Attachment to fibronectin or vitronectin makes human neutrophil migration sensitive to alterations in cytosolic free calcium concentration

Lysophosphatidylcholine Alleviates Acute Lung Injury by Regulating Neutrophil Motility and Neutrophil Extracellular Trap Formation

Sepsis is predominantly initiated by bacterial infection and can cause systemic inflammation, which frequently leads to rapid death of the patient. However, this acute systemic inflammatory response requires further investigation from the perspectives of clinical judgment criteria and early treatment strategies for the relief of symptoms. Lysophosphatidylcholine (LPC) 18:0 may relieve septic symptoms, but the relevant mechanism is not clearly understood. Therefore, we aimed to assess the effectiveness of LPC as a therapeutic treatment for acute inflammation in the lung induced by lipopolysaccharide in mice. Systemic inflammation of mice was induced by lipopolysaccharide (LPS) inoculation to investigate the role of LPC in the migration and the immune response of neutrophils during acute lung injury. By employing two-photon intravital imaging of the LPS-stimulated LysM-GFP mice and other in vitro and in vivo assays, we examined whether LPC alleviates the inflammatory effect of sepsis. We also tested the effect of LPC to human neutrophils from healthy control and sepsis patients. Our data showed that LPC treatment reduced the infiltration of innate immune cells into the lung. Specifically, LPC altered neutrophil migratory patterns and enhanced phagocytic efficacy in the damaged lung. Moreover, LPC treatment reduced the release of neutrophil extracellular trap (NET), which can damage tissue in the inflamed organ and exacerbate disease. It also reduced human neutrophil migration under inflammatory environment. Our results suggest that LPC can alleviate sepsis-induced lung inflammation by regulating the function of neutrophils. These findings provide evidence for the beneficial application of LPC treatment as a potential therapeutic strategy for sepsis.

TRPM2 ion channels steer neutrophils towards a source of hydrogen peroxide

Neutrophils must navigate accurately towards pathogens in order to destroy invaders and thus defend our bodies against infection. Here we show that hydrogen peroxide, a potent neutrophil chemoattractant, guides chemotaxis by activating calcium-permeable TRPM2 ion channels and generating an intracellular leading-edge calcium "pulse". The thermal sensitivity of TRPM2 activation means that chemotaxis towards hydrogen peroxide is strongly promoted by small temperature elevations, suggesting that an important function of fever may be to enhance neutrophil chemotaxis by facilitating calcium influx through TRPM2. Chemotaxis towards conventional chemoattractants such as LPS, CXCL2 and C5a does not depend on TRPM2 but is driven in a similar way by leading-edge calcium pulses. Other proposed initiators of neutrophil movement, such as PI3K, Rac and lyn, influence chemotaxis by modulating the amplitude of calcium pulses. We propose that intracellular leading-edge calcium pulses are universal drivers of the motile machinery involved in neutrophil chemotaxis.

Research advances on structure and biological functions of integrins

Integrins are an important family of adhesion molecules that were first discovered two decades ago. Integrins are transmembrane heterodimeric glycoprotein receptors consisting of α and β subunits, and are comprised of an extracellular domain, a transmembrane domain, and a cytoplasmic tail. Therein, integrin cytoplasmic domains may associate directly with numerous cytoskeletal proteins and intracellular signaling molecules, which are crucial for modulating fundamental cell processes and functions including cell adhesion, proliferation, migration, and survival. The purpose of this review is to describe the unique structure of each integrin subunit, primary cytoplasmic association proteins, and transduction signaling pathway of integrins, with an emphasis on their biological functions.

Computational modelling suggests dynamic interactions between Ca2+, IP3 and G protein-coupled modules are key to robust Dictyostelium aggregation

Under conditions of starvation, Dictyostelium cells begin a programme of development during which they aggregate to form a multicellular structure by chemotaxis, guided by propagating waves of cyclic AMP that are relayed robustly from cell to cell. In this paper, we develop and analyse a new model for the intracellular and extracellular cAMP dependent processes that regulate Dictyostelium migration. The model allows, for the first time, a quantitative analysis of the dynamic interactions between calcium, IP(3) and G protein-dependent modules that are shown to be key to the generation of robust cAMP oscillations in Dictyostelium cells. The model provides a mechanistic explanation for the transient increase in cytosolic free Ca(2+) concentration seen in recent experiments with the application of the calmodulin inhibitor calmidazolium (R24571) to Dictyostelium cells, and also allows elucidation of the effects of varying both the conductivity of stretch-activated channels and the concentration of external phosphodiesterase on the oscillatory regime of an individual cell. A rigorous analysis of the robustness of the new model shows that interactions between the different modules significantly reduce the sensitivity of the resulting cAMP oscillations to variations in the kinetics of different Dictyostelium cells, an essential requirement for the generation of the spatially and temporally synchronised chemoattractant cAMP waves that guide Dictyostelium aggregation.

Optical microscopy-based migration assay for human neutrophils

This unit describes an in vitro microscopy assay for examining the migration of human neutrophils in two dimensions to identify the underlying cause of a migration defect and to evaluate a variety of migration parameters that cannot be studied using migration through a porous filter. Freshly isolated human neutrophils a placed in the chamber, stimulated, and images are collected at various time points. The data can be used to determine the effects of a pharmacological treatment on the migration of individual cells.

Chemotaxis assays for eukaryotic cells

Chemotaxis is a complex response of a cell to an external stimulus. It involves detecting and measuring the concentration of the chemoattractant, biochemical transmission of the information, and the motility and adhesive changes associated with the response. This unit describes a number of chemotaxis assays that can be used to identify chemoattractants individually and in large-scale screenings, to distinguish chemotaxis from chemokinesis, and to analyze cellular behavioral and biochemical responses. Some of these assays such as the filter, under agarose, and small population assays, can be used to monitor the behavior of large groups of cells; the bridge, pipet, and upshift assays can be used to analyze the responses of single cells.

The recognition of adsorbed and denatured proteins of different topographies by β2 integrins and effects on leukocyte adhesion and activation

Leukocyte beta2 integrins Mac-1 and p150,95 are promiscuous cell-surface receptors that recognise and mediate cell adhesion to a variety of adsorbed and denatured proteins. We used albumin as a model protein to study whether leukocyte adhesion and activation depended on the nm-scale topography of a protein adlayer. Albumin adsorbed from the native conformation gave rise to different adlayer topographies and different amounts of adsorbed protein on hydrophobic and relatively hydrophilic polystyrene and silanised silicon-wafer surfaces, whereas adsorption of pre-denatured Alb resulted in similar adlayer topographies and similar amounts of adsorbed protein on these surfaces. All three distinct protein-adlayer topographies supported adhesion of in vitro differentiated, macrophage-like U937 and THP-1 cells, but did not support adhesion of their promonocytic precursors. Human monocytes freshly isolated from peripheral blood did not adhere to adsorbed albumin, not even in the presence of monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha chemokines. Adhesion of the macrophage-like cells to albumin in any of the three topographies was inhibited by antibodies against beta2 integrins, but not by antibodies against beta1 integrins, and did not induce secretion of the proinflammatory cytokine tumour necrosis factor-alpha.

Hg2+ and small-sized polyethylene glycols have inverse effects on membrane permeability, while both impair neutrophil cell motility

Toxic effects after exposure to mercury are well documented in human. Little is, however, known about how Hg(2+) affect host defense in general and neutrophil functions in particular. We show here that exposure of human neutrophils to HgCl(2) dose-dependently impairs chemoattractant-stimulated motility. Long-term exposure (5-10 min) to Hg(2+) yields a rapid influx of extracellular Ca(2+) followed by leakage of cytosolic fluorophores, as assessed using fura-2 and ratio imaging microscopy. The inhibition on motility was partly reversible, since pre-treated neutrophils placed in an Hg(2+)-free environment displayed higher migration rates. The Hg(2+)-induced fluxes were prevented by addition of small-sized polyethylene glycols (PEG 200-400), which also dose-dependently inhibited neutrophil transmigration. Localized, minute micropipette additions of Hg(2+) or PEG caused retraction of the leading edge and redirection of cell migration. Since Hg(2+) increases and PEGs decrease membrane permeability in a partially competitive manner, we suggest that the known aquaporin-inhibitor Hg(2+) alters membrane permeability by affecting the bidirectional flux through the leukocyte aquaporin-9 (AQP9) while small-sized PEGs yield decreased membrane permeability by becoming trapped in the promiscuous channel. The local additions of Hg(2+) or PEG probably force other cell regions to take over from those with blocked AQPs. Hence, the cells turn direction of motility away from the micromanipulator needle.

