Regulation of microtubule dynamic instability in vitro by differentially phosphorylated stathmin

A patient-derived stem cell model of hereditary spastic paraplegia with SPAST mutations

Hereditary spastic paraplegia (HSP) leads to progressive gait disturbances with lower limb muscle weakness and spasticity. Mutations in SPAST are a major cause of adult-onset, autosomal-dominant HSP. Spastin, the protein encoded by SPAST, is a microtubule-severing protein that is enriched in the distal axon of corticospinal motor neurons, which degenerate in HSP patients. Animal and cell models have identified functions of spastin and mutated spastin but these models lack the gene dosage, mutation variability and genetic background that characterize patients with the disease. In this study, this genetic variability is encompassed by comparing neural progenitor cells derived from biopsies of the olfactory mucosa from healthy controls with similar cells from HSP patients with SPAST mutations, in order to identify cell functions altered in HSP. Patient-derived cells were similar to control-derived cells in proliferation and multiple metabolic functions but had major dysregulation of gene expression, with 57% of all mRNA transcripts affected, including many associated with microtubule dynamics. Compared to control cells, patient-derived cells had 50% spastin, 50% acetylated α-tubulin and 150% stathmin, a microtubule-destabilizing enzyme. Patient-derived cells were smaller than control cells. They had altered intracellular distributions of peroxisomes and mitochondria and they had slower moving peroxisomes. These results suggest that patient-derived cells might compensate for reduced spastin, but their increased stathmin expression reduced stabilized microtubules and altered organelle trafficking. Sub-nanomolar concentrations of the microtubule-binding drugs, paclitaxel and vinblastine, increased acetylated α-tubulin levels in patient cells to control levels, indicating the utility of this cell model for screening other candidate compounds for drug therapies.

Spatial and temporal sensing limits of microtubule polarization in neuronal growth cones by intracellular gradients and forces

Neuronal growth cones are the most sensitive among eukaryotic cells in responding to directional chemical cues. Although a dynamic microtubule cytoskeleton has been shown to be essential for growth-cone turning, the precise nature of coupling of the spatial cue with microtubule polarization is less understood. Here we present a computational model of microtubule polarization in a turning neuronal growth cone. We explore the limits of directional cues in modifying the spatial polarization of microtubules by testing the role of microtubule dynamics, gradients of regulators, and retrograde forces along filopodia. We analyze the steady state and transition behavior of microtubules on being presented with a directional stimulus. Our model makes novel, to our knowledge, predictions about the minimal angular spread of the chemical signal at the growth cone and the fastest polarization times. A regulatory reaction-diffusion network based on the cyclic phosphorylation-dephosphorylation of a regulator predicts that the receptor-signal magnitude can generate the maximal polarization of microtubules and not feedback loops or amplifications in the network. Using both the phenomenological and network models, we have demonstrated some of the physical limits within which the microtubule polarization system works in turning the neuron.

Expression and phosphorylation of stathmin correlate with cell migration in esophageal squamous cell carcinoma

Microtubules play extensive roles in cellular processes, including cell motility. Stathmin is an important protein which destabilizes microtubules. The essential function of stathmin is closely associated with its phosphorylation status. Stathmin is overexpressed in many human cancers and has a significant relationship with clinical characteristics such as grade, tumor size and prognosis. We demonstrated that stathmin was overexpressed in ESCC tissues using both 2-DE and immunohistochemistry analysis. In addition, overexpression of stathmin was significantly correlated with histological grade in ESCC. However, no correlation was found with age, gender and lymph node metastasis. Knockdown of stathmin with siRNA impaired cell migration in KYSE30 and KYSE410 cells. When EC0156 cells were treated with paclitaxel, stathmin was stably phosphorylated and migration was impaired. These observations suggest that stathmin may have a more important function in ESCC development and migration. The present study provides further understanding of the importance of stathmin in ESCC therapy or diagnosis.

