Analysis of Signal Transduction Pathways in Human Eosinophils Activated by Chemoattractants and the T-Helper 2–Derived Cytokines Interleukin-4 and Interleukin-5

Activated eosinophils in early life impair lung development and promote long-term lung damage

Exaggeration of type 2 immune responses promotes lung inflammation and altered lung development; however, eosinophils, despite expansion in the postnatal lung, have not been specifically assessed in the context of neonatal lung disease. Furthermore, early life factors including prematurity and respiratory infection predispose infants to chronic obstructive pulmonary disease later in life. To assess eosinophils in the developing lung and how they may contribute to chronic lung disease, we generated mice harboring eosinophil-specific deletion of the negative regulatory enzyme SH2 domain-containing inositol 5' phosphatase-1. This increased the activity and number of pulmonary eosinophils in the developing lung, which was associated with impaired lung development, expansion of activated alveolar macrophages (AMφ), multinucleated giant cell formation, enlargement of airspaces, and fibrosis. Despite regression of eosinophils following completion of lung development, AMφ-dominated inflammation persisted, alongside lung damage. Bone marrow chimera studies showed that SH2 domain-containing inositol 5' phosphatase-1-deficient eosinophils were not sufficient to drive inflammatory lung disease in adult steady-state mice but once inflammation and damage were present, it could not be resolved. Depletion of eosinophils during alveolarization alleviated pulmonary inflammation and lung pathology, demonstrating an eosinophil-intrinsic effect. These results show that the presence of activated eosinophils during alveolarization aggravates AMφs and promotes sustained inflammation and long-lasting lung pathology.

GNA12 regulates C5a-induced migration by downregulating C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling

Gna12 has been identified as one of the reported inflammatory bowel disease (IBD) susceptibility genes in genome-wide association studies (GWAS). However, the function of GNA12 in intestinal homeostasis remains unknown. Here we report that GNA12, a G-protein α subunit, regulates C5a-induced migration in macrophages. Deficiency of GNA12 results in enhanced migration induced by C5a in macrophages. Mechanistically, GNA12 suppresses C5a-induced migration by downregulating the C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling. Therefore, our study reveals that GNA12 is an anti-inflammatory factor, which might alleviate the development of inflammation by inhibiting the excessive chemotactic migration of macrophages.

Reduced Mrp2 surface availability as PI3Kγ-mediated hepatocytic dysfunction reflecting a hallmark of cholestasis in sepsis

Sepsis-associated liver dysfunction manifesting as cholestasis is common during multiple organ failure. Three hepatocytic dysfunctions are considered as major hallmarks of cholestasis in sepsis: impairments of microvilli covering canalicular membranes, disruptions of tight junctions sealing bile-collecting canaliculae and disruptions of Mrp2-mediated hepatobiliary transport. PI3Kγ loss-of-function was suggested as beneficial in early sepsis. Yet, the PI3Kγ-regulated cellular processes in hepatocytes remained largely unclear. We analysed all three sepsis hallmarks for responsiveness to massive PI3K/Akt signalling and PI3Kγ loss-of-function, respectively. Surprisingly, neither microvilli nor tight junctions were strongly modulated, as shown by electron microscopical studies of mouse liver samples. Instead, quantitative electron microscopy proved that solely Mrp2 surface availability, i.e. the third hallmark, responded strongly to PI3K/Akt signalling. Mrp2 plasma membrane levels were massively reduced upon PI3K/Akt signalling. Importantly, Mrp2 levels at the plasma membrane of PI3Kγ KO hepatocytes remained unaffected upon PI3K/Akt signalling stimulation. The effect explicitly relied on PI3Kγ's enzymatic ability, as shown by PI3Kγ kinase-dead mice. Keeping the surface availability of the biliary transporter Mrp2 therefore is a cell biological process that may underlie the observation that PI3Kγ loss-of-function protects from hepatic excretory dysfunction during early sepsis and Mrp2 should thus take center stage in pharmacological interventions.

Regulation of platelet-activating factor-induced interleukin-8 expression by protein tyrosine phosphatase 1B

Background

Platelet-activating factor (PAF) is a potent lipid mediator whose involvement in the onset and progression of atherosclerosis is mediated by, among others, the modulation of cytokine expression patterns. The presence of multiple potential protein-tyrosine phosphatase (PTP) 1B substrates in PAF receptor signaling pathways brought us to investigate its involvement in PAF-induced cytokine expression in monocyte-derived dendritic cells (Mo-DCs) and to study the pathways involved in this modulation.

Methods

We used in-vitro-matured human dendritic cells and the HEK-293 cell line in our studies. PTP1B inhibition was though siRNAs and a selective inhibitor. Cytokine expression was studied with RT-PCR, luciferase assays and ELISA. Phosphorylation status of kinases and transcription factors was studied with western blotting.

Results

Here, we report that PTP1B was involved in the modulation of cytokine expression in PAF-stimulated Mo-DCs. A study of the down-regulation of PAF-induced IL-8 expression, by PTP1B, showed modulation of PAF-induced transactivation of the IL-8 promoter which was dependent on the presence of the C/EBPß -binding site. Results also suggested that PTP1B decreased PAF-induced IL-8 production by a glycogen synthase kinase (GSK)-3-dependent pathway via activation of the Src family kinases (SFK). These kinases activated an unidentified pathway at early stimulation times and the PI3K/Akt signaling pathway in a later phase. This change in GSK-3 activity decreased the C/EBPß phosphorylation levels of the threonine 235, a residue whose phosphorylation is known to increase C/EBPß transactivation potential, and consequently modified IL-8 expression.

Conclusion

The negative regulation of GSK-3 activity by PTP1B and the consequent decrease in phosphorylation of the C/EBPß transactivation domain could be an important negative feedback loop by which cells control their cytokine production after PAF stimulation.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0334-6) contains supplementary material, which is available to authorized users.

Protein Translation and Signaling in Human Eosinophils

We have recently reported that, unlike IL-5 and GM-CSF, IL-3 induces increased translation of a subset of mRNAs. In addition, we have demonstrated that Pin1 controls the activity of mRNA binding proteins, leading to enhanced mRNA stability, GM-CSF protein production and prolonged eosinophil (EOS) survival. In this review, discussion will include an overview of cap-dependent protein translation and its regulation by intracellular signaling pathways. We will address the more general process of mRNA post-transcriptional regulation, especially regarding mRNA binding proteins, which are critical effectors of protein translation. Furthermore, we will focus on (1) the roles of IL-3-driven sustained signaling on enhanced protein translation in EOS, (2) the mechanisms regulating mRNA binding proteins activity in EOS, and (3) the potential targeting of IL-3 signaling and the signaling leading to mRNA binding activity changes to identify therapeutic targets to treat EOS-associated diseases.

