The role of cyclic nucleotides in neutrophil migration

Role of β-Adrenergic Receptors and Estrogen in Cardiac Repair after Myocardial Infarction: An Overview

Acute myocardial infarction (MI) is associated with an intense inflammatory response that is critical for cardiac repair but is also involved in the pathogenesis of adverse cardiac remodeling, i.e., the set of size, geometry, and structure changes that represent the structural substrate for the development of post-MI heart failure. Deciphering the pathophysiological mechanisms underlying cardiac repair after MI is, therefore, critical to favorably regulate cardiac wound repair and to prevent development of heart failure. Catecholamines and estrogen play an active role in regulating the inflammatory response in the infarcted area. For example, stress-induced catecholamines alter recruitment and trafficking of leukocytes to the heart. Additionally, estrogen affects rate of cardiac rupture during the acute phase of MI, as well as infarct size and survival in animal models of MI. In this review, we will summarize the role of β-adrenergic receptors and estrogen in cardiac repair after infarction in preclinical studies.

Cell Migration Related to MDR-Another Impediment to Effective Chemotherapy?

Multidrug resistance, mediated by members of the ATP-binding cassette (ABC) proteins superfamily, has become one of the biggest obstacles in conquering tumour progression. If the chemotherapy outcome is considered successful, when the primary tumour volume is decreased or completely abolished, modulation of ABC proteins activity is one of the best methods to overcome drug resistance. However, if a positive outcome is represented by no metastasis or, at least, elongation of remission-free time, then the positive effect of ABC proteins inhibition should be compared with the several side effects it causes, which may inflict cancer progression and decrease overall patient health. Clinical trials conducted thus far have shown that the tested ABC modulators add limited or no benefits to cancer patients, as some of them are merely toxic and others induce unwanted drug–drug interactions. Moreover, the inhibition of certain ABC members has been recently indicated as potentially responsible for increased fibroblasts migration. A better understanding of the complex role of ABC proteins in relation to cancer progression may offer novel strategies in cancer therapy.

cAMP and cGMP Play an Essential Role in Galvanotaxis of Cell Fragments

Cell fragments devoid of the nucleus and major organelles are found in physiology and pathology, for example platelets derived from megakaryocytes, and cell fragments from white blood cells and glioma cells. Platelets exhibit active chemotaxis. Fragments from white blood cells display chemotaxis, phagocytosis, and bactericidal functions. Signaling mechanisms underlying migration of cell fragments are poorly understood. Here we used fish keratocyte fragments and demonstrated striking differences in signal transduction in migration of cell fragments and parental cells in a weak electric field. cAMP or cGMP agonists completely abolished directional migration of fragments, but had no effect on parental cells. The inhibition effects were prevented by pre-incubating with cAMP and cGMP antagonists. Blocking cAMP and cGMP downstream signaling by inhibition of PKA and PKG also recovered fragment galvanotaxis. Both perturbations confirmed that the inhibitory effect was mediated by cAMP or cGMP signaling. Inhibition of cathode signaling with PI3K inhibitor LY294002 also prevented the effects of cAMP or cGMP agonists. Our results suggest that cAMP and cGMP are essential for galvanotaxis of cell fragments, in contrast to the signaling mechanisms in parental cells.

Cyclic GMP and Cilia Motility

Motile cilia of the lungs respond to environmental challenges by increasing their ciliary beat frequency in order to enhance mucociliary clearance as a fundamental tenant of innate defense. One important second messenger in transducing the regulable nature of motile cilia is cyclic guanosine 3′,5′-monophosphate (cGMP). In this review, the history of cGMP action is presented and a survey of the existing data addressing cGMP action in ciliary motility is presented. Nitric oxide (NO)-mediated regulation of cGMP in ciliated cells is presented in the context of alcohol-induced cilia function and dysfunction.

Förster resonance energy transfer - an approach to visualize the spatiotemporal regulation of macromolecular complex formation and compartmentalized cell signaling

BACKGROUND

Signaling messengers and effector proteins provide an orchestrated molecular machinery to relay extracellular signals to the inside of cells and thereby facilitate distinct cellular behaviors. Formations of intracellular macromolecular complexes and segregation of signaling cascades dynamically regulate the flow of a biological process.

SCOPE OF REVIEW

In this review, we provide an overview of the development and application of FRET technology in monitoring cyclic nucleotide-dependent signalings and protein complexes associated with these signalings in real time and space with brief mention of other important signaling messengers and effector proteins involved in compartmentalized signaling.

MAJOR CONCLUSIONS

The preciseness, rapidity and specificity of cellular responses indicate restricted alterations of signaling messengers, particularly in subcellular compartments rather than globally. Not only the physical confinement and selective depletion, but also the intra- and inter-molecular interactions of signaling effectors modulate the direction of signal transduction in a compartmentalized fashion. To understand the finer details of various intracellular signaling cascades and crosstalk between proteins and other effectors, it is important to visualize these processes in live cells. Förster Resonance Energy Transfer (FRET) has been established as a useful tool to do this, even with its inherent limitations.

GENERAL SIGNIFICANCE

FRET technology remains as an effective tool for unraveling the complex organization and distribution of various endogenous signaling proteins, as well as the spatiotemporal dynamics of second messengers inside a single cell to distinguish the heterogeneity of cell signaling under normal physiological conditions and during pathological events.

Moving towards a paradigm: common mechanisms of chemotactic signaling in Dictyostelium and mammalian leukocytes

Chemotaxis, or directed migration of cells along a chemical gradient, is a highly coordinated process that involves gradient sensing, motility, and polarity. Most of our understanding of chemotaxis comes from studies of cells undergoing amoeboid-type migration, in particular the social amoeba Dictyostelium discoideum and leukocytes. In these amoeboid cells the molecular events leading to directed migration can be conceptually divided into four interacting networks: receptor/G protein, signal transduction, cytoskeleton, and polarity. The signal transduction network occupies a central position in this scheme as it receives direct input from the receptor/G protein network, as well as feedback from the cytoskeletal and polarity networks. Multiple overlapping modules within the signal transduction network transmit the signals to the actin cytoskeleton network leading to biased pseudopod protrusion in the direction of the gradient. The overall architecture of the networks, as well as the individual signaling modules, is remarkably conserved between Dictyostelium and mammalian leukocytes, and the similarities and differences between the two systems are the subject of this review.

Biphasic dose responses in biology, toxicology and medicine: accounting for their generalizability and quantitative features

The most common quantitative feature of the hormetic-biphasic dose response is its modest stimulatory response which at maximum is only 30-60% greater than control values, an observation that is consistently independent of biological model, level of organization (i.e., cell, organ or individual), endpoint measured, chemical/physical agent studied, or mechanism. This quantitative feature suggests an underlying "upstream" mechanism common across biological systems, therefore basic and general. Hormetic dose response relationships represent an estimate of the peak performance of integrative biological processes that are allometrically based. Hormetic responses reflect both direct stimulatory or overcompensation responses to damage induced by relatively low doses of chemical or physical agents. The integration of the hormetic dose response within an allometric framework provides, for the first time, an explanation for both the generality and the quantitative features of the hormetic dose response.

