Integrin-dependent homotypic adhesion of neutrophils. Arachidonic acid activates Raf-1/Mek/Erk via a 5-lipoxygenase- dependent pathway

CCR2 mediates the adverse effects of LPS in the pregnant mouse

In our earlier work, we found that intrauterine (i.u.) and intraperitoneal (i.p.) injection of LPS (10-μg serotype 0111:B4) induced preterm labor (PTL) with high pup mortality, marked systemic inflammatory response and hypotension. Here, we used both i.u. and i.p. LPS models in pregnant wild-type (wt) and CCR2 knockout (CCR2-/-) mice on E16 to investigate the role played by the CCL2/CCR2 system in the response to LPS. Basally, lower numbers of monocytes and macrophages and higher numbers of neutrophils were found in the myometrium, placenta, and blood of CCR2-/- vs. wt mice. After i.u. LPS, parturition occurred at 14 h in both groups of mice. At 7 h post-injection, 70% of wt pups were dead vs. 10% of CCR2-/- pups, but at delivery 100% of wt and 90% of CCR2-/- pups were dead. Myometrial and placental monocytes and macrophages were generally lower in CCR2-/- mice, but this was less consistent in the circulation, lung, and liver. At 7 h post-LPS, myometrial ERK activation was greater and JNK and p65 lower and the mRNA levels of chemokines were higher and of inflammatory cytokines lower in CCR2-/- vs. wt mice. Pup brain and placental inflammation were similar. Using the IP LPS model, we found that all measures of arterial pressure increased in CCR2-/- but declined in wt mice. These data suggest that the CCL2/CCR2 system plays a critical role in the cardiovascular response to LPS and contributes to pup death but does not influence the onset of inflammation-induced PTL.

Phosphoproteomics identify arachidonic-acid-regulated signal transduction pathways modulating macrophage functions with implications for ovarian cancer

Arachidonic acid (AA) is a polyunsaturated fatty acid present at high concentrations in the ovarian cancer (OC) microenvironment and associated with a poor clinical outcome. In the present study, we have unraveled a potential link between AA and macrophage functions.

Methods: AA-triggered signal transduction was studied in primary monocyte-derived macrophages (MDMs) by phosphoproteomics, transcriptional profiling, measurement of intracellular Ca²⁺ accumulation and reactive oxygen species production in conjunction with bioinformatic analyses. Functional effects were investigated by actin filament staining, quantification of macropinocytosis and analysis of extracellular vesicle release.

Results: We identified the ASK1 - p38δ/α (MAPK13/14) axis as a central constituent of signal transduction pathways triggered by non-metabolized AA. This pathway was induced by the Ca²⁺-triggered activation of calmodulin kinase II, and to a minor extent by ROS generation in a subset of donors. Activated p38 in turn was linked to a transcriptional stress response associated with a poor relapse-free survival. Consistent with the phosphorylation of the p38 substrate HSP27 and the (de)phosphorylation of multiple regulators of Rho family GTPases, AA impaired actin filament organization and inhibited actin-driven macropinocytosis. AA also affected the phosphorylation of proteins regulating vesicle biogenesis, and consistently, AA enhanced the release of tetraspanin-containing exosome-like vesicles. Finally, we identified phospholipase A₂ group 2A (PLA2G2A) as the clinically most relevant enzyme producing extracellular AA, providing further potentially theranostic options.

Conclusion: Our results suggest that AA contributes to an unfavorable clinical outcome of OC by impacting the phenotype of tumor-associated macrophages. Besides critical AA-regulated signal transduction proteins identified in the present study, PLA2G2A might represent a potential prognostic tool and therapeutic target to interfere with OC progression.

Emerging Roles of 5-Lipoxygenase Phosphorylation in Inflammation and Cell Death

5-Lipoxygenase (ALOX5) is an iron-containing and nonheme dioxygenase that catalyzes the peroxidation of polyunsaturated fatty acids such as arachidonic acid. ALOX5 is the rate-limiting enzyme for the biosynthesis of leukotrienes, a family of proinflammatory lipid mediators derived from arachidonic acid. ALOX5 also make great contributions to mediating lipid peroxidation. In recent years, it has been discovered that ALOX5 plays a central role in cell death including apoptosis, pyroptosis, and ferroptosis, a newly discovered type of cell death. According to the previous studies, ALOX5 can regulate cell death in two ways: one is inflammation and the other is lipid peroxidation. Meanwhile, it has been shown that ALOX5 activity is regulated by several factors including protein phosphorylation, ALOX5-interactng protein, redox state, and metal ions such as iron and calcium. In this review, we aim to summarize the knowledge on the emerging roles of ALOX5 protein phosphorylation in the regulation of cell death and inflammation in order to explore a potential target for human diseases.

Neutrophil swarming: an essential process of the neutrophil tissue response

Neutrophil infiltration into inflamed and infected tissues is a fundamental process of the innate immune response. While neutrophil interactions with the blood vessel wall have been intensely studied over the last decades, neutrophil dynamics beyond the vasculature have for a long time remained poorly investigated. Recent intravital microscopy studies of neutrophil populations directly at the site of tissue damage or microbial invasion have changed our perspective on neutrophil responses within tissues. Swarm-like migration patterns of neutrophils, referred to as 'neutrophil swarming', have been detected in diverse tissues under conditions of sterile inflammation and infection with various pathogens, including bacteria, fungi, and parasites. Current work has begun to unravel the molecular pathways choreographing the sequential phases of highly coordinated chemotaxis followed by neutrophil accumulation and the formation of substantial neutrophil clusters. It is now clear that intercellular communication among neutrophils amplifies their recruitment in a feed-forward manner, which provides them with a level of self-organization during neutrophil swarming. This review will summarize recent developments and current concepts on neutrophil swarming, an important process of the neutrophil tissue response with a critical role in maintaining the balance between host protection and inflammation-driven tissue destruction.

Chemoattractant concentration-dependent tuning of ERK signaling dynamics in migrating neutrophils

The directed migration (chemotaxis) of neutrophils toward the bacterial peptide N-formyl-Met-Leu-Phe (fMLP) is a crucial process in immune defense against invading bacteria. While navigating through a gradient of increasing concentrations of fMLP, neutrophils and neutrophil-like HL-60 cells switch from exhibiting directional migration at low fMLP concentrations to exhibiting circuitous migration at high fMLP concentrations. The extracellular signal-regulated kinase (ERK) pathway is implicated in balancing this fMLP concentration-dependent switch in migration modes. We investigated the role and regulation of ERK signaling through single-cell analysis of neutrophil migration in response to different fMLP concentrations over time. We found that ERK exhibited gradated, rather than all-or-none, responses to fMLP concentration. Maximal ERK activation occurred in response to about 100 nM fMLP, and ERK inactivation was promoted by p38. Furthermore, we found that directional migration of neutrophils reached a maximal extent at about 100 nM fMLP and that ERK, but not p38, was required for neutrophil migration. Thus, our data suggest that, in chemotactic neutrophils responding to fMLP, ERK displays gradated activation and p38-dependent inhibition and that these ERK dynamics promote neutrophil migration.

MEK1/2 inhibitors reverse acute vascular occlusion in mouse models of sickle cell disease

In sickle cell disease (SCD), treatment of recurrent vasoocclusive episodes, leading to pain crises and organ damage, is still a therapeutic challenge. Vasoocclusion is caused primarily by adherence of homozygous for hemoglobin S (SS) red blood cells (SSRBCs) and leukocytes to the endothelium. We tested the therapeutic benefits of MEK1/2 inhibitors in reversing vasoocclusion in nude and humanized SCD mouse models of acute vasoocclusive episodes using intravital microscopy. Administration of 0.2, 0.3, 1, or 2 mg/kg MEK1/2 inhibitor to TNF-α-pretreated nude mice before human SSRBC infusion inhibited SSRBC adhesion in inflamed vessels, prevented the progression of vasoocclusion, and reduced SSRBC organ sequestration. By use of a more clinically relevant protocol, 0.3 or 1 mg/kg MEK1/2 inhibitor given to TNF-α-pretreated nude mice after human SSRBC infusion and onset of vasoocclusion reversed SSRBC adhesion and vasoocclusion and restored blood flow. In SCD mice, 0.025, 0.05, or 0.1 mg/kg MEK1/2 inhibitor also reversed leukocyte and erythrocyte adhesion after the inflammatory trigger of vasoocclusion and improved microcirculatory blood flow. Cell adhesion was reversed by shedding of endothelial E-selectin, P-selectin, and αvβ3 integrin, and leukocyte CD44 and β2 integrin. Thus, MEK1/2 inhibitors, by targeting the adhesive function of SSRBCs and leukocytes, could represent a valuable therapeutic intervention for acute sickle cell vasoocclusive crises.

