Microtubule Post-translational Modifications Research Articles

Effects of P301L-TAU on post-translational modifications of microtubules in human iPSC-derived cortical neurons and TAU transgenic mice.

JOURNAL/nrgr/04.03/01300535-202508000-00025/figure1/v/2024-09-30T120553Z/r/image-tiff TAU is a microtubule-associated protein that promotes microtubule assembly and stability in the axon. TAU is missorted and aggregated in an array of diseases known as tauopathies. Microtubules are essential for neuronal function and regulated via a complex set of post-translational modifications, changes of which affect microtubule stability and dynamics, microtubule interaction with other proteins and cellular structures, and mediate recruitment of microtubule-severing enzymes. As impairment of microtubule dynamics causes neuronal dysfunction, we hypothesize cognitive impairment in human disease to be impacted by impairment of microtubule dynamics. We therefore aimed to study the effects of a disease-causing mutation of TAU (P301L) on the levels and localization of microtubule post-translational modifications indicative of microtubule stability and dynamics, to assess whether P301L-TAU causes stability-changing modifications to microtubules. To investigate TAU localization, phosphorylation, and effects on tubulin post-translational modifications, we expressed wild-type or P301L-TAU in human MAPT -KO induced pluripotent stem cell-derived neurons (iNeurons) and studied TAU in neurons in the hippocampus of mice transgenic for human P301L-TAU (pR5 mice). Human neurons expressing the longest TAU isoform (2N4R) with the P301L mutation showed increased TAU phosphorylation at the AT8, but not the p-Ser-262 epitope, and increased polyglutamylation and acetylation of microtubules compared with endogenous TAU-expressing neurons. P301L-TAU showed pronounced somatodendritic presence, but also successful axonal enrichment and a similar axodendritic distribution comparable to exogenously expressed 2N4R-wildtype-TAU. P301L-TAU-expressing hippocampal neurons in transgenic mice showed prominent missorting and tauopathy-typical AT8-phosphorylation of TAU and increased polyglutamylation, but reduced acetylation, of microtubules compared with non-transgenic littermates. In sum, P301L-TAU results in changes in microtubule PTMs, suggestive of impairment of microtubule stability. This is accompanied by missorting and aggregation of TAU in mice but not in iNeurons. Microtubule PTMs/impairment may be of key importance in tauopathies.

Efficient axonal transport of endolysosomes relies on the balanced ratio of microtubule tyrosination and detyrosination.

In neurons, the microtubule (MT) cytoskeleton forms the basis for long-distance protein transport from the cell body into and out of dendrites and axons. To maintain neuronal polarity, the axon initial segment (AIS) serves as a physical barrier, separating the axon from the somatodendritic compartment and acting as a filter for axonal cargo. Selective trafficking is further instructed by axonal enrichment of MT post-translational modifications, which affect MT dynamics and the activity of motor proteins. Here, we compared two knockout mouse lines lacking the respective enzymes for MT tyrosination and detyrosination, and found that both knockouts led to a shortening of the AIS. Neurons from both lines also showed an increased immobile fraction of endolysosomes present in the axon, whereas mobile organelles displayed shortened run distances in the retrograde direction. Overall, our results highlight the importance of maintaining the balance of tyrosinated and detyrosinated MTs for proper AIS length and axonal transport processes.