Multi-drug resistance protein 4 (MRP4)-mediated regulation of fibroblast cell migration reflects a dichotomous role of intracellular cyclic nucleotides

It has long been known that cyclic nucleotides and cyclic nucleotide-dependent signaling molecules control cell migration. However, the concept that it is not just the absence or presence of cyclic nucleotides, but a highly coordinated balance between these molecules that regulates cell migration, is new and revolutionary. In this study, we used multidrug resistance protein 4 (MRP4)-expressing cell lines and MRP4 knock-out mice as model systems and wound healing assays as the experimental system to explore this unique and emerging concept. MRP4, a member of a large family of ATP binding cassette transporter proteins, localizes to the plasma membrane and functions as a nucleotide efflux transporter and thus plays a role in the regulation of intracellular cyclic nucleotide levels. Here, we demonstrate that mouse embryonic fibroblasts (MEFs) isolated from Mrp4(-/-) mice have higher intracellular cyclic nucleotide levels and migrate faster compared with MEFs from Mrp4(+/+) mice. Using FRET-based cAMP and cGMP sensors, we show that inhibition of MRP4 with MK571 increases both cAMP and cGMP levels, which results in increased migration. In contrast to these moderate increases in cAMP and cGMP levels seen in the absence of MRP4, a robust increase in cAMP levels was observed following treatment with forskolin and isobutylmethylxanthine, which decreases fibroblast migration. In response to externally added cell-permeant cyclic nucleotides (cpt-cAMP and cpt-cGMP), MEF migration appears to be biphasic. Altogether, our studies provide the first experimental evidence supporting the novel concept that balance between cyclic nucleotides is critical for cell migration.

The effect of β-2 adrenoreceptor agonist inhalation on lungs donated after cardiac death in a canine lung transplantation model

BACKGROUND

It is a matter of great importance in a donation after cardiac death to attenuate ischemia-reperfusion injury (IRI) related to the inevitable warm ischemic time.

METHODS

Donor dogs were rendered cardiac-dead and left at room temperature. The dogs were allocated into 2 groups: the β-2 group (n = 5) received an aerosolized β-2 adrenoreceptor agonist (procaterol, 350 μg) and ventilation with 100% oxygen for 60 minutes starting at 240 minutes after cardiac arrest, and the control group (n = 6) received an aerosolized control solvent with the ventilation. Lungs were recovered 300 minutes after cardiac arrest. Recipient dogs underwent left single-lung transplantation to evaluate the functions of the left transplanted lung for 240 minutes after the reperfusion.

RESULTS

Oxygenation and dynamic compliance were significantly higher in the β-2 group than in the control group. The β-2 group revealed significantly higher levels of cyclic adenosine monophosphate and high-energy phosphates in the donor lung after the inhalation than before it. Histologic findings revealed that the β-2 group had less edema and fewer inflammatory cells.

CONCLUSION

Our results suggest that β-2 adrenoreceptor agonist inhalation during the pre-procurement period may ameliorate IRI.

Activity of β2-adrenergic receptor in oral squamous cell carcinoma is mediated by overexpression of the ADRBK2 gene: a pilot study

The β2-adrenergic receptor is most frequently involved in carcinogenic processes. Earlier studies have established a relation between the β2-adrenergic receptor and various characteristics of cancer including cell proliferation, apoptosis, chemotaxis, metastasis, tumor growth and angiogenesis. Our goal was to determine differential expression of the genes involved in adrenergic receptors using DNA microarrays and to confirm their under- or overexpression using real-time quantitative PCR. Five of the nine genes investigated showed significantly altered expression levels in tumor cells (p < 0.05). The gene product with the highest Z-score (restrictive statistical technique for selection of appropriate genes to study) was ADRBK2. Significantly, most of the overexpressed genes were related to β-adrenergic receptors. Real-time PCR analysis confirmed the up regulation observed in the microarrays, which indicated overexpression in 100% of the tumors. In oral squamous cell carcinomas, malignant cells and surrounding tissue overexpress the ADRBK2 gene.

Nitric oxide stimulates human neural progenitor cell migration via cGMP-mediated signal transduction

Neuronal migration is one of the most critical processes during early brain development. The gaseous messenger nitric oxide (NO) has been shown to modulate neuronal and glial migration in various experimental models. Here, we analyze a potential role for NO signaling in the migration of fetal human neural progenitor cells. Cells migrate out of cultured neurospheres and differentiate into both neuronal and glial cells. The neurosphere cultures express neuronal nitric oxide synthase and soluble guanylyl cyclase that produces cGMP upon activation with NO. By employing small bioactive enzyme activators and inhibitors in both gain and loss of function experiments, we show NO/cGMP signaling as a positive regulator of migration in neurosphere cultures of early developing human brain cells. Since NO signaling regulates cell movements from developing insects to mammalian nervous systems, this transduction pathway may have evolutionary conserved functions.

mTORC2 regulates neutrophil chemotaxis in a cAMP- and RhoA-dependent fashion

We studied the role of the target of rapamycin complex 2 (mTORC2) during neutrophil chemotaxis, a process that is mediated through the polarization of actin and myosin filament networks. We show that inhibition of mTORC2 activity, achieved via knock down (KD) of Rictor, severely inhibits neutrophil polarization and directed migration induced by chemoattractants, independently of Akt. Rictor KD also abolishes the ability of chemoattractants to induce cAMP production, a process mediated through the activation of the adenylyl cyclase 9 (AC9). Cells with either reduced or higher AC9 levels also exhibit specific and severe tail retraction defects that are mediated through RhoA. We further show that cAMP is excluded from extending pseudopods and remains restricted to the cell body of migrating neutrophils. We propose that the mTORC2-dependent regulation of MyoII occurs through a cAMP/RhoA-signaling axis, independently of actin reorganization during neutrophil chemotaxis.

Inhibitory Role of Sphingosine 1-Phosphate Receptor 2 in Macrophage Recruitment during Inflammation

Macrophage recruitment to sites of inflammation is an essential step in host defense. However, the mechanisms preventing excessive accumulation of macrophages remain relatively unknown. The lysophospholipid sphingosine 1-phosphate (S1P) promotes T and B cell egress from lymphoid organs by acting on S1P receptor 1 (S1P1R). More recently, S1P5R was shown to regulate NK cell mobilization during inflammation, raising the possibility that S1P regulates the trafficking of other leukocyte lineages. In this study, we show that S1P2R inhibits macrophage migration in vitro and that S1P2R-deficient mice have enhanced macrophage recruitment during thioglycollate peritonitis. We identify the signaling mechanisms used by S1P2R in macrophages, involving the second messenger cAMP and inhibition of Akt phosphorylation. In addition, we show that the phosphoinositide phosphatase and tensin homolog deleted on chromosome 10, which has been suggested to mediate S1P2R effects in other cell types, does not mediate S1P2R inhibition in macrophages. Our results suggest that S1P serves as a negative regulator of macrophage recruitment by inhibiting migration in these cells and identify an additional facet to the regulation of leukocyte trafficking by S1P.

