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PubMed2006

Domain 1 of the urokinase-type plasminogen activator receptor is required for its morphologic and functional, beta2 integrin-mediated connection with actin cytoskeleton in human microvascular endothelial cells: failure of association in systemic sclerosis endothelial cells.

OBJECTIVE: In systemic sclerosis (SSc) microvascular endothelial cells (MVECs), angiogenesis is blocked by matrix metalloproteinase 12-dependent cleavage of domain 1 of the urokinase-type plasminogen activator receptor (uPAR). Since integrins are associated with the invasive activity of uPAR in angiogenesis, this study was undertaken to show whether full-size and truncated uPAR are differentially associated with integrins and with motor components of the cytoskeleton. METHODS: SSc and normal MVECs were isolated from human skin biopsy specimens and studied by confocal laser scanning microscopy and immunoprecipitation to assess the mechanisms of association of truncated and full-size uPAR with integrins and the actin cytoskeleton. The integrin composition of the MVECs was studied by reverse transcription-polymerasechain reaction. Cell migration and capillary morphogenesis were studied on fibrinogen substrates. Involvement of Rac and Cdc42 was evaluated by Western blotting. RESULTS: Only full-size uPAR showed a connection with the actin cytoskeleton in ECs. This connection was mediated by the uPAR-associated alphaMu- and alphaX-subunits of beta2 integrin, and was absent from SSc MVECs. The cleaved uPAR was not associated with beta2 integrins or with actin. beta3 integrins were associated with both the full-size and cleaved uPAR at focal contacts. The uncoupling of uPAR from beta2 integrins in SSc MVECs impaired the activation of Rac and Cdc42 (thus inhibiting their mediation of uPAR-dependent cytoskeletal rearrangements and cell motility) and blocked the integrin-engagement-delivered signals to the actin cytoskeleton. Invasion and capillary morphogenesis on fibrinogen-coated substrates indicated that ligation of uPAR by uPA empowers the beta2/beta3 integrin-dependent invasion of fibrinogen, and that this system is impaired in SSc MVECs. CONCLUSION: The reduced angiogenic properties of SSc MVECs can be explained by the effects of uPAR truncation and the subsequent loss of the beta2 integrin-mediated connection of uPAR with the actin cytoskeleton in these ECs.

Actins↗
PubMed2005

Coronin proteins as multifunctional regulators of the cytoskeleton and membrane trafficking.

Coronins constitute an evolutionarily conserved family of WD-repeat actin-binding proteins, which can be clearly classified into two distinct groups based on their structural features. All coronins possess a conserved basic N-terminal motif and three to ten WD repeats clustered in one or two core domains. Dictyostelium and mammalian coronins are important regulators of the actin cytoskeleton, while the fly Dpod1 and the yeast coronin proteins crosslink both actin and microtubules. Apart from that, several coronins have been shown to be involved in vesicular transport. C. elegans POD-1 and Drosophila coro regulate the actin cytoskeleton, but also govern vesicular trafficking as indicated by mutant phenotypes. In both organisms, defects in cytoskeleton and trafficking lead to severe developmental defects ranging from abnormal cell division to aberrant formation of morphogen gradients. Finally, mammalian coronin 7 appears not to execute any cytoskeleton-related functions, but rather participates in regulating Golgi trafficking. Here, we review recent data providing more insight into molecular mechanisms underlying the regulation of F-actin structures, cytoskeletal rearrangements and intracellular membrane transport by coronin proteins and the way that they might link cytoskeleton with trafficking in development and disease.

Actins↗
PubMed1989

Changes in the association of actin-binding proteins with the actin cytoskeleton during chemotactic stimulation of Dictyostelium discoideum.