In the eye of the neutrophil swarm-navigation signals that bring neutrophils together in inflamed and infected tissues

Neutrophils are sentinel cells that express in higher vertebrates >30 chemokine and chemoattractant receptors to sense and quickly react to tissue damage signals. Intravital microscopy studies in mouse models of wounding, inflammation, and infection have revealed that neutrophils form cell swarms at local sites of tissue injury and cell death. This swarming response is choreographed by chemokines, lipids, and other chemoattractants, controlling sequential phases of highly coordinated chemotaxis, intercellular signal relay, and cluster formation among neutrophils. This review will give a brief overview about the basic principles and key molecules that have led to the refined multistep model of how neutrophils come together to isolate sites of tissue injury and microbial invasion from healthy tissue. Whereas auto- and paracrine signaling among neutrophils during later phases of swarming can provide a level of self-organization for robust navigation in diverse inflammatory settings, guidance factors from primary tissue lesions, resident bystander cells, and dying cells regulate the initial phases of the swarming response. This review will discuss how the specific environmental context and mixture of attractants at the locally inflamed site can lead to variants of the multistep attraction model and influence the extent of neutrophil swarming, ranging from accumulations of only few individual cells to the aggregation of several hundreds of neutrophils, as found in abscesses. Given the critical roles of neutrophils in both host protection and tissue destruction, novel insights on neutrophil swarming might provide useful for the therapeutic modulation of neutrophil-dependent inflammatory processes.

Choline Transporter-Like Protein-2: New von Willebrand Factor-Binding Partner Involved in Antibody-Mediated Neutrophil Activation and Transfusion-Related Acute Lung Injury

OBJECTIVE

In contrast to other antibodies involved in transfusion-related acute lung injury, anti-HNA-3a antibodies are incapable of inducing direct neutrophil activation and seem to interact with endothelial cells (ECs) primarily. In animal studies, anti-HNA-3a-mediated transfusion-related acute lung injury could be precipitated in the absence of neutrophils, but was stronger when neutrophils were present. In a different context the target protein of these antibodies, choline transporter-like protein-2 (CTL-2), was reported to interact with a protein of the inner ear carrying 2 von Willebrand factor (VWF) A-domains. These observations prompted us to investigate whether VWF might be involved in anti-HNA-3a-mediated neutrophil activation, and whether signaling via CD11b/CD18 is involved, as in various other experimental settings.

APPROACH AND RESULTS

Cell adhesion demonstrated specific binding of CTL-2 to VWF. Immunoprecipitation analysis of CTL-2/CD11b/CD18 coexpressing cells indicated that anti-HNA-3a colocalizes CTL-2 and CD11b/CD18 when VWF is present. Functional studies revealed that anti-HNA-3a-mediated neutrophil agglutination is an active, protein kinase C-dependent and partially Fc-dependent process. Agglutination and the production of reactive oxygen species seem to require the formation of a trimolecular complex between the target antigen (CTL-2), CD11b/CD18 and VWF. In line with these observations, anti-HNA-3a induced less severe transfusion-related acute lung injury and less neutrophil recruitment to the alveolar space in VWF knockout mice.

CONCLUSIONS

We introduce CTL-2 as a new binding partner for VWF. Interaction of neutrophils with VWF via CTL-2 allows anti-HNA-3a to induce signal transduction via CD11b/CD18, which leads to neutrophil activation and agglutination. In transfusion-related acute lung injury, this mechanism may further aggravate endothelial leakage.

In vivo imaging reveals PKA regulation of ERK activity during neutrophil recruitment to inflamed intestines

In vivo FRET demonstrates that ERK positively regulates the neutrophil recruitment cascade in the intestine by promoting adhesion and migration.

Many chemical mediators regulate neutrophil recruitment to inflammatory sites. Although the actions of each chemical mediator have been demonstrated with neutrophils in vitro, how such chemical mediators act cooperatively or counteractively in vivo remains largely unknown. Here, by in vivo two-photon excitation microscopy with transgenic mice expressing biosensors based on Förster resonance energy transfer, we time-lapse–imaged the activities of extracellular signal–regulated kinase (ERK) and protein kinase A (PKA) in neutrophils in inflamed intestinal tissue. ERK activity in neutrophils rapidly increased during spreading on the endothelial cells and showed positive correlation with the migration velocity on endothelial cells or in interstitial tissue. Meanwhile, in the neutrophils migrating in the interstitial tissue, high PKA activity correlated negatively with migration velocity. In contradiction to previous in vitro studies that showed ERK activation by prostaglandin E₂ (PGE₂) engagement with prostaglandin receptor EP4, intravenous administration of EP4 agonist activated PKA, inhibited ERK, and suppressed migration of neutrophils. The opposite results were obtained using nonsteroidal antiinflammatory drugs (NSAIDs). Therefore, NSAID-induced enteritis may be caused at least partially by the inhibition of EP4 receptor signaling of neutrophils. Our results demonstrate that ERK positively regulates the neutrophil recruitment cascade by promoting adhesion and migration steps.

BNC Protects H9c2 Cardiomyoblasts from H 2 O 2 -Induced Oxidative Injury through ERK1/2 Signaling Pathway

Buchang naoxintong capsule (BNC) is a traditional Chinese medicine approved for the treatment of cerebrovascular and cardiovascular diseases. However, little is known about the specific protective function or mechanism by which BNC protects against myocardial injury. This research was designed to investigate the cardioprotective effects of BNC in vitro model of hydrogen peroxide (H₂O₂)-induced H9c2 rat cardiomyoblasts. BNC intestinal absorption liquid was used in this study instead of drug-containing serum or extracting solution. Our study revealed that BNC preconditioning enhanced antioxidant function by increasing the activities of total-antioxygen capacity, total-superoxide dismutase, and catalase and by decreasing the production of reactive oxygen species and malondialdehyde. BNC preconditioning also activated extracellular signal-regulated kinases (ERK1/2) and inhibited apoptosis-related proteins such as poly ADP-ribose polymerase (PARP) and caspase-3. Additionally, preincubation with BNC reduced intracellular Ca²⁺ concentration, improved mitochondrial membrane potential, and decreased the apoptosis rate of H9c2 cells in a dose-dependent manner. These data demonstrated that BNC protects H9c2 cardiomyoblasts from H₂O₂-induced oxidative injury by increasing antioxidant abilities, activating ERK1/2, and blocking Ca²⁺-dependent and mitochondria-mediated apoptosis. Based on our results, the potency of BNC for protecting H9c2 cells from oxidative damage is comparable to that of trimetazidine.

Celecoxib enhances the anti-inflammatory effects of farnesylthiosalicylic acid on T cells independent of prostaglandin E(2) production

Celecoxib (Celebrex(®)), a non-steroidal anti-inflammatory drug and selective cyclooxygenase-2 inhibitor, is widely used to treat arthritis and other inflammatory disorders. Awareness of its anti-proliferative properties has prompted another indication for its use, in preventing colon polyps in high-risk populations. Farnesylthiosalicylic acid (FTS; Salirasib(®)), designed to inhibit oncogenic Ras and currently under evaluation in phase I/II and II clinical trials, was recently shown by our group to exert anti-inflammatory effects on both lymphocytes and mast cells. Here we examined whether celecoxib combined with FTS would enhance this anti-inflammatory activity. While each drug separately inhibited Ras activation in these cells, their combination yielded more marked inhibition as well as further inhibition of ERK phosphorylation, lymphocyte adhesion, and interleukin-2 secretion. The inhibitory effects, moreover, were independent of prostaglandin E(2) secretion. These data point to the promising potential of combined treatment with celecoxib and FTS for inflammatory disorders involving lymphocytes.

