Calmodulin-containing substructures of the centrosomal matrix released by microtubule perturbation

Molecular recording of calcium signals via calcium-dependent proximity labeling

Calcium ions serve as key intracellular signals. Local, transient increases in calcium concentrations can activate calcium sensor proteins that in turn trigger downstream effectors. In neurons, calcium transients play a central role in regulating neurotransmitter release and synaptic plasticity. However, it is challenging to capture the molecular events associated with these localized and ephemeral calcium signals. Here we present an engineered biotin ligase that generates permanent molecular traces in a calcium-dependent manner. The enzyme, calcium-dependent BioID (Cal-ID), biotinylates nearby proteins within minutes in response to elevated local calcium levels. The biotinylated proteins can be identified via mass spectrometry and visualized using microscopy. In neurons, Cal-ID labeling is triggered by neuronal activity, leading to prominent protein biotinylation that enables transcription-independent activity labeling in the brain. In summary, Cal-ID produces a biochemical record of calcium signals and neuronal activity with high spatial resolution and molecular specificity.

Phosphotyrosine proteomics in cells synchronized at monopolar cytokinesis reveals EphA2 as functioning in cytokinesis

Cytokinesis is the final step of the cell division in which cellular components are separated into two daughter cells. This process is regulated through the phosphorylation of different classes of proteins by serine/threonine (Ser/Thr) kinases such as Aurora B and Polo-like kinase 1 (PLK1). Conversely, the role of phosphorylation at tyrosine residues during cytokinesis has not been studied in detail yet. In this study, we performed a phosphotyrosine proteomic analysis of cells undergoing monopolar cytokinesis synchronized by using the Eg5 inhibitor (+)-S-trityl-l-cysteine (STLC) and the CDK1 inhibitor RO-3306. Phosphotyrosine proteomics gave 362 tyrosine-phosphorylated peptides. Western blot analysis of proteins revealed tyrosine phosphorylation in mitogen-activated protein kinase 14 (MAPK14), vimentin, ephrin type-A receptor 2 (EphA2), and myelin protein zero-like protein 1 (MPZL1) during monopolar cytokinesis. Additionally, we demonstrated that EphA2, a protein with unknown function during cytokinesis, is involved in cytokinesis. EphA2 knockdown accelerated epithelial cell transforming 2 (Ect2) knockdown-induced multinucleation, suggesting that EphA2 plays a role in cytokinesis in a particular situation. The list also included many proteins previously reported to play roles during cytokinesis. These results evidence that the identified phosphopeptides facilitate the identification of novel tyrosine phosphorylation signaling involved in regulating cytokinesis.

The FgVps39-FgVam7-FgSso1 Complex Mediates Vesicle Trafficking and Is Important for the Development and Virulence of Fusarium graminearum

Vesicle trafficking is an important event in eukaryotic organisms. Many proteins and lipids transported between different organelles or compartments are essential for survival. These processes are mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, Rab-GTPases, and multisubunit tethering complexes such as class C core vacuole or endosome tethering and homotypic fusion or vacuole protein sorting (HOPS). Our previous study has demonstrated that FgVam7, which encodes a SNARE protein involving in vesicle trafficking, plays crucial roles in growth, asexual or sexual development, deoxynivalenol production, and pathogenicity in Fusarium graminearum. Here, the affinity purification approach was used to identify FgVam7-interacting proteins to explore its regulatory mechanisms during vesicle trafficking. The orthologs of yeast Vps39, a HOPS tethering complex subunit, and Sso1, a SNARE protein localized to the vacuole or endosome, were identified and selected for further characterization. In yeast two-hybrid and glutathione-S-transferase pull-down assays, FgVam7, FgVps39, and FgSso1 interacted with each other as a complex. The ∆Fgvps39 mutant generated by targeted deletion was significantly reduced in vegetative growth and asexual development. It failed to produce sexual spores and was defective in plant infection and deoxynivalenol production. Further cellular localization and cytological examinations suggested that FgVps39 is involved in vesicle trafficking from early or late endosomes to vacuoles in F. graminearum. Additionally, the ∆Fgvps39 mutant was defective in vacuole morphology and autophagy, and it was delayed in endocytosis. Our results demonstrate that FgVam7 interacts with FgVps39 and FgSso1 to form a unique complex, which is involved in vesicle trafficking and modulating the proper development of infection-related morphogenesis in F. graminearum.

Fluorescent vinblastine probes for live cell imaging

Herein we describe the synthesis of several fluorescent analogues of the clinically approved microtubule destabilizing agent vinblastine. The evaluated probes are the most potent described and provides the first example of uptake, distribution and live cell imaging using this well known antimitotic agent.