Role of Tubulin Detyrosination in Platelet Biogenesis

Introduction. Microtubules are hollow cylindrical polymers that are made of α/β-tubulin heterodimers. They are involved in a broad range of essential functions such as cell division, intracellular trafficking or cell motility. Their functional diversity is thought to be regulated through the expression of distinct α- and β-tubulin isotypes together with several post-translational modifications (PTMs); a concept known as tubulin code. In the megakaryocytic lineage, while tubulin isotypes are well-known regulators of platelet biogenesis (TUBB1, TUBA4A, TUBA8) 1, the temporal regulation and biological significance of tubulin PTMs remain mostly unknown. Aims. This project aims to characterize the kinetics and to evaluate the functional importance of tubulin detyrosination, one of the main α-tubulin PTM, in platelet biogenesis. Methods. Analyzes were performed in megakaryocytes and platelets obtained from cultured human CD34 + hematopoietic stem and progenitor cells. To characterize the kinetics of tubulin detyrosination, the PTM and its modifying enzymes were monitored at the proteomic (Western Blot) and transcriptional (qRT-PCR) levels, at several defined stages of megakaryocyte differentiation. To evaluate the function of tubulin detyrosination, differentiation of CD34 + hematopoietic stem and progenitor cells was performed in the presence of the SVBP/VASH-detyrosinase inhibitor EpoY 2 or following CRISPR-mediated inactivation of the VASH detyrosinase co-factor SVBP. Results. Tubulin detyrosination levels progressively increased as megakaryocytes matured. This was accompanied by a gradual increase in the transcript levels of the detyrosinase VASH1, while those of its cofactor SVBP remained stable. Transcripts of the newly identified detyrosinase MATCAP 3 mirrored those of VASH1. Together, these results suggest that tubulin detyrosination occurring during platelet biogenesis could be mediated by both the SVBP-VASH1 complex and/or MATCAP, and prompt the question of their functional importance in the process. To evaluate this, we first focused on the SVBP-VASH1 complex with the inhibitor EpoY. Interestingly, while this compound had no impact on early megakaryocyte differentiation, the final stage of platelet biogenesis, proplatelet formation, was perturbed. In particular, proplatelets obtained in the presence of EpoY showed morphological alterations with thinner unbranched shafts, suggesting potential repercussions on platelet production. Preliminary data obtained with SVBP-inactivated megakaryocytes confirmed these observations. Follow-up work will aim to evaluate the downstream consequences on platelet production as well as the relative contribution of MATCAP. Conclusion. These results suggest that tubulin detyrosination could act as a potential regulator of terminal megakaryocyte maturation, and further highlight the importance of the microtubule cytoskeleton and the tubulin code in platelet biogenesis. References. 1. Kimmerlin, Q., Strassel, C., Eckly, A., and Lanza, F. (2023). The tubulin code in platelet biogenesis. Semin Cell Dev Biol 137, 63-73. 10.1016/j.semcdb.2022.01.010. 2. Hotta, T., Haynes, S.E., Blasius, T.L., Gebbie, M., Eberhardt, E.L., Sept, D., Cianfrocco, M., Verhey, K.J., Nesvizhskii, A.I., and Ohi, R. (2021). Parthenolide Destabilizes Microtubules by Covalently Modifying Tubulin. Curr Biol 31, 900-907 e906. 10.1016/j.cub.2020.11.055. 3. Landskron, L., Bak, J., Adamopoulos, A., Kaplani, K., Moraiti, M., van den Hengel, L.G., Song, J.Y., Bleijerveld, O.B., Nieuwenhuis, J., Heidebrecht, T., et al. (2022). Posttranslational modification of microtubules by the MATCAP detyrosinase. Science 376, eabn6020. 10.1126/science.abn6020.

Preprint Highlight: Detyrosination enrichment on microtubule subsets is established by the interplay between a stochastically acting enzyme and microtubule stability.

Microtubule detyrosination, the post-translational removal of a tyrosine residue on α-tubulin, marks a stable and rare subpopulation of microtubules. Vasohibin (VASH) is the main enzyme responsible for α-tubulin detyrosination and it binds to α-tubulin on polymerized microtubules. However, the dynamics underlying detyrosination remain unknown. The authors use quantitative super-resolution microscopy, single molecule tracking, and computational modeling to explore microtubule detyrosination. VASH engages with microtubules in a stochastic fashion and detyrosination depends on VASH concentration on single microtubules. As VASH accumulation requires microtubule stability, detyrosination occurs via a stabilization-detyrosination feedback mechanism. This work provides important and novel mechanistic insight into microtubule detyrosination and serves as an example for studying other microtubule post-translational modifications essential for cellular homeostasis.

Posttranslational modification of microtubules by the MATCAP detyrosinase.

