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At least 811 records · Page 45Linked to original sources
PubMed1998

Identification of polypeptides associated with an enriched cytoskeleton-protein body fraction from developing rice endosperm.

Recent evidence has shown that the prolamine polysomes are attached not only to the endoplasmic reticulum membranes that bound the prolamine protein bodies (PBs) but also to cytoskeleton elements associated with this subcellular fraction. To learn more about the nature of the proteins that are associated with this supra-macromolecular complex, proteins extracted from an enriched cytoskeleton-PB fraction were resolved by two-dimensional polyacrylamide gel electrophoresis under non-equilibrium conditions and analyzed for their composition by immunological and biochemical methods. Immunoblot analysis indicated the presence of the cytoskeletal proteins, actin and tubulin, and the cytoskeletal-associated protein EF1 alpha in this fraction. Microsequencing of selected polypeptides revealed a diversity of protein sequences. In addition to contaminating storage proteins which are selectively solubilized by the isolation procedure, several ribosomal proteins and histone H3 were also identified. Some of the remaining polypeptides showed partial homology to protein sequences deposited in the database, several of which are cytoskeleton-associated proteins.

Amino Acid Sequence↗
PubMed2002

Aluminum-induced rapid changes in the microtubular cytoskeleton of tobacco cell lines.

Aluminum (Al) is a major factor that limits plant growth in acid soils. It causes a cessation of root growth and changes in root morphology suggesting a role of the root cytoskeleton as a target of Al-toxicity. Here we report a rapid effect of Al on the microtubular cytoskeleton of the suspension tobacco cell lines BY-2 and VBI-0. Viability studies showed that the cells were more sensitive to Al during exponential phase as compared to stationary cells. During the first hours of exposure, Al induced the formation of additional bundles of cortical microtubules (cMTs), whereas the thickness of the individual bundles decreased. Prolonged exposure resulted in disorientation of cMTs. These changes of cMTs preceded the decrease of cell viability by several hours and were accompanied by an increase in the levels of alpha-tubulin (in its tyrosinated form) and elements of the tubulin-folding chaperone CCT. These findings suggest that the microtubular cytoskeleton is one of the early targets of Al toxicity.

Aluminum↗
PubMed2006

Change in the actin cytoskeleton during seismonastic movement of Mimosa pudica.

The seismonastic movement of Mimosa pudica is triggered by a sudden loss of turgor pressure. In the present study, we compared the cell cytoskeleton by immunofluorescence analysis before and after movement, and the effects of actin- and microtubule-targeted drugs were examined by injecting them into the cut pulvinus. We found that fragmentation of actin filaments and microtubules occurs during bending, although the actin cytoskeleton, but not the microtubules, was involved in regulation of the movement. Transmission electron microscopy revealed that actin cables became loose after the bending. We injected phosphatase inhibitors into the severed pulvinus to examine the effects of such inhibitors on the actin cytoskeleton. We found that changes in actin isoforms, fragmentation of actin filaments and the bending movement were all inhibited after injection of a tyrosine phosphatase inhibitor. We thus propose that the phosphorylation status of actin at tyrosine residues affects the dynamic reorganization of actin filaments and causes seismonastic movement.

Actins↗
PubMed2003

The role of nod factor substituents in actin cytoskeleton rearrangements in Phaseolus vulgaris.

In order to define the symbiotic role of some of the chemical substituents in the Rhizobium etli Nod factors (NFs), we purified Nod metabolites secreted by the SM25 strain, which carries most of the nodulation genes, and SM17 with an insertion in nodS. These NFs were analyzed for their capabilities to induce root hair curling and cytoskeletal rearrangements. The NFs secreted by strain SM17 lack the carbamoyl and methyl substituents on the nonreducing terminal residue and an acetyl moiety on the fucosyl residue on the reducing-terminal residue as determined by mass spectrometry. We have reported previously that the root hair cell actin cytoskeleton from bean responds with a rapid fragmentation of the actin bundles within 5 min of NF exposure, and also is accompanied by increases in the apical influxes and intracellular calcium levels. In this article, we report that methyl-bearing NFs are more active in inducing root hair curling and actin cytoskeleton rearrangements than nonmethylated NFs. However, the carbamoyl residue on the nonreducing terminal residue and the acetyl group at the fucosyl residue on the reducing terminal residue do not seem to have any effect on root hair curling induction or in actin cytoskeleton rearrangement.

Actins↗
PubMed2003

NAADP activates a Ca2+ current that is dependent on F-actin cytoskeleton.

