scholarly journals Reconstitution of human kinetochore in mitotic cell extracts reveals permitted and restricted assembly steps

2020 ◽  
Author(s):  
Ekaterina V. Tarasovetc ◽  
Praveen Kumar Allu ◽  
Iain M. Cheeseman ◽  
Ben E. Black ◽  
Ekaterina L. Grishchuk
Keyword(s):  
De Novo ◽  
Mitotic Cell ◽  
Binding Activity ◽  
Human Cells ◽  
Microtubule Binding ◽  
Cell Extracts ◽  
Inhibitory Mechanisms ◽  
Ndc80 Complex ◽  
Egg Extracts ◽  
Human Proteins

AbstractAssembly of a functional kinetochore is critical for accurate chromosome segregation. Hierarchical recruitment of soluble components during kinetochore assembly is a highly regulated mitotic event, but the underlying steps are not well understood. In yeast and Xenopus egg extracts, soluble kinetochore components can spontaneously assemble into microtubule-binding subcomplexes. Although the molecular interactions among specific kinetochore components are evolutionary conserved in eukaryotes, it remains unclear which de novo assembly steps are permitted in extracts of mitotic human cells. By analyzing the recruitment of GFP-fused kinetochore proteins from human mitotic cell extracts to inner kinetochore components immobilized on microbeads, we reconstructed the interaction between CENP-C and CENP-A–containing nucleosomes. However, subsequent phospho-dependent binding of the Mis12 complex was less efficient, whereas binding of the Ndc80 complex was inhibited. Consistently, the microtubule-binding activity of native kinetochore components, as well as those assembled using a combination of native and recombinant human proteins, was weaker than that of recombinant Ndc80 complex alone. Such inhibitory mechanisms that prevent interactions between different kinetochore components are likely to guard against spurious formation of kinetochores in the cytosol of mitotic human cells, and imply existence of specific regulatory mechanisms that permit these interactions at the assembling kinetochore.

scholarly journals Astrin-SKAP complex reconstitution reveals its kinetochore interaction with microtubule-bound Ndc80

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
David M Kern ◽  
Julie K Monda ◽  
Kuan-Chung Su ◽  
Elizabeth M Wilson-Kubalek ◽  
Iain M Cheeseman
Keyword(s):  
Chromosome Segregation ◽  
Human Cells ◽  
Cross Linking ◽  
Microtubule Binding ◽  
Binding Domains ◽  
Anaphase Onset ◽  
Ndc80 Complex ◽  
Outstanding Question ◽  
Dynamic Microtubule

Chromosome segregation requires robust interactions between the macromolecular kinetochore structure and dynamic microtubule polymers. A key outstanding question is how kinetochore-microtubule attachments are modulated to ensure that bi-oriented attachments are selectively stabilized and maintained. The Astrin-SKAP complex localizes preferentially to properly bi-oriented sister kinetochores, representing the final outer kinetochore component recruited prior to anaphase onset. Here, we reconstitute the 4-subunit Astrin-SKAP complex, including a novel MYCBP subunit. Our work demonstrates that the Astrin-SKAP complex contains separable kinetochore localization and microtubule binding domains. In addition, through cross-linking analysis in human cells and biochemical reconstitution, we show that the Astrin-SKAP complex binds synergistically to microtubules with the Ndc80 complex to form an integrated interface. We propose a model in which the Astrin-SKAP complex acts together with the Ndc80 complex to stabilize correctly formed kinetochore-microtubule interactions.

scholarly journals NF-κB Is Involved in Regulation of CD40 Ligand Expression on Mycobacterium bovis Bacillus Calmette-Guérin-Activated Human T Cells

