131-43. [PMID: 10740821 DOI: 10.1007/978-1-4615-4253-7_12] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
G2-arrested Xenopus oocytes are induced to enter M-phase of meiosis by progesterone stimulation. This process, known as meiotic maturation, requires the activation of p34cdc2/cyclin B complexes (pre-MPF) which is brought about by the prior translation of specific maternal mRNAs stored in the oocyte. One of these mRNAs encodes for the protein kinase Mos which has an essential role in oocyte maturation, most likely due to its ability to activate MAP kinase (MAPK). Here we review our current knowledge on the Mos/MAPK signalling pathway and a recently found connection between MAPK-activated p90rsk and the p34cdc2 inhibitory kinase Myt1. We also discuss a pathway that involves the protein kinase Plx1 and leads to the activation of the phosphatase Cdc25, as well as other regulators of p34cdc2/cyclin B activity which may have a role in oocyte maturation.
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Affiliation(s)
- A Palmer
- European Molecular Biology Laboratory, Heidelberg, Germany
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15
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Wang P, Hayden S, Masui Y. Transition of the blastomere cell cycle from cell size-independent to size-dependent control at the midblastula stage inXenopus laevis. ACTA ACUST UNITED AC 2000. [DOI: 10.1002/1097-010x(20000701)287:2%3c128::aid-jez3%3e3.0.co;2-g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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McMillan JN, Sia RA, Bardes ES, Lew DJ. Phosphorylation-independent inhibition of Cdc28p by the tyrosine kinase Swe1p in the morphogenesis checkpoint. Mol Cell Biol 1999; 19:5981-90. [PMID: 10454545 PMCID: PMC84473 DOI: 10.1128/mcb.19.9.5981] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The morphogenesis checkpoint in budding yeast delays cell cycle progression in G(2) when the actin cytoskeleton is perturbed, providing time for cells to complete bud formation prior to mitosis. Checkpoint-induced G(2) arrest involves the inhibition of the master cell cycle regulatory cyclin-dependent kinase, Cdc28p, by the Wee1 family kinase Swe1p. Results of experiments using a nonphosphorylatable CDC28(Y19F) allele suggested that the checkpoint stimulated two inhibitory pathways, one that promoted phosphorylation at tyrosine 19 (Y19) and a poorly characterized second pathway that did not require Cdc28p Y19 phosphorylation. We present the results from a genetic screen for checkpoint-defective mutants that led to the repeated isolation of the dominant CDC28(E12K) allele that is resistant to Swe1p-mediated inhibition. Comparison of this allele with the nonphosphorylatable CDC28(Y19F) allele suggested that Swe1p is still able to inhibit CDC28(Y19F) in a phosphorylation-independent manner and that both the Y19 phosphorylation-dependent and -independent checkpoint pathways in fact reflect Swe1p inhibition of Cdc28p. Remarkably, we found that a Swe1p mutant lacking catalytic activity could significantly delay the cell cycle in vivo during a physiological checkpoint response, even when expressed at single copy. The finding that a Wee1 family kinase expressed at physiological levels can inhibit a nonphosphorylatable cyclin-dependent kinase has broad implications for many checkpoint studies using such mutants in other organisms.
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Affiliation(s)
- J N McMillan
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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17
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Liu F, Rothblum-Oviatt C, Ryan CE, Piwnica-Worms H. Overproduction of human Myt1 kinase induces a G2 cell cycle delay by interfering with the intracellular trafficking of Cdc2-cyclin B1 complexes. Mol Cell Biol 1999; 19:5113-23. [PMID: 10373560 PMCID: PMC84354 DOI: 10.1128/mcb.19.7.5113] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Myt1 protein kinase functions to negatively regulate Cdc2-cyclin B complexes by phosphorylating Cdc2 on threonine 14 and tyrosine 15. Throughout interphase, human Myt1 localizes to the endoplasmic reticulum and Golgi complex, whereas Cdc2-cyclin B1 complexes shuttle between the nucleus and the cytoplasm. Here we report that overproduction of either kinase-active or kinase-inactive forms of Myt1 blocked the nuclear-cytoplasmic shuttling of cyclin B1 and caused cells to delay in the G2 phase of the cell cycle. The COOH-terminal 63 amino acids of Myt1 were identified as a Cdc2-cyclin B1 interaction domain. Myt1 mutants lacking this domain no longer bound cyclin B1 and did not efficiently phosphorylate Cdc2-cyclin B1 complexes in vitro. In addition, cells overproducing mutant forms of Myt1 lacking the interaction domain exhibited normal trafficking of cyclin B1 and unperturbed cell cycle progression. These results suggest that the docking of Cdc2-cyclin B1 complexes to the COOH terminus of Myt1 facilitates the phosphorylation of Cdc2 by Myt1 and that overproduction of Myt1 perturbs cell cycle progression by sequestering Cdc2-cyclin B1 complexes in the cytoplasm.