Increased cAMP levels modulate transforming growth factor-beta/Smad-induced expression of extracellular matrix components and other key fibroblast effector functions

cAMP is a key messenger of many hormones and neuropeptides, some of which modulate the composition of extracellular matrix. Treatment of human dermal fibroblasts with dibutyryl cyclic AMP and forskolin antagonized the inductive effects of transforming growth factor-beta (TGF-beta) on the expression of collagen, connective tissue growth factor, tissue inhibitor of matrix metalloproteinase-1, and plasminogen activator inhibitor type I, four prototypical TGF-beta-responsive genes. Increased intracellular cAMP prevented TGF-beta-induced Smad-specific gene transactivation, although TGF-beta-mediated Smad phosphorylation and nuclear translocation remained unaffected. However, increased cAMP levels abolished TGF-beta-induced interaction of Smad3 with its transcriptional co-activator cAMP-response element-binding protein (CREB)-binding protein (CBP)/p300. Overexpression of the transcriptional co-activator CBP/p300 rescued Smad-specific gene transcription in the presence of cAMP suggesting that sequestration of limited amounts of CBP/p300 by the activated cAMP/CREB pathway is the molecular basis of this inhibitory effect. These findings were extended by two functional assays. Increased intracellular cAMP levels suppressed the inductive activity of TGF-beta to contract mechanically unloaded collagen lattices and resulted in an attenuation of fibroblast migration of mechanically induced cell layer wounds. Of note, cAMP and TGF-beta synergistically induced hyaluronan synthase 2 (HAS2) expression and hyaluronan secretion, presumably via putative CREB-binding sites adjacent to Smad-binding sites within the HAS2 promoter. Our findings identify the cAMP pathway as a potent but differential and promoter-specific regulator of TGF-beta-mediated effects involved in extracellular matrix homeostasis.

Nitric oxide and cGMP signal transduction positively regulates the motility of human neuronal precursor (NT2) cells

Developmental studies in both vertebrates and invertebrates implicate an involvement of nitric oxide (NO) signaling in cell proliferation, neuronal motility, and synaptic maturation. However, it is unknown whether NO plays a role in the development of the human nervous system. We used a model of human neuronal precursor cells from a well-characterized teratocarcinoma cell line (NT2). The precursor cells proliferate during retinoic acid treatment as spherical aggregate culture that stains for nestin and betaIII-tubulin. Cells migrate out of the aggregates to acquire fully differentiated neuronal phenotypes. The cells express neuronal nitric oxide synthase and soluble guanylyl cyclase (sGC), an enzyme that synthesizes cGMP upon activation by NO. The migration of the neuronal precursor cell is blocked by the use of nNOS, sGC, and protein kinase G (PKG) inhibitors. Inhibition of sGC can be rescued by a membrane permeable analog of cGMP. In gain of function experiments the application of a NO donor and cGMP analog facilitate cell migration. Our results from the differentiating NT2 model neurons point towards a vital role of the NO/cGMP/PKG signaling cascade as positive regulator of cell migration in the developing human brain.

Stimulation of guanylyl cyclase-D by bicarbonate

Guanylyl cyclases (GCs) catalyze the conversion of GTP to the second messenger cGMP. While some transmembrane GCs are receptors for extracellular ligands, other transmembrane GCs such as retinal-specific GC-E and GC-F are stimulated by cellular proteins. GC-D is expressed in a special group of olfactory sensory neurons. However, the direct regulatory mechanism of GC-D activity is not completely understood. Here we have demonstrated that bicarbonate directly increases the activity of purified GC-D. Bicarbonate also increases the cGMP levels in cells expressing GC-D. These results identify bicarbonate as a small molecule that regulates GC-D.

Calcium and cyclic nucleotides affect TNF-alpha-induced stem cell migration

The purpose of this study was to study the effect of calcium, cyclic AMP (cAMP) and cyclic GMP (cGMP) on embryonic stem cell (ESC) motility during TNF-alpha-induced chemotaxis. ESCs were monitored using a chemotaxis chamber, with different concentrations of calcium or cAMP or cGMP added to the medium. Changes in intracellular calcium ([Ca(2+)](i)) were measured with the fluorescent dye fura-2/AM. We combined migratory parameters in a mathematical model and described it as "mobility". After adding calcium, a dose-dependant increase in cell speed was found. Cyclic AMP increased mobility as well as the [Ca(2+)](i). In contrast, adding dbcGMP resulted in a significant decrease in the mobility of the ESCs. During migration ESCs showed an increase in [Ca(2+)](i). Furthermore, TNF-alpha dramatically increased the movement as well as the directionality of ESCs. These results demonstrate that ESCs are highly motile and respond to different concentrations of calcium in a dose-related manner.

Hormetic Dose-Response Relationships in Immunology: Occurrence, Quantitative Features of the Dose Response, Mechanistic Foundations, and Clinical Implications

This article provides an assessment of the occurrence of immune-system-related hormetic-like biphasic dose-response relationships. Such dose-response relationships are extensive, with over 90 different immune response-related endpoints reported, induced by over 70 endogenous agonists, over 100 drugs, and over 40 environmental contaminants. Such hormetic responses were reported in over 30 animal models, over a dozen mammalian and human cell lines. These findings demonstrate that immune-system-related hormetic-like biphasic dose-response relationships are common and highly generalizable according to model, endpoint, and chemical class. The quantitative features of the dose response are generally consistent with previously published examples of hormetic dose responses for other biological endpoints. These findings were generally recognized and explicitly discussed by the original authors, often with consideration given to possible mechanistic foundations as well as numerous clinical implications. Despite the recognition by individual authors of the hormetic nature of these observed responses, the overall widespread nature of immune-related hormetic responses has been only little appreciated, with a general lack of insight into the highly generalizable nature of this phenomenon as well as the complex regulatory networks affecting biological switching mechanisms that result in the hormetic responses.

The synthetic melanocortin (CKPV)2 exerts broad anti-inflammatory effects in human neutrophils

Natural melanocortin peptides exert broad effects on the host and they have remarkable therapeutic potential. However, successful use of melanocortins as therapeutic agents depends on the design of molecules that have more stable pharmacological profiles. The synthetic peptide (CKPV)(2), based on the C-terminal sequence of alpha-melanocyte stimulating hormone (alpha-MSH), has anti-tumor necrosis factor-alpha (TNF-alpha) effects in vitro and in vivo and is a promising candidate to treat inflammation. Because neutrophil activity is a major target for anti-inflammatory therapies, we determined whether (CKPV)(2) modulates human neutrophil functions in vitro. Incubation of freshly-separated human neutrophils with 10(-12)-10(-6)M (CKPV)(2) significantly inhibited activities relevant to the inflammatory reaction. Neutrophil migration toward the two chemoattractants interleukin 8 (IL-8) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) was significantly inhibited by (CKPV)(2). (CKPV)(2) also inhibited reactive oxygen intermediate (ROI) production induced by phorbol 12-myristate 13-acetate (PMA), but not that induced by fMLP. Because these effects of (CKPV)(2) were abolished by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (ddAdo), they appear to be cAMP-dependent. Finally, the peptide reduced lipopolysaccharide (LPS)-stimulated expression of TNF-alpha, interleukin-1beta (IL-1beta), interleukin-8 (IL-8), and intercellular adhesion molecule 1 (ICAM-1), as well as TNF-alpha protein release in cell supernatants. The data indicate that (CKPV)(2) modulates broad cAMP-dependent, anti-inflammatory pathways in human neutrophils.

Beta2-agonist clenbuterol induced changes in the distribution of white blood cells in rats

Clenbuterol [CLE: 4-amino-alpha(t-butyl-amino)methyl-3,5-dichlorobenzyl alcohol] is well known as a potent beta2-adrenergic agonist and non-steroidal anabolic drug, and thus it is generally used for sports doping and asthma therapy. Although the functions of immune cells such as white blood cells (WBCs) have shown to be modulated through beta2-adrenoceptors, the effects of CLE on immune-responsive systems have not been elucidated systematically. Therefore, the effects of CLE on the number of WBCs were studied in rats. Male adult rats were divided into CLE-administered group and the control group to compare the number of total WBCs, neutrophils, monocytes, lymphocytes, eosinophils, and basophils. The administration (dose = 1.0 mg . kg(-1) body weight . day(-1), s.c.) of CLE was maintained for 30 days. CLE did not change the number of total WBCs during the experimental period. However, CLE increased significantly the number of neutrophils and monocytes, while CLE decreased drastically the number of lymphocytes and eosinophils. There was no significant change in the number of basophils between both groups. These results suggest that the administration of CLE induces drastic redistribution of WBCs in circulation without changing the number of total WBCs, and these responses of WBCs during the administration of CLE are sustained for at least 30 days.