2003 ◽  
Vol 10 (3) ◽  
pp. 376-382 ◽  
Author(s):  
Patricia Méndez-Samperio ◽  
Hilda Ayala ◽  
Abraham Vázquez
Keyword(s):  
T Cells ◽  
Mycobacterium Bovis ◽  
De Novo ◽  
Cd40 Ligand ◽  
Nuclear Factor Κb ◽  
Binding Activity ◽  
Cell Surface Expression ◽  
Membrane Expression ◽  
Activated T Cells ◽  
Cd40l Expression

ABSTRACT Interaction between CD40L (CD154) on activated T cells and its receptor CD40 on antigen-presenting cells has been reported to be important in the resolution of infection by mycobacteria. However, the mechanism(s) by which Mycobacterium bovis bacillus Calmette-Guérin (BCG) up-regulates membrane expression of CD40L molecules is poorly understood. This study was done to investigate the role of the nuclear factor κB (NF-κB) signaling pathway in the regulation of CD40L expression in human CD4+ T cells stimulated with BCG. Specific pharmacologic inhibition of the NF-κB pathway revealed that this signaling cascade was required in the regulation of CD40L expression on the surface of BCG-activated CD4+ T cells. These results were further supported by the fact that treatment of BCG-activated CD4+ T cells with these pharmacological inhibitors significantly down-regulated CD40L mRNA. In this study, inhibitor κBα (IκBα) and IκBβ protein production was not affected by the chemical protease inhibitors and, more importantly, BCG led to the rapid but transient induction of NF-κB activity. Our results also indicated that CD40L expression on BCG-activated CD4+ T cells resulted from transcriptional up-regulation of the CD40L gene by a mechanism which is independent of de novo protein synthesis. Interestingly, BCG-induced activation of NF-κB and the increased CD40L cell surface expression were blocked by the protein kinase C (PKC) inhibitors 1-[5-isoquinolinesulfonyl]-2-methylpiperazine and salicylate, both of which block phosphorylation of IκB. Moreover, rottlerin a Ca2+-independent PKC isoform inhibitor, significantly down-regulated CD40L mRNA in BCG-activated CD4+ T cells. These data strongly suggest that CD40L expression by BCG-activated CD4+ T cells is regulated via the PKC pathway and by NF-κB DNA binding activity.

Carcinogen-induced DNA amplification in vitro: overreplication of the simian virus 40 origin region in extracts from carcinogen-treated CO60 cells

1990 ◽  
Vol 10 (1) ◽  
pp. 75-83
Author(s):  
Y Berko-Flint ◽  
S Karby ◽  
D Hassin ◽  
S Lavi
Keyword(s):  
De Novo ◽  
Chinese Hamster ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Dna Molecules ◽  
Viral Origin ◽  
Cell Extracts ◽  
Origin Region

An in vitro system to study carcinogen-induced amplification in simian virus 40 (SV40)-transformed Chinese hamster (CO60) cells is described. SV40 amplification in this system resembled in many aspects the viral overreplication observed in drug-treated CO60 cells. Cytosolic extracts from N-methyl-N'-nitro-N-nitrosoguanidine-treated cells supported de novo DNA synthesis in the presence of excess exogenous T antigen and the SV40-containing plasmid pSVK1. The pattern of viral replication in these extracts was unique, since only the 2.4-kilobase-pair region spanning the origin was overreplicated, whereas distal sequences were not replicated significantly. Extracts from control cells supported only marginal levels of replication. In HeLa extracts, complete SV40 DNA molecules were replicated efficiently. The overreplication of the origin region in CO60 cell extracts was bidirectional and symmetrical. A fraction of the newly synthesized DNA molecules underwent a second round of replication, yielding MboI-sensitive fragments representing the 2.4-kilobase-pair region around the origin. The mechanisms controlling the amplification of the viral origin region, the nature of the cellular factors induced in the carcinogen-treated cells, and their putative association with general drug-induced SOS-like responses are discussed.