Retrograde trafficking from the endosome to the trans-Golgi network mediated by the retromer is required for fungal development and pathogenicity in Fusarium graminearum

In eukaryotes, the retromer is an endosome-localized complex involved in protein retrograde transport. However, the role of such intracellular trafficking events in pathogenic fungal development and pathogenicity remains unclear. The role of the retromer complex in Fusarium graminearum was investigated using cell biological and genetic methods. We observed the retromer core component FgVps35 (Vacuolar Protein Sorting 35) in the cytoplasm as fast-moving puncta. FgVps35-GFP co-localized with both early and late endosomes, and associated with the trans-Golgi network (TGN), suggesting that FgVps35 functions at the donor endosome membrane to mediate TGN trafficking. Disruption of microtubules with nocodazole significantly restricted the transportation of FgVps35-GFP and resulted in severe germination and growth defects. Mutation of FgVPS35 not only mimicked growth defects induced by pharmacological treatment, but also affected conidiation, ascospore formation and pathogenicity. Using yeast two-hybrid assays, we determined the interactions among FgVps35, FgVps26, FgVps29, FgVps17 and FgVps5 which are analogous to the yeast retromer complex components. Deletion of any one of these genes resulted in similar phenotypic defects to those of the ΔFgvps35 mutant and disrupted the stability of the complex. Overall, our results provide the first clear evidence of linkage between the retrograde transport mediated by the retromer complex and virulence in F. graminearum.

Subdiffraction resolution microscopy methods for analyzing centrosomes organization

In this chapter, we describe the current methods of examining the structure of centrosomes by fluorescence subdiffraction microscopy. By using recently developed microscopy techniques, centrosomal proteins can now be examined in cells with a resolution of only a few nanometers, a level of molecular detail beyond the reach of traditional cell biology methods as confocal and widefield microscopy. We emphasize imaging by three-dimensional structured illumination microscopy, stochastic optical reconstruction microscopy, and quantitative approaches to image data analysis.

Loss of PINK1 enhances neurodegeneration in a mouse model of Parkinson's disease triggered by mitochondrial stress

Parkinson's disease (PD) shows a complex etiology, where both genetic and environmental factors contribute to initiation and advance of pathology. Mitochondrial dysfunction and mutation of genes implicated in mitochondria quality control are recognized contributors to etiopathology and progression of PD. Here we report the development and characterization of a genetic mouse model of PD with a combined etiology comprising: 1) induction of mitochondrial stress achieved through the expression of a mitochondrial matrix protein that accumulates in an unfolded state and 2) deletion of PINK1 gene. Using this model we address the role of PINK1 in mitochondrial quality control and disease progression. To induce mitochondrial stress specifically in catecholaminergic neurons we generated transgenic animals where the conditional expression of mitochondrial unfolded ornithine transcarbamylase (dOTC) is achieved under the tyrosine hydroxylase (Th) promoter. The mice were characterized in terms of survival, growth and motor behaviour. The characterization was followed by analysis of cell death induced in dopaminergic neurons and responsiveness to l-dopa. We demonstrate that accumulation of dOTC in dopaminergic neurons causes neurodegeneration and motor behaviour impairment that illustrates a parkinsonian phenotype. This associates with l-dopa responsiveness validating the model as a model of PD. The combined transgenic model where dOTC is overexpressed in PINK1 KO background presents increased neurodegeneration as compared to dOTC transgenic in wild-type background. Moreover, this combined model does not show responsiveness to l-dopa. Our in vivo data show that loss of PINK1 accelerates neurodegenerative phenotypes induced by mitochondrial stress triggered by the expression of an unfolded protein in this organelle.

Enrichment of cell populations in metaphase, anaphase, and telophase by synchronization using nocodazole and blebbistatin: a novel method suitable for examining dynamic changes in proteins during mitotic progression

Mitosis is a continuous process to separate replicated chromosomes into two daughter cells through prophase, metaphase, anaphase, and telophase. Although a number of methods have been established to synchronize cells at different phases of the cell cycle, it is difficult to synchronize cells at the specific phases, anaphase and telophase, during mitosis because of the short duration of anaphase. Here, we show that HeLa S3 cells in anaphase and in telophase are successfully enriched by treatment with a combination of low concentrations of the microtubule-depolymerizing agent nocodazole and the myosin II inhibitor blebbistatin. After 9-h release from thymidine block at G1/S phase, addition of nocodazole at 20 ng/ml but not 40 ng/ml ensures rapid release from the nocodazole arrest. Subsequently, the cells are cultured in the presence of 50 μM blebbistatin for 20 and 50 min to enrich cells in anaphase and telophase, respectively. Western blot analysis verifies down-regulation of phospho-histone H3-Ser10, phospho-Aurora A/B/C, and cyclin B1 during M-phase progression. Furthermore, we show how the electrophoretic mobility shifts of the Src-family kinases c-Yes and c-Src can change in each phase of mitosis. These results provide a useful synchronization method for biochemically examining protein dynamics during M-phase progression.

