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Hartmann E, Fernàndez V, Moreno V, Valls J, Hernández L, Bosch F, Abrisqueta P, Klapper W, Dreyling M, Hoster E, Müller-Hermelink HK, Ott G, Rosenwald A, Campo E. Five-gene model to predict survival in mantle-cell lymphoma using frozen or formalin-fixed, paraffin-embedded tissue. J Clin Oncol 2008; 26:4966-72. [PMID: 18606985 DOI: 10.1200/jco.2007.12.0410] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PURPOSE Despite the common underlying translocation t(11;14) involving cyclin D1 that is present in nearly all cases of mantle-cell lymphoma (MCL), the clinical course of the disease is highly variable. The aim of the present study was to develop a quantitative gene expression-based model to predict survival in newly diagnosed patients with MCL that involves a minimum number of genes and is applicable to fresh-frozen and formalin-fixed, paraffin-embedded (FFPE) tumor samples. PATIENTS AND METHODS The expression of 33 genes with potential prognostic and pathogenetic impact in MCL was analyzed using quantitative reverse-transcription polymerase chain reactions (qRT-PCR) in a low-density array format in frozen tumor samples from 73 patients with MCL. Multivariate Cox methods and stepwise algorithms were applied to build gene expression-based survival predictors. An optimized five-gene model was subsequently applied to FFPE tumor samples from 13 patients with MCL from the initial series and to 42 independent MCL samples. RESULTS The optimized survival predictor was composed of the five genes RAN, MYC, TNFRSF10B, POLE2, and SLC29A2 and was validated for application in FFPE tissue samples. It allowed the survival prediction of patients with MCL with widely disparate clinical outcome and was superior to the immunohistochemical marker Ki-67, an established prognostic factor in MCL. CONCLUSION We here present a validated qRT-PCR-based test for survival prediction in patients with MCL that is applicable to fresh frozen as well as to FFPE tissue specimens. This test may prove useful to guide individualized treatment approaches for patients with MCL.
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Affiliation(s)
- Elena Hartmann
- Institute of Pathology, University of Würzburg, Würzburg, Germany
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52
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A survivin-ran complex regulates spindle formation in tumor cells. Mol Cell Biol 2008; 28:5299-311. [PMID: 18591255 DOI: 10.1128/mcb.02039-07] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Aberrant cell division is a hallmark of cancer, but the molecular circuitries of this process in tumor cells are not well understood. Here, we used a high-throughput proteomics screening to identify novel molecular partners of survivin, an essential regulator of mitosis overexpressed in cancer. We found that survivin associates with the small GTPase Ran in an evolutionarily conserved recognition in mammalian cells and Xenopus laevis extracts. This interaction is regulated during the cell cycle, involves Ran-GTP, requires a discrete binding interface centered on Glu65 in survivin, and is independent of the Ran effector Crm1. Disruption of a survivin-Ran complex does not affect the assembly of survivin within the chromosomal passenger complex or its cytosolic accumulation, but it inhibits the delivery of the Ran effector molecule TPX2 to microtubules. In turn, this results in aberrant mitotic spindle formation and chromosome missegregation in tumor, but not normal, cells. Therefore, survivin is a novel effector of Ran signaling, and this pathway may be preferentially exploited for spindle assembly in tumor cells.
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53
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Ran GTPase guanine nucleotide exchange factor RCC1 is phosphorylated on serine 11 by cdc2 kinase in vitro. Mol Biol Rep 2008; 36:717-23. [PMID: 18568422 DOI: 10.1007/s11033-008-9234-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Accepted: 03/17/2008] [Indexed: 10/22/2022]
Abstract
RCC1, a guanine nucleotide exchange factor for Ran GTPase, plays essential roles in the growth and viability of mammalian cells. Here, we examined the phosphorylation of specific serine and threonine residues of RCC1 in vivo and showed that RCC1 is indeed phosphorylated. Analysis by two-dimensional (2D) gel electrophoresis suggested that serine 11 (S11) of hamster RCC1 is phosphorylated in vivo. A point mutation of S11 of hamster RCC1 resulted in a decrease in the number of 2D gel spots, indicating a lack of phosphorylation at the mutant residue. S11 phosphorylation in vitro depended on cyclin B-cdc2 kinase. An RCC1 mutant in which all N-terminal serine and threonine residues were substituted with glutamate residues to mimic phosphorylation at these residues showed decreased binding to the karyopherin, KPNA4, compared with wild type RCC1. We conclude that RCC1 undergoes post-translational phosphorylation.
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Abstract
The small nuclear GTPase Ran controls the directionality of macromolecular transport between the nucleus and the cytoplasm. Ran also has important roles during mitosis, when the nucleus is dramatically reorganized to allow chromosome segregation. Ran directs the assembly of the mitotic spindle, nuclear-envelope dynamics and the timing of cell-cycle transitions. The mechanisms that underlie these functions provide insights into the spatial and temporal coordination of the changes that occur in intracellular organization during the cell-division cycle.
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Affiliation(s)
- Paul R Clarke
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY, Scotland, UK.
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55
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Zhao Q, Brkljacic J, Meier I. Two distinct interacting classes of nuclear envelope-associated coiled-coil proteins are required for the tissue-specific nuclear envelope targeting of Arabidopsis RanGAP. THE PLANT CELL 2008; 20:1639-51. [PMID: 18591351 PMCID: PMC2483365 DOI: 10.1105/tpc.108.059220] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Ran GTPase plays essential roles in multiple cellular processes, including nucleocytoplasmic transport, spindle formation, and postmitotic nuclear envelope (NE) reassembly. The cytoplasmic Ran GTPase activating protein RanGAP is critical to establish a functional RanGTP/RanGDP gradient across the NE and is associated with the outer surface of the NE in metazoan and higher plant cells. Arabidopsis thaliana RanGAP association with the root tip NE requires a family of likely plant-specific nucleoporins combining coiled-coil and transmembrane domains (CC-TMD) and WPP domain-interacting proteins (WIPs). We have now identified, by tandem affinity purification coupled with mass spectrometry, a second family of CC-TMD proteins, structurally similar, yet clearly distinct from the WIP family, that is required for RanGAP NE association in root tip cells. A combination of loss-of-function mutant analysis and protein interaction data indicates that at least one member of each NE-associated CC-TMD protein family is required for RanGAP targeting in root tip cells, while both families are dispensable in other plant tissues. This suggests an unanticipated complexity of RanGAP NE targeting in higher plant cells, contrasting both the single nucleoporin anchor in metazoans and the lack of targeting in fungi and proposes an early evolutionary divergence of the underlying plant and animal mechanisms.
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Affiliation(s)
- Qiao Zhao
- Department of Plant Cellular and Molecular Biology, Ohio State University, Columbus, Ohio 43210, USA
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56
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Torosantucci L, De Luca M, Guarguaglini G, Lavia P, Degrassi F. Localized RanGTP accumulation promotes microtubule nucleation at kinetochores in somatic mammalian cells. Mol Biol Cell 2008; 19:1873-82. [PMID: 18287525 PMCID: PMC2366853 DOI: 10.1091/mbc.e07-10-1050] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Revised: 02/01/2008] [Accepted: 02/08/2008] [Indexed: 11/11/2022] Open
Abstract
Centrosomes are the major sites for microtubule nucleation in mammalian cells, although both chromatin- and kinetochore-mediated microtubule nucleation have been observed during spindle assembly. As yet, it is still unclear whether these pathways are coregulated, and the molecular requirements for microtubule nucleation at kinetochore are not fully understood. This work demonstrates that kinetochores are initial sites for microtubule nucleation during spindle reassembly after nocodazole. This process requires local RanGTP accumulation concomitant with delocalization from kinetochores of the hydrolysis factor RanGAP1. Kinetochore-driven microtubule nucleation is also activated after cold-induced microtubule disassembly when centrosome nucleation is impaired, e.g., after Polo-like kinase 1 depletion, indicating that dominant centrosome activity normally masks the kinetochore-driven pathway. In cells with unperturbed centrosome nucleation, defective RanGAP1 recruitment at kinetochores after treatment with the Crm1 inhibitor leptomycin B activates kinetochore microtubule nucleation after cold. Finally, nascent microtubules associate with the RanGTP-regulated microtubule-stabilizing protein HURP in both cold- and nocodazole-treated cells. These data support a model for spindle assembly in which RanGTP-dependent abundance of nucleation/stabilization factors at centrosomes and kinetochores orchestrates the contribution of the two spindle assembly pathways in mammalian cells. The complex of RanGTP, the export receptor Crm1, and nuclear export signal-bearing proteins regulates microtubule nucleation at kinetochores.