Integrated Cellular and Plasma Proteomics of Contrasting B-cell Cancers Reveals Common, Unique and Systemic Signatures

Approximately 800,000 leukemia and lymphoma cases are diagnosed worldwide each year. Burkitt's lymphoma (BL) and chronic lymphocytic leukemia (CLL) are examples of contrasting B-cell cancers; BL is a highly aggressive lymphoid tumor, frequently affecting children, whereas CLL typically presents as an indolent, slow-progressing leukemia affecting the elderly. The B-cell-specific overexpression of the myc and TCL1 oncogenes in mice induce spontaneous malignancies modeling BL and CLL, respectively. Quantitative mass spectrometry proteomics and isobaric labeling were employed to examine the biology underpinning contrasting Eμ-myc and Eμ-TCL1 B-cell tumors. Additionally, the plasma proteome was evaluated using subproteome enrichment to interrogate biomarker emergence and the systemic effects of tumor burden. Over 10,000 proteins were identified (q<0.01) of which 8270 cellular and 2095 plasma proteins were quantitatively profiled. A common B-cell tumor signature of 695 overexpressed proteins highlighted ribosome biogenesis, cell-cycle promotion and chromosome segregation. Eμ-myc tumors overexpressed several methylating enzymes and underexpressed many cytoskeletal components. Eμ-TCL1 tumors specifically overexpressed ER stress response proteins and signaling components in addition to both subunits of the interleukin-5 (IL5) receptor. IL5 treatment promoted Eμ-TCL1 tumor proliferation, suggesting an amplification of IL5-induced AKT signaling by TCL1. Tumor plasma contained a substantial tumor lysis signature, most prominent in Eμ-myc plasma, whereas Eμ-TCL1 plasma contained signatures of immune-response, inflammation and microenvironment interactions, with putative biomarkers in early-stage cancer. These findings provide a detailed characterization of contrasting B-cell tumor models, identifying common and specific tumor mechanisms. Integrated plasma proteomics allowed the dissection of a systemic response and a tumor lysis signature present in early- and late-stage cancers, respectively. Overall, this study suggests common B-cell cancer signatures exist and illustrates the potential of the further evaluation of B-cell cancer subtypes by integrative proteomics.

IL-5 induces suspended eosinophils to undergo unique global reorganization associated with priming

The experiments described herein define a unique program of polarization of suspended human eosinophils stimulated with IL-5 family cytokines. We found that eosinophil granules and the nucleus move in opposite directions to form, respectively, a granular compartment and the nucleopod, a specialized uropod occupied by the nucleus and covered with adhesion receptors, including P-selectin glycoprotein ligand-1, CD44, and activated αMβ2 integrin. Ligated IL-5 family receptors localize specifically at the tip of the nucleopod in proximity to downstream signaling partners Janus tyrosine kinase 2, signal transducer and activator of transcription-1 and -5, and extracellular signal-regulated kinase. Microscopy and effects of cytochalasin B and nocodazole indicate that remodeling of filamentous actin and reorientation of the microtubule network are required for eosinophil polarization and nucleopod formation. IL-5 induces persistent polarization and extracellular signal-regulated kinase redistribution that are associated with eosinophil priming, a robust response on subsequent stimulation with N-formyl-methionyl-leucyl-phenylalanine. Global reorganization of cytoskeleton, organelles, adhesion receptors, and signaling molecules likely facilitates vascular arrest, extravasation, migration, granule release, and survival of eosinophils entering inflamed tissues from the bloodstream.

Regulation of spontaneous eosinophil apoptosis-a neglected area of importance

Asthma is characterized by the accumulation of eosinophils in the airways in most phenotypes. Eosinophils are inflammatory cells that require an external survival-prolonging stimulus such as granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin (IL)-5, or IL-3 for survival. In their absence, eosinophils are programmed to die by spontaneous apoptosis in a few days. Eosinophil apoptosis can be accelerated by Fas ligation or by pharmacological agents such as glucocorticoids. Evidence exists for the relevance of these survival-prolonging and pro-apoptotic agents in the regulation of eosinophilic inflammation in inflamed airways. Much less is known about the physiological significance and mechanisms of spontaneous eosinophil apoptosis even though it forms the basis of regulation of eosinophil longevity by pathophysiological factors and pharmacological agents. This review concentrates on discussing the mechanisms of spontaneous eosinophil apoptosis compared to those of glucocorticoid- and Fas-induced apoptosis. We aim to answer the question whether the external apoptotic stimuli only augment the ongoing pathway of spontaneous apoptosis or truly activate a specific pathway.

STAT6 controls the number of regulatory T cells in vivo, thereby regulating allergic lung inflammation

STAT6 plays a central role in IL-4-mediated allergic responses. Several studies indicate that regulatory T cells (Tregs) can be modulated by IL-4 in vitro. We previously showed that STAT6(-/-) mice are highly resistant to allergic lung inflammation even when wild-type Th2 effectors were provided and that they have increased numbers of Tregs. However, the role of STAT6 in modulating Tregs in vivo during allergic lung inflammation has not been thoroughly investigated. To examine Treg and STAT6 interaction during allergic inflammation, STAT6(-/-), STAT6xRAG2(-/-), and RAG2(-/-) mice were subjected to OVA sensitization and challenge following adoptive transfer of OVA-specific, wild-type Th2 effectors with or without prior Treg depletion/inactivation, using anti-CD25 (PC61). As expected, STAT6(-/-) mice were highly resistant to airway inflammation and remodeling. In contrast, allergic lung inflammation was partially restored in STAT6(-/-) mice treated with PC61 to levels observed in STAT6xRAG2(-/-) mice. In some cases, STAT6xRAG2(-/-) mice were also given natural Tregs along with Th2 effectors. Adoptive transfer of natural Tregs caused a substantial reduction in bronchoalveolar lavage eosinophil composition and suppressed airway remodeling and T cell migration into the lung in STAT6xRAG2(-/-) mice to levels comparable to those in STAT6(-/-) mice. These results demonstrate the STAT6-dependent suppression of Tregs in vivo to promote allergic airway inflammation.