Cytotoxicity of Vinca minor

Vinca minor L. (Apocynaceae) is a medicinal plant that has long been used to treat cerebral and memory disorders in European folk medicine. Furthermore, it contains more than 50 alkaloids, some of them having bisindole structure such as the antineoplastic alkaloids present in Catharanthus roseus (L.) G. Don (Apocynaceae). In this study, the plant's alkaloid extract was divided into three fractions and the cytotoxic effects on cell proliferation of HT-29, Caco-2, T47D, and NIH/3T3 cell lines were examined. All alkaloid fractions showed a dose-dependent cytotoxic effect on the cell lines. IC(50) values confirmed that the growth and proliferation of NIH/3T3 cells were less affected in comparison to other cell lines.

Gene variants associated with ischemic stroke: the cardiovascular health study

BACKGROUND AND PURPOSE

The purpose of this study was to determine whether 74 single nucleotide polymorphisms (SNPs), which had been associated with coronary heart disease, are associated with incident ischemic stroke.

METHODS

Based on antecedent studies of coronary heart disease, we prespecified the risk allele for each of the 74 SNPs. We used Cox proportional hazards models that adjusted for traditional risk factors to estimate the associations of these SNPs with incident ischemic stroke during 14 years of follow-up in a population-based study of older adults: the Cardiovascular Health Study (CHS).

RESULTS

In white CHS participants, the prespecified risk alleles of 7 of the 74 SNPs (in HPS1, ITGAE, ABCG2, MYH15, FSTL4, CALM1, and BAT2) were nominally associated with increased risk of stroke (one-sided P<0.05, false discovery rate=0.42). In black participants, the prespecified risk alleles of 5 SNPs (in KRT4, LY6G5B, EDG1, DMXL2, and ABCG2) were nominally associated with stroke (one-sided P<0.05, false discovery rate=0.55). The Val12Met SNP in ABCG2 was associated with stroke in both white (hazard ratio, 1.46; 90% CI, 1.05 to 2.03) and black (hazard ratio, 3.59; 90% CI, 1.11 to 11.6) participants of CHS. Kaplan-Meier estimates of the 10-year cumulative incidence of stroke were greater among Val allele homozygotes than among Met allele carriers in both white (10% versus 6%) and black (12% versus 3%) participants of CHS.

CONCLUSIONS

The Val12Met SNP in ABCG2 (encoding a transporter of sterols and xenobiotics) was associated with incident ischemic stroke in white and black participants of CHS.

Vinflunine, a novel microtubule inhibitor, suppresses calmodulin interaction with the microtubule-associated protein STOP

Vinca alkaloids vinblastine and vincristine and some of their derivatives such as vinorelbine are widely used in therapy of leukemia and several solid tumors. Their action is associated with alterations of the mitotic spindle functions that prevent the cell cycle progression and lead to mitotic block. A number of studies show that some Vinca alkaloids inhibit CaM-target interaction. The newest microtubule inhibitor, vinflunine (Javlor), currently in clinical trials, is remarkably more active than vinblastine against a number of tumors. Moreover, vinflunine is significantly less toxic than other Vinca alkaloids. The high antitumor activity of this molecule is not well understood since it binds to tubulin with an overall affinity several-fold lower than that of vinblastine or vincristine. In this study, we examined the interaction of Ca2+-CaM with vinflunine, vinblastine, and stable tubule only polypeptide (STOP) by using a combination of thermodynamic and mass spectrometric approaches. We characterized the influence of Vinca alkaloids on Ca2+-CaM-STOP complex formation. Our results revealed different binding modes to Ca2+-CaM for vinflunine and vinblastine, highlighting that adding fluorine atoms on the cleavamine moiety of the Vinca alkaloid molecule is critical for the localization of the drug on calmodulin. We demonstrate that vinflunine is a better inhibitor for STOP binding to calmodulin than vinblastine. We suggest that vinflunine action on calmodulin can have an effect on microtubule dynamics. These data may contribute to a better understanding of the superior antitumor efficiency and lower toxicity of vinflunine.

