PTRN-1/CAMSAP and NOCA-2/NINEIN are required for microtubule polarity in Caenorhabditis elegans dendrites

The neuronal microtubule cytoskeleton is key to establish axon-dendrite polarity. Dendrites are characterized by the presence of minus-end out microtubules, however the mechanisms that organize these microtubules minus-end out is still poorly understood. Here, we characterized the role of two microtubule minus-end related proteins in this process in Caenorhabditis elegans, the microtubule minus-end stabilizing protein CAMSAP (PTRN-1) and a NINEIN homologue (NOCA-2). We found that CAMSAP and NINEIN function in parallel to mediate microtubule organization in dendrites. During dendrite outgrowth, RAB-11 positive vesicles localized to the dendrite tip function as a microtubule organizing center (MTOC) to nucleate microtubules. In the absence of either CAMSAP or NINEIN, we observed a low penetrance MTOC vesicles mis-localization to the cell body, and a nearly fully penetrant phenotype in double mutant animals. This suggests that both proteins are important for localizing the MTOC vesicles to the growing dendrite tip to organize microtubules minus-end out. Whereas NINEIN localizes to the MTOC vesicles where it is important for the recruitment of the microtubule nucleator ?-tubulin, CAMSAP localizes around the MTOC vesicles and is co-translocated forward with the MTOC vesicles upon dendritic growth. Together, these results indicate that microtubule nucleation from the MTOC vesicles and microtubule stabilization are both important to localize the MTOC vesicles distally to organize dendritic microtubules minus-end out.

The Effects of Microtubule Stabilizing Drugs on Macrophage Immune-Mediated Endocytosis

<p>Microtubule stabilizing drugs (MSD) bind and stabilize microtubules, thus inhibiting their normal function. MSD exhibit anti-mitotic effects which makes them attractive as cancer chemotherapeutics and much of existing research has focused on these effects in proliferating cells. In contrast, we are interested in assessing the effects of microtubule stabilization on non-proliferating cells, such as macrophages, to determine potential mitosis-independent actions of MSD on microtubule function. Thus, we investigated the effects of MSD on macrophage receptor-mediated endocytosis of low density lipoproteins (LDL) and found no significant effect on the ability of paclitaxel-treated macrophages to endocytose LDL. Alterations to macrophage phagocytic and killing efficiency due to treatment with paclitaxel, peloruside or docetaxel, as well as the recently discovered compounds, ixabepilone, mycothiazole, and zampanolide were investigated. Treatment with paclitaxel, peloruside or docetaxel did not significantly inhibit phagocytosis or killing of bacteria. Results from confocal microscopy suggest that paclitaxel alters phagocytic kinetics in macrophages. Respectively, zampanolide and mycothiazole significantly inhibited macrophage bactericidal and killing ability, while Ixabepilone enhanced bacterial killing. MSD treatment also altered production of tumor necrosis factor alpha (TNF-a) and nitric oxide (NO) during bacterial killing. Optimal activation of macrophages with IFN-y did not alter the effects of MSD. Taken together, these results suggest that MSD have multiple immunomodulatory effects unrelated to their anti-mitotic effects. The data suggests that during MSD treatment, macrophage activity maybe altered or impaired, thus modifying the ability of patients to fight off bacterial infections.</p>

The Effects of Microtubule Stabilizing Drugs on Macrophage Immune-Mediated Endocytosis

<p>Microtubule stabilizing drugs (MSD) bind and stabilize microtubules, thus inhibiting their normal function. MSD exhibit anti-mitotic effects which makes them attractive as cancer chemotherapeutics and much of existing research has focused on these effects in proliferating cells. In contrast, we are interested in assessing the effects of microtubule stabilization on non-proliferating cells, such as macrophages, to determine potential mitosis-independent actions of MSD on microtubule function. Thus, we investigated the effects of MSD on macrophage receptor-mediated endocytosis of low density lipoproteins (LDL) and found no significant effect on the ability of paclitaxel-treated macrophages to endocytose LDL. Alterations to macrophage phagocytic and killing efficiency due to treatment with paclitaxel, peloruside or docetaxel, as well as the recently discovered compounds, ixabepilone, mycothiazole, and zampanolide were investigated. Treatment with paclitaxel, peloruside or docetaxel did not significantly inhibit phagocytosis or killing of bacteria. Results from confocal microscopy suggest that paclitaxel alters phagocytic kinetics in macrophages. Respectively, zampanolide and mycothiazole significantly inhibited macrophage bactericidal and killing ability, while Ixabepilone enhanced bacterial killing. MSD treatment also altered production of tumor necrosis factor alpha (TNF-a) and nitric oxide (NO) during bacterial killing. Optimal activation of macrophages with IFN-y did not alter the effects of MSD. Taken together, these results suggest that MSD have multiple immunomodulatory effects unrelated to their anti-mitotic effects. The data suggests that during MSD treatment, macrophage activity maybe altered or impaired, thus modifying the ability of patients to fight off bacterial infections.</p>

Pathomechanisms of Paclitaxel-Induced Peripheral Neuropathy

Peripheral neuropathy is one of the most common side effects of chemotherapy, affecting up to 60% of all cancer patients receiving chemotherapy. Moreover, paclitaxel induces neuropathy in up to 97% of all gynecological and urological cancer patients. In cancer cells, paclitaxel induces cell death via microtubule stabilization interrupting cell mitosis. However, paclitaxel also affects cells of the central and peripheral nervous system. The main symptoms are pain and numbness in hands and feet due to paclitaxel accumulation in the dorsal root ganglia. This review describes in detail the pathomechanisms of paclitaxel in the peripheral nervous system. Symptoms occur due to a length-dependent axonal sensory neuropathy, where axons are symmetrically damaged and die back. Due to microtubule stabilization, axonal transport is disrupted, leading to ATP undersupply and oxidative stress. Moreover, mitochondria morphology is altered during paclitaxel treatment. A key player in pain sensation and axonal damage is the paclitaxel-induced inflammation in the spinal cord as well as the dorsal root ganglia. An increased expression of chemokines and cytokines such as IL-1β, IL-8, and TNF-α, but also CXCR4, RAGE, CXCL1, CXCL12, CX3CL1, and C3 promote glial activation and accumulation, and pain sensation. These findings are further elucidated in this review.

MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane

The Golgi complex plays an active role in organizing asymmetric microtubule arrays essential for polarized vesicle transport. The coiled-coil protein MTCL1 stabilizes microtubules nucleated from the Golgi membrane. Here, we report an MTCL1 paralog, MTCL2, which preferentially acts on the perinuclear microtubules accumulated around the Golgi. MTCL2 associates with the Golgi membrane through the N-terminal coiled-coil region and directly binds microtubules through the conserved C-terminal domain without promoting microtubule stabilization. Knockdown of MTCL2 significantly impaired microtubule accumulation around the Golgi as well as the compactness of the Golgi ribbon assembly structure. Given that MTCL2 forms parallel oligomers through homo-interaction of the central coiled-coil motifs, our results indicate that MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane. Results of in vitro wound healing assays further suggest that this function of MTCL2 enables integration of the centrosomal and Golgi-associated microtubules on the Golgi membrane, supporting directional migration. Additionally, the results demonstrated the involvement of CLASPs and giantin in mediating the Golgi association of MTCL2.

MACF1 controls skeletal muscle function through the microtubule-dependent localization of extra-synaptic myonuclei and mitochondria biogenesis

Skeletal muscles are composed of hundreds of multinucleated muscle fibers (myofibers) whose myonuclei are regularly positioned all along the myofiber’s periphery except the few ones clustered underneath the neuromuscular junction (NMJ) at the synaptic zone. This precise myonuclei organization is altered in different types of muscle disease, including centronuclear myopathies (CNMs). However, the molecular machinery regulating myonuclei position and organization in mature myofibers remains largely unknown. Conversely, it is also unclear how peripheral myonuclei positioning is lost in the related muscle diseases. Here, we describe the microtubule-associated protein, MACF1, as an essential and evolutionary conserved regulator of myonuclei positioning and maintenance, in cultured mammalian myotubes, in Drosophila muscle, and in adult mammalian muscle using a conditional muscle-specific knockout mouse model. In vitro, we show that MACF1 controls microtubules dynamics and contributes to microtubule stabilization during myofiber’s maturation. In addition, we demonstrate that MACF1 regulates the microtubules density specifically around myonuclei, and, as a consequence, governs myonuclei motion. Our in vivo studies show that MACF1 deficiency is associated with alteration of extra-synaptic myonuclei positioning and microtubules network organization, both preceding NMJ fragmentation. Accordingly, MACF1 deficiency results in reduced muscle excitability and disorganized triads, leaving voltage-activated sarcoplasmic reticulum Ca2+ release and maximal muscle force unchanged. Finally, adult MACF1-KO mice present an improved resistance to fatigue correlated with a strong increase in mitochondria biogenesis.

Crystal structures of taxane-tubulin complexes: Implications for the mechanism of microtubule stabilization by Taxol

Paclitaxel (Taxol) is a first-line chemotherapeutic drug that promotes the curved to straight conformational transition of tubulin, an activation step that is necessary for microtubule formation. Crystallization of Taxol bound to tubulin has been long elusive. We found that baccatin III, the core structure of paclitaxel which lacks the C13 side chain, readily co-crystallizes with curved tubulin. Tailor-made taxanes with alternative side chains also co-crystallized, allowing us to investigate their binding modes. Interestingly, these Taxol derived compounds lost their microtubule stabilizing activity and cytotoxicity but kept their full microtubule binding affinity, and all induced lattice expansion upon binding. Additional nuclear magnetic resonance studies propose that Taxol binds to a small fraction of straight tubulin present in solution. Our results suggest a mode of action of Taxol, where the core structure is responsible for the interacting energy while the bulky hydrophobic C13 side chain enables binding selectively to straight tubulin and promotes stabilization.

Efficacy of a Covalent Microtubule Stabilizer in Taxane-Resistant Ovarian Cancer Models

Ovarian cancer often has a poor clinical prognosis because of late detection, frequently after metastatic progression, as well as acquired resistance to taxane-based therapy. Herein, we evaluate a novel class of covalent microtubule stabilizers, the C-22,23-epoxytaccalonolides, for their efficacy against taxane-resistant ovarian cancer models in vitro and in vivo. Taccalonolide AF, which covalently binds β-tubulin through its C-22,23-epoxide moiety, demonstrates efficacy against taxane-resistant models and shows superior persistence in clonogenic assays after drug washout due to irreversible target engagement. In vivo, intraperitoneal administration of taccalonolide AF demonstrated efficacy against the taxane-resistant NCI/ADR-RES ovarian cancer model both as a flank xenograft, as well as in a disseminated orthotopic disease model representing localized metastasis. Taccalonolide-treated animals had a significant decrease in micrometastasis of NCI/ADR-RES cells to the spleen, as detected by quantitative RT-PCR, without any evidence of systemic toxicity. Together, these findings demonstrate that taccalonolide AF retains efficacy in taxane-resistant ovarian cancer models in vitro and in vivo and that its irreversible mechanism of microtubule stabilization has the unique potential for intraperitoneal treatment of locally disseminated taxane-resistant disease, which represents a significant unmet clinical need in the treatment of ovarian cancer patients.