A Rac-cGMP signaling pathway

The small GTPase Rac and the second messenger cGMP (guanosine 3',5'-cyclic monophosphate) are critical regulators of diverse cell functions. When activated by extracellular signals via membrane signaling receptors, Rac executes its functions through engaging downstream effectors such as p21-activated kinase (PAK), a serine/threonine protein kinase. However, the molecular mechanism by which membrane signaling receptors regulate cGMP levels is not known. Here we have uncovered a signaling pathway linking Rac to the increase of cellular cGMP. We show that Rac uses PAK to directly activate transmembrane guanylyl cyclases (GCs), leading to increased cellular cGMP levels. This Rac/PAK/GC/cGMP pathway is involved in platelet-derived growth factor-induced fibroblast cell migration and lamellipodium formation. Our findings connect two important regulators of cellular physiological functions and provide a general mechanism for diverse receptors to modulate physiological responses through elevating cellular cGMP levels.

cAMP signaling in leukocyte transendothelial migration

The migration of leukocytes across the vascular endothelium is crucial for immunosurveillance as well as for inflammatory responses. Uncontrolled leukocyte transendothelial migration results in pathologies such as asthma, rheumatoid arthritis, and atherosclerosis. The molecular mechanisms that regulate leukocyte transendothelial migration involve signaling downstream of intracellular messengers such as cAMP, calcium, phosphoinositol lipids, or reactive oxygen species. Among these, cAMP is particularly intriguing because it is generated in both leukocytes and endothelial cells and regulates leukocyte chemotaxis as well as endothelial barrier function. In addition, physiological stimuli that induce cAMP production generate both pro- and antiinflammatory signals, underscoring the complexity of cAMP-driven signaling. This review discusses our current knowledge of the control of leukocyte transendothelial migration by two main cAMP effectors: protein kinase A and the Rap exchange factor Epac (Exchange protein directly activated by cAMP).

A chemoattractant-mediated Gi-coupled pathway activates adenylyl cyclase in human neutrophils

Neutrophils and Dictyostelium use conserved signal transduction pathways to decipher chemoattractant gradients and migrate directionally. In both cell types, addition of chemoattractants stimulates the production of cAMP, which has been suggested to regulate chemotaxis. We set out to define the mechanism by which chemoattractants increase cAMP levels in human neutrophils. We show that chemoattractants elicit a rapid and transient activation of adenylyl cyclase (AC). This activation is sensitive to pertussis toxin treatment but independent of phosphoinositide-3 kinase activity and an intact cytoskeleton. Remarkably, and in sharp contrast to Galpha(s)-mediated activation, chemoattractant-induced AC activation is lost in cell lysates. Of the nine, differentially regulated transmembrane AC isoforms in the human genome, we find that isoforms III, IV, VII, and IX are expressed in human neutrophils. We conclude that the signal transduction cascade used by chemoattractants to activate AC is conserved in Dictyostelium and human neutrophils and is markedly different from the canonical Galpha(s)-meditated pathway.

Neutrophil chemorepulsion in defined interleukin-8 gradients in vitro and in vivo

We report for the first time that primary human neutrophils can undergo persistent, directionally biased movement away from a chemokine in vitro and in vivo, termed chemorepulsion or fugetaxis. Robust neutrophil chemorepulsion in microfluidic gradients of interleukin-8 (IL-8; CXC chemokine ligand 8) was dependent on the absolute concentration of chemokine, CXC chemokine receptor 2 (CXCR2), and was associated with polarization of cytoskeletal elements and signaling molecules involved in chemotaxis and leading edge formation. Like chemoattraction, chemorepulsion was pertussis toxin-sensitive and dependent on phosphoinositide-3 kinase, RhoGTPases, and associated proteins. Perturbation of neutrophil intracytoplasmic cyclic adenosine monophosphate concentrations and the activity of protein kinase C isoforms modulated directional bias and persistence of motility and could convert a chemorepellent to a chemoattractant response. Neutrophil chemorepulsion to an IL-8 ortholog was also demonstrated and quantified in a rat model of inflammation. The finding that neutrophils undergo chemorepulsion in response to continuous chemokine gradients expands the paradigm by which neutrophil migration is understood and may reveal a novel approach to our understanding of the homeostatic regulation of inflammation.

Nitric oxide released by accessory cells mediates the gastrin-releasing peptide effect on murine lymphocyte chemotaxis

Several neuropeptides, including gastrin-releasing peptide (GRP), modulate the immune response, specifically lymphocyte chemotaxis. In the present work the effect of GRP on the chemotaxis of murine lymphocytes from different immune locations in both, total leukocyte populations and populations depleted of adherent cells have been studied. Specificity of the GRP effect on chemotaxis using an antagonist of the GRP receptor, as well as the implication of nitric oxide (NO), using inhibitors of NO synthase and donors of NO, were investigated. The effects of GRP stimulating the chemotaxis of lymphocytes from peritoneum, axillary nodes and spleen and decreasing the chemotaxis from thymus were receptor-specific and disappeared in lymphocytes from populations depleted of adherent cells. NO synthase inhibitors blocked the GRP effect on lymphocyte chemotaxis, and this action was reversed in the presence of l-arginine. Thus, the effect of GRP on murine lymphocyte chemotaxis appears to be mediated by NO secreted by adherent cells.

Rho, Rac, Pak and angiogenesis: old roles and newly identified responsibilities in endothelial cells

Angiogenesis-the develoment of microvasculature-requires, in part, directed endothelial cell motility and responsiveness to external signals. Several of the proteins, which modulate and/or direct endothelial cell motility and morphology in angiogenesis are the Rho GTPases (Rho, Rac, and Cdc42) and Pak (a downstream effector of Rac and Cdc42). Previously, overexpression and activation of Rho GTPases and Pak had been implicated in the development of cancer, through their roles in cancer cell transformation, stimulation of proliferation, inhibition of apoptosis, and migration. Yet regardless of the transformed status of cells within a tumor, without a blood supply most tumors cannot grow larger than 1-2 mm. The blood supply in tumors is provided by capillaries formed of endothelial cells in a process called angiogenesis. Consequently, there is enormous interest in the role of the wild type endothelial cells-and the signaling mechanisms required to support angiogenesis and subsequent growth of metastatic and aggressive cancers. Recent work has begun to uncover the roles of the Rho GTPases and Pak in the regulation of normal endothelial cell function. This review will discuss the current literature regarding the roles of Rho and Rac, and the Rac effector-Pak, in endothelial cells, and we will propose new avenues of research for interaction of the AGC kinase-PKG, with the Rho GTPases and Pak in the cell motility and cell morphology of endothelial cells.

Antiinflammatory effects of salmeterol after inhalation of lipopolysaccharide by healthy volunteers

RATIONALE

Salmeterol is a beta2-adrenoreceptor agonist used in the treatment of obstructive pulmonary disease. Salmeterol inhibits inflammatory responses by neutrophils and mononuclear cells in vitro and in mouse models of lung inflammation in vivo.

OBJECTIVE

To determine the effect of salmeterol on LPS-induced lung inflammation in humans.