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Affiliation(s)
- Liliana Torosantucci
- IBPM Institute of Molecular Biology and Pathology, National Research Council, c/o University of Rome “La Sapienza”, 00185 Rome, Italy
| | - Maria De Luca
- IBPM Institute of Molecular Biology and Pathology, National Research Council, c/o University of Rome “La Sapienza”, 00185 Rome, Italy
| | - Giulia Guarguaglini
- IBPM Institute of Molecular Biology and Pathology, National Research Council, c/o University of Rome “La Sapienza”, 00185 Rome, Italy
| | - Patrizia Lavia
- IBPM Institute of Molecular Biology and Pathology, National Research Council, c/o University of Rome “La Sapienza”, 00185 Rome, Italy
| | - Francesca Degrassi
- IBPM Institute of Molecular Biology and Pathology, National Research Council, c/o University of Rome “La Sapienza”, 00185 Rome, Italy
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57
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Abstract
Deregulated cell division is a hallmark of cancer, but whether tumor cells become dependent on specific mitotic mechanisms is not known. Here, we show that the small GTPase Ran, a regulator of mitotic spindle formation, is differentially overexpressed in human cancer as compared with normal tissues, in vivo. Acute silencing of Ran in various tumor cell types causes aberrant mitotic spindle formation, mitochondrial dysfunction, and apoptosis. This pathway does not require p53, Bax, or Smac, but is controlled by survivin as a novel Ran target in cancer. Conversely, loss of Ran in normal cells is well tolerated and does not result in mitotic defects or loss of cell viability. Therefore, tumor cells can become dependent on Ran signaling for cell division, and targeting this pathway may provide a novel and selective anticancer strategy.
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Affiliation(s)
- Fang Xia
- Department of Cancer Biology, Cancer Center, University of Massachusetts Medical School, Worcester, MA 01605, USA
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58
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Walczak CE, Heald R. Mechanisms of mitotic spindle assembly and function. INTERNATIONAL REVIEW OF CYTOLOGY 2008; 265:111-58. [PMID: 18275887 DOI: 10.1016/s0074-7696(07)65003-7] [Citation(s) in RCA: 279] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The mitotic spindle is the macromolecular machine that segregates chromosomes to two daughter cells during mitosis. The major structural elements of the spindle are microtubule polymers, whose intrinsic polarity and dynamic properties are critical for bipolar spindle organization and function. In most cell types, spindle microtubule nucleation occurs primarily at two centrosomes, which define the spindle poles, but microtubules can also be generated by the chromosomes and within the spindle itself. Many associated factors help organize the spindle, including molecular motors and regulators of microtubule dynamics. The past decade has provided a wealth of information on the molecular players that are critical for spindle assembly as well as a high-resolution view of the intricate movements and dynamics of the spindle microtubules and the chromosomes. In this chapter we provide a historical account of the key observations leading to current models of spindle assembly, as well as an up-to-date status report on this exciting field.
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Affiliation(s)
- Claire E Walczak
- Medical Sciences Program, Indiana University, Bloomington, Indiana 47405, USA
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59
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Phosphorylation by casein kinase 2 regulates Nap1 localization and function. Mol Cell Biol 2007; 28:1313-25. [PMID: 18086883 DOI: 10.1128/mcb.01035-07] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
In Saccharomyces cerevisiae, the evolutionarily conserved nucleocytoplasmic shuttling protein Nap1 is a cofactor for the import of histones H2A and H2B, a chromatin assembly factor and a mitotic factor involved in regulation of bud formation. To understand the mechanism by which Nap1 function is regulated, Nap1-interacting factors were isolated and identified by mass spectrometry. We identified several kinases among these proteins, including casein kinase 2 (CK2), and a new bud neck-associated protein, Nba1. Consistent with our identification of the Nap1-interacting kinases, we showed that Nap1 is phosphorylated in vivo at 11 sites and that Nap1 is phosphorylated by CK2 at three substrate serines. Phosphorylation of these serines was not necessary for normal bud formation, but mutation of these serines to either alanine or aspartic acid resulted in cell cycle changes, including a prolonged S phase, suggesting that reversible phosphorylation by CK2 is important for cell cycle regulation. Nap1 can shuttle between the nucleus and cytoplasm, and we also showed that CK2 phosphorylation promotes the import of Nap1 into the nucleus. In conclusion, our data show that Nap1 phosphorylation by CK2 appears to regulate Nap1 localization and is required for normal progression through S phase.
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60
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Tedeschi A, Ciciarello M, Mangiacasale R, Roscioli E, Rensen WM, Lavia P. RANBP1 localizes a subset of mitotic regulatory factors on spindle microtubules and regulates chromosome segregation in human cells. J Cell Sci 2007; 120:3748-61. [PMID: 17940066 DOI: 10.1242/jcs.009308] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The GTPase RAN has an established role in spindle assembly and in mitotic progression, although not all mechanisms are fully understood in somatic cells. Here, we have downregulated RAN-binding protein 1 (RANBP1), a RAN partner that has highest abundance in G2 and mitosis, in human cells. RANBP1-depleted cells underwent prolonged prometaphase delay often followed by apoptosis. Cells that remained viable assembled morphologically normal spindles; these spindles, however, were hyperstable and failed to recruit cyclin B1 or to restrict the localization of HURP (DLG7), a microtubule-stabilizing factor, to plus-ends. RANBP1 depletion did not increase the frequency of unattached chromosomes; however, RANBP1-depleted cells frequently showed lagging chromosomes in anaphase, suggesting that merotelic attachments form and are not efficiently resolved. These data indicate that RANBP1 activity is required for the proper localization of specific factors that regulate microtubule function; loss of this activity contributes to the generation of aneuploidy in a microtubule-dependent manner.
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Affiliation(s)
- Antonio Tedeschi
- IBPM Institute of Molecular Biology and Pathology, CNR National Research Council, Via degli Apuli 4, 00185 Rome, Italy
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61
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Bentley AM, Normand G, Hoyt J, King RW. Distinct sequence elements of cyclin B1 promote localization to chromatin, centrosomes, and kinetochores during mitosis. Mol Biol Cell 2007; 18:4847-58. [PMID: 17881737 PMCID: PMC2096604 DOI: 10.1091/mbc.e06-06-0539] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The mitotic cyclins promote cell division by binding and activating cyclin-dependent kinases (CDKs). Each cyclin has a unique pattern of subcellular localization that plays a vital role in regulating cell division. During mitosis, cyclin B1 is known to localize to centrosomes, microtubules, and chromatin. To determine the mechanisms of cyclin B1 localization in M phase, we imaged full-length and mutant versions of human cyclin B1-enhanced green fluorescent protein in live cells by using spinning disk confocal microscopy. In addition to centrosome, microtubule, and chromatin localization, we found that cyclin B1 also localizes to unattached kinetochores after nuclear envelope breakdown. Kinetochore recruitment of cyclin B1 required the kinetochore proteins Hec1 and Mad2, and it was stimulated by microtubule destabilization. Mutagenesis studies revealed that cyclin B1 is recruited to kinetochores through both CDK1-dependent and -independent mechanisms. In contrast, localization of cyclin B1 to chromatin and centrosomes is independent of CDK1 binding. The N-terminal domain of cyclin B1 is necessary and sufficient for chromatin association, whereas centrosome recruitment relies on sequences within the cyclin box. Our data support a role for cyclin B1 function at unattached kinetochores, and they demonstrate that separable and distinct sequence elements target cyclin B1 to kinetochores, chromatin, and centrosomes during mitosis.
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Affiliation(s)
- Anna M. Bentley
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Guillaume Normand
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Jonathan Hoyt
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Randall W. King
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
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62
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Abstract
"Mitosis: Spindle Assembly and Function," a conference in honor of Dr. Bill R. Brinkley, brought together many researchers to discuss progress in the field and celebrate the many contributions that Dr. Brinkley has made.
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Affiliation(s)
- Rebecca Heald
- Molecular and Cell Biology Department, University of California, Berkeley, Berkeley, CA 94720, USA.