Influence of 63Ser phosphorylation and dephosphorylation on the structure of the stathmin helical nucleation sequence: a molecular dynamics study

Phosphorylation is an important mechanism regulating protein-protein interactions involving intrinsically disordered protein regions. Stathmin, an archetypical example of an intrinsically disordered protein, is a key regulator of microtubule dynamics in which phosphorylation of 63Ser within the helical nucleation sequence strongly down-regulates the tubulin binding and microtubule destabilizing activities of the protein. Experimental studies on a peptide encompassing the 19-residue helical nucleation sequence of stathmin (residues 55-73) indicate that phosphorylation of 63Ser destabilizes the peptide's secondary structure by disrupting the salt bridges supporting its helical conformation. In order to investigate this hypothesis at atomic resolution, we performed molecular dynamics simulations of nonphosphorylated and phosphorylated stathmin-[55-73] at room temperature and pressure, neutral pH, and explicit solvation using the recently released GROMOS force field 54A7. In the simulations of nonphosphorylated stathmin-[55-73] emerged salt bridges associated with helical configurations. In the simulations of 63Ser phosphorylated stathmin-[55-73] these configurations dispersed and were replaced by a proliferation of salt bridges yielding disordered configurations. The transformation of the salt bridges was accompanied by emergence of numerous interactions between main and side chains, involving notably the oxygen atoms of the phosphorylated 63Ser. The loss of helical structure induced by phosphorylation is reversible, however, as a final simulation showed. The results extend the hypothesis of salt bridge derangement suggested by experimental observations of the stathmin nucleation sequence, providing new insights into regulation of intrinsically disordered protein systems mediated by phosphorylation.

Role of Oncoprotein 18 in metastasis of hepatocellular carcinoma

AIM: To explore the role of Oncoprotein 18 (Op18) in metastasis of hepatocellular carcinoma (HCC).

METHODS: Op18 expression was repressed in HCCLM3 cells by RNA interference, and interference effect was evaluated by RT-PCR and Western blot. Cell adhesion, migration and invasion were analyzed by cell adhesion assay and Transwell assay in vitro. Op18 expression was detected by RT-PCR and immunohistochemistry in 96 HCC specimens with or without metastasis.

RESULTS: Op18 expression was effectively inhibited by RNA interference in HCCLM3 cells. Cell adhesion was significantly suppressed in the RNAi group compared to the mock group (20 min: 0.616 ± 0.057 vs 0.944 ± 0.068; 40 min: 0.740 ± 0.0713 vs 1.196 ± 0.115; 60 min: 1.001 ± 0.083 vs 1.441 ± 0.053; all P < 0.05). Transwell assay revealed that cell migration and invasion decreased in the RNAi group compared to the mock group (migration: 0.145 ± 0.011 vs 0.206 ± 0.008; invasion: 0.127 ± 0.008 vs 0.168 ± 0.012; both P < 0.01). Op18 expression was detected in 96 HCC tissues with or without metastasis. RT-PCR demonstrated that Op18 was overexpressed in HCC tissues with metastasis (n = 48) compared with HCC tissues without metastasis (n = 48, Op18/GAPDH relative ratio: 0.560 ± 0.128 vs 0.414 ± 0.086); and IHC results also indicated that Op18 expression was up-regulated in HCC tissues with metastasis in comparison with HCC tissues without metastasis (integrated density: 624.771 ± 100.032 vs 413.786 ± 71.833, P < 0.01).

CONCLUSION: Overexpression of Op18 may play an important role in HCC metastasis.

Hyperdynamic microtubules, cognitive deficits, and pathology are improved in tau transgenic mice with low doses of the microtubule-stabilizing agent BMS-241027

Tau is a microtubule (MT)-stabilizing protein that is altered in Alzheimer's disease (AD) and other tauopathies. It is hypothesized that the hyperphosphorylated, conformationally altered, and multimeric forms of tau lead to a disruption of MT stability; however, direct evidence is lacking in vivo. In this study, an in vivo stable isotope-mass spectrometric technique was used to measure the turnover, or dynamicity, of MTs in brains of living animals. We demonstrated an age-dependent increase in MT dynamics in two different tau transgenic mouse models, 3xTg and rTg4510. MT hyperdynamicity was dependent on tau expression, since a reduction of transgene expression with doxycycline reversed the MT changes. Treatment of rTg4510 mice with the epothilone, BMS-241027, also restored MT dynamics to baseline levels. In addition, MT stabilization with BMS-241027 had beneficial effects on Morris water maze deficits, tau pathology, and neurodegeneration. Interestingly, pathological and functional benefits of BMS-241027 were observed at doses that only partially reversed MT hyperdynamicity. Together, these data suggest that tau-mediated loss of MT stability may contribute to disease progression and that very low doses of BMS-241027 may be useful in the treatment of AD and other tauopathies.