METHODS

Thirty-two healthy subjects were enrolled in a single-blinded, placebo-controlled study. Subjects inhaled 100 microg salmeterol or placebo (t=-0.5 h) followed by 100 microg LPS or normal saline (t=0 h; n=8/group). Measurements were performed in bronchoalveolar lavage fluid and purified alveolar macrophages obtained 6 h post-challenge.

MEASUREMENTS AND MAIN RESULTS

Inhalation of LPS was associated with neutrophil influx, neutrophil degranulation (myeloperoxidase, bactericidal/permeability-increasing protein and elastase), release of cytokines (tumor necrosis factor alpha and interleukin 6) and chemokines (interleukin 8, epithelial cell-derived neutrophil attractant 78, macrophage inflammatory proteins 1alpha and 1beta), activation of alveolar macrophages (upregulation of HLA-DR and CD71; enhanced expression of mRNAs for 13 different mediators of inflammation), and protein leakage (all p<0.05 vs. placebo/saline). Pretreatment with salmeterol inhibited LPS-induced neutrophil influx, neutrophil degranulation (myeloperoxidase), tumor necrosis factor alpha release, and HLA-DR expression (all p<0.05 vs. placebo/LPS), while not significantly influencing other responses.

CONCLUSION

Salmeterol exerts antiinflammatory effects in the pulmonary compartment of humans exposed to LPS.

STOP and GO with NO: nitric oxide as a regulator of cell motility in simple brains

During the formation of the brain, neuronal cell migration and neurite extension are controlled by extracellular guidance cues. Here, I discuss experiments showing that the messenger nitric oxide (NO) is an additional regulator of cell motility. NO is a membrane permeant molecule, which activates soluble guanylyl cyclase (sGC) and leads to the formation of cyclic GMP (cGMP) in target cells. The analysis of specific cells types in invertebrate models such as molluscs, insects and the medicinal leech provides insight how NO and cyclic nucleotides affect the wiring of nervous systems by regulating cell and growth-cone motility. Inhibition of the NOS and sGC enzymes combined with rescue experiments show that NO signalling orchestrates neurite outgrowth and filopodial dynamics, cell migration of enteric neurons, glial migration and axonogenesis of pioneer fibers. Cultured insect embryos are accessible model systems in which cellular mechanisms of NO-induced cytoskeletal reorganizations can be analyzed in natural settings. Finally, I will outline some indications that NO may also regulate cell motility in the developing and regenerating vertebrate nervous system.

Selective up-regulation of PDE1B2 upon monocyte-to-macrophage differentiation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a major regulator of monocyte to macrophage differentiation. In both humans and mice, the main phenotype of decreased GM-CSF function is pulmonary proteinosis due to aberrant function of alveolar macrophages. Recently, this cytokine has been shown to up-regulate a cyclic nucleotide phosphodiesterase, PDE1B. Two PDE1B variants with unique N-terminal sequences, PDE1B1 and PDE1B2, have been identified. Here, we report that the previously uncharacterized PDE1B2 is selectively increased by GM-CSF by stimulation of transcription at a previously unknown transcriptional start site. Analysis of the exon and intron organization of the PDE1B gene reveals that PDE1B2 has a different N-terminal sequence because of a separate first exon that is located 11.5 kb downstream from the PDE1B1 first exon. By using 5'-RACE, alignment of EST sequences, and a luciferase-reporter system, we provide evidence that PDE1B2 has a separate transcriptional start site from PDE1B1 that can be activated by monocyte differentiation. Furthermore, IL-4 treatment in the presence of GM-CSF, which shifts the differentiation from a macrophage to a dendritic cell phenotype, suppresses the up-regulation of PDE1B2. Induction of PDE1B2 is also found in T cells upon activation by PHA. Therefore, PDE1B2 may have a regulatory role in multiple immune cell types. Last, characterization of the catalytic properties of recombinant PDE1B2 shows that it prefers cGMP over cAMP as a substrate and, thus, is likely to regulate cGMP in macrophages. Also, PDE1B2 has a nearly 3-fold lower EC(50) for activation by calmodulin than PDE1B1.

Beta 2-adrenergic receptor regulation of human neutrophil function is sexually dimorphic

While the mechanisms underlying the marked sexual dimorphism in inflammatory diseases are not well understood, the sexually dimorphic sympathoadrenal axis profoundly affects the inflammatory response. We tested whether adrenergic receptor-mediated activation of human neutrophil function is sexually dimorphic, since neutrophils provide the first line of defense in the inflammatory response. There was a marked sexual dimorphism in beta(2)-adrenergic receptor binding, using the specific beta(2)-adrenergic receptor ligand, [(3)H]-dihydroalprenolol, with almost three times more binding sites on neutrophils from females (20,878 +/- 2470) compared to males (7331 +/- 3179). There was also a marked sexual dimorphism in the effects of isoprenaline, a beta-adrenergic receptor agonist, which increased nondirected locomotion (chemokinesis) in neutrophils obtained from females, while having no effect on neutrophils from males. Isoprenaline stimulated the release of a chemotactic factor from neutrophils obtained from females, but not from males. This chemotactic factor acts on the G protein-coupled CXC chemokine receptor 2 (CXCR2) chemokine receptor, since an anti-CXCR2 antibody and the selective nonpeptide CXCR2 antagonist SB225002, inhibited chemotaxis produced by this factor. While interleukin- (IL-) 8 is a principal CXCR2 ligand, isoprenaline did not produce an increase in IL-8 release from neutrophils. IL-8-induced chemotaxis was inhibited in a sexually dimorphic manner by isoprenaline, which also stimulated release of a mediator from neutrophils that induced chemotaxis, that was inhibited by anti-CXCR2 antibodies. These findings indicate an important role for adrenergic receptors in the modulation of neutrophil trafficking, which could contribute to sex-differences in the inflammatory response.

The ubiquitin-related protein PLIC-1 regulates heterotrimeric G protein function through association with Gbetagamma

PLIC-1, a newly described ubiquitin-related protein, inhibited both Jurkat migration toward SDF-1alpha and A431 wound healing, but the closely related PLIC-2 did not. PLIC-1 prevented the SDF-1alpha-induced activation of phospholipase C, decreased ligand-induced internalization of SDF-1alpha receptor CXCR4 and inhibited chemotaxis signaled by a transfected Gi-coupled receptor. However, PLIC-1 had no effect on Gs-mediated adenylyl cyclase activation, and inhibited only the Gbetagamma-dependent component of Gq-initiated increase in [Ca2+]i, which is consistent with selective inhibition of Gbetagamma function. PLIC-1 colocalized with G proteins in lamellae and pseudopods, and precipitated Gbetagamma in pull downs. Interaction with Gbetagamma did not require PLIC-1's ubiquitin-like or ubiquitin-associated domains, and proteasome inhibition had no effect on SDF-1alpha activation of phospholipase C, indicating that PLIC-1's inhibition of Gbetagamma did not result from effects on proteasome function. Thus, PLIC-1 inhibits Gi signaling by direct association with Gbetagamma; because it also interacts with CD47, a modulator of integrin function, it likely has a role integrating adhesion and signaling components of cell migration.

Treatment of acute and chronic gastrointestinal inflammation

Treating inflammation in the equine gastrointestinal tract remains a challenge. Our most potent anti-inflammatory drugs, COX inhibitors and glucocorticoids, have unwanted effects on the gastrointestinal tract and host defense that often limit their use. Newer strategies targeting specific cells and molecules that regulate a subset of the events occurring during inflammation are rapidly becoming available and should allow clinicians to reduce the detrimental effects of inflammation without inhibiting the beneficial aspects.

