An atypical protein kinase C, PKC zeta, regulates human eosinophil effector functions

Unique Lipid Signatures of Extracellular Vesicles from the Airways of Asthmatics

Asthma is a chronic inflammatory disease process involving the conductive airways of the human lung. The dysregulated inflammatory response in this disease process may involve multiple cell-cell interactions mediated by signaling molecules, including lipid mediators. Extracellular vesicles (EVs) are lipid membrane particles that are now recognized as critical mediators of cell-cell communication. Here, we compared the lipid composition and presence of specific lipid mediators in airway EVs purified from the bronchoalveolar lavage (BAL) fluid of healthy controls and asthmatic subjects with and without second-hand smoke (SHS) exposure. Airway exosome concentrations were increased in asthmatics, and correlated with blood eosinophilia and serum IgE levels. Frequencies of HLA-DR⁺ and CD54⁺ exosomes were also significantly higher in asthmatics. Lipidomics analysis revealed that phosphatidylglycerol, ceramide-phosphates, and ceramides were significantly reduced in exosomes from asthmatics compared to the non-exposed control groups. Sphingomyelin 34:1 was more abundant in exosomes of SHS-exposed asthmatics compared to healthy controls. Our results suggest that chronic airway inflammation may be driven by alterations in the composition of lipid mediators within airway EVs of human subjects with asthma.

Lipid Mediators of Allergic Disease: Pathways, Treatments, and Emerging Therapeutic Targets

Bioactive lipids are critical regulators of inflammation. Over the last 75 years, these diverse compounds have emerged as clinically-relevant mediators of allergic disease pathophysiology. Animal and human studies have demonstrated the importance of lipid mediators in the development of asthma, allergic rhinitis, urticaria, anaphylaxis, atopic dermatitis, and food allergy. Lipids are critical participants in cell signaling events which influence key physiologic (bronchoconstriction) and immune phenomena (degranulation, chemotaxis, sensitization). Lipid-mediated cellular mechanisms including: (1) formation of structural support platforms (lipid rafts) for receptor signaling complexes, (2) activation of a diverse family of G-protein coupled receptors, and (3) mediating intracellular signaling cascades by acting as second messengers. Here, we review four classes of bioactive lipids (platelet activating factor, the leukotrienes, the prostanoids, and the sphingolipids) with special emphasis on lipid synthesis pathways and signaling, atopic disease pathology, and the ongoing development of atopy treatments targeting lipid mediator pathways.

Platelet activating factor in allergies

The platelet-activating factor (PAF) produced and released by mast cells, basophils, neutrophils, eosinophils, fibroblasts, platelets, endothelial cells, and even cardiac muscle cells plays an important role in inflammatory and thrombotic diseases. PAF has been shown to be an important mediator in anaphylaxis. Serum level of the factor correlates with the severity of systemic reactions. PAF is also involved in asthamatic patients' bronchoconstriction, mucus hypersecretion, and inflammation of bronchi. Furthermore, increased plasma levels of PAF have been reported in patients with urticarial. Studies have shown that PAF increases the permeability of skin's capillaries and indices the development of wheals, flare, and inflammatory reactions in the skin.This review focuses on the actions of the PAF on the eosinophiles and mast cells. Following that pathophysiological mechanism of the PAF in anaphylaxis bronchial asthma and urticaria was discussed.

Role of eosinophils and their clinical significance in allergic inflammation

Eosinophils are believed to play roles in the pathophysiology of allergic inflammation, such as bronchial asthma. However, recent studies on anti-interleukin-5 monoclonal antibody treatment of asthmatic patients raised the possibility that eosinophils may play only a limited role. More recent studies established that eosinophils are essentially involved in the development of airway remodeling. Moreover, it is theoretically conceivable that eosinophils are a cellular source of lipid mediators, such as cysteinyl leukotrienes or platelet-activating factor in asthma. Even in the absence of interleukin-5, it is likely that the 'T-helper Type 2 network', including a cascade of vascular cell adhesion molecule-1, intercellular cell adhesion molecule-1, CC chemokines, granulocyte-macrophage colony-stimulating factor, for example, can maintain sufficient eosinophilic infiltration and effector functions, such as superoxide anion generation and degranulation. Long-term studies, wherein tissue eosinophils are eliminated effectively will be required to establish the exact roles of these cells in asthma. Finally, the authors will demonstrate that eosinophils have the potential for not only playing detrimental roles but also beneficial ones.