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63
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Xu XM, Meulia T, Meier I. Anchorage of Plant RanGAP to the Nuclear Envelope Involves Novel Nuclear-Pore-Associated Proteins. Curr Biol 2007; 17:1157-63. [PMID: 17600715 DOI: 10.1016/j.cub.2007.05.076] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2007] [Revised: 05/11/2007] [Accepted: 05/30/2007] [Indexed: 01/21/2023]
Abstract
The Ran GTPase controls multiple cellular processes including nucleocytoplasmic transport, spindle assembly, and nuclear envelope (NE) formation [1-4]. Its roles are accomplished by the asymmetric distribution of RanGTP and RanGDP enabled by the specific locations of the Ran GTPase-activating protein RanGAP and the nucleotide exchange factor RCC1 [5-8]. Mammalian RanGAP1 targeting to the NE and kinetochores requires interaction of its sumoylated C-terminal domain with the nucleoporin Nup358/RanBP2 [9-14]. In contrast, Arabidopsis RanGAP1 is associated with the NE and cell plate, mediated by an N-terminal, plant-specific WPP domain [15-18]. In the absence of RanBP2 in plants, the mechanism for spatially sequestering plant RanGAP is unknown. Here, Arabidopsis WPP-domain interacting proteins (WIPs) that interact with RanGAP1 in vivo and colocalize with RanGAP1 at the NE and cell plate were identified. Immunogold labeling indicates that WIP1 is associated with the outer NE. In a wip1-1/wip2-1/wip3-1 triple mutant, RanGAP1 is dislocated from the NE in undifferentiated root-tip cells, whereas NE targeting in differentiated root cells and targeting to the cell plate remain intact. We propose that WIPs are novel plant nucleoporins involved in RanGAP1 NE anchoring in specific cell types. Our data support a separate evolution of RanGAP targeting mechanisms in different kingdoms.
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Affiliation(s)
- Xianfeng Morgan Xu
- Plant Biotechnology Center and Department of Plant Cellular and Molecular Biology, The Ohio State University, Columbus, OH 43210, USA
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64
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Yang YL, Duan Q, Guo TB, Wang XX, Ruan Q, Xu GT, Zhang JW, Lu ZY, Xu M, Lu L, Dai W. BubR1 deficiency results in enhanced activation of MEK and ERKs upon microtubule stresses. Cell Prolif 2007; 40:397-410. [PMID: 17531083 PMCID: PMC6495970 DOI: 10.1111/j.1365-2184.2007.00443.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Accepted: 01/30/2007] [Indexed: 01/22/2023] Open
Abstract
UNLABELLED Disruption of microtubules activates the spindle checkpoint, of which BubR1 is a major component. Our early studies show that BubR1 haplo-insufficiency results in enhanced mitotic slippage in vitro and tumorigenesis in vivo. OBJECTIVE Given that both MAPKs/ERKs and MEK play an important role during mitosis, we investigated whether there existed regulatory relationship between the MAPK signalling pathway and BubR1. METHOD AND RESULTS Here, we have demonstrated that BubR1 deficiency is correlated with enhanced activation of MEK and ERKs after disruption of microtubule dynamics. Specifically, treatment with nocodazole and paclitaxel resulted in hyper-activation of ERKs and MEK in BubR1(+/-) murine embryonic fibroblasts (MEF) compared to that of wild-type MEFs. This enhanced activation of ERKs and MEK was at least partly responsible for more successful proliferation completion when cells were treated with nocodazole. BubR1 knockdown via RNAi resulted in enhanced activation of ERKs and MEK in HeLa cells, correlating with inhibition of PP1, a negative regulator of MEK. Moreover, when BubR1 was partially inactivated due to premature missegregation of chromosomes after Sgo1 depletion, phosphorylation of ERKs and MEK was enhanced in mitotic cells; in contrast, little, if any activated ERKs and MEK were detected in mitotic cells induced by nocodazole. Furthermore, BubR1, activated ERKs and activated MEK all localized to spindle poles during mitosis, and also, the proteins physically interacted with each other. CONCLUSION Our studies suggest that there exists a cross-talk between spindle checkpoint components and ERKs and MEK and that BubR1 may play an important role in mediating the cross-talk.
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Affiliation(s)
- Y. L. Yang
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Q. Duan
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - T. B. Guo
- Department of Medical Genetics, Shanghai Jiatong University, Shanghai, China
| | - X. X. Wang
- Department of Environmental Medicine, New York University School of Medicine, Tuxedo, NY, USA
| | - Q. Ruan
- Regeneron Pharmaceuticals Inc., Tarrytown, NY, USA
| | - G. T. Xu
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - J. W. Zhang
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Z. Y. Lu
- Department of Medical Genetics, Shanghai Jiatong University, Shanghai, China
| | - M. Xu
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- Department of Cell Biology Neurobiology and Anatomy, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - L. Lu
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- Division of Molecular Medicine, Harbor‐UCLA Medical Center, David Geffen School of Medicine, University of California Los Angeles, Torrance, CA, USA
| | - W. Dai
- Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
- Department of Environmental Medicine, New York University School of Medicine, Tuxedo, NY, USA
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65
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Affiliation(s)
- Jomon Joseph
- Lab No. 9, National Centre for Cell Science, Ganeshkhind, Pune 411 007, India.
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66
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Zuccolo M, Alves A, Galy V, Bolhy S, Formstecher E, Racine V, Sibarita JB, Fukagawa T, Shiekhattar R, Yen T, Doye V. The human Nup107-160 nuclear pore subcomplex contributes to proper kinetochore functions. EMBO J 2007; 26:1853-64. [PMID: 17363900 PMCID: PMC1847668 DOI: 10.1038/sj.emboj.7601642] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Accepted: 02/14/2007] [Indexed: 11/09/2022] Open
Abstract
We previously demonstrated that a fraction of the human Nup107-160 nuclear pore subcomplex is recruited to kinetochores at the onset of mitosis. However, the molecular determinants for its kinetochore targeting and the functional significance of this localization were not investigated. Here, we show that the Nup107-160 complex interacts with CENP-F, but that CENP-F only moderately contributes to its targeting to kinetochores. In addition, we show that the recruitment of the Nup107-160 complex to kinetochores mainly depends on the Ndc80 complex. We further demonstrate that efficient depletion of the Nup107-160 complex from kinetochores, achieved either by combining siRNAs targeting several of its subunits excluding Seh1, or by depleting Seh1 alone, induces a mitotic delay. Further analysis of Seh1-depleted cells revealed impaired chromosome congression, reduced kinetochore tension and kinetochore-microtubule attachment defects. Finally, we show that the presence of the Nup107-160 complex at kinetochores is required for the recruitment of Crm1 and RanGAP1-RanBP2 to these structures. Together, our data thus provide the first molecular clues underlying the function of the human Nup107-160 complex at kinetochores.
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Affiliation(s)
- Michela Zuccolo
- Institut Curie, Centre de Recherche, Paris, France
- UMR144 CNRS, Paris, France
| | - Annabelle Alves
- Institut Curie, Centre de Recherche, Paris, France
- UMR144 CNRS, Paris, France
| | - Vincent Galy
- Unité de Biologie Cellulaire du Noyau, URA 2582 CNRS - Institut Pasteur, Paris, France
| | - Stéphanie Bolhy
- Institut Curie, Centre de Recherche, Paris, France
- UMR144 CNRS, Paris, France
| | | | - Victor Racine
- Institut Curie, Centre de Recherche, Paris, France
- UMR144 CNRS, Paris, France
| | | | - Tatsuo Fukagawa
- Department of Molecular Genetics, National Institute of Genetics and SOKENDAI, Mishima, Shizuoka, Japan
| | | | - Tim Yen
- Fox Chase Cancer Center, Philadelphia, PA, USA
| | - Valérie Doye
- Institut Curie, Centre de Recherche, Paris, France
- UMR144 CNRS, Paris, France
- Institut Curie, Centre de Recherche, UMR144 CNRS, 26 rue d'Ulm, 75248 Paris Cedex 05, France. Tel.: +33 1 42 34 64 10; Fax: + 33 1 42 34 64 21; E-mail:
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67
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D'Angiolella V, Palazzo L, Santarpia C, Costanzo V, Grieco D. Role for non-proteolytic control of M-phase-promoting factor activity at M-phase exit. PLoS One 2007; 2:e247. [PMID: 17327911 PMCID: PMC1803016 DOI: 10.1371/journal.pone.0000247] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Accepted: 01/29/2007] [Indexed: 11/25/2022] Open
Abstract
M-phase Promoting Factor (MPF; the cyclin B-cdk 1 complex) is activated at M-phase onset by removal of inhibitory phosphorylation of cdk1 at thr-14 and tyr-15. At M-phase exit, MPF is destroyed by ubiquitin-dependent cyclin proteolysis. Thus, control of MPF activity via inhibitory phosphorylation is believed to be particularly crucial in regulating transition into, rather than out of, M-phase. Using the in vitro cell cycle system derived form Xenopus eggs, here we show, however, that inhibitory phosphorylation of cdk1 contributes to control MPF activity during M-phase exit. By sampling extracts at very short intervals during both meiotic and mitotic exit, we found that cyclin B1-associated cdk1 underwent transient inhibitory phosphorylation at tyr-15 and that cyclin B1-cdk1 activity fell more rapidly than the cyclin B1 content. Inhibitory phosphorylation of MPF correlated with phosphorylation changes of cdc25C, the MPF phosphatase, and physical interaction of cdk1 with wee1, the MPF kinase, during M-phase exit. MPF down-regulation required Ca++/calmodulin-dependent kinase II (CaMKII) and cAMP-dependent protein kinase (PKA) activities at meiosis and mitosis exit, respectively. Treatment of M-phase extracts with a mutant cyclin B1-cdk1AF complex, refractory to inhibition by phosphorylation, impaired binding of the Anaphase Promoting Complex/Cyclosome (APC/C) to its co-activator Cdc20 and altered M-phase exit. Thus, timely M-phase exit requires a tight coupling of proteolysis-dependent and proteolysis-independent mechanisms of MPF inactivation.