Nicotinic acid adenine dinucleotide phosphate (NAADP) is involved in the Ca2+ response observed at fertilization in several species, including starfish. In this study, we have employed Ca2+ imaging and the single-electrode voltage-clamp technique to investigate whether the NAADP-mediated Ca2+ entry discovered in our laboratory in starfish oocytes was underlain by a membrane current and whether the response to NAADP required an intact cytoskeleton. Uncaging of preinjected NAADP evoked a cortical Ca2+ flash that was followed by the spreading of the wave to the remainder of the cell. No Ca2+ increase was detected in Ca2+-free sea water. Under voltage-clamp conditions, the photoliberation of NAADP activated an inward rectifying membrane current, which reversed at potentials more positive than +50 mV and was abolished by removal of Ca2+ but not of Na+. The current was affected by preincubation with verapamil, SKF 96356, and thapsigargin but not by preinjection of heparin, 8-NH2- cyclic ADP-ribose, or both antagonists. The membrane current and the Ca2+ wave were inhibited by latrunculin-A and jasplakinolide, which depolymerize and stabilize actin cytoskeleton, respectively. These data offer the first demonstration that NAADP initiates a Ca2+ sweep by activating a Ca2+-permeable membrane current that requires an intact F-actin cytoskeleton as other Ca2+-permeable currents, such as ICRAC and IARC.

Actin Cytoskeleton↗
PubMed2006

A noncanonical SH3 domain binding motif links BK channels to the actin cytoskeleton via the SH3 adapter cortactin.

Calcium-activated potassium (BK) channels play a central role in regulating multiple physiological processes, from the control of blood flow to neuronal excitability. Coordinated regulation of BK channel activity by changes in actin cytoskeleton dynamics has been implicated in several of these processes and related disease states such as epilepsy and stroke. However, how BK channels interact with the actin cytoskeleton is essentially unknown. Here we demonstrate noncanonical Src homology domain 3 (SH3) binding site motifs in the intracellular C terminus of the BK channel pore-forming alpha-subunit that are conserved from fish to humans. These noncanonical motifs target multiple SH3 domain cellular signaling proteins to BK channels, including the SH3 adapter protein cortactin (EMS1). We demonstrate that cortactin provides a molecular bridge between BK channels and the cortical actin cytoskeleton in cells. Disruption of the SH3-mediated interaction prevents the regulation of BK channel activity controlled by changes in actin cytoskeletal dynamics. Targeting of cortactin to BK channels via a novel, noncanonical SH3 domain binding motif has important implications for the coordination of BK channel function in normal physiology and disease.

Actins↗
PubMed1993

Cholecystokinin JMV-180 and caerulein effects on the pancreatic acinar cell cytoskeleton.

We previously demonstrated that the supramaximally effective concentrations of caerulein caused marked changes in the apical cytoskeleton of the rat pancreatic acinar cell. These changes included ablation of microvilli, the terminal actin web, and intermediate filament bands. The present study was designed to elucidate part of the intracellular signalling mechanism mediating these changes. For these studies we used a cholecystokinin (CCK) analogue, CCK-JMV-180, that has been previously demonstrated not to inhibit enzyme secretion and to prevent the inhibition caused by caerulein. We investigated the effects of CCK-JMV-180 alone and in combination with supramaximal concentrations of caerulein on the morphology of the apical structures, on 1,2-diacylglycerol production (a measure of phospholipase C activity), and on amylase secretion in rat pancreatic acini. Supramaximally effective concentrations of caerulein caused inhibition of enzyme secretion. CCK-JMV-180 had no effect on the ultrastructure of the apical region of the acinar cell and it prevented the ablation of apical cytoskeleton induced by a supramaximal concentration of caerulein (10 nM). CCK-JMV-180 inhibited the increase in 1,2-diacylglycerol formation and the inhibition of amylase release caused by 10 nM caerulein. Mimicking the effect of 1,2-diacylglycerol on activation of protein kinase C with phorbol 12-myristate 13-acetate and reproducing changes in [Ca2+]i caused by 10 nM caerulein with 100 nM bombesin did not alter the apical cytoskeleton. These results suggest that the cytoskeletal changes observed with inhibitory concentrations of caerulein are caused by the phospholipase C effects of caerulein on membrane phospholipids.

Amylases↗
PubMed2002

The actin cytoskeleton: an essential component for enhanced TNFalpha production by adherent monocytes.