G alpha(q) acts as an adaptor protein in protein kinase C zeta (PKCzeta)-mediated ERK5 activation by G protein-coupled receptors (GPCR)

G(q)-coupled G protein-coupled receptors (GPCR) mediate the actions of a variety of messengers that are key regulators of different cellular functions. These receptors can regulate a highly interconnected network of biochemical routes that control the activity of several members of the mitogen-activated protein kinase (MAPK) family. The ERK5 MAPK has been shown to be activated by G(q)-coupled GPCR via unknown mechanisms. We find that the atypical protein kinase C (PKCzeta), previously reported to interact with the ERK5 activator MEK5 and to be involved in epidermal growth factor-mediated ERK5 stimulation, plays a crucial role in the activation of the ERK5 pathway by G(q)-coupled GPCR. Stimulation of ERK5 by G(q)-coupled GPCR is abolished upon pharmacological inhibition of PKCzeta as well as in embryonic fibroblasts obtained from PKCzeta-deficient mice. Both PKCzeta and MEK5 associate to G alpha(q) upon activation of GPCR, thus forming a ternary complex that seems essential for the activation of ERK5. These data put forward a novel function of G alpha(q) as a scaffold protein involved in the modulation of the ERK5 cascade by GPCR that could be relevant in G(q)-mediated physiological functions.

Beta2-integrin-mediated adhesion and intracellular Ca2+ release in human eosinophils

Human eosinophils spontaneously adhere to various substrates in the absence of exogenously added activators. In the present study a method was developed for characterizing eosinophil adhesion by measuring changes in impedance. Impedance measurements were performed in HCO(3)-buffered HybriCare medium maintained in a humidified 5% CO(2) incubator at 37 degrees C. Impedance increased by more than 1 kOmega within minutes after eosinophils made contact with the substrate, reaching a peak within 20 min. Blocking mobilization of intracellular [Ca(2+)] that precedes adhesion with BAPTA-AM (10 microM) completely inhibited the rise in impedance as well as the changes in cell shape typically observed in adherent cells. However, lowering the extracellular [Ca(2+)] with 2.5 mM EGTA did not inhibit the increase in impedance. Pretreatment with anti-CD18 antibody to block substrate interactions with beta(2)-integrins, or jasplakinolide (2 microM) to block actin reorganization, abolished the increase in impedance and adherent morphology of the cells. Exposure of eosinophils to the phosphatidylinositol 3 kinase inhibitor LY294002 (5 microM) or treatment with protein kinase C zeta pseudosubstrate to competitively inhibit activity of the enzyme significantly reduced the increase in impedance and inhibited the cell spreading associated with adhesion. These results demonstrate a novel method for measuring eosinophil adhesion and showed that, following formation of a tethered attachment, a rapid increase in intracellular [Ca(2+)] precedes the cytoskeletal rearrangements required for cell shape changes and plasma membrane-substrate interactions associated with adhesion.

Interferon-gamma enhances human eosinophil effector functions induced by granulocyte-macrophage colony-stimulating factor or interleukin-5

T helper (Th) 2-type cytokines play a dominant role in allergic inflammation. Accumulating evidence suggests that Th1-type cytokines antagonize Th2-type cytokine responses; however, recent studies demonstrate that Th1 cytokines might enhance Th2 immune responses. We examined whether interferon (IFN)-gamma, a representative Th1 cytokine, modifies the effector functions of human eosinophils stimulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-5. GM-CSF and IL-5 have significant functional homology, and contribute to the regulation of Th2 immunity. After the pretreatment of eosinophils with IFN-gamma, GM-CSF- or IL-5-induced eosinophil functions were examined, including superoxide anion generation, degranulation, adhesion, expression of GM-CSF receptor (R), IL-5R, or CD11b, and phosphorylation of intracellular signaling molecules. Superoxide anion generation was measured using the cytochrome c reduction method. Degranulation and cell adhesion were evaluated based on eosinophil-derived neurotoxin (EDN) contents in supernatants or adherent cells. Phosphorylation of signaling molecules was analyzed using a multiplex beads array system. Preincubation with IFN-gamma resulted in enhanced GM-CSF- or IL-5-induced superoxide anion generation and degranulation of human eosinophils, whereas stimulus-induced eosinophil adhesion was unaffected. In addition, IFN-gamma did not influence the expression of GM-CSFR, IL-5R, and CD11b. Furthermore, IFN-gamma upregulated GM-CSF- or IL-5-induced phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), and activating transcription factor (ATF)-2. Finally, we confirmed that MAPK inhibitors blocked the enhancement of stimuli-induced superoxide anion generation of IFN-gamma treated eosinophils. In conclusion, IFN-gamma might upregulate ERK, p38, or JNK/ATF-2 phosphorylation induced by GM-CSF or IL-5, leading to enhanced cytokine-induced eosinophil superoxide generation and degranulation.

Role of intracellular kinases in the regulation of equine eosinophil migration and actin polymerization

Inappropriately activated eosinophils can contribute to disease pathogenesis and intracellular signalling pathways that regulate functional responses may represent a therapeutic target. Little is known about intracellular signalling in equine eosinophils and this study examined the role of phospholipase C (PLC) and a range of protein kinases on responses to histamine and CCL11. Histamine (10(-4) M) or CCL11 (5.6 x 10(-9) M)-induced actin polymerization, migration and superoxide production by eosinophils from healthy horses were compared in the presence and absence of selective kinase inhibitors. Inhibition of phosphatidylinositol-3 kinase (PI3K) significantly reduced the response in each assay. In contrast, whilst inhibition of PLC decreased actin polymerization and superoxide production, an increase in migration was observed; the latter effect was also seen when protein kinase C (PKC) was inhibited. With the exception of histamine-induced migration, which was significantly reduced by blocking extracellular regulated kinase (ERK)1/2, activation of ERK1/2, p38 MAPK and tyrosine kinase did not appear to play an important role in the responses studied. These results suggest that equine eosinophil activation by histamine and CCL11 is mediated through PI3K. Whilst PLC activation is required for actin polymerization and superoxide production, migration may be negatively regulated by PLC and PKC. These kinases represent potential targets for modulating eosinophil activation by multiple stimuli.