Hel-N1/Hel-N2 proteins are bound to poly(A)+ mRNA in granular RNP structures and are implicated in neuronal differentiation

1996 ◽  
Vol 109 (3) ◽  
pp. 579-589 ◽  
Author(s):  
F.B. Gao ◽  
J.D. Keene
Keyword(s):  
Neuronal Differentiation ◽  
Protein Family ◽  
Rna Recognition Motifs ◽  
Mrna Metabolism ◽  
Cell Extracts ◽  
Multiple Protein ◽  
Human Proteins ◽  
Mature Neurons ◽  
Recognition Motifs

Human proteins Hel-N1 and Hel-N2 contain three RNA recognition motifs (RRMs), and are members of a family of proteins highly homologous to Drosophila ELAV, which is essential for neuronal differentiation. Both proteins bind to A+U-rich 3′ untranslated regions of a variety of growth-related mRNAs in vitro. Here we demonstrate that in medulloblastoma cells derived from childhood brain tumors, Hel-N1 and Hel-N2 are mainly expressed in the cytoplasm, but are detectable in the nucleus. Both proteins are associated with polysomes and can be UV-crosslinked to poly(A)+ mRNA in cell extracts. In the cytoplasm the Hel-N1 protein family resides in granular structures that may contain multiple protein molecules bound to each mRNA. Evidence supporting this multimeric ribonucleoprotein (RNP) model includes in vitro reconstitution and competition experiments in which addition of a single RRM (RRM3) can alter complex formation. As in medulloblastoma cells, the Hel-N1 protein family is present in granular particles in the soma and the proximal regions of dendrites of cultured neurons, and colocalizes with ribosomes. In addition, we demonstrate that expression of the Hel-N1 protein family is up-regulated during neuronal differentiation of embryonic carcinoma P19 cells. Our data suggest that the Hel-N1 protein family is associated with the translational apparatus and implicated in both mRNA metabolism and neuronal differentiation. Furthermore, our findings open the possibility that these proteins participate in mRNA homeostasis in the dendrites and soma of mature neurons.

scholarly journals Bimodal Interaction of Mammalian Polo-Like Kinase 1 and a Centrosomal Scaffold, Cep192, in the Regulation of Bipolar Spindle Formation

2015 ◽  
Vol 35 (15) ◽  
pp. 2626-2640 ◽  
Author(s):  
Lingjun Meng ◽  
Jung-Eun Park ◽  
Tae-Sung Kim ◽  
Eun Hye Lee ◽  
Suk-Youl Park ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Spindle Assembly ◽  
Human Cells ◽  
Mitotic Progression ◽  
Spindle Formation ◽  
Content Type ◽  
Bipolar Spindle ◽  
Egg Extracts ◽  
Cultured Human Cells ◽  
Bipolar Spindles

Serving as microtubule-organizing centers, centrosomes play a key role in forming bipolar spindles. The mechanism of how centrosomes promote bipolar spindle assembly in various organisms remains largely unknown. A recent study withXenopus laevisegg extracts suggested that the Plk1 ortholog Plx1 interacts with the phospho-T46 (p-T46) motif ofXenopusCep192 (xCep192) to form an xCep192-mediated xAurA-Plx1 cascade that is critical for bipolar spindle formation. Here, we demonstrated that in cultured human cells, Cep192 recruits AurA and Plk1 in a cooperative manner, and this event is important for the reciprocal activation of AurA and Plk1. Strikingly, Plk1 interacted with Cep192 through either the p-T44 (analogous toXenopusp-T46) or the newly identified p-S995 motif via its C-terminal noncatalytic polo-box domain. The interaction between Plk1 and the p-T44 motif was prevalent in the presence of Cep192-bound AurA, whereas the interaction of Plk1 with the p-T995 motif was preferred in the absence of AurA binding. Notably, the loss of p-T44- and p-S995-dependent Cep192-Plk1 interactions induced an additive defect in recruiting Plk1 and γ-tubulin to centrosomes, which ultimately led to a failure in proper bipolar spindle formation and mitotic progression. Thus, we propose that Plk1 promotes centrosome-based bipolar spindle formation by forming two functionally nonredundant complexes with Cep192.