Novel role of stathmin in microtubule-dependent control of endothelial permeability

Microtubule (MT) dynamics in vascular endothelium are modulated by vasoactive mediators and are critically involved in the control of endothelial cell (EC) permeability via Rho GTPase-dependent crosstalk with the actin cytoskeleton. However, the role of regulators in MT stability in these mechanisms remains unclear. This study investigated the involvement of the MT-associated protein stathmin in the mediation of agonist-induced permeability in EC cultures and vascular leak in vivo. Thrombin treatment of human pulmonary ECs induced rapid dephosphorylation and activation of stathmin. Inhibition of stathmin activity by small interfering RNA-based knockdown or cAMP-mediated phosphorylation abrogated thrombin-induced F-actin remodeling and Rho-dependent EC hyperpermeability, while expression of a phosphorylation-deficient stathmin mutant exacerbated thrombin-induced EC barrier disruption. Stathmin suppression preserved the MT network against thrombin-induced MT disassembly and release of Rho-specific guanine nucleotide exchange factor, GEF-H1. The protective effects of stathmin knockdown were observed in vivo in the mouse 2-hit model of ventilator-induced lung injury and were linked to MT stabilization and down-regulation of Rho signaling in the lung. These results demonstrate the mechanism of stathmin-dependent control of MT dynamics, Rho signaling, and permeability and suggest novel potential pharmacological interventions in the prevention of increased vascular leak via modulation of stathmin activity.

C-Terminal region of teneurin-1 co-localizes with dystroglycan and modulates cytoskeletal organization through an extracellular signal-regulated kinase-dependent stathmin- and filamin A-mediated mechanism in hippocampal cells

The pyramidal neurons in the hippocampus are extremely neuroplastic, and the complexity of dendritic branches can be dynamically altered in response to a variety of stimuli, including learning and stress. Recently, the teneurin family of proteins has emerged as an interneuronal and extracellular matrix signaling system that plays a significant role in brain development and neuronal communication. Encoded on the last exon of the teneurin genes is a new family of bioactive peptides termed the teneurin C-terminal-associated peptides (TCAPs). Previous studies indicate that TCAP-1 regulates axon fasciculation and dendritic morphology in the hippocampus. This study was aimed at understanding the molecular mechanisms by which TCAP-1 regulates these changes in the mouse hippocampus. Fluoresceinisothiocyanate (FITC)-labeled TCAP-1 binds to the pyramidal neurons of the CA2 and CA3, and dentate gyrus in the hippocampus of the mouse brain. Moreover, FITC-TCAP-1 co-localizes with β-dystroglycan upon binding to the plasma membrane of cultured immortalized mouse E14 hippocampal cells. In culture, TCAP-1 stimulates ERK1/2-dependent phosphorylation of the cytoskeletal regulatory proteins, stathmin at serine-25 and filamin A at serine-2152. In addition, TCAP-1 induces actin polymerization, increases immunoreactivity of tubulin-based cytoskeletal elements and causes a corresponding increase in filopodia formation and mean filopodia length in cultured hippocampal cells. We postulate that the TCAP-1 region of teneurin-1 has a direct action on the cytoskeletal reorganization that precedes neurite and process development in hippocampal neurons. Our data provides novel evidence that functionally links the teneurin and dystroglycan systems and provides new insight into the molecular mechanisms by which TCAP-1 regulates cytoskeletal dynamics in hippocampal neurons. The TCAP-dystroglycan system may represent a novel mechanism associated with the regulation of hippocampal-function.

Multifaceted functions of Siva-1: more than an Indian God of Destruction

Siva-1, as a p53-inducible gene, has been shown to induce extensive apoptosis in a number of different cell lines. Recent evidence suggests that Siva-1 functions as a part of the auto-regulatory feedback loop that restrains p53 through facilitating Mdm2-mediated p53 degradation. Also, Siva-1 plays an important role in suppressing tumor metastasis. Here we review the current understanding of Siva-1-mediated apoptotic signaling pathway. We also add comments on the p53-Siva-1 feedback loop, the novel function of Siva-1 in suppressing tumor metastasis, and their potential implications.

4-hydroxy-2-nonenal mediates genotoxicity and bystander effects caused by Enterococcus faecalis-infected macrophages

BACKGROUND & AIMS

Enterococcus faecalis is a human intestinal commensal that produces extracellular superoxide and promotes chromosome instability via macrophage-induced bystander effects. We investigated the ability of 4-hydroxy-2-nonenal (4-HNE), a diffusible breakdown product of ω-6 polyunsaturated fatty acids, to mediate these effects.