Hypoosmotic swelling and ammonia increase oxidative stress by NADPH oxidase in cultured astrocytes and vital brain slices

The role of NADPH oxidase (NOX) and the regulatory subunit p47(phox) for hypoosmotic ROS generation was studied in cultured rat astrocytes and brain slices of wilde type and p47(phox) knock-out mice. Cultured rat astrocytes express mRNAs encoding for the regulatory subunit p47(phox), NOX1, 2, and 4, and the dual oxidases (DUOX)1 and 2, but not NOX3. Hypoosmotic (205 mosmol/L) swelling of cultured astrocytes induced a rapid generation of ROS that was accompanied by serine phosphorylation of p47(phox) and prevented by the NADPH oxidase inhibitor apocynin. Apocynin also impaired the hypoosmotic tyrosine phosphorylation of Src. Both, hypoosmotic ROS generation and p47(phox) serine phosphorylation were sensitive to the acidic sphingomyelinase inhibitors AY9944 and desipramine, the protein kinase C (PKC)zeta-inhibitory pseudosubstrate peptide, the NMDA receptor antagonist MK-801 and the intracellular Ca(2+) chelator BAPTA-AM. Also hypoosmotic exposure of wilde type mouse cortical brain slices increased ROS generation, which was allocated in part to the astrocytes and which was absent in presence of apocynin and in cortical brain slices from p47(phox) knock-out mice. Also ammonia induced a rapid ROS production in cultured astrocytes and brain slices, which was sensitive to apocynin. The data suggest that astrocyte swelling triggers a p47(phox)-dependent NADPH oxidase-catalyzed ROS production. The findings further support a close interrelation between osmotic and oxidative stress in astrocytes, which may be relevant to different brain pathologies including hepatic encephalopathy.

Effects on Ligand Interaction and Membrane Translocation of the Positively Charged Arginine Residues Situated along the C1 Domain Binding Cleft in the Atypical Protein Kinase C Isoforms

The C1 domain zinc finger structure is highly conserved among the protein kinase C (PKC) superfamily members. As the interaction site for the second messenger sn-1,2-diacylglycerol (DAG) and for the phorbol esters, the C1 domain has been an important target for developing selective ligands for different PKC isoforms. However, the C1 domains of the atypical PKC members are DAG/phorbol ester-insensitive. Compared with the DAG/phorbol ester-sensitive C1 domains, the rim of the binding cleft of the atypical PKC C1 domains possesses four additional positively charged arginine residues (at positions 7, 10, 11, and 20). In this study, we showed that mutation to arginines of the four corresponding sites in the C1b domain of PKCdelta abolished its high potency for phorbol 12,13-dibutyrate in vitro, with only marginal remaining activity for phorbol 12-myristate 13-acetate in vivo. We also demonstrated both in vitro and in vivo that the loss of potency to ligands was cumulative with the introduction of the arginine residues along the rim of the binding cavity rather than the consequence of loss of a single, specific residue. Computer modeling reveals that these arginine residues reduce access of ligands to the binding cleft and change the electrostatic profile of the C1 domain surface, whereas the basic structure of the binding cleft is still maintained. Finally, mutation of the four arginine residues of the atypical PKC C1 domains to the corresponding residues in the deltaC1b domain conferred response to phorbol ester. We speculate that the arginine residues of the C1 domain of atypical PKCs may provide an opportunity for the design of ligands selective for the atypical PKCs.

Role of protein kinase C in eosinophil function

Protein kinase C (PKC) isoforms are being elucidated as an increasingly diverse family of enzymes involved in the downstream signal transduction and cell function in various types of cells. To date, 11 PKC isoforms have been identified; they are grouped according to their molecular structure and mode of activation: conventional PKCs (alpha, beta I, beta II, and gamma), novel PKCs (delta, epsilon, mu, theta, and eta), and atypical PKCs (zeta, and iota/lambda). Eosinophils are involved in the pathogenesis of allergic diseases such as bronchial asthma, pollinosis, and atopic dermatitis as well as in the inflammatory response to parasitic infections. Recent studies using selective activators and inhibitors of individual PKC isoforms have revealed that this enzyme is involved in eosinophil dynamics such as cell motility and other functions. However, the role of PKCs in eosinophil functions has been not wholly understood. In this review, we have focused upon and summarized the current knowledge regarding the role of PKC isoforms in eosinophil functions.