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

Inhibition of Plasma Membrane Calcium Pump Influences Intracellular Calcium Signaling Pathways in Breast Cancer

The plasma membrane calcium pump (PMCA) is an important transporter that maintains intracellular calcium concentration ([Ca²⁺]_i). It allows the calcium (Ca²⁺) from inside the cell to go out of the cell through the plasma membrane. For this, it cooperates with the proteins in the cell. The aim of this study is to demonstrate the effect of PMCA on intracellular calcium signaling in breast cancer cells. In this study, PMCA was inhibited by orthovanadate (OV), and changes in Calmodulin (CaM), Calcineurin (CaN) and cMyc proteins were demonstrated. Intracellular calcium accumulation was measured when PMCA was inhibited in MDA-MB-231 cells. At the same time, it was observed that the cell movement decreased with time. Over time, CaN and CaM were slightly suppressed, and cMyc protein was not expressed. As a result, when PMCA protein is targeted correctly in breast cancer cells, it has an indirect effect on cancer-promoting proteins.

Combined Metallomics/Transcriptomics Profiling Reveals a Major Role for Metals in Wound Repair

Endogenous metals are required for all life, orchestrating the action of diverse cellular processes that are crucial for tissue function. The dynamic wound healing response is underpinned by a plethora of such cellular behaviours, occurring in a time-dependent manner. However, the importance of endogenous metals for cutaneous repair remains largely unexplored. Here we combine ICP-MS with tissue-level RNA-sequencing to reveal profound changes in a number of metals, and corresponding metal-regulated genes, across temporal healing in mice. Wound calcium, magnesium, iron, copper and manganese are elevated at 7 days post-wounding, while magnesium, iron, aluminium, manganese and cobalt increase at 14 days post-wounding. At the level of transcription, wound-induced pathways are independently highly enriched for metal-regulated genes, and vice versa. Moreover, specific metals are linked to distinct wound-induced biological processes and converge on key transcriptional regulators in mice and humans. Finally, we reveal a potential role for one newly identified transcriptional regulator, TNF, in calcium-induced epidermal differentiation. Together, these data highlight potential new and diverse roles for metals in cutaneous wound repair, paving the way for further studies to elucidate the contribution of metals to cellular processes in the repair of skin and other tissues.

Circulating mitochondrial N-formyl peptides contribute to secondary nosocomial infection in patients with septic shock

Septic shock commonly leads to multiorgan injury both directly via tissue inflammation and secondarily via hypoperfusion, but both can result in mitochondrial N-formyl peptide (mtFP) release into the circulation. However, no studies have evaluated the role of circulating mtFPs during septic shock. We found that a relatively high plasma nicotinamide adenine dinucleotide dehydrogenase subunit-6 (the most potent human mtFP) level was independently associated with the development of secondary infection in patients with septic shock and that the increased susceptibility to secondary infection is partly attributed to the suppression of polymorphonuclear leukocyte (PMN) chemotaxis by mtFP occupancy of formyl peptide receptor-1. Incorporation of these findings into therapeutic strategies may improve clinical outcomes in septic shock patients by preventing PMN chemotactic anergy.

Secondary infections typically worsen outcomes of patients recovering from septic shock. Neutrophil [polymorphonuclear leukocytes (PMNs)] migration to secondarily inoculated sites may play a key role in inhibiting progression from local bacterial inoculation to secondary infection. Mitochondrial N-formyl peptide (mtFP) occupancy of formyl peptide receptor-1 (FPR1) has been shown to suppress PMN chemotaxis. Therefore, we studied the association between circulating mtFPs and the development of secondary infection in patients with septic shock. We collected clinical data and plasma samples from patients with septic shock admitted to the intensive care unit for longer than 72 h. Impacts of circulating nicotinamide adenine dinucleotide dehydrogenase subunit-6 (ND6) upon clinical outcomes were analyzed. Next, the role of ND6 in PMN chemotaxis was investigated using isolated human PMNs. Studying plasma samples from 97 patients with septic shock, we found that circulating ND6 levels at admission were independently and highly associated with the development of secondary infection (odds ratio = 30.317, 95% CI: 2.904 to 316.407, P = 0.004) and increased 90-d mortality (odds ratio = 1.572, 95% CI: 1.002 to 2.465, P = 0.049). In ex vivo experiments, ND6 pretreatment suppressed FPR1-mediated PMN chemotactic responses to bacterial peptides in the presence of multiple cytokines and chemokines, despite increased nondirectional PMN movements. Circulating mtFPs appear to contribute to the development of secondary infection and increased mortality in patients with septic shock who survive their early hyperinflammatory phase. The increased susceptibility to secondary infection is probably partly mediated by the suppression of FPR1-mediated PMN chemotaxis to secondary infected sites.