Signaling to migration in neutrophils: importance of localized pathways

Neutrophils, a major type of blood leukocytes, are indispensable for host defense of bacterial infections. Directed migration in a gradient of chemotactic stimuli enables these cells to rapidly find the site of infection and destroy the invading pathogens. Chemotactic factors bind to seven-transmembrane-domain receptors and activate heterotrimeric G-proteins. Downstream of these proteins a complex interrelated signaling network is activated in human neutrophils. Stimulation of phospholipase C beta results in activation of protein kinase C isoforms and increases in cytosolic calcium. Activation of the enzyme phosphoinositide 3-kinase results in increased production of phosphatidylinositol 3,4,5-trisphosphate and phosphatidyl 3,4-bisphosphate. In addition, small GTP-binding proteins of the Rho family, the mitogen-activated protein kinase cascade, tyrosine kinases and protein phosphatases are activated. The enzyme phosphoinositide 3-kinase and the small cytosolic GTP-binding proteins Rho and Rac emerge as key regulators of neutrophil migration. A steep internal gradient of phosphatidylinositol 3,4,5-trisphosphate, with a high concentration in the leading lamellae, is thought to regulate polarized actin polymerization and formation of protrusions, together with Rac which may be more directly involved in initiating actin reorganization. Rho may regulate localized myosin activation, tail retraction, cell body traction and dynamics of adhesion. The impact of these different signaling pathways on reversible actin polymerization, development of polarity, reversible adhesion and migration, and the putative targets of these pathways in neutrophils, are reviewed in this article. Insight into mechanisms regulating migration of neutrophils could potentially lead to novel therapeutic strategies for counteracting chronic activation of neutrophils which leads to tissue damage.

Membrane lipid organization is critical for human neutrophil polarization

In response to chemoattractants neutrophils extend an actin-rich pseudopod, which imparts morphological polarity and is required for migration. Even when stimulated by an isotropic bath of chemoattractant, neutrophils exhibit persistent polarization and continued lamellipod formation at the front, suggesting that the cells establish an internal polarity. In this report, we show that perturbing lipid organization by depleting plasma membrane cholesterol levels reversibly inhibits cell polarization and migration. Among other receptor-mediated responses, beta(2) integrin up-regulation was unaffected, and initial calcium mobilization was only partially reduced by cholesterol depletion, indicating that this treatment did not abrogate initial receptor-mediated signal transduction. Interestingly, cholesterol depletion did not prevent initial activation of the GTPase Rac or an initial burst of actin polymerization, but rather it inhibited prolonged activation of Rac and sustained actin polymerization. Collectively, these findings support a model in which the plasma membrane is organized into domains that aid in amplifying the chemoattractant gradient and maintaining cell polarization.

Analysis of retinal pigment epithelium integrin expression and adhesion to aged submacular human Bruch's membrane

PURPOSE

Uncultured aged retinal pigment epithelium (RPE) does not resurface aged Bruch's membrane after 24 hours in organ culture. These experiments assess whether culturing alters RPE integrin expression and resurfacing of Bruch's membrane.

METHODS

RNA was isolated from uncultured and cultured RPE of aged adult donor and fetal eyes. Integrin subunit messenger RNA (mRNA) expression was studied by reverse transcriptase-polymerase chain reaction (RT-PCR) and semiquantitative analysis of the amplified products. Cell surface integrin expression was assessed using flow cytometry. Passaged cultured fetal RPE and primary cultured aged RPE were seeded onto Bruch's membrane, and resurfacing was assessed with scanning electron microscopy.

RESULTS

Uncultured fetal RPE had low levels of alpha3 and beta5 mRNA compared to passaged cultured fetal RPE. Uncultured aged RPE had decreased alpha1-5 mRNA compared to primary cultured aged RPE. Cultured aged RPE had decreased beta4 and beta5 mRNA compared to passaged cultured fetal RPE. Flow cytometry confirmed the expression of alpha1-5, alphav, and beta1 protein on cultured fetal RPE and alpha1-3 and beta1 protein on cultured aged RPE. Twenty-four hours after seeding, cultured fetal and aged RPE resurfaced 99% +/- 1.3% and 76% +/- 22%, respectively, of aged submacular Bruch's membrane specimens from which native RPE had been debrided, exposing the native RPE basement membrane. Cultured fetal and aged RPE resurfaced 97% +/- 3.1% and 39% +/- 35%, respectively, of specimens in which the inner collagenous layer was exposed.

CONCLUSIONS

Uncultured aged RPE has low amounts of integrin subunits that form receptors for laminin, fibronectin, and collagens. Culturing up-regulates integrins and promotes more efficient aged RPE attachment to and survival on aged Bruch's membrane.

Motility enhancement by tumor-derived mutant E-cadherin is sensitive to treatment with epidermal growth factor receptor and phosphatidylinositol 3-kinase inhibitors

Diffuse-type gastric and lobular breast cancers are characterized by frequent mutations in the cell adhesion molecule E-cadherin. Here we report that tumor-associated mutations of E-cadherin enhanced random cell movement of transfected MDA-MB-435S mammary carcinoma cells as compared to wild-type (wt) E-cadherin-expressing cells. The mutations included in frame deletions of exons 8 or 9 and a point mutation in exon 8 which all affect putative calcium-binding sites within the linker region of the second and third extracellular domain. Motility enhancement by mutant E-cadherin was investigated by time-lapse laser scanning microscopy. Increased cell motility stimulated by mutant E-cadherin was influenced by cell-matrix interactions. The motility-increasing activity of mutant E-cadherin was blocked by application of pharmacological inhibitors of epidermal growth factor receptor and phosphatidylinositol (PI) 3-kinase. Investigation of the activation status of PI 3-kinase and the downstream signaling molecules Akt/protein kinase B and MAP kinase p44/42 showed that these kinases are not more strongly activated in mutant E-cadherin-expressing cells than in wt E-cadherin-expressing cells. Instead, the basal level of PI 3-kinase is necessary for mutant E-cadherin-enhanced cell motility. Our data suggest a critical role of E-cadherin mutations for the fine tuning of tumor cell motility.

Cytoskeleton-dependent membrane domain segregation during neutrophil polarization

On treatment with chemoattractant, the neutrophil plasma membrane becomes organized into detergent-resistant membrane domains (DRMs), the distribution of which is intimately correlated with cell polarization. Plasma membrane at the front of polarized cells is susceptible to extraction by cold Triton X-100, whereas membrane at the rear is resistant to extraction. After cold Triton X-100 extraction, DRM components, including the transmembrane proteins CD44 and CD43, the GPI-linked CD16, and the lipid analog, DiIC(16), are retained within uropods and cell bodies. Furthermore, CD44 and CD43 interact concomitantly with DRMs and with the F-actin cytoskeleton, suggesting a mechanism for the formation and stabilization of DRMs. By tracking the distribution of DRMs during polarization, we demonstrate that DRMs progress from a uniform distribution in unstimulated cells to small, discrete patches immediately after activation. Within 1 min, DRMs form a large cap comprising the cell body and uropod. This process is dependent on myosin in that an inhibitor of myosin light chain kinase can arrest DRM reorganization and cell polarization. Colabeling DRMs and F-actin revealed a correlation between DRM distribution and F-actin remodeling, suggesting that plasma membrane organization may orient signaling events that control cytoskeletal rearrangements and, consequently, cell polarity.

