Transient increases in cytosolic free calcium appear to be required for the migration of adherent human neutrophils

Modeling of granulocyte cytoskeletal responses following fMLP challenging

Formyl peptides released from Gram-negative bacteria ligate a group of specific mammalian receptors, expressed mainly on granulocytes, monocytes, and macrophages. Receptor ligation activates different transduction cascades, eventually leading to the release of reactive oxygen species and other bactericidal chemical species, and the activation of the actin cytoskeleton with extension of lamellipodia and migration toward the sites of maximal formyl peptide concentration. In vitro, under conditions of nongradient formyl peptide concentrations, lamellipodia form all around the cell contour (chemokinesis). In granulocytes challenged under these conditions with N-formyl-methionyl-leucyl-phenylalanine, (i) the power spectrum of the contour of activated cells shows a peak at a specific periodicity, indicating that the lamellipodial extension is not completely random but stochastically conforms to a deterministic scheme, and (ii) the morphological response (percent of cells exhibiting chemokinesis) tends to reach a maximum at certain drug concentrations, then declining at higher concentrations. Accordingly, the logarithm of the drug concentration-polarizing effect curve is bell-shaped. Herein we illustrate theoretical models for the simulation of these two components of the chemokinetic responses. We show that the main traits of the general morphology and arrangement of lamellipodia may be simulated by an algorithm that starting from a situation of random distribution of active receptors on the cell membrane, encompasses in the successive calculation cycles both a local autocatalytic enhancement of the actin polymerization and a relative inhibition of the actin polymerization at some distance from the more active polymerization foci. In addition, a drug log concentration-polarizing effect bell-shaped curve may be simulated by assuming that the N-formyl-methionyl-leucyl-phenylalanine, while binding with high affinity to the specific receptor, is also able to bind to another lower affinity receptor that may effect depolarizing actions or, more generally, metabolic blocking effects. Under these conditions, at low drug concentrations the polarizing effect brought about by the ligation of the specific receptor is largely predominant. However, as the drug concentration increases and the specific receptors approach saturation, the inhibitory effects become more and more powerful and the net polarizing effect is reduced.

Differential expression of CaMK-II genes during early zebrafish embryogenesis

CaMK-II is a highly conserved Ca(2+)/calmodulin-dependent protein kinase expressed throughout the lifespan of all vertebrates. During early development, CaMK-II regulates cell cycle progression and "non-canonical" Wnt-dependent convergent extension. In the zebrafish, Danio rerio, CaMK-II activity rises within 2 hr after fertilization. At the time of somite formation, zygotic expression from six genes (camk2a1, camk2b1, camk2g1, camk2g2, camk2d1, camk2d2) results in a second phase of increased activity. Zebrafish CaMK-II genes are 92-95% identical to their human counterparts in the non-variable regions. During the first three days of development, alternative splicing yields at least 20 splice variants, many of which are unique. Whole-mount in situ hybridization reveals that camk2g1 comprises the majority of maternal expression. All six genes are expressed strongly in ventral regions at the 18-somite stage. Later, camk2a1 is expressed in anterior somites, heart, and then forebrain. Camk2b1 is expressed in somites, mid- and forebrain, gut, retina, and pectoral fins. Camk2g1 appears strongly along the midline and then in brain, gut, and pectoral fins. Camk2g2 is expressed early in the midbrain and trunk and exhibits the earliest retinal expression. Camk2d1 is elevated early at somite boundaries, then epidermal tissue, while camk2d2 is expressed in discrete anterior locations, steadily increasing along either side of the dorsal midline and then throughout the brain, including the retina. These findings reveal a complex pattern of CaMK-II gene expression consistent with pleiotropic roles during development.

MscCa Regulation of Tumor Cell Migration and Metastasis

The acquisition of cell motility is a required step in order for a cancer cell to migrate from the primary tumor and spread to secondary sites (metastasize). For this reason, blocking tumor cell migration is considered a promising approach for preventing the spread of cancer. However, cancer cells just as normal cells can migrate by several different modes referred to as "amoeboid," "mesenchymal," and "collective cell." Under appropriate conditions, a single cell can switch between modes. A consequence of this plasticity is that a tumor cell may be able to avoid the effects of an agent that targets only one mode by switching modes. Therefore, a preferred strategy would be to target mechanisms that are shared by all modes. This chapter reviews the evidence that Ca(2+) influx via the mechanosensitive Ca(2+)-permeable channel (MscCa) is a critical regulator of all modes of cell migration and therefore represents a very good therapeutic target to block metastasis.

Influx of extracellular Ca2+ is necessary for electrotaxis in Dictyostelium

Intracellular free Ca2+ ([Ca2+](i)) is a pivotal signalling element in cell migration and is thought to be required for chemotaxis of Dictyostelium. Ca2+ signalling may also be important for electrotaxis. However this suggestion has been controversial. We show that electric fields direct Dictyostelium cells to migrate cathodally and increase [Ca2+](i) in Dictyostelium cells, as determined by Fluo-3 AM imaging and (45)Ca2+ uptake. Omission of extracellular Ca2+([Ca2+](e)) and incubation with EGTA abolished the electric-field-stimulated [Ca2+](i) rise and directional cell migration. This suggests a requirement for [Ca2+](e) in the electrotactic response. Deletion of iplA, a gene responsible for chemoattractant-induced [Ca2+](i) increase, had only a minor effect on the electric-field-induced [Ca2+](i) rise. Moreover, iplA-null Dictyostelium cells showed the same electrotactic response as wild-type cells. Therefore, iplA-independent Ca2+ influx is necessary for electrotactic cell migration. These results suggest that the [Ca2+](i) regulatory mechanisms induced by electric fields are different from those induced by cAMP and folic acid in Dictyostelium cells. Different roles of the iplA gene in chemoattractant-induced and electrically induced Ca2+ signalling, and different effects of [Ca2+](i) elevation on chemotaxis and electrotaxis indicate that the chemoattractant and electric cues activate distinctive initial signalling elements.

Ca2+ release from host intracellular stores and related signal transduction during Campylobacter jejuni 81-176 internalization into human intestinal cells

Campylobacter jejuni is the leading bacterial cause of human diarrhoeal disease in many parts of the world, including the USA. The ability of C. jejuni to invade the host intestinal epithelium is an important determinant of virulence. A common theme among pathogenic invasive micro-organisms is their ability to usurp the eukaryotic cell-signalling systems both to allow for invasion and to trigger disease pathogenesis. Ca(2+) is very important in a great variety of eukaryotic cell-signalling processes (e.g. calmodulin-activated enzymes, nuclear transcriptional upregulation, and cytoskeletal rearrangements). This study analyses the effects of Ca(2+) availability on invasion of human INT407 intestinal epithelial cells by C. jejuni strain 81-176. The ability of C. jejuni to invade INT407 cells was not blocked by chelation of any remaining extracellular Ca(2+) from host cells incubated in Ca(2+)-free, serum-free media. In contrast, C. jejuni invasion was markedly reduced either by chelating host intracellular Ca(2+) with 1,2-bis-(2-)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA, AM) or by blocking the release of Ca(2+) from intracellular stores with dantrolene or U73122. Moreover, Bay K8644, a plasma-membrane Ca(2+)-channel agonist, was observed to stimulate C. jejuni invasion, presumably by increasing host intracellular free Ca(2+) levels. Measurement of host-cell cytosolic Ca(2+) via spectrofluorimetry and fluorescence microscopy revealed an increase in Ca(2+) from 10 min post-infection. Monolayer pretreatment with either a calmodulin antagonist or a specific inhibitor of protein kinase C was found to cause a marked reduction in C. jejuni invasion, suggesting roles for these Ca(2+)-activated modulators in signal-transduction events involved in C. jejuni invasion. These results demonstrate that C. jejuni induces the mobilization of Ca(2+) from host intracellular stores, which is an essential step in the invasion of intestinal cells by this pathogen.