Mitofusin 2 regulates neutrophil adhesive migration and the actin cytoskeleton

Neutrophils rely on glycolysis for energy production. How mitochondria regulate neutrophil function is not fully understood. Here, we report that mitochondrial outer membrane protein Mitofusin 2 (MFN2) regulates neutrophil homeostasis and chemotaxis in vivoMfn2-deficient neutrophils are released from the hematopoietic tissue, trapped in the vasculature in zebrafish embryos, and not capable of chemotaxis. Consistent with this, human neutrophil-like cells that are deficient for MFN2 fail to arrest on activated endothelium under sheer stress or perform chemotaxis on 2D surfaces. Deletion of MFN2 results in a significant reduction of neutrophil infiltration to the inflamed peritoneal cavity in mice. Mechanistically, MFN2-deficient neutrophil-like cells display disrupted mitochondria-ER interaction, heightened intracellular Ca2+ levels and elevated Rac activation after chemokine stimulation. Restoring a mitochondria-ER tether rescues the abnormal Ca2+ levels, Rac hyperactivation and chemotaxis defect resulting from MFN2 depletion. Finally, inhibition of Rac activation restores chemotaxis in MFN2-deficient neutrophils. Taken together, we have identified that MFN2 regulates neutrophil migration via maintaining the mitochondria-ER interaction to suppress Rac activation, and uncovered a previously unrecognized role of MFN2 in regulating cell migration and the actin cytoskeleton.This article has an associated First Person interview with the first authors of the paper.

TRPC1 regulates fMLP-stimulated migration and chemotaxis of neutrophil granulocytes

Neutrophils form the first line of defense of the innate immune system and are rapidly recruited by chemotactic signals to sites of inflammation. Understanding the mechanisms of neutrophil chemotaxis is therefore of great interest for the potential development of new immunoregulatory therapies. It has been shown that members of the transient receptor potential (TRP) family of cation channels are involved in both cell migration and chemotaxis. In this study, we demonstrate that TRPC1 channels play an important role in fMLP mediated chemotaxis and migration of murine neutrophils. The knock-out of TRPC1 channels leads to an impaired migration, transmigration and chemotaxis of the neutrophils. In contrast, Ca²⁺ influx but not store release after activation of the TRPC1(-/-) neutrophils with fMLP is strongly enhanced. We show that the enhanced Ca²⁺ influx in the TRPC1(-/-) neutrophils is associated with a steepened front to rear gradient of the intracellular Ca²⁺ concentration with higher levels at the cell rear. Taken together, this paper highlights a distinct role of TRPC1 in neutrophil migration and chemotaxis. We propose that TRPC1 controls the activity of further Ca²⁺ influx channels and thus regulates the maintenance of intracellular Ca²⁺ gradients which are critical for cell migration. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

Role of ion channels and transporters in cell migration

Cell motility is central to tissue homeostasis in health and disease, and there is hardly any cell in the body that is not motile at a given point in its life cycle. Important physiological processes intimately related to the ability of the respective cells to migrate include embryogenesis, immune defense, angiogenesis, and wound healing. On the other side, migration is associated with life-threatening pathologies such as tumor metastases and atherosclerosis. Research from the last ≈ 15 years revealed that ion channels and transporters are indispensable components of the cellular migration apparatus. After presenting general principles by which transport proteins affect cell migration, we will discuss systematically the role of channels and transporters involved in cell migration.