The detyrosination-tyrosination cycle involves the removal and religation of the C-terminal tyrosine of α-tubulin and is implicated in cognitive, cardiac, and mitotic defects. The vasohibin-small vasohibin-binding protein (SVBP) complex underlies much, but not all, detyrosination. We used haploid genetic screens to identify an unannotated protein, microtubule associated tyrosine carboxypeptidase (MATCAP), as a remaining detyrosinating enzyme. X-ray crystallography and cryo-electron microscopy structures established MATCAP's cleaving mechanism, substrate specificity, and microtubule recognition. Paradoxically, whereas abrogation of tyrosine religation is lethal in mice, codeletion of MATCAP and SVBP is not. Although viable, defective detyrosination caused microcephaly, associated with proliferative defects during neurogenesis, and abnormal behavior. Thus, MATCAP is a missing component of the detyrosination-tyrosination cycle, revealing the importance of this modification in brain formation.

Ricolinostat induces microtubule acetylation and neurite regeneration in cellular models of diabetic and chemotheraphy-induced neuropathy

Peripheral nerves have unique regenerative capability, but two questions are still unanswered: what are the underlying mechanisms and why do some patients show higher spontaneous nerve fibers regeneration than others. Here we investigated if microtubule posttranslational modifications (PTMs) impact on neuronal regeneration in in vitro models of small fiber neuropathy (SFN) and predict intra-epidermal nerve fibers regeneration density (IENFD) in patients.

Interleukin-6 promotes microtubule stability in axons via Stat3 protein–protein interactions

SummaryThe interleukin-6 (IL-6) family of cytokines and its downstream effector, STAT3, are important mediators of neuronal health, repair, and disease throughout the CNS, including the visual system. Here, we elucidate a transcription-independent mechanism for the neuropoietic activities of IL-6 related to axon development, regeneration, and repair. We examined the outcome of IL-6 deficiency on structure and function of retinal ganglion cell (RGC) axons, which form the optic projection. We found that IL-6 deficiency substantially delays anterograde axon transport in vivo. The reduced rate of axon transport is accompanied by changes in morphology, structure, and post-translational modification of microtubules. In vivo and in vitro studies in mice and swine revealed that IL-6-dependent microtubule phenotypes arise from protein-protein interactions between STAT3 and stathmin. As in tumor cells and T cells, this STAT3-stathmin interaction stabilizes microtubules in RGCs. Thus, this IL-6-STAT3-dependent mechanism for axon architecture is likely a fundamental mechanism for microtubule stability systemically.

Loss of Deacetylation Enzymes Hdac6 and Sirt2 Promotes Acetylation of Cytoplasmic Tubulin, but Suppresses Axonemal Acetylation in Zebrafish Cilia.

Cilia are evolutionarily highly conserved organelles with important functions in many organs. The extracellular component of the cilium protruding from the plasma membrane comprises an axoneme composed of microtubule doublets, arranged in a 9 + 0 conformation in primary cilia or 9 + 2 in motile cilia. These microtubules facilitate transport of intraflagellar cargoes along the axoneme. They also provide structural stability to the cilium, which may play an important role in sensory cilia, where signals are received from the movement of extracellular fluid. Post-translational modification of microtubules in cilia is a well-studied phenomenon, and acetylation on lysine 40 (K40) of alpha tubulin is prominent in cilia. It is believed that this modification contributes to the stabilization of cilia. Two classes of enzymes, histone acetyltransferases and histone deacetylases, mediate regulation of tubulin acetylation. Here we use a genetic approach, immunocytochemistry and behavioral tests to investigate the function of tubulin deacetylases in cilia in a zebrafish model. By mutating three histone deacetylase genes (Sirt2, Hdac6, and Hdac10), we identify an unforeseen role for Hdac6 and Sirt2 in cilia. As expected, mutation of these genes leads to increased acetylation of cytoplasmic tubulin, however, surprisingly it caused decreased tubulin acetylation in cilia in the developing eye, ear, brain and kidney. Cilia in the ear and eye showed elevated levels of mono-glycylated tubulin suggesting a compensatory mechanism. These changes did not affect the length or morphology of cilia, however, functional defects in balance was observed, suggesting that the level of tubulin acetylation may affect function of the cilium.