Calcium signalling in growth cone migration

Growth cones, the motile structures at the tips of advancing axons and dendrites, respond to a wide range of cues by either turning towards or away from the cue. Cytosolic calcium signals appear to mediate a large fraction of both types of response. Calcium signals can be generated by influx through plasma membrane channels or by release from intracellular stores. While neurotransmitters can elicit calcium influx through ionotropic receptors, other chemical cues open plasma membrane voltage gated calcium channels by a mechanism other than a change of membrane voltage. In general attractive cues generate spatially and temporally restricted calcium increases that are difficult to detect using conventional indicators. One target for these calcium signals is calmodulin dependent protein kinase II. Repulsive cues generate spatially and temporally more diffuse calcium increases that can be more readily detected using fluorescent indicators. One target for these is the phosphatase calcineurin, which may act by dephosphorylating GAP43 and allowing the latter to cap actin filaments.

Regulation of microglial behavior by ion channel activity

Microglia play an important role in the central nervous system, where these cells, it is believed, have both neuroprotective and neurotoxic effects. In response to acute brain injury or during neurodegenerative and neuroinflammatory diseases, activated microglial cells undergo shape changes, migrate to the affected sites of neuronal damage, proliferate, and release a variety of substances, such as cytokines and reactive oxygen species (ROS). This review summarizes the physiological mechanisms underlying microglial activation and deactivation processes, with particular focus on the involvement of microglial ion channels. Microglial ion channels have been shown to be capable, by regulating membrane potential, cell volume, and intracellular ion concentrations, of modulating or facilitating proliferation, migration, cytokine secretion, shape changes, and the respiratory burst of microglial cells.

Local calcium transients contribute to disappearance of pFAK, focal complex removal and deadhesion of neuronal growth cones and fibroblasts

Cell adhesion is crucial for migration of cells during development, and cell-substrate adhesion of motile cells is accomplished through the formation and removal of focal complexes that are sites of cell-substrate contact. Because Ca2+ signaling regulates the rate of axon outgrowth and growth cone turning, we investigated the potential role of Ca2+ in focal complex dynamics. We describe a novel class of localized, spontaneous transient elevations of cytosolic Ca2+ observed both in Xenopus neuronal growth cones and fibroblasts that are 2-6 mum in spatial extent and 2-4 s in duration. They are distributed throughout growth cone lamellipodia and at the periphery of fibroblast pseudopodia, which are regions of high motility. In both cell types, these Ca2+ transients lead to disappearance of phosphorylated focal adhesion kinase (pFAK) and deadhesion from the substrate as assessed by confocal and internal reflection microscopy, respectively. The loss of pFAK is inhibited by cyclosporin A, suggesting that these Ca2+ transients exert their effects via calcineurin. These results identify an intrinsic mechanism for local cell detachment that may be modulated by agents that regulate motility.

Ion channel clustering enhances weak electric field detection by neutrophils: apparent roles of SKF96365-sensitive cation channels and myeloperoxidase trafficking in cellular responses

We have tested Galvanovskis and Sandblom's prediction that ion channel clustering enhances weak electric field detection by cells as well as how the elicited signals couple to metabolic alterations. Electric field application was timed to coincide with certain known intracellular chemical oscillators (phase-matched conditions). Polarized, but not spherical, neutrophils labeled with anti-K(v)1.3, FL-DHP, and anti-TRP1, but not anti-T-type Ca(2+) channels, displayed clusters at the lamellipodium. Resonance energy transfer experiments showed that these channel pairs were in close proximity. Dose-field sensitivity studies of channel blockers suggested that K(+) and Ca(2+) channels participate in field detection, as judged by enhanced oscillatory NAD(P)H amplitudes. Further studies suggested that K(+) channel blockers act by reducing the neutrophil's membrane potential. Mibefradil and SKF93635, which block T-type Ca(2+) channels and SOCs, respectively, affected field detection at appropriate doses. Microfluorometry and high-speed imaging of indo-1-labeled neutrophils was used to examine Ca(2+) signaling. Electric fields enhanced Ca(2+) spike amplitude and triggered formation of a second traveling Ca(2+) wave. Mibefradil blocked Ca(2+) spikes and waves. Although 10 microM SKF96365 mimicked mibefradil, 7 microM SKF96365 specifically inhibited electric field-induced Ca(2+) signals, suggesting that one SKF96365-senstive site is influenced by electric fields. Although cells remained morphologically polarized, ion channel clusters at the lamellipodium and electric field sensitivity were inhibited by methyl-beta-cyclodextrin. As a result of phase-matched electric field application in the presence of ion channel clusters, myeloperoxidase (MPO) was found to traffic to the cell surface. As MPO participates in high amplitude metabolic oscillations, this suggests a link between the signaling apparatus and metabolic changes. Furthermore, electric field effects could be blocked by MPO inhibition or removal while certain electric field effects were mimicked by the addition of MPO to untreated cells. Therefore, channel clustering plays an important role in electric field detection and downstream responses of morphologically polarized neutrophils. In addition to providing new mechanistic insights concerning electric field interactions with cells, our work suggests novel methods to remotely manipulate physiological pathways.

Ca2+ influx through L-type Ca2+ channels controls the trailing tail contraction in growth factor-induced fibroblast cell migration

Growth factor-induced cell migration underlies various physiological and pathological processes. The mechanisms by which growth factors regulate cell migration are not completely understood. Although intracellular elevation of Ca2+ is known to be critical in cell migration, the source of this Ca2+ elevation and the mechanism by which Ca2+ modulates this process in fibroblast cells are not well defined. Here we show that increase of cellular Ca2+ through Ca2+ influx, rather than Ca2+ release from intracellular stores, is essential for growth factor-induced fibroblast cell migration. Voltage-gated L-type Ca2+ channels, previously known to exist in excitable cells such as neurons and muscle cells, are shown here to be present in fibroblasts as well. Furthermore, these channels are responsible for the Ca2+ influx. L-type Ca2+ channel inhibitors block growth factor-induced Ca2+ influx and fibroblast cell migration. One mechanism by which Ca2+ signals control cell migration is to regulate the contraction of the trailing edge of migrating fibroblasts; this process is controlled by the small GTPase Rho in fast migrating cells such as leukocytes. Downstream of Ca2+, both calmodulin and myosin light chain kinase, but not calcineurin, are involved leading to phosphorylation of the myosin light chain at the trailing end. Thus, trailing edge contraction is critically regulated by Ca2+ influx through L-type Ca2+ channels in growth factor-induced fibroblast cell migration.

A 'pure' chemoattractant formylpeptide analogue triggers a specific signalling pathway in human neutrophil chemotaxis

As it has not yet been established whether the second messengers involved in the neutrophil response have identical or specific signalling requirements for each physiological function, protein kinase C (PKC) isoforms and mitogen activated protein kinases (MAPKs) were studied in human chemotaxis triggered by the full agonist for-Met-Leu-Phe-OMe (fMLP-OMe) and the 'pure' chemoattractant for-Thp-Leu-Ain-OMe [Thp1,Ain3] analogue. Experiments were performed in the presence or absence of extracellular Ca2+, known to be an important modulator of second messengers. Our data demonstrate that specific PKC beta1 translocation and p38 MAPK phosphorylation are strongly associated with the chemotactic response of the neutrophils triggered by both peptides, while Ca2+ is not necessary for chemotaxis to occur. PKC and MAPK inhibitors were used in Western blotting assays and in cell locomotion experiments to investigate if the MAPK signalling pathway was controlled by PKC activation. The most important finding emerging from this study is that PKC and MAPK activate the chemotactic function of human neutrophils by two independent pathways.

