scholarly journals Nuclear Isoforms of Neurofibromin Are Required for Proper Spindle Organization and Chromosome Segregation

Cells ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 2348
Author(s):  
Charoula Peta ◽  
Emmanouella Tsirimonaki ◽  
Dimitris Samouil ◽  
Kyriaki Georgiadou ◽  
Dimitra Mangoura
Keyword(s):  
Chromosome Segregation ◽  
Tumor Development ◽  
Abnormal Chromosome ◽  
Nuclear Localization Sequence ◽  
Neural Cells ◽  
Mitotic Spindles ◽  
Critical Function ◽  
Chromosome Congression ◽  
Associated Proteins ◽  
Localization Sequence

Mitotic spindles are highly organized, microtubule (MT)-based, transient structures that serve the fundamental function of unerring chromosome segregation during cell division and thus of genomic stability during tissue morphogenesis and homeostasis. Hence, a multitude of MT-associated proteins (MAPs) regulates the dynamic assembly of MTs in preparation for mitosis. Some tumor suppressors, normally functioning to prevent tumor development, have now emerged as significant MAPs. Among those, neurofibromin, the product of the Neurofibromatosis-1 gene (NF1), a major Ras GTPase activating protein (RasGAP) in neural cells, controls also the critical function of chromosome congression in astrocytic cellular contexts. Cell type- and development-regulated splicings may lead to the inclusion or exclusion of NF1exon51, which bears a nuclear localization sequence (NLS) for nuclear import at G2; yet the functions of the produced NLS and ΔNLS neurofibromin isoforms have not been previously addressed. By using a lentiviral shRNA system, we have generated glioblastoma SF268 cell lines with conditional knockdown of NLS or ΔNLS transcripts. In dissecting the roles of NLS or ΔNLS neurofibromins, we found that NLS-neurofibromin knockdown led to increased density of cytosolic MTs but loss of MT intersections, anastral spindles featuring large hollows and abnormal chromosome positioning, and finally abnormal chromosome segregation and increased micronuclei frequency. Therefore, we propose that NLS neurofibromin isoforms exert prominent mitotic functions.

scholarly journals Mars promotes dTACC dephosphorylation on mitotic spindles to ensure spindle stability

2008 ◽  
Vol 182 (1) ◽  
pp. 27-33 ◽  
Author(s):  
Shengjiang Tan ◽  
Ekaterina Lyulcheva ◽  
Jon Dean ◽  
Daimark Bennett
Keyword(s):  
Chromosome Segregation ◽  
Coiled Coil ◽  
Protein Phosphatase 1 ◽  
Mitotic Spindles ◽  
Developmental Context ◽  
Microtubule Associated Proteins ◽  
Associated Proteins ◽  
Spindle Stability ◽  
Map Function

Microtubule-associated proteins (MAPs) ensure the fidelity of chromosome segregation by controlling microtubule (MT) dynamics and mitotic spindle stability. However, many aspects of MAP function and regulation are poorly understood in a developmental context. We show that mars, which encodes a Drosophila melanogaster member of the hepatoma up-regulated protein family of MAPs, is essential for MT stabilization during early embryogenesis. As well as associating with spindle MTs in vivo, Mars binds directly to protein phosphatase 1 (PP1) and coimmunoprecipitates from embryo extracts with minispindles and Drosophila transforming acidic coiled-coil (dTACC), two MAPs that function as spindle assembly factors. Disruption of binding to PP1 or loss of mars function results in elevated levels of phosphorylated dTACC on spindles. A nonphosphorylatable form of dTACC is capable of rescuing the lethality of mars mutants. We propose that Mars mediates spatially controlled dephosphorylation of dTACC, which is critical for spindle stabilization.

scholarly journals Proteins Connecting the Nuclear Pore Complex with the Nuclear Interior

1999 ◽  
Vol 144 (5) ◽  
pp. 839-855 ◽  
Author(s):  
Caterina Strambio-de-Castillia ◽  
Günter Blobel ◽  
Michael P. Rout
Keyword(s):  
Nuclear Pore Complex ◽  
Nuclear Import ◽  
Nuclear Localization Sequence ◽  
Nuclear Pore ◽  
Reporter Protein ◽  
Double Deletion ◽  
Large Structures ◽  
Associated Proteins ◽  
Localization Sequence ◽  
Transport Factors

While much has been learned in recent years about the movement of soluble transport factors across the nuclear pore complex (NPC), comparatively little is known about intranuclear trafficking. We isolated the previously identified Saccharomyces protein Mlp1p (myosin-like protein) by an assay designed to find nuclear envelope (NE) associated proteins that are not nucleoporins. We localized both Mlp1p and a closely related protein that we termed Mlp2p to filamentous structures stretching from the nucleoplasmic face of the NE into the nucleoplasm, similar to the homologous vertebrate and Drosophila Tpr proteins. Mlp1p can be imported into the nucleus by virtue of a nuclear localization sequence (NLS) within its COOH-terminal domain. Overexpression experiments indicate that Mlp1p can form large structures within the nucleus which exclude chromatin but appear highly permeable to proteins. Remarkably, cells harboring a double deletion of MLP1 and MLP2 were viable, although they showed a slower net rate of active nuclear import and faster passive efflux of a reporter protein. Our data indicate that the Tpr homologues are not merely NPC-associated proteins but that they can be part of NPC-independent, peripheral intranuclear structures. In addition, we suggest that the Tpr filaments could provide chromatin-free conduits or tracks to guide the efficient translocation of macromolecules between the nucleoplasm and the NPC.

scholarly journals SENP1 and SENP2 affect spatial and temporal control of sumoylation in mitosis