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Affiliation(s)
- F Liu
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093, USA
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18
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De Smedt V, Crozet N, Jessus C. In vitro binding of free cdc2 and raf kinase to membrane vesicles: a possible new regulatory mechanism for cdc2 kinase activation in Xenopus oocyte. Microsc Res Tech 1999; 45:13-30. [PMID: 10206151 DOI: 10.1002/(sici)1097-0029(19990401)45:1<13::aid-jemt2>3.0.co;2-r] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The G2-M transition of the cell cycle is under the control of the M-phase promoting factor (MPF) formed of cdc2 kinase and cyclin B. The Xenopus prophase-blocked oocyte contains a stockpile of cyclin B2-cdc2 complexes that are maintained inactive by a double inhibitory phosphorylation on Thr-14 and Tyr-15 of cdc2. Free cdc2 molecules that are not associated with cyclin, are present in excess as compared to cyclin B2-associated cdc2. This pool of free cdc2 is permanently recruited to associate with neosynthetized cyclin B2 in the resting prophase oocyte, to feed up the pre-MPF stockpile. During re-entry into meiosis, free cdc2 could generate with newly synthesized cyclin B a small level of active MPF, that could serve as starter to initiate the conversion of pre-MPF into MPF. It was, therefore, of high interest to investigate whether free cdc2 interacts with other proteins and what could be its intracellular localization. To address these questions, we developed an in vitro system of membrane vesicles. We demonstrate here that free cdc2 is recovered in association with the external layer of membrane vesicles, whereas cyclin B2-associated cdc2 is not. Cyclin is able to associate in vitro with cdc2-containing membrane vesicles. This association does not induce the inhibitory cdc2 phosphorylations. However, it does not lead to active complexes, suggesting that membrane vesicles prevent cdc2 activation. C-Raf1, another kinase activated during reentry into meiosis, is also totally recovered in association with the membrane vesicles.
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Affiliation(s)
- V De Smedt
- Laboratoire de Physiologie de la Reproduction, ESA-CNRS 7080, Université Pierre et Marie Curie, Paris, France
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19
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Mowat MR, Stewart N. Mechanisms of cell cycle blocks at the G2/M transition and their role in differentiation and development. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 1999; 20:73-100. [PMID: 9928527 DOI: 10.1007/978-3-642-72149-6_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Affiliation(s)
- M R Mowat
- Manitoba Institute of Cell Biology, Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada
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20
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Affiliation(s)
- J Pines
- Wellcome/CRC Institute, Cambridge, UK.
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21
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Affiliation(s)
- M J Solomon
- Yale University School of Medicine, Department of Molecular Biophysics and Biochemistry, New Haven, Connecticut 06520-8024, USA.