Cyclic AMP-mobilizing agents and glucocorticoids modulate human smooth muscle cell migration

Hyperplasia and cell migration of smooth muscle are features of both airway and pulmonary vascular diseases. The precise cellular and molecular mechanisms that regulate smooth muscle migration in the lungs remain unknown. In this study, we examined the effect of cAMP-mobilizing agents and steroids on smooth muscle cell migration. Platelet-derived growth factor (PDGF), transforming growth factor-alpha, vascular endothelial growth factor, and basic fibroblast growth factor significantly stimulated cell migration in pulmonary vascular smooth muscle (PVSM) cells. Airway smooth muscle (ASM) migration was also stimulated by PDGF, transforming growth factor-alpha, and basic fibroblast growth factor, but vascular endothelial growth factor was without effect. Interestingly, the smooth muscle mitogen thrombin did not stimulate migration of either cell type. Agents capable of elevating intracellular cAMP inhibited basal (unstimulated) cell migration in both cell types, whereas their effects on PDGF-stimulated migration were more variable. Prostaglandin E2, salmeterol, and the phosphodiesterase type 4 inhibitor cilomolast inhibited basal ASM and PVSM migration by 30-60%. Prostaglandin E2 and cilomolast also inhibited PDGF-stimulated migration of ASM and PVSM cells, but salmeterol was without effect. Preincubation of ASM cells with dexamethasone or fluticasone inhibited basal and PDGF-stimulated migration, and enabled an inhibitory effect of salmeterol on PDGF-induced cell migration. Steroids alone did not stimulate cAMP production or cAMP/PKA-dependent gene transcription (CRE-Luc activity), but slightly augmented salmeterol-stimulated CRE-Luc activity. Collectively, these findings demonstrate that cAMP-mobilizing agents and steroids modulate human smooth muscle cell migration, likely by distinct mechanisms.

The maturing of hormesis as a credible dose-response model

Hormesis is a dose-response phenomenon that has received little recognition, credibility and acceptance as evidenced by its absence from major toxicological/risk assessment texts, governmental regulatory dose-response modeling for risk assessment, and non-visibility in major professional toxicological society national meetings. This paper traces the historical evolution of the hormetic dose-response hypothesis, why this model is not only credible but also more common than the widely accepted threshold model in direct comparative evaluation, and how the toxicological community made a critical error in rejecting hormesis, a rejection sustained over 70 years.

A novel function for chemokines: downregulation of neutrophil migration

Migration is a key function of stem cells during ontogenesis, of fibroblasts in wound healing and of immune cells in host defence. The signals that initiate migration are as important as signals that terminate migration, once the destination has been reached. We now show that formyl-methionyl-leucyl-phenylalanine (fMLP)-induced migration of neutrophils was inhibited by increasing concentrations of interleukin-8 (IL-8). IL-8 dose dependently increased the frequency and the duration of stop-periods, whereas the percentage of cells of a population that was locomotory active remained constant. The stop-signal delivered by IL-8 was intracellularly transduced by a dichotomic pathway: (i) the activation of the adenylyl cyclase leads to an increase of cytosolic cyclic adenosine monophosphate, which results in an activation of the sarcoplasmatic/endoplasmatic reticulum calcium ATPase pump and a calcium sequestration; (ii) the activation of the phospholipase Cbeta (PLCbeta) generates inositol-1,4,5-phosphate (IP3) and diacylglycerol (DAG), which results in IP3-mediated release of intracellularly stored calcium in the endoplasmatic reticulum and DAG-mediated activation of protein kinase C. Thus, we show for the first time that a chemokine, IL-8, in concert with fMLP, downregulates the neutrophil migration through the regulation of the intracellular calcium concentration via the adenylyl cyclase and the PLCbeta2.

Hemin, a heme oxygenase substrate analog, both inhibits and enhances neutrophil random migration and chemotaxis

BACKGROUND

Carbon monoxide (CO), is an endogenously produced gas, generated by the rate-limiting enzyme heme oxygenase (HO), present in man throughout the respiratory tract. CO can elicit important physiological responses like bronchial relaxation and vasodilation. Both HO expression and CO levels in the airways increase in response to hypoxic challenge and to a wide variety of inflammatory stimuli, such as intermittent allergic rhinitis, asthma and upper respiratory tract infections. A role for CO in airway regulation and inflammation has therefore been suggested. However, information about CO-induced effects on cells involved in airway inflammation is scarce. The present study was designed to investigate if the HO substrate analog hemin could affect neutrophil random migration, and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induced chemotaxis.

METHODS

Hemin was added to and incubated with whole blood and the effects of the anticipated CO production were then evaluated on isolated neutrophils using a chemotaxis chamber.

RESULTS

A biphasic dose-response curve emerged for both the neutrophil spontaneous random migration and the fMLP-induced chemotaxis. Low concentrations of hemin (10(-11) m to 10(-9) m) enhanced the migratory response, whereas higher concentrations (10(-7) m and 10(-5) m) inhibited migration. The inhibition induced by hemin on fMLP-induced migration was abolished after pre-treatment with Rp-8Br-cyclicGMPS, an inhibitor of cyclicGMP.

CONCLUSIONS

The present data indicate that endogenously produced CO can affect both spontaneous and stimulated neutrophil migration, partly via a cyclicGMP-related process, hence strengthening the idea of a role for CO in airway inflammation.

Migration of human monocytes in response to procalcitonin

OBJECTIVE

Circulating serum levels of procalcitonin rise significantly during bacterial infection. Because calcitonin is known to be a monocyte chemoattractant, we investigated whether procalcitonin, a prohormone of calcitonin, also affects leukocyte migration.

DESIGN

Prospective, controlled in vitro study.

SETTING

University research laboratories.

INTERVENTIONS

Forearm venous blood polymorphonuclear neutrophils and monocytes were isolated from healthy human donors. Cell migration was assessed in a blindwell chemotaxis chamber. The distance of migration into filter micropores was measured. To biochemically confirm functional data on cell migration, effects of procalcitonin on cellular levels of cyclic adenosine monophosphate were measured by high-performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

Both procalcitonin and calcitonin elicited dose-dependent migration of monocytes at concentrations from the femtomolar to the micromolar range. Neutrophils did not migrate toward procalcitonin or calcitonin, nor was their oxygen free radical release affected as measured fluorimetrically. Checkerboard analysis of monocyte locomotion revealed procalcitonin-induced migration as true chemotaxis. Pretreatment of monocytes with procalcitonin or calcitonin rapidly deactivated their migratory response to formyl-Met-Leu-Phe, and both also induced homologous deactivation of migration. Procalcitonin elevated levels of cyclic adenosine monophosphate in monocytes.

CONCLUSIONS

In vitro procalcitonin is a monocyte chemoattractant that deactivates chemotaxis in the presence of additional inflammatory mediators. Procalcitonin stimulates cyclic adenosine monophosphate production in monocytes, suggesting that its action may be specific and comparable with calcitonin, which exerts similar functions.

Failure of neutrophil chemotactic function in septic patients

OBJECTIVE

To investigate the in vitro chemotactic function of neutrophils obtained from patients with sepsis.

DESIGN

Prospective study in which purified neutrophils obtained from septic patients and nonseptic control volunteers were assayed for chemotactic function induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) and leukotriene B4. The sera nitrate concentrations also were quantified.

SETTING

University hospital.

PATIENTS

Twenty patients with sepsis caused by different infectious foci.

INTERVENTIONS

Routine blood tests, blood or other site cultures, blood collection for neutrophil purification sera collection for nitrate assay.

