latrunculin-b and jasplakinolide

Sexual reproduction in higher plants uses pollination, involving interactions between pollen and pistil. Self-incompatibility (SI) prevents self-fertilization, providing an important mechanism to promote outbreeding. SI is controlled by the S-locus; discrimination occurs between incompatible pollen, which is rejected, while compatible pollen can achieve fertilization. In Papaver rhoeas, S proteins encoded by the pistil part of the S-locus interact with incompatible pollen to effect rapid inhibition of tip growth. This self-incompatible interaction triggers a Ca(2+)-dependent signalling cascade. SI-specific events triggered in incompatible pollen include rapid depolymerization of the actin cytoskeleton; phosphorylation of soluble inorganic pyrophosphatases, and activation of a MAPK. It has recently been shown that programmed cell death (PCD) is triggered by SI. This provides a precise mechanism for the specific destruction of 'self' pollen. Recent data providing evidence for SI-induced caspase-3-like protease activity, and the involvement of actin depolymerization and MAPK activation in SI-mediated PCD will be discussed. These studies not only significantly advance our understanding of the mechanisms involved in SI, but also contribute to our understanding of functional links between signalling components and initiation of PCD in a plant cell. Recent data demonstrating SI-mediated modification of soluble inorganic pyrophosphatases are also described.

Topics: Actins; Bridged Bicyclo Compounds, Heterocyclic; Calcium Signaling; Caspase 3; Cell Death; Cytoskeleton; Depsipeptides; MAP Kinase Signaling System; Papaver; Pollen; Pollination; Thiazolidines

Superimposition of force fluctuations on contracted tracheal smooth muscle (TSM) has been used to simulate normal breathing. Breathing has been shown to reverse lung resistance of individuals without asthma and animals given methacholine to contract their airways; computed tomography scans also demonstrated bronchial dilation after a deep inhalation in normal volunteers. This reversal of airway resistance and bronchial constriction are absent (or much diminished) in individuals with asthma. Many studies have demonstrated that superimposition of force oscillations on contracted airway smooth muscle results in substantial smooth muscle lengthening. Subsequent studies have shown that this force fluctuation-induced relengthening (FFIR) is a physiologically regulated phenomenon. We hypothesized that actin filament length in the smooth muscle of the airways regulates FFIR of contracted tissues. We based this hypothesis on the observations that bovine TSM strips contracted using acetylcholine (ACh) demonstrated amplitude-dependent FFIR that was sensitive to mitogen-activated protein kinase (p38 MAPK) inhibition- an upstream regulator of actin filament assembly. We demonstrated latrunculin B (sequesters actin monomers thus preventing their assimilation into filaments resulting in shorter filaments) greatly increases FFIR and jasplakinolide (an actin filament stabilizer) prevents the effects of latrunculin B incubation on strips of contracted canine TSM. We suspect that p38 MAPK inhibition and latrunculin B predispose to shorter actin filaments. These studies suggest that actin filament length may be a key determinant of airway smooth muscle relengthening and perhaps breathing-induced reversal of agonist-induced airway constriction.

Topics: Acetylcholine; Actin Cytoskeleton; Animals; Asthma; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Humans; Mitogen-Activated Protein Kinases; Muscle Contraction; Muscle, Smooth; Myosins; Stress, Mechanical; Thiazoles; Thiazolidines

Chromosome congression and segregation have been widely known to be coordinated by the function of the dynamic spindle microtubules. But recent work suggests that oocytes may employ a unique actin-dependent mechanism of chromosome delivery to the spindle.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Chromosome Segregation; Depsipeptides; Models, Biological; Nocodazole; Oocytes; Phalloidine; Spindle Apparatus; Starfish; Thiazoles; Thiazolidines

To investigate plasmodesmata (PD) function, a useful technique is to monitor the effect on cell-to-cell transport of applying an inhibitor of a physiological process, protein, or other cell component of interest. Changes in PD transport can then be monitored in one of several ways, most commonly by measuring the cell-to-cell movement of fluorescent tracer dyes or of free fluorescent proteins. Effects on PD structure can be detected in thin sections of embedded tissue observed using an electron microscope, most commonly a Transmission Electron Microscope (TEM). This chapter outlines commonly used inhibitors, methods for treating different tissues, how to detect altered cell-to-cell transport and PD structure, and important caveats.

Topics: Actins; Arabidopsis; Biological Transport; Bridged Bicyclo Compounds, Heterocyclic; Cytochalasin B; Cytotoxins; Depsipeptides; Fixatives; Fluorescent Dyes; Gene Expression; Green Fluorescent Proteins; Image Processing, Computer-Assisted; Microinjections; Microscopy, Electron, Transmission; Microscopy, Fluorescence; Microtomy; Phalloidine; Plant Roots; Plasmodesmata; Profilins; Recombinant Fusion Proteins; Thiazolidines; Tissue Fixation; Tradescantia

Nucleation-promoting factors (NPFs) control the spatio-temporal activity of Arp2/3 complex in cells]. Thus, WASP and the WAVE complex direct the formation of branched actin networks at the leading edge during cell motility and endo/exocytosis, whereas the WASH complex is involved in endosomal transport. Less understood are WHAMM and JMY, two NPFs with similar domain architecture. JMY is found in the nucleus and the cytosol and is involved in transcriptional regulation, cell motility, and trans-Golgi transport. WHAMM was reported to bind microtubules and to be involved in ER to cis-Golgi transport. Here, we show that WHAMM directs the activity of Arp2/3 complex for autophagosome biogenesis through an actin-comet tail motility mechanism. Macroautophagy--the process by which cytosolic material is engulfed into autophagosomes for degradation and/or recycling--was recently shown to involve actin, but the mechanism is unknown. We found that WHAMM forms puncta that colocalize and comigrate with the autophagy markers LC3, DFCP1, and p62 through a WHAMM-dependent actin-comet tail mechanism. Under starvation, WHAMM and actin are observed at the interface between neighboring autophagosomes, whose number and size increase with WHAMM expression. Interfering with actin polymerization, inhibiting Arp2/3 complex, knocking down WHAMM, or blocking its interaction with Arp2/3 complex through mutagenesis all inhibit comet tail formation and reduce the size and number of autophagosomes. Finally, JMY shows similar localization to WHAMM and could be involved in similar processes. These results reveal a link between Arp2/3-complex-dependent actin assembly and autophagy.

Topics: Actin-Related Protein 2-3 Complex; Actins; Autophagy; Bridged Bicyclo Compounds, Heterocyclic; Calnexin; Cell Line; Comet Assay; Depsipeptides; Dynamic Light Scattering; Endoplasmic Reticulum; Green Fluorescent Proteins; Humans; Luminescent Proteins; Membrane Proteins; Microtubule-Associated Proteins; Models, Molecular; Nocodazole; Phagosomes; Protein Structure, Tertiary; Red Fluorescent Protein; SEC Translocation Channels; Thiazolidines

Cancer cells typically demonstrate altered morphology during the various stages of disease progression as well as metastasis. While much is known about how altered cell morphology in cancer is a result of genetic regulation, less is known about how changes in cell morphology affect cell function by influencing gene expression. In this study, we altered cell morphology in different types of cancer cells by disrupting the actin cytoskeleton or by modulating attachment and observed a rapid up-regulation of growth differentiation factor 15 (GDF15), a member of the transforming growth factor-beta (TGF-β) super-family. Strikingly, this up-regulation was sustained as long as the cell morphology remained altered but was reversed upon allowing cell morphology to return to its typical configuration. The potential significance of these findings was examined in vivo using a mouse model: a small number of cancer cells grown in diffusion chambers that altered morphology increased mouse serum GDF15. Taken together, we propose that during the process of metastasis, cancer cells experience changes in cell morphology, resulting in the increased production and secretion of GDF15 into the surrounding environment. This indicates a possible relationship between serum GDF15 levels and circulating tumor cells may exist. Further investigation into the exact nature of this relationship is warranted.

Topics: Actin Cytoskeleton; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Adhesion; Cell Shape; Depsipeptides; Gene Expression Regulation, Neoplastic; Growth Differentiation Factor 15; HCT116 Cells; Humans; Mice, Nude; Neoplasm Metastasis; Neoplasms; Neoplastic Cells, Circulating; RNA, Messenger; Thiazolidines; Time Factors; Tumor Microenvironment; Up-Regulation

Multiple cellular events like dynamic actin reorganization and hydrogen peroxide (H(2)O(2)) production were demonstrated to be involved in abscisic acid (ABA)-induced stomatal closure. However, the relationship between them as well as the underlying mechanisms remains poorly understood. Here, we showed that H(2)O(2) generation is indispensable for ABA induction of actin reorganization in guard cells of Arabidopsis that requires the presence of ARP2/3 complex. H(2)O(2) -induced stomatal closure was delayed in the mutants of arpc4 and arpc5, and the rate of actin reorganization was slowed down in arpc4 and arpc5 in response to H(2)O(2), suggesting that ARP2/3-mediated actin nucleation is required for H(2)O(2) -induced actin cytoskeleton remodelling. Furthermore, the expression of H(2)O(2) biosynthetic related gene AtrbohD and the accumulation of H(2)O(2) was delayed in response to ABA in arpc4 and arpc5, demonstrating that misregulated actin dynamics affects H(2)O(2) production upon ABA treatment. These results support a possible causal relation between the production of H(2)O(2) and actin dynamics in ABA-mediated guard cell signalling: ABA triggers H(2)O(2) generation that causes the reorganization of the actin cytoskeleton partially mediated by ARP2/3 complex, and ARP2/3 complex-mediated actin dynamics may feedback regulate H(2)O(2) production.

Topics: Abscisic Acid; Actin Cytoskeleton; Actin-Related Protein 2-3 Complex; Actins; Arabidopsis; Arabidopsis Proteins; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Hydrogen Peroxide; Models, Biological; Mutation; Plant Stomata; Polymerization; Protein Subunits; Thiazolidines

Polarized migrating cells display signal transduction events, such as activation of phosphatidylinositol 3-kinase (PI3K) and Scar/Wave, and respond more readily to chemotactic stimuli at the leading edge. We sought to determine the basis of this polarized sensitivity. Inhibiting actin polymerization leads to uniform sensitivity. However, when human neutrophils were "stalled" by simultaneously blocking actin and myosin dynamics, they maintained the gradient of responsiveness to chemoattractant and also displayed noise-driven PIP3 flashes on the basal membrane, localized toward the front. Thus, polarized sensitivity does not require migration or cytoskeletal dynamics. The threshold for response is correlated with the static F-actin distribution, but not cell shape or volume changes, membrane fluidity, or the preexisting distribution of PI3K. The kinetics of responses to temporal and spatial stimuli were consistent with the local excitation global inhibition model, but the overall direction of the response was biased by the internal axis of polarity.

Topics: Actins; Amides; Bridged Bicyclo Compounds, Heterocyclic; Cell Polarity; Cell Shape; Cell Size; Cells, Immobilized; Chemotactic Factors; Chemotaxis; Cytoskeleton; Depsipeptides; HL-60 Cells; Humans; Kinetics; Membrane Fluidity; Microscopy, Fluorescence; Neutrophils; Protein Structure, Tertiary; Proto-Oncogene Proteins c-akt; Pyridines; Thiazolidines

We identify Xenopus ADF/cofilin (XAC) and its activator, Slingshot phosphatase (XSSH), as key regulators of actin dynamics essential for spindle microtubule assembly during Xenopus oocyte maturation. Phosphorylation of XSSH at multiple sites within the tail domain occurs just after germinal vesicle breakdown (GVBD) and is accompanied by dephosphorylation of XAC, which was mostly phosphorylated in immature oocytes. This XAC dephosphorylation after GVBD is completely suppressed by latrunculin B, an actin monomer-sequestering drug. On the other hand, jasplakinolide, an F-actin-stabilizing drug, induces dephosphorylation of XAC. Effects of latrunculin B and jasplakinolide are reconstituted in cytostatic factor-arrested extracts (CSF extracts), and XAC dephosphorylation is abolished by depletion of XSSH from CSF extracts, suggesting that XSSH functions as an actin filament sensor to facilitate actin filament dynamics via XAC activation. Injection of anti-XSSH antibody, which blocks full phosphorylation of XSSH after GVBD, inhibits both meiotic spindle formation and XAC dephosphorylation. Coinjection of constitutively active XAC with the antibody suppresses this phenotype. Treatment of oocytes with jasplakinolide also impairs spindle formation. These results strongly suggest that elevation of actin dynamics by XAC activation through XSSH phosphorylation is required for meiotic spindle assembly in Xenopus laevis.