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22
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Abstract
In eukaryotes, mitosis is initiated by M phase promoting factor (MPF), composed of B-type cyclins and their partner protein kinase, CDK1. In animal cells, MPF is cytoplasmic in interphase and is translocated into the nucleus after mitosis has begun, after which it associates with the mitotic apparatus until the cyclins are degraded in anaphase. We have used a fusion protein between human cyclin B1 and green fluorescent protein (GFP) to study this dynamic behaviour in real time, in living cells. We found that when we injected cyclin B1-GFP, or cyclin B1-GFP bound to CDK1 (i.e. MPF), into interphase nuclei it is rapidly exported into the cytoplasm. Cyclin B1 nuclear export is blocked by leptomycin B, an inhibitor of the recently identified export factor, exportin 1 (CRM1). The nuclear export of MPF is mediated by a nuclear export sequence in cyclin B1, and an export-defective cyclin B1 accumulates in interphase nuclei. Therefore, during interphase MPF constantly shuttles between the nucleus and the cytoplasm, but the bulk of MPF is retained in the cytoplasm by rapid nuclear export. We found that a cyclin mutant with a defective nuclear export signal does not enhance the premature mitosis caused by interfering with the regulatory phosphorylation of CDK1, but is more sensitive to inhibition by the Wee1 kinase.
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Affiliation(s)
- A Hagting
- Wellcome/CRC Institute and Department of Zoology, Tennis Court Road, Cambridge, CB2 1QR, UK
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23
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Rieder CL, Khodjakov A. Mitosis and checkpoints that control progression through mitosis in vertebrate somatic cells. PROGRESS IN CELL CYCLE RESEARCH 1998; 3:301-12. [PMID: 9552424 DOI: 10.1007/978-1-4615-5371-7_24] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
During mitosis in vertebrates the sister kinetochores on each replicated chromosome interact with two separating arrays of astral microtubules to form a bipolar spindle that produces and/or directs the forces for chromosome motion. In order to ensure faithful chromosome segregation cells have evolved mechanisms that delay progress into and out of mitosis until certain events are completed. At least two of these mitotic "checkpoint controls" can be identified in vertebrates. The first prevents nuclear envelope breakdown, and thus spindle formation, when the integrity of some nuclear component(s) is compromised. The second prevents chromosome disjunction and exit from mitosis until all of the kinetochores are attached to the spindle.
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Affiliation(s)
- C L Rieder
- Laboratory of Cell Regulation, Wadsworth Center, Albany, New York 12201-0509, USA
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24
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Pérez-Mongiovi D, Chang P, Houliston E. A propagated wave of MPF activation accompanies surface contraction waves at first mitosis in Xenopus. J Cell Sci 1998; 111 ( Pt 3):385-93. [PMID: 9427686 DOI: 10.1242/jcs.111.3.385] [Citation(s) in RCA: 44] [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 the period of mitosis, two surface contraction waves (SCWs) progress from the animal to vegetal poles of the Xenopus egg. It has been shown that these SCWs occur in parallel with the activation of MPF and with its subsequent inactivation in the animal and vegetal hemispheres, suggesting that they are responses to propagated waves of MPF activity across the egg. We have analysed the mechanism of MPF regulation in different regions of the egg in detail in relation to SCW progression. The distributions of histone HI kinase activity and of Cdc2 and cyclin B (the catalytic and regulatory subunits of MPF) were followed by dissection of intact eggs following freezing and in cultured fragments separated by ligation. Cdc2 was found to be distributed evenly throughout the egg cytoplasm. Loss of phosphorylated (inactive) forms of Cdc2 coincided spatially with the wave of MPF activation, while cyclin B2 accumulation occurred in parallel in animal and vegetal regions. In ligated vegetal pole fragments no MPF activation or Cdc2 dephosphorylation were detectable. A wave of cyclin B destruction that occurred in concert with the second SCW was also blocked. Taken together these results indicate that the triggering mechanism for MPF activation requires components specific to the animal cytoplasm, acting via Cdc2 dephosphorylation, and that MPF activation subsequently propagates autocatalytically across the egg. SCW progression in the vegetal hemisphere was followed directly by time-lapse videomicroscopy of subcortical mitochondrial islands. The first SCW traversed the vegetal pole at the time of MPF activation in this region. Like MPF activation and inactivation, SCWs were blocked in the vegetal region by ligation. These observations reinforce the hypothesis that the first SCW is a direct consequence of the MPF activation wave. It may reflect depolymerisation of the subcortical microtubule network since it coincided exactly with the arrest of the microtubule-dependent movement of ‘cortical rotation’ and was related in direction in most eggs. The cyclin B destruction wave and associated cortical contraction of the second SCW may be localised downstream consequences of the MPF activation wave, or they may propagate independently from the animal cytoplasm.