2013 ◽  
Vol 24 (22) ◽  
pp. 3483-3495 ◽  
Author(s):  
Caelin Cubeñas-Potts ◽  
Jacqueline D. Goeres ◽  
Michael J. Matunis
Keyword(s):  
Rna Interference ◽  
Chromosome Segregation ◽  
Nuclear Pore Complex ◽  
Sister Chromatid ◽  
Mitotic Chromosome ◽  
Nuclear Pore ◽  
Temporal Control ◽  
Chromosome Congression ◽  
Associated Proteins ◽  
Sister Chromatid Separation

Sumoylation of centromere, kinetochore, and other mitotic chromosome-associated proteins is essential for chromosome segregation. The mechanisms regulating spatial and temporal sumoylation of proteins in mitosis, however, are not well understood. Here we show that the small ubiquitin-related modifier (SUMO)–specific isopeptidases SENP1 and SENP2 are targeted to kinetochores in mitosis. SENP2 targeting occurs through a mechanism dependent on the Nup107-160 subcomplex of the nuclear pore complex and is modulated through interactions with karyopherin α. Overexpression of SENP2, but not other SUMO-specific isopeptidases, causes a defect in chromosome congression that depends on its precise kinetochore targeting. By altering SENP1 kinetochore associations, however, this effect on chromosome congression could be phenocopied. In contrast, RNA interference–mediated knockdown of SENP1 delays sister chromatid separation at metaphase, whereas SENP2 knockdown produces no detectable phenotypes. Our findings indicate that chromosome segregation depends on precise spatial and temporal control of sumoylation in mitosis and that SENP1 and SENP2 are important mediators of this control.

scholarly journals Two Tails for Neurofibromin: A Tale of Two Microtubule-Associated Proteins

2021 ◽  
Author(s):  
Charoula Peta ◽  
Emmanouella Tsirimonaki ◽  
Constantinos Fedonidis ◽  
Xeni Koliou ◽  
Nikos Sakellaridis ◽  
...  
Keyword(s):  
Splice Variants ◽  
Point Mutations ◽  
Neurofibromatosis Type ◽  
Nuclear Localization Sequence ◽  
Major Theme ◽  
Patient Counselling ◽  
Associated Proteins ◽  
Localization Sequence ◽  
Specific Alternative ◽  
Cell Type Specific

Neurofibromatosis type 1, NF-1, is a common monogenic (NF1) disease, characterized by highly variable clinical presentation and high predisposition for tumors, especially those of astrocytic origin (low- to high-grade gliomas). Unfortunately, very few genotype–phenotype correlations have been possible, and the numerous identified mutations do not offer help for prognosis and patient counselling. Whole gene deletion in animals does not successfully model the disease, as NF-1 cases caused by point mutations could be differentially affected by cell type-specific alternative splice variants of NF1. In this chapter, we will discuss the differential Microtubule-Associated-Protein (MAP) properties of NLS or ΔNLS neurofibromins, produced by the alternatively splicing of exon 51, which also contains a Nuclear Localization Sequence (NLS), in the assembly of the mitotic spindle and in faithful genome transmission. We will also commend on the major theme that emerges about NLS-containing tumor suppressors that function as mitotic MAPs.

Elongator's toxin-target (TOT) function is nuclear localization sequence dependent and suppressed by post-translational modification

2003 ◽  
Vol 49 (5) ◽  
pp. 1297-1307 ◽  
Author(s):  
Lars Fichtner ◽  
Daniel Jablonowski ◽  
Angelika Schierhorn ◽  
Hiroko K. Kitamoto ◽  
Michael J. R. Stark ◽  
...  
Keyword(s):  
Nuclear Localization ◽  
Nuclear Localization Sequence ◽  
Post Translational Modification ◽  
Sequence Dependent ◽  
Localization Sequence

Novel properties of the protein kinase CK2-site-regulated nuclear- localization sequence of the interferon-induced nuclear factor IFI 16

2000 ◽  
Vol 353 (1) ◽  
pp. 69-77 ◽  
Author(s):  
Lyndall J. BRIGGS ◽  
Ricky W. JOHNSTONE ◽  
Rachel M. ELLIOT ◽  
Chong-Yun XIAO ◽  
Michelle DAWSON ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Nuclear Localization ◽  
Nuclear Import ◽  
Protein Kinase Ck2 ◽  
Protein Import ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Nuclear Localization Sequence ◽  
Localization Sequence ◽  
Kinase Ck2

Members of the interferon-induced class of nuclear factors possess a putative CcN motif, comparable with that within proteins such as the simian virus 40 large tumour antigen (T-ag), which confers phosphorylation-mediated regulation of nuclear-localization sequence (NLS)-dependent nuclear import. Here we examine the functionality of the interferon-induced factor 16 (IFI 16) CcN motif, demonstrating its ability to target a heterologous protein to the nucleus, and to be phosphorylated specifically by the CcN-motif-phosphorylating protein kinase CK2 (CK2). The IFI 16 NLS, however, has novel properties, conferring ATP-dependent nuclear import completely independent of cytosolic factors, as well as binding to nuclear components. The IFI 16 NLS is not recognized with high affinity by the NLS-binding importin heterodimer, and transport mediated by it is insensitive to non-hydrolysable GTP analogues. The IFI 16 NLS thus mediates nuclear import through a pathway completely distinct from that of conventional NLSs, such as that of T-ag, but intriguingly resembling that of the NLS of the HIV-1 transactivator protein Tat. Since the IFI 16 CK2 site enhances nuclear import through facilitating binding to nuclear components, this represents a novel mechanism by which the site regulates nuclear-protein import, and constitutes a difference between the IFI 16 and Tat NLSs that may be of importance in the immune response.

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