Microtubule-mediated NF-κB activation in the TNF-α signaling pathway (original) (raw)
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Oncogene, 1999
Activation of the NF-kB transcription factors has been shown to be directly in¯uenced by changes in the microtubule cytoskeleton network. To better understand cytoskeletal regulation of NF-kB, experiments were performed to determine whether the microtubule (MT) stabilizing agent taxol could modulate NF-kB activation in the presence of dierent NF-kB inducers. Pretreatment of murine NIH3T3 and human 293 cells with 5 mM taxol resulted in complete inhibition of phorbol, 12myristate, 13-acetate (PMA) mediated NF-kB activation, detected as the loss of DNA binding and reduced NF-kB dependent reporter gene activity. Furthermore, in COS-7 and NIH3T3 cells, PMA-induced IkBa turnover was dramatically reduced in taxol treated cells, mediated via the inhibition of IkBa phosphorylation. However, taxol did not prevent TNF-a induced IkBa phosphorylation, degradation, or NF-kB activation, indicating that TNF-a acts through a microtubule-independent pathway. In vitro kinase assays with PMA stimulated cell extracts demonstrated that taxol reduced protein kinase C activity by 30%, thus implicating the loss of PKC activity as a possible regulatory target of taxol-mediated suppression of NF-kB. Since PMA causes modulation of cytoarchitecture through PKC activation, microtubule integrity and cell morphology was analysed by indirect immuno¯uorescence. Both PMA and nocodazole, a MT depolymerizing agent, caused microtubule depolymerization, whereas TNF-a did not alter MT integrity; concomitant taxol treatment blocked both nocodazole and PMA induced depolymerization of MTs, as well as NF-kB induction, thus demonstrating a link between microtubule depolymerization and NF-kB activation. These observations illustrate a novel biological activity of taxol as a selective inhibitor of NF-kB activity, suggesting a link between the state of microtubule integrity and gene regulation.
Drugs that target dynamic microtubules: A new molecular perspective
Medicinal Research …, 2011
Microtubules have long been considered an ideal target for anticancer drugs because of the essential role they play in mitosis, forming the dynamic spindle apparatus. As such, there is a wide variety of compounds currently in clinical use and in development that act as antimitotic agents by altering microtubule dynamics. Although these diverse molecules are known to affect microtubule dynamics upon binding to one of the three established drug domains (taxane, vinca alkaloid, or colchicine site), the exact mechanism by which each drug works is still an area of intense speculation and research. In this study, we review the effects of microtubule-binding chemotherapeutic agents from a new perspective, considering how their mode of binding induces conformational changes and alters biological function relative to the molecular vectors of microtubule assembly or disassembly. These "biological vectors" can thus be used as a spatiotemporal context to describe molecular mechanisms by which microtubule-targeting drugs work.
Influence of microtubule-associated proteins on the differential effects of paclitaxel and docetaxel
Journal of Protein Chemistry, 1996
Microtubules are complex structures arising in part from the polymerization of tubulin dimers. Tubutin binds to a wide range of drugs which have been used as probes for tubulin conformation and assembly properties. There is some evidence that taxol and taxotere have differing effects on tubulin conformation. Previous work has shown that MAP2 and Tau, although they both induce microtubule assembly, have qualitatively different effects on tubulin's behavior. Since most microtubules in vivo are likely to be associated with MAPs, we decided to characterize the differential effects of MAP2, Tau, taxol, and taxotere on tubulin polymerization with the aim of understanding the mechanisms through which these agents stimulate microtubule assembly. Furthermore, the inhibitive effect of calcium has been used to elucidate the ability of the two drugs to force tubulin assembly. These observations suggest that docetaxel, in addition to its greater efficiency in tubulin assembly, may have the capacity to differently alter certain classes of microtubules. Tau and MAP2 accessory proteins may represent important cofactors modulating the effects of taxoids.
Proceedings of the National Academy of Sciences, 2007
Tubulin cofactor B (TCoB) plays an important role in microtubule dynamics by facilitating the dimerization of ␣and -tubulin. Recent evidence suggests that p21-activated kinase 1 (Pak1), a major signaling nodule in eukaryotic cells, phosphorylates TCoB on Ser-65 and Ser-128 and plays an essential role in microtubule regrowth. However, to date, no upstream signaling molecules have been identified to antagonize the functions of TCoB, which might help in maintaining the equilibrium of microtubules. Here, we discovered that TCoB is efficiently nitrated, mainly on Tyr-64 and Tyr-98, and nitrated-TCoB attenuates the synthesis of new microtubules. In addition, we found that nitration of TCoB antagonizes signaling-dependent phosphorylation of TCoB, whereas optimal nitration of TCoB requires the presence of functional Pak1 phosphorylation sites, thus providing a feedback mechanism to regulate phosphorylation-dependent MT regrowth. Together these findings identified TCoB as the third cytoskeleton protein to be nitrated and suggest a previously undescribed mechanism, whereby growth factor signaling may coordinately integrate nitric oxide signaling in the regulation of microtubule dynamics. § To whom correspondence may be addressed.