Topics: Actin Cytoskeleton; Actin Depolymerizing Factors; Actins; Animals; Binding Sites; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Electrophoresis, Polyacrylamide Gel; Female; Immunoblotting; Meiosis; Microscopy, Fluorescence; Mutation; Oocytes; Phosphoprotein Phosphatases; Phosphorylation; Spindle Apparatus; Thiazolidines; Xenopus laevis; Xenopus Proteins

Electroporation is a physical method of transferring molecules into cells and tissues. It takes advantage of the transient permeabilization of the cell membrane induced by electric field pulses, which gives hydrophilic molecules access to the cytoplasm. This method offers high transfer efficiency for small molecules that freely diffuse through electrically permeabilized membranes. Larger molecules, such as plasmid DNA, face several barriers (plasma membrane, cytoplasmic crowding, and nuclear envelope), which reduce transfection efficiency and engender a complex mechanism of transfer. Our work provides insight into the way electrotransferred DNA crosses the cytoplasm to reach the nucleus. For this purpose, single-particle tracking experiments of fluorescently labeled DNA were performed. Investigations were focused on the involvement of the cytoskeleton using drugs disrupting or stabilizing actin and tubulin filaments as the two relevant cellular networks for particle transport. The analysis of 315 movies (~4,000 trajectories) reveals that DNA is actively transported through the cytoskeleton. The large number of events allows a statistical quantification of the DNA motion kinetics inside the cell. Disruption of both filament types reduces occurrence and velocities of active transport and displacements of DNA particles. Interestingly, stabilization of both networks does not enhance DNA transport.

Topics: Actins; Active Transport, Cell Nucleus; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane Permeability; Cell Nucleus; Cell Tracking; CHO Cells; Cricetulus; Cytoplasm; Cytoskeleton; Depsipeptides; Electroporation; Humans; Microscopy, Fluorescence; Paclitaxel; Plasmids; Thiazolidines; Transfection; Tubulin

The relationship between ordered plasma membrane nanodomains, known as lipid rafts, and actin filaments is the focus of this study. Plasma membrane order was followed in live cells at 37°C using laurdan and di-4-ANEPPDHQ to report on lipid packing. Disrupting actin polymerisation decreased the fraction of ordered domains, which strongly argue that unstimulated cells have a basal level of ordered domains. Stabilising actin filaments had the opposite effect and increased the proportion of ordered domains. Decreasing the plasma membrane level of 4-phosphate-inositides lowers the number of attachment points for actin filaments and reduced the proportion of ordered domains. Aggregation of plasma membrane molecules, both lipid raft and non-lipid raft markers, lead to the formation of ordered domains. The increase in ordered domains was correlated with an increase in actin filaments just beneath the plasma membrane. In live cell plasma membrane blebs, which are detached from the underlying actin filaments, the fraction of ordered domains was low and GM1 could not be patched to form ordered domains. We conclude that ordered domains form when actin filaments attach to the plasma membrane. This downplays lipid-lipid interactions as the main driving force behind the formation of ordered membrane domains in vivo, giving greater prominence to membrane-intracellular filament interactions.

Topics: Actin Cytoskeleton; Actins; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane; Cell Survival; Depsipeptides; Humans; Image Processing, Computer-Assisted; Jurkat Cells; K562 Cells; Lipid Bilayers; Lipids; Membrane Microdomains; Protein Structure, Tertiary; Spectrophotometry; T-Lymphocytes; Temperature; Thiazolidines; Unilamellar Liposomes

Latrunculin depolymerizes and jasplakinolide polymerizes β-cell actin microfilaments. Both increase insulin secretion when Ca(2+) enters β-cells during depolarization by glucose, sulfonylureas or potassium. Mouse islets were held hyperpolarized with diazoxide, and stimulated with acetylcholine to test the role of microfilaments in insulin secretion triggered by intracellular Ca(2+) mobilization and store-operated Ca(2+) entry (SOCE). Jasplakinolide slightly attenuated Ca(2+) mobilization and did not affect SOCE, but consistently inhibited the attending insulin secretion. Latrunculin did not affect Ca(2+) changes induced by acetylcholine, but consistently increased insulin secretion, its effect being larger in response to Ca(2+) entry than to Ca(2+) mobilization. Microfilaments have thus a distinct impact on exocytosis of insulin granules depending on the source of triggering Ca(2+).

Topics: Acetylcholine; Actin Cytoskeleton; Animals; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Depsipeptides; Diazoxide; Exocytosis; Female; Insulin; Insulin Secretion; Islets of Langerhans; Mice; Potassium Chloride; Thiazolidines

Changes in actin dynamics represent the primary response of the plant cell to extracellular signaling. Recent studies have now revealed that actin remodeling is involved in abiotic stress tolerance in plants. In our current study, the relationship between the changes in actin dynamics and the reactive oxygen species (ROS) level at the initial stages of salt stress was investigated in the elongation zone of the Arabidopsis root tip. We found that a 200 mM NaCl treatment disrupted the dynamics of the actin filaments within 10 min and increased the ROS levels in the elongation zone cells of the Arabidopsis root tip. We further found that the NADPH oxidase activity inhibitor, diphenyleneiodonium, treatment blocked this ROS increase under salt stress conditions. The roles of actin dynamics and the NADPH oxidases in ROS generation were further analyzed using the actin-specific agents, latrunculin B (Lat-B) and jasplakinolide (Jasp), and mutants of Arabidopsis NADPH oxidase AtrbohC. Lat-B and Jasp promote actin depolymerization and polymerization, respectively, and both were found to enhance the ROS levels following NaCl treatment. However, this response was abolished in the atrbohC mutants. Our present results thus demonstrate that actin dynamics are involved in regulating the ROS level in Arabidopsis root under salt stress conditions.. Salt stress disrupts the dynamics of the actin filaments in Arabidopsis in the short term which are involved in regulating the ROS levels that arise under salt stress conditions via the actions of the AtrbohC.

Topics: Actins; Arabidopsis; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Gene Expression Regulation, Plant; Meristem; NADPH Oxidases; Plant Roots; Reactive Oxygen Species; Sodium Chloride; Stress, Physiological; Thiazolidines

Secretion of vesicular contents by exocytosis is a fundamental cellular process. Increasing evidence suggests that post-fusion events play an important role in determining the composition and quantity of the secretory output. In particular, regulation of fusion pore dilation and closure is considered a key regulator of the post-fusion phase. However, depending on the nature of the cargo, additional mechanisms might be essential to facilitate effective release. We have recently described that in alveolar type II (ATII) cells, lamellar bodies (LBs), which are secretory vesicles that store lung surfactant, are coated with actin following fusion with the plasma membrane. Surfactant, a lipoprotein complex, does not readily diffuse out of fused LBs following opening and dilation of the fusion pore. Using fluorescence microscopy, atomic force microscopy and biochemical assays, we present evidence that actin coating and subsequent contraction of the actin coat is essential to facilitate surfactant secretion. Latrunculin B prevents actin coating of fused LBs and inhibits surfactant secretion almost completely. Simultaneous imaging of the vesicle membrane and the actin coat revealed that contraction of the actin coat compresses the vesicle following fusion. This leads to active extrusion of vesicle contents. Initial actin coating of fused vesicles is dependent on activation of Rho and formin-dependent actin nucleation. Actin coat contraction is facilitated by myosin II. In summary, our data suggest that fusion pore opening and dilation itself is not sufficient for release of bulky vesicle cargos and that active extrusion mechanisms are required.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Extracellular Space; Fetal Proteins; Fluorescence Recovery After Photobleaching; Formins; Membrane Fusion; Microfilament Proteins; Microscopy, Atomic Force; Myosin Type II; Nuclear Proteins; Pulmonary Surfactants; Rats; Rats, Sprague-Dawley; rhoA GTP-Binding Protein; Secretory Vesicles; Thiazolidines

Polar auxin transport, which depends on polarized subcellular distribution of AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX) influx carriers and PIN-FORMED (PIN) efflux carriers, mediates various processes of plant growth and development. Endosomal recycling of PIN1 is mediated by an adenosine diphosphate (ADP)ribosylation factor (ARF)-GTPase exchange factor protein, GNOM. However, the mediation of auxin influx carrier recycling is poorly understood. Here, we report that overexpression of OsAGAP, an ARF-GTPase-activating protein in rice, stimulates vesicle transport from the plasma membrane to the Golgi apparatus in protoplasts and transgenic plants and induces the accumulation of early endosomes and AUX1. AUX1 endosomes could partially colocalize with FM4-64 labeled early endosome after actin disruption. Furthermore, OsAGAP is involved in actin cytoskeletal organization, and its overexpression tends to reduce the thickness and bundling of actin filaments. Fluorescence recovery after photobleaching analysis revealed exocytosis of the AUX1 recycling endosome was not affected in the OsAGAP overexpression cells, and was only slightly promoted when the actin filaments were completely disrupted by Lat B. Thus, we propose that AUX1 accumulation in the OsAGAP overexpression and actin disrupted cells may be due to the fact that endocytosis of the auxin influx carrier AUX1 early endosome was greatly promoted by actin cytoskeleton disruption.

Topics: Actins; ADP-Ribosylation Factors; Arabidopsis; Bacterial Proteins; Bridged Bicyclo Compounds, Heterocyclic; Cytoskeleton; Depsipeptides; Endocytosis; Endosomes; Fluorescence Recovery After Photobleaching; GTPase-Activating Proteins; Luminescent Proteins; Models, Biological; Oryza; Plant Proteins; Plant Roots; Plants, Genetically Modified; Protein Transport; Protoplasts; Recombinant Fusion Proteins; Subcellular Fractions; Thiazolidines; trans-Golgi Network

In eukaryotic cells, the actin and microtubule (MT) cytoskeletal networks are dynamic structures that organize intracellular processes and facilitate their rapid reorganization. In plant cells, actin filaments (AFs) and MTs are essential for cell growth and morphogenesis. However, dynamic interactions between these two essential components in live cells have not been explored. Here, we use spinning-disc confocal microscopy to dissect interaction and cooperation between cortical AFs and MTs in Arabidopsis thaliana, utilizing fluorescent reporter constructs for both components. Quantitative analyses revealed altered AF dynamics associated with the positions and orientations of cortical MTs. Reorganization and reassembly of the AF array was dependent on the MTs following drug-induced depolymerization, whereby short AFs initially appeared colocalized with MTs, and displayed motility along MTs. We also observed that light-induced reorganization of MTs occurred in concert with changes in AF behavior. Our results indicate dynamic interaction between the cortical actin and MT cytoskeletons in interphase plant cells.

Topics: Actin Cytoskeleton; Animals; Antineoplastic Agents; Arabidopsis; Bridged Bicyclo Compounds, Heterocyclic; Cytoskeleton; Depsipeptides; Microtubules; Plant Cells; Plant Proteins; Recombinant Fusion Proteins; Thiazolidines

The actin cytoskeleton is regulated by factors that influence polymer assembly, disassembly, and network rearrangement. Drugs that inhibit these events have been used to test the role of actin dynamics in a wide range of cellular processes. Previous methods of arresting actin rearrangements take minutes to act and work well in some contexts, but can lead to significant actin reorganization in cells with rapid actin dynamics, such as neutrophils. In this paper, we report a pharmacological cocktail that not only arrests actin dynamics but also preserves the structure of the existing actin network in neutrophil-like HL-60 cells, human fibrosarcoma HT1080 cells, and mouse NIH 3T3 fibroblast cells. Our cocktail induces an arrest of actin dynamics that initiates within seconds and persists for longer than 10 min, during which time cells maintain their responsivity to external stimuli. With this cocktail, we demonstrate that actin dynamics, and not simply morphological polarity or actin accumulation at the leading edge, are required for the spatial persistence of Rac activation in HL-60 cells. Our drug combination preserves the structure of the existing cytoskeleton while blocking actin assembly, disassembly, and rearrangement, and should prove useful for investigating the role of actin dynamics in a wide range of cellular signaling contexts.