Migrating oligodendrocyte progenitor cells swell prior to soma dislocation

The migration of oligodendrocyte progenitor cells (OPCs) to the white matter is an indispensable requirement for an intact brain function. The mechanism of cell migration in general is not yet completely understood. Nevertheless, evidence is accumulating that besides the coordinated rearrangement of the cytoskeleton, a finetuned interplay of ion and water fluxes across the cell membrane is essential for cell migration. One part of a general hypothesis is that a local volume increase towards the direction of movement triggers a mechano-activated calcium influx that regulates various procedures at the rear end of a migrating cell. Here, we investigated cell volume changes of migrating OPCs using scanning ion conductance microscopy. We found that during accelerated migration OPCs undergo an increase in the frontal cell body volume. These findings are supplemented with time lapse calcium imaging data that hint an increase in calcium content the frontal part of the cell soma.

The regulation of integrin function by divalent cations

Integrins are a family of α/β heterodimeric adhesion metalloprotein receptors and their functions are highly dependent on and regulated by different divalent cations. Recently advanced studies have revolutionized our perception of integrin metal ion-binding sites and their specific functions. Ligand binding to integrins is bridged by a divalent cation bound at the MIDAS motif on top of either α I domain in I domain-containing integrins or β I domain in α I domain-less integrins. The MIDAS motif in β I domain is flanked by ADMIDAS and SyMBS, the other two crucial metal ion binding sites playing pivotal roles in the regulation of integrin affinity and bidirectional signaling across the plasma membrane. The β-propeller domain of α subunit contains three or four β-hairpin loop-like Ca(2+)-binding motifs that have essential roles in integrin biogenesis. The function of another Ca(2+)-binding motif located at the genu of α subunit remains elusive. Here, we provide an overview of the integrin metal ion-binding sites and discuss their roles in the regulation of integrin functions.

Developmental distribution of plasma membrane Ca2+-ATPase isoforms in chick cerebellum

The plasma membrane Ca(2+)-ATPase (PMCA) is highly expressed in the nervous system, but little information is available about its implication in neuronal development. We have analyzed the expression and localization of different isoforms of PMCA in membrane vesicles and sections of chick cerebellum from embryonic day 10 to hatching. We found that the relative amount of each PMCA isoform and their spatiotemporal distribution in the cerebellum are directly linked to precise cellular types during the cerebellar maturation, even in a non-neural tissue as choroid plexus. Purkinje cells contain the highest diversity of PMCA isoforms of the cerebellar cortex since the moment of its morphogenesis. From embryonic day 15, the PMCA2 was highly expressed in the whole Purkinje cell, while PMCAs 1 and 3 had a more restricted distribution in the soma and dendritic branches, and these distributions were evolving according with cell maturation. Other cellular types seem to contain a specific combination of isoforms, but with a well-defined distribution pattern at late moments of development. Thus, PMCAs 1 and 3 were located in the soma of molecular layer interneurons, and only the PMCA2 was observed in granule cells at hatching. Furthermore, PMCA isoforms are also expressed in cellular compartments characterized by a high amount of synapses, suggesting a key role of these proteins in synaptogenesis and in the maturation of neuronal electrophysiological properties.

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.

Cells move when ions and water flow

Cell migration is a process that plays an important role throughout the entire life span. It starts early on during embryogenesis and contributes to shaping our body. Migrating cells are involved in maintaining the integrity of our body, for instance, by defending it against invading pathogens. On the other side, migration of tumor cells may have lethal consequences when tumors spread metastatically. Thus, there is a strong interest in unraveling the cellular mechanisms underlying cell migration. The purpose of this review is to illustrate the functional importance of ion and water channels as part of the cellular migration machinery. Ion and water flow is required for optimal migration, and the inhibition or genetic ablation of channels leads to a marked impairment of migration. We briefly touch cytoskeletal mechanisms of migration as well as cell-matrix interactions. We then present some general principles by which channels can affect cell migration before we discuss each channel group separately.

Lymphocyte calcium signaling from membrane to nucleus

Ca(2+) signals control a variety of lymphocyte responses, ranging from short-term cytoskeletal modifications to long-term changes in gene expression. The identification of molecules and channels that modulate Ca(2+) entry into T and B lymphocytes has both provided details of the molecular events leading to immune responses and raised controversy. Here we review studies of the pathways that allow Ca(2+) entry, the function of Ca(2+) in the regulation of cell polarity and motility and the principles by which Ca(2+)-dependent transcription regulates lymphocyte function.