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Affiliation(s)
- D Pérez-Mongiovi
- Unité de Biologie Cellulaire Marine, ERS 643 CNRS-Université Paris VI, Station Zoologique, 06230 Villefranche-sur-mer, France
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25
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Murakami MS, Vande Woude GF. Analysis of the early embryonic cell cycles of Xenopus; regulation of cell cycle length by Xe-wee1 and Mos. Development 1998; 125:237-48. [PMID: 9486797 DOI: 10.1242/dev.125.2.237] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Xenopus, cdc2 tyrosine phosphorylation is detected in the first 60–75 minute cell cycle but not in the next eleven cell cycles (cycles 2–12) which are only 30 minutes long. Here we report that the wee1/cdc25 ratio increases before the first mitotic interphase. We show that the Xe-wee1 protein is absent in stage VI oocytes and is expressed from meiosis II until gastrulation. A dominant negative form of Xe-wee1 (KM wee1) reduced the level cdc2 tyrosine phosphorylation and length of the first cycle. However, the ratio of wee1/cdc25 did not decrease after the first cycle and therefore did not explain the lack of cdc2 tyrosine phosphorylation in, nor the rapidity of, cycles 2–12. Furthermore, there was no evidence for a wee1/myt1 inhibitor in cycles 2–12. We examined the role of Mos in the first cycle because it is present during the first 20 minutes of this cycle. We arrested the rapid embryonic cell cycle (cycle 2 or 3) with Mos and restarted the cell cycle with calcium ionophore; the 30 minute cycle was converted into a 60 minute cycle, with cdc2 tyrosine phosphorylation. In addition, the injection of a non-degradable Mos (MBP-Mos) into the first cycle resulted in a dramatic elongation of this cycle (to 140 minutes). MBP-Mos did not delay DNA replication or the translation of cyclins A or B; it did, however, result in the marked accumulation of tyrosine phosphorylated cdc2. Thus, while the wee1/cdc25 ratio changes during development, these changes may not be responsible for the variety of cell cycles observed during early Xenopus embryogenesis. Our experiments indicate that Mos/MAPK can also contribute to cell cycle length.
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Affiliation(s)
- M S Murakami
- ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, MD 21702, USA
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26
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Abrieu A, Fisher D, Simon MN, Dorée M, Picard A. MAPK inactivation is required for the G2 to M-phase transition of the first mitotic cell cycle. EMBO J 1997; 16:6407-13. [PMID: 9351823 PMCID: PMC1170247 DOI: 10.1093/emboj/16.21.6407] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Down-regulation of MAP kinase (MAPK) is a universal consequence of fertilization in the animal kingdom, although its role is not known. Here we show that MAPK inactivation is essential for embryos, both vertebrate and invertebrate, to enter first mitosis. Suppressing down-regulation of MAPK at fertilization, for example by constitutively activating the upstream MAPK cascade, specifically suppresses cyclin B-cdc2 kinase activation and its consequence, entry into first mitosis. It thus appears that MAPK functions in meiotic maturation by preventing unfertilized eggs from proceeding into parthenogenetic development. The most general effect of artificially maintaining MAPK activity after fertilization is prevention of the G2 to M-phase transition in the first mitotic cell cycle, even though inappropriate reactivation of MAPK after fertilization may lead to metaphase arrest in vertebrates. Advancing the time of MAPK inactivation in fertilized eggs does not, however, speed up their entry into first mitosis. Thus, sustained activity of MAPK during part of the first mitotic cell cycle is not responsible for late entry of fertilized eggs into first mitosis.