Triton-insoluble cytoskeletons were isolated from Dictyostelium discoideum AX3 cells prior to and following stimulation with 2'deoxy cyclic adenosine monophosphate (cAMP). Temporal changes in the content of actin and a 120,000 dalton actin-binding protein (ABP-120) in cytoskeletons following stimulation were monitored. Both actin and ABP-120 were incorporated into the cytoskeleton at 30-40 seconds following stimulation, which is cotemporal with the onset of pseudopod extension during stimulation of amoebae with chemoattractants. Changes in the content of total cytoskeletal protein and cytoskeletal myosin were determined under the same experimental conditions as controls. These proteins exhibited different kinetics from those of cytoskeletal ABP-120 and actin following the addition of 2'deoxy cAMP. The authors concluded that the association of ABP-120 with the cytoskeleton is regulated during cAMP signalling. Furthermore, these results indicate that ABP-120 is involved in cross-linking newly assembled actin filaments into the cytoskeleton during chemoattractant-stimulated pseudopod extension.

Actins↗
PubMed1998

Rho directs activation-associated changes in rat hepatic stellate cell morphology via regulation of the actin cytoskeleton.

Hepatic stellate cell activation, thought to play a key role in fibrosis of the liver, is characterized by changes in cellular morphology. The intracellular signals regulating morphological alterations associated with stellate cell activation are uncertain. The ras-like guanosine triphosphate-binding protein, rho, has recently emerged as an important regulator of the actin cytoskeleton, and consequently cell morphology. The aim of this study was to test the hypothesis that rho signaling pathways direct activation-associated morphological changes in stellate cells by regulating the actin cytoskeleton. The morphology and actin cytoskeleton of primary rat hepatic stellate cells were studied with phase contrast, differential interference contrast, and epifluorescence microscopy. Immunohistochemistry and immunoblot analysis were used to examine rho expression and activity, respectively. Quiescent and activated stellate cells were investigated in the absence and presence of C3 transferase, a bacterial toxin that specifically inhibits rho. Stellate cell activation was characterized by the development of prominent intracellular fibers, and the loss of dendrite-like processes and perinuclear retinoid droplets. Moreover, activation was accompanied by the formation of prominent actin stress fibers and focal adhesions. Both rho expression and activity were demonstrated in stellate cells. C3 transferase blocked and reversed, both activation-associated morphological alterations and activation-associated changes in the actin cytoskeleton, in quiescent and activated stellate cells, respectively. These results indicate that rho directs activation-associated changes in rat hepatic stellate cell morphology via regulation of the actin cytoskeleton.

Actins↗
PubMed1995

Differential synthesis and cytoskeletal deposition of neurofilament subunits before and during axonal outgrowth in NB2a/d1 cells: evidence that segregation of phosphorylated subunits within the axonal cytoskeleton involves selective deposition.

NB2a/d1 cells constitutively express and extensively phosphorylate neurofilament (NF) triplet proteins. However, only hypophosphorylated NFs are observed within the Triton-insoluble perikaryal cytoskeletons of undifferentiated and differentiated cells, while phosphorylated NF isoforms accumulate exclusively within the axonal neurites elaborated following treatment with dbcAMP. We examined NF synthesis and distribution of newly synthesized subunits by immunoprecipitation from 35S-methionine-radiolabeled undifferentiated and dbcAMP-treated differentiated cells. Following a 15 min pulse radiolabeling, NF-H isoforms migrating from approximately 160-200 kDa, NF-M isoforms migrating from approximately 97 k-145 Da, and a single 70 kDa NF-L isoform were readily detectable within Triton-soluble fractions from both undifferentiated and differentiated cells. During chase analyses in the absence of radiolabel, the entire spectrum of isoforms was present in Triton-soluble and -insoluble fractions from both undifferentiated and differentiated cells. However, differentiated cells displayed a significant increase in radiolabel associated with each subunit and isoform. Normalization of their NF synthesis levels to those of undifferentiated cells revealed that differentiated cells deposited 10-fold more radiolabeled subunits into the Triton-insoluble cytoskeleton as compared to undifferentiated cells. Similar levels of radiolabeled subunits were observed throughout the 2 hr period in dbcAMP-treated cells. By contrast, radiolabeled subunits and isoforms increased in undifferentiated cytoskeletons during the chase period, although final levels remained substantially lower than those observed in cytoskeletons of dbcAMP-treated cells. These data were considered with respect to potential mechanisms by which the phosphorylated NFs are normally excluded from perikaryal cytoskeletons. The presence of extensively phosphorylated subunits within perikarya indicates the presence of necessary NF kinases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

The cytoskeleton and disease.