Rigidity sensing at the leading edge through alphavbeta3 integrins and RPTPalpha

Cells require optimal substrate stiffness for normal function and differentiation. The mechanisms for sensing matrix rigidity and durotaxis, however, are not clear. Here we showed that control, Shp2-/-, integrin beta1-/-, and talin1-/- cell lines all spread to a threefold greater area on fibronectin (FN)-coated rigid polyacrylamide surfaces than soft. In contrast, RPTPalpha-/- cells spread to the same area irrespective of rigidity on FN surfaces but spread 3x greater on rigid collagen IV-coated surfaces than soft. RPTPalpha and alphavbeta3 integrins were shown previously to be colocalized at leading edges and antibodies to alphavbeta3 blocked FN rigidity sensing. When FN beads were held with a rigid laser trap at the leading edge, stronger bonds to the cytoskeleton formed than when held with a soft trap; whereas back from the leading edge and in RPTPalpha-/- cells, weaker bonds were formed with both rigid and soft laser traps. From the rigidity of the trap, we calculate that a force of 10 pN generated in 1 s is sufficient to activate the rigidity response. We suggest that RPTPalpha and alphavbeta3 at the leading edge are critical elements for sensing FN matrix rigidity possibly through SFK activation at the edge and downstream signaling.

The role of Ca2+ transport across the plasma membrane for cell migration

Cell migration plays a central role in many physiological and pathophysiological processes. On a cellular level it is based on a highly coordinated restructuring of the cytoskeleton, a continuous cycle of adhesion and de-adhesion as well as on the activity of ion channels and transporters. The cytoplasmic Ca2+ ([Ca2+]i) concentration is an important coordinator of these intracellular processes. Thus, [Ca2+]i must be tightly controlled in migrating cells. This is among other things achieved by the activity of Ca2+ permeable channels, the plasma membrane Ca2+-ATPase (PMCA) and the Na+/Ca2+ exchanger (NCX) in the plasma membrane. Here, we wanted to determine the functional role of these transport proteins in cell migration. We therefore quantified the acute effect of inhibitors of these transport proteins (Gd3+, vanadate, KB-R7943) on migration, [Ca2+]i, and intracellular pH (pHi) of MDCK-F cells. Migration was monitored with computer-assisted time-lapse video microscopy. [Ca2+]i and pHi were measured with the fluorescent indicators fura-2 and BCECF. NCX expression in MDCK-F cells was verified with ion substitution experiments, and expression of PMCA was tested with RT-PCR. All blockers lead to a rapid impairment of cell migration. However, the most prominent effect is elicited by NCX-inhibition with KB-R7943. NCX-blockade leads to an almost complete inhibition of migration which is accompanied by a dose-dependent increase of [Ca2+]i and an intracellular alkalinisation. We show that inhibition of NCX and PMCA strongly affects lamellipodial dynamics of migrating MDCK-F cells. Taken together, our results show that PMCA and in particular NCX are of critical importance for cell migration.

How adhesion, migration, and cytoplasmic calcium transients influence interleukin-1beta mRNA stabilization in human monocytes

We investigated the mechanisms by which primary human monocyte migration and the production of important cytokines are co-regulated. Motile monocytes underwent cyclic morphologic and adhesive changes that were associated with intracellular free calcium changes; in such cells, cytokine transcripts were unstable and translationally repressed. Agents that activate monocytes, including lipopolysacharrides (LPS), cytomegalovirus (CMV), and tumor necrosis factor (TNFalpha), have been shown to de-repress translation and these agents stabilize adhesion-induced transcripts for IL-lbeta and IL-8 and markedly diminish cell migration in the presence of autologous serum. LPS suppressed Rho A activity and either this agent or C3 transferase elevated intracellular free calcium, stabilized transcripts, and, in tandem, inhibited cell migration by preventing tail retraction, a prerequisite for cell translocation. These results, therefore, suggest that monocyte activating agents inhibit the RhoA pathway and continuously elevate intracellular calcium leading to a concomitant decrease in monocyte migration and stabilization of cytokine transcripts prior to translation.