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Affiliation(s)
- A Abrieu
- Centre de Recherches de Biochimie Macromoléculaire, Montpellier, France
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27
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de Moor CH, Richter JD. The Mos pathway regulates cytoplasmic polyadenylation in Xenopus oocytes. Mol Cell Biol 1997; 17:6419-26. [PMID: 9343404 PMCID: PMC232494 DOI: 10.1128/mcb.17.11.6419] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Cytoplasmic polyadenylation controls the translation of several maternal mRNAs during Xenopus oocyte maturation and requires two sequences in the 3' untranslated region (UTR), the U-rich cytoplasmic polyadenylation element (CPE), and the hexanucleotide AAUAAA. c-mos mRNA is polyadenylated and translated soon after the induction of maturation, and this protein kinase is necessary for a kinase cascade culminating in cdc2 kinase (MPF) activation. Other mRNAs are polyadenylated later, around the time of cdc2 kinase activation. To determine whether there is a hierarchy in the cytoplasmic polyadenylation of maternal mRNAs, we ablated c-mos mRNA with an antisense oligonucleotide. This prevented histone B4 and cyclin A1 and B1 mRNA polyadenylation, indicating that the polyadenylation of these mRNAs is Mos dependent. To investigate a possible role of cdc2 kinase in this process, cyclin B was injected into oocytes lacking c-mos mRNA. cdc2 kinase was activated, but mitogen-activated protein kinase was not. However, polyadenylation of cyclin B1 and histone B4 mRNA was still observed. This demonstrates that cdc2 kinase can induce cytoplasmic polyadenylation in the absence of Mos. Our data further indicate that although phosphorylation of the CPE binding protein may be involved in the induction of Mos-dependent polyadenylation, it is not required for Mos-independent polyadenylation. We characterized the elements conferring Mos dependence (Mos response elements) in the histone B4 and cyclin B1 mRNAs by mutational analysis. For histone B4 mRNA, the Mos response elements were in the coding region or 5' UTR. For cyclin B1 mRNA, the main Mos response element was a CPE that overlaps with the AAUAAA hexanucleotide. This indicates that the position of the CPE can have a profound influence on the timing of cytoplasmic polyadenylation.
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Affiliation(s)
- C H de Moor
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical Center, Worcester 01655, USA
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28
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Nishijima H, Nishitani H, Seki T, Nishimoto T. A dual-specificity phosphatase Cdc25B is an unstable protein and triggers p34(cdc2)/cyclin B activation in hamster BHK21 cells arrested with hydroxyurea. J Cell Biol 1997; 138:1105-16. [PMID: 9281587 PMCID: PMC2136770 DOI: 10.1083/jcb.138.5.1105] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
By incubating at 30 degrees C in the presence of an energy source, p34(cdc2)/cyclin B was activated in the extract prepared from a temperature-sensitive mutant, tsBN2, which prematurely enters mitosis at 40 degrees C, the nonpermissive temperature (Nishimoto, T. , E. Eilen, and C. Basilico. 1978. Cell. 15:475-483), and wild-type cells of the hamster BHK21 cell line arrested in S phase, without protein synthesis. Such an in vitro activation of p34(cdc2)/cyclin B, however, did not occur in the extract prepared from cells pretreated with protein synthesis inhibitor cycloheximide, although this extract still retained the ability to inhibit p34(cdc2)/cyclin B activation. When tsBN2 cells arrested in S phase were incubated at 40 degrees C in the presence of cycloheximide, Cdc25B, but not Cdc25A and C, among a family of dual-specificity phosphatases, Cdc25, was lost coincidentally with the lack of the activation of p34(cdc2)/cyclin B. Consistently, the immunodepletion of Cdc25B from the extract inhibited the activation of p34(cdc2)/cyclin B. Cdc25B was found to be unstable (half-life < 30 min). Cdc25B, but not Cdc25C, immunoprecipitated from the extract directly activated the p34(cdc2)/cyclin B of cycloheximide-treated cells as well as that of nontreated cells, although Cdc25C immunoprecipitated from the extract of mitotic cells activated the p34(cdc2)/cyclin B within the extract of cycloheximide-treated cells. Our data suggest that Cdc25B made an initial activation of p34(cdc2)/cyclin B, which initiates mitosis through the activation of Cdc25C.
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Affiliation(s)
- H Nishijima
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-82, Japan
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29
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Affiliation(s)
- T Weinert
- Department of Molecular and Cellular Biology, University of Arizona, Tuscon, AZ 85721, USA.