MEASUREMENTS AND MAIN RESULTS

Neutrophils from septic patients exhibited significantly less chemotactic activity than neutrophils obtained from healthy volunteers, in response to FMLP (93.4 +/- 6.6 vs. 51 +/- 8.3 migrated neutrophils) and leukotriene B4 (90.2 +/- 10 vs. 42.4 +/- 11.6 migrated neutrophils) stimuli, in a microchemotaxis chamber assay. The impaired chemotaxis occurred mainly in neutrophils from nonsurvivor patients. The extent of neutrophil chemotaxis inhibition (survivor/nonsurvivor) was 33.43%/61.67% and 43.4%/86.98%, in response to FMLP and leukotriene B4, respectively. Increased serum nitrate (micromoles of NO2 + NO3) concentrations were detected in septic patients, compared with controls, but no differences were found between survivor (91.84 +/- 14.12) and nonsurvivor (102.6 +/- 17.36) groups.

CONCLUSIONS

Septic patients present suppressed neutrophil chemotactic responses to FMLP and leukotriene B4 stimuli compared with healthy controls. This is accompanied by increased serum concentrations of nitrate. The impairment of neutrophil chemotaxis was observed mainly in the cells obtained from nonsurvivor patients and may thus be an additional factor contributing to disease outcome.

Cell migration/chemotaxis: biphasic dose responses

The dose-dependent effects of chemoattractants on target cell migration such as tumor cells, fibroblasts, and especially neutrophils were assessed. In general, the dose-response characteristics were strikingly biphasic in nature and were independent of both the target tissue and chemoattractant agent. The assessment included evaluations of the quantitative features of the dose-response relationship, mechanistic foundations of the biphasic responsiveness and clinical applications.

The vasodilator-stimulated phosphoprotein is regulated by cyclic GMP-dependent protein kinase during neutrophil spreading

The expression and phosphorylation state of the vasodilator-stimulated phosphoprotein (VASP), a membrane-associated focal adhesion protein, was investigated in human neutrophils. Adhesion and spreading of neutrophils induced the rapid phosphorylation of VASP. The phosphorylation of VASP was dependent on cell spreading, as VASP was expressed as a dephosphorylated protein in round adherent cells and was phosphorylated at the onset of changes in cell shape from round to spread cells. Immunofluorescence microscopy demonstrated that VASP was localized at the cell cortex in round cells and redistributed to focal adhesions at the ventral surface of the cell body during cell spreading. Dual labeling of spread cells indicated that VASP was colocalized with F-actin in filopodia and in focal adhesions, suggesting that the phosphorylation of VASP during cell spreading may be involved in focal adhesion complex organization and actin dynamics. VASP is a prominent substrate for both cGMP-dependent protein kinase (cGK) and cAMP-dependent protein kinase. Evidence suggested that cGK regulated neutrophil spreading, as both VASP phosphorylation and neutrophil spreading were inhibited by Rp-8-pCPT-cGMPS (cGK inhibitor), but not KT5720 (cAMP-dependent protein kinase inhibitor). In contrast, neutrophil spreading was accelerated when cGMP levels were elevated with 8-Br-cGMP, a direct activator of cGK. Furthermore, the same conditions that lead to VASP phosphorylation during neutrophil adherence and spreading induced significant elevations of cGMP in neutrophils. These results indicate that cGMP/cGK signal transduction is required for neutrophil spreading, and that VASP is a target for cGK regulation.

Negative regulation of epithelium-neutrophil interactions via activation of CD44

Polymorphonuclear neutrophil (PMN) migration across epithelia is a common feature of active inflammation. Given the suggested role of carbohydrates in this process, we examined the receptor CD44. The standard CD44 isoform was expressed at the cell surface of PMN. PMN migration across model polarized intestinal epithelia was reduced (by 60%) if the CD44 receptor was activated by either a specific antibody (clone IM7) or the natural soluble ligand, hyaluronic acid. This inhibitory effect following receptor activation occurred with both basolateral-to-apical- and apical-to-basolateral-directed migration. The anti-CD44 antibody similarly reduced PMN migration through filters in the absence of epithelia, while preincubation of the antibody with the epithelium did not alter subsequent PMN transepithelial migration. These data suggest that PMN, rather than epithelial, CD44 is responsible for these effects. A similar inhibitory effect of anti-CD44 antibody was also observed on migration of intraepithelial lymphocytes. The molecular mechanism involved in such negative signaling following CD44 activation may include modulation of outside-in cell signaling. While neither the anti-CD44 antibody nor CD44 ligand affected PMN mobilization of intracellular Ca(2+), both led to increased adenylate cyclase activity, an inhibitory signal for PMN migration. Together, these results suggest that CD44 of PMN may potentially serve as a negative regulator of leukocyte migration across biological surfaces such as columnar epithelia.

Ectopic expression of Bcl-2 switches over nuclear signalling for cAMP-induced apoptosis to granulocytic differentiation

The IPC-81 myeloid leukaemia cells undergo apoptosis rapidly after cAMP stimulation (6 h) and cell death is prevented by early over-expression of the cAMP-inducible transcription repressor ICER, that blocks cAMP-dependent nuclear signalling. Therefore, the expression of specific genes controlled by CRE-containing promoters is likely to determine cell fate. We now show that cAMP-induced cell death also is abrogated by the over-expression of the anti-apoptotic gene, Bcl-2. Contrary to ICER, Bcl-2 does not affect cAMP-signalling and allows the analysis of cAMP responses in death rescued cells. The Bcl-2 transfected cells treated with 8-CPT-cAMP were growth-arrested and thereafter cells embarked in granulocytic differentiation, with no additional stimulation. Neutrophilic polynuclear granulocytes benefited from a long life span in G0-G1 and remained functional (phagocytosis). This work demonstrates that, using anti-apoptosis regulators, 'death signals' could be exploited to trigger distinct biological responses. Indeed, cAMP signal can trigger several simultaneously developing biological programs, in the same cell, i.e., growth regulation, apoptosis and differentiation. This cell system should prove useful to determine how a tumour cell can be re-programmed for either apoptosis or functional maturation by physiological signals.

Nitric oxide induces chemotaxis of neutrophil-like HL-60 cells and translocation of cofilin to plasma membranes

Nitric oxide (NO) plays various important roles in the physiological system. With regard to chemotaxis of neutrophils, there are reports that endogenous NO is a mediator of chemotaxis, and others that exogenous NO inhibits chemotaxis. It is also reported that NO itself expressed chemotactic activity. On the other hand, we have recently proposed the importance of cofilin, an actin-binding phosphoprotein, in phagocyte functions through dephosphorylation and translocation to the plasma membrane regions. Because chemotaxis is a phenomenon of dynamic cell movement, cofilin, a regulator of the cytoskeletal system, may be involved in its mechanisms. To clarify further the effect of NO on functions of leukocytes and to examine the effect of NO on cofilin, we investigated the chemotaxis of neutrophil-like HL-60 cells induced by NO, as well as the influence of NO on the phosphorylation and intracellular distribution of cofilin. Two NO donors, 3-[2-hydroxy-1-(1-methylethyl)-2-nitrosohydrazino]-1-propanamin e (NOC5) and S-nitroso-N-acetylpenicillamine (SNAP), were shown to cause chemotaxis, and, 2-(4-carboxyphenyl)-4,4,5, 5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO), a NO-specific scavenger, inhibited the chemotaxis induced by NO-donors, suggesting that NO itself released from the NO donors has chemotactic activity. LY-83583 and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), inhibitors of soluble guanylate cyclase, inhibited the chemotaxis to NO donors, which implies that soluble guanylate cyclase is involved in the signaling pathway of this NO action. We also found that NO caused translocation of cofilin to the cell periphery, though dephosphorylation of cofilin was not detected. These results demonstrate that NO has chemotactic activity for neutrophils and caused the translocation of cofilin to the plasma membrane regions without its dephosphorylation.

