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Microtubule Assembly (microtubule + assembly)
Selected AbstractsTOGp regulates microtubule assembly and density during mitosis and contributes to chromosome directional instabilityCYTOSKELETON, Issue 8 2009Lynne Cassimeris Abstract TOGp, a member of the XMAP215 MAP family, is required for bipolar mitotic spindle assembly. To understand how TOGp contributes to spindle assembly, we examined microtubule dynamics after depleting TOGp by siRNA. Fluorescence recovery after photobleaching of GFP-tubulin demonstrated that spindle microtubule turnover is slowed two-fold in the absence of TOGp. Consistent with photobleaching results, microtubule regrowth after washout of the microtubule depolymerizing drug nocodazole was slower at the centrosomes and in the vicinity of mitotic chromatin in cells depleted of TOGp. The slower microtubule turnover is likely due to either nucleation or the transitions of dynamic instability because TOGp depletion did not effect the rate of plus end growth, measured by tracking EB1-GFP at microtubule ends. In contrast, microtubule regrowth after nocodazole washout was unaffected by prior depletion of TACC3, a centrosomal protein that interacts with TOGp. Kinetochore fibers in both untreated and TOGp-depleted cells were stable to incubation at 4°C or lysis in buffer containing calcium indicating that stable kinetochore-microtubule attachments are formed in the absence of TOGp. Depletion of TOGp, but not TACC3, reduced kinetochore oscillations during prometaphase/metaphase. Defects in oscillations are not due simply to multipolarity or loss of centrosome focus in the TOGp-depleted cells, since kinetochore oscillations appear normal in cells treated with the proteosome inhibitor MG132, which also results in multipolar spindles and centrosome fragmentation. We hypothesize that TOGp is required for chromosome motility as a downstream consequence of reduced microtubule dynamics and/or density. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] The control of microtubule stability in vitro and in transfected cells by MAP1B and SCG10CYTOSKELETON, Issue 11 2006Percy Bondallaz Abstract In neurons, the regulation of microtubules plays an important role for neurite outgrowth, axonal elongation, and growth cone steering. SCG10 family proteins are the only known neuronal proteins that have a strong destabilizing effect, are highly enriched in growth cones and are thought to play an important role during axonal elongation. MAP1B, a microtubule-stabilizing protein, is found in growth cones as well, therefore it was important to test their effect on microtubules in the presence of both proteins. We used recombinant proteins in microtubule assembly assays and in transfected COS-7 cells to analyze their combined effects in vitro and in living cells, respectively. Individually, both proteins showed their expected activities in microtubule stabilization and destruction respectively. In MAP1B/SCG10 double-transfected cells, MAP1B could not protect microtubules from SCG10-induced disassembly in most cells, in particular not in cells that contained high levels of SCG10. This suggests that SCG10 is more potent to destabilize microtubules than MAP1B to rescue them. In microtubule assembly assays, MAP1B promoted microtubule formation at a ratio of 1 MAP1B per 70 tubulin dimers while a ratio of 1 SCG10 per two tubulin dimers was needed to destroy microtubules. In addition to its known binding to tubulin dimers, SCG10 binds also to purified microtubules in growth cones of dorsal root ganglion neurons in culture. In conclusion, neuronal microtubules are regulated by antagonistic effects of MAP1B and SCG10 and a fine tuning of the balance of these proteins may be critical for the regulation of microtubule dynamics in growth cones. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] Modulation of Alp4 function in Schizosaccharomyces pombe induces novel phenotypes that imply distinct functions for nuclear and cytoplasmic ,-tubulin complexesGENES TO CELLS, Issue 4 2006Hirohisa Masuda The ,-tubulin complex acts as a nucleation unit for microtubule assembly. It remains unknown, however, how spatial and temporal regulation of the complex activity affects microtubule-mediated cellular processes. Alp4 is one of the essential components of the S. pombe,-tubulin complex. We show here that overproduction of a carboxy-terminal form of Alp4 (Alp4C) and its derivatives tagged to a nuclear localization signal or to a nuclear export signal affect localization of ,-tubulin complexes and induces novel phenotypes that reflect distinct functions of nuclear and cytoplasmic ,-tubulin complexes. Nuclear Alp4C induces a Wee1-dependent G2 delay, reduces the levels of the ,-tubulin complex at the spindle pole body, and results in defects in mitotic progression including spindle assembly, cytoplasmic microtubule disassembly, and chromosome