Monocyte adherence induces the formation of focal adhesions, the interaction sites of intracellular signaling molecules and cytoskeletal proteins such as actin. We previously demonstrated that adherence potentiates human monocyte LPS-induced TNFalpha production. Hence, we hypothesized that the actin cytoskeleton is integral to adherence-induced priming for enhanced LPS-induced TNFalpha production. In contrast to nonadherent cells, LPS induced significant transcription of TNFalpha mRNA and production of TNFalpha in adherent monocytes. Disrupting the actin cytoskeleton with cytochalasin D (CD) in adherent monocytes inhibited LPS-induced TNFalpha production by 55%, thereby abrogating adherence-induced priming. Moreover, CD pretreatment abrogated adherence-induced activation of Pyk2, a major focal adhesion kinase, and ERK 1/2, a component of the mitogen-activated protein kinase (MAPK) signaling pathway, and it completely inhibited LPS-induced ERK 1/2 activation. However, CD treatment of nonadherent monocytes failed to inhibit cytokine production. In conclusion, the actin cytoskeleton is integral in the reprogramming of the monocyte for enhanced cytokine production and in maintaining this "primed" state.

Actins↗
PubMed1994

The cytoskeleton and membrane transport.

This review summarizes recent studies demonstrating that the actin-based cytoskeleton regulates the activity of many ion channels and transport proteins. Stretch-activated ion channels; channels conductive to chloride, to sodium, and to potassium; electroneutral transport proteins, including the Na(+)-K(+)-2Cl-cotransporter, the Na+/H+ exchanger, and the organic osmolyte transporter; as well as water channels are all regulated by the actin cytoskeleton. Several potential mechanisms whereby the actin cytoskeleton and microtubules regulate transport protein activity are discussed.

Animals↗
PubMed2005

Integrin-linked kinase in renal disease: connecting cell-matrix interaction to the cytoskeleton.

PURPOSE OF REVIEW: Cellular functions like proliferation, differentiation, migration, morphogenesis and apoptosis are modulated by the extracellular matrix. Integrins are the prototypic heterodimeric transmembrane matrix receptors with competing affinities for individual extracellular matrix ligands. The intracellular integrin domain clusters cytoplasmic proteins into focal adhesion plaques for bidirectional (outside-in and inside-out) signalling. Integrin-linked kinase organizes the connections of the extracellular matrix via integrins to the cytoskeleton and is involved in adhesion plaque signalling. In this review, an introduction of integrin-linked kinase structure and function is followed by a summary of our current understanding of integrin-linked kinase in renal disease with special focus on glomerular cell-matrix interaction. RECENT FINDINGS: Differential regulation of integrin-linked kinase has been observed during the pathogenesis of glomerular disease and tubulo-interstitial fibrosis. In outside-in signalling integrin-linked kinase mediates the response of renal cells to alterations in matrix and growth factor environments. Inside-out signalling transduces inflammatory and oxidative stress responses into decreased matrix attachment. Downstream signalling of integrin-linked kinase activates the Wnt pathway with a switch towards a proliferative, mesenchymal phenotype. In concert with interacting molecules integrin-linked kinase influences the actin cytoskeleton, resulting in shape change and focal adhesion dysfunction observed in podocyte failure and tubulo-interstitial fibrosis. SUMMARY: Integrin-linked kinase has emerged as a key player at the interface between extracellular matrix, integrins, actin-based cytoskeleton and cellular phenotype in kidney diseases. Future studies focusing on interacting molecules and modification of integrin-linked kinase function in vivo will better define the role of cell matrix signalling in progressive renal failure.

Animals↗
PubMed2005

Lipid rafts and regulation of the cytoskeleton during T cell activation.

The ability of polarized cells to initiate and sustain directional responses to extracellular signals is critically dependent on direct communication between spatially organized signalling modules in the membrane and the underlying cytoskeleton. Pioneering work in T cells has shown that the assembly of signalling modules critically depends on the functional compartmentalization of membrane lipids into ordered microdomains or lipid rafts. The significance of rafts in T cell activation lies not only in their ability to recruit the signalling partners that eventually assemble into a mature immunological synapse but also in their ability to regulate actin dynamics and recruit cytoskeletal associated proteins, thereby achieving the structural polarization underlying stability of the synapse-a critical prerequisite for activation to be sustained. Lipid rafts vary quite considerably in size and visualizing the smallest of them in vivo has been challenging. Nonetheless it is now been shown quite convincingly that a surprisingly large proportion-in the order of 50%-of external membrane lipids (chiefly cholesterol and glycosphingolipids) can be dynamically localized in these liquid ordered rafts. Complementary inner leaflet rafts are less well characterized, but contain phosphoinositides as an important functional component that is crucial for regulating the behaviour of the actin cytoskeleton. This paper provides an overview of the interdependency between signalling and cytoskeletal polarization, and in particular considers how regulation of the cytoskeleton plays a crucial role in the consolidation of rafts and their stabilization into the immunological synapse.