Topics: Actins; Amides; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Polarity; Cell Shape; Depsipeptides; Enzyme Activation; Fluorescence Recovery After Photobleaching; HL-60 Cells; Humans; Mice; Microscopy, Fluorescence; NIH 3T3 Cells; Protein Multimerization; Pyridines; rac GTP-Binding Proteins; Thiazolidines; Time-Lapse Imaging

Myofibroblasts typically appear in the myocardium after insults to the heart like mechanical overload and infarction. Apart from contributing to fibrotic remodeling, myofibroblasts induce arrhythmogenic slow conduction and ectopic activity in cardiomyocytes after establishment of heterocellular electrotonic coupling in vitro. So far, it is not known whether α-smooth muscle actin (α-SMA) containing stress fibers, the cytoskeletal components that set myofibroblasts apart from resident fibroblasts, are essential for myofibroblasts to develop arrhythmogenic interactions with cardiomyocytes.. We investigated whether pharmacological ablation of α-SMA containing stress fibers by actin-targeting drugs affects arrhythmogenic myofibroblast-cardiomyocyte cross-talk.. Experiments were performed with patterned growth cell cultures of neonatal rat ventricular cardiomyocytes coated with cardiac myofibroblasts. The preparations exhibited slow conduction and ectopic activity under control conditions. Exposure to actin-targeting drugs (Cytochalasin D, Latrunculin B, Jasplakinolide) for 24 hours led to disruption of α-SMA containing stress fibers. In parallel, conduction velocities increased dose-dependently to values indistinguishable from cardiomyocyte-only preparations and ectopic activity measured continuously over 24 hours was completely suppressed. Mechanistically, antiarrhythmic effects were due to myofibroblast hyperpolarization (Cytochalasin D, Latrunculin B) and disruption of heterocellular gap junctional coupling (Jasplakinolide), which caused normalization of membrane polarization of adjacent cardiomyocytes.. The results suggest that α-SMA containing stress fibers importantly contribute to myofibroblast arrhythmogeneicity. After ablation of this cytoskeletal component, cells lose their arrhythmic effects on cardiomyocytes, even if heterocellular electrotonic coupling is sustained. The findings identify α-SMA containing stress fibers as a potential future target of antiarrhythmic therapy in hearts undergoing structural remodeling.

Topics: Actins; Action Potentials; Animals; Animals, Newborn; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Bridged Bicyclo Compounds, Heterocyclic; Cell Communication; Cell Shape; Cells, Cultured; Coculture Techniques; Cytochalasin D; Depsipeptides; Dose-Response Relationship, Drug; Gap Junctions; Myocytes, Cardiac; Myofibroblasts; Phenotype; Rats; Rats, Wistar; Stress Fibers; Thiazolidines; Time Factors

Aorta organ culture has been widely used as an ex vivo model for studying vessel pathophysiology. Recent studies show that the vascular smooth muscle cells (VSMCs) in organ culture undergo drastic dedifferentiation within the first few hours (termed early phenotypic modulation). Loss of tensile stress to which aorta is subject in vivo is the cause of this early phenotypic modulation. However, no underlying molecular mechanism has been discovered thus far. The purpose of the present study is to identify intracellular signals involved in the early phenotypic modulation of VSMC in organ culture. We find that the drastic VSMC dedifferentiation is accompanied by accelerated actin cytoskeleton dynamics and downregulation of SRF and myocardin. Among the variety of signal pathways examined, increasing actin polymerization by jasplakinolide is the only one hindering VSMC dedifferentiation in organ culture. Moreover, jasplakinolide reverses actin dynamics during organ culture. Latrunculin B (disrupting actin cytoskeleton) and jasplakinolide respectively suppressed and enhanced the expression of VSMC markers, SRF, myocardin, and CArG-box-mediated SMC promoters in PAC1, a VSMC line. These results identify actin cytoskeleton degradation as a major intracellular signal for loss of tensile stress-induced early phenotypic modulation of VSMC in organ culture. This study suggests that disrupting actin cytoskeleton integrity may contribute to the pathogenesis of vascular diseases.

Topics: Actins; Animals; Biomarkers; Bridged Bicyclo Compounds, Heterocyclic; Cell Dedifferentiation; Cytoskeleton; Depsipeptides; Down-Regulation; ets-Domain Protein Elk-4; Mice; Mice, Inbred C57BL; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nuclear Proteins; Organ Culture Techniques; Phenotype; Stress, Mechanical; Thiazolidines; Trans-Activators

The cytoskeleton is an important factor in the functional and structural adaption of cells to mechanical forces. In this study we investigated the impact of microtubules and the acto-myosin machinery on the kinetics of force-induced reorientation of NIH3T3 fibroblasts. These cells were subjected to uniaxial stretching forces that are known to induce cellular reorientation perpendicular to the stretch direction. We found that disruption of filamentous actin using cytochalasin D and latrunculin B as well as an induction of a massive unpolarized actin polymerization by jasplakinolide, inhibited the stretch-induced reorientation. Similarly, blocking of myosin II activity abolished the stretch-induced reorientation of cells but, interestingly, increased their motility under stretching conditions in comparison to myosin-inhibited nonstretched cells. Investigating the contribution of microtubules to the cellular reorientation, we found that, although not playing a significant role in reorientation itself, microtubule stability had a significant impact on the kinetics of this event. Overall, we conclude that acto-myosin, together with microtubules, regulate the kinetics of force-induced cell reorientation.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Movement; Cell Polarity; Cells, Cultured; Cytochalasin D; Depsipeptides; Heterocyclic Compounds, 4 or More Rings; Kinetics; Mice; Microtubules; NIH 3T3 Cells; Nocodazole; Paclitaxel; Structure-Activity Relationship; Thiazolidines

Mitochondria are dynamic organelles that move along actin filaments, and serve as calcium stores in plant cells. The positioning and dynamics of mitochondria depend on membrane-cytoskeleton interactions, but it is not clear whether microfilament cytoskeleton has a direct effect on mitochondrial function and Ca2+ storage. Therefore, we designed a series of experiments to clarify the effects of actin filaments on mitochondrial Ca2+ storage, cytoplasmic Ca2+ concentration ([Ca2+]c), and the interaction between mitochondrial Ca2+ and cytoplasmic Ca2+ in Arabidopsis root hairs.. In this study, we found that treatments with latrunculin B (Lat-B) and jasplakinolide (Jas), which depolymerize and polymerize actin filaments respectively, decreased membrane potential and Ca2+ stores in the mitochondria of Arabidopsis root hairs. Simultaneously, these treatments induced an instantaneous increase of cytoplasmic Ca2+, followed by a continuous decrease. All of these effects were inhibited by pretreatment with cyclosporin A (Cs A), a representative blocker of the mitochondrial permeability transition pore (mPTP). Moreover, we found there was a Ca2+ concentration gradient in mitochondria from the tip to the base of the root hair, and this gradient could be disrupted by actin-acting drugs.. Based on these results, we concluded that the disruption of actin filaments caused by Lat-B or Jas promoted irreversible opening of the mPTP, resulting in mitochondrial Ca2+ release into the cytoplasm, and consequent changes in [Ca2+]c. We suggest that normal polymerization and depolymerization of actin filaments are essential for mitochondrial Ca2+ storage in root hairs.

Topics: Actin Cytoskeleton; Arabidopsis; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Depsipeptides; Electrodes; Endoplasmic Reticulum; Fluoresceins; Fluorescence; Intracellular Space; Membrane Potential, Mitochondrial; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Permeability Transition Pore; Models, Biological; Plant Roots; Thiazolidines

In the human autoimmune blistering skin disease pemphigus vulgaris autoantibodies (PV-IgG), which are mainly directed against keratinocyte cell adhesion molecules desmoglein (Dsg) 3 and Dsg1, cause keratinocyte cell dissociation (acantholysis). Recent studies reported that loss of keratinocyte cell adhesion was accompanied by profound alterations of the actin cytoskeleton. Nevertheless, the relevance of actin reorganization in this process is unclear at present. In this study, we provide evidence for an important role of actin reorganization in pemphigus pathogenesis. In parallel to loss of cell adhesion and fragmentation of Dsg3 staining along cell borders, PV-IgG treatment resulted in striking changes in actin cytoskeleton organization. Moreover, in experiments using fluorescence recovery after photobleaching (FRAP), PV-IgG were detected to interfere with actin dynamics. Therefore, we investigated whether pharmacological manipulation of actin polymerization modulates pathogenic effects of PV-IgG. Pharmacological stabilization of actin filaments via jasplakinolide significantly blocked cell dissociation and Dsg3 fragmentation, whereas cytochalasin D-induced actin depolymerization strongly enhanced pathogenic effects of PV-IgG. To substantiate these findings, we studied whether the protective effects of Rho GTPases, which are potent regulators of the actin cytoskeleton and were shown to be involved in pemphigus pathogenesis, were dependent on modulation of actin dynamics. Cytotoxic necrotizing factor-1 (CNF-1)-mediated activation of Rho-GTPases enhanced the cortical junction-associated actin belt and blunted PV-IgG-induced cell dissociation. However, when actin polymerization was blocked under these conditions via addition of latrunculin B, the protective effects of CNF-1 were abrogated. Taken together, these experiments indicate that reorganization of cortical actin filaments is a critical step in PV-IgG-induced keratinocyte dissociation.

Topics: Actins; Autoantibodies; Bacterial Toxins; Bridged Bicyclo Compounds, Heterocyclic; Cell Adhesion; Cell Line; Cytochalasin D; Depsipeptides; Desmoglein 3; Enzyme Activation; Escherichia coli Proteins; Fluorescence Recovery After Photobleaching; Humans; Immunoglobulin G; Keratinocytes; Pemphigus; rho GTP-Binding Proteins; Thiazolidines; Time Factors

In Alzheimer's disease (AD), rod-like cofilin aggregates (cofilin-actin rods) and thread-like inclusions containing phosphorylated microtubule-associated protein (pMAP) tau form in the brain (neuropil threads), and the extent of their presence correlates with cognitive decline and disease progression. The assembly mechanism of these respective pathological lesions and the relationship between them is poorly understood, yet vital to understanding the causes of sporadic AD. We demonstrate that, during mitochondrial inhibition, activated actin-depolymerizing factor (ADF)/cofilin assemble into rods along processes of cultured primary neurons that recruit pMAP/tau and mimic neuropil threads. Fluorescence resonance energy transfer analysis revealed colocalization of cofilin-GFP (green fluorescent protein) and pMAP in rods, suggesting their close proximity within a cytoskeletal inclusion complex. The relationship between pMAP and cofilin-actin rods was further investigated using actin-modifying drugs and small interfering RNA knockdown of ADF/cofilin in primary neurons. The results suggest that activation of ADF/cofilin and generation of cofilin-actin rods is required for the subsequent recruitment of pMAP into the inclusions. Additionally, we were able to induce the formation of pMAP-positive ADF/cofilin rods by exposing cells to exogenous amyloid-beta (Abeta) peptides. These results reveal a common pathway for pMAP and cofilin accumulation in neuronal processes. The requirement of activated ADF/cofilin for the sequestration of pMAP suggests that neuropil thread structures in the AD brain may be initiated by elevated cofilin activation and F-actin bundling that can be caused by oxidative stress, mitochondrial dysfunction, or Abeta peptides, all suspected initiators of synaptic loss and neurodegeneration in AD.

Topics: Actin Depolymerizing Factors; Actins; Adenosine Triphosphate; Alzheimer Disease; Amino Acid Motifs; Amyloid beta-Peptides; Animals; Animals, Newborn; Antimycin A; Brain; Bridged Bicyclo Compounds, Heterocyclic; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cells, Cultured; Chick Embryo; Depsipeptides; Enzyme Inhibitors; Fluorescence Resonance Energy Transfer; Green Fluorescent Proteins; Humans; Hydrogen Peroxide; Ionophores; Neurites; Neurons; Organ Culture Techniques; Oxidants; p21-Activated Kinases; Peptide Fragments; Phosphorylation; Rats; RNA, Small Interfering; Serine; tau Proteins; Thiazolidines; Transfection

The actin cytoskeleton regulates exocytosis in all secretory cells. In neutrophils, Rac2 GTPase has been shown to control primary (azurophilic) granule exocytosis. In this report, we propose that Rac2 is required for actin cytoskeletal remodeling to promote primary granule exocytosis. Treatment of neutrophils with low doses (< or = 10 microM) of the actin-depolymerizing drugs latrunculin B (Lat B) or cytochalasin B (CB) enhanced both formyl peptide receptor- and Ca(2+) ionophore-stimulated exocytosis. Higher concentrations of CB or Lat B, or stabilization of F-actin with jasplakinolide (JP), inhibited primary granule exocytosis measured as myeloperoxidase release but did not affect secondary granule exocytosis determined by lactoferrin release. These results suggest an obligatory role for F-actin disassembly before primary granule exocytosis. However, lysates from secretagogue-stimulated neutrophils showed enhanced actin polymerization activity in vitro. Microscopic analysis showed that resting neutrophils contain significant cortical F-actin, which was redistributed to sites of primary granule translocation when stimulated. Exocytosis and actin remodeling was highly polarized when cells were primed with CB; however, polarization was reduced by Lat B preincubation, and both polarization and exocytosis were blocked when F-actin was stabilized with JP. Treatment of cells with the small molecule Rac inhibitor NSC23766 also inhibited actin remodeling and primary granule exocytosis induced by Lat B/fMLF or CB/fMLF, but not by Ca(2+) ionophore. Therefore, we propose a role for F-actin depolymerization at the cell cortex coupled with Rac-dependent F-actin polymerization in the cell cytoplasm to promote primary granule exocytosis.

