Cardiac hypertrophic and developmental regulation of the beta-tubulin multigene family.
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Increased microtubule density, through viscous loading of active myofilaments, causes contractile dysfunction of hypertrophied and failing pressure-overloaded myocardium, which is normalized by microtubule depolymerization. We have found this to be based on augmented tubulin synthesis and microtubule stability. We show here that increased tubulin synthesis is accounted for by marked transcriptional up-regulation of the beta1- and beta2-tubulin isoforms, that hypertrophic regulation of these genes recapitulates their developmental regulation, and that the greater proportion of beta1-tubulin protein may have a causative role in the microtubule stabilization found in cardiac hypertrophy. (+info)
Decreases in cAMP phosphodiesterase activity in hepatocytes cultured with herbimycin A due to cellular microtubule polymerization related to inhibition of tyrosine phosphorylation of alpha-tubulin.
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The increase in cellular cAMP concentration during 10-min incubation of rat hepatocytes with glucagon or forskolin was enhanced markedly when the hepatocytes had been cultured for several hours with herbimycin A. This effect of herbimycin was accompanied by inhibition of tyrosine-phosphorylation of cellular proteins including alpha-tubulin, antagonized by coaddition of Na3VO4 plus H2O2, which also antagonized the herbimycin-induced tyrosine phosphorylation, and overcome by the addition to the 10-min incubation medium of a certain inhibitor of cAMP phosphodiesterase (PDE), which caused a huge accumulation of cAMP. The effective PDE inhibitors were 4-[3-(cyclopentyloxy)-4-methoxyphenyl]-2-pyrrolidinone (rolipram) and 4-(3-butyloxy-4-methoxyphenyl)-2-imidazolidinone (Ro-20-1724, a PDE4 inhibitor), in addition to 3-isobutyl-1-methylxanthine (a nonselective inhibitor). Rapid breakdown of the once-accumulated cAMP in cultured hepatocytes during the subsequent incubation without PDE inhibitors was progressively prevented when the concentration of herbimycin was increased from 0.3 to 10 microM during prior culture. This effect of herbimycin to inhibit PDE activity in intact cells was abolished by coaddition of a microtubule-disrupting agent, either colchicine or vinblastine, into the culture, but remained unchanged if the vinblastine-containing medium was further supplemented with taxol, a microtubule-stabilizing agent, which by itself mimicked the effect of herbimycin. None of these agents, which thus affected PDE activity in intact cells, inhibited the PDE activity assayable in the cell lysates. The taxol-like and vinblastine-suppressible action of herbimycin to stimulate microtubular assembly was antagonized by Na3VO4/H2O2, as confirmed by confocal microscopic images of the cells stained with fluorescein-bound anti-(alpha-tubulin). Thus, 4-h culture of hepatocytes with herbimycin inhibits phosphorylation of the C-terminal tyrosine residue of alpha-tubulin, thereby stimulating formation of a microtubular network which is responsible for the inhibition of PDE4 in the intact cells by an unknown mechanism. (+info)
The translation in vitro of mRNA from developing cysts of Artemia salina.
(19/5514)
Successive stages in the development of the brine shrimp cyst were used as a model for studying differentiation at the level of mRNA transcription and translation. The poly (A)-containing mRNA from dormant cysts and free-swimming larvae (nauplii) was found to be efficiently translated in a wheat-germ cell-free system, and electrophoretic patterns of translation products in vitro resembled those of the endogenous proteins extracted from the equivalent developmental stages. Each stage, however, exhibits a characteristic protein pattern. Two low-molecular-weight proteins prominent in the cyst disappeared almost completely in the nauplius stage, whereas the proportion of actin increased 3-fold. Parallel patterns were observed upon translation in vitro of the respective mRNA preparations. The percentage of the acidic protein, tubulin, decreased somewhat during development. (+info)
The carboxy-terminal sequence Asp427-Glu432 of beta-tubulin plays an important function in axonemal motility.
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Flagellar motility is the result of specific interactions between axonemal microtubular proteins and the dynein motors. Tubulin, the main component of microtubule, is a very polymorphic protein resulting from the expression of several isogenes and from the existence of various post-translational modifications. In order to characterize tubulin isoforms and tubulin domains that are important for flagellar movement, we prepared monoclonal antibodies against axonemal proteins from whole sea-urchin sperm tails. The monoclonal antibodies obtained were screened for their potency to inhibit demembranated-reactivated sperm models and for their monospecific immunoreactivity on immunoblot. Among the different antibodies we obtained, D66 reacted specifically with a subset of beta-tubulin isoforms. Limited proteolysis, HPLC, peptide sequencing, mass spectroscopy and immunoblotting experiments indicated that D66 recognized an epitope localized in the primary sequence Gln423-Glu435 of the C-terminal domain of Lytechinus pictus beta2-tubulin, and that this sequence belongs to class IVb. The use of synthetic peptides and immunoblotting analysis further narrowed the amino acids important for antibody recognition to Asp427-Glu432. Because the primary effect of this antibody on sperm motility is to decrease the flagellar beat frequency, we suggest that this sequence is involved in the tubulin-dynein head interaction. (+info)
beta-tubulin mRNA as a marker of Cryptosporidium parvum oocyst viability.