METHODS

4-HNE was purified from E faecalis-infected macrophages; its genotoxicity was assessed in human colon cancer (HCT116) and primary murine colon epithelial (YAMC) cell lines.

RESULTS

4-HNE induced G(2)-M cell cycle arrest, led to formation γH2AX foci, and disrupted the mitotic spindle in both cell lines. Binucleate tetraploid cells that formed after incubation with 4-HNE were associated with the activation of stathmin and microtubule catastrophe. Silencing glutathione S-transferase α4, a scavenger of 4-HNE, increased the susceptibility of epithelial cells to 4-HNE-induced genotoxicity. Interleukin-10 knockout mice colonized with superoxide-producing E faecalis developed inflammation and colorectal cancer, whereas colonization with a superoxide-deficient strain resulted in inflammation but not cancer. 4-HNE-protein adducts were found in the lamina propria and macrophages in areas of colorectal inflammation.

CONCLUSIONS

4-HNE can act as an autochthonous mitotic spindle poison in normal colonic epithelial and colon cancer cells. This finding links the macrophage-induced bystander effects to colorectal carcinogenesis.

The Chlamydia effector chlamydial outer protein N (CopN) sequesters tubulin and prevents microtubule assembly

Chlamydia species are obligate intracellular pathogens that utilize a type three secretion system to manipulate host cell processes. Genetic manipulations are currently not possible in Chlamydia, necessitating study of effector proteins in heterologous expression systems and severely complicating efforts to relate molecular strategies used by Chlamydia to the biochemical activities of effector proteins. CopN is a chlamydial type three secretion effector that is essential for virulence. Heterologous expression of CopN in cells results in loss of microtubule spindles and metaphase plate formation and causes mitotic arrest. CopN is a multidomain protein with similarity to type three secretion system "plug" proteins from other organisms but has functionally diverged such that it also functions as an effector protein. We show that CopN binds directly to αβ-tubulin but not to microtubules (MTs). Furthermore, CopN inhibits tubulin polymerization by sequestering free αβ-tubulin, similar to one of the mechanisms utilized by stathmin. Although CopN and stathmin share no detectable sequence identity, both influence MT formation by sequestration of αβ-tubulin. CopN displaces stathmin from preformed stathmin-tubulin complexes, indicating that the proteins bind overlapping sites on tubulin. CopN is the first bacterial effector shown to disrupt MT formation directly. This recognition affords a mechanistic understanding of a strategy Chlamydia species use to manipulate the host cell cycle.

Modulating microtubule stability enhances the cytotoxic response of cancer cells to Paclitaxel

The extracellular matrix protein TGFBI enhances the cytotoxic response of cancer cells to paclitaxel by affecting integrin signals that stabilize microtubules. Extending the implications of this knowledge, we tested the more general hypothesis that cancer cell signals which increase microtubule stability before exposure to paclitaxel may increase its ability to stabilize microtubules and thereby enhance its cytotoxicity. Toward this end, we carried out an siRNA screen to evaluate how genetic depletion affected microtubule stabilization, cell viability, and apoptosis. High content microscopic analysis was carried out in the absence or presence of paclitaxel. Kinase knockdowns that stabilized microtubules strongly enhanced the effects of paclitaxel treatment. Conversely, kinase knockdowns that enhanced paclitaxel-mediated cytotoxicity sensitized cells to microtubule stabilization by paclitaxel. The siRNA screen identified several genes that have not been linked previously to microtubule regulation or paclitaxel response. Gene shaving and Bayesian resampling used to classify these genes suggested three pathways of paclitaxel-induced cell death related to apoptosis and microtubule stability, apoptosis alone, or neither process. Our results offer a functional classification of the genetic basis for paclitaxel sensitivity and they support the hypothesis that stabilizing microtubules prior to therapy could enhance antitumor responses to paclitaxel treatment.