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Affiliation(s)
- Vincenzo D'Angiolella
- Faculty of Biotechnological Sciences and Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano,” University of Napoli Federico II, Italy
- Department of Pathology, New York University, New York, United States of America
| | - Luca Palazzo
- Faculty of Biotechnological Sciences and Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano,” University of Napoli Federico II, Italy
- CEINGE Biotecnologie Avanzate, Napoli, Italy
| | - Concetta Santarpia
- Faculty of Biotechnological Sciences and Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano,” University of Napoli Federico II, Italy
- CEINGE Biotecnologie Avanzate, Napoli, Italy
| | - Vincenzo Costanzo
- Clare Hall Laboratories, London Research Institute, London, United Kingdom
| | - Domenico Grieco
- Faculty of Biotechnological Sciences and Dipartimento di Biologia e Patologia Cellulare e Molecolare “L. Califano,” University of Napoli Federico II, Italy
- CEINGE Biotecnologie Avanzate, Napoli, Italy
- * To whom correspondence should be addressed. E-mail:
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Goodman B, Zheng Y. Mitotic spindle morphogenesis: Ran on the microtubule cytoskeleton and beyond. Biochem Soc Trans 2007; 34:716-21. [PMID: 17052181 DOI: 10.1042/bst0340716] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Assembly and disassembly of the mitotic spindle are essential for both chromosome segregation and cell division. The small G-protein Ran has emerged as an important regulator of spindle assembly. In this review, we look at the role of Ran in different aspects of spindle assembly, including its effects on microtubule assembly dynamics and microtubule organization. In addition, we examine the possibility of a spindle matrix and the role Ran might play in such a structure.
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Affiliation(s)
- B Goodman
- Department of Embryology, Carnegie Institution of Washington, Johns Hopkins University, Baltimore, MD 21218, USA
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69
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Russo J, Balogh GA, Heulings R, Mailo DA, Moral R, Russo PA, Sheriff F, Vanegas J, Russo IH. Molecular basis of pregnancy-induced breast cancer protection. Eur J Cancer Prev 2007; 15:306-42. [PMID: 16835503 DOI: 10.1097/00008469-200608000-00006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
We have postulated that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland characterized by a specific genomic signature imprinted by the physiological process of pregnancy. In the present work, we show evidence that the breast tissue of postmenopausal parous women has had a shifting of stem cell 1 to stem cell 2 with a genomic signature different from similar structures derived from postmenopausal nulliparous women that have stem cell 1. Those genes that are significantly different are grouped in major categories on the basis of their putative functional significance. Among them are those gene transcripts related to immune surveillance, DNA repair, transcription, chromatin structure/activators/co-activators, growth factor and signal transduction pathway, transport and cell trafficking, cell proliferation, differentiation, cell adhesion, protein synthesis and cell metabolism. From these data, it was concluded that during pregnancy there are significant genomic changes that reflect profound alterations in the basic physiology of the mammary gland that explain the protective effect against carcinogenesis. The implication of this knowledge is that when the genomic signature of protection or refractoriness to carcinogenesis is acquired by the shifting of stem cell 1 to stem cell 2, the hormonal milieu induced by pregnancy or pregnancy-like conditions is no longer required. This is a novel concept that challenges the current knowledge that a chemopreventive agent needs to be given for a long period to suppress a metabolic pathway or abrogate the function of an organ.
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Affiliation(s)
- Jose Russo
- Breast Cancer Research Laboratory, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
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Canovas PM, Guadagno TM. Functional analysis of survivin in spindle assembly inXenopusegg extracts. J Cell Biochem 2007; 100:217-29. [PMID: 16888809 DOI: 10.1002/jcb.21065] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Survivin is a member of the inhibitor of apoptosis (IAP) protein family that serves critical roles in mitosis and cytokinesis. Many studies have suggested Survivin's involvement in spindle regulation, but direct biochemical evidence for this has been lacking. Using the cell-free system of Xenopus egg extracts, we tested whether Survivin was necessary for the assembly of metaphase spindles. Removal or inhibition of Xenopus Survivin causes the disruption in the formation of metaphase spindles. In particular, we observe the generation of microtubule (MT) asters or poorly formed shortened spindle structures. In the latter phenotype the spindle structures display a decrease pole-to-pole length and a reduction of MTs around the chromatin indicating that Survivin may promote the stabilization of MT-chromatin interactions. In addition, function analysis of Survivin's conserved phosphorylation site Thr34 (Thr43 in Xenopus) and tubulin-binding domain was also assessed in regulating spindle assembly. Treatment of Xenopus egg extracts with a recombinant Survivin mutant that contained an alanine residue substitution at Thr43 (SURT43A mutant) or that was missing the C-terminal tubulin-binding domain (SURCL mutant) produced an increased frequency of MT asters and shorten abnormal spindle structures in Xenopus egg extracts. Interestingly, a phosphomimetic mutation made at residue Thr43 of Survivin (SURT43E mutant) generated a high frequency of MT asters implying that premature 'activation' of Survivin may interfere with an early stage of spindle assembly. Taken together, we propose that Survivin is a necessary component of the mitotic spindle and its phosphorylation at residue Thr43 is important for Survivin function in spindle assembly.
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Affiliation(s)
- Pedro M Canovas
- Molecular Oncology Program, H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida 33612, USA
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72
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Ryan KJ, Zhou Y, Wente SR. The karyopherin Kap95 regulates nuclear pore complex assembly into intact nuclear envelopes in vivo. Mol Biol Cell 2006; 18:886-98. [PMID: 17182855 PMCID: PMC1805111 DOI: 10.1091/mbc.e06-06-0525] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Nuclear pore complex (NPC) assembly in interphase cells requires that new NPCs insert into an intact nuclear envelope (NE). Our previous work identified the Ran GTPase as an essential component in this process. We proposed that Ran is required for targeting assembly factors to the cytoplasmic NE face via a novel, vesicular intermediate. Although the molecular target was not identified, Ran is known to function by modulating protein interactions for karyopherin (Kap) beta family members. Here we characterize loss-of-function Saccharomyces cerevisiae mutants in KAP95 with blocks in NPC assembly. Similar to defects in Ran cycle mutants, nuclear pore proteins are no longer localized properly to the NE in kap95 mutants. Also like Ran cycle mutants, the kap95-E126K mutant displayed enhanced lethality with nic96 and nup170 mutants. Thus, Kap95 and Ran are likely functioning at the same stage in assembly. However, although Ran cycle mutants accumulate small cytoplasmic vesicles, cells depleted of Kap95 accumulated long stretches of cytoplasmic membranes and had highly distorted NEs. We conclude that Kap95 serves as a key regulator of NPC assembly into intact NEs. Furthermore, both Kap95 and Ran may provide spatial cues necessary for targeting of vesicular intermediates in de novo NPC assembly.
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Affiliation(s)
- Kathryn J Ryan
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232-8240, USA.
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Abstract
The Ran GTPase controls many cellular functions, including nucleocytoplasmic trafficking, spindle assembly, nuclear assembly and cell-cycle progression. Considerable evidence suggests that diffusible Ran-GTP near mitotic chromatin facilitates the release of critical factors from nuclear transport receptors, thereby promoting organization of mitotic spindles with respect to chromosomes. In addition to this role of soluble Ran-GTP, Ran has two important but less understood roles at mitotic kinetochores. Namely, it is essential for regulation of the spindle assembly checkpoint and for assembly of microtubule fibres that attach kinetochores to spindle poles. Here, I will briefly summarize evidence for these kinetochore-associated functions and mention some of the issues that remain to be addressed regarding them.
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Affiliation(s)
- M Dasso
- Laboratory of Gene Regulation and Development, NICHD (National Institute of Child Health and Human Development)/NIH (National Institutes of Health), Bethesda, MD 20892-5431, USA.