Protein kinase C-delta regulates thrombin-induced ICAM-1 gene expression in endothelial cells via activation of p38 mitogen-activated protein kinase

The procoagulant thrombin promotes the adhesion of polymorphonuclear leukocytes to endothelial cells by a mechanism involving expression of intercellular adhesion molecule 1 (ICAM-1) via an NF-kappaB-dependent pathway. We now provide evidence that protein kinase C-delta (PKC-delta) and the p38 mitogen-activated protein (MAP) kinase pathway play a critical role in the mechanism of thrombin-induced ICAM-1 gene expression in endothelial cells. We observed the phosphorylation of PKC-delta and p38 MAP kinase within 1 min after thrombin challenge of human umbilical vein endothelial cells. Pretreatment of these cells with the PKC-delta inhibitor rottlerin prevented the thrombin-induced phosphorylation of p38 MAP kinase, suggesting that p38 MAP kinase signals downstream of PKC-delta. Inhibition of PKC-delta or p38 MAP kinase by pharmacological and genetic approaches markedly decreased the thrombin-induced NF-kappaB activity and resultant ICAM-1 expression. The effects of PKC-delta inhibition were secondary to inhibition of IKKbeta activation and of subsequent NF-kappaB binding to the ICAM-1 promoter. The effects of p38 MAP kinase inhibition occurred downstream of IkappaBalpha degradation without affecting the DNA binding function of nuclear NF-kappaB. Thus, PKC-delta signals thrombin-induced ICAM-1 gene transcription by a dual mechanism involving activation of IKKbeta, which mediates NF-kappaB binding to the ICAM-1 promoter, and p38 MAP kinase, which enhances transactivation potential of the bound NF-kappaB p65 (RelA).

Increased intracellular calcium is required for spreading of rat islet beta-cells on extracellular matrix

Rat islet beta-cells spread in response to glucose when attached on the matrix produced by a rat bladder carcinoma cell line (804G). Furthermore, in a mixed population of cells, it has been observed previously that spread cells secrete more insulin acutely in response to glucose, compared with cells that remain rounded. These results suggest bi-directional signaling between the islet beta-cell and the extracellular matrix. In the present study, the role of increased intracellular free Ca2+ concentration [Ca2+]i as an intracellular step linking glucose stimulation and beta-cell spreading (inside-out signaling) was investigated. Purified rat beta-cells were attached to this matrix and incubated under various conditions known to affect [Ca2+]i. The effect of glucose on beta-cell spreading was mimicked by 25 mmol/l KCl (which induces calcium influx) and inhibited by diazoxide (which impairs depolarization and calcium entry) and by the L-type Ca2+ channel blocker SR-7037. When a 24-h incubation at 16.7 glucose was followed by 24 h at 2.8 mmol/l, beta-cells that had first spread regained a round phenotype. In the presence of thapsigargin, spreading progressed throughout the experiment, suggesting that capture of calcium by the endoplasmic reticulum is involved in the reversibility of spreading previously induced by glucose. Spreading was still observed in degranulated beta-cells and in botulinum neurotoxin E-expressing beta-cells when exocytosis was prevented. In summary, the results indicate that increased [Ca2+]i is required for the glucose-induced spreading of beta-cells on 804G matrix and that it is not a consequence of exocytotic processes that follow elevation of [Ca2+]i.

Cellular receptors and hantavirus pathogenesis

Hantaviruses cause two potentially lethal diseases, HPS and HFRS, and both diseases result in defects in vascular permeability and platelet function. Human beta 3 integrins confer cellular susceptibility to HPS- and HFRS-causing hantaviruses, a fact directly linking platelets, endothelial cells, and hantavirus diseases to the use of [figure: see text] cellular receptors that maintain capillary integrity and regulate platelet function. The role of vitronectin, PAI-1, uPAR, and complement cascades in hantavirus pathogenesis are unstudied but may contribute to specific disease syndromes effected by hantaviruses. The divergence of hantavirus surface glycoproteins and common beta 3-integrin usage provides further insight into the interaction of hantaviruses with cells. G1 and G2 glycoprotein variation is likely to contribute to additional interactions that determine pathogenic responses to individual viruses. beta 3-integrin usage also suggests that common elements exist on G1 or the more highly conserved G2 surface glycoprotein, which mediate viral attachment to integrins. Although there is currently no data defining the virion attachment protein, the development of antibodies that recognize the hantavirus attachment protein and block integrin interactions is of interest since it is likely to provide an additional point for therapeutic intervention and vaccine development. There are a plethora of effects that could be elicited by hantavirus regulation of cellular beta 3 integrins and their ligands that are consistent with hantavirus diseases. Since beta 3 integrins are critical adhesive receptors on platelets and endothelial cells and regulate both vascular permeability and platelet activation and adhesion, the use of these receptors by hantaviruses is likely to be fundamental to hantavirus pathogenesis. The lack of an animal model for hantavirus pathogenesis has prevented a systematic analysis of immune and cellular responses to hantavirus infections, and it impedes our ability to study protective or therapeutic approaches to hantavirus diseases. However, recent findings suggest that human beta 3 integrins within transgenic mice may provide animal models of hantavirus pathogenesis and have the potential to radically alter the ability to investigate hantavirus disease.

Tumor invasion as dysregulated cell motility

Investigations across a range of disciplines over the past decade have brought the study of cell motility and its role in invasion to an exciting threshold. The biophysical forces proximally involved in generating cell locomotion, as well as the underlying signaling and genomic regulatory processes, are gradually becoming elucidated. We now appreciate the intricacies of the many cellular and extracellular events that modulate cell migration. This has enabled the demonstration of a causal role of cell motility in tumor progression, with various points of 'dysregulation' of motility being responsible for promoting invasion. In this paper, we describe key fundamental principles governing cell motility and branch out to describe the essence of the data that describe these principles. It has become evident that many proposed models may indeed be converging into a tightly-woven tapestry of coordinated events which employ various growth factors and their receptors, adhesion receptors (integrins), downstream molecules, cytoskeletal components, and altered genomic regulation to accomplish cell motility. Tumor invasion occurs in response to dysregulation of many of these modulatory points; specific examples include increased signaling from the EGF receptor and through PLC gamma, altered localization and expression of integrins, changes in actin modifying proteins and increased transcription from specific promoter sites. This diversity of alterations all leading to tumor invasion point to the difficulty of correcting causal events leading to tumor invasion and rather suggest that the underlying common processes required for motility be targeted for therapeutic intervention.

Integrin-mediated adhesion regulates cell polarity and membrane protrusion through the Rho family of GTPases

Integrin-mediated adhesion is a critical regulator of cell migration. Here we demonstrate that integrin-mediated adhesion to high fibronectin concentrations induces a stop signal for cell migration by inhibiting cell polarization and protrusion. On fibronectin, the stop signal is generated through alpha 5 beta 1 integrin-mediated signaling to the Rho family of GTPases. Specifically, Cdc42 and Rac1 activation exhibits a biphasic dependence on fibronectin concentration that parallels optimum cell polarization and protrusion. In contrast, RhoA activity increases with increasing substratum concentration. We find that cross talk between Cdc42 and Rac1 is required for substratum-stimulated protrusion, whereas RhoA activity is inhibitory. We also show that Cdc42 activity is inhibited by Rac1 activation, suggesting that Rac1 activity may down-regulate Cdc42 activity and promote the formation of stabilized rather than transient protrusion. Furthermore, expression of RhoA down-regulates Cdc42 and Rac1 activity, providing a mechanism whereby RhoA may inhibit cell polarization and protrusion. These findings implicate adhesion-dependent signaling as a mechanism to stop cell migration by regulating cell polarity and protrusion via the Rho family of GTPases.

Roles of phospholipid signaling in chemoattractant-induced responses

Chemoattractants, including chemokines, play a central role in regulation of inflammatory reactions by attracting and activating leukocytes. These molecules have been found to regulate metabolism of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) via phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K). Recent studies of mouse lines that lack PLC-(beta)2, PLC-(beta)3, or PI3K(gamma) demonstrate that chemoattractants act through PLC-(beta)2 and PLC-(beta)3 to hydrolyze PtdIns(4,5)P(2) and through PI3K(gamma) to phosphorylate PtdIns(4,5)P(2) in mouse neutrophils. These studies also confirmed the importance and revealed new roles of these signaling pathways in chemoattractant-induced responses.