Arachidonate 5 lipoxygenase expression in papillary thyroid carcinoma promotes invasion via MMP-9 induction

Arachidonate 5-lipoxygenase (ALOX5) expression and activity has been implicated in tumor pathogenesis, yet its role in papillary thyroid carcinoma (PTC) has not been characterized. ALOX5 protein and mRNA were upregulated in PTC compared to matched, normal thyroid tissue, and ALOX5 expression correlated with invasive tumor histopathology. Evidence suggests that PTC invasion is mediated through the induction of matrix metalloproteinases (MMPs) that can degrade and remodel the extracellular matrix (ECM). A correlation between MMP-9 and ALOX5 protein expression was established by immunohistochemical analysis of PTC and normal thyroid tissues using a tissue array. Transfection of ALOX5 into a PTC cell line (BCPAP) increased MMP-9 secretion and cell invasion across an ECM barrier. The ALOX5 product, 5(S)-hydroxyeicosatetraenoic acid also increased MMP-9 protein expression by BCPAP in a dose-dependent manner. Inhibitors of MMP-9 and ALOX5 reversed ALOX5-enhanced invasion. Here we describe a new role for ALOX5 as a mediator of invasion via MMP-9 induction; this ALOX5/MMP9 pathway represents a new avenue in the search for functional biomarkers and/or potential therapeutic targets for aggressive PTC.

Pleiotropic vasoprotective effects of statins: the chicken or the egg?

Statins (3-hydroxy-3-methyl glutaryl coenzyme A [HMG-CoA] reductase inhibitors) are the most commonly used lipid-lowering drugs. Their main lipid-lowering effect is achieved by an increase in the expression of low-density lipoprotein cholesterol receptors associated with inhibition of cholesterol synthesis through inhibition of HMG-CoA reductase - the first and rate-limiting step in cholesterol synthesis. However, beyond cholesterol synthesis inhibition, inhibition of the HMG-CoA reductase affects as well the synthesis of other molecules with significant roles in different, yet often intercalating, metabolic pathways. On this basis, and supported by an increasing series of advocating epidemiological and experimental data, an extended dialogue has been established over the last few years regarding the nonlipid or "pleiotropic" actions of statins.

Arachidonic Acid metabolites in the cardiovascular system: the role of lipoxygenase isoforms in atherogenesis with particular emphasis on vascular remodeling

Vascular remodeling refers to lasting structural alterations in the vessel wall that are initiated in response to external and internal stimuli. These changes are distinct from acute functional responses of blood vessels when challenged by increased blood pressure, altered hemodynamics, or vasoactive mediators. In early atherogenesis, when lesion formation is starting to impact local hemodynamics, the vessel wall responds with outward vascular remodeling to maintain normal blood flow. However, inward remodeling may also occur during the time course of plaque formation, contributing to vascular stenosis. Lipoxygenases form a heterogeneous family of lipid-peroxidizing enzymes, which have been implicated in atherogenesis. Several lines of in vitro and in vivo evidence indicated their involvement in disease development, but the precise function of different lipoxygenase isoforms is still a matter of discussion. Vascular remodeling is an early response during plaque development; therefore, lipoxygenases may be involved in this process. Unfortunately, little is known about the potential role of lipoxygenase isoforms in vascular remodeling. This review will briefly summarize our knowledge of the role of lipoxygenases in vascular biology and will critically review the activities of the 3 most athero-relevant lipoxygenase isoforms in atherogenesis, with particular emphasis on vascular remodeling.

Protein kinase C-alpha and -delta are required for NADPH oxidase activation in WKYMVm-stimulated IMR90 human fibroblasts

The regulation of the activation of non phagocytic NADPH oxidase is poorly understood. Previously we demonstrated that in fibroblasts the exposure to WKYMVm induced p47(phox) phosphorylation and translocation and that these effects were mediated by ERKs activation. Protein kinase C (PKC) is reported to be involved in regulating the phosphorylation of NADPH oxidase components in polymorphonucleate cells stimulated via FPRL1 receptor, but its involvement in fibroblasts was not demonstrated. Therefore, we investigated in IMR90 cells exposed to WKYMVm the role of PKC isoenzymes in the activation of NADPH oxidase-like enzyme. Preincubation with general pharmacological inhibitors of PKC, before stimulation with WKYMVm, prevented the ERKs activation, p47(phox) phosphorylation and translocation. The analysis of cellular partitioning of PKC isoenzymes demonstrated that PKCalpha and PKCdelta translocated from the cytosolic to the membrane fraction upon stimulation with WKYMVm. Preincubation with Gö6976 or with rottlerin prevented the phosphorylation and translocation of NADPH oxidase regulatory subunit.

Samul extract protects against the H2O2-induced apoptosis of H9c2 cardiomyoblasts via activation of extracellular regulated kinases (Erk) 1/2

Samul extract, containing Radix Rehmanniae, Radix Angelicae Gigantis, Radix Paeoniae, and Rhizoma Cnidii, has been traditionally used for treatment of ischemic heart and brain damages in Oriental medicine. However, little is known about the mechanism by which Samul rescues cells from cytotoxic damage. This study was designed to investigate the protective mechanisms of Samul on H(2)O(2)-induced death of H9c2 cells. Treatment with H(2)O(2) markedly decreased the viability of H9c2 cells in a dose- and time-dependent manner, which was significantly prevented by pre-treatment with Samul. The nature of death of H9c2 cells by H(2)O(2) was demonstrated by apoptotic features, including ladder-pattern fragmentation of genomic DNA and chromatin condensation, which were markedly abolished by pretreatment of Samul in H(2)O(2)-treated cells. We further demonstrated that MEK inhibitor, PD98059, dose-dependently attenuated the protective effects of Samul against H(2)O(2), whereas inhibitors of Jnk and p38 did not. Consistently, Samul induced the early phosphorylation of Erk, p44, in H(2)O(2)-treated cells. In addition, treatment with Samul also resulted in an increase of expression of anti-apotogenic Bcl2 protein, which was decreased by H(2)O(2). However, it inhibited the expression of apotogenic Bax protein in H(2)O(2)-treated cells. Taken together, these results suggest that the protective effects of Samul against oxidative damage may be achieved via activation of MAP kinase, Erk as well as Bcl2 family proteins.

Identification of novel oligodendroglioma-associated candidate tumor suppressor genes in 1p36 and 19q13 using microarray-based expression profiling

Loss of heterozygosity (LOH) on chromosomal arms 1p and 19q is the most common genetic alteration in oligodendroglial tumors and associated with response to radio- and chemotherapy as well as favorable prognosis. Using microsatellite analysis, we previously identified the chromosomal regions 1p36.22-p36.31 and 19q13.3, as candidate tumor suppressor gene regions being commonly deleted in these tumors. To identify genes within these regions that are downregulated in oligodendroglial tumors with LOH 1p/19q, we performed cDNA microarray-based RNA expression profiling of 35 gliomas with known allelic status on 1p and 19q, including 7 oligodendrogliomas and 8 diffuse astrocytomas of World Health Organization (WHO) grade II, as well as 14 anaplastic oligodendrogliomas and 6 anaplastic oligoastrocytomas of WHO grade III. The microarrays used for expression profiling carried approximately 7,000 gene-specific cDNAs, with complete coverage of the genes located in 1p36.13-p36.31 and 19q13.2-q13.33. Microarray analysis identified 8 genes from these regions (MGC4399, SRM, ICMT, RPL18, FTL, ZIN, FLJ10781 and DBP), which all showed significantly lower expression in 1p/19q-deleted gliomas when compared to gliomas without 1p/19q losses. Quantitative real-time reverse transcription-PCR analyses were performed for the MGC4399, ICMT and RPL18 genes and confirmed the microarray findings. In addition, we found that the cytosolic phospholipase A2 (PLA2G4C) gene at 19q13.3 demonstrated significantly lower expression in anaplastic oligodendrogliomas (WHO grade III) when compared to well-differentiated oligodendrogliomas (WHO grade II). Taken together, our study provides a set of interesting novel candidate genes that may play important roles in the pathogenesis of oligodendroglial tumors.