(21/5514)
Determining the viability of waterborne Cryptosporidium parvum oocysts remains a technical challenge. rRNA and mRNA were evaluated in a reverse transcription (RT)-PCR assay as potential markers of oocyst viability. The rationale for this approach is the rapid turnover and postmortem decay of cellular RNA. The beta-tubulin mRNA and an anonymous mRNA transcript were chosen as potential markers because they are the only mRNA species in C. parvum known to possess introns. This feature facilitated the distinction between genuine RT-PCR products and PCR products originating from copurifying DNA. Prolonged incubation at room temperature of initially viable oocysts resulted in a gradual decrease in mRNA levels, which correlated with the loss of oocyst infectivity to neonatal mice. In contrast, oocysts stored at 4 degrees C for over 39 weeks maintained their infectivity and displayed no decrease in the level of beta-tubulin RT-PCR product. The postmortem decay of two mRNA species demonstrates that RT-PCR analysis can provide information on the viability of C. parvum oocysts. The methodological similarity between PCR detection and RT-PCR viability analysis could facilitate the development of a combined detection and viability assay. (+info)
GMAP-210, A cis-Golgi network-associated protein, is a minus end microtubule-binding protein.
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We report that a peripheral Golgi protein with a molecular mass of 210 kD localized at the cis-Golgi network (Rios, R.M., A.M. Tassin, C. Celati, C. Antony, M.C. Boissier, J.C. Homberg, and M. Bornens. 1994. J. Cell Biol. 125:997-1013) is a microtubule-binding protein that associates in situ with a subpopulation of stable microtubules. Interaction of this protein, now called GMAP-210, for Golgi microtubule-associated protein 210, with microtubules in vitro is direct, tight and nucleotide-independent. Biochemical analysis further suggests that GMAP-210 specifically binds to microtubule ends. The full-length cDNA encoding GMAP-210 predicts a protein of 1, 979 amino acids with a very long central coiled-coil domain. Deletion analyses in vitro show that the COOH terminus of GMAP-210 binds to microtubules whereas the NH2 terminus binds to Golgi membranes. Overexpression of GMAP-210-encoding cDNA induced a dramatic enlargement of the Golgi apparatus and perturbations in the microtubule network. These effects did not occur when a mutant lacking the COOH-terminal domain was expressed. When transfected in fusion with the green fluorescent protein, the NH2-terminal domain associated with the cis-Golgi network whereas the COOH-terminal microtubule-binding domain localized at the centrosome. Altogether these data support the view that GMAP-210 serves to link the cis-Golgi network to the minus ends of centrosome-nucleated microtubules. In addition, this interaction appears essential for ensuring the proper morphology and size of the Golgi apparatus. (+info)
Direct observations of the mechanical behaviors of the cytoskeleton in living fibroblasts.
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Cytoskeletal proteins tagged with green fluorescent protein were used to directly visualize the mechanical role of the cytoskeleton in determining cell shape. Rat embryo (REF 52) fibroblasts were deformed using glass needles either uncoated for purely physical manipulations, or coated with laminin to induce attachment to the cell surface. Cells responded to uncoated probes in accordance with a three-layer model in which a highly elastic nucleus is surrounded by cytoplasmic microtubules that behave as a jelly-like viscoelastic fluid. The third, outermost cortical layer is an elastic shell under sustained tension. Adhesive, laminin-coated needles caused focal recruitment of actin filaments to the contacted surface region and increased the cortical layer stiffness. This direct visualization of actin recruitment confirms a widely postulated model for mechanical connections between extracellular matrix proteins and the actin cytoskeleton. Cells tethered to laminin-treated needles strongly resisted elongation by actively contracting. Whether using uncoated probes to apply simple deformations or laminin-coated probes to induce surface-to-cytoskeleton interaction we observed that experimentally applied forces produced exclusively local responses by both the actin and microtubule cytoskeleton. This local accomodation and dissipation of force is inconsistent with the proposal that cellular tensegrity determines cell shape. (+info)
Association of polo-like kinase with alpha-, beta- and gamma-tubulins in a stable complex.
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The polo-like kinase (Plk) family has been shown to have an important role in the regulation of the cell-division cycle, especially in organization of the spindle structure, in species from fungi to humans. Recent reports have demonstrated that in mammalian cells Plk is associated with components of the anaphase-promoting complex and a peptidyl-prolyl isomerase, Pin1. To characterize a putative Plk-containing complex, we fractionated mitotic cell lysates on a gel-filtration column. The Plk complex was eluted from the column at molecular sizes ranging from 669 to 2500 kDa in the presence of detergent and high concentrations of salt. Specific associations of Plk with alpha-, beta- and gamma-tubulins in both interphase and mitotic cells were shown by reciprocal immunoprecipitations and immunoblottings and were independent of the microtubule polymerization state, whereas binding assays in vitro indicated that Plk interacts with alpha- and beta-tubulins directly. In addition, mitotic Plk was able to phosphorylate associated tubulins in vitro. Finally, we show that the kinase domain of the Plk molecule is both required and sufficient for its binding to tubulins in vivo. The specific interaction between Plk and tubulins might provide a molecular basis for the physiological functions of Plk in regulating the cell cycle, particularly in establishing the normal bipolar spindle. (+info)