Visualisation of macropinosome maturation by the recruitment of sorting nexins

We report that phosphoinositol-binding sorting nexin 5 (SNX5) associates with newly formed macropinosomes induced by EGF stimulation. We used the recruitment of GFP-SNX5 to macropinosomes to track their maturation. Initially, GFP-SNX5 is sequestered to discrete subdomains of the macropinosome; these subdomains are subsequently incorporated into highly dynamic, often branched, tubular structures. Time-lapse videomicroscopy revealed the highly dynamic extension of SNX5-labelled tubules and their departure from the macropinosome body to follow predefined paths towards the perinuclear region of the cell, before fusing with early endosomal acceptor membranes. The extension and departure of these tubular structures occurs rapidly over 5-10 minutes and is dependent upon intact microtubules. As the tubular structures depart from the macropinosome there is a reduction in the surface area and an increase in tension of the limiting membrane of the macropinosome. In addition to the recruitment of SNX5 to the macropinosome, Rab5, SNX1 and EEA1 are also recruited by newly formed macropinosomes, followed by the accumulation of Rab7. SNX5 forms heterodimers with SNX1 and this interaction is required for endosome association of SNX5. We propose that the departure of SNX5-positive tubules represents a rapid mechanism of recycling components from macropinosomes thereby promoting their maturation into Rab7-positive structures. Collectively these findings provide a detailed real-time characterisation of the maturation process of the macropinocytic endosome.

Non-equivalence of embryonic and somatic cell nuclei affecting spindle composition in clones

Cloning by nuclear transfer remains inefficient but is more efficient when nuclei from embryonic cells or embryonic stem cells (ECNT) are employed as compared with somatic cells (SCNT). The factors determining efficiency have not been elucidated. We find that somatic and embryonic nuclei differ in their ability to organize meiotic and mitotic spindles of normal molecular composition. Calmodulin, a component of meiotic and mitotic spindle chromosome complexes (SCCs), displays sharply reduced association with the SCC forming after SCNT but not ECNT. This defect persists in mitotic spindles at least through the second mitosis, despite abundant calmodulin expression in the cell, and correlates with slow chromosome congression. We propose that somatic cell nuclei lack factors needed to direct normal SCC formation in oocytes and early embryos. These results reveal a striking control of SCC formation by the transplanted nucleus and provide the first identified molecular correlate of donor stage-dependent restriction in nuclear potency.

Review: tubulin function, action of antitubulin drugs, and new drug development

Anticancer agents that interfere with microtubulin function are in widespread use in man and have a broad spectrum of activity against both hematological malignancies and solid tumors. The mechanisms of actions of these agents have been better defined during the past decade, indicating that there are distinct binding sites for these agents and that they interfere with microtubulin dynamics (growth and shortening of tubules) at low concentrations and only evoke microtubulin aggregation or dissociation at high concentrations. Tubulin has been recently described in the nucleus of cells and in mitochondria. Downstream events from tubulin binding are believed to be critical events for the generation of apoptosis in the malignant cell. The effects of vinca alkaloids and taxanes are distinct, suggesting that the interference with the tubulin cap by high-affinity binding of effective agents is not the only mechanism of cytotoxic effect, and the low-affinity binding of drug, which distorts microtubulin function, may also be important. The epothilones share some of the binding characteristics of the taxanes and are in clinical trials because of cytoxic activity in taxane resistant cells. Tubulin has additional target sites for anticancer drugs including interference with the binding and function of microtubule associated proteins and interference with motor proteins which are essential for the transport of substances within the cell. Because many of these microtubule associated proteins have an ATP binding site, both computer-aided design and combinatorial chemistry techniques can be used to make agents to interfere with their function analogous to imatinib mesylate (Gleevec). Agents that interfere with the motor protein kinesin are entering clinical trials.

Calmodulin spatial dynamics in RBL-2H3 mast cells

A line of rat basophilic leukaemia (RBL) cells, a model of mast cells, stably expressing EGFP-tagged calmodulin secreted normally in response to standard agonists. As reported for other cell types, calmodulin was concentrated in the mitotic spindle poles of dividing cells. In unstimulated interphase cells calmodulin was concentrated in the cell cortex and at a single central location. Disruption of cortical actin eliminated the concentration of calmodulin at the cortex while the central calmodulin concentration was associated with an enrichment of tubulin and is likely to represent the centrosome. Following stimulation with either an agonist that crosslinks Fc receptors or co-application of phorbol ester and a calcium ionophore the interior of the cells lost calmodulin while cortical fluorescence became more pronounced but also less uniform. After stimulation discrete bright puncta of calmodulin-EGFP (CaM-EGFP) appeared in the cell interior. Puncta colocalised with moving lysotracker-labelled granules, suggesting that calmodulin may play a role in organising their transport. Our results show that in interphase RBL cells a large fraction of the calmodulin pool is associated with targets in the actin cytoskeleton and demonstrate the utility of this model system for studying calmodulin biology.