scholarly journals Characterization of the Crithidia fasciculata mRNA Cycling Sequence Binding Proteins

2001 ◽  
Vol 21 (14) ◽  
pp. 4453-4459 ◽  
Author(s):  
Riaz Mahmood ◽  
Bidyottam Mittra ◽  
Jane C. Hines ◽  
Dan S. Ray
Keyword(s):  
Cell Cycle ◽  
Protein Complexes ◽  
Coiled Coil ◽  
High Specificity ◽  
Binding Activity ◽  
Mrna Levels ◽  
Crithidia Fasciculata ◽  
Cysteine Motif ◽  
Cell Extracts ◽  
Sequence Elements

ABSTRACT The Crithidia fasciculata cycling sequence binding protein (CSBP) binds with high specificity to sequence elements in several mRNAs that accumulate periodically during the cell cycle. Mutations in these sequence elements abolish both cycling of the mRNA and binding of CSBP. Two genes, CSBPA andCSBPB, encoding putative subunits of CSBP have been cloned and were found to be present in tandem on the same DNA molecule and to be closely related. CSBPA andCSBPB are predicted to encode proteins with sizes of 35.6 and 42.0 kDa, respectively. Both CSBPA and CSBPB proteins have a predicted coiled-coil domain near the N terminus and a novel histidine and cysteine motif near the C terminus. The latter motif is conserved in other trypanosomatid species. Gel sieving chromatography and glycerol gradient sedimentation results indicate that CSBP has a molecular mass in excess of 200 kDa and an extended structure. Recombinant CSBPA and CSBPB also bind specifically to the cycling sequence and together can be reconstituted to give an RNA gel shift similar to that of purified CSBP. Proteins in cell extracts bind to an RNA probe containing six copies of the cycling sequence. The RNA-protein complexes contain both CSBPA and CSBPB, and the binding activity cycles in near synchrony with target mRNA levels.CSBPA and CSBPB mRNA and protein levels show little variation throughout the cell cycle, suggesting that additional factors are involved in the cyclic binding to the cycling sequence elements.

scholarly journals Phorbol ester induces the biosynthesis of glycosylated and nonglycosylated plasminogen activator inhibitor 2 in high excess over urokinase-type plasminogen activator in human U-937 lymphoma cells.

1987 ◽  
Vol 104 (3) ◽  
pp. 705-712 ◽  
Author(s):  
C Genton ◽  
E K Kruithof ◽  
W D Schleuning
Keyword(s):  
Plasminogen Activator ◽  
Phorbol Ester ◽  
Large Scale ◽  
De Novo ◽  
Plasminogen Activator Inhibitor ◽  
Conditioned Media ◽  
Cell Extracts ◽  
Type Plasminogen Activator ◽  
Urokinase Type Plasminogen Activator ◽  
Activator Inhibitor

The tumor-promoting phorbol ester PMA induces changes in the histiocytic human lymphoma cell line U-937 akin to cellular differentiation (Ralph, P., N. Williams, M. A. S. Moore, and P. B. Litcofsky, 1982, Cell. Immunol., 71:215-223) and concomitantly stimulates the biosynthesis of plasminogen activator inhibitor 2 (PAI 2) and of urokinase-type plasminogen activator (u-PA). PAI 2 is found in a nonglycosylated intracellular and a glycosylated secreted form. The former appears to be identical to PAI 2 previously purified from placental extracts and large-scale U-937 cell cultures. The sixfold increase of PAI 2 antigen measured 24 h after PMA treatment in cell extracts and conditioned media is accompanied by an equal increase of active PAI 2 mRNA, whereas the 6 to 13-fold increase of u-PA antigen in the same samples is associated with only a 1.5-fold mRNA increase. The increase of PAI 2, but not of u-PA, biosynthesis requires transcription. A 50-fold molar excess of PAI 2 over u-PA is found in both extracts and conditioned media of PMA-treated cells. PAI 2 represents at least 0.3% of total de novo synthesized protein 24 h after induction with PMA. Thus, PAI 2, but not u-PA, is an abundant product of this precursor analogue of the mononuclear phagocyte lineage, and might represent a new marker for monocyte/macrophage differentiation.