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Orjalo AV, Arnaoutov A, Shen Z, Boyarchuk Y, Zeitlin SG, Fontoura B, Briggs S, Dasso M, Forbes DJ. The Nup107-160 nucleoporin complex is required for correct bipolar spindle assembly. Mol Biol Cell 2006; 17:3806-18. [PMID: 16807356 PMCID: PMC1593160 DOI: 10.1091/mbc.e05-11-1061] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Nup107-160 complex is a critical subunit of the nuclear pore. This complex localizes to kinetochores in mitotic mammalian cells, where its function is unknown. To examine Nup107-160 complex recruitment to kinetochores, we stained human cells with antisera to four complex components. Each antibody stained not only kinetochores but also prometaphase spindle poles and proximal spindle fibers, mirroring the dual prometaphase localization of the spindle checkpoint proteins Mad1, Mad2, Bub3, and Cdc20. Indeed, expanded crescents of the Nup107-160 complex encircled unattached kinetochores, similar to the hyperaccumulation observed of dynamic outer kinetochore checkpoint proteins and motors at unattached kinetochores. In mitotic Xenopus egg extracts, the Nup107-160 complex localized throughout reconstituted spindles. When the Nup107-160 complex was depleted from extracts, the spindle checkpoint remained intact, but spindle assembly was rendered strikingly defective. Microtubule nucleation around sperm centrosomes seemed normal, but the microtubules quickly disassembled, leaving largely unattached sperm chromatin. Notably, Ran-GTP caused normal assembly of microtubule asters in depleted extracts, indicating that this defect was upstream of Ran or independent of it. We conclude that the Nup107-160 complex is dynamic in mitosis and that it promotes spindle assembly in a manner that is distinct from its functions at interphase nuclear pores.
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Affiliation(s)
- Arturo V Orjalo
- Sections of Cell and Developmental Biology, Division of Biological Sciences, University of California-San Diego Medical School, La Jolla, CA 92093-0347, USA
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75
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Kaláb P, Pralle A, Isacoff EY, Heald R, Weis K. Analysis of a RanGTP-regulated gradient in mitotic somatic cells. Nature 2006; 440:697-701. [PMID: 16572176 DOI: 10.1038/nature04589] [Citation(s) in RCA: 284] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Accepted: 01/18/2006] [Indexed: 11/08/2022]
Abstract
The RanGTPase cycle provides directionality to nucleocytoplasmic transport, regulating interactions between cargoes and nuclear transport receptors of the importin-beta family. The Ran-importin-beta system also functions in mitotic spindle assembly and nuclear pore and nuclear envelope formation. The common principle underlying these diverse functions throughout the cell cycle is thought to be anisotropy of the distribution of RanGTP (the RanGTP gradient), driven by the chromatin-associated guanine nucleotide exchange factor RCC1 (refs 1, 4, 5). However, the existence and function of a RanGTP gradient during mitosis in cells is unclear. Here we examine the Ran-importin-beta system in cells by conventional and fluorescence lifetime microscopy using a biosensor, termed Rango, that increases its fluorescence resonance energy transfer signal when released from importin-beta by RanGTP. Rango is predominantly free in mitotic cells, but is further liberated around mitotic chromatin. In vitro experiments and modelling show that this localized increase of free cargoes corresponds to changes in RanGTP concentration sufficient to stabilize microtubules in extracts. In cells, the Ran-importin-beta-cargo gradient kinetically promotes spindle formation but is largely dispensable once the spindle has been established. Consistent with previous reports, we observe that the Ran system also affects spindle pole formation and chromosome congression in vivo. Our results demonstrate that conserved Ran-regulated pathways are involved in multiple, parallel processes required for spindle function, but that their relative contribution differs in chromatin- versus centrosome/kinetochore-driven spindle assembly systems.
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Affiliation(s)
- Petr Kaláb
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200, USA
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76
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Affiliation(s)
- Lucy F Pemberton
- Department of Microbiology, Center for Cell Signaling, University of Virginia, Charlottesville, VA 22908, USA.
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77
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Silverman-Gavrila RV, Wilde A. Ran is required before metaphase for spindle assembly and chromosome alignment and after metaphase for chromosome segregation and spindle midbody organization. Mol Biol Cell 2006; 17:2069-80. [PMID: 16481399 PMCID: PMC1415283 DOI: 10.1091/mbc.e05-10-0991] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Ran pathway has been shown to have a role in spindle assembly. However, the extent of the role of the Ran pathway in mitosis in vivo is unclear. We report that perturbation of the Ran pathway disrupted multiple steps of mitosis in syncytial Drosophila embryos and uncovered new mitotic processes that are regulated by Ran. During the onset of mitosis, the Ran pathway is required for the production, organization, and targeting of centrosomally nucleated microtubules to chromosomes. However, the role of Ran is not restricted to microtubule organization, because Ran is also required for the alignment of chromosomes at the metaphase plate. In addition, the Ran pathway is required for postmetaphase events, including chromosome segregation and the assembly of the microtubule midbody. The Ran pathway mediates these mitotic events, in part, by facilitating the correct targeting of the kinase Aurora A and the kinesins KLP61F and KLP3A to spindles.
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78
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Ciciarello M, Lavia P. New CRIME plots. Ran and transport factors regulate mitosis. EMBO Rep 2006; 6:714-6. [PMID: 16065064 PMCID: PMC1369157 DOI: 10.1038/sj.embor.7400499] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2005] [Accepted: 07/04/2005] [Indexed: 11/09/2022] Open
Affiliation(s)
- Marilena Ciciarello
- Marilena Ciciarello and Patrizia Lavia are at the Institute of Molecular Biology and Pathology, National Research Council, Via degli Apuli 4, Rome 00185, Italy
| | - Patrizia Lavia
- Marilena Ciciarello and Patrizia Lavia are at the Institute of Molecular Biology and Pathology, National Research Council, Via degli Apuli 4, Rome 00185, Italy
- Tel: +39 06 4991 7536; Fax: +39 06 445 7529;
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79
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Chan GK, Liu ST, Yen TJ. Kinetochore structure and function. Trends Cell Biol 2005; 15:589-98. [PMID: 16214339 DOI: 10.1016/j.tcb.2005.09.010] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Revised: 08/30/2005] [Accepted: 09/22/2005] [Indexed: 11/16/2022]
Abstract
The vertebrate kinetochore is a complex structure that specifies the attachments between the chromosomes and microtubules of the spindle and is thus essential for accurate chromosome segregation. Kinetochores are assembled on centromeric chromatin through complex pathways that are coordinated with the cell cycle. In the light of recent discoveries on how proteins assemble onto kinetochores and interact with each other, we review these findings in this article (which is part of the Chromosome Segregation and Aneuploidy series), and discuss their implications for the current mitotic checkpoint models - the template model and the two-step model. The template model proposes that Mad1-Mad2 at kinetochores acts as a template to change the conformation of another binding molecule of Mad2. This templated change in conformation is postulated as a mechanism for the amplification of the 'anaphase wait' signal. The two-step model proposes that the mitotic checkpoint complex (MCC) is the kinetochore-independent anaphase inhibitor, and the role of the unaligned kinetochore is to sensitize the anaphase-promoting complex/cyclosome (APC/C) to MCC-mediated inhibition.
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Affiliation(s)
- Gordon K Chan
- Department of Oncology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 1Z2.
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80
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Quimby BB, Arnaoutov A, Dasso M. Ran GTPase regulates Mad2 localization to the nuclear pore complex. EUKARYOTIC CELL 2005; 4:274-80. [PMID: 15701789 PMCID: PMC549331 DOI: 10.1128/ec.4.2.274-280.2005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In yeast and mammalian cells, the spindle assembly checkpoint proteins Mad1p and Mad2p localize to the nuclear pore complex (NPC) during interphase. Deletion of MAD1 or MAD2 did not affect steady-state nucleocytoplasmic distribution of a classical nuclear localization signal-containing reporter, a nuclear export signal-containing reporter, or Ran localization. We utilized cells with conditional mutations in the yeast Ran GTPase pathway to examine the relationship between Ran and targeting of checkpoint regulators to the NPC. Mutations that disrupt the concentration of Ran in the nucleus displaced Mad2p but not Mad1p from the NPC. The displacement of Mad2p in M-phase cells was correlated with activation of the spindle checkpoint. Our observations demonstrate that Mad2p localization at NPCs is sensitive to nuclear levels of Ran and suggest that release of Mad2p from NPCs is closely linked with spindle assembly checkpoint activation in yeast. This is the first evidence indicating that Ran affects the localization of Mad2p to the NPC.
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Affiliation(s)
- B Booth Quimby
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-5431, USA.