Novel mechanism of enhanced nociception in a model of AIDS therapy-induced painful peripheral neuropathy in the rat

To elucidate the underlying mechanisms involved in AIDS therapy-induced peripheral neuropathy, we have developed a model of nucleoside analog reverse transcriptase inhibitor-induced painful peripheral neuropathy in the rat, using 2',3'-dideoxycytidine (ddC), 2',3'-dideoxyinosine (ddI) and 2',3'-didehydro-3'-deoxythymidine (d4T), AIDS chemotherapeutic drugs that are also components of AIDS highly active anti-retroviral therapy. Administration of ddC, ddI and d4T produced dose-dependent mechanical hypersensitivity and allodynia. Peripheral administration of inhibitors of protein kinase A, protein kinase C, protein kinase G, p42/p44-mitogen-activated protein kinase (ERK1/2) and nitric oxide synthase, which have demonstrated anti-hyperalgesic effects in other models of metabolic and toxic painful peripheral neuropathies, had no effect on ddC-, ddI- and d4T-induced hypersensitivity. Since suramin, an anti-parasitic and anti-cancer drug, which shares with the anti-retroviral nucleoside analogs, mitochondrial toxicity, altered regulation of intracellular calcium, and a sensory neuropathy in humans, also produced mechanical hypersensitivity that was not sensitive to the above second messenger inhibitors we evaluated the role of intracellular calcium. Intradermal or spinal injection of intracellular calcium modulators (TMB-8 and Quin-2), which had no effect on nociception in control rats, significantly attenuated and together eliminated ddC and suramin-induced mechanical hypersensitivity. In electrophysiology experiments in ddC-treated rats, C-fibers demonstrated alterations in pattern of firing as indicated by changes in the distribution of interspike intervals to sustained suprathreshold stimuli without change in mechanical activation thresholds or in number of action potentials in response to threshold and suprathreshold stimulation. This study provides evidence for a novel, calcium-dependent, mechanism for neuropathic pain in a model of AIDS therapy-induced painful peripheral neuropathy.

CC-chemokine receptor CCR5-del32 mutation as a modifying pathogenetic factor in type I diabetes

The purpose of this study was to determine the CCR5-del32 allele frequency in type I (insulin-dependent) and type II (noninsulin-dependent) diabetes patients, and to test whether and how this mutation is associated with both types of diabetes. Thirty-eight type I diabetes and 111 type II diabetes patients' genotyping was performed by polymerase chain reaction assaying, and amplified products were digested with restriction enzyme EcoRI. The results were analyzed using statistical methods. No statistical differences were found in CCR5-del32 allele frequencies in types I and II diabetes patients compared with the control group of native Estonians. However, an association exists between CCR5 gene polymorphism and the clinical course of type I diabetes. In the case of wild-type CCR5, the disease starts at an earlier age. In type II diabetes, there was a difference between genotypes in morbidity to concomitant diseases, being higher in the CCR5 wild-type genotype.

Chemotactic signaling pathways in neutrophils: from receptor to actin assembly

In this review, we present an overview of the signaling elements between neutrophil chemotactic receptors and the actin cytoskeleton that drives cell motility. From receptor-ligand interactions, activation of heterotrimeric G-proteins, their downstream effectors PLC and PI-3 kinase, the activation of small GTPases of the Rho family, and their regulation of particular cytoskeletal regulatory proteins, we describe pathways specific to the chemotaxing neutrophil and elements documented to be important for neutrophil function.

Integrin-dependent neutrophil migration in extravascular tissue

Leukocyte recruitment to sites of injury or infection involves sequential interactions with endothelium and extravascular tissue components. While the intravascular events in this process have been extensively studied, the mechanisms regulating subsequent passage through the surrounding tissue are less well characterized. The migrating white blood cells need to establish transient and dynamic adhesive contacts with extracellular matrix proteins. Integrin receptors expressed on the leukocyte surface play a central role in these interactions, mediating linkages between the cytoskeloton and the external environment. This chapter focuses on roles of integrin molecules in neutrophil locomotion and the adhesive mechanisms that govern the motility of these cells in the extravascular tissue.