Cytoskeletal research in recent years has revolutionized cell biology and biomedicine. The cytoskeleton spans the cytoplasm and interconnects the cell nucleus with the extracellular matrix, thereby forming a structural link between molecules involved in cell communication on the one hand, and gene expression on the other. Since the cytoskeleton is involved in virtually all cellular processes, abnormalities in this essential cellular component frequently result in disease. In this introduction, the basic structure of the cytoskeleton is briefly outlined. Furthermore, the disease processes in which the cytoskeleton plays a decisive role, and which are reviewed in detail in the papers in this issue, are briefly introduced. The advances in our understanding of the cytoskeleton and its function in disease will lead to new diagnostic and therapeutic applications in the foreseeable future.

Actins↗
PubMed2004

The cell wall sensor Wsc1p is involved in reorganization of actin cytoskeleton in response to hypo-osmotic shock in Saccharomyces cerevisiae.

The cell wall is essential to preserve osmotic integrity of yeast cells. Some phenotypic traits of cell wall mutants suggest that, as a result of a weakening of the cell wall, hypo-osmotic stress-like conditions are created. Consequent expansion of the cell wall and stretching of the plasma membrane trigger a complex response to prevent cell lysis. In this work we examined two conditions that generate a cell wall and membrane stress: one is represented by the cell wall mutant gas1Delta and the other by a hypo-osmotic shock. We examined the actin cytoskeleton and the role of the cell wall sensors Wsc1p and Mid2p in these stress conditions. In the gas1 null mutant cells, which lack a beta(1,3)-glucanosyltransferase activity required for cell wall assembly, a constitutive marked depolarization of actin cytoskeleton was found. In a hypo-osmotic shock wild-type cells showed a transient depolarization of actin cytoskeleton. The percentage of depolarized cells was maximal at 30 min after the shift and then progressively decreased until cells reached a new steady-state condition. The maximal response was proportional to the magnitude of the difference in the external osmolarity before and after the shift within a given range of osmolarities. Loss of Wsc1p specifically delayed the repolarization of the actin cytoskeleton, whereas Wsc1p and Mid2p were essential for the maintenance of cell integrity in gas1Delta cells. The control of actin cytoskeleton is an important element in the context of the compensatory response to cell wall weakening. Wsc1p appears to be an important regulator of the actin network rearrangements in conditions of cell wall expansion and membrane stretching.

Actins↗
PubMed1995

Translocation of cortactin (p80/85) to the actin-based cytoskeleton during thrombin receptor-mediated platelet activation.

Cortactin (p80/85) was discovered as a src kinase substrate and an actin filament binding protein. We investigated translocation of cortactin to the cytoskeleton during thrombin receptor-mediated platelet activation. Only a few percent of total cortactin (minor cortactin pool) translocates to the cytoskeleton as early as 5 s after platelet activation, while about 40% of total cortactin (major cortactin pool) is thereafter recovered in the cytoskeleton during platelet aggregation. Pretreatment of platelets with cytochalasin D suppresses completely this translocation, indicating that the translocation is dependent on actin polymerization. Inhibition of platelet aggregation by a tetrapeptide with the sequence RGDS, chelator of extracellular Ca2+, or a nonstirring condition results in marked suppression of translocation of the major cortactin pool. These results suggest that a minor cortactin pool translocates to the cytoskeleton independent of GPII-bIIIa (alpha IIb beta 3 integrin) engagement, and a major pool requires GPIIbIIIa-mediated signals into the cell for the translocation. Methyl 2,5-hydroxycinamate, a tyrosine kinase inhibitor, inhibits tyrosine phosphorylation of cortactin without affecting its translocation, indicating that tyrosine phosphorylation is not essential for the translocation. Morphological studies reveal that cortactin is colocalized with filamentous actin in aggregated platelets and that it is localized at the cell peripheries along actin filaments in spread platelets. Taking these together, we have demonstrated in this paper that the translocation of cortactin is associated with the reorganization of the actin-based cytoskeleton during platelet activation, particularly with platelet aggregation.