Protein pattern of Xenopus laevis embryos grown in simulated microgravity

Numerous studies indicate that microgravity affects cell growth and differentiation in many living organisms, and various processes are modified when cells are placed under conditions of weightlessness. However, until now, there is no coherent explanation for these observations, and little information is available concerning the biomolecules involved. Our aim has been to investigate the protein pattern of Xenopus laevis embryos exposed to simulated microgravity during the first 6 days of development. A proteomic approach was applied to compare the protein profiles of Xenopus embryos developed in simulated microgravity and in normal conditions. Attention was focused on embryos that do not present visible malformations in order to investigate if weightlessness has effects at protein level in the absence of macroscopic alterations. The data presented strongly suggest that some of the major components of the cytoskeleton vary in such conditions. Three major findings are described for the first time: (i) the expression of important factors involved in the organization and stabilization of the cytoskeleton, such as Arp (actin-related protein) 3 and stathmin, is heavily affected by microgravity; (ii) the amount of the two major cytoskeletal proteins, actin and tubulin, do not change in such conditions; however, (iii) an increase in the tyrosine nitration of these two proteins can be detected. The data suggest that, in the absence of morphological alterations, simulated microgravity affects the intracellular movement system of cells by altering cytoskeletal proteins heavily involved in the regulation of cytoskeleton remodelling.

Cytotoxic effects of bilberry extract on MCF7-GFP-tubulin breast cancer cells

Bilberry (European blueberry) has been reported to have many biological effects, including anticancer activity. In this study, we investigated the antiproliferative effects of bilberry extract in relation to its ability to induce apoptosis and affect microtubule assembly and organization in MCF7 human breast cancer cells. We observed that bilberry extract inhibited cell proliferation in a concentration-dependent fashion with a 50% inhibitory concentration of 0.3-0.4 mg/mL, in concert with induction of apoptotic cell death. At these concentrations there was no selective inhibition of mitosis or any other cell cycle stage, nor was there any apparent effect on the microtubule or actin cytoskeletons. However, somewhat higher extract concentrations (0.5-0.9 mg/mL) did cause an increase in the fraction of cells at the G(2)/M phase of the cell cycle, together with destruction of microtubules and formation of punctate tubulin aggregates in the cells. Bilberry extract at 0.3-0.4 mg/mL did not appreciably inhibit microtubule polymerization in vitro, but significant inhibition of polymerization (approximately 30%) did occur at higher extract concentrations (0.5-1 mg/mL). We conclude that bilberry extract as ingested by humans, not just the purified anthocyanins it contains, inhibits proliferation of and induces apoptosis in breast cancer cells at its lowest effective concentrations via a mechanism that does not involve action on microtubules or on mitosis. We further conclude that at somewhat higher concentrations the extract modifies microtubule organization in cells and causes accumulation of cells at mitosis by a direct action on microtubules.

c-Jun N-terminal kinase phosphorylation of stathmin confers protection against cellular stress

The cell stress response encompasses the range of intracellular events required for adaptation to stimuli detrimental to cell survival. Although the c-Jun N-terminal kinase (JNK) is a stress-activated kinase that can promote either cell survival or death in response to detrimental stimuli, the JNK-regulated mechanisms involved in survival are not fully characterized. Here we show that in response to hyperosmotic stress, JNK phosphorylates a key cytoplasmic microtubule regulatory protein, stathmin (STMN), on conserved Ser-25 and Ser-38 residues. In in vitro biochemical studies, we identified STMN Ser-38 as the critical residue required for efficient phosphorylation by JNK and identified a novel kinase interaction domain in STMN required for recognition by JNK. We revealed that JNK was required for microtubule stabilization in response to hyperosmotic stress. Importantly, we also demonstrated a novel cytoprotective function for STMN, as the knockdown of STMN levels by siRNA was sufficient to augment viability in response to hyperosmotic stress. Our findings show that JNK targeting of STMN represents a novel stress-activated cytoprotective mechanism involving microtubule network changes.

Significance of STMN1 expression in esophageal squamous cell carcinoma

AIM: To investigate the expression of Stathmin 1 (STMN1) protein in esophageal squamous cell carcinoma (ESCC) tissue and cell lines and to evaluate its correlation with the clinicopathologic parameters of ESCC.

METHODS: One-dimensional (1-D) Western blot was performed to determine the expression of STMN1 in 8 ESCC cell lines. Two-dimensional (2-D) Western blot was used to determine modified STMN1 in KYSE180 cells. Western blot and immunohistochemistry (IHC) were employed to determine the expression of STMN1 in ESCC specimens. The chi-square test was used to analyze IHC results.