Interleukin-5 enhances the migration and invasion of bladder cancer cells via ERK1/2-mediated MMP-9/NF-κB/AP-1 pathway: involvement of the p21WAF1 expression

Inflammatory cytokines may be a critical component of epithelial cancer progression. We examined the role of interleukin (IL)-5 in the migration of bladder cancer cells. The expression of IL-5 and its receptor IL-5Rα was enhanced in patients with muscle invasive bladder cancers (MIBC), and then it was detected in bladder cancer cell lines 5637 and T-24. IL-5 increased migration and MMP-9 expression via activation of transcription factors NF-κB and AP-1, and induced activation of ERK1/2 and Jak-Stat signaling in both cells. Treatment with ERK1/2 inhibitor U0126 significantly inhibited induction of migration, MMP-9 expression, and activation of NF-κB and AP-1 in IL-5-treated cells. However, none of the Jak inhibitors affected the IL-5-induced migration of bladder cancer cells. Moreover, gene knockdown for IL-5Rα, using siRNA transfection, suppressed migration, ERK1/2 activation, MMP-9 expression, as well as the binding activation of NF-κB and AP-1 in IL-5-treated bladder cancer cells. Similar results were observed in βc siRNA (si-βc) transfected cells. Unexpectedly, IL-5 treatment resulted in significant induction of p21WAF1 in both cell lines. The p21WAF1-specific small interfering RNA inhibited IL-5-induced cell migration, ERK activity, MMP-9 expression, and activation of NF-κB and AP-1 in bladder cancer cells. The effects of IL-5-induced cell responses were confirmed by transfection of IL-5 gene, which demonstrated that p21WAF1 participates in the induction of cell migration, leading to an increase in ERK1/2-mediated MMP-9 expression through activation of NF-κB and AP-1 in IL-5-treated bladder cancer cells. These unexpected results provide a theoretical basis for the therapeutic targeting of IL-5 in bladder cancer.

Identification of pro-inflammatory cytokines associated with muscle invasive bladder cancer; the roles of IL-5, IL-20, and IL-28A

We used gene expression profiling to identify inflammatory cytokines that correlate with bladder cancer development. Gene expression profiles of the tissue samples were investigated using cDNA microarrays that contained 103 non-muscle invasive bladder cancers (NMIBC), 62 muscle invasive bladder cancers (MIBC), 58 samples of histologically normal-looking surrounding tissues, and 10 normal, healthy subjects who served as the control cohort for comparison. We grouped the data-sets according to biological characterizations and focused on immune response genes with at least 2-fold differential expression in MIBC vs. controls. The experimental data-set identified 36 immune-related genes that were significantly altered in MIBC samples. In addition, 10 genes were up-regulated and 26 genes were down-regulated in MIBC samples compared with the normal tissues. Among the 10 up-regulated molecules examined, the capacity for both wound-healing migration and invasion was enhanced in response to IL-5, IL-20, and IL-28A in bladder cancer cell lines (253J and EJ cells), compared with untreated cells. The expression levels of IL-5, IL-20, and IL-28A were increased in patients with MIBC. All 3 cytokines and their receptors were produced in bladder cancer cell lines, as determined by real-time PCR, immunoblot analysis and confocal immunofluorescence. Up-regulation of MMP-2 and MMP-9 was found after IL-5, IL-20, and IL-28A stimulation in both cell types. Moreover, an EMSA assay showed that treatment with IL-5, IL-20, and IL-28A induced activation of the transcription factors NF-κB and AP-1 that regulate the MMP-9 promoter. Finally, activation of MAPK and Jak-Stat signaling was observed after the addition of IL-5, IL-20, and IL-28A to bladder cancer cells. This study suggests the presence of specific inflammatory cytokine (IL-5, IL-20, and IL-28A)-mediated association in bladder cancer development. All 3 cytokines may be important new molecular targets for the modulation of migration and invasion in bladder cancer.

IL-4 engagement of the type I IL-4 receptor complex enhances mouse eosinophil migration to eotaxin-1 in vitro

Background

Previous work from our laboratory demonstrated that IL-4Rα expression on a myeloid cell type was responsible for enhancement of Th2-driven eosinophilic inflammation in a mouse model of allergic lung inflammation. Subsequently, we have shown that IL-4 signaling through type I IL-4 receptors on monocytes/macrophages strongly induced activation of the IRS-2 pathway and a subset of genes characteristic of alternatively activated macrophages. The direct effect(s) of IL-4 and IL-13 on mouse eosinophils are not clear. The goal of this study was determine the effect of IL-4 and IL-13 on mouse eosinophil function.

Methods

Standard Transwell chemotaxis assay was used to assay migration of mouse eosinophils and signal transduction was assessed by Western blotting.

Results

Here we determined that (i) mouse eosinophils express both type I and type II IL-4 receptors, (ii) in contrast to human eosinophils, mouse eosinophils do not chemotax to IL-4 or IL-13 although (iii) pre-treatment with IL-4 but not IL-13 enhanced migration to eotaxin-1. This IL-4-mediated enhancement was dependent on type I IL-4 receptor expression: γC-deficient eosinophils did not show enhancement of migratory capacity when pre-treated with IL-4. In addition, mouse eosinophils responded to IL-4 with the robust tyrosine phosphorylation of STAT6 and IRS-2, while IL-13-induced responses were considerably weaker.

Conclusions

The presence of IL-4 in combination with eotaxin-1 in the allergic inflammatory milieu could potentiate infiltration of eosinophils into the lungs. Therapies that block IL-4 and chemokine receptors on eosinophils might be more effective clinically in reducing eosinophilic lung inflammation.

C3b-induced eosinophil degranulation involves PI3-kinases and is inhibited by protein kinase C activity

Selective release of individual eosinophil granule proteins has been demonstrated in eosinophilic conditions and in vitro using different stimuli. The aim of this study was to investigate if selective release of eosinophil cationic protein (ECP), eosinophil protein X/eosinophil derived-neurotoxin (EPX/EDN) and eosinophil peroxidase (EPO) could be due to the involvement of different signal transduction pathways. Peripheral blood granulocytes from healthy donors were incubated with Wortmannin, LY294002, Genistein, Staurosporine, GÖ6976 or PD98059 prior to the induction of degranulation by C3b. The released amounts of ECP, EPO and EPX/EDN were determined by immunoassays, and related to the total cell content of respective protein. Wortmannin caused a significant, dose-dependent inhibition of all three granule proteins. LY294002 (10⁻⁶ M) also inhibited the release of all proteins. Genistein (10⁻⁶ M) inhibited the release of ECP, whereas the release of EPO was increased. However, there was a tendency towards similar concentration-dependent patterns of release of all three proteins. Staurosporine (10⁻⁷ M), GÖ6976 (10⁻⁶ M) and PD98059 (10⁻⁵ M) caused an increased release of the three proteins. PI3-kinases play an important role in the C3b-induced release of ECP, EPO and EPX/EDN, whereas protein kinase C seems to have inhibitory effects on C3b-induced degranulation.