Cyclic changes in keratocyte speed and traction stress arise from Ca2+-dependent regulation of cell adhesiveness

The activation of stretch-activated calcium channels (SACs) in keratocytes can induce spatially coordinated increases in traction stress that promote protrusion at the cell front, while simultaneously inducing retraction at the rear. To investigate how this occurs, we correlated calcium-induced changes in traction stress with alterations in cell speed and shape. Cyclic changes in these parameters were associated with each calcium transient. In addition, an inverse relationship was found between traction stress and cell speed, suggesting that alternating changes in adhesiveness were occurring at the rear. We investigated this further by inhibiting or inducing calcium transients and observing the effects on traction stress, cell speed and shape. Inhibition of calcium transients prevented retraction and led to a slow increase in traction stress. In addition, large aggregates of vinculin developed at the lateral rear edges of treated keratocytes, consistent with an increase in adhesiveness. Induction of a calcium transient resulted in a rapid retraction, involving both increased traction stress and adhesion disassembly at the rear. We also found that keratocytes exhibiting frequent transients generated larger traction stress and moved significantly faster than other cells. Together, these data suggest that calcium transients coordinate changes in adhesiveness with SAC-mediated cycles of mechano-chemical feedback.

Calmodulin spatial dynamics in RBL-2H3 mast cells

A line of rat basophilic leukaemia (RBL) cells, a model of mast cells, stably expressing EGFP-tagged calmodulin secreted normally in response to standard agonists. As reported for other cell types, calmodulin was concentrated in the mitotic spindle poles of dividing cells. In unstimulated interphase cells calmodulin was concentrated in the cell cortex and at a single central location. Disruption of cortical actin eliminated the concentration of calmodulin at the cortex while the central calmodulin concentration was associated with an enrichment of tubulin and is likely to represent the centrosome. Following stimulation with either an agonist that crosslinks Fc receptors or co-application of phorbol ester and a calcium ionophore the interior of the cells lost calmodulin while cortical fluorescence became more pronounced but also less uniform. After stimulation discrete bright puncta of calmodulin-EGFP (CaM-EGFP) appeared in the cell interior. Puncta colocalised with moving lysotracker-labelled granules, suggesting that calmodulin may play a role in organising their transport. Our results show that in interphase RBL cells a large fraction of the calmodulin pool is associated with targets in the actin cytoskeleton and demonstrate the utility of this model system for studying calmodulin biology.

Cutting edge: optical microspectrophotometry supports the existence of gel phase lipid rafts at the lamellipodium of neutrophils: apparent role in calcium signaling

Although much progress has been made in elucidating the biochemical properties of lipid rafts, there has been less success in identifying these structures within living cell membranes, which has led to some concern regarding their existence. One difficulty in analyzing lipid rafts using optical microscopy is their small size. We now test the existence of lipid rafts in polarized neutrophils, which redistribute lipid raft markers into comparatively large lamellipodia. Optical microspectrophotometry of Laurdan-labeled neutrophils revealed a large blue shift at lamellipodia relative to cell bodies. This blue shift disappeared after exposure to methyl-beta-cyclodextrin (m beta CD), which disrupts lipid rafts. The Ca(2+) channel transient receptor potential-like channel-1, a lipid raft marker, traffics to lamellipodia, but redistributes uniformly about cells after exposure to m beta CD. This is accompanied by disruption of Ca(2+) waves normally initiated at lamellipodia. Thus, m beta CD-sensitive lipid-ordered domains are present at and participate in signaling from the lamellipodia of living neutrophils.

Completion of neuronal migration regulated by loss of Ca(2+) transients

The migration of immature neurons constitutes one of the major processes by which the central nervous system takes shape. Completing the migration at the final destination requires the loss of cell body motility, but little is known about the signaling mechanisms underlying this process. Here, we show that a loss of transient Ca(2+) elevations triggers the completion of cerebellar granule cell migration. Simultaneous observation of the intracellular Ca(2+) levels and cell movement in cerebellar slices of the early postnatal mice revealed that granule cells exhibit distinct frequencies of the transient Ca(2+) elevations as they migrate in different cortical layers, and complete the migration only after the loss of Ca(2+) elevations. The reduction of the Ca(2+) elevation frequency by decreasing Ca(2+) influx, or by inhibiting the activity of phospholipase C, PKC, or Ca(2+)/calmodulin, halted the granule cell movement prematurely. In contrast, increasing the Ca(2+) elevation frequency by increasing Ca(2+) release from internal stores, or by elevating intracellular cAMP levels, significantly delayed the completion of granule cell migration. The timing of the loss of Ca(2+) elevations was intrinsically set in the granule cells and influenced by external cues. These results suggest that Ca(2+) signaling, dictated by multiple signaling systems, functions as a mediator for completing the migration of immature neurons.

Functional importance of Ca2+-activated K+ channels for lysophosphatidic acid-induced microglial migration

Abstract Migration of microglial cells towards damaged tissue plays a key role in central nervous system regeneration under pathological conditions. Using time lapse video microscopy we show that lysophosphatidic acid (LPA) enhances chemokinetic migration of murine microglial cells. In the presence of 1 micro m LPA, the mean migration rate of microglial cells was increased 3.8-fold. In patch-clamp studies we demonstrate that LPA induces activation of a Ca(2+)-activated K(+) current. Microglial Ca(2+)-activated K(+) currents were abolished by either 50 nm charybdotoxin or 10 micro m clotrimazole. In contrast, 5 micro m paxilline did not have any significant effects on Ca(2+)-activated K(+) currents. The LPA-stimulated migration of microglial cells was inhibited by blockers of IKCa1 Ca(2+)-activated K(+) channels. The mean migration rate of LPA-stimulated cells was decreased by 61% in the presence of 50 nm charybdotoxin or by 51% during exposure to 10 micro m clotrimazole. Microglial migration was not inhibited by 5 micro m paxilline. It is concluded that IKCa1 Ca(2+)-activated K(+) channels are required for LPA-stimulated migration of microglial cells.

Human beta-defensin-2 functions as a chemotactic agent for tumour necrosis factor-alpha-treated human neutrophils

Neutrophils are the effector cells in both innate and adaptive immunity, where they perform the functions of phagocytosis and killing of bacteria. They respond to a large number of chemoattractants, but their response to epithelial cell-derived human beta-defensins (hBD) has not been investigated. Here we report that hBD-2, but not hBD-1, is a specific chemoattractant for tumour necrosis factor (TNF)-alpha-treated human neutrophils. The optimal concentration required for maximal chemotactic activity was 5 micro g/ml. The effect of hBD-2 on neutrophils was dependent on the G-protein-phospholipase C pathway, as demonstrated by inhibition by pertussis toxin and U-73122. In addition, ligand-receptor analysis indicated that the binding of hBD-2 was markedly inhibited by macrophage inflammatory protein (MIP)-3alpha, a specific and unique ligand for CCR6. Furthermore, anti-CCR6 antibody could almost completely suppress the cell migration induced by hBD-2, suggesting that hBD-2 mainly utilizes CCR6 as a functional receptor. Thus, our finding that hBD-2 is a potent chemoattractant for human neutrophils through specific receptors provides a novel mechanism by which this peptide contributes to the host defence system by recruiting neutrophils to inflammation/infection sites. This also suggests an important link between epithelial cell-derived antibacterial peptides and neutrophils during infection or inflammation.