segregation. In contrast, cytoplasmic Alp4C induces oscillatory nuclear movement and affects levels of cell polarity markers, Bud6 and Tip1, at the cell ends. These results demonstrate that regulation of nuclear ,-tubulin complex activity is essential for cell cycle progression through the G2/M boundary and M phase, whereas regulation of cytoplasmic ,-tubulin complex activity is important for nuclear positioning and cell polarity control during interphase. [source] ERK inhibitor PD98059 enhances docetaxel-induced apoptosis of androgen-independent human prostate cancer cellsINTERNATIONAL JOURNAL OF CANCER, Issue 3 2003Stanislav Zelivianski Abstract Anticancer drugs docetaxel and vinorelbine suppress cell growth by altering microtubule assembly and activating the proapoptotic signal pathway. Vinorelbine and docetaxel have been approved for treating several advanced cancers. However, their efficacy in the management of advanced hormone-refractory prostate cancer remains to be clarified. Microtubule damage by some anticancer drugs can activate the ERK survival pathway, which conversely compromises chemotherapeutic efficacy. We analyzed the effect of ERK inhibitors PD98059 and U0126 on vinorelbine- and docetaxel-induced cell growth suppression of androgen-independent prostate cancer cells. In androgen-independent C-81 LNCaP cells, inhibition of ERK by PD98059, but not U0126, plus docetaxel resulted in enhanced growth suppression by an additional 20% compared to the sum of each agent alone (p < 0.02). The combination treatment of docetaxel plus PD98059 also increased cellular apoptosis, which was in part due to the inactivation of Bcl-2 by increasing phosphorylated Bcl-2 by more than 6-fold and Bax expression by 3-fold over each agent alone. At these dosages, docetaxel alone caused only marginal phosphorylation of Bcl-2 (10%). Docetaxel plus U0126 had only 20% added effect on Bcl-2 phosphorylation compared to docetaxel alone. Nevertheless, both U0126 and PD98059 exhibited an enhanced effect on docetaxel-induced growth suppression in PC-3 cells. No enhanced effect was observed for vinorelbine plus PD98059 or U0126. Thus, the combination therapy of docetaxel plus PD98059 may represent a new anticancer strategy, requiring lower drug dosages compared to docetaxel monotherapy. This may lower the cytotoxicity and enhance tumor suppression in vivo. This finding of a combination effect could be of potential clinical importance in treating hormone-refractory prostate cancer. © 2003 Wiley-Liss, Inc. [source] Indole, a core nucleus for potent inhibitors of tubulin polymerization,MEDICINAL RESEARCH REVIEWS, Issue 2 2007Andrea Brancale Abstract Microtubules are the basic components of cell structure, which take part in a wide number of pivotal cellular functions. Drugs that are able to modulate the microtubule assembly either by inhibition of tubulin polymerization or by blocking microtubule disassembly are of great interest in anti-cancer therapy. Several tubulin polymerization inhibitors characterized by the presence of an indole nucleus have been obtained from natural sources or have been prepared by semi-synthesis. In the last decade an ever increasing number of synthetic indoles have been reported. We have reviewed anti-tubulin agents obtained by synthesis having an indole as core nucleus. The synthesis, the biological activity, and the structure,activity relationship aspects of 3-formyl-2-phenylindoles, heterocombretastatins, diarylindoles, 2-aroylindoles, D-24851, 2-aryl-3-aroylindoles, 3-aroyl- and 1-aroylindoles, and arylthioindoles are discussed. © 2006 Wiley Periodicals, Inc. Med Res Rev [source] Interactions of tobacco microtubule-associated protein MAP65-1b with microtubulesTHE PLANT JOURNAL, Issue 1 2004Catherine Wicker-Planquart Summary Tobacco microtubule associated protein (MAP65) (NtMAP65s) constitute a family of microtubule-associated proteins with apparent molecular weight around 65 kDa that collectively induce microtubule bundling and promote microtubule assembly in vitro. They are associated with most of the tobacco microtubule arrays in situ. Recently, three NtMAP65s belonging to the NtMAP65-1 subfamily have been cloned. Here we investigated in vitro the biochemical properties of one member of this family, the tobacco NtMAP65-1b. We demonstrated that recombinant NtMAP65-1b is a microtubule-binding and a microtubule-bundling protein. NtMAP65-1b has no effect on microtubule polymerization rate and binds microtubules with an estimated equilibrium constant of dissociation (Kd) of 0.57 µm. Binding of NtMAP65-1b to microtubules occurs through the carboxy-terminus of tubulin, as NtMAP65-1b was no longer able to bind subtilisin-digested tubulin. In vitro, NtMAP65-1b stabilizes microtubules against depolymerization induced by cold, but not against katanin-induced destabilization. The biological implications of these results are discussed. [source] | ||||||||||