Requirement of functional ryanodine receptor type 3 for astrocyte migration

Astrocyte motility plays an important role in the response of the brain to injury and during regeneration. We used two in vitro assays, a wound-healing model and a chemotaxis assay, to study mechanisms that control astrocyte motility. Ryanodine receptors (RyR), intracellular calcium-release channels, modulate intracellular Ca2+ levels, and also motility: 1) blocking RyR with antagonizing concentration of ryanodine (200 microM) strongly attenuated motility and 2) motility of astrocytes cultured from homozygous RyR type 3 knockout mice was impaired strongly compared with wild-type. In contrast, MIP-1a-induced chemotaxis was neither impaired in the presence of ryanodine nor in the cells from the knockout animals. Reverse transcription-polymerase chain reaction (RT-PCR) analysis combined with Western blotting and immunocytochemistry confirmed the expression of RyR type 3, but not type 1 or 2 in cultured and acutely isolated astrocytes. RyR in astrocytes are linked to Ca2+ signaling because the RyR agonist 4-chloro-m-cresol induced a release of Ca2+ from intracellular stores. These results indicate that astrocytes express only RyR type 3 and that this receptor is important for controlling astrocyte motility.

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.

Dancing to the tune of chemokines

Since their discovery 13 years ago, chemokines have emerged as the most important regulators of leukocyte trafficking. On target cells, chemokines bind to seven-transmembrane-domain receptors that are coupled to heterotrimeric Gi proteins. The common response of all cells to chemokine stimulation is chemotaxis. In addition, leukocyte activation triggers diverse signal transduction cascades; which cascade is triggered depends on the chemokine and receptor engaged. The selective activation of distinct pathways suggests that the receptors couple not only to G proteins but also to additional downstream effectors. This review discusses recent advances in the elucidation of the signal transduction that occurs in proximity to receptors and that leads to the early biochemical events in leukocyte activation.

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.

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.

Phosphatidylinositol 3'-kinase-mediated calcium mobilization regulates chemotaxis in phosphatidic acid-stimulated human neutrophils

Phosphatidylinositol 3'-kinase (PI 3'-kinase) plays an important role in the migration of hepatocytes, endothelial cells and neoplastic cells to agonists which activate cellular tyrosine kinases. We examined the PI 3'-kinase-dependent chemotactic responses of neutrophilic leukocytes induced by phosphatidic acid (PA) in order to clarify mechanisms by which the enzyme potentially influences cellular migration. Western analysis of immunoprecipitates indicated that PA induced the tyrosine phosphorylation of three distinct proteins involved in functional activation which co-immunoprecipitated in PA-stimulated cells. These proteins were identified as lyn, syk and the 85 kDa regulatory subunit of PI 3'-kinase. Chemotactic responses to PA but not to several other neutrophil agonists were inhibited by the PI 3'-kinase inhibitors wortmannin and LY294002. Chemotactic inhibition resulted from upstream inhibition of calcium mobilization. Chelation of extracellular calcium by ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) did not affect the PA-induced chemotaxis, whereas chelation of intracellular calcium by 1, 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) attenuated this response. Thus, changes in intracellular Ca(2+) levels that can be effected by Ca(2+) mobilized from intracellular stores in the absence of Ca(2+) influx regulate PA-induced chemotaxis. Furthermore, PI 3'-kinase inhibition blunted the agonist-dependent generation of inositol 1,4,5-trisphosphate (IP(3)), suggesting that PI 3'-kinase exerted its effects on calcium mobilization from intracellular sources by mediating activation of phospholipase C (PLC) in PA-stimulated cells. Moreover, the PI 3'-kinase inhibitor LY294002 also inhibited phosphorylation of syk in PA-stimulated cells. We, therefore, propose that products of PI 3'-kinase confined to the inner leaflet of the plasma membrane play a role in activation of syk, calcium mobilization and induction of chemotactic migration.

Regulation of Human Eosinophil Migration Across Lung Epithelial Monolayers by Distinct Calcium Signaling Mechanisms in the Two Cell Types