Tubulin acetylation enhances lung cancer resistance to paclitaxel-induced cell death through Mcl-1 stabilization

The posttranslational modifications (PTMs) of microtubules have been reported to play an important role in cancer aggressiveness, including apoptosis resistance. In this study, we aimed to investigate the biological role of microtubule PTMs in the regulation of paclitaxel responsiveness. The acetylated tubulin (Ace-tub) level was strongly associated with paclitaxel sensitivity, as observed in patient-derived primary lung cancer cells and xenografted immunodeficient mice. We showed that paclitaxel-resistant H460 lung cancer cells, generated by a stepwise increase in paclitaxel, exhibited markedly increased tubulin acetylation and consequently acquired paclitaxel resistance. Upregulation of tubulin acetylation by overexpression of α-tubulin acetyltransferase 1 wild-type (αTAT1wt), an enzyme required for acetylation, or by treatment with trichostatin A (TSA), a histone deacetylase 6 (HDAC6) inhibitor, significantly attenuated paclitaxel-induced apoptosis. Investigation of the underlying mechanism revealed that the levels of antiapoptotic Mcl-1 appeared to increase in αTAT1wt-overexpressing and TSA-treated cells compared to control cells, whereas the levels of other antiapoptotic regulatory proteins were unchanged. On the other hand, decreased tubulin acetylation by αTAT1 RNA interference downregulated Mcl-1 expression in patient-derived primary lung cancer and paclitaxel-resistant lung cancer cells. A microtubule sedimentation assay demonstrated that Mcl-1 binds to microtubules preferentially at Ace-type, which prolongs the Mcl-1 half-life (T1/2). Furthermore, immunoprecipitation analysis revealed that polyubiquitination of Mcl-1 was extensively decreased in response to TSA treatment. These data indicate that tubulin acetylation enhances the resistance to paclitaxel-induced cell death by stabilizing Mcl-1 and protecting it from ubiquitin–proteasome-mediated degradation.

Microtubule polyglutamylation is important for regulating cytoskeletal architecture and motility in Trypanosoma brucei.

The shape of kinetoplastids, such as Trypanosoma brucei, is precisely defined during the stages of the life cycle and governed by a stable subpellicular microtubule cytoskeleton. During the cell cycle and transitions between life cycle stages, this stability has to transiently give way to a dynamic behaviour to enable cell division and morphological rearrangements. How these opposing requirements of the cytoskeleton are regulated is poorly understood. Two possible levels of regulation are activities of cytoskeleton-associated proteins and microtubule post-translational modifications (PTMs). Here, we investigate the functions of two putative tubulin polyglutamylases in T. brucei, TTLL6A and TTLL12B. Depletion of both proteins leads to a reduction in tubulin polyglutamylation in situ and is associated with disintegration of the posterior cell pole, loss of the microtubule plus-end-binding protein EB1 and alterations of microtubule dynamics. We also observe a reduced polyglutamylation of the flagellar axoneme. Quantitative motility analysis reveals that the PTM imbalance correlates with a transition from directional to diffusive cell movement. These data show that microtubule polyglutamylation has an important role in regulating cytoskeletal architecture and motility in the parasite T. bruceiThis article has an associated First Person interview with the first author of the paper.

Microtubules regulate cardiomyocyte transversal Young's modulus.

The field of cardiomyocyte mechanobiology is gaining significant attention, due to accumulating evidence concerning the significant role of cellular mechanical effects on the integrated function of the heart. To date, the protein titin has been demonstrated as a major contributor to the cardiomyocytes Young’s modulus (YM). The microtubular network represents another potential regulator of cardiac mechanics. However, the contribution of microtubules (MTs) to the membrane YM is still understudied and has not been interrogated in the context of myocardial infarction (MI) or mechanical loading and unloading. Using nanoscale mechanoscanning ion conductance microscopy, we demonstrate that MTs contribute to cardiomyocyte transverse YM in healthy and pathological states with different mechanical loading. Specifically, we show that posttranslational modifications of MTs have differing effects on cardiomyocyte YM: Acetylation provides flexibility, whereas detyrosination imparts rigidity. Further studies demonstrate that there is no correlation between the total protein amount of acetylated and detyrosinated MT. Yet, in the polymerized-only populations, an increased level of acetylation results in a decline of detyrosinated MTs in an MI model.