Actins↗
PubMedDate not supplied

A new technique for isolation and visualization of the Xenopus egg cortex reveals a complex cytoskeleton.

This paper demonstrates the first images of the isolated cortex of the Xenopus laevis egg viewed as a whole mount. The cortex was isolated by mechanically restraining it in a folding hexagonal mesh electron microscopy grid, dried by passage through the carbon dioxide critical point, and viewed in an intermediate voltage electron microscope at 400 kV. Using this approach, we have obtained new views of the Xenopus egg cortex that demonstrate a complex cytoskeleton. Stereo micrographs demonstrate three-dimensional views of the cortical organelles and their interaction with the cytoskeleton. These images demonstrate the presence of a dense meshwork of filaments located just beneath the plasma membrane, referred to as the submembranous cytoskeleton. In addition, there is an array of filaments interconnecting the organelles and securing them to the submembranous cytoskeleton and plasma membrane. The development of this technique for visualization of the egg cortex will facilitate further analysis of the role of the cortical cytoskeleton in fertilization and early embryogenesis.

Animals↗
PubMed2005

The type III cytotoxins of Yersinia and Pseudomonas aeruginosa that modulate the actin cytoskeleton.

Initial studies of how bacterial toxins modulate the actin cytoskeleton have focused primarily on the mode of action of these toxins. More recently, studies have addressed the molecular interactions of these toxins with host cell signaling pathways and how toxins modulate cellular physiology. Although each individual toxin has a unique mode of action, general themes have started to emerge between bacterial pathogens. During the course of an infection, many pathogenic bacteria produce toxins that target the actin cytoskeleton and its regulatory proteins. Toxins can either act as positive regulators promoting the assembly of filamentous actin structures or, alternatively, as negative regulators promoting actin filament disassembly. Modulation of the actin cytoskeleton facilitates various infectious processes critical for the success of the pathogen. Intracellular bacteria such as Salmonella typhimurium utilize toxins to promote both assembly and disassembly of the actin cytoskeleton during the infection process. Temporal regulation of toxin activities results in internalization of the bacterium by epithelial cells into specialized vacuoles permissive for growth. In contrast, Yersinia utilizes actin modulating toxins to block internalization by professional antigen-presenting cells such as macrophages and dendritic cells. Modulation of the immune response through the production of actin-regulating toxins appears to be a common approach adopted by several extracellular pathogens. Thus the repertoire of actin-modifying toxins produced by various species is specifically tailored to facilitate the lifestyle of the pathogen. The presence of multiple toxins that modulate the activation state of actin shows the importance of interfering with the cytoskeleton to neutralize the host's innate immune system for the survival and growth of Yersinia and P. aeruginosa.

Actins↗
PubMed1994

A sequence of cytoskeleton changes related to the formation of neurofibrillary tangles and neuropil threads.