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81
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Azuma Y, Arnaoutov A, Anan T, Dasso M. PIASy mediates SUMO-2 conjugation of Topoisomerase-II on mitotic chromosomes. EMBO J 2005; 24:2172-82. [PMID: 15933717 PMCID: PMC1150894 DOI: 10.1038/sj.emboj.7600700] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Accepted: 05/09/2005] [Indexed: 11/09/2022] Open
Abstract
Here we show that the PIASy protein is specifically required for mitotic modification of Topoisomerase-II by SUMO-2 conjugation in Xenopus egg extracts. PIASy was unique among the PIAS family members in its capacity to bind mitotic chromosomes and recruit Ubc9 onto chromatin. These properties were essential, since PIASy mutants that did not bind chromatin or failed to recruit Ubc9 were functionally inactive. We observed that PIASy depletion eliminated essentially all chromosomal accumulation of EGFP-SUMO-2-conjugated species, suggesting that it is the primary E3-like factor for mitotic chromosomal substrates of SUMO-2. PIASy-dependent SUMO-2-conjugated species were highly concentrated on the inner centromere, and inhibition of PIASy blocked anaphase sister chromatid segregation in egg extracts. Taken together, our observations suggest that PIASy is a critical regulator of mitotic SUMO-2 conjugation for Topoisomerase-II and other chromosomal substrates, and that its activity may have particular relevance for centromeric functions required for proper chromosome segregation.
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Affiliation(s)
- Yoshiaki Azuma
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD, USA
| | - Alexei Arnaoutov
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD, USA
| | - Tadashi Anan
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD, USA
| | - Mary Dasso
- Laboratory of Gene Regulation and Development, NICHD, NIH, Bethesda, MD, USA
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Umeda M, Izaddoost S, Cushman I, Moore MS, Sazer S. The fission yeast Schizosaccharomyces pombe has two importin-alpha proteins, Imp1p and Cut15p, which have common and unique functions in nucleocytoplasmic transport and cell cycle progression. Genetics 2005; 171:7-21. [PMID: 15937127 PMCID: PMC1456536 DOI: 10.1534/genetics.105.042598] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The nuclear import of classical nuclear localization signal-containing proteins depends on importin-alpha transport receptors. In budding yeast there is a single importin-alpha gene and in higher eukaryotes there are multiple importin-alpha-like genes, but in fission yeast there are two: the previously characterized cut15 and the more recently identified imp1. Like other importin-alpha family members, Imp1p supports nuclear protein import in vitro. In contrast to cut15, imp1 is not essential for viability, but imp1delta mutant cells exhibit a telophase delay and mild temperature-sensitive lethality. Differences in the cellular functions that depend on Imp1p and Cut15p indicate that they each have unique physiological roles. They also have common roles because the imp1delta and the cut15-85 temperature-sensitive mutations are synthetically lethal; overexpression of cut15 partially suppresses the temperature sensitivity, but not the mitotic delay in imp1delta cells; and overexpression of imp1 partially suppresses the mitotic defect in cut15-85 cells but not the loss of viability. Both Imp1p and Cut15p are required for the efficient nuclear import of both an SV40 nuclear localization signal-containing reporter protein and the Pap1p component of the stress response MAP kinase pathway. Imp1p and Cut15p are essential for efficient nuclear protein import in S. pombe.
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Affiliation(s)
- Makoto Umeda
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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83
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Arnaoutov A, Azuma Y, Ribbeck K, Joseph J, Boyarchuk Y, Karpova T, McNally J, Dasso M. Crm1 is a mitotic effector of Ran-GTP in somatic cells. Nat Cell Biol 2005; 7:626-32. [PMID: 15908946 DOI: 10.1038/ncb1263] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The Ran GTPase controls multiple cellular processes, including nuclear transport, mitotic checkpoints, spindle assembly and post-mitotic nuclear envelope reassembly. Here we examine the mitotic function of Crm1, the Ran-GTP-binding nuclear export receptor for leucine-rich cargo (bearing nuclear export sequence) and Snurportin-1 (ref. 3). We find that Crm1 localizes to kinetochores, and that Crm1 ternary complex assembly is essential for Ran-GTP-dependent recruitment of Ran GTPase-activating protein 1 (Ran-GAP1) and Ran-binding protein 2 (Ran-BP2) to kinetochores. We further show that Crm1 inhibition by leptomycin B disrupts mitotic progression and chromosome segregation. Analysis of spindles within leptomycin B-treated cells shows that their centromeres were under increased tension. In leptomycin B-treated cells, centromeres frequently associated with continuous microtubule bundles that spanned the centromeres, indicating that their kinetochores do not maintain discrete end-on attachments to single kinetochore fibres. Similar spindle defects were observed in temperature-sensitive Ran pathway mutants (tsBN2 cells). Taken together, our findings demonstrate that Crm1 and Ran-GTP are essential for Ran-BP2/Ran-GAP1 recruitment to kinetochores, for definition of kinetochore fibres and for chromosome segregation at anaphase. Thus, Crm1 is a critical Ran-GTP effector for mitotic spindle assembly and function in somatic cells.
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Affiliation(s)
- Alexei Arnaoutov
- Laboratory of Gene Regulation and Development, NICHD, NIH, Building 18, Room 106, Bethesda, MD 20892-5431, USA
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Maiato H, DeLuca J, Salmon ED, Earnshaw WC. The dynamic kinetochore-microtubule interface. J Cell Sci 2005; 117:5461-77. [PMID: 15509863 DOI: 10.1242/jcs.01536] [Citation(s) in RCA: 282] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The kinetochore is a control module that both powers and regulates chromosome segregation in mitosis and meiosis. The kinetochore-microtubule interface is remarkably fluid, with the microtubules growing and shrinking at their point of attachment to the kinetochore. Furthermore, the kinetochore itself is highly dynamic, its makeup changing as cells enter mitosis and as it encounters microtubules. Active kinetochores have yet to be isolated or reconstituted, and so the structure remains enigmatic. Nonetheless, recent advances in genetic, bioinformatic and imaging technology mean we are now beginning to understand how kinetochores assemble, bind to microtubules and release them when the connections made are inappropriate, and also how they influence microtubule behaviour. Recent work has begun to elucidate a pathway of kinetochore assembly in animal cells; the work has revealed that many kinetochore components are highly dynamic and that some cycle between kinetochores and spindle poles along microtubules. Further studies of the kinetochore-microtubule interface are illuminating: (1) the role of the Ndc80 complex and components of the Ran-GTPase system in microtubule attachment, force generation and microtubule-dependent inactivation of kinetochore spindle checkpoint activity; (2) the role of chromosomal passenger proteins in the correction of kinetochore attachment errors; and (3) the function of microtubule plus-end tracking proteins, motor depolymerases and other proteins in kinetochore movement on microtubules and movement coupled to microtubule poleward flux.
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Affiliation(s)
- Helder Maiato
- Laboratory of Cell Regulation, NYSDH-Division of Molecular Medicine, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, USA
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86
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Jeong SY, Rose A, Joseph J, Dasso M, Meier I. Plant-specific mitotic targeting of RanGAP requires a functional WPP domain. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2005; 42:270-82. [PMID: 15807788 DOI: 10.1111/j.1365-313x.2005.02368.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The small GTPase Ran is involved in nucleocytoplasmic transport, spindle formation, nuclear envelope (NE) formation, and cell-cycle control. In vertebrates, these functions are controlled by a three-dimensional gradient of Ran-GTP to Ran-GDP, established by the spatial separation of Ran GTPase-activating protein (RanGAP) and the Ran guanine nucleotide exchange factor RCC1. While this spatial separation is established by the NE during interphase, it is orchestrated during mitosis by association of RCC1 with the chromosomes and RanGAP with the spindle and kinetochores. SUMOylation of vertebrate RanGAP1 is required for NE, spindle, and centromere association. Arabidopsis RanGAP1 (AtRanGAP1) lacks the SUMOylated C-terminal domain of vertebrate RanGAP, but contains a plant-specific N-terminal domain (WPP domain), which is necessary and sufficient for its targeting to the NE in interphase. Here we show that the human and plant RanGAP-targeting domains are kingdom specific. AtRanGAP1 has a mitotic trafficking pattern uniquely different from that of vertebrate RanGAP, which includes targeting to the outward-growing rim of the cell plate. The WPP domain is necessary and sufficient for this targeting. Point mutations in conserved residues of the WPP domain also abolish targeting to the nuclear rim and the cell plate, suggesting that the same mechanism is involved in both targeting events. These results indicate that plant and animal RanGAPs undergo different migration patterns during cell division, which require their kingdom-specific targeting domains.
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Affiliation(s)
- Sun Yong Jeong
- Plant Biotechnology Center and Department of Plant Cellular and Molecular Biology, The Ohio State University, Columbus, OH 43210, USA
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87
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Abstract
Proper segregation of chromosomes during cell division is essential for the maintenance of genetic stability. During this process chromosomes must establish stable functional interactions with microtubules through the kinetochore, a specialized protein structure located on the surface of the centromeric heterochromatin. Stable attachment of kinetochores to a number of microtubules results in the formation of a kinetochore fibre that mediates chromosome movement. How the kinetochore fibre is formed and how chromosome motion is produced and regulated remain major questions in cell biology. Here we look at some of the history of research devoted to the study of kinetochore-microtubule interaction and attempt to identify significant advances in the knowledge of the basic processes. Ultrastructural work has provided substantial insights into the structure of the kinetochore and associated microtubules during different stages of mitosis. Also, recent in-vivo studies have probed deep into the dynamics of kinetochore-attached microtubules suggesting possible models for the way in which kinetochores harness the capacity of microtubules to do work and turn it into chromosome motion. Much of the research in recent years suggests that indeed multiple mechanisms are involved in both formation of the k-fibre and chromosome motion. Thus, rather than moving to a unified theory, it has become apparent that most cell types have the capacity to build the spindle using multiple and probably redundant mechanisms.