Actins↗
PubMed1995

Actin cortical cytoskeleton and cell wall synthesis in regenerating protoplasts of the Saccharomyces cerevisiae actin mutant DBY 1693.

The relationship between the actin cytoskeleton and cell wall synthesis was studied by light and electron microscopy in protoplasts of Saccharomyces cerevisiae DBY 1693 containing the act1-1 allele. Since protoplasting also disturbs the actin cytoskeleton, these mutant protoplasts had a double error in their actin cytoskeletons. In the period between the onset of wall synthesis and completion of the wall, protoplasts grown at the permissive temperature showed an even distribution of actin patches all over the surface on which a new cell wall was being synthesized. After wall completion, actin patches partially disappeared, but then re-appeared, accumulated in growth regions at the start of polarized growth. This was compared with the pattern of actin patches observed in intact temperature-sensitive actin mutant cells cultivated at the permissive temperature. Electron microscopy of freeze-etched replicas revealed finger-like invaginations of the plasma membrane in both the actin mutant cells and their protoplasts. These structures showed a very similar distribution to the actin patches detected by rhodamine phalloidin staining in the fluorescence microscope. A hypothesis is presented, explaining the role of actin patches/finger-like invaginations of the plasma membrane in the synthesis of beta-(1-->3)-D-glucan wall microfibrils in yeast cells.

Actins↗
PubMed2003

Cytoskeleton confinement and tension of red blood cell membranes.

We analyze theoretically both the static and dynamic fluctuation spectra of the red blood cell in a unified manner, using a simple model of the composite membrane. In this model, the two-dimensional spectrin network that forms the cytoskeleton is treated as a rigid shell, located at a fixed, average distance from the lipid bilayer. The cytoskeleton thereby confines both the static and dynamic fluctuations of the lipid bilayer. The sparse connections of the cytoskeleton and bilayer induce a surface tension, for wavelengths larger than the bilayer persistence length. The predictions of the model give a consistent account for both the wave vector and frequency dependence of the experimental data.

Animals↗
PubMed2003

Enhanced gravitropism of roots with a disrupted cap actin cytoskeleton.

The actin cytoskeleton has been proposed to be a major player in plant gravitropism. However, understanding the role of actin in this process is far from complete. To address this problem, we conducted an analysis of the effect of Latrunculin B (Lat B), a potent actin-disrupting drug, on root gravitropism using various parameters that included detailed curvature kinetics, estimation of gravitropic sensitivity, and monitoring of curvature development after extended clinorotation. Lat B treatment resulted in a promotion of root curvature after a 90 degrees reorientation in three plant species tested. More significantly, the sensitivity of maize (Zea mays) roots to gravity was enhanced after actin disruption, as determined from a comparison of presentation time of Lat B-treated versus untreated roots. A short 10-min gravistimulus followed by extended rotation on a 1-rpm clinostat resulted in extensive gravitropic responses, manifested as curvature that often exceeded 90 degrees. Application of Lat B to the cap or elongation zone of maize roots resulted in the disruption of the actin cytoskeleton, which was confined to the area of localized Lat B application. Only roots with Lat B applied to the cap displayed the strong curvature responses after extended clinorotation. Our study demonstrates that disrupting the actin cytoskeleton in the cap leads to the persistence of a signal established by a previous gravistimulus. Therefore, actin could function in root gravitropism by providing a mechanism to regulate the proliferation of a gravitropic signal originating from the cap to allow the root to attain its correct orientation or set point angle.

Actins↗
PubMed1996

Failed antigen presentation after UVB radiation correlates with modifications of Langerhans cell cytoskeleton.

Acute low-dose ultraviolet B radiation (UVR) impairs contact hypersensitivity (CH) induction in genetically defined strains of mice by a mechanism triggered by cis-urocanic acid (UCA) and dependent upon tumor necrosis factor-alpha (TNF-alpha). UVR, TNF-alpha, and cis-UCA cause similar morphologic changes among Langerhans cells, which spawns the speculation that UVR impairs CH induction in part by altering the Langerhans cell cytoskeleton. To examine this speculation, we studied the expression of vimentin in Langerhans cells after treatment with UVR, TNF-alpha, and cis-UCA. All treatments caused a reduction in expression of vimentin within the cytoplasm of Langerhans cells. Because partial loss of detectable vimentin may correlate with cytoskeletal disruption, we evaluated the effects of vinblastine, an agent that disrupts the cytoskeleton by disassembling microtubules, on Langerhans cell density and morphology. Epicutaneous treatment with vinblastine caused a reduction in Langerhans cell density, a loss of dendrites, and a reduction in vimentin expression. When dinitrofluorobenzene was painted on vinblastine-treated skin of BALB/c or C3H/HeN mice, only feeble CH was induced. Consequently, we propose that UVR prevents CH induction in susceptible mice by disrupting the cytoskeleton of Langerhans cells, thereby preventing them from carrying out their crucial role as antigen-presenting cells.