Frontal sections of the temporal lobe including the transentorhinal/entorhinal region, amygdala, and/or hippocampus from human adult brains are studied for cytoskeleton changes using immunostaining with the antibodies AT8 and Alz-50 and selective silver impregnation methods for neurofibrillary changes of the Alzheimer type. For the purpose of correlation, the two methods are carried out one after the other on the same section. Layer pre-alpha in the transentorhinal/entorhinal region harbours nerve cells which are among the first nerve cells in the entire brain to show the development of neurofibrillary changes. This presents the opportunity for study of both early events in the destruction of the cytoskeleton in individual neurons, and to relate changes which occur in the neuronal processes in the absence of alterations in their immediate surroundings to those happening in the soma. Immunoreactions with the AT8 antibody in particular reveal a clear sequence of changes in the neuronal cytoskeleton. Group 1 neurons present initial cytoskeleton changes in that the soma, dendrites, and axon are completely marked by granular AT8 immunoreactive material. These neurons appear quite normal and turn out to be devoid of argyrophilic material when observed in silver-stained sections. Group 2 neurons show changes in the cellular processes. The terminal tuft of the apical dendrite is replaced by tortuous varicose fibres and coarse granules. The distal portions of the dendrites are curved and show appendages and thickened portions. Intensely homogeneously immunostained rod-like inclusions are encountered in these thickened portions and in the soma. A number of these rod-like inclusions are visible after silver staining, as well. Group 3 neurons display even more pronounced alterations of their distal--most dendritic portions. The intermediate dendritic parts lose immunoreactivity, but the soma is homogeneously immunostained. Silver staining reveals in most of the distal dendritic parts neuropil threads, and in the soma a classic neurofibrillary tangle. Group 4 structures are marked by accumulations of coarse AT8-immunoreactive granules. Silver staining provides evidence that the fibrillary material has become an extraneuronal, "early" ghost tangle. Finally, group 5 structures present "late" ghost tangles in silver-stained sections but fail to demonstrate AT8 immunoreactivity. It is suggested that the altered tau protein shown by the antibody AT8 represents an early cytoskeleton change which eventually leads to the formation of argyrophilic neurofibrillary tangles and neuropil threads.

Adult↗
PubMed1995

Chemoattractant-induced NADPH oxidase activity in human monocytes is terminated without any association of receptor-ligand complex to cytoskeleton.

When the chemotactic peptide formylmethionyl-leucyl-phenylalanine binds to its cell surface receptor, a transmembrane signal is generated that activates the superoxide-producing NADPH oxidase of human phagocytes. Comparing monocytes and neutrophils with regard to the production of superoxide anion induced by the peptide, we found a similar time-course for both types of cells. In neutrophils, ligand binding induced a conversion of the receptor to a high-affinity form, a change suggested to be due to an association of the receptor-ligand complex to the Triton X-100-insoluble cytoskeleton. This event has been hypothesized to terminate the signal that activates the NADPH oxidase and thereby results in cessation of the cellular production of superoxide anion. Neutrophils preincubated with the cytoskeleton-disrupting drug cytochalasin B showed an increased and prolonged superoxide anion production after activation with the peptide, thus indicating that the cytoskeleton is involved in terminating this response. Formylmethionyl-leucyl-phenylalanine was also found to induce polymerization of actin in monocytes; however, cytochalasin B had no effect on the peptide-induced generation of superoxide anion in these cells. Furthermore, also in monocytes, ligand binding induced a conversion of the receptor to a high-affinity form; however, the receptor-ligand complex did not coisolate with the Triton X-100-insoluble cytoskeleton. These results indicate that, in monocytes, the NADPH oxidase activating pathway is terminated without any association of the receptor-ligand complex to the Triton X-100-insoluble cytoskeleton.

Actins↗
PubMed1997

Acute cellular damage in medial smooth muscle cells following experimental coronary angioplasty in dog. Damage of cytoskeleton and apoptosis.