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30
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Ellerby HM, Martin SJ, Ellerby LM, Naiem SS, Rabizadeh S, Salvesen GS, Casiano CA, Cashman NR, Green DR, Bredesen DE. Establishment of a cell-free system of neuronal apoptosis: comparison of premitochondrial, mitochondrial, and postmitochondrial phases. J Neurosci 1997; 17:6165-78. [PMID: 9236228 PMCID: PMC3913837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Apoptosis is a fundamental process required for normal development of the nervous system and is triggered during neurodegenerative disease. To dissect the molecular events leading to neuronal cell death, we have developed a cell-free model of neuronal apoptosis. The model faithfully reproduces key elements of apoptosis, including chromatin condensation, DNA fragmentation, caspase activation/processing, and selective substrate cleavage. We report that cell-free apoptosis is activated in premitochondrial, mitochondrial, and postmitochondrial phases by tamoxifen, mastoparan, and cytochrome c, respectively, allowing a functional ordering of these proapoptotic modulators. Furthermore, this is the first report of mitochondrial-mediated activation of cell-free apoptosis in a cell extract. Although Bcl-2 blocks activation at the premitochondrial and mitochondrial levels, it does not affect the postmitochondrial level. The cell-free system described here provides a valuable tool to elucidate the molecular events leading to neuronal cell death.
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Affiliation(s)
- H M Ellerby
- The Burnham Institute, La Jolla Cancer Research Center, La Jolla, California 92037, USA
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31
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de Vantéry C, Stutz A, Vassalli JD, Schorderet-Slatkine S. Acquisition of meiotic competence in growing mouse oocytes is controlled at both translational and posttranslational levels. Dev Biol 1997; 187:43-54. [PMID: 9224673 DOI: 10.1006/dbio.1997.8599] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Full-grown mouse oocytes spontaneously resume meiosis in vitro when released from their follicular environment. By contrast, growing oocytes are not competent to resume meiosis; the molecular basis of meiotic competence is not known. Entry into M phase of the eukaryotic cell cycle is controlled by MPF, a catalytically active complex comprising p34cdc2 kinase and cyclin B. Incompetent oocytes contain levels of cyclin B comparable to those in competent oocytes, while their level of p34cdc2 is markedly lower; p34cdc2 accumulates abruptly at the end of oocyte growth, at the time of meiotic competence acquisition. We show here that this change in p34cdc2 concentration is not secondary to a corresponding change in the concentration of the cognate mRNA, indicating that translational control may be involved. Microinjection of translatable p34cdc2 mRNA into incompetent oocytes yielded high levels of the protein, but it did not lead to resumption of meiosis. Similarly, microinjection of cyclin B1 mRNA resulted in accumulation of the protein, but not in the acquisition of meiotic competence. By contrast, the microinjection of both p34cdc2 and cyclin B1 mRNAs in incompetent oocytes induced histone H1 and MAP kinase activation, germinal vesicle breakdown, and entry into M-phase including the translational activation of a dormant mRNA. Thus, endogenous cyclin B1 in incompetent oocytes is not available for interaction with p34cdc2, suggesting that a posttranslational event must occur to achieve meiotic competence. Microinjection of either p34cdc2 or cyclin B1 mRNAs accelerated meiotic reinitiation of okadaic acid-treated incompetent oocytes. Taken together, these results suggest that acquisition of meiotic competence by mouse oocytes is regulated at both translational and posttranslational levels.