In asthmatic patients, eosinophils massively infiltrate the lung tissues and migrate through lung epithelium into the airways. The regulatory mechanisms involved are obscure. We studied the role of calcium in the migration of human eosinophils across monolayers of human lung epithelial H292 cell line cells induced by combined chemotactic solutions of platelet-activating factor and C5a. The transepithelial migration of eosinophils was attenuated by depletion of the external Ca2+ in the migration system, whereas the eosinophil migration itself was unaffected as evidenced by measuring eosinophil chemotaxis in the Boyden chamber in the absence of epithelial cells. Buffering of intracellular Ca2+ in eosinophils with 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA/AM) inhibited both eosinophil transepithelial migration and eosinophil chemotaxis in the Boyden chamber, suggesting the importance of intracellular Ca2+ in eosinophil transmigration. Although loading of BAPTA/AM or addition of thapsigargin to the epithelial cells effectively changed their cytoplasmic free Ca2+ concentrations, neither of these treatments affected transepithelial migration of eosinophils. Interestingly, addition of La3+ (0.2 mM) to epithelial cells suppressed eosinophil transmigration whereas addition of La3+ to eosinophils did not. Taken together, these results show the importance of Ca2+ in eosinophil migration across lung epithelium and support a distinctive regulatory role of intracellular and extracellular Ca2+ for the two cell types involved in this process; i.e., the transmigration of human eosinophils across a monolayer of lung epithelial cells is regulated by the intracellular Ca2+ in eosinophils, whereas the ability of the lung epithelial cell monolayer to allow eosinophil passage is dependent on the extracellular Ca2+.

Activated Lymphocytes Promote Endothelial Cell Detachment from Matrix: A Role for Modulation of Endothelial Cell β1 Integrin Affinity

In vivo, MHC class I-restricted injury of allogeneic tissue or cells infected by intracellular pathogens occurs in the absence of classical cytolytic effector mechanisms and Ab. Modulation of the target cell adhesion to matrix may be an additional mechanism used to injure vascular or epithelial cells in inflammation. We studied the mechanisms of human umbilical vein endothelial cell (EC) detachment from matrix-coated plastic following contact by concanamycin A-treated lymphocytes as an in vitro model of perforin-independent modulation of EC basement membrane adhesion. Human PBL were depleted of monocytes, stimulated, then added to an EC monolayer plated on either fibronectin or type I collagen matrices. Activated, but not resting, PBL induced progressive EC detachment from the underlying matrix. Injury of the EC monolayer required direct cell contact with the activated lymphocytes because no detachment was seen when the PBL were placed above a Transwell membrane. Moreover plasma membranes prepared from activated but not resting PBL induced EC detachment. Adherent EC stimulated with activated PBL did not show evidence of apoptosis using TUNEL and annexin V staining at time points before EC detachment was observed. Finally, neither the matrix metalloproteinase inhibitors o-phenanthroline and BB-94 nor aprotinin blocked EC detachment. However, activation of EC β1 integrin using mAb TS2/16 or Mg2+ decreased EC detachment. These data indicate that cell-cell contact between activated PBL and EC reduces adhesion of EC to the underlying matrix, at least in part by inducing changes in the affinity of the endothelial β1 integrin.

Forces on adhesive contacts affect cell function

Cellular forces acting on the adhesive contacts made with the extracellular matrix (ECM) contribute significantly to cell shape, viability, signal transduction and motility. In the past two years, research has determined how cell spreading influences cell viability as well as cytoskeletal organization. The cytoskeleton generates a level of tension against the ECM that is proportional to ECM stiffness. The strength of this tension exerted against the ECM affects the migratory speed of the cell.

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.

IFN-gamma induces calcium transients and increases the capacitative calcium entry in human neutrophils

We have previously reported that long-term priming of human polymorphonuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gamma) increased the fMLP-stimulated calcium influx. We now show that also after short-term incubation with IFN-gamma, PMN calcium metabolism is modulated. Single adherent cells in three different calcium-containing buffers (high, normal, and low [Ca2+]) were stimulated with the bacterial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma. The results of this protocol indicated that IFN-gamma increases both calcium influx and calcium sequestration. Store dependent Ca2+ influx, directly measured on readdition of calcium to Tg-treated cells incubated in EGTA buffer, was significantly enhanced in IFN-gamma-treated cells. This effect of IFN-gamma was enhanced by the tyrosine kinase inhibitor herbimycin A. Strikingly, in low extracellular calcium concentrations, IFN-gamma induced calcium transients in 20%-60% of the cells. The proportion of PMN responding with Ca2+ transients increased with decreasing extracellular calcium concentration. Average lagtime from addition of IFN-gamma to a response that could be measured was 7.3 sec, and average increase in [Ca2+] above the basal level was 790 nM. These IFN-gamma-induced transients could not be depressed by herbimycin A. Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly affect calcium sequestration in human PMN.