Calcium transients induce spatially coordinated increases in traction force during the movement of fish keratocytes

The coordination of protrusion with retraction is essential for continuous cell movement. In fish keratocytes the activation of stretch-activated calcium channels, and the resulting increase in intracellular calcium, trigger release of the rear cell margin when forward movement is impeded. Although it is likely that retraction involves a calcium-dependent increase in cytoskeletal contractility, it is not known how the timing, magnitude and localization of contractile forces are organized during retraction. We have addressed this question using a new gelatin traction force assay in combination with calcium imaging to determine what changes in cytoskeletal force production accompany calcium-induced retraction. We find that individual calcium transients are followed within seconds by a rapid increase in traction stress that is maintained, or increases in a stepwise manner, until retraction occurs. Increases in traction stress are accompanied by a distinct sequence of changes in the spatial distribution of large traction stresses. Regions of increased traction stress enlarge at the lateral cell margins and expand forward along the cell margin. In particular, rearward facing propulsive' tractions at the leading edge of the cell, which are normally very low, increase several fold. Following retraction, a precipitous drop in traction stress is observed. Such distinct variations in traction stress are not observed in cells when calcium transients are absent. These results suggest a mechanism by which global increases in intracellular calcium can locally regulate contractile force production, in order to maintain a rapid highly directed mode of movement.

Calcium signaling in chemorepellant Slit2-dependent regulation of neuronal migration

Migration of neuronal precursor cells in the developing brain is guided by extracellular cues, but intracellular signaling processes underlying the guidance of neuronal migration are largely unknown. By examining the migration of cerebellar granule neurons along the surface of cocultured astroglial cells, we found that an extracellular gradient of Slit2, a chemorepellant for neuronal migration in vivo, caused a reversal in the direction of migration without affecting the migration speed. A Slit2 gradient elevated the intracellular concentration of Ca2+, probably due to calcium release from the internal store, led to a reversal of the preexisting asymmetric intracellular Ca2+ distribution in the soma of migrating neurons, and this reversal was closely related with its action of reversing the migrating direction. Asymmetric Ca2+ distribution in the soma was both necessary and sufficient for directing neuronal migration. These results have demonstrated an important role for Ca2+ in mediating neuronal responses to Slit2 and suggest a general mechanism for neuronal guidance.

Vacuolar H+-ATPase in human breast cancer cells with distinct metastatic potential: distribution and functional activity

Tumor cells thrive in a hypoxic microenvironment with an acidic extracellular pH. To survive in this harsh environment, tumor cells must exhibit a dynamic cytosolic pH regulatory system. We hypothesize that vacuolar H(+)-ATPases (V-ATPases) that normally reside in acidic organelles are also located at the cell surface, thus regulating cytosolic pH and exacerbating the migratory ability of metastatic cells. Immunocytochemical data revealed for the first time that V-ATPase is located at the plasma membrane of human breast cancer cells: prominent in the highly metastatic and inconspicuous in the lowly metastatic cells. The V-ATPase activities in isolated plasma membranes were greater in highly than in lowly metastatic cells. The proton fluxes via V-ATPase evaluated by fluorescence spectroscopy in living cells were greater in highly than in lowly metastatic cells. Interestingly, lowly metastatic cells preferentially used the ubiquitous Na(+)/H(+) exchanger and HCO(3)(-)-based H(+)-transporting mechanisms, whereas highly metastatic cells used plasma membrane V-ATPases. The highly metastatic cells were more invasive and migratory than the lowly metastatic cells. V-ATPase inhibitors decreased the invasion and migration in the highly metastatic cells. Altogether, these data indicate that V-ATPases located at the plasma membrane are involved in the acquisition of a more metastatic phenotype.

How do cells move along surfaces?

The movement of cells along surfaces is a complex phenomenon that consists of several interrelated processes, including cell-substratum adhesion, and extension and retraction of the cell edge, in which the actin cytoskeleton plays a crucial role. The past decade has seen increasingly detailed molecular-based investigations into cell motility, but it is still not known how molecular events are integrated to give cell movement. Molecular studies are now beginning to be linked to a more global concept of how whole cells move, and this combined approach promises to yield new insights into cell locomotion.

Visualizing signals moving in cells

Cells display a highly complex spatiotemporal organization, required to exert a wide variety of different functions, for example, detection, processing, and propagation of nerve impulses by neurons; contraction and relaxation by muscle cells; movement by leukocytes; and adsorption and secretion of nutrients and metabolites by epithelial cells lining the gut. Successful execution of these complex processes requires highly dynamic information transfer between different regions and compartments within cells. Through the development of fluorescent sensors for intracellular signaling molecules coupled with improved microscopic imaging techniques, it has now become possible to investigate signal propagation in cells with high spatial and temporal resolution.

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.

Role of calcium in E-selectin induced phenotype of T84 colon carcinoma cells

The adhesion of cancer cells to the endothelium during the metastatic process involves the interaction of specific cell-cell adhesion receptors on the cell surface. E-selectin on endothelial cells and sialyl Lewis X carbohydrate component on tumor cells are mainly implicated in the adhesion of colon carcinoma cells to the endothelium of target organ. In this paper we show that binding of E-selectin to T84 colon tumor cells causes approximately a twofold increase in intracellular calcium concentration. In particular, using two inhibitors of receptor operated calcium channels, CAI and SK&F 96365, we present evidences that the augmentation in cytoplasmic calcium originates from ionic influx from extracellular sources. Furthermore, we demonstrated that modulation of [Ca2+]i by engagement of E-selectin receptor starts signal transduction pathways that affect cell spreading, tyrosine phosphorylation signaling, and cancer cell motility.

Intracellular calcium waves accompany neutrophil polarization, formylmethionylleucylphenylalanine stimulation, and phagocytosis: a high speed microscopy study

Using high sensitivity fluorescence imaging with shutter speeds approximately 600,000 times faster than those of video frames, we have characterized Ca2+ waves within cells in exquisite detail to reveal Ca2+ signaling routes. Polarized neutrophils exhibited a counterclockwise rotating ryanodine-sensitive juxtamembrane Ca2+ wave during temporal calcium spikes. During stimulation with fMLP, a chemotactic factor, two Ca2+ waves traveling in opposite directions around the perimeter of the cell emanated from sites of stimulation (the clockwise wave is verapamil sensitive). Phagocytosed targets exhibit counterclockwise Ca2+ waves traveling about their periphery originating from the plasma membrane. This study: 1) outlines the technology to observe Ca2+ signaling circuitry within small living cells; 2) shows that extracellular spatial information in the form of a chemotactic factor gradient is transduced into intracellular chemical patterns, which provides fresh insights in signaling; 3) suggests that a line of communication exits between the cell surface and phagosomes; and 4) suggests that spatiotemporal Ca2+ patterns contribute to drug actions.