Chemoattractant-induced signaling via the Ras-ERK and PI3K-Akt networks, along with leukotriene C4 release, is dependent on the tyrosine kinase Lyn in IL-5- and IL-3-primed human blood eosinophils

Human blood eosinophils exhibit a hyperactive phenotype in response to chemotactic factors after cell "priming" with IL-5 family cytokines. Earlier work has identified ERK1/2 as molecular markers for IL-5 priming, and in this article, we show that IL-3, a member of the IL-5 family, also augments fMLP-stimulated ERK1/2 phosphorylation in primary eosinophils. Besides ERK1/2, we also observed an enhancement of chemotactic factor-induced Akt phosphorylation after IL-5 priming of human blood eosinophils. Administration of a peptide antagonist that targets the Src family member Lyn before cytokine (IL-5/IL-3) priming of blood eosinophils inhibited the synergistic increase of fMLP-induced activation of Ras, ERK1/2 and Akt, as well as the release of the proinflammatory factor leukotriene C(4). In this study, we also examined a human eosinophil-like cell line HL-60 clone-15 and observed that these cells exhibited significant surface expression of IL-3Rs and GM-CSFRs, as well as ERK1/2 phosphorylation in response to the addition of IL-5 family cytokines or the chemotactic factors fMLP, CCL5, and CCL11. Consistent with the surface profile of IL-5 family receptors, HL-60 clone-15 recapitulated the enhanced fMLP-induced ERK1/2 phosphorylation observed in primary blood eosinophils after priming with IL-3/GM-CSF, and small interfering RNA-mediated knockdown of Lyn expression completely abolished the synergistic effects of IL-3 priming on fMLP-induced ERK1/2 phosphorylation. Altogether, our data demonstrate a central role for Lyn in the mechanisms of IL-5 family priming and suggest that Lyn contributes to the upregulation of the Ras-ERK1/2 and PI3K-Akt cascades, as well as the increased leukotriene C(4) release observed in response to fMLP in "primed" eosinophils.

The signaling mechanism of eosinophil activation

Eosinophils play an important role in certain aspects of asthma pathogenesis. This review focuses on the mechanism of activation of eosinophils by the growth factor interleukin-5 and the CC chemokine receptor-3. Interleukin-5 activates members of the Janus and Src family of kinases. The latter kinases are largely responsible for the generation of initial signaling events. CC chemokine receptor-3, in contrast, signals through heterotrimeric G-proteins. Subsequently, various signaling pathways are activated, which converge on four major pathways - the mitogen-activated protein kinase pathway, the phosphoinositide-3 kinase pathway, the calcium signaling pathway and the Janus-signal transducer and activator of transcription signaling pathway. The biologic consequences of many of these signaling pathways are also discussed.

Interleukin 5 in the link between the innate and acquired immune response

Interleukin-5 (IL-5) is an interdigitating homodimeric glycoprotein that is initially identified by its ability to support the in vitro growth and differentiation of mouse B cells and eosinophils. IL-5 transgenic mouse shows two predominant features, remarkable increase in B-1 cells resulting in enhanced serum antibody levels, predominantly IgM, IgA, and IgE classes and in expansion of eosinophil numbers in the blood and eosinophil infiltration into various tissues. Conversely, mice lacking a functional gene for IL-5 or IL-5 receptor alpha chain (IL-5Ralpha) display a number of developmental and functional impairments in B cells and eosinophils. IL-5 receptor (IL-5R) comprises alpha and betac chains. IL-5 specifically binds to IL-5Ralpha and induces the recruitment of betac to IL-5R. Although precise mechanisms on cell-lineage-specific IL-5Ralpha expression remain elusive, several transcription factors including Sp1, E12/E47, Oct-2, and c/EBPbeta have been shown to regulate its expression in B cells and eosinophils. JAK2 and JAK1 tyrosine kinase are constitutively associated with IL-5Ralpha and betac, respectively, and are activated by IL-5 stimulation. IL-5 activates at least three different signaling pathways including JAK2/STAT5 pathway, Btk pathway, and Ras/ERK pathway. IL-5 is one of key cytokines for mouse B cell differentiation in general, particularly for fate-determination of terminal B cell differentiation to antibody-secreting plasma cells. IL-5 critically regulates homeostatic proliferation and survival of and natural antibody production by B-1 cells, and enhances the AID and Blimp-1 expression in activated B-2 cells leading to induce mu to gamma1 class switch recombination and terminal differentiation to IgM- and IgG1-secreting plasma cells, respectively. In humans, major target cells of IL-5 are eosinophils. IL-5 appears to play important roles in pathogenesis of asthma, hypereosinophilic syndromes, and eosinophil-dependent inflammatory diseases. Clinical studies will provide a strong impetus for investigating the means of modulating IL-5 effects. We will discuss the role of IL-5 in the link between innate and acquired immune response, particularly emphasis of the molecular basis of IL-5-dependent B cell activation, allergen-induced chronic inflammation and hypereosinophilic syndromes on a novel target for therapy.

IL-5 and eosinophilia

While Interleukin-5 (IL-5) is initially identified by its ability to support the growth and differentiation of activated B cells, overexpression of IL-5 significantly increases eosinophil numbers and antibody levels predominantly from an expanded population of B-1 cells in vivo. Conversely, mice lacking a functional gene for IL-5 or IL-5 receptor alpha chain (IL-5Ralpha) display a number of developmental and functional impairments in B cell and eosinophil lineages. In addition to the JAK-STAT and Btk pathway, the Ras-extracellular signal-regulated kinase (ERK) signals are important for IL-5-dependent cell survival. IL-5 critically regulates expression of genes involved in cell survival, IgH switch recombination, maturation in B cells and genes required for growth, survival, and effector function of eosinophils. IL-5Ralpha expression in B cells, but not in eosinophils is regulated by Oct-2. Eosinophilia is associated with a wide variety of conditions, including asthma and atopic diseases, helminth infections, drug hypersensitivity, and neoplastic disorders. In humans, the biologic effects of IL-5 are best characterized for eosinophils. The Sprouty-related Ena/VASP homology 1-domain containing protein (Spred)-1 negatively controls eosinophil numbers and functions by modulating IL-5 signaling in allergic asthma. We will emphasize that IL-5 plays a pivotal role in the innate and acquired immune response and eosinophilia.

