Actin polymerisation regulates integrin-mediated adhesion as well as rigidity of neutrophils

Drug-induced changes of cytoskeletal structure and mechanics in fibroblasts: an atomic force microscopy study

The effect of various drugs affecting the integrity of different components of the cytoskeleton on the elasticity of two fibroblast cell lines was investigated by elasticity measurements with an atomic force microscope (AFM). Disaggregation of actin filaments always resulted in a distinct decrease in the cell's average elastic modulus indicating the crucial importance of the actin network for the mechanical stability of living cells. Disruption or chemical stabilization of microtubules did not affect cell elasticity. For the f-actin-disrupting drugs different mechanisms of drug action were observed. Cytochalasins B and D and Latrunculin A disassembled stress fibers. For Cytochalasin D this was accompanied by an aggregation of actin within the cytosol. Jasplakinolide disaggregated actin filaments but did not disassemble stress fibers. Fibrous structures found in AFM images and elasticity maps of fibroblasts could be identified as stress fibers by correlation of AFM data and fluorescence images.

Function of the cytoskeleton in human neutrophils and methods for evaluation

The cytoskeleton plays a critical role in the determination of cell shape and serves as a scaffold for critical cellular enzymes and adhesion molecules. It provides structural integrity for the cell and regulates the function of many biochemical events that are critical to cellular function. The microfilamentous cytoskeleton participates in force generation necessary for shape change and motion. In neutrophils and other motile cells, polymerization of actin likely drives extension of the lamellae and participates in force generation through interaction with myosin, by polymerization alone and by osmotic mechanisms. Here, we will focus on the microfilamentous cytoskeleton in the neutrophil and briefly review its function as well as some direct and indirect methods that have been used to asses its role in neutrophil function. The discussion will address general approaches and leaves the details of the methods to the references.

Function of alpha3beta1-tetraspanin protein complexes in tumor cell invasion. Evidence for the role of the complexes in production of matrix metalloproteinase 2 (MMP-2)

Tumor cell migration through the three- dimensional extracellular matrix (ECM) environment is an important part of the metastatic process. We have analyzed a role played by the integrin-tetraspanin protein complexes in invasive migration by culturing MDA-MB-231 cells within Matrigel. Using time-lapse video recording, we demonstrated that the Matrigel-embedded cells remain round and exhibit only limited ability for migration by extending short, highly dynamic pseudopodia. The alpha3beta1-tetraspanin protein complexes were clustered on the thin microvilli-like protrusions extending from both the main cell body and pseudopodia. Ligation of the alpha3beta1-tetraspanin protein complexes with monoclonal antibodies specifically stimulates production of matrix metalloproteinase 2 (MMP-2) and induces formation of long invasive protrusions within Matrigel. Accordingly, treatment with the monoclonal antibodies to various tetraspanin proteins and to the alpha3 integrin subunit increases invasive potential of the MDA-MB-231 cells in the Matrigel-penetration assay. A specific inhibitor of phosphoinositide 3-kinase (PI3K), LY294002, negated the effect of the monoclonal antibodies on the morphology of the Matrigel-embedded cells and on production of MMP-2. Interestingly, broad-spectrum inhibitors of protein tyrosine kinases (genistein) and protein tyrosine phosphatases (orthovanadate), and actin filament stabilizing compound (jasplakinolide), also block protrusive activity of the Matrigel-embedded cells but have no effect on the production of MMP-2. These results indicate that alpha3beta1-tetraspanin protein complexes may control invasive migration of tumor cells by using at least two PI3K-dependent signaling mechanisms: through rearrangement of the actin cytoskeleton and by modulating the MMP-2 production.

Effects of jarastatin, a novel snake venom disintegrin, on neutrophil migration and actin cytoskeleton dynamics

A new disintegrin, an RGD-containing peptide of 6 kDa called jarastatin, was purified from Bothrops jararaca venom. It is a potent inhibitor of platelet aggregation induced by ADP, collagen, and thrombin. The effect of jarastatin on neutrophil migration in vivo and in vitro and on the actin cytoskeleton dynamics of these cells was investigated. Incubation in vitro with jarastatin significantly inhibited, in a concentration-dependent manner, the chemotaxis of human neutrophils toward fMLP, IL-8, and jarastatin itself. Despite this inhibitory effect, jarastatin induced neutrophil chemotaxis. A significant increase of F-actin content was observed in jarastatin-treated neutrophils. Furthermore, as demonstrated by confocal microscopy after FITC-phalloidin labeling, these cells accumulated F-actin at the plasmalemma, a distribution similar to that observed in fMLP-stimulated cells. Pretreatment of mice with jarastatin inhibited neutrophil migration into peritoneal cavities induced by carrageenan injection. The results suggest that binding of jarastatin to neutrophil integrins promotes cellular activation and triggers a dynamic alteration of the actin filament system and that this is one of the first event in integrin-mediated signaling.