Induction of cancer cell migration by epidermal growth factor is initiated by specific phosphorylation of tyrosine 1248 of c-erbB-2 receptor via EGFR

Induction of tumor cell migration is a key step in invasion and metastasis. Here we report that the epidermal growth factor (EGF)-induced cell migration of breast cancer cells is attributed to a transient, rather than a sustained, activation of phospholipase C (PLC)-gamma1 due to c-erbB-2 signaling. EGF stimulation of EGF receptor (EGFR) overexpressing cells resulted in long-term PLC-gamma1 tyrosine phosphorylation and sustained levels of inositol-1,4,5-triphosphate (IP3) and diacylglycerol (DAG) producing sinusoidal calcium oscillations. In contrast, c-erbB-2/EGFR expressing cells displayed baseline transient calcium oscillations after EGF treatment due to short-term PLC-gamma1 tyrosine phosphorylation and short-term IP3 and DAG turnover. A third cell line expressing a point-mutated c-erbB-2 receptor that lacks the autophosphorylation Y1248 was generated to investigate whether the different PLC-gamma1 activation was attributed to this structure. Neither PLC-gamma1 tyrosine phosphorylation nor IP3 and DAG turnover and calcium oscillations were observed in this cell line, indicating the modulation of the PLC-g1 activation time course by c-erbB-2 signaling. Induction of cell migration was solely observable in the c-erbB-2-positive cell line as proved by the mode of actin reorganization and a cell migration assay, using a 3D-collagen lattice. In summary, c-erbB-2 up-regulation switches on the cell migration program by modulating the time course of PLC-gamma1 activation.

Glutamate antagonists limit tumor growth

The management of malignancies in humans constitutes a major challenge for contemporary medicine. Despite progress in chemotherapy, bone marrow transplantation, surgical measures, and radiation technologies, and in immunological and immunomodulatory approaches, humans continue to succumb to cancer due to tumor recurrence and metastatic disease. The excitatory neurotransmitter glutamate, which regulates proliferation and migration of neuronal progenitors and immature neurons during the development of the mammalian nervous system, is present in peripheral cancers. Since both neuronal progenitors and tumor cells possess propensity to proliferate and to migrate, and since glutamate and glutamate receptors are known to modify these phenomena in the nervous system, we proceeded to investigate the possible influence of glutamate antagonists on the proliferation and migration of tumor cells. We found and recently reported that glutamate N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) antagonists inhibit the proliferation of human colon adenocarcinoma, astrocytoma, breast and lung carcinoma, and neuroblastoma cells in vitro. The antiproliferative effect of glutamate antagonists is Ca(2+)-dependent and results from decreased cell division and increased cell death. Glutamate antagonists produce morphological alterations in tumor cells, which consist of reduced membrane ruffling and pseudopodial protrusions, and decrease their motility and invasive growth. Furthermore, glutamate antagonists enhance in vitro cytostatic and cytotoxic effects of common chemotherapeutic agents used in cancer therapy. These findings demonstrate the anticancer potential of glutamate antagonists and suggest that they may be used as an adjunctive measure in the treatment of cancer.

Role of Ca2+/calmodulin regulated signaling pathways in chemoattractant induced neutrophil effector functions. Comparison with the role of phosphotidylinositol-3 kinase

In human neutrophils, both changes in intracellular Ca(2+) concentrations, [Ca(2+)]i, and activation of phosphatidylinositol-3 kinase (PtdIns3K) have been proposed to play a role in regulating cellular function induced by chemoattractants. In this study we have investigated the role of [Ca(2+)]i and its effector molecule calmodulin in human neutrophils. Increased [Ca(2+)]i alone was sufficient to induce phosphorylation of extracellular signal-regulated protein kinase 2 (ERK2), p38 mitogen activated kinase (p38 MAPK), protein kinase B (PKB) and glycogen synthase kinase-3alpha (GSK-3alpha). Inhibition of calmodulin using a calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7), did not effect N-formyl-methionyl-leucyl-phenylalanine (fMLP) induced ERK, p38 MAPK or GSK-3alpha phosphorylation, but attenuated fMLP induced PKB phosphorylation. PCR analysis of human neutrophil cDNA demonstrated variable expression of members of the Ca(2+)/calmodulin-dependent kinase family. The roles of calmodulin and PtdIns3K in regulating neutrophil effector functions were further compared. Neutrophil migration was abrogated by inhibition of calmodulin, while no effect was observed when PtdIns3K was inhibited. In contrast, production of reactive oxygen species was sensitive to inhibition of both calmodulin and PtdIns3K. Finally, we demonstrated that chemoattractants are unable to modulate neutrophil survival, despite activation of PtdIns3K and elevation [Ca(2+)]i. Taken together, our data indicate critical roles for changes in [Ca(2+)]i and calmodulin activity in regulating neutrophil migration and respiratory burst and suggest that chemoattractant induced PKB phosphorylation may be mediated by a Ca(2+)/calmodulin sensitive pathway in human neutrophils.

Power spectral analysis of the shape of fMLP-stimulated granulocytes. A tool for the study of cytoskeletal organization under normal and pathological conditions

fMLP (N-formyl-methionyl-leucyl-phenylalanine) is a powerful activator of granulocytes, eliciting different metabolic responses, such as generation of reactive oxygen species, production of arachidonic acid metabolites, and release of lysosomal enzymes. fMLP determines also a dramatic rearrangement of the actin cytoskeleton; under non-gradient conditions this entails characteristic alterations in cell shape (chemokinesis), while under gradient conditions it is instrumental in promoting cell migration up the gradient (chemotaxis). Here we analyze mathematically the cell contour of fMLP-stimulated human granulocytes stimulated with fMLP under non-gradient conditions, using the methods for study of stochastic series. The cell contours were drawn and divided into 200 segments of equal linear length and the angles between consecutive segments were computed. The derived series of angles were examined for autocorrelations and from the autocorrelation function the power spectrum was calculated. Our results show that the pattern of lamellipodial extensions of the cell membrane is not entirely randomly-designed, but it is partly regulated by deterministic components, as revealed by the presence of statistically significant periodicities. Soon after fMLP stimulation, the power spectrum of the cell contours exhibits a single distinct peak at frequency 0.07, indicating a prevalence of prominent lamellipodia, each one covering in the average 1/15 of the linearized cell contour. Some 30 min after fMLP stimulation the power spectrum becomes flatter (indicating a general decrement of the deterministic component), but still presents one single peak; the latter is shifted to the right (frequency 0.13), indicating the prevalence of less prominent and regular, but more numerous, protrusions, each one covering 1/20 to 1/30 of the cell contour.

The involvement of HAb18G/CD147 in regulation of store-operated calcium entry and metastasis of human hepatoma cells

The present study examined the effect of hepatoma-associated antigen HAb18G (homologous to CD147) expression on the NO/cGMP-regulated Ca(2+) mobilization and metastatic process of human hepatoma cells. HAb18G/CD147 cDNA was transfected into human 7721 hepatoma cells to obtain a cell line stably expressing HAb18G/CD147, T7721, as demonstrated by Northern blot and immunocytochemical studies. 8-Bromo-cGMP (cGMP) inhibited the thapsigargin-induced Ca(2+) entry in a concentration-dependent manner in 7721 cells. The cGMP-induced inhibition was abolished by an inhibitor of protein kinase G, KT5823 (1 microm). However, expression of HAb18G/CD147 in T7721 cells decreased the inhibitory response to cGMP. A similar concentration-dependent inhibitory effect on the Ca(2+) entry was observed in 7721 cells in response to a NO donor, (+/-)-S-nitroso-N-acetylpenicillamine (SNAP). The inhibitory effect of SNAP on the thapsigargin-induced Ca(2+) entry was significantly reduced in HAb18G/CD147-expressing T7721 cells, indicating a role for HAb18G/CD147 in NO/cGMP-regulated Ca(2+) entry. Experiments investigating metastatic potentials demonstrated that HAb18G/CD147-expressing T7721 cells attached to the Matrigel-coated culture plates and invaded through Matrigel-coated permeable filters at the rate significantly greater than that observed in 7721 cells. Both the attachment and invasion rates could be suppressed by SNAP, and the inhibitory effect of SNAP could be reversed by NO inhibitor, N(G)-nitro-l-arginine methyl ester. The sensitivity of the attachment and invasion rates to cGMP was significantly reduced in T7721 cells as compared with 7721 cells when cells were pretreated with thapsigargin. The difference in the sensitivity between the two cells could be abolished by a Ca(2+) channel blocker, Ni(2+) (3 mm). These results suggest that HAb18G/CD147 enhances metastatic potentials in human hepatoma cells by disrupting the regulation of store-operated Ca(2+) entry by NO/cGMP.