Microtubule-dependent processes precede pathological calcium influx in excitotoxin-induced axon degeneration.

Axon degeneration and axonal loss is a feature of neurodegenerative disease and injury and occurs via programmed pathways that are distinct from cell death pathways. While the pathways of axonal loss following axon severing are well described, less is known about axonal loss following other neurodegenerative insults. Here we use primary mouse cortical neuron cultures grown in compartmentalized chambers to investigate the role of calcium in the degeneration of axons that occurs following a somal insult by the excitotoxin kainic acid. Calcium influx has been implicated in both excitotoxicity and axon degeneration mechanisms, however the link between a somal insult and axonal calcium increase is unclear. Live imaging of axons demonstrated that pharmacologically preventing intracellular calcium increases through the endoplasmic reticulum or mitochondria significantly (p<0.05) reduced axon degeneration. Live calcium-imaging with the Ca2+ indicator Fluo-4 demonstrated that kainic acid exposure to the soma resulted in a rapid, and transient, increase in calcium in the axon, which occured even at low kainic acid concentrations that do not cause axon degeneration within 24h. However, this calcium transient was followed by a gradual increase in axonal calcium, which was associated with axonal loss. Furthermore, treatment with a range of doses of the microtubule stabilizing drug taxol, which protects against axon fragmentation in this model, prevented this gradual calcium increase, suggesting that the intra-axonal calcium changes are downstream of microtubule associated events. Biochemical analysis of taxol treated neurons demonstrated a shift in microtubule post-translational modifications, with a significant (p<0.05) increase in acetylated tubulin and a significant (p<0.05) decrease in tyrosinated tubulin, suggestive of a more stable microtubule pool. Together our results suggest that axonal degeneration following excitotoxicity is dependent on an increase in axonal calcium, which is downstream of a microtubule-dependent event.

The focal adhesion scaffold protein Hic-5 regulates vimentin organization in fibroblasts.

Focal adhesion (FA)-stimulated reorganization of the F-actin cytoskeleton regulates cellular size, shape, and mechanical properties. However, FA cross-talk with the intermediate filament cytoskeleton is poorly understood. Genetic ablation of the FA-associated scaffold protein Hic-5 in mouse cancer-associated fibroblasts (CAFs) promoted a dramatic collapse of the vimentin network, which was rescued following EGFP-Hic-5 expression. Vimentin collapse correlated with a loss of detergent-soluble vimentin filament precursors and decreased vimentin S72/S82 phosphorylation. Additionally, fluorescence recovery after photobleaching analysis indicated impaired vimentin dynamics. Microtubule (MT)-associated EB1 tracking and Western blotting of MT posttranslational modifications indicated no change in MT dynamics that could explain the vimentin collapse. However, pharmacological inhibition of the RhoGTPase Cdc42 in Hic-5 knockout CAFs rescued the vimentin collapse, while pan-formin inhibition with SMIFH2 promoted vimentin collapse in Hic-5 heterozygous CAFs. Our results reveal novel regulation of vimentin organization/dynamics by the FA scaffold protein Hic-5 via modulation of RhoGTPases and downstream formin activity.

Microtubules: Evolving roles and critical cellular interactions.

Microtubules are cytoskeletal elements known as drivers of directed cell migration, vesicle and organelle trafficking, and mitosis. In this review, we discuss new research in the lens that has shed light into further roles for stable microtubules in the process of development and morphogenesis. In the lens, as well as other systems, distinct roles for characteristically dynamic microtubules and stabilized populations are coming to light. Understanding the mechanisms of microtubule stabilization and the associated microtubule post-translational modifications is an evolving field of study. Appropriate cellular homeostasis relies on not only one cytoskeletal element, but also rather an interaction between cytoskeletal proteins as well as other cellular regulators. Microtubules are key integrators with actin and intermediate filaments, as well as cell–cell junctional proteins and other cellular regulators including myosin and RhoGTPases to maintain this balance.Impact statementThe role of microtubules in cellular functioning is constantly expanding. In this review, we examine new and exciting fields of discovery for microtubule’s involvement in morphogenesis, highlight our evolving understanding of differential roles for stabilized versus dynamic subpopulations, and further understanding of microtubules as a cellular integrator.