Structural organization of the neutrophil NADPH oxidase: phosphorylation and translocation during priming and activation

The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is part of the microbicidal arsenal used by human polymorphonuclear neutrophils (PMNs) to eradicate invading pathogens. The production of a superoxide anion (O2-) into the phagolysosome is the precursor for the generation of more potent products, such as hydrogen peroxide and hypochlorite. However, this production of O2- is dependent on translocation of the oxidase subunits, including gp91phox, p22phox, p47phox, p67phox, p40phox, and Rac2 from the cytosol or specific granules to the plasma membrane. In response to an external stimuli, PMNs change from a resting, nonadhesive state to a primed, adherent phenotype, which allows for margination from the vasculature into the tissue and chemotaxis to the site of infection upon activation. Depending on the stimuli, primed PMNs display altered structural organization of the NADPH oxidase, in that there is phosphorylation of the oxidase subunits and/or translocation from the cytosol to the plasma or granular membrane, but there is not the complete assembly required for O2- generation. Activation of PMNs is the complete assembly of the membrane-linked and cytosolic NADPH oxidase components on a PMN membrane, the plasma or granular membrane. This review will discuss the individual components associated with the NADPH oxidase complex and the function of each of these units in each physiologic stage of the PMN: rested, primed, and activated.

AMPA receptor phosphorylation is selectively regulated by constitutive phospholipase A(2) and 5-lipoxygenase activities

The present investigation provides the first indication that constitutive, calcium-independent phospholipase A2 activity (iPLA2) modulates phosphorylation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) subtype of glutamate receptors. Preincubation of frozen-thawed brain sections with two iPLA2 inhibitors, bromoenol lactone (BEL) or palmitoyl trifluoromethyl ketone (PACO), produced a dose-dependent enhancement in phosphorylation at both Ser831 and Ser845 sites on the GluR1 subunit of AMPA receptors. This effect was not associated with changes in phosphorylation at the Ser sites of either the GluR2/3 subunits of AMPA receptors or the NR1 subunits of N-methyl-D-aspartate (NMDA) receptors, nor was it reproduced by inhibition of the calcium-dependent form of PLA2 activity. These results suggest that the effects of these inhibitors are selective to GluR1 subunits and that they are dependent on iPLA2 activity. The ability of iPLA2 inhibitors to increase GluR1 phosphorylation was mimicked by the 5-lipoxygenase (5-LO) inhibitor MK-886, but not by blockers of 12-lipoxygenase (12-LO) or cyclooxygenase. Additional experiments indicated that calcium-mediated truncation of GluR1 subunits was reduced by iPLA2 inhibitors, an effect that was not correlated with overall changes in the distribution of AMPA receptors between intracellular and membrane compartments prepared from whole brain sections. However, quantitative autoradiographic analysis indicated enhanced 3H-AMPA binding to the CA1 stratum radiatum of the hippocampus in BEL-treated sections. Saturation kinetics experiments demonstrated that this binding augmentation was due to an increase in the maximal number of AMPA binding sites. Altogether, our results point to the conclusion that basal iPLA2 activity, through the generation of 5-LO metabolites, regulates AMPA receptor phosphorylation of GluR1 subunits, an effect that might selectively influence the number of membrane receptors in area CA1 of the hippocampus.

Leukotriene B4mediates p47phox phosphorylation and membrane translocation in polyunsaturated fatty acid-stimulated neutrophils

Polyunsaturated fatty acids (PUFAs) and leukotriene B(4) (LTB(4)) are involved in many inflammatory and physiological conditions. The role of arachidonic acid (AA) and linoleic acid (LA) in promoting the assembly of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits is well known, but the involvement of LTB(4) and other 5-lipoxygenase (5-LO) pathway metabolites of AA in hydrogen peroxide (H(2)O(2)) production by PUFA-stimulated polymorphonuclear leukocytes (PMNs) has not been investigated. We examined this question by determining H(2)O(2) production as well as phosphorylation and membrane translocation of the p47phox subunit of NADPH oxidase. Elicited peritoneal PMNs from rats and from 5-LO-deficient or wild-type mice were pretreated with or without inhibitors of LT biosynthesis and antagonists of the receptors for LTB(4) and cysteinyl LTs for 20 min before stimulation with AA (at 5 and 20 microM) or LA (at 20 microM). PUFAs elicited H(2)O(2) production in a dose-dependent manner, and pharmacologic or genetic inhibition of LT synthesis decreased H(2)O(2) production by approximately 40% when compared with untreated controls. LTB(4) was the moiety responsible for H(2)O(2) production, as revealed by studies using receptor antagonists and its exogenous addition. LTB(4) itself also promoted p47phox phosphorylation and translocation. These results identify a heretofore unrecognized role for activation of 5-LO and subsequent production of LTB(4) in stimulation of PMN NADPH oxidase activation by PUFAs.

Activation of extracellular signal-regulated kinase couples platelet-activating factor-induced adhesion and delayed apoptosis of human neutrophils

Platelet-activating factor (PAF) promotes adhesion of neutrophil granulocytes to the endothelium, which is also linked to neutrophil survival. Here we report that PAF can prolong neutrophil survival by suppressing spontaneous apoptosis. PAF induced concurrent activation of the Ras/Raf-1/mitogen-activated protein kinase kinase (MAPKK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt pathways. ERK activation tightly correlated with up-regulation of CD11b/CD18 expression and beta(2)-integrin-dependent homotypic adhesion. These actions of PAF were markedly attenuated by the MAPKK/ERK inhibitor PD98059, but not by the phosphatidylinositol 3-kinase inhibitor wortmannin. By contrast, concurrent activation of ERK and Akt was required to inhibit caspase-3 activation and consequently to delay apoptosis. Consistently, pharmacological inhibition of either ERK or Akt partially reversed the anti-apoptotic action of PAF; however, they did not produce additive inhibition. These results indicate that PAF-induced activation of ERK contributes to both the expression of the pro-adhesive phenotype and repression of neutrophil apoptosis, thereby amplifying the inflammatory response.

Tocotrienol: The Natural Vitamin E to Defend the Nervous System?

Vitamin E is essential for normal neurological function. It is the major lipid-soluble, chain-breaking antioxidant in the body, protecting the integrity of membranes by inhibiting lipid peroxidation. Mostly on the basis of symptoms of primary vitamin E deficiency, it has been demonstrated that vitamin E has a central role in maintaining neurological structure and function. Orally supplemented vitamin E reaches the cerebrospinal fluid and brain. Vitamin E is a generic term for all tocopherols and their derivatives having the biological activity of RRR-alpha-tocopherol, the naturally occurring stereoisomer compounds with vitamin E activity. In nature, eight substances have been found to have vitamin E activity: alpha-, beta-, gamma- and delta-tocopherol; and alpha-, beta-, gamma- and delta-tocotrienol. Often, the term vitamin E is synonymously used with alpha-tocopherol. Tocotrienols, formerly known as zeta, , or eta-tocopherols, are similar to tocopherols except that they have an isoprenoid tail with three unsaturation points instead of a saturated phytyl tail. Although tocopherols are predominantly found in corn, soybean, and olive oils, tocotrienols are particularly rich in palm, rice bran, and barley oils. Tocotrienols possess powerful antioxidant, anticancer, and cholesterol-lowering properties. Recently, we have observed that alpha-tocotrienol is multi-fold more potent than alpha-tocopherol in protecting HT4 and primary neuronal cells against toxicity induced by glutamate as well as by a number of other toxins. At nanomolar concentration, tocotrienol, but not tocopherol, completely protected neurons by an antioxidant-independent mechanism. Our current work identifies two major targets of tocotrienol in the neuron: c-Src kinase and 12-lipoxygenase. Dietary supplementation studies have established that tocotrienol, fed orally, does reach the brain. The current findings point towards tocotrienol as a potent neuroprotective form of natural vitamin E.

CpG motifs in bacterial DNA delay apoptosis of neutrophil granulocytes

Human neutrophil granulocytes die rapidly, and their survival is contingent upon rescue from programmed cell death by signals from the environment. We now show that a novel signal for delaying neutrophil apoptosis is unmethylated CpG motifs prevalent in bacterial DNA (CpG- DNA). Human neutrophils express toll-like receptor 9 that recognizes these motifs. CpG-DNA, but not mammalian DNA or methylated bacterial DNA, markedly enhanced neutrophil viability by delaying spontaneous apoptosis. Endosomal maturation of CpG-DNA is prerequisite for these actions and was coupled to concurrent activation of the extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt signaling pathways, leading to phosphorylation of BAD at Ser112 and Ser136, respectively, and to prevention of decreases in mitochondrial transmembrane potential, cytochrome c release and caspase-3 activation. Consistently, pharmacological inhibition of either ERK or phosphatidylinositol 3-kinase partially reversed these actions of CpG-DNA; however, they did not produce additive inhibition. Furthermore, intravenous injection of CpG-DNA (200 microg/kg) into rats evoked slight decreases in blood pressure and induced a modest leukocytosis, whereas it effectively suppressed neutrophil apoptosis as assayed ex vivo. Our results indicate that unmethylated CpG motifs in bacterial DNA promote neutrophil survival by suppressing the apoptotic machinery and may therefore contribute to prolongation and amplification of inflammation.