Topics: Actins; Aminoquinolines; Bridged Bicyclo Compounds, Heterocyclic; Calcimycin; Calcium; Cytochalasin B; Cytoskeleton; Depsipeptides; Dose-Response Relationship, Drug; Enzyme Inhibitors; Exocytosis; Humans; Ionophores; Microscopy, Electron, Transmission; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Pyrimidines; rac GTP-Binding Proteins; RAC2 GTP-Binding Protein; Respiratory Burst; Secretory Vesicles; Thiazolidines; Time Factors

Shiga toxins (Stx), released into the intestinal lumen by enterohemorrhagic Escherichia coli (EHEC), are major virulence factors responsible for gastrointestinal and systemic illnesses. These pathologies are believed to be due to the action of the toxins on endothelial cells, which express the Stx receptor, the glycosphingolipid Gb3. To reach the endothelial cells, Stx must translocate across the intestinal epithelial monolayer. This process is poorly understood. We investigated Stx1 movement across the intestinal epithelial T84 cell model and the role of actin turnover in this transcytosis. We showed that changes in the actin cytoskeleton due to latrunculin B, but not cytochalasin D or jasplakinolide, significantly facilitate toxin transcytosis across T84 monolayers. This trafficking is transcellular and completely inhibited by tannic acid, a cell impermeable plasma membrane fixative. This indicates that actin turnover could play an important role in Stx1 transcellular transcytosis across intestinal epithelium in vitro. Since EHEC attachment to epithelial cells causes an actin rearrangement, this finding may be highly relevant to Stx-induced disease.

Topics: Actins; Biological Transport; Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Cytochalasin D; Depsipeptides; Dextrans; Epithelial Cells; Fluorescent Antibody Technique; Humans; Immunoblotting; Intestinal Mucosa; Shiga Toxin 1; Thiazolidines

Freeze-fracture electron microscopy (FFEM) indicates that aquaporin-4 (AQP4) water channels can assemble in cell plasma membranes in orthogonal arrays of particles (OAPs). We investigated the determinants and dynamics of AQP4 assembly in OAPs by tracking single AQP4 molecules labeled with quantum dots at an engineered external epitope. In several transfected cell types, including primary astrocyte cultures, the long N-terminal "M1" form of AQP4 diffused freely, with diffusion coefficient approximately 5 x 10(-10) cm(2)/s, covering approximately 5 microm in 5 min. The short N-terminal "M23" form of AQP4, which by FFEM was found to form OAPs, was relatively immobile, moving only approximately 0.4 microm in 5 min. Actin modulation by latrunculin or jasplakinolide did not affect AQP4-M23 diffusion, but deletion of its C-terminal postsynaptic density 95/disc-large/zona occludens (PDZ) binding domain increased its range by approximately twofold over minutes. Biophysical analysis of short-range AQP4-M23 diffusion within OAPs indicated a spring-like potential, with a restoring force of approximately 6.5 pN/microm. These and additional experiments indicated that 1) AQP4-M1 and AQP4-M23 isoforms do not coassociate in OAPs; 2) OAPs can be imaged directly by total internal reflection fluorescence microscopy; and 3) OAPs are relatively fixed, noninterconvertible assemblies that do not require cytoskeletal or PDZ-mediated interactions for formation. Our measurements are the first to visualize OAPs in live cells.

Topics: Amino Acid Sequence; Animals; Aquaporin 4; Bridged Bicyclo Compounds, Heterocyclic; Chlorocebus aethiops; COS Cells; Cytoskeleton; Depsipeptides; Epitopes; Freeze Fracturing; Microscopy, Fluorescence; Models, Biological; Molecular Sequence Data; Protein Conformation; Quantum Dots; Thiazolidines

Pharmacological agents were used to investigate the possible involvement of actin in signalling chains associated with abscisic acid (ABA)-induced ion release from the guard cell vacuole, a process which is absolutely essential for stomatal closure. Effects on the ABA-induced transient stimulation of tonoplast efflux were measured, using (86)Rb in isolated guard cells of Commelina communis, together with effects on stomatal apertures. In the response to 10 microm ABA (triggered by Ca(2+) influx rather than internal Ca(2+) release), jasplakinolide (stabilizing actin filaments) and latrunculin B (depolymerizing actin filaments) had opposite effects. Both closure and the vacuolar efflux transient were inhibited by jasplakinolide but enhanced by latrunculin B. At 10 microm ABA prevention of mitogen-activated protein (MAP) kinase activation by PD98059 partially inhibited closure and reduced the efflux transient. By contrast, latrunculin B inhibited the efflux transient at 0.1 microm ABA (involving internal Ca(2+) release rather than Ca(2+) influx). The results suggest that 10 microm ABA activates Ca(2+)-dependent vacuolar ion efflux via a Ca(2+)-permeable influx channel which is maintained closed by interaction with F-actin. A MAP kinase is also involved, in a chain similar to that postulated for Ca(2+)-dependent gene expression in cold acclimation.

Topics: Abscisic Acid; Actins; Arabidopsis; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Flavonoids; Ion Transport; Plant Leaves; Potassium; Rubidium; Signal Transduction; Thiazolidines; Time Factors; Vacuoles

Insulin-increased prolactin gene transcription in GH4 cells was enhanced by binding on fibronectin. This was mediated by receptor-like protein tyrosine phosphatase alpha, which activated Src, Rho, and phosphatidylinositol 3-kinase. It suggested that insulin signaling to gene transcription was partly dependent on actin rearrangement. This was confirmed through studies using inhibitors of actin treadmilling. Cytochalasin D, jasplakinolide, latrunculin B, and swinholide A altered the actin cytoskeleton of GH4 cells, as assessed by Alexa Fluor phalloidin staining, and inhibited insulin-increased prolactin gene transcription. These reagents did not affect the controls. Nor was it due to a gross defect of insulin signaling because activation/translocation of glycogen synthase kinase 3beta and mammalian target of rapamycin were not affected. Expression of wild-type and mutant actin treadmilling agents, Cdc42, TC10, neuronal Wiskott-Aldrich syndrome protein, and Nck, indicated that they were essential to insulin-increased prolactin gene expression, and suggested that activation of p21 associated kinase (PAK) might also be essential to this process. PAK expression also increased and PAK mutants decreased prolactin promoter activity in insulin-treated cells. The activation of PAK in the presence of inhibitors was also consistent with a role in activation of insulin-increased prolactin gene expression. Finally, small interfering RNA-mediated reduction of PAK decreased the effect of insulin on prolactin gene expression. Thus, it is likely that insulin activation of actin treadmilling through Cdc42/TC10 and neuronal Wiskott-Aldrich syndrome protein activates PAK and prolactin gene transcription.

Topics: Actins; Animals; Blotting, Western; Bridged Bicyclo Compounds, Heterocyclic; cdc42 GTP-Binding Protein; Cytochalasin D; Depsipeptides; Electrophoresis, Polyacrylamide Gel; Gene Expression; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Insulin; Marine Toxins; Microscopy, Fluorescence; Mutation; p21-Activated Kinases; PC12 Cells; Phosphorylation; Prolactin; Protein Kinases; Rats; rho GTP-Binding Proteins; RNA, Small Interfering; Signal Transduction; Thiazolidines; TOR Serine-Threonine Kinases; Transcription, Genetic; Transfection

Cell membranes are laterally organized into functionally discrete domains that include the cholesterol-dependent membrane "rafts." However, how membrane domains are established and maintained remains unresolved and controversial but often requires the actin cytoskeleton. In this study, we used fluorescence resonance energy transfer to measure the role of the actin cytoskeleton in the co-clustering of membrane raft-associated fluorescent proteins (FPs) and FPs targeted to the nonraft membrane fraction. By fitting the fluorescence resonance energy transfer data to an isothermal binding equation, we observed a specific co-clustering of raft-associated donor and acceptor probes that was sensitive to latrunculin B (Lat B), which disrupts the actin cytoskeleton. Conversely, treating with jasplakinolide to enhance actin polymerization increased co-clustering of the raft-associated FPs over that of the nonraft probes. We also observed by immunoblotting experiments that the actin-dependent co-clustering coincided with regulation of the raft-associated Src family kinase Lck. Specifically, Lat B decreased the phosphorylation of the C-terminal regulatory tyrosine of Lck (Tyr505), and combining the Lat B with filipin further decreased the Tyr505 phosphorylation. Furthermore, the Lat B-dependent changes in Lck regulation required CD45 because no significant changes occurred in treated T cells lacking CD45 expression. These data define a role for the actin cytoskeleton in promoting co-clustering of raft-associated proteins and show that this property is important toward regulating raft-associated signaling proteins such as Lck.

Topics: Actins; Anti-Bacterial Agents; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Cholesterol; Cytoskeleton; Depsipeptides; Filipin; Fluorescence Resonance Energy Transfer; Fluorescent Dyes; Green Fluorescent Proteins; Humans; Jurkat Cells; Leukocyte Common Antigens; Lymphocyte Specific Protein Tyrosine Kinase p56(lck); Membrane Microdomains; Membrane Proteins; Phosphorylation; Thiazolidines

Actin has been suggested as an essential component in the membrane fusion stage of exocytosis. In some model systems disruption of the actin filament network associated with exocytotic membranes results in a decrease in secretion. Here we analyze the fast Ca2+-triggered membrane fusion steps of regulated exocytosis using a stage-specific preparation of native secretory vesicles (SV) to directly test whether actin plays an essential role in this mechanism. Although present on secretory vesicles, selective pharmacological inhibition of actin did not affect the Ca2+-sensitivity, extent, or kinetics of membrane fusion, nor did the addition of exogenous actin or an anti-actin antibody. There was also no discernable affect on inter-vesicle contact (docking). Overall, the results do not support a direct role for actin in the fast, Ca2+-triggered steps of regulated membrane fusion. It would appear that actin acts elsewhere within the exocytotic cycle.

Topics: Actin Depolymerizing Factors; Actins; Animals; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Depsipeptides; Exocytosis; Membrane Fusion; Secretory Vesicles; Strongylocentrotus purpuratus; Thiazoles; Thiazolidines

The aim of this study was to clarify the role of the actin cytoskeleton during chemotactic peptide fMet-Leu-Phe (fMLF)-stimulated respiratory burst in human neutrophil granulocytes. Reactive oxygen species (ROS) was measured as luminol-amplified chemiluminescence (CL) and F-actin content as bodipy phallacidin fluorescence in neutrophils treated with latrunculin B or jasplakinolide, an inhibitor and activator of actin polymerization, respectively. Latrunculin B markedly decreased, whereas jasplakinolide increased, the F-actin content in neutrophils, unstimulated or stimulated with fMLF. Latrunculin B enhanced the fMLF-triggered ROS-production more than tenfold. Jasplakinolide initially inhibited the fMLF-induced CL-response, however, caused a potent second sustained phase (>400% of control). Both actin drugs triggered a substantial CL-response when added 5-25 min after fMLF. This was also valid for chemotactic doses of fMLF, where latrunculin B and jasplakinolide amplified the ROS-production 5-10 times. By using specific signal transduction inhibitors, we found that the NADPH oxidase activation triggered by destabilization of the actin cytoskeleton occurs downstream of phospholipase C and protein kinase C but is mediated by Rho GTPases and tyrosine phosphorylation. In conclusion, rearrangements of the actin cytoskeleton are a prerequisite in connecting ligand/receptor activation, generation of second messengers and assembly of the NADPH oxidase in neutrophil granulocytes.

Topics: Actins; Bridged Bicyclo Compounds, Heterocyclic; Chemotactic Factors; Cytoskeleton; Depsipeptides; Enzyme Inhibitors; Humans; Luminescent Measurements; N-Formylmethionine Leucyl-Phenylalanine; NADPH Oxidases; Neutrophils; Respiratory Burst; Signal Transduction; Thiazoles; Thiazolidines

Self-incompatibility (SI) prevents inbreeding through specific recognition and rejection of incompatible pollen. In incompatible Papaver rhoeas pollen, SI triggers a Ca2+ signaling cascade, resulting in the inhibition of tip growth, actin depolymerization, and programmed cell death (PCD). We investigated whether actin dynamics were implicated in regulating PCD. Using the actin-stabilizing and depolymerizing drugs jasplakinolide (Jasp) and latrunculin B, we demonstrate that changes in actin filament levels or dynamics play a functional role in initiating PCD in P. rhoeas pollen, triggering a caspase-3-like activity. Significantly, SI-induced PCD in incompatible pollen was alleviated by pretreatment with Jasp. This represents the first account of a specific causal link between actin polymerization status and initiation of PCD in a plant cell and significantly advances our understanding of the mechanisms involved in SI.