Microtubule acetylation but not detyrosination promotes focal adhesion dynamics and astrocyte migration.

Microtubules play a crucial role in mesenchymal migration by controlling cell polarity and the turnover of cell adhesive structures on the extracellular matrix. The polarized functions of microtubules imply that microtubules are locally regulated. Here, we investigated the regulation and role of two major tubulin post-translational modifications, acetylation and detyrosination, which have been associated with stable microtubules. Using primary astrocytes in a wound healing assay, we show that these tubulin modifications are independently regulated during cell polarization and differently affect cell migration. In contrast to microtubule detyrosination, αTAT1 (ATAT1)-mediated microtubule acetylation increases in the vicinity of focal adhesions and promotes cell migration. We further demonstrate that αTAT1 increases focal adhesion turnover by promoting Rab6-positive vesicle fusion at focal adhesions. Our results highlight the specificity of microtubule post-translational modifications and bring new insight into the regulatory functions of tubulin acetylation.This article has an associated First Person interview with the first author of the paper.

Resistance to anti-tubulin agents: From vinca alkaloids to epothilones.

This review describes the mechanism of action - inhibition of microtubules - and the most important mechanisms of resistance for vinca alkaloids, taxanes and epothilones. Resistance is a major problem in vinca and taxane chemotherapy and arises in most cases from overexpression of efflux pumps that transport the drugs out of the cancer cells and from modifications of the target, the microtubules, by overexpression of tubulin isotypes or by attachment of proteins to the ends of the microtubules so that the target is no longer recognized by the drugs. In some cases, however, this process can have the opposite effect, leading to sensitization, e.g., for vinca alkaloids in cases where taxanes are not or no longer effective. The link between resistance due to efflux pumps and the pharmacokinetics and metabolism of the drugs is also covered. Other types of resistance that are addressed include detoxification of drugs within the cancer cell and blockade of apoptosis, post-translational modifications of microtubules and other protein pathways, micro-RNAs, induction of oncogenes, and cancer stem cells, which, taken together, offer particularly multifold possibilities for preventing drug activity. The use of biomarkers for the prediction of clinical outcome and for the direction of future therapy is also addressed.

Detyrosinated microtubules spatially constrain lysosomes facilitating lysosome-autophagosome fusion.

Microtubule post-translational modifications impart functional diversity to microtubules by affecting their dynamics, organization, and interaction with proteins. Using super-resolution microscopy, we show that only a small subpopulation of microtubules are detyrosinated in epithelial cells, while acetylated and tyrosinated microtubules comprise the majority of all microtubules. Surprisingly, lysosomes are enriched by approximately threefold on detyrosinated microtubules. Further, their motility on detyrosinated microtubules is impaired, showing shorter runs and more frequent and longer pauses. Lysosome enrichment is mediated through a kinesin-1-dependent mechanism, since knocking down this motor abolishes enrichment. Finally, correlative live-cell and super-resolution microscopy showed that lysosomes interact with autophagosomes on detyrosinated microtubules. Removal of detyrosinated microtubules or knockdown of kinesin-1 leads to a decrease in the percentage of autolysosomes, a fusion intermediate of autophagosomes and lysosomes. Taken together, our data reveal a new role of detyrosinated microtubules as hubs that spatially concentrate lysosomes on a small subset of microtubules and facilitate their interaction and fusion with autophagosomes to initiate autophagy.

Microtubule polyglutamylation and acetylation drive microtubule dynamics critical for platelet formation