Animals↗
PubMed2006

Atomic force microscopy imaging of actin cortical cytoskeleton of Xenopus laevis oocyte.

In this study we report an atomic force microscopy (AFM) investigation of the actin cortical cytoskeleton of Xenopus laevis oocytes. Samples consisted of inside-out orientated plasma membrane patches of X. laevis oocytes with overhanging cytoplasmic material. They were spread on a freshly cleaved mica surface, subsequently treated with Triton X-100 detergent and chemically fixed. The presence of actin fibres in oocyte patches was proved by fluorescence microscopy imaging. Contact mode AFM imaging was performed in air in constant force conditions. Reproducible high-resolution AFM images of a filamentous structure were obtained. The filamentous structure was identified as an actin cortical cytoskeleton, investigating its disaggregation induced by cytochalasin D treatment. The thinnest fibres showed a height of 7 nm in accordance with the diameter of a single actin microfilament. The results suggest that AFM imaging can be used for the high-resolution study of the actin cortical cytoskeleton of the X. laevis oocyte and its modifications mediated by the action of drugs and toxins.

Actins↗
PubMed2006

Identification of plant cytoskeleton-interacting proteins by screening for actin stress fiber association in mammalian fibroblasts.

Taking advantage of the high conservation of the cytoskeleton building blocks actin and tubulin between plant and animal kingdoms, we developed a functional genomic screen for the isolation of new plant cytoskeleton-binding proteins that uses a mammalian cell expression system. A yellow fluorescent protein (YFP)-fusion cDNA library from Arabidopsis was inserted into rat fibroblasts and screened for fluorescent chimeras localizing to cytoskeletal structures. The high-throughput screen was performed by an automated microscope. An initial set of candidate genes identified in the screen was isolated, sequenced, the full-length cDNAs were synthesized by RT-PCR and tested by biochemical approaches to verify the ability of the genes to bind actin directly. Alternatively, indirect binding via interaction with other actin-binding proteins was studied. The full-length cDNAs were transferred back to plants as YFP chimeras behind the CAMV-35S promoter. We give here two examples of new plant cytoskeletal proteins identified in the pilot screen. ERD10, a member of the dehydrin family of proteins, was localized to actin stress fibers in rat fibroblasts. Its direct binding to actin filaments was confirmed by several biochemical approaches. Touch-induced calmodulin-like protein, TCH2, was also localized to actin stress fibers in fibroblasts, but was unable to bind actin filaments directly in vitro. Nevertheless, it did bind to the IQ domains of Arabidopsis myosin VIII in a calcium-dependent manner. Further evidence for a cytoskeletal function of ERD10 was obtained in planta; GFP-ERD10 was able to protect the actin cytoskeleton from latrunculin-mediated disruption in Nicotiana benthamiana leaves.

Actins↗
PubMed1992

Disruption of the cytoskeleton-extracellular matrix linkage promotes the accumulation of plasminogen activators in F9 derived parietal endoderm.

When F9 teratocarcinoma cells are treated with retinoic acid plus cyclic AMP (RACF9) they differentiate into parietal endoderm. Differentiation is accompanied by the acquisition of substrate adhesion sites and a change in the pattern of gene expression, including the synthesis of tissue-type plasminogen activator (tPA). We demonstrate here that dihydrocytochalasin B (DHCB) treatment of differentiating F9 cells prevents the assembly of a structured actin cytoskeleton and generates a more rounded and stellate cell morphology. This morphological change is accompanied by the accumulation of the usually visceral endoderm-specific marker urokinase-type plasminogen activator (uPA) and an increase in tPA levels in comparison to untreated RACF9 controls. The increase in tPA accumulation is preceded by an increase in tPA mRNA levels. These effects are reversible, with a lag, when DHCB is removed, and PA accumulation can be stimulated within 24 h when differentiated cells are exposed to DHCB. Exposure to the microtubule disrupting agent colchicine has no effect on uPA or tPA accumulation. In addition, antibody directed against the beta 1 integrin subunit can also specifically elicit increased PA production. Thus disturbing the cytoskeleton and cytoskeleton associated substrate adhesions promotes PA accumulation.

Actins↗