Microtubules as a target for anticancer drugs
Nature Reviews Cancer, 2004
Highly dynamic mitotic-spindle microtubules are among the most successful targets for anticancer therapy. Microtubule-targeted drugs, including paclitaxel and Vinca alkaloids, were previously considered to work primarily by increasing or decreasing the cellular microtubule mass. ...
Analytical Cellular Pathology, 2015
Microtubules are dynamic and structural cellular components involved in several cell functions, including cell shape, motility, and intracellular trafficking. In proliferating cells, they are essential components in the division process through the formation of the mitotic spindle. As a result of these functions, tubulin and microtubules are targets for anticancer agents. Microtubule-targeting agents can be divided into two groups: microtubule-stabilizing, and microtubule-destabilizing agents. The former bind to the tubulin polymer and stabilize microtubules, while the latter bind to the tubulin dimers and destabilize microtubules. Alteration of tubulin-microtubule equilibrium determines the disruption of the mitotic spindle, halting the cell cycle at the metaphase-anaphase transition and, eventually, resulting in cell death. Clinical application of earlier microtubule inhibitors, however, unfortunately showed several limits, such as neurological and bone marrow toxicity and the eme...
Oncogene, 1999
Drug design targeted at microtubules has led to the advent of some potent anti-cancer drugs. In the present study, we demonstrated that microtubule-binding agents (MBAs) taxol and colchicine induced immediate early gene (c-jun and ATF3) expression, cell cycle arrest, and apoptosis in the human breast cancer cell line MCF-7. To elucidate the signal transduction pathways that mediate such biological activities of MBAs, we studied the involvement of mitogen-activated protein (MAP) kinases. Treatment with taxol, colchicine, or other MBAs (vincristine, podophyllotoxin, nocodazole) stimulated the activity of c-jun N-terminal kinase 1 (JNK1) in MCF-7 cells. In contrast, p38 was activated only by taxol and none of the MBAs changed the activity of extracellular signal-regulated protein kinase 2 (ERK2). Activation of JNK1 or p38 by MBAs occurred subsequent to the morphological changes in the microtubule cytoskeleton induced by these compounds. Furthermore, baccatine III and b-lumicolchicine, inactive analogs of taxol and colchicine, respectively, did not activate JNK1 or p38. These results suggest that interactions between microtubules and MBAs are essential for the activation of these kinases. Pretreatment with the antioxidants N-acetyl-L-cysteine (NAC), ascorbic acid or vitamin E, blocked H 2 O 2-or doxorubicininduced JNK1 activity, but had no eect on JNK1 activation by MBAs, excluding a role for oxidative stress. However, BAPTA/AM, a speci®c intracellular Ca 2+ chelator, attenuated JNK1 activation by taxol but not by colchicine, and had no eect on microtubule changes induced by taxol. Thus, stabilization or depolymerization of microtubules may regulate JNK1 activity via distinct downstream signaling pathways. The dierential activation of MAP kinases opens up a new avenue for addressing the mechanism of action of antimicrotubule drugs.
The Role of the Microtubules in Tumor Necrosis Factor-α–Induced Endothelial Cell Permeability
American Journal of Respiratory Cell and Molecular Biology, 2003
Tumor necrosis factor (TNF)-␣, a major proinflammatory cytofilaments, intermediate filaments, and microtubules (3). Tukine, triggers endothelial cell activation and barrier dysfunction mor necrosis factor (TNF)-␣, a proinflammatory cytokine which are implicated in the pathogenesis of pulmonary edema secreted by macrophages and endothelial cells, has been associated with acute lung injury syndromes. The mechanisms implicated in endothelial cell activation, increased endotheof TNF-␣-induced vascular permeability are not completely unlial cell permeability, and pulmonary edema formation (4, 5). derstood. Our initial experiments demonstrated that TNF-␣-However, the exact mechanisms by which TNF-␣ triggers induced decreases in transendothelial electrical resistance across vascular barrier dysfunction are not precisely defined. We human pulmonary artery endothelial cells are independent of and others have noted that TNF-␣ induces endothelial actin myosin light chain phosphorylation catalyzed by either myosin microfilament rearrangement and intercellular gap formalight chain kinase or Rho kinase. We next assessed the involvement of another cytoskeletal component, the tubulin-based micro-tion that parallel the development of transendothelial pertubule network, and found TNF-␣ to induce a decrease in stable meability (5, 6). It is less clear which signaling pathways tubulin content and partial dissolution of peripheral microare orchestrating these morphologic changes of endothelial tubule network as evidenced by anti-acetylated tubulin and cells and their relative direct contribution to the vascular anti--tubulin immunofluorescent staining, respectively. Microbarrier dysfunction. We have previously shown that TNF-␣ tubule-stabilizing agents, paclitaxel and epothilone B, signifiinduces significant actin microfilament rearrangement by cantly attenuated TNF-␣-induced decreases in transendothelial myosin light chain phosphorylation, as a consequence of electrical resistance, inhibited the cytokine-induced increases the coordinated action of the myosin light chain kinase in actin stress fibers, formation of intercellular gap, and restored (MLCK) and Rho kinase (5). However, TNF-␣-induced the TNF-␣-compromised vascular endothelial (VE)-cadherinendothelial cell barrier dysfunction was shown to evolve based cell-cell junctions. Importantly, neither TNF-␣ nor pacliin an MLCK-and Rho kinase-independent fashion (5), taxel treatment was associated with endothelial cell apoptosis. Inhibition of p38 mitogen-activated protein kinase by SB203580 suggesting that MLCK-independent microfilament changes significantly attenuated TNF-␣-induced microtubule destabiliand/or other cytoskeletal structures, such as intermediate zation, actin rearrangement, and endothelial barrier dysfunction. filaments, microtubules, and adherens junctions may be These results strongly suggest the involvement of microtubule involved. Although it was previously shown that TNF-␣ rearrangement in TNF-␣-induced endothelial cell permeability triggers microtubule disassembly (7), the role of the microvia p38 mitogen-activated protein kinase activation.