Cyclooxygenase-2-derived E prostaglandins down-regulate matrix metalloproteinase-1 expression in fibroblast-like synoviocytes via inhibition of extracellular signal-regulated kinase activation

We examined the regulation of matrix metalloproteinase (MMP) production by mitogen-activated protein kinases and cyclooxygenases (COXs) in fibroblast-like synoviocytes (FLSCs). IL-1beta and TNF-alpha stimulated FLSC extracellular signal-regulated kinase (ERK) activation as well as MMP-1 and -13 release. Pharmacologic inhibitors of ERK inhibited MMP-1, but not MMP-13 expression. Whereas millimolar salicylates inhibited both ERK and MMP-1, nonsalicylate COX and selective COX-2 inhibitors enhanced stimulated MMP-1 release. Addition of exogenous PGE(1) or PGE(2) inhibited MMP-1, reversed the effects of COX inhibitors, and inhibited ERK activation, suggesting that COX-2 activity tonically inhibits MMP-1 production via ERK inhibition by E PGs. Exposure of FLSCs to nonselective COX and selective COX-2 inhibitors in the absence of stimulation resulted in up-regulation of MMP-1 expression in an ERK-dependent manner. Moreover, COX inhibition sufficient to reduce PGE levels increased ERK activity. Our data indicate that: 1) ERK activation mediates MMP-1 but not MMP-13 release from FLSCs, 2) COX-2-derived E PGs inhibit MMP-1 release from FLSCs via inhibition of ERK, and 3) COX inhibitors, by attenuating PGE inhibition of ERK, enhance the release of MMP-1 by FLSC.

The eicosanoid cascade: possible role in gliomas and meningiomas

Eicosanoids constitute a large family of biologically active lipid mediators that are produced by two enzyme classes, cyclooxygenases (COX-1 and COX-2) and lipoxygenases (5-LO, 12-LO, and 15-LO). Increasing evidence suggests that in addition to a variety of epithelial malignancies, the two most common types of human brain tumour, gliomas and meningiomas, aberrantly overexpress eicosanoid producing enzymes and release a spectrum of eicosanoids that may promote tumorigenesis and the development of peritumorous brain oedema. Glioma and meningioma cells are killed in vitro and in animal models when exposed to COX-2 and 5-LO inhibitors, and their effectiveness is under investigation in clinical trials for treatment of patients with malignant brain tumours. However, despite research into the role of the eicosanoid cascade in the tumorigenesis of human brain tumours, many important questions remain unanswered. Current and newer agents that specifically target key players of the eicosanoid cascade could change the approach to treating brain tumours, because their benefits may lie in their synergism with conventional cytotoxic treatments and/or with other novel agents targeted against other procarcinogenic pathways.

Carboxyl methylation of Ras regulates membrane targeting and effector engagement

Post-translational modification of Ras proteins includes prenylcysteine-directed carboxyl methylation. Because Ras participates in Erk activation by epidermal growth factor (EGF), we tested whether Ras methylation regulates Erk activation. EGF stimulation of Erk was inhibited by AFC (N-acetyl-S-farnesyl-L-cysteine), an inhibitor of methylation, but not AGC (N-acetyl-S-geranyl-L-cysteine), an inactive analog of AFC. AFC inhibited Ras methylation as well as the activation of pathway enzymes between Ras and Erk but did not inhibit EGF receptor phosphorylation, confirming action at the level of Ras. Transient transfection of human prenylcysteine-directed carboxyl methyltransferase increased EGF-stimulated Erk activation. AFC but not AGC inhibited movement of transiently transfected green fluorescent protein-Ras from the cytosol to the plasma membrane of COS-1 cells and depleted green fluorescent protein-Ras from the plasma membrane in stably transfected Madin-Darby canine kidney cells, suggesting that methylation regulates Erk by ensuring proper membrane localization of Ras. However, when COS-1 cells were transfected with Ras complexed to CD8, plasma membrane localization of Ras was unaffected by AFC, yet EGF-stimulated Erk activation was inhibited by AFC. Thus, Ras methylation appears to regulate Erk activation both through the localization of Ras as well as the propagation of Ras-dependent signals.

The lipid and non-lipid effects of statins

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, more commonly known as statins, are a class of drug widely used for the treatment of hypercholesterolaemia in patients with established cardiovascular disease as well as those at high risk of developing atherosclerosis. Their predominant action is to reduce circulating levels of low-density lipoprotein (LDL) cholesterol; to a smaller degree, they also increase high-density lipoprotein (HDL) cholesterol and reduce triglyceride concentrations. In recent years, however, there has been an increasing body of evidence that their effects on lipid profile cannot fully account for their cardiovascular protective actions: their beneficial effects are too rapid to be easily explained by their relatively slow effects on atherogenesis and too large to be accounted for by their relatively small effects on plaque regression. Experimental models have revealed that statins exert a variety of other cardiovascular effects, which would be predicted to be of clinical benefit: they possess anti-inflammatory properties, as evidenced by their ability to reduce the accumulation of inflammatory cells in atherosclerotic plaques; they inhibit vascular smooth muscle cell proliferation, a key event in atherogenesis; they inhibit platelet function, thereby limiting both atherosclerosis and superadded thrombosis; and they improve vascular endothelial function, largely through augmentation of nitric oxide (NO) generation. The relative importance of the lipid- and non-lipid-related effects of the statins in the clinical situation remains the subject of much continuing research.

Acetyl-11-keto-beta-boswellic acid (AKBA) is cytotoxic for meningioma cells and inhibits phosphorylation of the extracellular-signal regulated kinase 1 and 2

Acetyl-11-keto-beta-boswellic acid (AKBA) is a naturally occurring pentacyclic triterpene isolated from the gum resin exudate from the stem of the tree Boswellia serrata (frankincense). AKBA has been recently identified as a novel, orally active, non-redox and non-competitive 5-lipoxygenase inhibitor that also inhibits topisomerase I and II in vitro. Because natural pentacyclic triterpenes have an antiproliferative effect against different tumor types, we investigated the effects of AKBA on the proliferation of 11 primary cell cultures established from human surgical specimens of meningiomas, common central nervous system tumors. Treatment of meningioma cells by AKBA revealed a potent cytotoxic activity with half-maximal inhibitory concentrations in the range of 2-8 microM. At similar, physiologically achievable concentrations, AKBA rapidly (within minutes) and potently inhibited the phosphorylation of extracellular signal-regulated kinase 1 and 2 (Erk-1 and Erk-2) in meningioma cells stimulated with platelet-derived growth factor BB. High expression level of 5-LO was detected in primary meningioma cells and surgical specimens by immunoblotting analysis, suggesting the possible role of 5-LO in meningioma tumorigenesis. Considering the critical importance of the Erk-1/2 signal transduction pathway not only in meningiomas but in other human neoplasms, the interruption of signaling through this evolutionarily conserved pathway might be one of the mechanisms by which AKBA induces suppression of proliferation and apoptosis of different tumor types.

Arachidonic acid activates phospholipase D in human neutrophils; essential role of endogenous leukotriene B4 and inhibition by adenosine A2A receptor engagement

We report in human neutrophils (PMN) that phospholipase D (PLD) was stimulated by micromolar concentrations of arachidonic acid (AA) and nanomolar concentrations of leukotriene B(4) (LTB(4)), and eicosapentaenoic acid was inactive. The stimulatory effect of AA occurred only when adenosine was eliminated from PMN suspensions or when PMN were incubated with adenosine A(2A) receptor antagonists. The mechanism of AA-induced PLD activation was investigated. The results show that AA- and LTB(4)-induced PLD activation were inhibited by the LTB(4) receptor 1 (BLTR1) antagonist CP 105,696, whereas the LTA(4) hydrolase inhibitor SC57461A and the LT biosynthesis inhibitor MK-0591 inhibited AA- but not LTB(4)-mediated PLD activation. The AA-induced ARF1 and RhoA translocation to PMN membranes was inhibited by CP 105,696 and SC57461A. These results provide evidence of a requirement for an autocrine-stimulatory loop involving LTB(4) and BLTR1 in the translocation of small GTPases to membranes and the activation of PMN PLD by AA.