The purpose of the present study was to investigate the responses of the cytoskeleton and the presence of apoptosis following acute damage of medial smooth muscle cells after percutaneous transluminal coronary angioplasty (PTCA). We killed 20 dogs, 4h and 4 days after PTCA (n=10 in each group). Ten dogs without PTCA were used as controls. PTCA was achieved by inflating balloon catheters two times, for 60s each time, to 150 PSI, followed by a 60-s deflation. The coronary artery obtained from each dog was fixed in 10% formalin neutral buffer solution. The response of the cytoskeleton was studied immunohistochemically. using monoclonal antibodies against alpha-smooth muscle actin, vimentin, and beta-tubulin. Proliferation was determined by proliferating cell nuclear antigen (PCNA), and DNA fragmentation indicating apoptosis was determined by in situ nick end labeling. Four h after PTCA, endothelial denudation, microscopic mural thrombi, rupture of the internal elastic membrane, medial tear, and stretched smooth muscle cells with nuclei were found at the PTCA site. An immunohistochemical study revealed diffuse reduction or defective immunoreactivity in each cytoskeleton of medial smooth muscle cells, 4h after PTCA. The extent of positive immunoreactivity in the media decreased to 45+/-11% in alpha-smooth muscle actin (control value, 80+/-10%), 9+/-8% in vimentin (control value, 83+/-9%), and 10+/-7% in beta-tubulin (control value, 75+/-8%). The decrease was more significant in vimentin and beta-tubulin than in alpha-smooth muscle actin. Four days after PTCA, the features were diffuse cell death and the focal proliferation of medial cells, as well as macroscopic intramural thrombi. The extent of positive immunoreactivity in the media was 15+/-9% in alpha-smooth muscle actin, 13+/-7% in vimentin, and 14+/-11% in beta-tubulin. There were no smooth muscle cells with positive PCNA (0%) in the control and 4-h groups, but 4 days after PTCA the percentage was 19+/-4%. In situ nick end labeling showed DNA fragmentation in the nuclei of medial smooth muscle cells at a rate of 15+/-5% 4h after PTCA and at 8+/-6% 4 days after PTCA, compared with 0% in the control. We concluded that severe damage of the cytoskeleton and medial smooth muscle cell death were induced immediately after PTCA, followed by proliferation of smooth muscle cells. Apoptosis may be partially involved in the death of smooth muscle cells, in addition to necrosis. Damage to the cytoskeleton and apoptosis may play an important role in the pathogenesis of acute lesions and the proliferation of smooth muscle cells after PTCA.

Angioplasty, Balloon, Coronary↗
PubMed1998

Disruption of the actin cytoskeleton abolishes high affinity 3H-glibenclamide binding in rat aortic rings.

The interaction between the cytoskeleton and the ATP-sensitive K+ channel (KATP channel) was studied in rat aortic rings by examining the binding of the sulphonylurea blocker, 3H-glibenclamide, and of the opener, 3H-P1075. The actin cytoskeleton disrupting agents, cytochalasin D (1 microM) and latrunculin B (1 microM), abolished the high affinity component of 3H-glibenclamide binding. Preincubation with the actin cytoskeleton stabilizing agent, phalloidin (10 microM) prevented the effect of cytochalasin D. In contrast, binding of the opener, 3H-P1075, and inhibition of this binding by glibenclamide, were unaffected by cytochalasin D (3 microM). Colchicine (100 microM), which disassembles microtubules, had no effect on the binding of 3H-glibenclamide and 3H-P1075. The data show that high affinity binding of glibenclamide, which mediates the effects of the sulphonylurea in this preparation, requires the presence of an intact actin cytoskeleton. Binding of the opener is unaffected by the state of the cytoskeleton and preserves a conformational state in which high affinity binding of glibenclamide to the sulphonylurea receptor can occur.

Actins↗
PubMed2003

Hypaphorine, an indole-3-acetic acid antagonist delivered by the ectomycorrhizal fungus Pisolithus tinctorius, induces reorganisation of actin and the microtubule cytoskeleton in Eucalyptus globulus ssp bicostata root hairs.

Hypaphorine, an indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius Coker & Couch., counteracts indole-3-acetic acid (IAA) activity and controls the rate of root hair elongation in Eucalyptus globulus ssp. bicostata. The present investigation shows that hypaphorine changes cytoskeletal organisation in elongating root hairs of the host. The actin cytoskeleton was investigated by two different fixation and labelling procedures, which gave similar results. In control root hairs, actin organisation was characterised by (i) an actin cap at the very tip region, (ii) a subapical region with reduced labelling and containing fine actin filaments, and (iii) axial bundles of actin filaments running from the subapical part to the base of the root hair. In the hypaphorine-treated root hairs no actin cap was distinguished. The fine actin filaments occurring in the subapical region were replaced by a few thick actin filament bundles that extended from the subapical region toward the root hair tip. In the hypaphorine-treated hairs the total number of actin filament bundles along most of the root hair length was significantly reduced, presumably due to aggregation of pre-existing actin filaments. The first signs of alteration to the cytoskeleton could be detected as soon as 15 min after hypaphorine treatment. In hypaphorine-treated, but not in control root hairs, a patch of aggregated microtubules regularly occurred at a distance of approximately 10 microm from the tip, possibly as a consequence of changes induced by hypaphorine in the actin cytoskeleton. The hypaphorine-induced aggregations in the actin and microtubule cytoskeletons could stabilise the structure of cytoskeletal elements, which in turn could hinder the vesicle delivery at the tip necessary for elongation. Such cytoskeletal alterations may be a consequence of the antagonism between IAA and hypaphorine. The latter view was supported by restoration of the actin cytoskeleton in hypaphorine-treated root hairs by IAA application.