scholarly journals The kinetoplastid kinetochore protein KKT4 is an unconventional microtubule tip–coupling protein

2018 ◽  
Vol 217 (11) ◽  
pp. 3886-3900 ◽  
Author(s):  
Aida Llauró ◽  
Hanako Hayashi ◽  
Megan E. Bailey ◽  
Alex Wilson ◽  
Patryk Ludzia ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Binding Activity ◽  
Significant Similarity ◽  
Load Bearing ◽  
Kinetochore Protein ◽  
Microtubule Binding ◽  
Binding Domains ◽  
Microtubule Binding Domain ◽  
Coupling Protein

Kinetochores are multiprotein machines that drive chromosome segregation by maintaining persistent, load-bearing linkages between chromosomes and dynamic microtubule tips. Kinetochores in commonly studied eukaryotes bind microtubules through widely conserved components like the Ndc80 complex. However, in evolutionarily divergent kinetoplastid species such as Trypanosoma brucei, which causes sleeping sickness, the kinetochores assemble from a unique set of proteins lacking homology to any known microtubule-binding domains. Here, we show that the T. brucei kinetochore protein KKT4 binds directly to microtubules and maintains load-bearing attachments to both growing and shortening microtubule tips. The protein localizes both to kinetochores and to spindle microtubules in vivo, and its depletion causes defects in chromosome segregation. We define a microtubule-binding domain within KKT4 and identify several charged residues important for its microtubule-binding activity. Thus, despite its lack of significant similarity to other known microtubule-binding proteins, KKT4 has key functions required for driving chromosome segregation. We propose that it represents a primary element of the kinetochore–microtubule interface in kinetoplastids.

scholarly journals Extensive non-canonical phosphorylation in human cells revealed using strong-anion exchange-mediated phosphoproteomics

2017 ◽  
Author(s):  
Gemma Hardman ◽  
Simon Perkins ◽  
Zheng Ruan ◽  
Natarajan Kannan ◽  
Philip Brownridge ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Protein Phosphorylation ◽  
Anion Exchange ◽  
Human Cell ◽  
Cell Biology ◽  
Human Cells ◽  
Phosphopeptide Enrichment ◽  
Cell Extracts ◽  
Strong Anion Exchange ◽  
Acid Labile

Protein phosphorylation is a ubiquitous post-translational modification (PTM) that regulates all aspects of life. To date, investigation of human cell signalling has focussed on canonical phosphorylation of serine (Ser), threonine (Thr) and tyrosine (Tyr) residues. However, mounting evidence suggests that phosphorylation of histidine also plays a central role in regulating cell biology. Phosphoproteomics workflows rely on acidic conditions for phosphopeptide enrichment, which are incompatible with the analysis of acid-labile phosphorylation such as histidine. Consequently, the extent of non-canonical phosphorylation is likely to be under-estimated. We report an Unbiased Phosphopeptide enrichment strategy based on Strong Anion Exchange (SAX) chromatography (UPAX), which permits enrichment of acid-labile phosphopeptides for characterisation by mass spectrometry. Using this approach, we identify extensive and positional phosphorylation patterns on histidine, arginine, lysine, aspartate and glutamate in human cell extracts, including 310 phosphohistidine and >1000 phospholysine sites of protein modification. Remarkably, the extent of phosphorylation on individual non-canonical residues vastly exceeds that of basal phosphotyrosine. Our study reveals the previously unappreciated diversity of protein phosphorylation in human cells, and opens up avenues for exploring roles of acid-labile phosphorylation in any proteome using mass spectrometry.

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