Low concentrations of fibrinogen increase cell migration speed on fibronectin/fibrinogen composite cables

Optimal cell migration rate in a given direction (velocity) is a function of speed and directional persistence. Migration speed has been reported to be a function of adhesion strength such that optimal cell migration occurs where the cell is able to form enough stable attachments for good traction while allowing attachments at the trailing end to be broken during locomotion. This is particularly important in peripheral nerve regeneration where rapid Schwann cell recruitment across the injury site will lead to better functional recovery and reduced end organ atrophy. The aim here was to investigate the effects of changing adhesion properties of Fn materials by adding fibrinogen in order to design an optimal material for repair processes. Cell migration on Fn/Fg-cables increased with increasing content of %Fg to a peak cell migration velocity (Schwann cells) of 49 microm/h, at 50% Fg. Further increases in Fg content hindered cell migration. Vinculin-rich attachment plaques were reduced in a dose-dependent manner as the content of %Fg was increased whilst cells at the optimum Fg proportion for cell migration were moderately well spread. These results support the idea that optimum cell migration rates occur at intermediate attachment conditions, in this case at 50% Fg. These results show that incorporation of Fg into Fn-based materials will enhance the speed of Schwann cell migration and this would be likely to improve peripheral nerve regeneration. Indeed, directionally aligned Fn-based materials can now be engineered to give optimal cell velocity during repair cell recruitment in a range of tissue repair or tissue engineering applications.

Oriented endocytic recycling of α5β1 in motile neutrophils

During cell migration, integrin attachments to the substratum provide the means to generate the traction and force necessary to achieve locomotion. Once the cell has moved over these attachments, however, it is equally important that integrins detach from the substratum. The fate of integrins after detachment may include release from the cell, lateral diffusion across the cell surface, or endocytosis and redelivery to the cell surface. Polymorphonuclear neutrophils (PMNs) become stuck on the extracellular matrix proteins fibronectin and vitronectin when their intracellular free calcium concentration ([Ca++]i) is buffered. Taking advantage of this feature of PMN migration, we investigated the fate of integrins to differentiate among various models of migration. We demonstrate that 5β1, one of the fibronectin-binding integrins, is responsible for immobilization of [Ca++]i-buffered PMNs on fibronectin. We find that 5 and β1 are in endocytic vesicles in PMNs and that 5 colocalizes with a marker for an endocytic recycling compartment. When [Ca++]i is buffered, 5 and β1 become concentrated in clusters in the rear of the adherent cells, suggesting that [Ca++]i transients are required for 5β1 detachment from the substratum. Inhibition of 5β1 detachment by buffering [Ca++]i results in the depletion of 5 from both endocytic vesicles and the recycling compartment, providing compelling evidence that integrins are normally recycled by way of endocytosis and intracellular trafficking during cell migration. This model is further refined by our demonstration that the endocytic recycling compartment reorients to retain its localization just behind the leading lamella as PMNs migrate, indicating that membrane recycling during neutrophil migration has directionality.

Neutrophil polarity and locomotion are associated with surface redistribution of leukosialin (CD43), an antiadhesive membrane molecule

This study analyzed the behavior of an antiadhesive membrane molecule, CD43, in neutrophil polarization and locomotion. CD43 cross-linking by antibodies induced neutrophil locomotion, with CD43 molecules clustered at the uropod of polarized neutrophils. In contrast, CD11b/CD18 cross-linking by antibodies did not affect either cell polarization or locomotion. Stimulation of suspended or adherent neutrophils with chemotactic peptide results in cell polarization and locomotion and a concomitant redistribution of CD43 to the uropod. This process is entirely reversible. The study also investigated which actin-binding protein could be involved in CD43 lateral redistribution. -Actinin and moesin are preferentially adsorbed on Sepharose beads bearing a recombinant CD43 intracellular domain. Analysis by immunofluorescence confocal microscopy shows a codistribution of moesin during CD43 lateral redistribution. By contrast, -actinin is located at the leading edge, an area devoid of CD43. These results shed new light on the role of CD43 membrane redistribution, which appears to be directly related to neutrophil polarity and locomotion.

Oriented endocytic recycling of α5β1 in motile neutrophils

During cell migration, integrin attachments to the substratum provide the means to generate the traction and force necessary to achieve locomotion. Once the cell has moved over these attachments, however, it is equally important that integrins detach from the substratum. The fate of integrins after detachment may include release from the cell, lateral diffusion across the cell surface, or endocytosis and redelivery to the cell surface. Polymorphonuclear neutrophils (PMNs) become stuck on the extracellular matrix proteins fibronectin and vitronectin when their intracellular free calcium concentration ([Ca++]i) is buffered. Taking advantage of this feature of PMN migration, we investigated the fate of integrins to differentiate among various models of migration. We demonstrate that 5β1, one of the fibronectin-binding integrins, is responsible for immobilization of [Ca++]i-buffered PMNs on fibronectin. We find that 5 and β1 are in endocytic vesicles in PMNs and that 5 colocalizes with a marker for an endocytic recycling compartment. When [Ca++]i is buffered, 5 and β1 become concentrated in clusters in the rear of the adherent cells, suggesting that [Ca++]i transients are required for 5β1 detachment from the substratum. Inhibition of 5β1 detachment by buffering [Ca++]i results in the depletion of 5 from both endocytic vesicles and the recycling compartment, providing compelling evidence that integrins are normally recycled by way of endocytosis and intracellular trafficking during cell migration. This model is further refined by our demonstration that the endocytic recycling compartment reorients to retain its localization just behind the leading lamella as PMNs migrate, indicating that membrane recycling during neutrophil migration has directionality.

Neutrophil polarity and locomotion are associated with surface redistribution of leukosialin (CD43), an antiadhesive membrane molecule

This study analyzed the behavior of an antiadhesive membrane molecule, CD43, in neutrophil polarization and locomotion. CD43 cross-linking by antibodies induced neutrophil locomotion, with CD43 molecules clustered at the uropod of polarized neutrophils. In contrast, CD11b/CD18 cross-linking by antibodies did not affect either cell polarization or locomotion. Stimulation of suspended or adherent neutrophils with chemotactic peptide results in cell polarization and locomotion and a concomitant redistribution of CD43 to the uropod. This process is entirely reversible. The study also investigated which actin-binding protein could be involved in CD43 lateral redistribution. -Actinin and moesin are preferentially adsorbed on Sepharose beads bearing a recombinant CD43 intracellular domain. Analysis by immunofluorescence confocal microscopy shows a codistribution of moesin during CD43 lateral redistribution. By contrast, -actinin is located at the leading edge, an area devoid of CD43. These results shed new light on the role of CD43 membrane redistribution, which appears to be directly related to neutrophil polarity and locomotion.

Ca2+-dependent myosin II activation is required for uropod retraction during neutrophil migration

Buffering of intracellular Ca2+ transients in human neutrophils leads to reduced motility due to defective uropod detachment on fibronectin and vitronectin-coated surfaces. Since one potential target of a rise in [Ca2+]i is the activation of myosin II, we characterized the role of myosin II during motility. Treatment of neutrophils with a myosin inhibitor (2,3-butanedione monoxime), or myosin light chain kinase inhibitors (ML-7, ML-9, or KT5926) resulted in impaired uropod retraction and a dose-dependent decrease in chemokinesis following stimulation with N-formyl-Met-Leu-Phe (fMLP). Treatment with ML-9 resulted in a redistribution of F-actin and talin to the non-retracted uropods, mimicking the redistribution observed during [Ca2+]i buffering. Impairment of uropod retraction and redistribution of F-actin and talin by myosin II inhibition was only observed on adhesive substrates such as fibronectin and not on poorly adhesive substrates such as human serum-coated glass. At higher concentrations of ML-9, cell polarization was inhibited and pseudopod extension occurred radially. Using an antibody specific for serine 19-phosphorylated regulatory light chain of myosin II, regions of activated myosin II were found at the leading edge as well as the uropod in motile fMLP-stimulated cells. [Ca2+]i depletion caused a 50% decrease in the level of serine 19-phosphorylated myosin II suggesting that activation of myosin II by intracellular Ca2+ transients may be an essential step in establishing a polarized pseudopod and providing the force required for uropod retraction during PMN motility on adhesive surfaces.