Inflammation and melanoma growth and metastasis: the role of platelet-activating factor (PAF) and its receptor

An inflammatory tumor microenvironment fosters tumor growth, angiogenesis and metastatic progression. Platelet-activating factor (PAF) is an inflammatory biolipid produced from membrane glycerophospholipids. Through the activity of its G-protein coupled receptor, PAF triggers a variety of pathological reactions including tumor neo-angiogenesis. Several groups have demonstrated that inhibiting PAF-PAF receptor pathway at the level of a ligand or receptor results in an effective inhibition of experimental tumor growth and metastasis. In particular, our group has recently demonstrated that PAF receptor antagonists can effectively inhibit the metastatic potential of human melanoma cells in nude mice. Furthermore, we showed that PAF stimulated the phosphorylation of CREB and ATF-1 in metastatic melanoma cells, which resulted in overexpression of MMP-2 and MT1-MMP. Our data indicate that PAF acts as a promoter of melanoma metastasis in vivo. Since only metastatic melanoma cells overexpress CREB/ATF-1, we propose that these cells are better equipped to respond to PAF within the tumor microenvironment when compared to their non-metastatic counterparts.

The role of the complement anaphylatoxins in the recruitment of eosinophils

Eosinophils are blood and tissue immune cells that participate in a diverse range of activities normally beneficial for the host defense, but in circumstances of untoward inflammatory conditions these cells can be responsible for pathological responses. Accordingly the transit of eosinophils from the blood to tissues is a subject of considerable importance in immunology. In this article we review how the complement anaphylatoxins, C3a and C5a bring about eosinophil extravasation. These mediators do not merely provide a chemotactic or haptotactic gradient but are responsible for orchestrating innumerable responses by other cells types, including of endothelial cells, mast cells, and basophils in order to create an environment that is conducive for eosinophil infiltration. C5a has the capacity to prime the endothelium directly to present P-selectin, and C5a stimulated generation of eosinophil hydrogen peroxide and other oxidants can cause additional upregulation of endothelial P-selectin and ICAM-1. Moreover, the anaphylatoxins have the ability to recruit mast cells and basophils and can stimulate these cells to release IL-4 and IL-13, which by augmenting endothelial VCAM-1, convey some selectivity for eosinophils. The anaphylatoxins also have the capability to evoke the release and activation of eosinophil MMP-9, which is employed by this cell type to digest its way past the subendothelial matrix. Finally, because C3a and C5a can stimulate the generation of nitric oxide along with the secretion of histamine and LTC4 from several cell types, the anaphylatoxins can bring about an increase in vascular permeability that facilitates eosinophil accumulation at sites of allergic inflammation.

Differential regulation of interleukin 5-stimulated signaling pathways by dynamin

Through the yeast two-hybrid screen we have identified dynamin-2 as a molecule that interacts with the alpha subunit of the interleukin (IL) 5 receptor. Dynamin-2 is a GTPase that is critical for endocytosis. We have shown that dynamin-2 interacts with the IL-5 receptor-associated tyrosine kinases, Lyn and JAK2, in eosinophils. Tyrosine phosphorylation of dynamin is markedly enhanced upon IL-5 stimulation. The inhibition of tyrosine kinases results in complete abolition of ligand-induced receptor endocytosis. Inhibition of dynamin by a dominant-negative mutant or by small interfering RNA results in enhancement of IL-5-stimulated ERK1/2 signaling and cell proliferation. In contrast, the absence of a functional dynamin does not affect STAT5 or AKT phosphorylation or cell survival. Thus, we have identified specific functions for dynamin in the IL-5 signaling pathway and demonstrated its role in receptor endocytosis and termination of the ERK1/2 signaling pathway.

Interleukin-3, -5, and granulocyte macrophage colony-stimulating factor induce adhesion and chemotaxis of human eosinophils via p38 mitogen-activated protein kinase and nuclear factor kappaB

Hematopoietic cytokines such as interleukin (IL)-3, IL-5, and granulocyte macrophage colony-stimulating factor (GM-CSF) play a fundamental role in eosinophil functions in allergic asthma. The intracellular signal transduction mechanisms of these cytokines regulating the activation of eosinophils have been potential therapeutic targets. We investigated the roles of p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappa-B (NF-kappaB) in IL-3, IL-5, and GM-CSF-induced adhesion, morphological changes, and subsequence transmigration of human eosinophils. IL-3, IL-5, and GM-CSF could augment the phosphorylation of p38 MAPK and nucleus translocation of NF-kappaB in eosinophils. cDNA expression arrays demonstrated that the gene expression levels of several adhesion molecules including intercellular adhesion molecule-1 (ICAM-1), alpha6, beta2 integrin (CD18), and CD44 were upregulated by these cytokines. Results from functional assays showed that adhesion of eosinophils onto airway epithelial cells was enhanced after IL-3 and IL-5 but not GM-CSF stimulation. These cytokines could markedly induce shape change and augment the transmigration of eosinophils. Moreover, administration of either p38 MAPK inhibitor, SB 203580, or proteasome inhibitor, N-cbz-Leu-Leu-leucinal (MG-132), could inhibit the cytokine-induced adhesion, shape change, and transmigration of eosinophils. Together, our findings suggest that IL-3, IL-5, and GM-CSF regulated the adhesion and chemotaxis of human eosinophils through shared signaling pathways involving both p38 MAPK and NF-kappaB. Our results therefore shed light on the further development of more effective agents for allergic and inflammatory diseases.