Life Sciences, 1992
Microtubules, with intermediate filaments and microfilaments, are the components of the cell skeleton which determinates the shape of a cell. Microtubules are involved in different functions including the assembly of mitotic spindle, in dividing cells, or axon extension, in neurons. In the first case, microtubules are highly dynamic, while in the second case microtubules are quite stable, suggesting that microtubule with different physical properties (stability) are involved in different functions. Thus, to understand the mechanisms of microtubule functions it is very important to understand microtubule dynamics. Historically, tubulin, the main component of microtubules, was first characterized as the major component of the mitotic spindle that binds to colchicine. Afterwards, it was found that tubulin is particularly more abundant in brain than in other tissues. Therefore, the roles of microtubules in mitosis, and in neurons, have been more extensively analyzed and, in this review, these roles will be discussed.
Mechanism of Action of Antitumor Drugs that Interact with Microtubules and Tubulin
Current Medicinal Chemistry-Anti-Cancer Agents, 2012
Microtubules, major structural components in cells, are the target of a large and diverse group of natural product anticancer drugs. Given the success of this class of drugs in cancer treatment, it can be argued that microtubules represent the single best cancer target identified to date. Microtubules are highly dynamic assemblies of the protein tubulin. They readily polymerize and depolymerize in cells, and they undergo two interesting kinds of dynamics called dynamic instability and treadmilling. These dynamic behaviors are crucial to mitosis, the process of chromosomal division to form new cells. Microtubule dynamics are highly regulated during the cell cycle by endogenous cellular regulators. In addition, many antitumor drugs and natural compounds alter the polymerization dynamics of microtubules, blocking mitosis, and consequently, inducing cell death by apoptosis. These drugs include several that inhibit microtubule polymerization at high drug concentrations, namely, the Vinca alkaloids, cryptophycins, halichondrins, estramustine, and colchicine. Another group of these compounds stimulates microtubule polymerization and stabilizes microtubules at high concentrations. These include Taxol™, Taxotere™, eleutherobins, epothilones, laulimalide, sarcodictyins, and discodermolide. Importantly, considerable evidence indicates that, at lower concentrations, these drugs have a common mechanism of action; they suppress the dynamics of microtubules without appreciably changing the mass of microtubules in the cell. The drugs bind to diverse sites on tubulin and at different positions within the microtubule, and they have diverse effects on microtubule dynamics. However, by their common mechanism of suppression microtubule dynamics, they all block mitosis at the metaphase/anaphase transition, and induce cell death. I. MICROTUBULES AS TARGETS FOR ANTI-CANCER DRUGS Microtubules are major dynamic structural components in cells. They are important in the development and maintenance of cell shape, in cell reproduction and division, in cell signaling, and in cellular movement [1]. Microtubules are the target of a diverse group of anticancer drugs, most of which are derived from natural products. Given the success of this class of drugs, the mitotic inhibitors, it can be argued that microtubules represent the single best cancer target identified to date [2] [3]. Microtubules are highly dynamic polymers of heterodimers of α and β tubulin, arranged parallel to a cylindrical axis to form tubes of 25 nm diameter that may be many µm long. Polymerization of microtubules occurs by a nucleation-elongation mechanism in which the formation of a short microtubule 'nucleus' is followed by elongation of the microtubule at its ends by the reversible, noncovalent addition of tubulin dimers. Microtubules are not simple equilibrium polymers. They exhibit complex polymerization dynamics that use energy provided by the hydrolysis of GTP, and these dynamics are crucial to their cellular functions. A large number of chemically diverse substances bind to