Calreticulin couples calcium release and calcium influx in integrin-mediated calcium signaling

The engagement of integrin alpha7 in E63 skeletal muscle cells by laminin or anti-alpha7 antibodies triggered transient elevations in the intracellular free Ca(2+) concentration that resulted from both inositol triphosphate-evoked Ca(2+) release from intracellular stores and extracellular Ca(2+) influx through voltage-gated, L-type Ca(2+) channels. The extracellular domain of integrin alpha7 was found to associate with both ectocalreticulin and dihydropyridine receptor on the cell surface. Calreticulin appears to also associate with cytoplasmic domain of integrin alpha7 in a manner highly dependent on the cytosolic Ca(2+) concentration. It appeared that intracellular Ca(2+) release was a prerequisite for Ca(2+) influx and that calreticulin associated with the integrin cytoplasmic domain mediated the coupling of between the Ca(2+) release and Ca(2+) influx. These findings suggest that calreticulin serves as a cytosolic activator of integrin and a signal transducer between integrins and Ca(2+) channels on the cell surface.

Migration of human vascular smooth muscle cells involves serum-dependent repeated cytosolic calcium transients

Migration of vascular smooth muscle cells (VSMC) is a key event in the formation of neointima during atherosclerosis. Fura-2 loaded VSMCs were used to investigate calcium homeostasis during cell migration. Multiple spontaneous transient increases in cytosolic free calcium [Ca(2+)](i)were observed in single human VSMCs migrating on type I collagen. Such [Ca(2+)](i)transients were dependent on the presence of serum or PDGF-BB. Removal of serum, or loading cells with BAPTA, abolished the transients and decreased cell migration speed. The transients were not affected by disruption of cell polarization by dihydrocytochalasin B. Adhesion was used to investigate the specific role of cell-substrate interactions in the generation of transients. Transients are seen in VSMCs adhering either on collagen or on poly-L-lysine, suggesting that generation of transients is not strictly dependent on integrins. Buffering [Ca(2+)](i) with BAPTA led to accumulation of (beta)1 integrins at the cellular tail, and to increased release of integrin on the extracellular matrix. These results demonstrate a role for [Ca(2+)](i) transients in the rapid, serum-dependent migration of VSMCs. These [Ca(2+)](i)transients are present in migrating VSMCs only when two simultaneous events occur: (1) substrate independent spreading and (2) stimulation of cells by serum components such as PDGF-BB.

Neutrophil inhibitory factor abrogates neutrophil adhesion by blockade of CD11a and CD11b beta(2) integrins

We studied the basis of inhibition of polymorphonuclear leukocyte (PMN) adhesion induced by neutrophil inhibitory factor (NIF), a 41-kDa CD11/CD18 beta(2) integrin-binding protein isolated from the canine hookworm (Ancylostoma caninum). NIF blocked PMN adhesion in a concentration-dependent manner with complete blockade occurring at approximately 10 nM NIF. Because CD11a and CD11b beta(2) integrins are functionally active on stimulated PMNs, and yet NIF is postulated to inhibit only CD11b integrin by binding to its I domain, we evaluated the contributions of CD11a and CD11b beta(2) integrins in the mechanism of inhibition of PMN adhesion to endothelial cells. We observed an additive inhibitory effect (>90% inhibition) of PMN adhesion to endothelial cells when NIF was used in combination with anti-CD11b monoclonal antibodies, which alone at saturating concentrations reduced PMN adhesion by only 50%. NIF also prevented aggregation of phorbol ester-stimulated JY lymphoblastoid cells that expressed only the functionally active CD11a, suggesting that NIF also can inhibit CD11a-dependent response. We transduced the NIF cDNA into human dermal microvessel endothelial cells in which NIF synthesis and release prevented PMN adhesion to the transduced human dermal microvessel endothelial cells. These data indicated that the potent antiadhesive effect of NIF may be the result of inhibition of CD11a and CD11b beta(2) integrins on PMNs. Moreover, the strategy of NIF release from transduced endothelial cells suggests the feasibility of blocking the CD11a- and CD11b beta(2) integrin-dependent PMN adhesion and PMN migration responses specifically at sites of endothelial cell activation.

Cell motility mediated by rho and Rho-associated protein kinase plays a critical role in intrahepatic metastasis of human hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) can invade the portal vein and metastasizes to other parts of the liver even at a relatively early stage of the disease, with less tumor spread occurring outside the liver. This intrahepatic metastasis is the main cause of liver failure and death in HCC patients. To analyze the mechanisms of intrahepatic metastasis we have constructed metastatic models using orthotopic implantation of human HCC cell lines. Five HCC cell lines formed liver tumors after injection into the livers of SCID mice, and of those 5 cell lines, Li7 and KYN-2 cells also resulted in vascular tumor thrombi and intrahepatic metastasis. These 2 cell lines had markedly higher cell motilities than the other 3 cell lines in vitro. Their motilities appeared to be Rho-mediated; serum and lysophosphatidic acid (LPA) evoked actin reorganization and motility of Li7 cells, and C3 exoenzyme exposure reduced the motility of both serum-stimulated Li7 cells and KYN-2 cells. Dominant negative and active forms of p160 Rho-associated coiled-coil forming protein kinase (p160ROCK), one of the downstream effectors of Rho, were separately and stably introduced into Li7 cells. Dominant active p160ROCK transfectants showed increased motility that was independent of serum and LPA, and dominant negative p160ROCK transfectants showed reduced motility under stimulation. Furthermore, implantation of dominant negative p160ROCK transfectants resulted in a reduced metastatic rate in vivo compared with the parent cells or a control transfectant. These findings indicate that cell motility mediated by the Rho/p160ROCK signaling pathway plays a critical role in intrahepatic metastasis of human HCC.

Chemotaxis of Rat Mast Cells Toward Adenine Nucleotides

Rat mucosal mast cells express P2 purinoceptors, occupation of which mobilizes cytosolic Ca2+ and activates a potassium conductance. The primary function of this P2 system in mast cell biology remains unknown. Here, we show that extracellular ADP causes morphological changes in rat bone marrow-cultured mast cells (BMMC) typical of those occurring in cells stimulated by chemotaxins, and that the nucleotides ADP, ATP, and UTP are effective chemoattractants for rat BMMC. ADP was also a chemotaxin for murine J774 monocytes. The nucleotide selectivity and pertussis toxin sensitivity of the rat BMMC migratory response suggest the involvement of P2U receptors. Poorly hydrolyzable derivatives of ADP and ATP were effective chemotaxins, obviating a role for adenosine receptors. Buffering of external Ca2+ at 100 nM or reduction of the electrical gradient driving Ca2+ entry (by elevating external K+) blocked ADP-driven chemotaxis, suggesting a role for Ca2+ influx in this process. Anaphylatoxin C5a was a potent chemotaxin (EC50 ≈0.5 nM) for J774 monocytes, but it was inactive on rat BMMC in the presence or absence of laminin. Ca2+ removal or elevated [K+] had modest effects on C5a-driven chemotaxis of J774 cells, implicating markedly different requirements for Ca2+ signaling in C5a- vs ADP-mediated chemotaxis. This is supported by the observation that depletion of Ca2+ stores with thapsigargin completely blocked migration induced by ADP but not C5a. These findings suggest that adenine nucleotides liberated from parasite-infested tissue could participate in the recruitment of mast cells by intestinal mucosa.

The integrin alpha9beta1 mediates adhesion to activated endothelial cells and transendothelial neutrophil migration through interaction with vascular cell adhesion molecule-1

The integrin alpha9beta1 has been shown to be widely expressed on smooth muscle and epithelial cells, and to mediate adhesion to the extracellular matrix proteins osteopontin and tenascin-C. We have found that the peptide sequence this integrin recognizes in tenascin-C is highly homologous to the sequence recognized by the closely related integrin alpha4beta1, in the inducible endothelial ligand, vascular cell adhesion mole-cule-1 (VCAM-1). We therefore sought to determine whether alpha9beta1 also recognizes VCAM-1, and whether any such interaction would be biologically significant. In this report, we demonstrate that alpha9beta1 mediates stable cell adhesion to recombinant VCAM-1 and to VCAM-1 induced on human umbilical vein endothelial cells by tumor necrosis factor-alpha. Furthermore, we show that alpha9beta1 is highly and selectively expressed on neutrophils and is critical for neutrophil migration on VCAM-1 and tenascin-C. Finally, alpha9beta1 and alpha4 integrins contribute to neutrophil chemotaxis across activated endothelial monolayers. These observations suggest a possible role for alpha9beta1/VCAM-1 interactions in extravasation of neutrophils at sites of acute inflammation.