Actins↗
PubMed1985

Coordinate release of myosin and a high molecular weight microtubule-associated protein from PC12 cytoskeletons by ATP.

The association of two high molecular weight (HMW) structural proteins with the cytoskeletons of rat pheochromocytoma cells, PC12, is regulated by ATP and other nucleotides. Exposure of PC12 cytoskeletons to ATP resulted in the selective solubilization of two HMW proteins, identified as myosin and a 280 kD microtubule-associated protein. These two proteins were rapidly released from the cytoskeleton following incubation with ATP, GTP, CTP, and ADP; non-hydrolysable ATP analog caused protein release to a less marked extent. The effect of the latter two nucleotides indicated that the release of the myosin and the HMW microtubule-associated protein was likely to be the result of nucleotide-induced conformational changes in one or both proteins. Myosin and the HMW microtubule-associated proteins interact with actin in vitro in a nucleotide-sensitive manner. The present data demonstrate that similar interactions are likely to exist within the intact cytoskeleton and suggest that the associations of these structural proteins with the cytoskeleton are regulated by common mechanisms. The results also suggest that the cells may differentially regulate the stability of a subset of these structural proteins in their interactions with other cytoskeletal elements.

Adenosine Triphosphate↗
PubMed1987

Plasmodium falciparum: fine structural changes in the cytoskeletons of infected erythrocytes.

Following parasitization by Plasmodium falciparum, numerous changes take place in the host erythrocyte membrane. In this study, we used the technique of whole cell mount electron microscopy to determine if the ultrastructure of the erythrocyte cytoskeleton changed following parasitization with knobby and knobless strains of P. falciparum. Using this technique, a network of spectrin filaments (3-10 X 45-120 nm) branching from electron dense junctions (15-25 nm in diameter), the presumed site of bands 4.1 and actin, were visualized. The overall architecture of normal and parasitized erythrocyte cytoskeletons was the same: however, additional patches (35 to 60 nm in size) and aggregates (30 X 150 nm) of electron dense material were present in parasitized skeletons. The ultrastructure of knobby and knobless cytoskeletons was similar, except knobless skeletons usually did not possess the larger aggregates of material. Antigens associated with the erythrocyte cytoskeleton of cells infected with knobby and knobless strains, but not uninfected cells, were demonstrated by indirect immunofluorescence. Results suggest that antigens, associated with the erythrocyte cytoskeleton, may contribute to perturbations in the host erythrocyte membrane.

Animals↗
PubMed1989

Association of phosphatidylinositol kinase and phosphatidylinositol 4-phosphate kinase activities with the cytoskeleton in human platelets.

The inositol lipid kinases were investigated in the cytoskeletons of human platelets. In the absence of added lipids the kinases were only barely detectable in the Triton-soluble fractions and undetectable in cytoskeletons of resting cells. However at least 30% of the total phosphatidylinositol kinase was present in the cytoskeleton as revealed by saturation of the enzyme. Phosphatidylinositol 4-phosphate kinase was also found in significant amounts in the cytoskeletons. On the other hand, both enzymes being only recovered in the particulate fraction of the cells, we suggest that inositol lipid kinases may be present near the anchoring points of the cytoskeletons at the membranes.

1-Phosphatidylinositol 4-Kinase↗