Activation of Mitogen-Activated Protein Kinase Regulates Eotaxin-Induced Eosinophil Migration

Eotaxin is a potent eosinophil chemoattractant that plays an important role in regulating eosinophil tissue levels both in healthy individuals and in diseases associated with significant eosinophil infiltrates, such as the allergic inflammation observed in asthma. Here, we demonstrate that treatment of eosinophils with eotaxin induces the phosphorylation of the mitogen-activated protein kinases (MAPKs) p42 and p44, leading to kinase activation. Blockade of MAPK activation by the MAPK kinase inhibitor PD98059 leads to a dramatic decrease in eotaxin-induced eosinophil rolling in vivo and chemotaxis in vitro. This blockade in the leukocyte migration process is consistent with the observed inhibition of actin polymerization and rearrangement within the eosinophil following treatment with MAPK inhibitor. It is suggested, therefore, that the intrinsic mechanism of eotaxin-induced eosinophil rolling and migration involves activation of the p42/p44 MAPK, possibly through regulation of the cytoskeletal rearrangements necessary for chemotaxis.

Alteration of Actin Organization by Jaspamide Inhibits Ruffling, but not Phagocytosis or Oxidative Burst, in HL-60 Cells and Human Monocytes

Jaspamide, a naturally occurring cyclic peptide isolated from the marine sponge Hemiastrella minor, has fungicidal and growth-inhibiting activities. Exposure of promyelocytic HL-60 cells and human monocytes to jaspamide induces a dramatic reorganization of actin from a typical fibrous network to focal aggregates. HL-60 cells exposed to 5 × 10−8 mol/L or 10−7 mol/L jaspamide exhibited a reduced proliferation rate. In addition, 10−7mol/L jaspamide induced maturation of HL-60 cells as indicated by the appearance of a lobulated nucleus in 55% ± 5% of the cells and immunophenotypic maturation of the leukemia cells (upregulation of CD16 and CD14 B antigens). Further characterization has shown that F-actin is aggregated both in HL-60 cells and in human monocytes exposed to 10−7 mol/L jaspamide. Well-spread cultured human monocytes contracted and adopted round shapes after treatment with jaspamide. Moreover, a dose-dependent increase in both total actin and de novo synthesized portions of the soluble actin was observed in jaspamide-treated HL-60 cells. Jaspamide treatment inhibits ruffling and intracellular movement in HL-60 cells and monocytes, but does not affect phagocytic activity or respiratory burst activity. The consequential effects of jaspamide-induced actin reorganization on ruffling, versus its negligible effect on phagocytosis and oxidative burst, may shed light on molecular mechanisms of actin involvement in these processes. Jaspamide disrupts the actin cytoskeleton of normal and malignant mammalian cells with no significant effect on phagocytic activity and may, therefore, be considered as a novel therapeutic agent.

Alteration of Actin Organization by Jaspamide Inhibits Ruffling, but not Phagocytosis or Oxidative Burst, in HL-60 Cells and Human Monocytes

Jaspamide, a naturally occurring cyclic peptide isolated from the marine sponge Hemiastrella minor, has fungicidal and growth-inhibiting activities. Exposure of promyelocytic HL-60 cells and human monocytes to jaspamide induces a dramatic reorganization of actin from a typical fibrous network to focal aggregates. HL-60 cells exposed to 5 × 10−8 mol/L or 10−7 mol/L jaspamide exhibited a reduced proliferation rate. In addition, 10−7mol/L jaspamide induced maturation of HL-60 cells as indicated by the appearance of a lobulated nucleus in 55% ± 5% of the cells and immunophenotypic maturation of the leukemia cells (upregulation of CD16 and CD14 B antigens). Further characterization has shown that F-actin is aggregated both in HL-60 cells and in human monocytes exposed to 10−7 mol/L jaspamide. Well-spread cultured human monocytes contracted and adopted round shapes after treatment with jaspamide. Moreover, a dose-dependent increase in both total actin and de novo synthesized portions of the soluble actin was observed in jaspamide-treated HL-60 cells. Jaspamide treatment inhibits ruffling and intracellular movement in HL-60 cells and monocytes, but does not affect phagocytic activity or respiratory burst activity. The consequential effects of jaspamide-induced actin reorganization on ruffling, versus its negligible effect on phagocytosis and oxidative burst, may shed light on molecular mechanisms of actin involvement in these processes. Jaspamide disrupts the actin cytoskeleton of normal and malignant mammalian cells with no significant effect on phagocytic activity and may, therefore, be considered as a novel therapeutic agent.