RESULTS: STMN1 was widely expressed in ESCC cells, including WHCO1, EC0156, KYSE510, KYSE180, KYSE170, KYSE150, KYSE140 and KYSE30 cell lines. Two STMN1 protein spots were detected in KYSE180 cells on 2-D Western blot: one stronger signal and one weaker signal located in more basic area, which suggests that STMN1 protein may be modified in KYSE180 cells. Western blot analysis showed that STMN1 was overexpressed in 69.2% (9/13) of ESCC specimens compared with their normal epithelial counterparts. IHC assay also demonstrated that the positive rate of STMN1 expression was significantly higher in ESCC tissue than in matched adjacent normal tissue (P < 0.05). STMN1 expression is not correlated with age, gender, differentiation, tumor grade and lymph node metastasis.

CONCLUSION: The expression of STMN1 protein is up-regulated in both ESCC tissue and cell lines and may be modified in some ESCC cell lines. STMN1 might exert an oncogenic function in ESCC. Dynamic measurement of STMN1 expression level might aid to evaluate the progression of ESCC.

The 90-kDa heat shock protein Hsp90 protects tubulin against thermal denaturation

Hsp90 and tubulin are among the most abundant proteins in the cytosol of eukaryotic cells. Although Hsp90 plays key roles in maintaining its client proteins in their active state, tubulin is essential for fundamental processes such as cell morphogenesis and division. Several studies have suggested a possible connection between Hsp90 and the microtubule cytoskeleton. Because tubulin is a labile protein in its soluble form, we investigated whether Hsp90 protects it against thermal denaturation. Both proteins were purified from porcine brain, and their interaction was characterized in vitro by using spectrophotometry, sedimentation assays, video-enhanced differential interference contrast light microscopy, and native polyacrylamide gel electrophoresis. Our results show that Hsp90 protects tubulin against thermal denaturation and keeps it in a state compatible with microtubule polymerization. We demonstrate that Hsp90 cannot resolve tubulin aggregates but that it likely binds early unfolding intermediates, preventing their aggregation. Protection was maximal at a stoichiometry of two molecules of Hsp90 for one of tubulin. This protection does not require ATP binding and hydrolysis by Hsp90, but it is counteracted by geldanamycin, a specific inhibitor of Hsp90.

Regulation of microtubule dynamics through phosphorylation on stathmin by Epstein-Barr virus kinase BGLF4

Stathmin is an important microtubule (MT)-destabilizing protein, and its activity is differently attenuated by phosphorylation at one or more of its four phosphorylatable serine residues (Ser-16, Ser-25, Ser-38, and Ser-63). This phosphorylation of stathmin plays important roles in mitotic spindle formation. We observed increasing levels of phosphorylated stathmin in Epstein-Barr virus (EBV)-harboring lymphoblastoid cell lines (LCLs) and nasopharyngeal carcinoma (NPC) cell lines during the EBV lytic cycle. These suggest that EBV lytic products may be involved in the regulation of stathmin phosphorylation. BGLF4 is an EBV-encoded kinase and has similar kinase activity to cdc2, an important kinase that phosphorylates serine residues 25 and 38 of stathmin during mitosis. Using an siRNA approach, we demonstrated that BGLF4 contributes to the phosphorylation of stathmin in EBV-harboring NPC. Moreover, we confirmed that BGLF4 interacts with and phosphorylates stathmin using an in vitro kinase assay and an in vivo two-dimensional electrophoresis assay. Interestingly, unlike cdc2, BGLF4 was shown to phosphorylate non-proline directed serine residues of stathmin (Ser-16) and it mediated phosphorylation of stathmin predominantly at serines 16, 25, and 38, indicating that BGLF4 can down-regulate the activity of stathmin. Finally, we demonstrated that the pattern of MT organization was changed in BGLF4-expressing cells, possibly through phosphorylation of stathmin. In conclusion, we have shown that a viral Ser/Thr kinase can directly modulate the activity of stathmin and this contributes to alteration of cellular MT dynamics and then may modulate the associated cellular processes.

From signaling pathways to microtubule dynamics: the key players

Microtubules are highly dynamic structures whose regulation is crucial for cell division, cell polarity, cell migration, or neuronal differentiation. Because they contribute to most cellular functions, they must be regulated in response to extracellular and intracellular signals. The parameters of microtubule dynamics are numerous and complex and the connection between signaling pathways and regulation of microtubule dynamics remain obscure. Recent observations reveal key players that can both integrate the diversity of signaling cascades and directly influence microtubule dynamics. I review here how modifications of the tubulin dimer, tubulin modifying enzymes, and microtubule-associated proteins are directly involved in the regulation of microtubule behavior and functions.