Cell permeant polyphosphoinositide-binding peptides that block cell motility and actin assembly

Polyphosphoinositides (PPIs) affect the localization and activities of many cellular constituents, including actin-modulating proteins. Several classes of polypeptide sequences, including pleckstrin homology domains, FYVE domains, and short linear sequences containing predominantly hydrophobic and cationic residues account for phosphoinositide binding by most such proteins. We report that a ten-residue peptide derived from the phosphatidylinositol 4,5-bisphosphate (PIP(2)) binding region in segment 2 of gelsolin, when coupled to rhodamine B has potent PIP(2) binding activity in vitro; crosses the cell membrane of fibroblasts, platelets, melanoma cells, and neutrophils by a process not involving endocytosis; and blocks cell motility. This peptide derivative transiently disassembles actin filament structures in GFP-actin-expressing NIH3T3 fibroblasts and prevents thrombin- or chemotactic peptide-stimulated actin assembly in platelets and neutrophils, respectively, but does not block the initial [Ca(2+)] increase caused by these agonists. The blockage of actin assembly and motility is transient, and cells recover motility within an hour after their immobilization by 5-20 microm peptide. This class of reagents confirms the critical relation between inositol lipids and cytoskeletal structure and may be useful to probe the location and function of polyphosphoinositides in vivo.

Endothelin-1 and nitric oxide affect human cerebromicrovascular endothelial responses and signal transduction

Endothelium plays a central role in regulating the vascular tone, blood flow and blood brain barrier (BBB) permeability. The experiments presented here examine the mechanisms by which nitric oxide (NO) and endothelin-1 (ET-1) may be involved in these processes. The findings indicate that ET-1-stimulated [Ca2+]i accumulation occurs through activation of ETA receptor. The capacity of NO to affect this response was indicated by results showing: 1) a two-fold increase in ET-1-stimulated [Ca2+]i by L-NAME, the inhibitor of nitric oxide synthase, and 2) a dose-dependent decrease in [Ca2+]i accumulation by pretreatment with Nor-1 (NO donor). Abrogation of this Nor-1 effect by ODQ (an inhibitor of guanylyl cyclase) or Rp-8-pCPT-cGMPS (an inhibitor of protein kinase G) and inhibition of ET-1 stimulated intracellular Ca2+ accumulation by 8-bromo-cGMP (a permeable, analog of cGMP) substantiate the involvement of interplay between ET-1 and NO in [Ca2+]i accumulation in HBMEC. ET-1 treatment also increased thickness of F-actin cytoskeletal filaments in HBMEC. This effect was attenuated by pretreatment with NO; NO also rarefied F-actin filaments in control cultures. The findings support a linkage between NO and ET-1 in regulating microvascular tone, microcirculation and BBB permeability and indicate a role for cGMP/cGMP protein kinase system and cytoskeletal changes in responses of HBMEC.

Cell motility in a new single-cell wound model

Until now researchers have used a monolayer of cultured cells to investigate cell motility toward an injured cell. However, we suspect that, when using this method, adjacent cells move to the free space due to relief of contact inhibition. The current study was designed to investigate the cell motility nearby an injured cell in varying cell connectivity. A low-power laser beam was used to damage one cell selectively with the silver coating beads. After injury, we observed the cell motility in three different cell types: (1) those immediately adjacent to the injured cell, (2) those removed from the injured cell by interposition of another cell, and (3) those removed from the injured cell by free space. The cells that are in direct contact with the injured cell moved toward the injured cell within 1.5-3.0 h. Indirectly connected cells and cells with no contact, on the other hand, showed no significant movement toward the injured cell. This suggests that the cell motility toward the cell injury is not only due to relief of contact inhibition but might also be caused by cell-to-cell signaling via cell connection. The current method will provide a tool to create a cell injury without damaging adjacent cells.

Ionomycin causes activation of p38 and p42/44 mitogen-activated protein kinases in human neutrophils

Many receptor-linked agents that prime or activate the NADPH oxidase in polymorphonuclear neutrophils (PMNs) elicit changes in cytosolic Ca2+ concentration and activate mitogen-activated protein (MAP) kinases. To investigate the role of Ca2+ in the activation of p38 and p42/44 MAP kinases, we examined the effects of the Ca2+-selective ionophore ionomycin on priming and activation of the PMN oxidase. Ionomycin caused a rapid rise in cytosolic Ca2+ that was due to both a release of cytosolic Ca2+ stores and Ca2+ influx. Ionomycin also activated (2 microM) and primed (20-200 nM) the PMN oxidase. Dual phosphorylation of p38 MAP kinase and phosphorylation of its substrate activating transcription factor-2 were detected at ionomycin concentrations that prime or activate the PMN oxidase, while dual phosphorylation of p42/44 MAP kinase and phosphorylation of its substrate Elk-1 were elicited at 0.2-2 microM. SB-203580, a p38 MAP kinase antagonist, inhibited ionomycin-induced activation of the oxidase (68 +/- 8%, P < 0.05) and tyrosine phosphorylation of 105- and 72-kDa proteins; conversely, PD-98059, an inhibitor of MAP/extracellular signal-related kinase 1, had no effect. Treatment of PMNs with thapsigargin resulted in priming of the oxidase and activation of p38 MAP kinase. Chelation of cytosolic but not extracellular Ca2+ completely inhibited ionomycin activation of p38 MAP kinase, whereas chelation of extracellular Ca2+ abrogated activation of p42/44 MAP kinase. These results demonstrate the importance of changes in cytosolic Ca2+ for MAP kinase activation in PMNs.

Glutamate antagonists limit tumor growth

Neuronal progenitors and tumor cells possess propensity to proliferate and to migrate. Glutamate regulates proliferation and migration of neurons during development, but it is not known whether it influences proliferation and migration of tumor cells. We demonstrate that glutamate antagonists inhibit proliferation of human tumor cells. Colon adenocarcinoma, astrocytoma, and breast and lung carcinoma cells were most sensitive to the antiproliferative effect of the N-methyl-d-aspartate antagonist dizocilpine, whereas breast and lung carcinoma, colon adenocarcinoma, and neuroblastoma cells responded most favorably to the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate antagonist GYKI52466. The antiproliferative effect of glutamate antagonists was Ca(2+) dependent and resulted from decreased cell division and increased cell death. Morphological alterations induced by glutamate antagonists in tumor cells consisted of reduced membrane ruffling and pseudopodial protrusions. Furthermore, glutamate antagonists decreased motility and invasive growth of tumor cells. These findings suggest anticancer potential of glutamate antagonists.

Function and spatial distribution of ion channels and transporters in cell migration

Cell migration plays a central role in many physiological and pathophysiological processes, such as embryogenesis, immune defense, wound healing, or the formation of tumor metastases. Detailed models have been developed that describe cytoskeletal mechanisms of cell migration. However, evidence is emerging that ion channels and transporters also play an important role in cell migration. The purpose of this review is to examine the function and subcellular distribution of ion channels and transporters in cell migration. Topics covered will be a brief overview of cytoskeletal mechanisms of migration, the role of ion channels and transporters involved in cell migration, and ways by which a polarized distribution of ion channels and transporters can be achieved in migrating cells. Moreover, a model is proposed that combines ion transport with cytoskeletal mechanisms of migration.