Topics: Actin Cytoskeleton; Actins; Apoptosis; Biopolymers; Bridged Bicyclo Compounds, Heterocyclic; Caspase 3; Caspases; Depsipeptides; Papaver; Pollen; Thiazoles; Thiazolidines

Using Fura-2AM microfluorimetry, effect of actin filament modifiers and vesicular trafficking inhibitor on the store-dependent Ca2+ entry induced by purinergic agonists (ATP, UTP) and endoplasmic Ca2+-ATPase inhibitors (thapsigargin, cyclopiazonic acid) in rat peritoneal macrophages was investigated. It was shown that inhibition of actin polymerization by latrunculin B had a biphasic time-dependent effect on Ca2+ entry, showing an initial potentiation followed by inhibition of Ca2+ entry. Moreover, addition of latrunculin B after induction of store-dependent Ca2+ entry inhibited the Ca2+ influx. Jasplakinolide, which reorganizes actin filaments into a tight cortical layer adjacent to the plasma membrane, prevented activation of store-dependent Ca2+ entry but did not modify this process after its activation. Vesicular transport inhibitor brefeldin A, which inactivates arfproteins, inhibited activation of store-dependent Ca2+ entry but did not alter this mechanism once being initiated. These data are compatible with the sectretion-like coupling model for store-dependent Ca2+ entry in macrophages based on a reversible trafficking and coupling of Ca2+ store with the plasma membrane.

Topics: Animals; Brefeldin A; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Calcium Channels; Depsipeptides; Macrophages, Peritoneal; Rats; Thiazolidines

We hypothesized that differences in actin filament length could influence force fluctuation-induced relengthening (FFIR) of contracted airway smooth muscle and tested this hypothesis as follows. One-hundred micromolar ACh-stimulated canine tracheal smooth muscle (TSM) strips set at optimal reference length (Lref) were allowed to shorten against 32% maximal isometric force (Fmax) steady preload, after which force oscillations of +/-16% Fmax were superimposed. Strips relengthened during force oscillations. We measured hysteresivity and calculated FFIR as the difference between muscle length before and after 20-min imposed force oscillations. Strips were relaxed by ACh removal and treated for 1 h with 30 nM latrunculin B (sequesters G-actin and promotes depolymerization) or 500 nM jasplakinolide (stabilizes actin filaments and opposes depolymerization). A second isotonic contraction protocol was then performed; FFIR and hysteresivity were again measured. Latrunculin B increased FFIR by 92.2 +/- 27.6% Lref and hysteresivity by 31.8 +/- 13.5% vs. pretreatment values. In contrast, jasplakinolide had little influence on relengthening by itself; neither FFIR nor hysteresivity was significantly affected. However, when jasplakinolide-treated tissues were then incubated with latrunculin B in the continued presence of jasplakinolide for 1 more h and a third contraction protocol performed, latrunculin B no longer substantially enhanced TSM relengthening. In TSM treated with latrunculin B + jasplakinolide, FFIR increased by only 3.03 +/- 5.2% Lref and hysteresivity by 4.14 +/- 4.9% compared with its first (pre-jasplakinolide or latrunculin B) value. These results suggest that actin filament length, in part, determines the relengthening of contracted airway smooth muscle.

Topics: Acetylcholine; Actin Cytoskeleton; Animals; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Dogs; Dose-Response Relationship, Drug; In Vitro Techniques; Muscle Contraction; Muscle, Smooth; Stress, Mechanical; Thiazoles; Thiazolidines; Trachea

In the renal medullary thick ascending limb (MTAL), inhibiting the basolateral NHE1 Na(+)/H(+) exchanger with amiloride or nerve growth factor (NGF) results secondarily in inhibition of the apical NHE3 Na(+)/H(+) exchanger, thereby decreasing transepithelial HCO3- absorption. MTALs from rats were studied by in vitro microperfusion to identify the mechanism underlying cross-talk between the two exchangers. The basolateral addition of 10 microM amiloride or 0.7 nM NGF decreased HCO3- absorption by 27-32%. Jasplakinolide, which stabilizes F-actin, or latrunculin B, which disrupts F-actin, decreased basal HCO3- absorption by 30% and prevented the inhibition by amiloride or NGF. Jasplakinolide had no effect on HCO3- absorption in tubules bathed with amiloride or a Na(+)-free bath to inhibit NHE1. Jasplakinolide and latrunculin B did not prevent inhibition of HCO3- absorption by vasopressin or stimulation by hyposmolality, factors that regulate HCO3- absorption through primary effects on apical Na(+)/H(+) exchange. Treatment of MTALs with amiloride or NGF for 15 min decreased polymerized actin with no change in total cell actin, as assessed both by fluorescence microscopy and by actin Triton X-100 solubility. Jasplakinolide prevented amiloride-induced actin remodeling. Vasopressin, which inhibits HCO3- absorption by an amount similar to that observed with amiloride and NGF but does not act via NHE1, did not affect cellular F-actin content. These results indicate that basolateral NHE1 regulates apical NHE3 and HCO3- absorption in the MTAL by controlling the organization of the actin cytoskeleton.

Topics: Absorption; Actins; Amiloride; Animals; Bicarbonates; Bridged Bicyclo Compounds, Heterocyclic; Colchicine; Depsipeptides; Epithelium; Loop of Henle; Male; Nerve Growth Factor; Rats; Rats, Sprague-Dawley; Sodium; Sodium-Hydrogen Exchanger 1; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers; Solubility; Thiazoles; Thiazolidines

The role of actin in endocytosis of G protein-coupled receptors is poorly defined. In the present study, we demonstrate that agents that depolymerize (latrunculin B and cytochalasin D) or stabilize (jasplakinolide) the actin cytoskeleton blocked agonist-induced endocytosis of the beta isoform of the thromboxane A(2) receptor (TPbeta) in HEK293 cells. This suggests that endocytosis of TPbeta requires active remodeling of the actin cytoskeleton. On the other hand, disruption of microtubules with colchicine did not affect endocytosis of the receptor. Expression of wild-type and mutant forms of the small GTPases RhoA and Cdc42 potently inhibited endocytosis of TPbeta, further indicating a role for the dynamic regulation of the actin cytoskeleton in this pathway. Agonist treatment of TPbeta in HEK293 cells resulted in the formation of actin stress fibers through Galpha(q/11) signaling. Because we previously showed that endocytosis of TPbeta is dependent on arrestins, we decided to explore the relation between arrestin-2 and -3 and actin in endocytosis of this receptor. Interestingly, we show that the inhibition of TPbeta endocytosis by the actin toxins in HEK293 cells was overcome by the overexpression of arrestin-3, but not of arrestin-2. These results indicate that the actin cytoskeleton is not essential in arrestin-3-mediated endocytosis of TPbeta. However, arrestin-3 could not promote endocytosis of the TPbetaY339A and TPbetaI343A carboxyl-terminal mutants when the actin cytoskeleton was disrupted. Our data provide new evidence that the actin cytoskeleton plays an essential role in TPbeta endocytosis. Furthermore, our work suggests the existence of actin-dependent and -independent arrestin-mediated pathways of endocytosis.

Topics: Actins; Antineoplastic Agents; Arrestins; Bridged Bicyclo Compounds, Heterocyclic; cdc42 GTP-Binding Protein; Cell Line; Clathrin; Cloning, Molecular; Colchicine; Cytochalasin D; Cytoskeleton; Depsipeptides; Endocytosis; Enzyme-Linked Immunosorbent Assay; GTP-Binding Protein alpha Subunits, Gq-G11; Humans; Marine Toxins; Microscopy, Fluorescence; Nucleic Acid Synthesis Inhibitors; Phosphoproteins; Plasmids; Protein Binding; Protein Structure, Tertiary; Receptors, G-Protein-Coupled; Receptors, Thromboxane A2, Prostaglandin H2; rhoA GTP-Binding Protein; Signal Transduction; Thiazoles; Thiazolidines; Time Factors; Transfection

Actin polymerization is important in the control of pollen tube growth. Thus, treatment of pollen tubes with low concentrations of latrunculin B (Lat-B), which inhibits actin polymerization, permits streaming but reversibly blocks oscillatory growth. In the current study, we employ Jasplakinolide (Jas), a sponge cyclodepsipeptide that stabilizes actin microfilaments and promotes polymerization. Uniquely, Jas (2 microM) blocks streaming in the shank of the tube, but induces the formation of a toroidal-shaped domain in the swollen apex, of which longitudinal optical sections exhibit circles of motion. The polarity of this rotary motion is identical to that of reverse fountain motility in control pollen tubes, with the forward direction occurring at the edge of the cell and the rearward direction in the cell interior. Support for the idea that actin polymerization in the apical domain contributes to the formation of this rotary motility activity derives from the appearance therein of aggregates and flared cables of F-actin, using immunofluorescence, and by the reduction in G-actin as indicated with fluorescent DNAse. In addition, Jas reduces the tip-focused Ca2+ gradient. However, the alkaline band appears in the swollen apex and is spatially localized with the reverse fountain streaming activity. Taken together, our results support the idea that actin polymerization promotes reversal of streaming in the apex of the lily pollen tube.

Topics: Actin Cytoskeleton; Actins; Antifungal Agents; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Calcium Signaling; Cell Movement; Cell Polarity; Cytochalasin D; Cytoplasm; Cytoplasmic Streaming; Deoxyribonucleases; Depsipeptides; Flowers; Germination; Lilium; Nucleic Acid Synthesis Inhibitors; Pollen; Polymers; Reproduction; Thiazoles; Thiazolidines

Visualization of flowing neutrophils colliding with adherent 1-mum-diameter beads presenting P-selectin allowed the simultaneous measurement of collision efficiency (epsilon), membrane tethering fraction (f), membrane tether growth dynamics, and PSGL-1/P-selectin binding lifetime. For 1391 collisions analyzed over venous wall shear rates from 25 to 200 s(-1), epsilon decreased from 0.17 to 0.004, whereas f increased from 0.15 to 0.70, and the average projected membrane tether length, L(tether)(m), increased from 0.35 mum to approximately 2.0 mum over this shear range. At all shear rates tested, adhesive collisions lacking membrane tethers had average bond lifetimes less than those observed for collisions with tethers. For adhesive collisions that failed to form membrane tethers, the regressed Bell parameters (consistent with single bond Monte Carlo simulation) were zero-stress off-rate, k(off)(0) = 0.56 s(-1) and reactive compliance, r = 0.10 nm, similar to published atomic force microscopy (AFM) measurements. For all adhesion events (+/- tethers), the bond lifetime distributions were more similar to those obtained by rolling assay and best simulated by Monte Carlo with the above Bell parameters and an average of 1.48 bonds (n = 1 bond (67%), n = 2 (22%), and n = 3-5 (11%)). For collisions at 100 s(-1), pretreatment of neutrophils with actin depolymerizing agents, latrunculin or cytochalasin D, had no effect on epsilon, but increased L(tether)(m) by 1.74- or 2.65-fold and prolonged the average tether lifetime by 1.41- or 1.65-fold, respectively. Jasplakinolide, an actin polymerizing agent known to cause blebbing, yielded results similar to the depolymerizing agents. Conversely, cholesterol-depletion with methyl-beta-cyclodextrin or formaldehyde fixation had no effect on epsilon, but reduced L(tether)(m) by 66% or 97% and reduced the average tether lifetime by 30% or 42%, respectively. The neutrophil-bead collision assay combines advantages of atomic force microscopy (small contact zone), aggregometry (discrete interactions), micropipette manipulation (tether visualization), and rolling assays (physiologic flow loading). Membrane tether growth can be enhanced or reduced pharmacologically with consequent effects on PSGL-1/P-selectin lifetimes.

Topics: Actins; beta-Cyclodextrins; Biophysics; Bridged Bicyclo Compounds, Heterocyclic; Cell Adhesion; Cell Membrane; Cell Movement; Cholesterol; Cytochalasin D; Depsipeptides; Formaldehyde; Humans; Kinetics; Mechanics; Membrane Glycoproteins; Microscopy, Atomic Force; Microspheres; Models, Statistical; Monte Carlo Method; Neutrophils; P-Selectin; Protein Binding; Selectins; Stress, Mechanical; Thiazoles; Thiazolidines

Phosphoinositide 3-kinase (PI3-kinase) has been shown to link leptin receptor activation to stimulation of large conductance Ca2+-activated K+ (BK) channels and subsequent inhibition of hippocampal epileptiform-like activity. However, the downstream targets of PI3-kinase in this action of leptin are unknown. Here we show that BK channel activation by leptin is dependent on the actin cytoskeleton, as it is prevented by actin filament stabilization and mimicked by actin disruption. Fluorescent labeling of polymerized actin filaments revealed that leptin promotes the rapid rearrangement of actin filaments via activation of PI 3-kinase; an action paralleled by discrete increases in PtdIns(3,4,5)P3 immunoreactivity in close proximity to BK channels. After leptin exposure, there was also an actin-dependent increase in the association of BK channel immunoreactivity with synaptic markers. These data are consistent with the notion that leptin activates BK channels via PI 3-kinase-dependent reorganization of actin filaments and subsequent clustering of BK channels at synapses.