Extracellular calcium regulates HeLa cell morphology during adhesion to gelatin: role of translocation and phosphorylation of cytosolic phospholipase A2

Attachment of HeLa cells to gelatin induces the release of arachidonic acid (AA), which is essential for cell spreading. HeLa cells spreading in the presence of extracellular Ca2+ released more AA and formed more distinctive lamellipodia and filopodia than cells spreading in the absence of Ca2+. Addition of exogenous AA to cells spreading in the absence of extracellular Ca2+ restored the formation of lamellipodia and filopodia. To investigate the role of cytosolic phospholipase A2 (cPLA2) in regulating the differential release of AA and subsequent formation of lamellipodia and filopodia during HeLa cell adhesion, cPLA2 phosphorylation and translocation from the cytosol to the membrane were evaluated. During HeLa cell attachment and spreading in the presence of Ca2+, all cPLA2 became phosphorylated within 2 min, which is the earliest time cell attachment could be measured. In the absence of extracellular Ca2+, the time for complete cPLA2 phosphorylation was lengthened to <4 min. Maximal translocation of cPLA2 from cytosol to membrane during adhesion of cells to gelatin was similar in the presence or absence of extracellular Ca2+ and remained membrane associated throughout the duration of cell spreading. The amount of total cellular cPLA2 translocated to the membrane in the presence of extracellular Ca2+ went from <20% for unspread cells to >95% for spread cells. In the absence of Ca2+ only 55-65% of the total cPLA2 was translocated to the membrane during cell spreading. The decrease in the amount translocated could account for the comparable decrease in the amount of AA released by cells during spreading without extracellular Ca2+. Although translocation of cPLA2 from cytosol to membrane was Ca2+ dependent, phosphorylation of cPLA2 was attachment dependent and could occur both on the membrane and in the cytosol. To elucidate potential activators of cPLA2, the extracellular signal-related protein kinase 2 (ERK2) and protein kinase C (PKC) were investigated. ERK2 underwent a rapid phosphorylation upon early attachment followed by a dephosphorylation. Both rates were enhanced during cell spreading in the presence of extracellular Ca2+. Treatment of cells with the ERK kinase inhibitor PD98059 completely inhibited the attachment-dependent ERK2 phosphorylation but did not inhibit cell spreading, cPLA2 phosphorylation, translocation, or AA release. Activation of PKC by phorbol ester (12-O-tetradecanoylphorbol-13-acetate) induced and attachment-dependent phosphorylation of both cPLA2 and ERK2 in suspension cells. However, in cells treated with the PKC inhibitor Calphostin C before attachment, ERK2 phosphorylation was inhibited, whereas cPLA2 translocation and phosphorylation remained unaffected. In conclusion, although cPLA2-mediated release of AA during HeLa cell attachment to a gelatin substrate was essential for cell spreading, neither ERK2 nor PKC appeared to be responsible for the attachment-induced cPLA2 phosphorylation and the release of AA.

Regulation of integrin-mediated adhesion during cell migration

Migrating cells form dynamic and highly regulated adhesive interactions with their environment. In particular, integrin-mediated adhesions to the extracellular matrix (ECM) play a central role in cell migration. This review focuses on recent advances in understanding the adhesive mechanisms that regulate cell detachment at the rear of migrating fibroblasts and neutrophils. The contribution of several key adhesive regulators is discussed, including myosin mediated cell contractility, tyrosine phosphorylation, rho, calcium fluxes, and calpain. A challenge for future investigation will be to determine how adhesive events are spatially and temporally coordinated to promote productive directional cell movements.

Deconstructing (and reconstructing) cell migration

An overriding objective in cell biology is to be able to relate properties of particular molecular components to cell behavioral functions and even physiology. In the "traditional" mode of molecular cell biology, this objective has been tackled on a molecule-by-molecule basis, and in the "future" mode sometimes termed "functional genomics," it might be attacked in a high-throughput, parallel manner. Regardless of the manner of approach, the relationship between molecular-level properties and cell-level function is exceedingly difficult to elucidate because of the large number of relevant components involved, their high degree of interconnectedness, and the inescapable fact that they operate as physico-chemical entities-according to the laws of kinetics and mechanics-in space and time within the cell. Cell migration is a prominent representative example of such a cell behavioral function that requires increased understanding for both scientific and technological advance. This article presents a framework, derived from an engineering perspective regarding complex systems, intended to aid in developing improved understanding of how properties of molecular components influence the function of cell migration. That is, cell population migration behavior can be deconstructed as follows: first in terms of a mathematical model comprising cell population parameters (random motility, chemotaxis/haptotaxis, and chemokinesis/haptokinesis coefficients), which in turn depend on characteristics of individual cell paths that can be analyzed in terms of a mathematical model comprising individual cell parameters (translocation speed, directional persistence time, chemotactic/haptotactic index), which in turn depend on cell-level physical processes underlying motility (membrane extension and retraction, cell/substratum adhesion, cell contractile force, front-vs.-rear asymmetry), which in turn depend on molecular-level properties of the plethora of components involved in governance and regulation of these processes. Hence, the influence of any molecular component on cell population migration can be understood by reconstructing these relationships from the molecular level to the physical process level to the individual cell path level to the cell population distribution level. This approach requires combining experimental, theoretical, and computational methodologies from molecular biology, biochemistry, biophysics, and bioengineering.

Cytosolic free calcium and the cytoskeleton in the control of leukocyte chemotaxis

In response to a chemotactic gradient, leukocytes extravasate and chemotax toward the site of pathogen invasion. Although fundamental in the control of many leukocyte functions, the role of cytosolic free Ca2+ in chemotaxis is unclear and has been the subject of debate. Before becoming motile, the cell assumes a polarized morphology, as a result of modulation of the cytoskeleton by G protein and kinase activation. This morphology may be reinforced during chemotaxis by the intracellular redistribution of Ca2+ stores, cytoskeletal constituents, and chemoattractant receptors. Restricted subcellular distributions of signaling molecules, such as Ca2+, Ca2+/calmodulin, diacylglycerol, and protein kinase C, may also play a role in some types of leukocyte. Chemotaxis is an essential function of most cells at some stage during their development, and a deeper understanding of the molecular signaling and structural components involved will enable rational design of therapeutic strategies in a wide variety of diseases.

Calcium waves induced by large voltage pulses in fish keratocytes

Intracellular calcium waves in fish keratocytes are induced by the application of electric field pulses with amplitudes between 55 and 120 V/cm and full width at half-maximum of 65-100 ms. Calcium concentrations were imaged using two-photon excited fluorescence microscopy (Denk et al., 1990 Science. 248:73-76; Williams et al. 1994 FASEB J. 8:804-813) and the ratiometric calcium indicator indo-1. The applied electric field pulses induced waves with fast calcium rise times and slow decays, which nucleated in the lamellipodium at the hyperpolarized side of the cells and, less frequently, at the depolarized side. The effectiveness of wave generation was determined by the change induced in the membrane potential, which is about half the field strength times the cell width in the direction of the field. Stimulation of waves began at voltage drops across the cell above 150 mV and saturated at voltage drops above 300 mV, where almost all cells exhibited a wave. Waves were not induced in low-calcium media and were blocked by the nonselective calcium channel blockers cobalt chloride and verapamil, but not by specific organic antagonists of voltage-sensitive calcium channel conductance. Thapsigargin stopped wave propagation in the cell body, indicating that calcium release from intracellular stores is necessary. Thus a voltage pulse stimulates Ca2+ influx through calcium channels in the plasma membrane, and if the intracellular calcium concentration reaches a threshold, release from intracellular stores is induced, creating a propagating wave. These observations and the measured parameters (average velocity approximately 66 micron/s and average rise time approximately 68 ms) are consistent with a wave amplification model in which[equation, see text] determines the effective diffusivity of the propagating molecules, D approximately 300 micron2/s (Meyer, 1991. Cell. 64:675-678).