Cell type-dependent activation of 5-lipoxygenase by arachidonic acid

5-Lipoxygenase (5-LO) is the key enzyme in the biosynthesis of proinflammatory leukotrienes. We show that stimulation of polymorphonuclear leukocytes (PMNL), rat basophilic leukemia (RBL)-1, or transfected HeLa cells with arachidonic acid (AA) caused prominent 5-LO product formation that coincided with the activity of extracellular signal-regulated kinases (ERKs) and p38 mitogen-activated protein kinase. 5-LO product formation in AA-stimulated PMNL and RBL-1 cells was independent of Ca2+. However, in HeLa cells expressing a 5-LO mutant lacking potential 5-LO phosphorylation sites, removal of Ca2+ caused a prominent loss of 5-LO activity. For Mono Mac 6 (MM6) cells, AA failed to activate ERKs, and AA-induced 5-LO product formation was only minute. Also, activation of ERKs by phorbol esters did not lead to prominent 5-LO product synthesis. Instead, 5-LO activation in MM6 cells required Ca2+ or alternative signaling pathways induced by hyperosmotic stress. In summary, mechanisms for activation of 5-LO differ considerably between cell types.

The effect of humic acid on the adhesibility of neutrophils

Humic acid (HA), a fluorescent allomelanin, has been implicated as an etiological agent of Blackfoot disease (BFD), a peripheral vascular disease prevailing in the southwest of Taiwan. Clinical and pathological studies reveal that it is similar to atherosclerosis. In this report, the effect of HA on human neutrophils is studied because prolonged and enhanced activation of neutrophils adhered on endothelium may damage the endothelium and initiate the process of thrombosis and vasculitis.

METHODS

Neutrophils, treated with various concentrations of HA, were added to culture plates, cultured human umbilical vein endothelial cells (HUVECs), or human umbilical vein endothelium tissue culture for 15 or 30 min. The adhesion of neutrophils was measured qualitatively and quantitatively. The mechanism of neutrophil activation was studied with free radical production and various kinase measurements and their activities' assays.

RESULTS

HA was shown to enhance, in a dose-dependent manner, the adhesion of neutrophils on the culture plates, cultured human umbilical vein endothelial cells, and human umbilical vein endothelium tissue culture. The adhesion-enhancing ability of HA is elicited through activation of ERK, P38 mitogen-activated kinase (P38MAPK), and phosphoinositide 3 kinase (PI3K) in neutrophils. HA also induces the NF-kappaB activation in neutrophils.

CONCLUSION

HA treatment markedly enhanced adhesion and superoxide radical production of neutrophils, the characteristics of activated neutrophils; and all these stimulation effects were blocked by several kinase inhibitors, reflecting the involvement of the ERK, P38MAPK, and PI3K on the activation of neutrophils. The induction of NF-kappaB implied that the consequence of neutrophil activation by HA were similar to other stimulants. The prolonged neutrophil activation will further damage endothelium cell and cause thrombosis, vaculitis, as well as arteriosclerosis. This may partially explain why HA consumption will cause BFD.

Extracellular signal-regulated kinases phosphorylate 5-lipoxygenase and stimulate 5-lipoxygenase product formation in leukocytes

5-lipoxygenase (5-LO) is the key enzyme in the biosynthesis of proinflammatory leukotrienes. Here, we demonstrate that extracellular signal-regulated kinases (ERKs) can phosphorylate 5-LO in vitro. Efficient phosphorylation required the presence of unsaturated fatty acids and was abolished when Ser-663 was mutated to alanine. In intact HeLa cells stimulated with arachidonic acid (AA), impaired 5-LO product formation was evident in cells expressing the S663A-5-LO mutant compared with cells expressing wild-type 5-LO. For Mono Mac 6 cells, priming with phorbol myristate acetate (PMA) before stimulation with ionophore was required for ERK1/2 activation and efficient 5-LO phosphorylation, in parallel with substantial AA release and 5-LO product formation. Inhibition of PKC by GF109203x or MEK1/2 by U0126 (or PD98059) abolished the 5-LO up-regulation effects of PMA. In contrast, these inhibitors failed to suppress 5-LO product formation induced by stimuli such as AA plus ionophore, which apparently do not involve the ERK1/2 pathway. Based on inhibitor studies, ERKs are also involved in AA-stimulated 5-LO product formation in PMNL, whereas a role for ERKs is not apparent in 5-LO activation induced by ionophore or cell stress. Finally, the data suggest that ERKs and p38 MAPK-regulated MAPKAPKs can act in conjunction to stimulate 5-LO by phosphorylation.

alpha 2B-adrenergic receptor activates MAPK via a pathway involving arachidonic acid metabolism, matrix metalloproteinases, and epidermal growth factor receptor transactivation

We have investigated the mechanisms whereby alpha(2B)-adrenergic receptor (alpha(2B)-AR) promotes MAPK activation in a clone of the renal tubular cell line, LLC-PK1, transfected with the rat nonglycosylated alpha(2)-AR gene. Treatment of LLC-PK1-alpha(2B) with UK14304 or dexmedetomidine caused arachidonic acid (AA) release and ERK2 phosphorylation. AA release was abolished by prior treatment of the cells with pertussis toxin, quinacrine, or methyl arachidonyl fluorophosphonate but not by the addition of the MEK inhibitor U0126. The effects of alpha(2)-agonists on MAPK phosphorylation were mimicked by cell exposure to exogenous AA. On the other hand, quinacrine abolished the effects of UK14304, but not of AA, suggesting that AA released through PLA2 is responsible for MAPK activation by alpha(2B)-AR. The effects of alpha(2)-agonists or AA were PKC-independent and were attenuated by indomethacin and nordihydroguaiaretic acid. Treatment with batimastat, CRM 197, or tyrphostin AG1478 suppressed MAPK phosphorylation promoted by alpha(2)-agonist or AA. Furthermore, conditioned culture medium from UK14304-treated LLC-PK1-alpha(2B) induced MAPK phosphorylation in wild-type LLC-PK1. Based on these data, we propose a model whereby activation of MAPK by alpha(2B)-AR is mediated through stimulation of PLA2, AA release, generation of AA derivatives, activation of matrix metalloproteinases, release of heparin-binding EGF-like growth factor, transactivation of epidermal growth factor receptor, and recruitment of Shc. Whether this pathway is particular to alpha(2B)-AR and LLC-PK1 or whether it can be extended to other cell types and/or other G-protein-coupled receptors remains to be established.

Signaling pathways involved in IL-8-dependent activation of adhesion through Mac-1

In human neutrophils, IL-8 induces chemotaxis, the respiratory burst, and granule release, and enhances cellular adhesion, a beta(2) integrin-dependent event. IL-8 stimulates neutrophil adhesion to purified fibrinogen in a Mac-1-dependent manner. Mitogen-activated protein kinase (MAPK) activation was detected in human neutrophil lysates after treatment with IL-8 and PMA, but not the activating mAb CBR LFA 1/2. IL-8-stimulated neutrophil adhesion to fibrinogen was blocked 50% by the MAPK/extracellular signal-related kinase-activating enzyme inhibitor PD098059. Adhesion was blocked approximately 75% by inhibition of the phosphatidylinositol-3 kinase (PI3K) pathway with LY294002, supporting that activation of both MAPK and PI3K may play a role in IL-8-dependent inside-out signals that activate Mac-1. Activation of MAPK was inhibited in IL-8-stimulated cells in the presence of PI3K inhibitors LY294002 or wortmannin, supporting a model in which PI3K is upstream of MAPK. IL-8-stimulated neutrophil adhesion was inhibited 50% by bisindolylmaleimide-I, implicating protein kinase C (PKC) in the intracellular signaling from the IL-8R to Mac-1. A 74-kDa molecular mass species was detected by an activation-specific Ab to PKC when cells were stimulated with PMA or IL-8, but not a beta(2)-activating Ab. Inhibition of either MAPK or PKC resulted in partial inhibition of IL-8-stimulated polymorphonuclear neutrophil adhesion, and treatment with both inhibitors simultaneously completely abolished IL-8-stimulated adhesion to ligand. Inhibition of PI3K blocked MAPK activation, but not PKC activation, suggesting a branch point that precedes PI3K activation. These data suggest that both MAPK and PKC are activated in response to IL-8 stimulation, and that these may represent independent pathways for beta(2) integrin activation in neutrophils.