BackgroundUpon maturation in the bone marrow, polyploid megakaryocytes elongate very long and thin cytoplasmic branches called proplatelets. Proplatelets enter the sinusoids blood vessels in which platelets are ultimately released. Microtubule dynamics, bundling, sliding, and coiling, drive these dramatic morphological changes whose regulation remains poorly understood. Microtubule properties are defined by tubulin isotype composition and post-translational modification patterns. It remains unknown whether microtubule post-translational modifications occur in proplatelets and if so, whether they contribute to platelet formation.ResultsHere, we show that in proplatelets from mouse megakaryocytes, microtubules are both acetylated and polyglutamylated. To bypass the difficulties of working with differentiating megakaryocytes, we used a cell model that allowed us to test the functions of these modifications. First, we show that α2bβ3integrin signaling in D723H cells is sufficient to induce β1tubulin expression and recapitulate the specific microtubule behaviors observed during proplatelet elongation and platelet release. Using this model, we found that microtubule acetylation and polyglutamylation occur with different spatio-temporal patterns. We demonstrate that microtubule acetylation, polyglutamylation, and β1tubulin expression are mandatory for proplatelet-like elongation, swelling formation, and cytoplast severing. We discuss the functional importance of polyglutamylation of β1tubulin-containing microtubules for their efficient bundling and coiling during platelet formation.ConclusionsWe characterized and validated a powerful cell model to address microtubule behavior in mature megakaryocytes, which allowed us to demonstrate the functional importance of microtubule acetylation and polyglutamylation for platelet release. Furthermore, we bring evidence of a link between the expression of a specific tubulin isotype, the occurrence of microtubule post-translational modifications, and the acquisition of specific microtubule behaviors. Thus, our findings could widen the current view of the regulation of microtubule behavior in cells such as osteoclasts, spermatozoa, and neurons, which express distinct tubulin isotypes and display specific microtubule activities during differentiation.

Modyfikacje potranslacyjne tubuliny

Zarówno wolna tubulina, jak i tubulina wbudowana w mikrotubule może być modyfikowana potranslacyjnie poprzez przyłączenie różnorodnych grup funkcyjnych. Wśród kilkunastu zidentyfikowanych modyfikacji α- i β-tubuliny, przynajmniej niektóre zmiany potranslacyjne, jak acetylacja, detyrozynacja czy glutamylacja są zachowane w toku ewolucji od pierwotniaków do człowieka. Modyfikacje potranslacyjne tworzą specyficzny wzór na powierzchni mikrotubul, nazwany kodem tubulinowym, który jest rozpoznawany i „interpretowany” przez białka oddziałujące z mikrotubulami. W efekcie modyfikacje potranslacyjne tubuliny wpływają zarówno bezpośrednio na właściwości mikrotubul, jak i pośrednio, przez białka towarzyszące mikrotubulom. Poziom modyfikacji potranslacyjnych tubuliny na poszczególnych mikrotubulach jest zróżnicowany i zależy od rodzaju tworzonych struktur mikrotubularnych oraz typu komórek. Dodatkowo, poziom modyfikacji potranslacyjnych tubuliny może zmieniać się zależnie od stadium cyklu komórkowego lub stopnia zróżnicowania komórki. Intensywne badania prowadzone w ciągu ostatnich lat zaowocowały odkryciem kluczowych enzymów modyfikujących α- i β-tubulinę oraz częściowo, mechanizmu ich działania. Nadal jednak jesteśmy dalecy od pełnego zrozumienia roli modyfikacji potranslacyjnych mikrotubul w regulacji procesów komórkowych.

α-Tubulin Acetylation Restricts Axon Overbranching by Dampening Microtubule Plus-End Dynamics in Neurons.

Axon growth is tightly controlled to establish functional neural circuits during brain development. Despite the belief that cytoskeletal dynamics is critical for cell morphology, how microtubule acetylation regulates axon development in the mammalian central nervous system remains unclear. Here, we report that loss of α-tubulin acetylation by ablation of MEC-17 in mice predisposes neurons to axon overbranching and overgrowth. Introduction of MEC-17F183A lacking α-tubulin acetyltransferase activity into MEC-17-deficient neurons failed to rescue axon defects. Moreover, loss of α-tubulin acetylation led to increases in microtubule debundling, microtubule invasion into filopodia and growth cones, and microtubule plus-end dynamics along the axon. Taxol application dampened microtubule hyperdynamics and suppressed axon overbranching and overgrowth in MEC-17-deficient neurons. Thus, our study reveals that α-tubulin acetylation acts as a brake for axon overbranching and overgrowth by dampening microtubule dynamics, providing insight into the role of microtubule post-translational modifications in regulating neural development.