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Affiliation(s)
- Helder Maiato
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
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88
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Abstract
Microtubules are dynamic polymers required for many aspects of eukaryotic cell function. The interphase microtubule network is essential for intracellular transport, organization, and cell polarization, whereas the mitotic spindle is required for chromosome segregation and cell division. Studies in different areas such as cell migration, mitosis, and asymmetric cell division have shown that Ran, Rho, and heterotrimeric G proteins regulate many aspects of microtubule functions. This review surveys how G protein-signaling coordinates microtubule polymerization and organization with specific cellular activities.
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Affiliation(s)
- Yixian Zheng
- Department of Embryology, Carnegie Institution of Washington and Howard Hughes Medical Institute, Baltimore, MD 21210, USA.
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89
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Gadea BB, Ruderman JV. Aurora kinase inhibitor ZM447439 blocks chromosome-induced spindle assembly, the completion of chromosome condensation, and the establishment of the spindle integrity checkpoint in Xenopus egg extracts. Mol Biol Cell 2004; 16:1305-18. [PMID: 15616188 PMCID: PMC551494 DOI: 10.1091/mbc.e04-10-0891] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Aurora family kinases contribute to accurate progression through several mitotic events. ZM447439 ("ZM"), the first Aurora family kinase inhibitor to be developed and characterized, was previously found to interfere with the mitotic spindle integrity checkpoint and chromosome segregation. Here, we have used extracts of Xenopus eggs, which normally proceed through the early embryonic cell cycles in the absence of functional checkpoints, to distinguish between ZM's effects on the basic cell cycle machinery and its effects on checkpoints. ZM clearly had no effect on either the kinetics or amplitude in the oscillations of activity of several key cell cycle regulators. It did, however, have striking effects on chromosome morphology. In the presence of ZM, chromosome condensation began on schedule but then failed to progress properly; instead, the chromosomes underwent premature decondensation during mid-mitosis. ZM strongly interfered with mitotic spindle assembly by inhibiting the formation of microtubules that are nucleated/stabilized by chromatin. By contrast, ZM had little effect on the assembly of microtubules by centrosomes at the spindle poles. Finally, under conditions where the spindle integrity checkpoint was experimentally induced, ZM blocked the establishment, but not the maintenance, of the checkpoint, at a point upstream of the checkpoint protein Mad2. These results show that Aurora kinase activity is required to ensure the maintenance of condensed chromosomes, the generation of chromosome-induced spindle microtubules, and activation of the spindle integrity checkpoint.
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Affiliation(s)
- Bedrick B Gadea
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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90
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Abstract
Importin beta, once thought to be exclusively a nuclear transport receptor, is emerging as a global regulator of diverse cellular functions. Importin beta acts positively in multiple interphase roles: in nuclear import, as a chaperone for highly charged nuclear proteins, and as a potential motor adaptor for movement along microtubules. In contrast, importin beta plays a negative regulatory role in mitotic spindle assembly, centrosome dynamics, nuclear membrane formation, and nuclear pore assembly. In most of these, importin beta is counteracted by its regulator, Ran-GTP. In light of this, the recent discovery of Ran's involvement in spindle checkpoint control suggested a potential new arena for importin beta action, although it is also possible that one of importin beta's relatives, the karyopherin family of proteins, manages this checkpoint. Lastly, importin beta plays a role in transducing damage signals from the axons of injured neurons back to the cell body.
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Affiliation(s)
- Amnon Harel
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California, San Diego, 9500 Gilman Drive, Room 2124A, Pacific Hall, La Jolla, CA 92093, USA
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91
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Abstract
Recent work has provided new insights into the mechanism of spindle assembly. Growing evidence supports a model in which the small GTPase Ran plays a central role in this process. Here, we examine the evidence for the existence of a RanGTP gradient around mitotic chromosomes and some controversial data on the role that chromosomes play in spindle assembly. We review the current knowledge on the Ran downstream targets for spindle assembly and we focus on the multiple roles of TPX2, one of the targets of RanGTP during cell division.
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Affiliation(s)
- Oliver J Gruss
- Cell Biology and Biophysics Program, European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg 69117, Germany.
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92
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Ciciarello M, Mangiacasale R, Thibier C, Guarguaglini G, Marchetti E, Di Fiore B, Lavia P. Importin beta is transported to spindle poles during mitosis and regulates Ran-dependent spindle assembly factors in mammalian cells. J Cell Sci 2004; 117:6511-22. [PMID: 15572412 DOI: 10.1242/jcs.01569] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Spatial control is a key issue in cell division. The Ran GTPase regulates several fundamental processes for cell life, largely acting through importin molecules. The best understood of these is protein import through the nuclear envelope in interphase, but roles in mitotic spindle assembly are also established. In mammalian cells, in which centrosomes are major spindle organizers, a link is emerging between the Ran network, centrosomes and spindle poles. Here, we show that, after nuclear envelope breakdown, importin beta is transported to the spindle poles in mammalian cells. This localization is temporally regulated from prometaphase until anaphase, when importin beta dissociates from poles and is recruited back around reforming nuclei. Importin beta sediments with mitotic microtubules in vitro and its accumulation at poles requires microtubule integrity and dynamics in vivo. Furthermore, RNA interference-dependent inactivation of TPX2, the major Ran-dependent spindle organizer, abolishes importin beta accumulation at poles. Importin beta has a functional role in spindle pole organization, because overexpression yields mitotic spindles with abnormal, fragmented poles. Coexpression of TPX2 with importin beta mitigates these abnormalities. Together, these results indicate that the balance between importins and spindle regulators of the TPX2 type is crucial for spindle formation. Targeting of TPX2/importin-beta complexes to poles is a key aspect in Ran-dependent control of the mitotic apparatus in mammalian cells.
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Affiliation(s)
- Marilena Ciciarello
- Institute of Molecular Biology and Pathology, Section of Genetics, CNR Consiglio Nazionale delle Ricerche, Via degli Apuli 4, Rome 00185, Italy
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93
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Mosammaparast N, Pemberton LF. Karyopherins: from nuclear-transport mediators to nuclear-function regulators. Trends Cell Biol 2004; 14:547-56. [PMID: 15450977 DOI: 10.1016/j.tcb.2004.09.004] [Citation(s) in RCA: 258] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The karyopherin beta (or importin beta) family comprises soluble transport factors that mediate the movement of proteins and RNAs between the nucleus and cytoplasm. Recent studies have extended the role of karyopherins to regulating assembly of the nuclear pore complex (NPC), assembly of the nuclear envelope, mitosis and replication. New data also address how karyopherins specifically recognize and transport many distinct cargoes and traverse the NPC. These data raise the possibility that, although there might be a universal mechanism for nuclear transport, specific interactions between karyopherins and components of the NPC might function to regulate differentially the ability of the different karyopherins to cross the NPC.
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Affiliation(s)
- Nima Mosammaparast
- Center for Cell Signaling and Department of Microbiology, University of Virginia, Charlottesville, VA 22908, USA
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94
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Kline-Smith SL, Walczak CE. Mitotic spindle assembly and chromosome segregation: refocusing on microtubule dynamics. Mol Cell 2004; 15:317-27. [PMID: 15304213 DOI: 10.1016/j.molcel.2004.07.012] [Citation(s) in RCA: 229] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The quest to find the underlying mechanisms of mitosis has taken many turns, which have largely been directed by the development of sensitive microscopes, enhanced microtubule-labeling techniques, advances in tubulin biochemistry, and genome-wide surveys to find the molecular "missing pieces" to the puzzle. Much of the work over the past decade has focused on the role of molecular motors in producing the necessary forces for spindle assembly and chromosome segregation. Recently, there has been a resurgence in research directed at understanding the intricate regulation of microtubule dynamics and organization during mitosis. This comes in part from the identification of new proteins involved in microtubule regulation as well as advances in fluorescence imaging that allow visualization of mitotic processes that previously have never been observed.