The protein tyrosine phosphatase SHP-1 regulates integrin-mediated adhesion of macrophages

The Src homology 2 domain phosphatase-1 (SHP-1) is a tyrosine phosphatase containing two amino-terminal SH2 domains and is expressed primarily by hematopoietic-derived cells [1]. The viable motheaten (Hcphme-v) mutant mice (mev) suffer from progressive inflammation due to a deficiency of SHP-1 enzyme activity [2,3] and die at 3-4 months of age from macrophage and neutrophil accumulation in the lung [4]. The mechanism by which SHP-1 deficiency leads to inflammation is unknown. We found that macrophages from mev mice adhered and spread to a greater extent than normal macrophages through alpha m beta 2 integrin-mediated contacts. Whereas macrophages deficient in the transmembrane tyrosine phosphatase CD45 (CD45-/-) spontaneously detached from alpha m beta 2 integrin contacts [5], cells deficient in both CD45 and SHP-1 did not. In SHP-1 deficient macrophages there was a 10-15-fold increase in D-3 phospholipid products of phosphatidylinositol (PI) 3-kinase. Concomitantly, there was a 2-5-fold increase in membrane-associated PI 3-kinase activity in mev macrophages relative to normal macrophages. Treatment of macrophages with the PI 3-kinase inhibitors wortmannin or LY294002 resulted in a dramatic detachment of cells, indicating that PI 3-kinase activity is required for adhesion. These data demonstrate that SHP-1 is necessary for detachment from alpha m beta 2 integrin-mediated contacts in primary macrophages and suggest that a defect in this pathway may contribute to inflammatory disease.

Na+/Ca2+ exchanger overexpression impairs calcium signaling in fibroblasts: inhibition of the [Ca2+] increase at the cell periphery and retardation of cell adhesion

We examined the Ca2+ handling property and cell function of CCL39 fibroblasts highly overexpressing the cardiac isoform (NCX1) of Na+/ Ca2+ exchanger. In NCX1 transfectants in 146 mM Na+, ionomycin, alpha-thrombin or thapsigargin only produced a small transient increase in [Ca2+]i compared to the large increase seen in control cells, although resting [Ca2+]i was not significantly different between these cells. In Na+-free medium, in contrast, the [Ca2+]i responses in NCX1 transfectants and control cells stimulated with these agents were not different, indicating that the Ca2+ content of the intracellular store(s) does not decrease on NCX1 transfection. The expression levels of the endoplasmic reticulum and plasma membrane Ca2+-ATPases, and thrombin- or serum-stimulated cell growth were not altered in NCX1 transfectants. The latter finding suggests that Ca2+ signaling in the nucleus is not impaired appreciably. On fluorescence imaging and confocal microscopy, we found that [Ca2+] did not increase in the peripheral cytoplasm of these cells treated with alpha-thrombin in Na+-containing medium. In these NCX1 transfectants, activation of the plasma membrane Ca2+-activated K+ channels by thrombin or ionomycin was markedly suppressed, and the integrin-mediated adhesion to substrate was significantly delayed compared with control cells. NCX1-overexpressing CCL39 cells thus seem to be a good model with which we can study the Ca2+-regulated membrane processes under physiologically relevant conditions.

Physical and biochemical regulation of integrin release during rear detachment of migrating cells

Cell migration can be considered as a repeated cycle of membrane protrusion and attachment, cytoskeletal contraction and rear detachment. At intermediate and high levels of cell-substratum adhesiveness, cell speed appears to be rate-limited by rear detachment, specifically by the disruption of cytoskeleton-adhesion receptor-extracellular matrix (ECM) linkages. Often, cytoskeletal linkages fracture to release integrin adhesion receptors from the cell. Cell-extracellular matrix bonds may also dissociate, allowing the integrins to remain with the cell. To investigate molecular mechanisms involved in fracturing these linkages and regulating cell speed, we have developed an experimental system to track integrins during the process of rear retraction in Chinese hamster ovary (CHO) cells. Integrin expression level was varied by transfecting CHO B2 cells, which express very little endogenous alpha5 integrin, with a plasmid containing human alpha5 integrin cDNA and sorting the cells into three populations with different alpha5 expression levels. Receptor/ligand affinity was varied using CHO cells transfected with either alphaIIbbeta3 or alphaIIbbeta3(beta1-2), a high affinity variant. alphaIIbbeta3(beta1-2) is activated to a higher affinity state with an anti-LIBS2 antibody. Fluorescent probes were conjugated to non-adhesion perturbing anti-integrin antibodies, which label integrins in CHO cells migrating on a matrix-coated glass coverslip. The rear retraction area was determined using phase contrast microscopy and integrins initially in this area were tracked by fluorescence microscopy and a cooled CCD camera. We find that rear retraction rate appears to limit cell speed at intermediate and high adhesiveness, but not at low adhesiveness. Upon rear retraction, the amount of integrin released from the cell increases as extracellular matrix concentration, receptor level and receptor-ligand affinity increase. In fact, integrin release is a constant function of cell-substratum adhesiveness and the number of cell-substratum bonds. In the adhesive regime where rear detachment limits the rate of cell migration, cell speed has an inverse relationship to the amount of integrin released at the rear of the cell. At high cell-substratum adhesiveness, calpain, a Ca2+-dependent protease, is also involved in release of cytoskeletal linkages during rear retraction. Inhibition of calpain results in decreased integrin release from the cell membrane, and consequently a decrease in cell speed, during migration. These observations suggest a model for rear retraction in which applied tension and calpain-mediated cytoskeletal linkage cleavage are required at high adhesiveness, but only applied tension is required at low adhesiveness.

Calcium/calmodulin-dependent protein kinase II controls alpha5beta1 integrin-mediated inside-out signaling

Fibronectin binding on alpha5beta1 integrin is strictly dependent on intracellular calcium. Using an in vitro assay, we previously found that either calcineurin inhibitors or a blocking calcineurin monoclonal antibody added to cell lysates completely abolished the fibronectin/integrin interaction, which suggested that the activity of calcineurin, a calcium/calmodulin-dependent phosphatase, was required to counteract some kinase activity and maintain the high affinity state of alpha5beta1. In this paper, we show that blocking of the calcium/calmodulin kinase II (CaMKII) activity with the specific inhibitor KN-62 or with its pseudosubtrate Autocamtide-2 preserved the high affinity state of the integrin even under experimental conditions that inhibit calcineurin. Conversely, the addition of purified CaMKII to the cell lysate inhibited alpha5beta1 binding to fibronectin in vitro. Consistent with these results, cell adhesion on fibronectin was stimulated by KN-62. Moreover, Scatchard analysis of fibronectin binding on CHO cells revealed that KN-62 decreased the Kd value from 0.3 to 0.05 microM. Finally the expression of exogenous constitutively active CaMKII resulted in a dramatic defect in cell adhesion with no significant modification in alpha5beta1 cell surface expression. In summary our results demonstrate that CaMKII controls the affinity state of the integrin alpha5beta1 in vitro and in living cells.

Differential regulation of interleukin-8 and intercellular adhesion molecule-1 by H2O2 and tumor necrosis factor-alpha in endothelial and epithelial cells

The reactive oxygen intermediate H2O2 can function as a signaling molecule to activate gene expression. In this study, we demonstrate that oxidant stress induced by tumor necrosis factor alpha (TNFalpha) or H2O2 differentially regulates intercellular adhesion molecule-1 (ICAM-1) and interleukin-8 (IL-8) gene expression in endothelial and epithelial cells. Northern blot analysis revealed that TNFalpha induced both ICAM-1 and IL-8 expression in either the A549 lung epithelial cell line or the human microvessel endothelial cell line (HMEC-1). In contrast, H2O2 selectively induced only ICAM-1 in HMEC-1 and only IL-8 in A549. This cell type-specific pattern of IL-8 expression was also observed in several other endothelial and epithelial cells. TNFalpha induced greater IL-8 gene expression as compared with H2O2, but the kinetics of induction were similar. The induction of epithelial IL-8 message was accompanied by a corresponding increase in functional IL-8 protein secretion as determined by a neutrophil motility assay. The increased neutrophil motility stimulated by conditioned media from H2O2- or TNFalpha-exposed A549 cells was completely inhibited by an anti-IL-8 antibody. TNFalpha and H2O2 also induced a differential pattern of CC chemokine expression in A549. While TNFalpha induced both RANTES and MCP-1, H2O2 induced only MCP-1. These data suggest that epithelial cells under oxidant stress contribute to the inflammatory cytokine network by selective production of IL-8, MCP-1, and RANTES, which may critically influence the site-specific recruitment of leukocyte subsets.