Arachidonic acid promotes phosphorylation of 5-lipoxygenase at Ser-271 by MAPK-activated protein kinase 2 (MK2)

We demonstrated previously that 5-lipoxygenase (5-LO), a key enzyme in leukotriene biosynthesis, can be phosphorylated by p38 MAPK-regulated MAPKAP kinases (MKs). Here we show that mutation of Ser-271 to Ala in 5-LO abolished MK2 catalyzed phosphorylation and clearly reduced phosphorylation by kinases prepared from stimulated polymorphonuclear leukocytes and Mono Mac 6 cells. Compared with heat shock protein 27 (Hsp-27), 5-LO was a weak substrate for MK2. However, the addition of unsaturated fatty acids (i.e. arachidonate 1-50 microm) up-regulated phosphorylation of 5-LO, but not of Hsp-27, by active MK2 in vitro, resulting in a similar phosphorylation as for Hsp-27. 5-LO was phosphorylated also by other serine/threonine kinases recognizing the motif Arg-Xaa-Xaa-Ser (protein kinase A, Ca(2+)/calmodulin-dependent kinase II), but these activities were not increased by fatty acids. HeLa cells expressing wild type 5-LO or S271A-5-LO, showed prominent 5-LO activity when incubated with Ca(2+)-ionophore plus arachidonate. However, when stimulated with only exogenous arachidonic acid, activity for the S271A mutant was significantly lower as compared with wild type 5-LO. It appears that phosphorylation at Ser-271 is more important for 5-LO activity induced by a stimulus that does not prominently increase intracellular Ca(2+) and that arachidonic acid stimulates leukotriene biosynthesis also by promoting this MK2-catalyzed phosphorylation.

Extracellular signal-regulated kinase plays an essential role in endothelin-1-induced homotypic adhesion of human neutrophil granulocytes

1. Endothelin-1 (ET-1) stimulates integrin-dependent adhesion of neutrophil granulocytes to endothelial cells, one of the early key events in acute inflammation. However, the signalling pathway(s) of ET-1-stimulated neutrophil adhesive responses has not been elucidated. Previous studies indicated that extracellular signal-regulated kinase (ERK) activation could mediate rapid responses of neutrophil granulocytes to various stimuli. In this study, we investigated the role of ERK signalling in human neutrophil granulocytes challenged with ET-1. 2. ET-1 rapidly down-regulated the expression of L-selectin and up-regulated the expression of CD11b/CD18 on the neutrophil surface. Concomitantly, ET-1 induced homotypic adhesion (aggregation) of neutrophils, that was blocked by a monoclonal antibody to CD18. 3. ET-1, through ET(A) receptors, evoked activation of Ras and subsequent phosphorylation of Raf-1, mitogen-activated protein kinase kinase (MAPK/ERK kinase) and ERK 1/2. ERK activation by ET-1 was rapid, concordant with the kinetics of ET-1-stimulated neutrophil aggregation. 4. Neutrophil responses to ET-1 were markedly attenuated by the MAPK/ERK kinase inhibitor PD98059, whereas inhibitors of p38 MAPK, tyrosine kinases and phosphatidylinositol 3-kinase had no detectable effects. We have observed a tight correlation between neutrophil ERK activation and homotypic adhesion. 5. These data indicate an essential role for ERK in mediating ET-1-stimulated adhesive responses of human neutrophil granulocytes.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

Boswellic acids activate p42(MAPK) and p38 MAPK and stimulate Ca(2+) mobilization

Here we show that extracts of Boswellia serrata gum resins and its constituents, the boswellic acids (BAs), activate the mitogen-activated protein kinases (MAPK) p42(MAPK) and p38 in isolated human polymorphonuclear leukocytes (PMNL). MAPK activation was rapid and transient with maximal activation after 1-2.5 min of exposure and occurred in a dose-dependent manner. The keto-BAs (11-keto-beta-BA and 3-O-acetyl-11-beta-keto-BA) gave substantial kinase activation at 30 microM, whereas other BAs lacking the 11-keto group were less effective. Moreover, 11-keto-BAs induced rapid and prominent mobilization of free Ca(2+) in PMNL. Inhibitor studies revealed that phosphatidylinositol 3-kinase (PI 3-K) is involved in BA-induced MAPK activation, whereas a minor role was apparent for protein kinase C. MAPK activation by 3-O-acetyl-11-beta-keto-BA was partially inhibited when Ca(2+) was removed by chelation. Our results suggest that 11-keto-BAs might function as potent activators of PMNL by stimulation of MAPK and mobilization of intracellular Ca(2+).

Loss of pentameric symmetry of C-reactive protein is associated with promotion of neutrophil-endothelial cell adhesion

The classic acute-phase reactant C-reactive protein (CRP) is a cyclic pentameric protein that diminishes neutrophil accumulation in inflamed tissues. When the pentamer is dissociated, CRP subunits undergo conformational rearrangement that results in expression of a distinctive isomer with unique antigenic and physicochemical characteristics (termed modified CRP (mCRP)). Recently, mCRP was detected in the wall of normal human blood vessels. We studied the impact and mechanisms of action of mCRP on expression of adhesion molecules on human neutrophils and their adhesion to human coronary artery endothelial cells. Both CRP and mCRP (0.1-200 microg/ml) down-regulated neutrophil L-selectin expression in a concentration-dependent fashion. Furthermore, mCRP, but not CRP, up-regulated CD11b/CD18 expression and stimulated neutrophil extracellular signal-regulated kinase activity, which was accompanied by activation of p21(ras) oncoprotein, Raf-1, and mitogen-activated protein kinase kinase. These actions of mCRP were sensitive to the mitogen-activated protein kinase kinase inhibitor PD98059. mCRP markedly enhanced attachment of neutrophils to LPS-activated human coronary artery endothelial when added together with neutrophils. This effect of mCRP was attenuated by an anti-CD18 mAb. Thus, loss of pentameric symmetry in CRP is associated with appearance of novel bioactivities in mCRP that enhance neutrophil localization and activation at inflamed or injured vascular sites.

Oxidative stress and eicosanoids in the kidneys of hyperglycemic rats treated with dehydroepiandrosterone

Oxidative stress plays a crucial role in the pathogenesis of chronic diabetic complications. Normoglycemic and streptozotocin-diabetic rats were treated with dehydroepiandrosterone (DHEA) (4 mg/d per rat) for 3 weeks. At the end of treatment, hydroxynonenal, hydroperoxyeicosatetraenoic acids and antioxidant levels, as well as Na/K-ATPase activity and membrane fatty acids composition were evaluated in kidney homogenates. Chronic hyperglycemia caused a marked increase of both hydroxynonenal and lipoxygenase pathway products and a drop in both GSH levels and membrane Na/K-ATPase activity. DHEA treatment restored the antioxidant levels to close to the control value and considerably reduced hydroxynonenal and hydroperoxyeicosatetraenoic acid levels. Moreover, DHEA counteracted the detrimental effect of hyperglycemia on membrane function: the drop of Na/K-ATPase activity in diabetic animals was significantly inhibited by DHEA treatment. These results show that DHEA reduces oxidative stress and the consequent increase of lipoxygenase pathway products induced by experimental diabetes in rat kidney; they also suggest that, by reducing the inflammatory response to oxidative stress, DHEA treatment might delay the progression of diabetic kidney disease.

Matrix metalloproteinases regulate neutrophil-endothelial cell adhesion through generation of endothelin-1[1-32]

We recently reported that matrix metalloproteinase 2 (MMP-2, gelatinase A) cleaves big endothelin 1 (ET-1), yielding the vasoactive peptide ET-1[1-32]. We tested whether ET-1[1-32] could affect the adhesion of human neutrophils to coronary artery endothelial cells (HCAEC). ET-1[1-32] rapidly down-regulated the expression of L-selectin and up-regulated expression of CD11b/CD18 on the neutrophil surface, with EC50 values of 1-3 nM. These actions of ET-1[1-32] were mediated via ETA receptors and did not require conversion of ET-1[1-32] into ET-1 by neutrophil proteases, as revealed by liquid chromatography and mass spectroscopy. Moreover, ET-1[1-32] evoked release of neutrophil gelatinase B, which cleaved big ET-1 to yield ET-1[1-32], thus revealing a positive feedback loop for ET-1[1-32] generation. Up-regulation of CD11b/CD18 expression and gelatinase release was tightly associated with activation of extracellular signal-regulated kinase (Erk). Stimulation of Erk activity was due to activation of Ras, Raf-1, and MEK (MAPK kinase). ET-1[1-32] also produced slight increases in the expression of ICAM-1 and E-selectin on HCAEC, and markedly enhanced beta2 integrin-dependent adhesion of neutrophils to activated HCAEC. These results are the first indication that gelatinolytic MMPs via cleavage of big ET-1 to yield ET-1[1-32] activate neutrophils and promote leukocyte-endothelial cell adhesion and, consequently, neutrophil trafficking into inflamed tissues.