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Affiliation(s)
- Susan L Kline-Smith
- Department of Anatomy and Cell Biology, Indiana University Medical Sciences Program, Bloomington, IN 47405, USA
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95
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Kerres A, Vietmeier-Decker C, Ortiz J, Karig I, Beuter C, Hegemann J, Lechner J, Fleig U. The fission yeast kinetochore component Spc7 associates with the EB1 family member Mal3 and is required for kinetochore-spindle association. Mol Biol Cell 2004; 15:5255-67. [PMID: 15371542 PMCID: PMC532008 DOI: 10.1091/mbc.e04-06-0443] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A critical aspect of mitosis is the interaction of the kinetochore with spindle microtubules. Fission yeast Mal3 is a member of the EB1 family of microtubule plus-end binding proteins, which have been implicated in this process. However, the Mal3 interaction partner at the kinetochore had not been identified. Here, we show that the mal3 mutant phenotype can be suppressed by the presence of extra Spc7, an essential kinetochore protein associated with the central centromere region. Mal3 and Spc7 interact physically as both proteins can be coimmunoprecipitated. Overexpression of a Spc7 variant severely compromises kinetochore-microtubule interaction, indicating that the Spc7 protein plays a role in this process. Spc7 function seems to be conserved because, Spc105, a Saccharomyces cerevisiae homolog of Spc7, identified by mass spectrometry as a component of the conserved Ndc80 complex, can rescue mal3 mutant strains.
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Affiliation(s)
- Anne Kerres
- Institut für Mikrobiologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
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96
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Okai T, Araki Y, Tada M, Tateno T, Kontani K, Katada T. Novel small GTPase subfamily capable of associating with tubulin is required for chromosome segregation. J Cell Sci 2004; 117:4705-15. [PMID: 15331635 DOI: 10.1242/jcs.01347] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The small GTPase superfamily, which includes the Ras, Rho/Rac, Rab, Arf and Ran subfamilies, serves as a signal transducer to regulate cell proliferation and differentiation, actin cytoskeleton, membrane trafficking, and nuclear transport. Here, we identify novel GTPases (human Gie1 and Gie2) that form a distinct subfamily of the small GTPases in terms of their sequences and intracellular function. Gie stands for `novel GTPase indispensable for equal segregation of chromosomes', and this subfamily is conserved in multicellular organisms. Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation. Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis. Furthermore, overexpression of Gie mutants that lack putative effector domains but have tubulin-binding ability induced micronucleus formation. Thus, this is the first report showing that a small GTPase subfamily capable of associating with microtubules might be involved in chromosome segregation.
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Affiliation(s)
- Takuro Okai
- Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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97
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Baï SW, Rouquette J, Umeda M, Faigle W, Loew D, Sazer S, Doye V. The fission yeast Nup107-120 complex functionally interacts with the small GTPase Ran/Spi1 and is required for mRNA export, nuclear pore distribution, and proper cell division. Mol Cell Biol 2004; 24:6379-92. [PMID: 15226438 PMCID: PMC434257 DOI: 10.1128/mcb.24.14.6379-6392.2004] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have characterized Schizosaccharomyces pombe open reading frames encoding potential orthologues of constituents of the evolutionarily conserved Saccharomyces cerevisiae Nup84 vertebrate Nup107-160 nuclear pore subcomplex, namely Nup133a, Nup133b, Nup120, Nup107, Nup85, and Seh1. In spite of rather weak sequence conservation, in vivo analyses demonstrated that these S. pombe proteins are localized at the nuclear envelope. Biochemical data confirmed the organization of these nucleoporins within conserved complexes. Although examination of the S. cerevisiae and S. pombe deletion mutants revealed different viability phenotypes, functional studies indicated that the involvement of this complex in nuclear pore distribution and mRNA export has been conserved between these highly divergent yeasts. Unexpectedly, microscopic analyses of some of the S. pombe mutants revealed cell division defects at the restrictive temperature (abnormal septa and mitotic spindles and chromosome missegregation) that were reminiscent of defects occurring in several S. pombe GTPase Ran (Ran(Sp))/Spi1 cycle mutants. Furthermore, deletion of nup120 moderately altered the nuclear location of Ran(Sp)/Spi1, whereas overexpression of a nonfunctional Ran(Sp)/Spi1-GFP allele was specifically toxic in the Deltanup120 and Deltanup133b mutant strains, indicating a functional and genetic link between constituents of the S. pombe Nup107-120 complex and of the Ran(Sp)/Spi1 pathway.
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98
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Joseph J, Liu ST, Jablonski SA, Yen TJ, Dasso M. The RanGAP1-RanBP2 complex is essential for microtubule-kinetochore interactions in vivo. Curr Biol 2004; 14:611-7. [PMID: 15062103 DOI: 10.1016/j.cub.2004.03.031] [Citation(s) in RCA: 222] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2003] [Revised: 01/27/2004] [Accepted: 02/18/2004] [Indexed: 11/17/2022]
Abstract
RanGAP1 is the activating protein for the Ran GTPase. Vertebrate RanGAP1 is conjugated to a small ubiquitin-like protein, SUMO-1. This modification promotes association of RanGAP1 with the interphase nuclear pore complex (NPC) through binding to the nucleoporin RanBP2, also known as Nup358. During mitosis, RanGAP1 is concentrated at kinetochores in a microtubule- (MT) and SUMO-1-dependent fashion. RanBP2 is also abundantly found on kinetochores in mitosis. Here we show that ablation of proteins required for MT-kinetochore attachment (Hec1/Ndc80, Nuf2 ) disrupts RanGAP1 and RanBP2 targeting to kinetochores. No similar disruption was observed after ablation of proteins nonessential for MT-kinetochore interactions (CENP-I, Bub1, CENP-E ). Acquisition of RanGAP1 and RanBP2 by kinetochores is temporally correlated in untreated cells with MT attachment. These patterns of accumulation suggest a loading mechanism wherein the RanGAP1-RanBP2 complex may be transferred along the MT onto the kinetochore. Depletion of RanBP2 caused mislocalization of RanGAP1, Mad1, Mad2, CENP-E, and CENP-F, as well as loss of cold-stable kinetochore-MT interactions and accumulation of mitotic cells with multipolar spindles and unaligned chromosomes. Taken together, our observations indicate that RanBP2 and RanGAP1 are targeted as a single complex that is both regulated by and essential for stable kinetochore-MT association.
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Affiliation(s)
- Jomon Joseph
- National Institutes of Health, National Institute of Child Health and Human Development, Building 18, Room 106, 18 Library Drive, MSC-5431, Bethesda, MD 20892, USA
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99
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Hutchins JRA, Moore WJ, Hood FE, Wilson JSJ, Andrews PD, Swedlow JR, Clarke PR. Phosphorylation Regulates the Dynamic Interaction of RCC1 with Chromosomes during Mitosis. Curr Biol 2004; 14:1099-104. [PMID: 15203004 DOI: 10.1016/j.cub.2004.05.021] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2004] [Revised: 04/28/2004] [Accepted: 04/29/2004] [Indexed: 10/26/2022]
Abstract
The small GTPase Ran has multiple roles during the cell division cycle, including nuclear transport, mitotic spindle assembly, and nuclear envelope formation. However, regulation of Ran during cell division is poorly understood. Ran-GTP is generated by the guanine nucleotide exchange factor RCC1, the localization of which to chromosomes is necessary for the fidelity of mitosis in human cells. Using photobleaching techniques, we show that the chromosomal interaction of human RCC1 fused to green fluorescent protein (GFP) changes during progression through mitosis by being highly dynamic during metaphase and more stable toward the end of mitosis. The interaction of RCC1 with chromosomes involves the interface of RCC1 with Ran and requires an N-terminal region containing a nuclear localization signal. We show that this region contains sites phosphorylated by mitotic protein kinases. One site, serine 11, is targeted by CDK1/cyclin B and is phosphorylated in mitotic human cells. Phosphorylation of the N-terminal region of RCC1 inhibits its binding to importin alpha/beta and maintains the mobility of RCC1 during metaphase. This mechanism may be important for the localized generation of Ran-GTP on chromatin after nuclear envelope breakdown and may play a role in the coordination of progression through mitosis.
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Affiliation(s)
- James R A Hutchins
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY, Scotland, United Kingdom
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100
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Abstract
Cancer cells contain abnormal number of chromosomes (aneuploidy), which is a prevalent form of genetic instability in human cancers. Defects in a cell cycle surveillance mechanism called the spindle checkpoint contribute to chromosome instability and aneuploidy. In response to straying chromosomes in mitosis, the spindle checkpoint inhibits the ubiquitin ligase activity of the anaphase-promoting complex or cyclosome (APC/C), thus preventing precocious chromosome segregation and ensuring the accurate partition of the genetic material. We review recent progress toward the understanding of the molecular mechanism of the spindle checkpoint and its role in guarding genome integrity at the chromosome level.
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Affiliation(s)
- Rajnish Bharadwaj
- Department of Pharmacology, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9041, USA
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