An anti-inflammatory role for a phosphoinositide 3-kinase inhibitor LY294002 in a mouse asthma model

Phosphoinositide 3-kinase (PI3K) exhibits broad functional effects in immune cells. We investigated the role of PI3K in allergic airway inflammation using LY294002, a specific PI3K inhibitor, in a mouse asthma model. BALB/c mice were sensitized and challenged with ovalbumin (OVA), and developed airway eosinophilia, mucus hypersecretion, elevation in cytokine levels, and airway hyperresponsiveness. Intratracheal administration of LY294002 significantly inhibited OVA-induced increases in total cell counts, eosinophil counts, and IL-5, IL-13, and eotaxin levels in bronchoalveolar lavage fluid. Histological studies show that LY294002 dramatically inhibited OVA-induced lung tissue eosinophilia and airway mucus production. In addition, LY294002 significantly suppressed OVA-induced airway hyperresponsiveness to inhaled methacholine. Western blot analysis of whole lung lysates shows that LY294002 markedly attenuated OVA-induced serine phosphorylation of Akt, a direct downstream substrate of PI3K. Taken together, our findings suggest that inhibition of PI3K signaling pathway can suppress T-helper type 2 (Th2) cytokine production, eosinophil infiltration, mucus production, and airway hyperresponsiveness in a mouse asthma model and may have therapeutic potential for the treatment of allergic airway inflammation.

Regulation of interleukin-5-induced beta2-integrin adhesion of human eosinophils by phosphoinositide 3-kinase

We examined the role of phosphoinositide 3-kinase (PI3K) in integrin-mediated eosinophil adhesion. Deltap85, a dominant-negative form of the class IA PI3K adaptor subunit, was fused to an HIV-TAT protein transduction domain (TAT-Deltap85). Recombinant TAT-Deltap85 inhibited interleukin (IL)-5-stimulated phosphorylation of protein kinase B, a downstream target of PI3K. beta(2)-Integrin-dependent adhesion caused by IL-5 to the plated intracellular adhesion molecule-1 surrogate, bovine serum albumin, was inhibited by TAT-Deltap85 in a concentration-dependent manner. Similarly, two PI3K inhibitors, wortmannin and LY294002, blocked eosinophil adhesion to plated bovine serum albumin. By contrast, beta(1)-integrin-mediated eosinophil adhesion to vascular cell adhesion moelcule-1 was not blocked by TAT-Deltap85, wortmannin, or LY294002. Rottlerin, a protein kinase C (PKC)-delta inhibitor, also blocked beta(2)-integrin adhesion of eosinophils caused by IL-5, whereas beta(1) adhesion to vascular cell adhesion molecule-1 was not affected. IL-5 caused translocation of PKCdelta from the cytosol to cell membrane; inhibition of PI3K by wortmannin blocked translocation of PKCdelta. Western blot analysis demonstrated that extracellular signal-regulated kinase phosphorylation, a critical intermediary in adhesion elicited by IL-5, was blocked by inhibition of either PI3K or PKC-delta. These data suggest that extracellular signal-regulated kinase-mediated adhesion of beta(2)-integrin caused by IL-5 is mediated in human eosinophils by a class IA PI3K through activation of a PKCdelta pathway.

Spred-1 negatively regulates allergen-induced airway eosinophilia and hyperresponsiveness

T helper 2 cytokines, including interleukin (IL)-4, IL-5, and IL-13, play a critical role in allergic asthma. These cytokines transmit signals through the Janus kinase/signal transducer and activator of transcription (STAT) and the Ras–extracellular signal-regulated kinase (ERK) signaling pathways. Although the suppressor of cytokine signaling (SOCS) family proteins have been shown to regulate the STAT pathway, the mechanism regulating the ERK pathway has not been clarified. The Sprouty-related Ena/VASP homology 1–domain-containing protein (Spred)-1 has recently been identified as a negative regulator of growth factor–mediated, Ras-dependent ERK activation. Here, using Spred-1–deficient mice, we demonstrated that Spred-1 negatively regulates allergen-induced airway eosinophilia and hyperresponsiveness, without affecting helper T cell differentiation. Biochemical assays indicate that Spred-1 suppresses IL-5–dependent cell proliferation and ERK activation. These data indicate that Spred-1 negatively controls eosinophil numbers and functions by modulating IL-5 signaling in allergic asthma.

Andrographolide acts through inhibition of ERK1/2 and Akt phosphorylation to suppress chemotactic migration

We now evaluated the anti-inflammatory mechanisms of andrographolide on complement 5a (C5a)-induced macrophage recruitment in vitro. Andrographolide concentration dependently inhibited cell migration toward C5a with an IC50 of 5.6+/-0.7 microM. With relatively specific kinase inhibitors (PD98059, SB203580, SP600125, wortmannin and LY294002, respectively) the results showed that extracellular signal-regulated kinase1/2 (ERK1/2), p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol-3-kinase (PI3K) were necessary for C5a-induced migration, whereas c-Jun N-terminal kinase (JNK) was nonessential. Andrographolide significantly attenuated C5a-stimulated phosphorylation of ERK1/2, and of its upstream activator, MAP kinase-ERK kinase (MEK1/2). C5a-activated ERK1/2 phosphorylation was 86+/-9% inhibited by 30 microM andrographolide. Under the same conditions, however, andrographolide failed to affect C5a-stimulated p38 MAPK and JNK phosphorylation. Andrographolide also strongly abolished C5a-stimulated Akt phosphorylation, a downstream target protein for PI3K. These results indicate that inhibition of cell migration by interfering with ERK1/2 and PI3K/Akt signal pathways may contribute to the anti-inflammatory activity of andrographolide.

C5a differentially stimulates the ERK1/2 and p38 MAPK phosphorylation through independent signaling pathways to induced chemotactic migration in RAW264.7 macrophages

We elucidate the roles of various protein kinases involved in complement 5a (C5a)-induced cell migration. Results showed that extracellular signal-regulated kinase1/2 (ERK1/2), p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol 3-kinase (P13K) were necessary for C5a-induced migration, whereas protein kinase C and c-Jun N-terminal kinase (JNK) were nonessential. C5a-induced migration was also suppresses by phospholipase C (PLC) inhibitor U73122 and pertussis toxin (PTX). We found that C5a-induced, time-dependent (1) ERK1/2 phosphorylation was markedly diminished by PTX, U73122, P13K inhibitors wortmannin and LY294002 and ERK1/2 inhibitor PD98059; (2) Akt phosphorylation was also attenuated by the above inhibitors except PD98059; (3) p38 MAPK phosphorylation was only affected by PTX. Furthermore, C5a also stimulated PLCbeta(2) membrane translocation in a time-dependent manner that occurred early prior to Akt phosphorylation and could be abolished only by PTX and U73122. These results suggest that C5a, through the activation of PTX-sensitive G protein, to differentially stimulate ERK1/2 and p38 MAPK phosphorylation and evoke cell migration. That is, ERK1/2 but not p38 MAPK phosphorylation is down stream of P13K/Akt and modulated by PLC. Additionally, beta(2) isoform may be one of the participates in C5a signal and acts more upstream of P13K/Akt.