Structure of apoptosis-linked protein ALG-2: insights into Ca2+-induced changes in penta-EF-hand proteins

BACKGROUND

The Ca2+ binding apoptosis-linked gene-2 (ALG-2) protein acts as a proapoptotic factor in a variety of cell lines and is required either downstream or independently of caspases for apoptosis to occur. ALG-2 belongs to the penta-EF-hand (PEF) protein family and has two high-affinity and one low-affinity Ca2+ binding sites. Like other PEF proteins, its N terminus contains a Gly/Pro-rich segment. Ca2+ binding is required for the interaction with the target protein, ALG-2 interacting protein 1 (AIP1).

RESULTS

We present the 2.3 A resolution crystal structure of Ca2+-Ioaded des1-20ALG-2 (aa 21-191), which was obtained by limited proteolysis of recombinant ALG-2 with elastase. The molecule contains eight alpha helices that fold into five EF-hands, and, similar to other members of this protein family, the molecule forms dimers. Ca2+ ions bind to EF1, EF3, and, surprisingly, to EF5. In the related proteins calpain and grancalcin, the EF5 does not bind Ca2+ and is thought to primarily facilitate dimerization. Most importantly, the conformation of des1-20ALG-2 is significantly different from that of calpain and grancalcin. This difference can be described as a rigid body rotation of EF1-2 relative to EF4-5 and the dimer interface, with a hinge within the EF3 loop. An electron density, which is interpreted as a hydrophobic Gly/Pro-rich decapeptide that is possibly derived from the cleaved N terminus, was found in a hydrophobic cleft between these two halves of the molecule.

CONCLUSIONS

A different relative orientation of the N- and C-terminal halves of des1-20ALG-2 in the presence of Ca2+ and the peptide as compared to other Ca2+loaded PEF proteins changes substantially the shape of the molecule, exposing a hydrophobic patch on the surface for peptide binding and a large cleft near the dimer interface. We postulate that the binding of a Gly/ Pro-rich peptide in the presence of Ca2+ induces a conformational rearrangement in ALG-2, and that this mechanism is common to other PEF proteins.

Purinoceptor-mediated calcium mobilization and proliferation in HaCaT keratinocytes

To investigate the effect of nucleotides on cytosolic free calcium mobilization and proliferation activity in HaCaT keratinocytes, nucleotides-induced intracellular free calcium concentration ([Ca(2+)](i)) and cell proliferation observed. [Ca(2+)](i) to the extracellular nucleotides was determined using Ca(2+) sensitive indicator, Fura-2/AM with digital video fluorescence imaging microscopy, and cell proliferation was evaluated by counting of cell number. An adenosine 5'-triphosphate (ATP)-induced [Ca(2+)](i) increase was observed from the concentration of 10(-8) M and was more conspicuous at higher concentrations in a concentration-dependent manner. Additionally, other nucleotides such as ADP, UTP, and 2-me-S-ATP also induced a [Ca(2+)](i) increase in a concentration-dependent manner. However, adenosine induced a slight increase of [Ca(2+)](i) only at 10(-3) M. alpha,-methylene-ATP did not evoke any rise in [Ca(2+)](i). The maximal response observed occurred with ATP and UTP at a concentration of 10(-4) M. The ATP-induced transient [Ca(2+)](i) increase was attenuated by the pretreatment with phospholipase C (PLC) inhibitor, U-73122 (10 microM) for 30 min. ATP-induced [Ca(2+)](i) increase and cell proliferation were inhibited by putative P2Y receptor antagonist, suramin (10(-4) M). When the HaCaT cells were stimulated with nucleotides on a concentration of 10(-4) M and cultured for 5 days, the order of effect on cell proliferation was observed to be ATP>UTP>ADP>2-me-S-ATP. Based on these results, we suggest that extracellular ATP stimulate HaCaT keratinocytes proliferation via purinoceptor-mediated [Ca(2+)](i) mobilization

Actin polymerization in response to different chemoattractants is reduced in granulocytes from chronic myeloid leukemia patients

Chronic myeloid leukemia (CML), a hematopoietic stem cell disorder, is characterized by the presence of Philadelphia chromosome (Ph1). Earlier studies have shown that various functions, such as chemotaxis, fluid phase pinocytosis, phagocytosis, and degranulation in response to chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP), were defective in polymorphonuclear leukocytes (PMNL) from CML patients. These functions depend on actin microfilaments (MF). Further studies showed that fMLP-induced actin polymerization was lower in CML PMNL. To see if this defect is specific to stimulation by fMLP alone or is a global phenomenon involving other chemoattractant receptors, chemotaxis and actin polymerization were studied in response to fMLP, an analog of fMLP, formyl-methionine-1 aminocyclooctane 1 carboxylic acid-phenyalanine-O-methionine (FACC8), platelet-activating factor (PAF), and leukotriene B4 (LTB4). These compounds bind to different chemoattractant receptors. Chemotaxis and actin polymerization in response to all four chemoattractants were significantly lower in CML PMNL compared with PMNL from normal subjects and were differentially affected for the different chemoattractants. These results suggest a global phenomenon involving all four chemoattractant-stimulated pathways. This lower amount of F-actin may be responsible for the defective chemotaxis seen in these cells.

Activation of human neutrophils with chemotactic peptide, opsonized zymosan and the calcium ionophore A23187, but not with a phorbol ester, is accompanied by efflux and store-operated influx of calcium

The objective of this study was to monitor alterations in cellular Ca2+ metabolism following activation of neutrophils with receptor- (chemotactic peptide, FMLP, 1 microM; opsonized zymosan, OZ, 0.5 mg/ml) and non-receptor (calcium ionophore, A23187, 1 microM; phorbol 12-myristate 13-acetate, PMA, 25 ng/ml)-mediated stimuli of the pro-inflammatory functions of these cells. Ca2+ fluxes in activated neutrophils were measured using a fura-2-based spectrofluorimetric method in combination with radiometric (45Ca) procedures which facilitate distinction between net efflux and net influx of the cation. Exposure of neutrophils to receptor-mediated stimuli and to A23187 was associated with an abrupt increase in cytosolic Ca2+ coincident with a rapid efflux of the cation which terminated at around 30 s. In the case of FMLP and OZ, this was followed by a delayed (30-60 s), store-operated influx of Ca2+, which was complete at around 5 min after addition of the stimulus. With A23187, however, influx of Ca2+ occurred immediately following activation of the cells. There were no detectable alterations in cytosolic Ca2+ or measurable net efflux or influx of the cation above control levels in PMA-activated neutrophils. These data demonstrate that FMLP, OZ- and A23187-mediated alterations in neutrophil cytosolic Ca2+ are due to mobilization of both intracellular and extracellular cation, while activation of neutrophils by PMA is independent of alterations in cytosolic Ca2+.