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Affiliation(s)
- C de Vantéry
- Clinique de Stérilité et d'Endocrinologie Gynécologique, Département de Gynécologie et Obstétrique, Maternité, Hôpital Cantonal Universitaire de Geneve, Genèva, Switzerland
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32
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Blasina A, Paegle ES, McGowan CH. The role of inhibitory phosphorylation of CDC2 following DNA replication block and radiation-induced damage in human cells. Mol Biol Cell 1997; 8:1013-23. [PMID: 9201712 PMCID: PMC305710 DOI: 10.1091/mbc.8.6.1013] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
It has been suggested that the survival response of p53 defective tumor cells to agents that inhibit DNA replication or damage DNA may be largely dependent on cell cycle checkpoints that regulate the onset of mitosis. In human cells, the mitosis-inducing kinase CDC2/cyclin B is inhibited by phosphorylation of threonine-14 and tyrosine-15, but the roles of these phosphorylations in enforcing checkpoints is not known. We have investigated the situation in a human cervical carcinoma cell line (HeLa cells) and found that low level expression of a mutant nonphosphorylatable form of CDC2 abrogates regulation of the endogenous CDC2/cyclin B. Disruption of this pathway is toxic and renders cells highly sensitive to killing by DNA damage or by inhibition of DNA replication. These findings establish the importance of inhibitory phosphorylation of CDC2 in the survival mechanism used by human cells when exposed to some of the most common forms of anticancer therapy.
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Affiliation(s)
- A Blasina
- Department of Molecular Biology, Scripps Research Institute, La Jolla, California 92037, USA
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33
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Abstract
During embryogenesis, cell division must be spatially and temporally regulated with respect to other developmental processes. Leech embryos undergo a series of unequal and asynchronous cleavages to produce individually recognizable cells whose lineages, developmental fates and cell cycle properties have been characterized. Thus, leech embryos provide an opportunity to examine the regulation of cell division at the level of individual well-characterized cells within a community of different types of cells. Isolation of leech homologues of some of the highly conserved regulators of the cell division cycle, and characterization of their patterns of maternal and zygotic expression, indicate that the cell divisions of early leech embryos are regulated by cell type-specific mechanisms. These studies with leech embryos contribute to the emerging appreciation of the diverse mechanisms by which animals regulate cell division during early development.
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Affiliation(s)
- S T Bissen
- Department of Biology, University of Missouri-St Louis 63121-4499, USA.
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34
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Kominami K, Okura N, Kawamura M, DeMartino GN, Slaughter CA, Shimbara N, Chung CH, Fujimuro M, Yokosawa H, Shimizu Y, Tanahashi N, Tanaka K, Toh-e A. Yeast counterparts of subunits S5a and p58 (S3) of the human 26S proteasome are encoded by two multicopy suppressors of nin1-1. Mol Biol Cell 1997; 8:171-87. [PMID: 9017604 PMCID: PMC276068 DOI: 10.1091/mbc.8.1.171] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Nin1p, a component of the 26S proteasome of Saccharomyces cerevisiae, is required for activation of Cdc28p kinase at the G1-S-phase and G2-M boundaries. By exploiting the temperature-sensitive phenotype of the nin1-1 mutant, we have screened for genes encoding proteins with related functions to Nin1p and have cloned and characterized two new multicopy suppressors, SUN1 and SUN2, of the nin1-1 mutation. SUN1 can suppress a null nin1 mutation, whereas SUN2, an essential gene, does not. Sun1p is a 268-amino acid protein which shows strong similarity to MBP1 of Arabidopsis thaliana, a homologue of the S5a subunit of the human 26S proteasome. Sun1p binds ubiquitin-lysozyme conjugates as do S5a and MBP1. Sun2p (523 amino acids) was found to be homologous to the p58 subunit of the human 26S proteasome. cDNA encoding the p58 component was cloned. Furthermore, expression of a derivative of p58 from which the N-terminal 150 amino acids had been removed restored the function of a null allele of SUN2. During glycerol density gradient centrifugation, both Sun1p and Sun2p comigrated with the known proteasome components. These results, as well as other structural and functional studies, indicate that both Sun1p and Sun2p are components of the regulatory module of the yeast 26S proteasome.
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Affiliation(s)
- K Kominami
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan
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35
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Lew DJ, Kornbluth S. Regulatory roles of cyclin dependent kinase phosphorylation in cell cycle control. Curr Opin Cell Biol 1996; 8:795-804. [PMID: 8939679 DOI: 10.1016/s0955-0674(96)80080-9] [Citation(s) in RCA: 245] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Cyclins and cyclin-dependent kinases (Cdks) are universal regulators of cell cycle progression in eukaryotic cells. Cdk activity is controlled by phosphorylation at three conserved sites, and many of the enzymes that act on these sites have now been identified. Although the biochemistry of Cdk phosphorylation is relatively well understood, the regulatory roles of such phosphorylation are, in many cases, obscure. Recent studies have uncovered new and unexpected potential roles, and prompted re-examination of previously assumed roles, of Cdk phosphorylation.