Topics: Actins; Animals; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Cytochalasin D; Cytoskeleton; Depsipeptides; Electrophysiology; Hippocampus; Image Processing, Computer-Assisted; Immunohistochemistry; Large-Conductance Calcium-Activated Potassium Channels; Leptin; Magnesium; Microscopy, Confocal; Microscopy, Fluorescence; Models, Biological; Neurons; Nocodazole; Nucleic Acid Synthesis Inhibitors; Phosphatidylinositol 3-Kinases; Porifera; Potassium Channels; Potassium Channels, Calcium-Activated; Rats; Synapses; Thiazoles; Thiazolidines; Time Factors; Tubulin Modulators

The fluorescent dye Lucifer Yellow (LY) is a well-known and widely-used marker for fluid-phase endocytosis. In this paper, both light and electron microscopy revealed that LY was internalized into transition zone cells of the inner cortex of intact maize root apices. The internalized LY was localized within tubulo-vesicular compartments invaginating from the plasma membrane at actomyosin-enriched pit-fields and individual plasmodesmata, as well as within adjacent small peripheral vacuoles. The internalization of LY was blocked by pretreating the roots with the F-actin depolymerizing drug latrunculin B, but not with the F-actin stabilizer jasplakinolide. F-actin enriched plasmodesmata and pit-fields of the inner cortex also contain abundant plant-specific unconventional class VIII myosin(s). In addition, 2,3 butanedione monoxime, a general inhibitor of myosin ATPases, partially inhibited the uptake of LY into cells of the inner cortex. Conversely, loss of microtubules did not inhibit fluid-phase endocytosis of LY into these cells. In conclusion, specialized actin- and myosin VIII-enriched membrane domains perform a tissue-specific form of fluid-phase endocytosis in maize root apices. The possible physiological relevance of this process is discussed.

Topics: Actins; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Endocytosis; Fluorescent Dyes; Immunohistochemistry; Isoquinolines; Microscopy, Immunoelectron; Myosins; Peptides, Cyclic; Plant Roots; Thiazoles; Thiazolidines; Zea mays

mDia1, a Rho effector, belongs to the Formin family of proteins, which shares the conserved tandem FH1-FH2 unit structure. Formins including mDia1 accelerate actin nucleation while interacting with actin filament fast-growing ends. Here our single-molecule imaging revealed fast directional movement of mDia1 FH1-FH2 for tens of microns in living cells. The movement of mDia1 FH1-FH2 was blocked by actin-perturbing drugs, and the speed of mDia1 FH1-FH2 movement appeared to correlate with actin elongation rates. In vitro, mDia1 FH1-FH2 associated persistently with the growing actin barbed end. mDia1 probably moves processively along the growing end of actin filaments in cells, and Formins may be a molecular motility machinery that is independent from motor proteins.

Topics: Actin Cytoskeleton; Actins; Animals; Biopolymers; Bridged Bicyclo Compounds, Heterocyclic; Carrier Proteins; Cytochalasin D; Depsipeptides; Formins; Mice; Microtubules; Movement; Mutation; Myosins; Peptides, Cyclic; Recombinant Fusion Proteins; rhoA GTP-Binding Protein; Thiazoles; Thiazolidines; Xenopus

We have previously demonstrated that vasopressin increases the water permeability of the inner medullary collecting duct (IMCD) by inducing trafficking of aquaporin-2 to the apical plasma membrane and that this response is dependent on intracellular calcium mobilization and calmodulin activation. Here, we address the hypothesis that this water permeability response is mediated in part through activation of the calcium/calmodulin-dependent myosin light chain kinase (MLCK) and regulation of non-muscle myosin II. Immunoblotting and immunocytochemistry demonstrated the presence of MLCK, the myosin regulatory light chain (MLC), and the IIA and IIB isoforms of the non-muscle myosin heavy chain in rat IMCD cells. Two-dimensional electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry identified two isoforms of MLC, both of which also exist in phosphorylated and non-phosphorylated forms. 32P incubation of the inner medulla followed by autoradiography of two-dimensional gels demonstrated increased 32P labeling of both isoforms in response to the V2 receptor agonist [deamino-Cys1,D-Arg8]vasopressin (DDAVP). Time course studies of MLC phosphorylation in IMCD suspensions (using immunoblotting with anti-phospho-MLC antibodies) showed that the increase in phosphorylation could be detected as early as 30 s after exposure to vasopressin. The MLCK inhibitor ML-7 blocked the DDAVP-induced MLC phosphorylation and substantially reduced [Arg8]vasopressin (AVP)-stimulated water permeability. AVP-induced MLC phosphorylation was associated with a rearrangement of actin filaments (Alexa Fluor 568-phalloidin) in primary cultures of IMCD cells. These results demonstrate that MLC phosphorylation by MLCK represents a downstream effect of AVP-activated calcium/calmodulin signaling in IMCD cells and point to a role for non-muscle myosin II in regulation of water permeability by vasopressin.

Topics: Actins; Amino Acid Sequence; Animals; Aquaporin 2; Aquaporins; Azepines; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Deamino Arginine Vasopressin; Depsipeptides; Electrophoresis, Gel, Two-Dimensional; Gizzard, Non-avian; Immunoblotting; Immunochemistry; Immunohistochemistry; Kidney Tubules, Collecting; Male; Mass Spectrometry; Molecular Sequence Data; Myosin Type II; Myosin-Light-Chain Kinase; Naphthalenes; Osmosis; Peptides; Perfusion; Phosphorylation; Protein Isoforms; Proteome; Rats; Rats, Sprague-Dawley; Signal Transduction; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Thiazoles; Thiazolidines; Time Factors; Turkey; Vasopressins; Water

We have used a modified, dual pipette assay to quantify the strength of cadherin-dependent cell-cell adhesion. The force required to separate E-cadherin-expressing paired cells in suspension was measured as an index of intercellular adhesion. Separation force depended on the homophilic interaction of functional cadherins at the cell surface, increasing with the duration of contact and with cadherin levels. Severing the link between cadherin and the actin cytoskeleton or disrupting actin polymerization did not affect initiation of cadherin-mediated adhesion, but prevented it from developing and becoming stronger over time. Rac and Cdc42, the Rho-like small GTPases, were activated when E-cadherin-expressing cells formed aggregates in suspension. Overproduction of the dominant negative form of Rac or Cdc42 permitted initial E-cadherin-based adhesion but affected its later development; the dominant active forms prevented cell adhesion outright. Our findings highlight the crucial roles played by Rac, Cdc42, and actin cytoskeleton dynamics in the development and regulation of strong cell adhesion, defined in terms of mechanical forces.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cadherins; cdc42 GTP-Binding Protein; Cell Adhesion; Cell Line; Cell Separation; Cytoskeleton; Depsipeptides; Mice; rac GTP-Binding Proteins; Thiazoles; Thiazolidines; Time Factors

Activation of airway epithelial Na-K-2Cl cotransporter (NKCC)1 requires increased activity of protein kinase C (PKC)-delta, which localizes predominantly to the actin cytoskeleton. Prompted by reports of a role for actin in NKCC1 function, we studied a signaling mechanism linking NKCC1 and PKC. Stabilization of actin polymerization with jasplakinolide increased activity of NKCC1, whereas inhibition of actin polymerization with latrunculin B prevented hormonal activation of NKCC1. Protein-protein interactions among NKCC1, actin, and PKC-delta were verified by Western blot analysis of immunoprecipitated proteins. PKC-delta was detected in immunoprecipitates of NKCC1 and vice versa. Actin was also detected in immunoprecipitates of NKCC1 and PKC-delta. Pulldown of endogenous actin revealed the presence of NKCC1 and PKC-delta. Binding of recombinant PKC-delta to NKCC1 was not detected in overlay assays. Rather, activated PKC-delta bound to actin, and this interaction was prevented by a peptide encoding deltaC2, a C2-like domain based on the amino acid sequence of PKC-delta. deltaC2 also blocked stimulation of NKCC1 function by methoxamine. Immunofluorescence and confocal microscopy revealed PKC-delta in the cytosol and cell periphery. Merged images of cells stained for actin and PKC-delta indicated colocalization of PKC-delta and actin at the cell periphery. The results indicate that actin is critical for the activation of NKCC1 through a direct interaction with PKC-delta.

Topics: Acetophenones; Actin Cytoskeleton; Adrenergic alpha-Agonists; Animals; Benzopyrans; Bridged Bicyclo Compounds, Heterocyclic; Bumetanide; Cell Compartmentation; Cell Membrane; Cells, Cultured; Cytosol; Depsipeptides; Dose-Response Relationship, Drug; Enzyme Inhibitors; Epithelial Cells; Humans; Immunohistochemistry; Isoenzymes; Methoxamine; Peptides, Cyclic; Protein Binding; Protein Kinase C; Protein Kinase C-delta; Protein Structure, Tertiary; Respiratory Mucosa; Sodium-Potassium-Chloride Symporters; Solute Carrier Family 12, Member 2; Thiazoles; Thiazolidines

Mesangial cells in diverse glomerular diseases become myofibroblast-like, characterized by activation of smooth muscle alpha-actin (alpha-SMA) expression. In cultured mesangial cells, serum-deprivation markedly increases alpha-SMA expression, cell size, and stress fiber formation. Since stress fibers are assembled from actin monomers, we investigated the hypothesis that alterations in stress fiber formation regulate alpha-SMA expression and hypertrophy. Human mesangial cells were treated with agents that disrupt or stabilize actin stress fibers. Depolymerization of actin stress fibers in serum-deprived cells with actin-depolymerizing agents, cytochalasin B (CytB) and latrunculin B (LatB), or with inhibitors of Rho-kinase, Y-27632 and HA-1077 decreased alpha-SMA mRNA as judged by Northern blot analysis. Western blot analysis showed that CytB also reduced alpha-SMA protein levels. In serum-fed cells, agents that stabilized actin stress fibers, jasplakinolide (Jas) and phalloidin, increased alpha-SMA mRNA and protein. Treatment of human or rat mesangial cells with CytB, LatB, or Y-27632 decreased alpha-SMA promoter activity. In contrast, Jas increased promoter activity 5.6-fold in rat mesangial cells. The presence of an RNA polymerase inhibitor blocked degradation of alpha-SMA mRNA in cells treated with CytB suggesting that destabilization of this message is dependent on a newly transcribed or rapidly degraded factor. Inhibition of actin polymerization by CytB, LatB, Y-27623, and HA-1077 inhibited incorporation of (3)[H]-leucine into newly synthesized protein. Additionally, CytB and LatB decreased cell volume as determined by flow cytometry. Collectively, these results indicate that the state of polymerization of the actin cytoskeleton regulates alpha-SMA expression, hypertrophy, and myofibroblast differentiation in mesangial cells.

Topics: Actin Cytoskeleton; Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Size; Cells, Cultured; Cytochalasin B; Depsipeptides; Enzyme Inhibitors; Fibroblasts; Glomerular Mesangium; Humans; Intracellular Signaling Peptides and Proteins; Myocytes, Smooth Muscle; Peptides, Cyclic; Phalloidine; Phenotype; Promoter Regions, Genetic; Protein Serine-Threonine Kinases; Rats; rho-Associated Kinases; RNA Stability; RNA, Messenger; Thiazoles; Thiazolidines; Transcriptional Activation

Rho proteins (Rho, Rac, Cdc 42) are known to control the organization of the actin cytoskeleton as well as gene expression. Inhibition of Rho proteins by Clostridium difficile toxin B disrupted the F-actin cytoskeleton and enhanced cytokine-induced inducible nitric oxide synthase (iNOS) expression in human epithelial cells. Also specific inhibition by Y-27632 of p160ROCK, which mediates Rho effects on actin fibers, caused a disruption of the actin cytoskeleton and a superinduction of cytokine-induced iNOS expression. Accordingly, direct disruption of the actin cytoskeleton by cytochalasin D, latrunculin B, or jasplakinolide enhanced cytokine-induced iNOS expression. The transcription factor serum response factor (SRF) has been described as mediating actin cytoskeleton-dependent regulation of gene expression. Direct targets of SRF are activating protein 1 (AP1)-dependent genes. All compounds used inhibited SRF- and AP1-dependent reporter gene expression in DLD-1 cells. However, the enhancing effect of the actin cytoskeleton-disrupting compounds on human iNOS promoter activity was much less pronounced than the effect on iNOS mRNA expression. Therefore, besides transcriptional mechanisms, posttranscriptional effects seem to be involved in the regulation of iNOS expression by the above compounds. In conclusion, our data suggest that Rho protein-mediated changes of the actin cytoskeleton negatively modulate the expression of human iNOS.