Inhibition of interleukin-8-activated human neutrophil chemotaxis by thapsigargin in a calcium- and cyclic AMP-dependent way

Chemotactic migration of human neutrophils, induced by interleukin-8 (IL-8) or other activators, was inhibited by thapsigargin in the high nanomolar range. The degree of inhibition depended on the type of activator. Other inhibitors of Ca(2+)-ATPases associated with intracellular calcium stores, such as cyclopiazonic acid and 2,5-di-(tert-butyl)-1,4-benzohydroquinone, equally inhibited IL-8-activated migration. Inhibition of migration by thapsigargin and the other ATPase inhibitors occurred only in the presence of extracellular Ca2+; migration was not inhibited in the presence of EGTA. La3+ reversed thapsigargin-induced inhibition to a large degree; other calcium channel blockers gave a partial reversal (econazole, verapamil, and SK&F 96365) or had no effect (gadolinium chloride and Ni2+). Using electroporated cells and Ca buffers, it was shown that inhibition started at about 0.2 microM and was complete at a cytosolic Ca concentration of about 2 microM. It appears that under certain conditions the thapsigargin-induced influx of extracellular calcium, causing relatively high local calcium concentrations, initiates or permits a process which may be detrimental to chemotactic migration. Cyclic AMP (cAMP; adenosine 3',5'-cyclic monophosphate) is probably involved in this process, because thapsigargin increased the cAMP level and cAMP inhibited IL-8-activated migration in a calcium-dependent way. The hypothesis that cAMP is involved in the effect of thapsigargin on migration is supported by the finding that very low concentrations of thapsigargin stimulate neutrophil migration in the absence of other chemoattractants. The results suggest that thapsigargin causes a (compartmentalized) increase in cAMP, which results in a calcium-dependent modulation of migration.

Sphingosine 1-phosphate stimulates tyrosine phosphorylation of focal adhesion kinase and chemotactic motility of endothelial cells via the G(i) protein-linked phospholipase C pathway

We have previously shown that sphingosine 1-phosphate (S1P) stimulates motility of human umbilical vein endothelial cells (HUVECs) (O.-H. Lee et al., Biochem. Biophys. Res. Commun. 264, 743-750, 1999). To investigate the molecular mechanisms by which S1P stimulates HUVEC motility, we examined tyrosine phosphorylation of p125 focal adhesion kinase (p125(FAK)) which is important for cell migration. S1P induces a rapid increase in tyrosine phosphorylation of p125(FAK). Compared with other structurally related lipid metabolites such as sphingosine, C2-ceramide, and lysophosphatidic acid, S1P uniquely stimulated p125(FAK) tyrosine phosphorylation and migration of HUVECs. The effect of S1P on p125(FAK) tyrosine phosphorylation was markedly reduced by treatment with pertussis toxin or U73122, a phospholipase C (PLC) inhibitor. As a downstream signal of PLC, p125(FAK) tyrosine phosphorylation in response to S1P was totally blocked by depletion of the intracellular calcium pool. However, protein kinase C (PKC) inhibitor had no effect on the response to S1P. Finally, chemotaxis assays revealed that inhibition of PLC but not PKC significantly abrogated S1P-stimulated HUVEC migration. These results suggest that the G(i)-coupled receptor-mediated PLC-Ca(2+) signaling pathway may be importantly involved in S1P-stimulated focal adhesion formation and migration of endothelial cells.

Inhibition of Ca2+ influx by pentoxifylline in NR8383 alveolar macrophages

Pentoxifylline (PTF), a phosphodiesterase (PDE) inhibitor, can prevent inflammation and tissue damage in animal and in vitro human studies. However, the underlying mechanism remains unclear. Since Ca2+ is a critical signal regulating the release of inflammatory mediators in macrophages, the effects of PTF on Ca2+ influx were examined in NR8383 alveolar macrophages (AMs). PTF induced a dose-dependent inhibition on Ca2+ influx activated by zymosan and by protein kinase C (PKC) activators 1,2-dioctanoyl-sn-glycerol (DOG) or phorbol-12-myristate 13-acetate (PMA). The inhibition appeared to be specifically on the receptor-operated Ca2+ entry. The capacitative Ca2+ entry was not affected by PTF. The inhibition was not due to altered cAMP levels since the zymosan-activated Ca2+ influx was not affected by the adenylate cyclase activator forskolin, nor by dibutyryl cAMP. Pretreatment with protein tyrosine kinase (PTK) inhibitor genistein abolished zymosan-induced, but not DOG-induced Ca2+ influx, suggesting that PTK is an upstream element of the signaling cascade and not the target of PTF. The Ca2+ entry activated by zymosan and by PKC activators was inhibited by the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Moreover, activation of MAPK by C6-ceramide (C6C) triggered a similar Ca2+ influx as elicited by zymosan and PKC activators, suggesting that MAPK is an element of the pathway. The C6C-induced Ca2+ influx was also inhibited by PTF. These results indicate that PTF blocks the receptor-operated Ca2+ influx in NR8383 AMs by inhibiting PDE which may acts as a downstream element of the signaling pathway or by direct interaction with Ca2+ channels.

Nitric oxide and C-type atrial natriuretic peptide stimulate primary aortic smooth muscle cell migration via a cGMP-dependent mechanism: relationship to microfilament dissociation and altered cell morphology

Migration of aortic smooth muscle cells is thought to be of essential importance in vascular restenosis, remodeling, and angiogenesis. Recent studies have shown that NO donors inhibit the migration of subcultured aortic smooth muscle cells. However, there is evidence that NO elicits opposite effects on cell proliferation in primary versus subcultured cells, indicating fundamental differences among different models of aortic smooth muscle cell cultures. The purpose of the current study was to investigate the effect of NO donors on migration of primary cultures of rat aortic smooth muscle cells and to compare and contrast their response with those in subcultured cells. A second purpose was to investigate some of the underlying mechanisms associated with NO-induced effects on cell migration. We report that 2 NO donors, S-nitroso-N-acetylpenicillamine (SNAP) and 2, 2-(hydroxynitrosohydrazino)bis-ethanamine, stimulated the migration of primary cells in a wounded-culture model as well as in a transwell migration model. The effect of NO donors was mimicked by 2 cGMP analogues and C-type natriuretic peptide and blocked by a specific inhibitor of guanyl cyclase, 1H-(1,2,4)oxadiazolo[4,3, -a]quinoxalin-1-one, indicating the involvement of cGMP as second messenger. Moreover, neither NO donors nor cGMP analogues altered migration of primary cultures stimulated by either FBS or angiotensin II. In contrast to its effect in primary cultures, SNAP did not alter basal or stimulated migration of subcultured cells, except at a relatively high concentration of 1 mmol/L, at which migration was inhibited. The migration-stimulatory effect of NO donors and cGMP was associated with altered cell morphology and dissociation of actin filaments, consistent with recent studies indicating that cell morphology and cytoskeletal organization influence cell migration. The results suggest the possible involvement of NO-induced cell migration in vascular injury or remodeling, representing conditions in which vascular NO levels would be expected to be elevated.