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Affiliation(s)
- D J Lew
- Department of Molecular Cancer Biology, Box 3686, Duke University Medical Center, Durham, NC 27710, USA.
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36
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Knudsen KE, Knudsen ES, Wang JY, Subramani S. p34cdc2 kinase activity is maintained upon activation of the replication checkpoint in Schizosaccharomyces pombe. Proc Natl Acad Sci U S A 1996; 93:8278-83. [PMID: 8710861 PMCID: PMC38661 DOI: 10.1073/pnas.93.16.8278] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
All eukaryotes use feedback controls to order and coordinate cell cycle events. In Schizosaccharomyces pombe, several classes of checkpoint genes serve to ensure that DNA replication is complete and free of error before the onset of mitosis. Wild-type cells normally arrest upon inhibition of DNA synthesis or in response to DNA damage, although the exact mechanisms controlling this arrest are unclear. Genetic evidence in fission yeast suggests that the dependence of mitosis upon completion of DNA replication is linked to the regulation of the p34cdc2 cyclin-dependent kinase. It has been hypothesized that inhibition of DNA synthesis triggers down-regulation of p34cdc2 kinase activity, although this has never been shown biochemically. We analyzed the activity of p34cdc2 in wild-type and checkpoint-defective cells treated with a DNA synthesis inhibitor. Using standard in vitro assays we demonstrate that p34cdc2 kinase activity is maintained in wild-type cells arrested at the replication checkpoint. We also used a novel in vivo assay for p34cdc2 kinase activity, in which we expressed a fragment of the human retinoblastoma tumor suppressor protein in fission yeast. Phosphorylation of this fragment of the human retinoblastoma tumor suppressor protein is dependent on p34cdc2 kinase activity, and this activity is also maintained in cells arrested at the replication checkpoint. These data suggest that the mechanism for cell-cycle arrest in response to incomplete DNA synthesis is not dependent on the attenuation of p34cdc2 activity.
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Affiliation(s)
- K E Knudsen
- Department of Biology, University of California at San Diego, La Jolla 92093-0322, USA
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37
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Ye XS, Fincher RR, Tang A, O'Donnell K, Osmani SA. Two S-phase checkpoint systems, one involving the function of both BIME and Tyr15 phosphorylation of p34cdc2, inhibit NIMA and prevent premature mitosis. EMBO J 1996; 15:3599-610. [PMID: 8670863 PMCID: PMC451970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We demonstrate that there are at least two S-phase checkpoint mechanisms controlling mitosis in Aspergillus. The first responds to the rate of DNA replication and inhibits mitosis via tyrosine phosphorylation of p34cdc2. Cells unable to tyrosine phosphorylate p34cdc2 are therefore viable but are unable to tolerate low levels of hydroxyurea and prematurely enter lethal mitosis when S-phase is slowed. However, if the NIMA mitosis-promoting kinase is inactivated then non-tyrosine-phosphorylated p34cdc2 cannot promote cells prematurely into mitosis. Lack of tyrosine-phosphorylated p34cdc2 also cannot promote mitosis, or lethality, if DNA replication is arrested, demonstrating the presence of a second S-phase checkpoint mechanism over mitotic initiation which we show involves the function of BIME. In order to overcome the S-phase arrest checkpoint over mitosis it is necessary both to prevent tyrosine phosphorylation of p34cdc2 and also to inactivate BIME. Lack of tyrosine phosphorylation of p34cdc2 allows precocious expression of NIMA during S-phase arrest, and lack of BIME then allows activation of this prematurely expressed NIMA by phosphorylation. The mitosis-promoting NIMA kinase is thus a target for S-phase checkpoint controls.
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Affiliation(s)
- X S Ye
- Weis Center for Research, Geisinger Clinic, Danville, PA 17822-2617, USA
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