Topics: Actin Cytoskeleton; Bacterial Proteins; Bacterial Toxins; Bridged Bicyclo Compounds, Heterocyclic; Cytochalasin D; Cytokines; Cytoskeleton; Depsipeptides; Enzyme Inhibitors; Eukaryotic Cells; Gene Expression Regulation, Enzymologic; Humans; Intracellular Signaling Peptides and Proteins; Nitric Oxide; Nitric Oxide Synthase; Peptides, Cyclic; Promoter Regions, Genetic; Protein Serine-Threonine Kinases; rho GTP-Binding Proteins; rho-Associated Kinases; RNA, Messenger; Serum Response Factor; Thiazoles; Thiazolidines; Transcription Factor AP-1; Transcription, Genetic; Tumor Cells, Cultured

Actin participates in several intracellular trafficking pathways. We now find that actin, bound to the surface of purified yeast vacuoles in the absence of cytosol or cytoskeleton, regulates the last compartment mixing stage of homotypic vacuole fusion. The Cdc42p GTPase is known to be required for vacuole fusion. We now show that proteins of the Cdc42p-regulated actin remodeling cascade (Cdc42p --> Cla4p --> Las17p/Vrp1p --> Arp2/3 complex --> actin) are enriched on isolated vacuoles. Vacuole fusion is dramatically altered by perturbation of the vacuole-bound actin, either by mutation of the ACT1 gene, addition of specific actin ligands such as latrunculin B or jasplakinolide, antibody to the actin regulatory proteins Las17p (yeast Wiskott-Aldrich syndrome protein) or Arp2/3, or deletion of actin regulatory genes. On docked vacuoles, actin is enriched at the "vertex ring" membrane microdomain where fusion occurs and is required for the terminal steps leading to membrane fusion. This role for actin may extend to other trafficking systems.

Topics: Actins; Adaptor Proteins, Signal Transducing; Antibodies; Bridged Bicyclo Compounds, Heterocyclic; Carrier Proteins; cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; Cytoskeletal Proteins; Depsipeptides; Fungal Proteins; Ligands; Membrane Fusion; Membrane Microdomains; Mutation; Peptides, Cyclic; Protein Binding; Saccharomyces cerevisiae Proteins; Thiazoles; Thiazolidines; Trans-Activators; Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; Vacuoles; Wiskott-Aldrich Syndrome Protein; Yeasts

Osmotic shock stimulates the translocation of the glucose transporter Glut 4 to plasma membrane by a tyrosine kinase signaling pathway involving Gab-1 (the Grb2-associated binder-1 protein). We show here that, in response to osmotic shock, Gab-1 acts as a docking protein for phospholipase Cgamma1, the p85 subunit of the phosphoinositide 3-kinase and Crk-II. It has been shown that the adapter Crk-II is constitutively associated with C3G, a GDP to GTP exchange factor for several small GTP-binding proteins. We found that inhibition of the activity of phosphoinositide 3-kinase or phospholipase C did not prevent the stimulation of glucose transport by osmotic shock, whereas inactivation of Rho proteins by Clostridium difficile toxin B severely inhibited glucose uptake. Among the Rho family members, overexpression of dominant-interfering TC10/T31N mutant inhibited osmotic shock-mediated Glut 4 translocation suggesting that TC10 is required for this process. Further, disruption of cortical actin integrity by latrunculin B or jasplakinolide severely impaired osmotic shock-induced glucose transport. In contrast, osmotic shock increased the amount of cortical actin associated with caveolin-enriched plasma membrane domains. These data provide the first evidence that activation of TC10 and remodeling of cortical actin, which could occur through the TC10 signaling, are required for osmotic shock-mediated Glut 4 translocation and glucose uptake.

Topics: 3T3 Cells; Adaptor Proteins, Signal Transducing; Animals; Biological Transport; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Deoxyglucose; Depsipeptides; Electrophoresis, Polyacrylamide Gel; Glucose; Glucose Transporter Type 4; Isoenzymes; Mice; Microscopy, Fluorescence; Mitogen-Activated Protein Kinases; Monosaccharide Transport Proteins; Muscle Proteins; Osmosis; Osmotic Pressure; Peptides, Cyclic; Phosphatidylinositol 3-Kinases; Phospholipase C gamma; Phosphoproteins; Precipitin Tests; Protein Binding; Protein Transport; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-crk; rho GTP-Binding Proteins; Signal Transduction; Thiazoles; Thiazolidines; Time Factors; Type C Phospholipases; Tyrosine

This study examines the effects of actin microfilament-disrupting drugs on events of fertilization, with emphasis on gamete membrane interactions. Mouse eggs, freed of their zonae pellucidae, were treated with drugs that perturb the actin cytoskeleton by different mechanisms (cytochalasin B, cytochalasin D, jasplakinolide, latrunculin B) and then inseminated. Cytochalasin B, jasplakinolide, and latrunculin B treatments resulted in a decrease in the percentage of eggs fertilized and the average number of sperm fused per egg. However, cytochalasin D treatment resulted in an increase in the average number of sperm fused per egg and the percentage of polyspermic eggs. This increase in polyspermy occurred despite the observation that cytochalasin D treatment caused a decrease in sperm-egg binding and did not affect spontaneous acrosome reactions or sperm motility. This suggested that cytochalasin D-treated eggs had an impaired ability to establish a block to polyspermy at the level of the plasma membrane. The effect of cytochalasin D on the block to polyspermy was not due to a general disruption of egg activation because sperm-induced calcium oscillations and cortical granule exocytosis were similar in cytochalasin D-treated and control eggs. However, buffering of intracellular calcium levels with the calcium chelator BAPTA-AM resulted in an increase in polyspermy. Together, these data suggest that a postfertilization decrease in egg membrane receptivity to sperm requires functions of the egg actin cytoskeleton that are disrupted by cytochalasin D. Furthermore, egg activation-associated increased intracellular calcium levels are necessary but not sufficient to affect postfertilization membrane dynamics that contribute to a membrane block to polyspermy.

Topics: Acrosome; Acrosome Reaction; Actin Cytoskeleton; Animals; Bridged Bicyclo Compounds, Heterocyclic; Calcimycin; Calcium; Cytochalasin B; Cytochalasin D; Cytoskeleton; Depsipeptides; Exocytosis; Female; Fertilization in Vitro; Male; Mice; Oocytes; Peptides, Cyclic; Signal Transduction; Sperm Motility; Spermatozoa; Thiazoles; Thiazolidines

Many critical cellular processes, including proliferation, vesicle trafficking, and secretion, are regulated by both phospholipase D (PLD) and the actin microfilament system. Stimulation of human PLD1 results in its association with the detergent-insoluble actin cytoskeleton, but the molecular mechanisms and functional consequences of PLD-actin interactions remain incompletely defined. Biochemical and pharmacologic modulation of actin polymerization resulted in complex bidirectional effects on PLD activity, both in vitro and in vivo. Highly purified G-actin inhibited basal and stimulated PLD activity, whereas F-actin produced the opposite effects. Actin-induced modulation of PLD activity was independent of the activating stimulus. The efficacy and potency of the effects of actin were isoform-specific but broadly conserved among actin family members. Human betagamma-actin was only 45% as potent and 40% as efficacious as rabbit skeletal muscle alpha-actin, whereas its inhibitory profile was similar to the single actin species from the yeast, Saccharomyces cerevisiae. Use of actin polymerization-specific reagents indicated that PLD1 binds both monomeric G-actin, as well as actin filaments. These data are consistent with a model in which the physical state of the actin cytoskeleton is a critical determinant of its regulation of PLD activity.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane; Cytosol; Deoxyribonuclease I; Depsipeptides; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Kinetics; Macromolecular Substances; Magnesium Chloride; Mammals; Marine Toxins; Peptides, Cyclic; Phalloidine; Phospholipase D; Protein Isoforms; Tetradecanoylphorbol Acetate; Thiazoles; Thiazolidines; U937 Cells

In gradients of external chemo-attractant, mammalian neutrophilic leukocytes (neutrophils) and Dictyostelium discoideum amoebae adopt a polarized morphology and selectively accumulate lipid products of phosphatidylinositol-3-OH kinases (PI(3)Ks), including PtdIns(3,4,5)P(3), at their up-gradient edges; the internal PtdIns(3,4,5)P(3) gradient substantially exceeds that of the external attractant. An accompanying report presents evidence for a positive feedback loop that amplifies the gradient of internal signal: PtdIns(3,4,5)P(3) at the leading edge stimulates its own accumulation by inducing activation of one or more Rho GTPases (Rac, Cdc42, and/or Rho), which in turn increase PtdIns(3,4,5)P(3) accumulation. Here we show that interruption of this feedback by treatment with PI(3)K inhibitors reduces the size and stability of pseudopods and causes cells to migrate in jerky trajectories that deviate more from the up-gradient direction than do those of controls. Moreover, amplification of the internal PtdIns(3,4,5)P(3) gradient is markedly impaired by latrunculin or jasplakinolide, toxins that inhibit polymerization or depolymerization of actin, respectively. Thus reciprocal interplay between PtdIns(3,4,5)P(3) and polymerized actin initiates and maintains the asymmetry of intracellular signals responsible for cell polarity and directed motility.

Topics: Animals; Bridged Bicyclo Compounds, Heterocyclic; Cell Movement; Cell Polarity; Chemotaxis; Depsipeptides; Dictyostelium; Enzyme Inhibitors; Feedback, Physiological; HL-60 Cells; Humans; Marine Toxins; Neutrophils; Peptides, Cyclic; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Phosphates; Pseudopodia; Thiazoles; Thiazolidines

Mitogen-activated protein kinases (MAPKs) are involved in stress signaling to the actin cytoskeleton in yeast and animals. We have analyzed the function of the stress-activated alfalfa MAP kinase SIMK in root hairs. In epidermal cells, SIMK is predominantly nuclear. During root hair formation, SIMK was activated and redistributed from the nucleus into growing tips of root hairs possessing dense F-actin meshworks. Actin depolymerization by latrunculin B resulted in SIMK relocation to the nucleus. Conversely, upon actin stabilization with jasplakinolide, SIMK co-localized with thick actin cables in the cytoplasm. Importantly, latrunculin B and jasplakinolide were both found to activate SIMK in a root-derived cell culture. Loss of tip-focused SIMK and actin was induced by the MAPK kinase inhibitor UO 126 and resulted in aberrant root hairs. UO 126 inhibited targeted vesicle trafficking and polarized growth of root hairs. In contrast, overexpression of gain-of-function SIMK induced rapid tip growth of root hairs and could bypass growth inhibition by UO 126. These data indicate that SIMK plays a crucial role in root hair tip growth.

Topics: Actin Cytoskeleton; Actins; Active Transport, Cell Nucleus; Bridged Bicyclo Compounds, Heterocyclic; Butadienes; Cell Nucleus; Cell Polarity; Cell Surface Extensions; Cytoplasm; Depsipeptides; Enzyme Activation; MAP Kinase Signaling System; Medicago sativa; Microscopy, Video; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Nicotiana; Nitriles; Peptides, Cyclic; Plant Proteins; Plant Roots; Recombinant Fusion Proteins; Thiazoles; Thiazolidines

Smooth muscle cell (SMC) differentiation is regulated by a complex array of local environmental cues, but the intracellular signaling pathways and the transcription mechanisms that regulate this process are largely unknown. We and others have shown that serum response factor (SRF) contributes to SMC-specific gene transcription, and because the small GTPase RhoA has been shown to regulate SRF, the goal of the present study was to test the hypothesis that RhoA signaling is a critical mechanism for regulating SMC differentiation. Coexpression of constitutively active RhoA in rat aortic SMC cultures significantly increased the activity of the SMC-specific promoters, SM22 and SM alpha-actin, whereas coexpression of C3 transferase abolished the activity of these promoters. Inhibition of either stress fiber formation with the Rho kinase inhibitor Y-27632 (10 microm) or actin polymerization with latrunculin B (0.5 microm) significantly decreased the activity of SM22 and SM alpha-actin promoters. In contrast, increasing actin polymerization with jasplakinolide (0.5 microm) increased SM22 and SM alpha-actin promoter activity by 22-fold and 13-fold, respectively. The above interventions had little or no effect on the transcription of an SRF-dependent c-fos promoter or on a minimal thymidine kinase promoter that is not SRF-dependent. Taken together, the results of these studies indicate that in SMC, RhoA-dependent regulation of the actin cytoskeleton selectively regulates SMC differentiation marker gene expression by modulating SRF-dependent transcription. The results also suggest that RhoA signaling may serve as a convergence point for the multiple signaling pathways that regulate SMC differentiation.