Biochemical assessment of intracellular signal transduction pathways in eosinophils: implications for pharmacotherapy

Allergic asthma and allergic rhinitis are inflammatory diseases of the airway. Cytokines and chemokines produced by T helper (Th) type 2 cells (GM-CSF, IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13), eotaxin, transforming growth factor-beta, and IL-11 orchestrate most pathophysiological processes of the late-phase allergic reaction, including the recruitment, activation, and delayed apoptosis of eosinophils, as well as eosinophilic degranulation to release eosinophilic cationic protein, major basic protein, and eosinophil-derived neurotoxin. These processes are regulated through an extensive network of interactive intracellular signal transduction pathways that have been intensively investigated recently. Our present review updates the cytokine and chemokine-mediated signal transduction mechanisms including the RAS-RAF-mitogen-activated protein kinases, Janus kinases (signal transducers and activators of transcription), phosphatidylinositol 3-kinase, nuclear factor-kappa B, activator protein-1, GATA, and cyclic AMP-dependent pathways, and describes the roles of different signaling pathways in the regulation of eosinophil differentiation, recruitment, degranulation, and expression of adhesion molecules. We shall also discuss different biochemical methods for the assessment of various intracellular signal transduction molecules, and various antagonists of receptors, modulators, and inhibitors of intracellular signaling molecules, many of which are potential therapeutic agents for treating allergic diseases.

(S)-Albuterol activates pro-constrictory and pro-inflammatory pathways in human bronchial smooth muscle cells

BACKGROUND

Pro-constrictory and proinflammatory properties of (S)-albuterol have been widely reported both under in vivo and in vitro conditions. However, underlying mechanisms are unclear.

OBJECTIVE

We examined and compared the cellular effects of albuterol enantiomers on key intracellular molecules involved in constrictory and inflammatory pathways in human bronchial smooth muscle cells (hBSMCs).

METHODS

Primary hBSMCs were grown in culture and treated with various concentrations of albuterol enantiomers for various periods. Methacholine was used to stimulate cells. The expression and activity of Gs and Gi proteins, the intracellular free calcium concentration ([Ca2+]i), the activity of phosphatidylinositol 3'-OH-kinase (PI3) kinase, and the transcriptional nuclear factor kappaB (NF-kappaB) level were examined.

RESULTS

There was a significant increase in the expression and activity of Gialpha-1 protein and a decrease in the expression of Gs protein in hBSMCs after 8 hours of treatment with (S)-albuterol. These effects of (S)-albuterol were observed in a dose-dependent manner. Nonreceptor-mediated activation of adenylate cyclase by forskolin was attenuated with (S)-albuterol. Treatment of the cells for 24 hours with (S)-albuterol significantly increased [Ca2+]i on stimulation with methacholine. Interestingly, the effect of (R)-albuterol was opposite to that of (S)-albuterol. The effect of the racemic albuterol in some cases was similar to that of (S)-albuterol. (S)-Albuterol significantly activated both PI3 kinase and NF-kappaB in hBSMCs.

CONCLUSION

These studies demonstrated an (S)-albuterol-induced increase in the expression and activity of pro-constrictory pathways involving Gialpha-1 protein and [Ca2+]i and a decrease in the activity of the bronchodilatory pathway involving Gs proteins in hBSNMCs. Additionally, (S)-albuterol activated proinflammatory pathways involving PI3 kinase and NF-kappaB. Because (S)-albuterol metabolizes at least 10-fold slower than (R)-albuterol and has a longer elimination half-life, these cellular effects of (S)-albuterol might explain the detrimental effect seen with chronic administration of racemic albuterol in the treatment of airway diseases, such as bronchial asthma.

The signaling pathways of erythropoietin and interferon-gamma differ in preventing the apoptosis of mature erythroid progenitor cells

Interferon (IFN)-gamma is a survival factor for mature erythroid progenitor cells. To elucidate related survival mechanisms, we compared the role of phosphatidylinositol 3-kinase (PI3-kinase) in the survival signals of IFN-gamma and erythropoietin (EPO). Human erythroid colony-forming cells (ECFCs) purified from peripheral blood were used, and Ly294002 was used as a PI3-kinase inhibitor. Treating ECFCs with a high concentration of Ly294002 (50 micromol/L) in the presence of EPO and/or IFN-gamma reduced cell viability by inducing apoptosis. However, treating cells with a lower concentration of Ly294002 (10 micromol/L) did not affect the antiapoptotic function of IFN-gamma and abolished the antiapoptotic effect of EPO. Adding IFN-gamma or EPO induced Bcl-x expression in ECFCs, as determined by Western blotting, and expression was suppressed in the presence of Ly294002. We also examined the phosphorylation of the protein kinase Akt, the downstream target of PI3-kinase. EPO stimulation significantly increased the level of Akt phosphorylation, but IFN-gamma did not. These results suggest that IFN-gamma plays a role in preventing the apoptosis of erythroid progenitor cells by affecting Bcl-x expression, thereby reducing the disruption of the mitochondrial transmembrane potential via PI3-kinase pathways that are related to but distinct from the EPO pathway.

Singlet oxygen-induced activation of Akt/protein kinase B is independent of growth factor receptors

Singlet oxygen (1O2)-induced cytotoxicity is believed to be responsible for responses to photodynamic therapy and for apoptosis of T helper cells after UV-A treatment. Other cytotoxic oxidants, such as hydrogen peroxide and peroxynitrite have been shown to stimulate cell survival signaling pathways in addition to causing cell death. Both these oxidants stimulate the Akt/protein kinase B survival signaling pathway through activation of membrane tyrosine kinase growth factor receptors. We evaluated the ability of 1O2 to activate the Akt/protein kinase B pathway in NIH 3T3 cells and examined potential activation pathways. Exposure of fibroblasts to 1O2 elicited a strong and sustained phosphorylation of Akt, which occurred concurrently with phosphorylation of p38 kinase, a proapoptotic signal. Inhibition of phosphatidylinositol-3-OH kinase (PI3-K) completely blocked Akt phosphorylation. Significantly, cell death induced by 1O2 was enhanced by inhibition of PI3-K, suggesting that activation of Akt by 1O2 may contribute to fibroblast survival under this form of oxidative stress. 1O2 treatment did not induce phosphorylation of platelet-derived growth factor receptor (PDGFR) or activate SH-PTP2, a substrate of growth factor receptors, suggesting that PDGFR was not activated. In addition, specific inhibition of PDGFR did not affect Akt phosphorylation elicited by 1O2. Activation of neither focal adhesion kinase (FAK) nor Ras protein, both of which mediate responses to reactive oxygen species, appeared to be pathways for the 1O2-induced activation of the PI3-K-Akt survival pathway. Thus, activation of Akt by 1O2 is mediated by PI3-K and contributes to a survival response that counteracts cell death after 1O2-induced injury. However, unlike the response to other oxidants, activation of the PI3-K-Akt by 1O2 does not involve activation of growth factor receptors, FAK or Ras protein.