Genome-wide identification of Arabidopsis coiled-coil proteins and establishment of the ARABI-COIL database

Increasing evidence demonstrates the importance of long coiled-coil proteins for the spatial organization of cellular processes. Although several protein classes with long coiled-coil domains have been studied in animals and yeast, our knowledge about plant long coiled-coil proteins is very limited. The repeat nature of the coiled-coil sequence motif often prevents the simple identification of homologs of animal coiled-coil proteins by generic sequence similarity searches. As a consequence, counterparts of many animal proteins with long coiled-coil domains, like lamins, golgins, or microtubule organization center components, have not been identified yet in plants. Here, all Arabidopsis proteins predicted to contain long stretches of coiled-coil domains were identified by applying the algorithm MultiCoil to a genome-wide screen. A searchable protein database, ARABI-COIL (http://www.coiled-coil.org/arabidopsis), was established that integrates information on number, size, and position of predicted coiled-coil domains with subcellular localization signals, transmembrane domains, and available functional annotations. ARABI-COIL serves as a tool to sort and browse Arabidopsis long coiled-coil proteins to facilitate the identification and selection of candidate proteins of potential interest for specific research areas. Using the database, candidate proteins were identified for Arabidopsis membrane-bound, nuclear, and organellar long coiled-coil proteins.

Xeroderma pigmentosum group C protein possesses a high affinity binding site to human centrin 2 and calmodulin

Human centrin 2 (HsCen2), a member of the EF-hand superfamily of Ca2+-binding proteins, is commonly associated with centrosome-related structures. The protein is organized in two domains, each containing two EF-hand motifs, but only the C-terminal half exhibits Ca2+ sensor properties. A significant fraction of HsCen2 is localized in the nucleus, where it was recently found associated with the xeroderma pigmentosum group C protein (XPC), a component of the nuclear excision repair pathway. Analysis of the XPC sequence (940 residues), using a calmodulin target recognition software, enabled us to predict two putative binding sites. The binding properties of the two corresponding peptides were investigated by isothermal titration calorimetry. Only one of the peptides (P1-XPC) interacts strongly (Ka = 2.2 x 10(8) m-1, stoichiometry 1:1) with HsCen2 in a Ca2+-dependent manner. This peptide also binds, with a similar affinity (Ka = 1.1 x 10(8) m-1) to a C-terminal construct of HsCen2, indicating that the interaction with the integral protein is mainly the result of the contribution of the C-terminal half. The second peptide (P2-XPC) failed to show any detectable binding either to HsCen2 or to its C-terminal lobe. The two peptides interact with different affinities and mechanisms with calmodulin. Circular dichroism and nuclear magnetic resonance were used to structurally characterize the complex formed by the C-terminal domain of HsCen2 with P1-XPC.

Dissociating the centrosomal matrix protein AKAP450 from centrioles impairs centriole duplication and cell cycle progression

Centrosomes provide docking sites for regulatory molecules involved in the control of the cell division cycle. The centrosomal matrix contains several proteins, which anchor kinases and phosphatases. The large A-Kinase Anchoring Protein AKAP450 is acting as a scaffolding protein for other components of the cell signaling machinery. We selectively perturbed the centrosome by modifying the cellular localization of AKAP450. We report that the expression in HeLa cells of the C terminus of AKAP450, which contains the centrosome-targeting domain of AKAP450 but not its coiled-coil domains or binding sites for signaling molecules, leads to the displacement of the endogenous centrosomal AKAP450 without removing centriolar or pericentrosomal components such as centrin, gamma-tubulin, or pericentrin. The centrosomal protein kinase A type II alpha was delocalized. We further show that this expression impairs cytokinesis and increases ploidy in HeLa cells, whereas it arrests diploid RPE1 fibroblasts in G1, thus further establishing a role of the centrosome in the regulation of the cell division cycle. Moreover, centriole duplication is interrupted. Our data show that the association between centrioles and the centrosomal matrix protein AKAP450 is critical for the integrity of the centrosome and for its reproduction.