Topics: Actins; Amides; Animals; Aorta; Biomarkers; Biopolymers; Bridged Bicyclo Compounds, Heterocyclic; Cell Differentiation; Cells, Cultured; Cytochalasin D; Depsipeptides; DNA-Binding Proteins; Fluorescent Antibody Technique; Gene Expression Regulation; Genes, Reporter; Muscle, Smooth, Vascular; Nuclear Proteins; Peptides, Cyclic; Promoter Regions, Genetic; Pyridines; Rats; rhoA GTP-Binding Protein; Serum Response Factor; Signal Transduction; Stress Fibers; Thiazoles; Thiazolidines; Transcription, Genetic; Transfection

Lipopolysaccharide (LPS), a potent activator of human monocytes, induced F-actin polymerization in a concentration- and time-dependent manner. To test whether cytoskeletal events participate in the control of the LPS-induced ROI and TNF-alpha production, three natural occurring actin-modulating substances, cytochalasin D (Cyt D), latrunculin B (Lat B), and jasplakinolide (JK), were used. Here we show that treatment of monocytes with Cyt D, Lat B, or JK led to a rearrangement of the actin cytoskeleton, which upon addition of LPS was further modified. Cyt D and Lat B induced generation of ROI in the absence of LPS and enhanced the LPS-triggered respiratory burst. JK also proved to be a potent activator of ROI-production but only in the presence of LPS. TNF-alpha production was hardly affected by the three substances. There was no correlation between a specific state of Cyt D-, Lat B-, or JK-modified actin polymerization and ROI-production. Inhibitors of ADP-ribosylation proved to be activators of F-actin polymerization. They were shown to prevent ROI- and TNF-alpha production and to reduce the capability of LPS to mediate maximal F-actin assembly. At concentrations at which inhibition was greatest, maximal blockage of ROI and TNF-alpha production was observed. These findings may argue for a role of ADP-ribosylation in the transduction pathways mediating the biological responses, with involvement in the assembly of actin-containing cytoskeletal microfilaments.

Topics: Actin Cytoskeleton; Actins; Adenosine Diphosphate Ribose; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Cytochalasin D; Depsipeptides; Dose-Response Relationship, Drug; Humans; In Vitro Techniques; Lipopolysaccharides; Monocytes; Nucleic Acid Synthesis Inhibitors; Peptides, Cyclic; Phosphorylation; Polymers; Reactive Oxygen Species; Thiazoles; Thiazolidines; Tumor Necrosis Factor-alpha

The B cell antigen receptor (BCR) plays two central roles in B cell activation: to internalize antigens for processing and presentation, and to initiate signal transduction cascades that both promote B cells to enter the cell cycle and facilitate antigen processing by accelerating antigen transport. An early event in B cell activation is the association of BCR with the actin cytoskeleton, and an increase in cellular F-actin. Current evidence indicates that the organization of actin filaments changes in response to BCR-signaling, making actin filaments good candidates for regulation of BCR-antigen targeting. Here, we have analyzed the role of actin filaments in BCR-mediated antigen transport, using actin filament-disrupting reagents, cytochalasin D and latrunculin B, and an actin filament-stabilizing reagent, jasplakinolide. Perturbing actin filaments, either by disrupting or stabilizing them, blocked the movement of BCR from the plasma membrane to late endosomes/lysosomes. Cytochalasin D-treatment dramatically reduced the rate of internalization of BCR, and blocked the movement of the BCR from early endosomes to late endosomes/lysosomes, without affecting BCR-signaling. Thus, BCR-trafficking requires functional actin filaments for both internalization and movement to late endosomes/lysosomes, defining critical control points in BCR-antigen targeting.

Topics: Actins; Animals; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Cell Line; Cell Membrane; Cross-Linking Reagents; Cytochalasin D; Cytoskeleton; Depsipeptides; Dose-Response Relationship, Drug; Endosomes; Humans; Hybridomas; Lymphocyte Activation; Lysosomes; Mice; Microscopy, Electron; Microscopy, Fluorescence; Nucleic Acid Synthesis Inhibitors; Peptides, Cyclic; Phosphorylation; Protein Transport; Rats; Receptors, Antigen, B-Cell; Signal Transduction; Thiazoles; Thiazolidines; Time Factors; Tyrosine

Interleukin-1beta (IL-1beta) induces the inducible nitric oxide synthase (iNOS), resulting in the release of nitric oxide (NO) from glomerular mesangial cells. In this study, we demonstrated that disruption of F-actin formation by sequestration of G-actin with the toxin latrunculin B (LatB) dramatically potentiated IL-1beta-induced iNOS protein expression in a dose-dependent manner. LatB by itself had little or no effect on iNOS expression. Staining of F-actin with nitrobenzoxadiazole (NBD)-phallacidin demonstrated that LatB significantly impaired F-actin stress fiber formation. Jasplakinolide (Jasp), which binds to and stabilizes F-actin, suppressed iNOS expression enhanced by LatB. These data strongly suggest that actin cytoskeletal dynamics regulates IL-1beta-induced iNOS expression. We demonstrated that LatB decreases serum response factor (SRF) activity as determined by reporter gene assays, whereas Jasp increases SRF activity. The negative correlation between SRF activity and iNOS expression suggests a negative regulatory role for SRF in iNOS expression. Overexpression of a dominant negative mutant of SRF increases the IL-1beta-induced iNOS expression, providing direct evidence that SRF inhibits iNOS expression.

Topics: Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Cytoskeleton; Depsipeptides; DNA-Binding Proteins; Gene Expression Regulation, Enzymologic; Genes, fos; Genes, Reporter; Glomerular Mesangium; Interleukin-1; Kinetics; Luciferases; Male; Marine Toxins; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nuclear Proteins; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Serum Response Factor; Thiazoles; Thiazolidines; Transcription Factors; Transfection

To determine effects of the marine macrolides swinholide A (Swin A) and jasplakinolide (Jas), alone or in conjunction with latrunculin B (Lat B) on outflow facility in monkeys.. Total outflow facility was measured by two-level constant-pressure perfusion of the anterior chamber before and after exchange with Swin A, Jas, or vehicles followed by continuous anterior chamber infusion of drug or vehicle, in opposite eyes of cynomolgus monkeys. The effect of a facility-ineffective dose of Jas plus a threshold or submaximal facility-effective dose of the actin depolymerizer Lat B on outflow facility was also determined.. Ten or 100 nM Swin A or 20, 100, or 500 nM Jas had no significant effect on outflow facility. However, 500 nM Swin A and 2.5 microM Jas significantly increased facility by 80% +/- 21% and 157% +/- 57% (mean +/- SEM) respectively, adjusted for corresponding baselines and resistance washout in contralateral control eyes. The facility increase in the eye treated with 500 nM Jas with 60 or 200 nM Lat B was similar to that in the eye treated with 60 or 200 nM Lat B only.. Swin A (which severs actin filaments and sequesters actin dimers) and Lat B (which sequesters actin monomers) similarly increase outflow facility. The potent inducer of actin polymerization Jas (500 nM) neither inhibits nor potentiates the facility increase induced by Lat B (60 or 200 nM). A higher dose of Jas increases rather than decreases outflow facility.

Topics: Animals; Anterior Chamber; Bridged Bicyclo Compounds, Heterocyclic; Depsipeptides; Dose-Response Relationship, Drug; Drug Combinations; Macaca fascicularis; Marine Toxins; Peptides, Cyclic; Thiazoles; Thiazolidines

Cell adhesion to extracellular matrix is an important physiological stimulus for organization of the actin-based cytoskeleton. Adhesion to the matrix glycoprotein thrombospondin-1 (TSP-1) triggers the sustained formation of F-actin microspikes that contain the actin-bundling protein fascin. These structures are also implicated in cell migration, which may be an important function of TSP-1 in tissue remodelling and wound repair. To further understand the function of fascin microspikes, we examined whether their assembly is regulated by Rho family GTPases. We report that expression of constitutively active mutants of Rac or Cdc42 triggered localization of fascin to lamellipodia, filopodia, and cell edges in fibroblasts or myoblasts. Biochemical assays demonstrated prolonged activation of Rac and Cdc42 in C2C12 cells adherent to TSP-1 and activation of the downstream kinase p21-activated kinase (PAK). Expression of dominant-negative Rac or Cdc42 in C2C12 myoblasts blocked spreading and formation of fascin spikes on TSP-1. Spreading and spike assembly were also blocked by pharmacological inhibition of F-actin turnover. Shear-loading of monospecific anti-fascin immunoglobulins, which block the binding of fascin to actin into cytoplasm, strongly inhibited spreading, actin cytoskeletal organization and migration on TSP-1 and also affected the motility of cells on fibronectin. We conclude that fascin is a critical component downstream of Rac and Cdc42 that is needed for actin cytoskeletal organization and cell migration responses to thrombospondin-1.

Topics: 3T3 Cells; Actins; Animals; Bridged Bicyclo Compounds, Heterocyclic; Carrier Proteins; cdc42 GTP-Binding Protein; Cell Adhesion; Cell Line; Depsipeptides; Fibronectins; Mice; Microfilament Proteins; Muscle, Skeletal; Peptides, Cyclic; rac GTP-Binding Proteins; Recombinant Proteins; Stress, Mechanical; Thiazoles; Thiazolidines; Thrombospondin 1; Transfection; Vinculin

Shear-induced binding of von Willebrand factor (vWf) to the platelet glycoprotein (GP) Ib/V/IX complex plays a key role in initiating platelet adhesion and aggregation at sites of vascular injury. This study demonstrated that pretreating human platelets with inhibitors of actin polymerization, cytochalasin D or latrunculin B, dramatically enhances platelet aggregation induced by vWf. The effects of these inhibitors were specific to the vWf-GPIbalpha interaction because they enhanced vWf-induced aggregation of Glanzmann thrombasthenic platelets and Chinese hamster ovary (CHO) cells transfected with GPIb/V/IX. Moreover, cytochalasin D enhanced the extent of platelet aggregation induced by high shear stress (5000 s(-1)) and also lowered the shear threshold required to induce aggregation from 3000 s(-1) to as low as 500 s(-1). Studies of CHO cells expressing GPIbalpha cytoplasmic tail truncation mutants that failed to bind actin-binding protein-280 (deletion of residues 569-610 or 535-568) demonstrated that the linkage between GPIb and actin-binding protein-280 was not required for vWf-induced actin polymerization, but was critical for the enhancing effects of cytochalasin D on vWf-induced cell aggregation. Taken together, these studies suggest a fundamentally important role for the cytoskeleton in regulating the adhesive function of GPIb/V/IX.

Topics: Actin Cytoskeleton; Actins; Adenosine Diphosphate; Alprostadil; Animals; Antibodies, Monoclonal; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; CHO Cells; Cricetinae; Cytochalasin D; Cytoskeleton; Depsipeptides; Humans; Mutagenesis, Site-Directed; Peptides, Cyclic; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIb-IX Complex; Platelet Glycoprotein GPIIb-IIIa Complex; Stress, Mechanical; Thiazoles; Thiazolidines; Thrombasthenia; Transfection; von Willebrand Factor

Arabidopsis thaliana trichomes provide an attractive model system to dissect molecular processes involved in the generation of shape and form in single cell morphogenesis in plants. We have used transgenic Arabidopsis plants carrying a GFP-talin chimeric gene to analyze the role of the actin cytoskeleton in trichome cell morphogenesis. We found that during trichome cell development the actin microfilaments assumed an increasing degree of complexity from fine filaments to thick, longitudinally stretched cables. Disruption of the F-actin cytoskeleton by actin antagonists produced distorted but branched trichomes which phenocopied trichomes of mutants belonging to the 'distorted' class. Subsequent analysis of the actin cytoskeleton in trichomes of the distorted mutants, alien, crooked, distorted1, gnarled, klunker and wurm uncovered actin organization defects in each case. Treatments of wild-type seedlings with microtubule-interacting drugs elicited a radically different trichome phenotype characterized by isotropic growth and a severe inhibition of branch formation; these trichomes did not show defects in actin cytoskeleton organization. A normal actin cytoskeleton was also observed in trichomes of the zwichel mutant which have reduced branching. ZWICHEL, which was previously shown to encode a kinesin-like protein is thought to be involved in microtubule-linked processes. Based on our results we propose that microtubules establish the spatial patterning of trichome branches whilst actin microfilaments elaborate and maintain the overall trichome pattern during development.

Topics: Actins; Arabidopsis; Bridged Bicyclo Compounds, Heterocyclic; Cytoskeleton; Depsipeptides; Microtubules; Morphogenesis; Mutagenesis; Peptides, Cyclic; Phalloidine; Phenotype; Plants, Genetically Modified; Thiazoles; Thiazolidines