Hypertonic immunomodulation is reversible and accompanied by changes in CD11b expression

BACKGROUND

In a two-hit model of hemorrhagic shock and lipopolysaccharide (LPS), we previously showed that hypertonic saline (HTS) resuscitation reduced lung sequestration of neutrophils and the accompanying injury. This effect was partially attributed to suppressed expression of the surface adhesion molecule CD11b. This study investigates the duration of this protective effect after a single HTS dose and the usefulness of repeated infusions.

MATERIAL AND METHODS

The previous two-hit rodent model was used. Neutrophil lung sequestration was measured by bronchoalveolar fluid cell count. CD11b expression was followed by flow cytometry. In vitro studies used isolated human neutrophils.

RESULTS

Eighteen hours following resuscitation, the protective effect of HTS was lost. At this time, LPS caused an increase in both neutrophil lung sequestration and CD11b expression, regardless of the resuscitation regimen used. A second infusion of HTS prevented these changes and restored the lung protection observed earlier. In vitro studies showed that the duration of hypertonic pretreatment is an important determinant of cell responsiveness under the isotonic conditions: Four but not 2 h hypertonic exposure was able to prevent upregulation of CD11b induced by LPS added immediately after reestablishing isotonicity.

CONCLUSIONS

This study demonstrates that HTS resuscitation lessens lung neutrophil sequestration and CD11b surface expression induced by LPS. This protective effect is transient but can be restored by a second HTS infusion suggesting that maintenance of beneficial effect necessitates repeated HTS addition. The reversibility ensures rapid modulation of neutrophil functions, thereby preventing acute tissue damage without causing long-lasting immunosuppression.

Hypertonicity prevents lipopolysaccharide-stimulated CD11b/CD18 expression in human neutrophils in vitro: role for p38 inhibition

BACKGROUND

Neutrophil sequestration in the lungs plays an important role in the development of acute respiratory distress syndrome. We previously reported that hypertonic saline resuscitation attenuated lung injury after hemorrhagic shock and lipopolysaccharide (LPS) by abolishing neutrophil CD11b up-regulation. We investigated the mechanism underlying this effect.

METHODS

Human neutrophils were exposed to LPS in the presence or absence of hypertonicity or SB203580 (p38 inhibitor). CD11b and CD14 were studied by immunofluorescence and p38 phosphorylation by immunoblotting.

RESULTS

Hypertonicity had no effect on CD11b or CD14, caused a weak p38 phosphorylation, and completely prevented the LPS-induced p38 phosphorylation and CD11b up-regulation. p38 inhibition also abrogated CD11b up-regulation by LPS.

CONCLUSION

MAPKp38 is important in CD11b regulation by LPS. The inhibitory effect of hypertonicity on the LPS-mediated effect may contribute to its protective anti-inflammatory effect observed in vivo. Transient hypertonicity might minimize organ injury in diseases characterized by neutrophil-mediated damage such as ARDS.

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.

Immunomodulatory Effects of Hypertonic Resuscitation on the Development of Lung Inflammation Following Hemorrhagic Shock

Hypertonic resuscitation fluids are known to be effective in restoring circulating volume in the hypovolemic trauma patient. Previous studies have suggested that hypertonicity might exert effects on immune cells leading to an altered host response. The present studies evaluated the effect of hypertonic resuscitation on the development of lung injury in a hemorrhagic shock model in which antecedent shock primes for increased lung neutrophil sequestration in response to intratracheal LPS. Resuscitation with hypertonic saline significantly reduced albumin leak, bronchoalveolar lavage fluid neutrophil counts, and the degree of histopathologic injury compared with resuscitation with Ringer’s lactate. Both in vivo and in vitro data suggest that this beneficial effect may be related to altered adhesion molecule expression by the neutrophil. Specifically, hypertonicity induced shedding of L-selectin and prevented LPS-stimulated expression and activation of CD11b, both of which might contribute to reduced sequestration in the lung. Impaired up-regulation of lung ICAM-1 may have also participated, although ex vivo studies suggest that alterations in neutrophils were sufficient to account for the effect. Lung cytokine-induced neutrophil chemoattractant did not differ between animals resuscitated with hypertonic saline vs Ringer’s lactate. Considered together, these studies demonstrate a possible novel approach to inhibiting organ injury in disease processes characterized by neutrophil-mediated damage.