Endothelial [Ca2+]i signaling during transmigration of polymorphonuclear leukocytes

Vascular endothelium plays an important role in regulating the transendothelial migration of polymorphonuclear leukocytes (PMNs). In this study, the intracellular calcium ion ([Ca2+]i) signaling of endothelial cells (ECs) during PMN transmigration was examined at the single-cell level. Human umbilical vein ECs were cultured on a thin layer of collagen gel. The ECs were labeled with fura-2, immersed in formyl-Met-Leu-Phe, and subsequently perfused with fresh buffer to establish a gradient of chemoattractant across the EC monolayer. The entire process of PMN rolling on, adhering to, and transmigrating across the EC monolayer was recorded under both phase-contrast and fluorescence optics. The data showed the following: (1) At high concentration (approximately 3 × 106/mL), both PMN suspension and its supernatant stimulated frequent EC [Ca2+]i elevations across the monolayer; (2) when used at lower concentration (approximately 5 × 105/mL) to avoid the interference of soluble factors, PMN transmigration, but not rolling or adhesion, was accompanied by EC [Ca2+]i elevation; (3) the latter EC [Ca2+]i elevation occurred simultaneously in ECs adjacent to the transmigration site, but not in those that were not in direct contact with the transmigrating PMNs; (4) this EC [Ca2+]i elevation was an initial and required event for PMN transmigration; and (5) PMNs pretreated with 5,5′-dimethyl-1,2-bis(2-aminophenoxy)ethane-N, N, N′, N′-tetraacetic acid transmigrated with the accompanying EC [Ca2+]i elevation, but they became elongated in the collagen gel. In conclusion, PMNs induce adjacent EC [Ca2+]i signaling, which apparently mediates the “gating” step for their subsequent transmigration.

Endothelial [Ca2+]i signaling during transmigration of polymorphonuclear leukocytes

Vascular endothelium plays an important role in regulating the transendothelial migration of polymorphonuclear leukocytes (PMNs). In this study, the intracellular calcium ion ([Ca2+]i) signaling of endothelial cells (ECs) during PMN transmigration was examined at the single-cell level. Human umbilical vein ECs were cultured on a thin layer of collagen gel. The ECs were labeled with fura-2, immersed in formyl-Met-Leu-Phe, and subsequently perfused with fresh buffer to establish a gradient of chemoattractant across the EC monolayer. The entire process of PMN rolling on, adhering to, and transmigrating across the EC monolayer was recorded under both phase-contrast and fluorescence optics. The data showed the following: (1) At high concentration (approximately 3 × 106/mL), both PMN suspension and its supernatant stimulated frequent EC [Ca2+]i elevations across the monolayer; (2) when used at lower concentration (approximately 5 × 105/mL) to avoid the interference of soluble factors, PMN transmigration, but not rolling or adhesion, was accompanied by EC [Ca2+]i elevation; (3) the latter EC [Ca2+]i elevation occurred simultaneously in ECs adjacent to the transmigration site, but not in those that were not in direct contact with the transmigrating PMNs; (4) this EC [Ca2+]i elevation was an initial and required event for PMN transmigration; and (5) PMNs pretreated with 5,5′-dimethyl-1,2-bis(2-aminophenoxy)ethane-N, N, N′, N′-tetraacetic acid transmigrated with the accompanying EC [Ca2+]i elevation, but they became elongated in the collagen gel. In conclusion, PMNs induce adjacent EC [Ca2+]i signaling, which apparently mediates the “gating” step for their subsequent transmigration.

Involvement of Iba1 in membrane ruffling and phagocytosis of macrophages/microglia

Ionized calcium binding adaptor molecule 1, Iba1, is an EF hand calcium binding protein whose expression is restricted to macrophages/microglia. In this study, Iba1 was shown to colocalize with F-actin in membrane ruffles induced by macrophage colony-stimulating factor and in phagocytic cups formed during zymosan phagocytosis. Expression of mutant Iba1 carrying either N- or C-terminal deletions or carrying a substitution in the calcium binding domain, suppressed the membrane ruffling and the phagocytosis. These results indicate that Iba1 is a key molecule in membrane ruffling and the phagocytosis of macrophages/microglia. Furthermore, Iba1 colocalized with a small GTPase Rac in the membrane ruffles and the phagocytic cups. The Iba1 mutants also suppressed membrane ruffling induced by dominant active Rac1V12, but do not affect microspikes by Cdc42V12 and stress fibers by RhoAV14. These observations suggest that Iba1 is involved in Rac and calcium signaling pathways.

How calcium causes microtubule depolymerization

The effects of calcium (Ca) were assessed using video-enhanced differential interference contrast light microscopy on individual microtubules in vitro. Phosphocellulose-purified (PC) and microtubule associated protein (MAP)-containing preparations of porcine brain tubulin were assembled in a flow chamber onto sperm axoneme fragments and the pattern of growth and shortening of the microtubules was observed. Tubulin plus Ca was then added to the chamber and observation continued. Ca promoted the disassembly of microtubules by specifically promoting the catastrophe reaction in both PC- and MAP-containing microtubules, without an appreciable change in elongation rate. The effect on catastrophe frequency increased very rapidly above 0.5 mM free Ca, implying a possible cooperative effect. The rescue rate remained very high after Ca addition in MAP-containing microtubules, and the shortening rate was unchanged, while in phosphocellulose-purified microtubules, rescue appeared to be decreased by Ca addition and shortening rates increased 4 to 6-fold. These results illustrate that Ca can directly destabilize growing microtubule ends without changing the effective concentration of free tubulin, and that this effect can be seen even against the background of the profound differences in dynamics conferred by the microtubule-associated proteins. Considered within models of the GTP cap, the results imply that high Ca may act to increase the rate of GTP hydrolysis within the cap.

A peptide of the alpha 3(IV) chain of type IV collagen modulates stimulated neutrophil function via activation of cAMP-dependent protein kinase and Ser/Thr protein phosphatase

Previous reports from our laboratories showed that type IV collagen from anterior lens capsule (ALC) inhibited stimulated neutrophil function. This property was shown to reside in the region comprising residues 185-203 of the non-collagenous domain (NC1) of the alpha 3(IV) chain. We also reported that ALC-type IV collagen or the synthetic alpha 3(IV) 185-203 peptide, induced a rise in intracellular cAMP which persisted for up to 60 minutes. In the present work we extend our previous studies on signal transduction by alpha 3(IV) 185-203 and we provide new data showing the involvement of cAMP-dependent PKA and protein phosphatases. The data also show that the alpha 3(IV) peptide triggered a rise in intracellular calcium that was dependent on phospholipase C activation. Inhibitors of the Ca(2+)/calmodulin system suppressed both the alpha 3(IV) 185-203 peptide-induced cAMP increase and the inhibitory activity of the peptide on f-Met-Leu-Phe triggered O(2)(-) generation. When alpha 3(IV) 185-203 peptide-induced calcium mobilization was blocked by U-73122, an inhibitor of phospholipase C activation, or by BAPTA/AM, a chelator of intracellular calcium, the inhibitory effect of the peptide on PMA-triggered O(2)(-) production was also abolished. These findings provide evidence that signal transduction by the alpha 3(IV) peptide occurs via pathways which involve calcium. Indeed, the cAMP increase was shown to be mediated by adenosine and adenosine A2 receptors and required calcium elevation, since adenosine deaminase, theophilline, dimethylpropargylxanthine, trifluoperazine or autocamtide-2 related inhibitory peptide, suppressed the activity of the alpha 3(IV) peptide. The inhibitory effect of the peptide on f-Met-Leu-Phe-induced O(2)(-) generation was slightly affected by 1 microM KT5720 or H89, two inhibitors of cAMP-dependent PKA, but was completely suppressed by 10 nM calyculin A or 10 microM okadaic acid, two inhibitors of ser/thr phosphatases. These results suggest that Ser/Thr protein phosphatases and/or cAMP-dependent PKA are involved in signal transduction by the alpha 3(IV) 185-203 peptide and is consistent with the concept that adenosine receptor occupancy modulates neutrophil function.

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.

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.

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.