Protein kinases C translocation responses to low concentrations of arachidonic acid

Arachidonic acid (AA) directly activates protein kinases C (PKC) and may thereby serve as a regulatory signal during cell stimulation. The effect, however, requires a > or =20 microm concentration of the fatty acid. We find that human polymorphonuclear neutrophils (PMN) equilibrated with a ligand for the diacylglycerol receptor on PKC, [(3)H]phorbol dibutyrate (PDB), increased binding of [(3)H]PDB within 15 s of exposure to > or =10-30 nm AA. Other unsaturated fatty acids, but not a saturated fatty acid, likewise stimulated PDB binding. These responses, similar to those caused by chemotactic factors, resulted from a rise in the number of diacylglycerol receptors that were plasma membrane-associated and therefore accessible to PDB. Unlike chemotactic factors, however, AA was fully active on cells overloaded with Ca(2+) chelators. The major metabolites of AA made by PMN, leukotriene B(4) and 5-hydroxyicosatetraenoate, did not mimic AA, and an AA antimetabolite did not block responses to AA. AA also induced PMN to translocate cytosolic PKCalpha, beta(II), and delta to membranes. This response paralleled PDB binding with respect to dose requirements, time, Ca(2+)-independence, resistance to an AA antimetabolite, and induction by another unsaturated fatty acid but not by a saturated fatty acid. Finally, HEK 293 cells transfected with vectors encoding PKCbeta(I) or PKCdelta fused to the reporter enhanced green fluorescent protein (EGFP) were studied. AA caused EGFP-PKCbeta translocation from cytosol to plasma membrane at > or =0.5 microm, and EGFP-PKCdelta translocation from cytosol to nuclear and, to a lesser extent, plasma membrane at as little as 30 nm. We conclude that AA induces PKC translocations to specific membrane targets at concentrations 2-4 orders of magnitude below those activating the enzymes. These responses, at least as they occur in PMN, do not require changes in cell Ca(2+) or oxygenation of the fatty acid. AA seems more suited for signaling the movement than activation of PKC.

Plasmin-induced expression of cytokines and tissue factor in human monocytes involves AP-1 and IKKbeta-mediated NF-kappaB activation

It was previously shown that plasmin activates human peripheral monocytes in terms of lipid mediator release and chemotactic migration. Here it is demonstrated that plasmin induces proinflammatory cytokine release and tissue factor (TF) expression by monocytes. Plasmin 0.043 to 1.43 CTA U/mL, but not active site-blocked plasmin, triggered concentration-dependent expression of mRNA for interleukin-1alpha (IL-1alpha), IL-1beta, tumor necrosis factor-alpha (TNF-alpha), and TF with maximum responses after 4 hours. Plasmin-mediated mRNA expression was inhibited in a concentration-dependent manner by the lysine analogue trans-4-(aminomethyl)cyclohexane-1-carboxylic acid (t-AMCA). Increases in mRNA levels were followed by concentration- and time-dependent release of IL-1alpha, IL-1beta and TNF-alpha and by TF expression on monocyte surfaces. Neither cytokines nor TF could be detected when monocytes were preincubated with actinomycin D or cycloheximide. Electrophoretic mobility shift assays indicated plasmin-induced activation of NF-kappaB; DNA-binding complexes were composed of p50, p65, and c-Rel, as shown by supershift experiments. Nuclear translocation of NF-kappaB/Rel proteins coincided with IkappaBalpha degradation. At variance with endotoxic lipopolysaccharide, plasmin elicited the rapid degradation of another cytoplasmic NF-kappaB inhibitor, p105. Proteolysis of NF-kappaB inhibitors was apparently due to transient activation of IkappaB kinase (IKK) beta that reached maximum activity at 1 hour after plasmin stimulation. In addition, AP-1 binding was increased in plasmin-treated monocytes, with most complexes composed of JunD, c-Fos, and FosB. These findings further substantiate the role of plasmin as a proinflammatory activator of human monocytes and reveal an important new link between the plasminogen-plasmin system and inflammation. (Blood. 2001;97:3941-3950)

The neutrophil: function and regulation in innate and humoral immunity

The neutrophil is a critical effector cell in humoral and innate immunity and plays vital roles in phagocytosis and bacterial killing. Discussed here are the neutrophil components necessary for these processes and the diseases in which these components are either lacking or dysfunctional, illustrating that normal neutrophil function is vital for health.

Peroxynitrite induces integrin-dependent adhesion of human neutrophils to endothelial cells via activation of the Raf-1/MEK/Erk pathway

Accumulating evidence suggests that enhanced peroxynitrite (ONOO-) formation occurs during inflammation. We have studied the impact and the mechanisms of ONOO- action on expression of adhesion molecules on human neutrophils and coronary artery endothelial cells (HCAEC) and binding of neutrophils to HCAEC. Addition of ONOO- (0.1 to 200 5M) to isolated neutrophils resulted in a concentration-dependent down-regulation of L-selectin expression, and up-regulation of CD11b/CD18 expression. ONOO- stimulation of Erk activity was accompanied by activation of Ras, Raf-1 and MEK (mitogen-activated protein kinase kinase), and was sensitive to the MEK inhibitor PD 98059. We have observed a tight association between Erk activation and changes in CD11b/CD18 expression. ONOO- also evoked activation of neutrophil p38 MAPK. Neither ONOO--induced up-regulation of CD11b/CD18 expression nor Erk activation was affected by SB 203580, a selective inhibitor of p38 MAPK. ONOO- by itself had little effect on expression of ICAM-1 and E-selectin on HCAEC, whereas it markedly enhanced attachment of neutrophils to lipopolysaccharide-activated HCAEC only when it was added together with neutrophils. Increases in neutrophil adhesion evoked by ONOO- were blocked by an anti-CD18 monoclonal antibody. These data suggest that ONOO- activates Erk in neutrophils via the Ras/Raf-1/MEK signal transduction pathway, leading to up-regulation of surface expression of CD11b/CD18 and consequently to increased neutrophil adhesion to endothelial cells.

Eicosanoid activation of extracellular signal-regulated kinase1/2 in human epidermoid carcinoma cells

12(S)-Hydroxyeicosatetraenoic acid (12(S)-HETE), a 12-lipoxygenase metabolite of arachidonic acid, has multiple effects on tumor and endothelial cells, including stimulation of invasion and angiogenesis. However, the signaling mechanisms controlling these physiological processes are poorly understood. In a human epidermoid carcinoma cell line (i.e. A431), 12(S)-HETE activates extracellular signal-regulated kinases 1/2 (ERK1/2), which is mediated by upstream kinases MEK and Raf. 12(S)-HETE stimulates phosphorylation of phospholipase Cgamma1 and activity of protein kinase Calpha (PKCalpha). In addition, independent of PKC 12(S)-HETE increases tyrosine phosphorylation of Shc, and Grb2, stimulates association between Shc and Src, and increases the activity of Ras, via Src family kinases. Furthermore, at low (10-100 nm) concentrations 12(S)-HETE counteracts epidermal growth factor-stimulated activation of ERK1/2 via stimulating protein tyrosine phosphatases. We also present evidence that 12(S)-HETE stimulates ERK1/2 via G proteins and that A431 cells have multiple binding sites for 12(S)-HETE. Finally, inhibition of 12-lipoxygenase induced apoptosis of A431 cells, which was reversed by addition of exogenous 12(S)-HETE. Collectively we demonstrate that the activation of ERK1/2 by 12(S)-HETE may be regulated by multiple receptors triggering PKC-dependent and PKC-independent pathways in A431 cells.