Distribution of plasmalemmal Ca(2+)-pump and caveolin in the corneal epithelium during the wound healing process

PURPOSE

Caveolae are small plasmalemmal invaginations which are assumed to play various physiological functions. In the present study, distribution of two caveolae-specific proteins, the plasmalemmal Ca(2+)-pump and caveolin, was examined in the corneal epithelium in the normal state and after artificial wounding.

METHODS

A central epithelial ablation was made in the mouse cornea by a razor blade. After various intervals, the corneas were excised, fixed, and rapidly frozen. The specimens were subjected to immunofluorescence microscopy and immunoelectron microscopy, using antibodies against the plasmalemmal Ca(2+)-pump or caveolin.

RESULTS

In the normal corneal epithelium, both plasmalemmal Ca(2+)-pump and caveolin were observed along the cell surface by immunofluorescence microscopy, and were localized to caveolae by immunogold electron microscopy. In the regenerating epithelium, 12-18 h after injury, plasmalemmal Ca(2+)-pump was seen as many dots in the cytoplasm by immunofluorescence microscopy; in contrast, caveolin persisted along the cell surface. Immunoelectron microscopy revealed that the labeling for the plasmalemmal Ca(2+)-pump was located around membranous structures in the cytoplasm and was scarce along the plasma membrane, while caveolin remained in caveolae. The Ca(2+)-pump regained normal distribution when the wound was closed. By quantitation in electron micrographs, the number of caveolae per unit plasma membrane length was found to be decreased in the wounded corneal epithelium.

CONCLUSIONS

The present results indicate that caveolae undergo compositional modification during the wound healing process of the corneal epithelium. Considering putative caveolar functions, the phenomenon may be related to possible fluctuations of the intracellular Ca(2+)-concentration in the regenerating epithelium.

Controlling the molecular motor of neutrophil chemotaxis

Our defence against microbes depends largely on the ability of neutrophils to migrate from the blood stream to sites of infection. Although the ability of animal cells to move may be primitive, and also fundamental for a number of phenomena in biology, the cellular mechanism by which neutrophils are able to move rapidly towards the infection remains an enigma. Even though the structures of the receptors involved have been sequenced and many of the molecules involved in neutrophil adherence and traction identified, the essential mechanisms that control and regulate the neutrophil motor remain obscure. Here, an outline of the fundamental inadequacies in our current understanding is given, along with some recent developments that promise to produce some significant advances.

Cross talk between adhesion molecules: control of N-cadherin activity by intracellular signals elicited by beta1 and beta3 integrins in migrating neural crest cells

During embryonic development, cell migration and cell differentiation are associated with dynamic modulations both in time and space of the repertoire and function of adhesion receptors, but the nature of the mechanisms responsible for their coordinated occurrence remains to be elucidated. Thus, migrating neural crest cells adhere to fibronectin in an integrin-dependent manner while maintaining reduced N-cadherin-mediated intercellular contacts. In the present study we provide evidence that, in these cells, the control of N-cadherin may rely directly on the activity of integrins involved in the process of cell motion. Prevention of neural crest cell migration using RGD peptides or antibodies to fibronectin and to beta1 and beta3 integrins caused rapid N-cadherin-mediated cell clustering. Restoration of stable intercellular contacts resulted essentially from the recruitment of an intracellular pool of N-cadherin molecules that accumulated into adherens junctions in tight association with the cytoskeleton and not from the redistribution of a preexisting pool of surface N-cadherin molecules. In addition, agents that cause elevation of intracellular Ca2+ after entry across the plasma membrane were potent inhibitors of cell aggregation and reduced the N-cadherin- mediated junctions in the cells. Finally, elevated serine/ threonine phosphorylation of catenins associated with N-cadherin accompanied the restoration of intercellular contacts. These results indicate that, in migrating neural crest cells, beta1 and beta3 integrins are at the origin of a cascade of signaling events that involve transmembrane Ca2+ fluxes, followed by activation of phosphatases and kinases, and that ultimately control the surface distribution and activity of N-cadherin. Such a direct coupling between adhesion receptors by means of intracellular signals may be significant for the coordinated interplay between cell-cell and cell-substratum adhesion that occurs during embryonic development, in wound healing, and during tumor invasion and metastasis.

Effects of buffering intracellular free calcium on neutrophil migration through three-dimensional matrices

Repeated transient increases in intracellular free calcium levels ([Ca2-]i) are required for polymorphonuclear neutrophil migration on two-dimensional surfaces coated with fibronectin or vitronectin. Cells in which [Ca2+]i is buffered with quin2 become stuck on these substrates. Neutrophils migrating through the extracellular matrix in vivo encounter these and other substrates in a three-dimensional architecture that may alter the spatial distribution of adhesion receptors in contact with the matrix. In this study, we used fluorescence confocal microscopy to obtain moving three-dimensional images of neutrophils migrating through a biological tissue (human amnion) in the presence and absence of [Ca2+]i-buffering with quin2. In the absence of buffering, [Ca2+]i transients similar to those seen in cells migrating in two-dimensions were observed. [Ca2+]i-buffered neutrophils were able to migrate into the matrix, but they became attached firmly to the substrate at the rear of the cell, resulting in a drastically elongated morphology. Immunofluorescence revealed that neutrophils adhered to regions of the matrix that contained fibronectin. RGD-containing peptides and antibodies that block integrin adhesion receptors for fibronectin and vitronectin were able to rescue the migration of quin2-treated cells through three-dimensional gels containing fibronectin and vitronectin. These data show that neutrophils migrating through physiologically relevant, three-dimensional matrices undergo repetitive increases in [Ca2+]i that are required for integrin-mediated detachment from the matrix.

Integrin-ligand binding properties govern cell migration speed through cell-substratum adhesiveness

Migration of cells in higher organisms is mediated by adhesion receptors, such as integrins, that link the cell to extracellular-matrix ligands, transmitting forces and signals necessary for locomotion. Whether cells will migrate or not on a given substratum, and also their speed, depends on several variables related to integrin-ligand interactions, including ligand levels, integrin levels, and integrin-ligand binding affinities. These and other factors affect the way molecular systems integrate to effect and regulate cell migration. Here we show that changes in cell migration speed resulting from three separate variables-substratum ligand level, cell integrin expression level, and integrin-ligand binding affinity-are all quantitatively predictable through the changes they cause in a single unifying parameter: short-term cell-substratum adhesion strength. This finding is consistent with predictions of a mathematical model for cell migration. The ligand concentration promoting maximum migration speed decreases reciprocally as integrin expression increases. Increases in integrin-ligand affinity similarly result in maximal migration at reciprocally lower ligand concentrations. The maximum speed attainable, however, remains unchanged as ligand concentration, integrin expression, or integrin-ligand affinity vary, suggesting that integrin coupling with intracellular motors remains unaltered.

Integrin-mediated calcium signaling and regulation of cell adhesion by intracellular calcium

Integrins are ubiquitous trans-membrane adhesion molecules that mediate the interaction of cells with the extracellular matrix (ECM). Integrins link cells to the ECM by interacting with the cell cytoskeleton. In cases such as leukocyte binding, integrins mediate cell-cell interactions and cell-ECM interactions. Recent research indicates that integrins also function as signal transduction receptors, triggering a number of intracellular signaling pathways that regulate cell behavior and development. A number of integrins are known to stimulate changes in intracellular calcium levels, resulting in integrin activation. Although changes in intracellular calcium regulate a vast number of cellular functions, this review will discuss the stimulation of calcium signaling by integrins and the role of intracellular calcium in the regulation of integrin-mediated adhesion.