CXCR3-mediated chemotaxis of human T cells is regulated by a Gi- and phospholipase C-dependent pathway and not via activation of MEK/p44/p42 MAPK nor Akt/PI-3 kinase

The chemokines CXCL9, 10, and 11 exert their action via CXC chemokine receptor-3 (CXCR3), a receptor highly expressed on activated T cells. These interferon gamma (IFNgamma)-induced chemokines are thought to be crucial in directing activated T cells to sites of inflammation. As such, they play an important role in several chronic inflammatory diseases including ulcerative colitis, multiple sclerosis, artherosclerosis, and delayed-type hypersensitivity reactions of the skin. In this study, we first demonstrate that in COS-7 cells heterologously expressing CXCR3, CXCL11 is a potent activator of the pertussis toxin (PTX)-sensitive p44/p42 mitogen-activated protein kinase (MAPK) and Akt/phosphatidylinositol 3 kinase (PI3K) pathways. Next, we show that these signal transduction pathways are also operative and PTX sensitive in primary human T cells expressing CXCR3. Importantly, abrogation of these signaling cascades by specific inhibitors did not block the migration of T cells toward CXCR3 ligands, suggesting that MAPK and Akt activation is not crucial for CXCR3-mediated chemotaxis of T cells. Finally, we demonstrate that CXCR3-targeting chemokines control T-cell migration via PTX-sensitive, phospholipase C pathways and phosphatidylinositol kinases other than class I PI3Kgamma.

Inhibition of CCL11, CCL24, and CCL26-induced degranulation in HL-60 eosinophilic cells by specific inhibitors of MEK1/MEK2, p38 MAP kinase, and PI 3-kinase

Eosinophilic leukocytes are the cellular hallmark of allergic inflammation. Apart from being potent eosinophils chemoattractants, the eotaxins CCL11, CCL24 and CCL26 are capable of activating eosinophils to generate reactive oxygen species, lipid mediators of inflammation and degranulation of toxic granule proteins. Due to their central role in eosinophil trafficking and activation, understanding the signal transduction mechanism of the eotaxin-induced eosinophil effector functions may provide an innovative therapeutic strategy for eosinophil-associated diseases. Thus, these investigations were conducted to delineate signal transduction mechanisms of CCL11, CCL24 and CCL26-induced eosinophil peroxidase (EPO) degranulation following pretreatment of cells with or without a specific inhibitor of MEK1/MEK2 (U0126), inhibitor of p38 MAP kinase (SB203580) or a specific inhibitor of PI 3-kinase (LY294002). Results have shown that CCR3-mediated eotaxin-induced eosinophilic degranulation was concentration-dependently reduced by specific inhibitors of ERK1/ERK2, p38 MAP kinase and PI 3-kinase. However, the rank order of U0126 with respect to inhibition of chemokine-induced degranulation was CCL11 = CCL24 > CCL26. Potentiation of eotaxin-induced EPO degranulation by IL-5 was also seen. These investigations have not only confirmed the reported co-operativity between IL-5 and the eotaxins but also showed that the eosinophil-degranulating capabilities of the eotaxin CCL11, CCL24 and CCL26 is a consequence of activation of ERK1/ERK2, p38 MAP kinase and PI 3-kinase. Thus, these signaling molecules may provide the biochemical basis for mechanism-based therapy of allergic inflammatory diseases.

Human eosinophils are activated by cysteine proteases and release inflammatory mediators

BACKGROUND

Recent studies suggest that serine proteases are involved in various biological responses through activation of protease-activated receptors (PARs). However, the functions of other proteases, such as cysteine proteases, are poorly understood and need elucidation.

OBJECTIVE

We examined the effects of an authentic cysteine protease, papain, and a protease derived from the mite allergen, Der f 1, on functions of human eosinophils.

METHODS

Purified eosinophils were incubated with papain or Der f 1. Eosinophil activation was monitored by superoxide anion generation and by degranulation. Intracellular signaling pathways were investigated through use of pharmacologic approaches.

RESULTS

We found that papain potently induces human eosinophils to degranulate and to produce superoxide anion. A cysteine protease inhibitor, E-64, abolished the stimulatory effects of papain, which suggests that the protease activity of papain is necessary to trigger eosinophil responses. The eosinophil's response to papain was enhanced by IL-5 and mediated by activation of the phosphatidylinositol 3-kinase/Akt pathway. Interestingly, whereas a serine protease, trypsin, activated eosinophils through PAR2, the effects of papain were not inhibited by an antibody to PAR2, which suggests another novel mechanism for the eosinophils' response to cysteine proteases. It is likely that these observations are clinically important, because eosinophils were activated by a natural cysteine protease allergen, Der f 1, and released granule proteins.

CONCLUSION

Human eosinophils are probably equipped with machineries that recognize and respond to cysteine proteases, such as those found at allergic inflammation sites; the result is active release of proinflammatory mediators.

Identification of UNC119 as a novel activator of SRC-type tyrosine kinases

Lyn, an Src-type tyrosine kinase, is associated with the interleukin (IL)-5 receptor in eosinophils. The mechanism of its activation is unknown. Through yeast two-hybrid screening we have cloned and characterized a new signaling molecule, Unc119, that associates with IL-5Ralpha and Src family tyrosine kinases. Unc119 induces the catalytic activity of these kinases through interaction with Src homology 2 and 3 domains. IL-5 stimulation of eosinophils increases Unc119 association with Lyn and induces its catalytic activity. Lyn is important for eosinophil survival. Eosinophils that are transduced with Unc119 have increased Lyn activity and demonstrate prolonged survival in the absence of IL-5. Inhibition of Unc119 down-regulates eosinophil survival. To our knowledge Unc119 is the first receptor-associated activator of Src family tyrosine kinases.

A parallel signal-transduction pathway for eotaxin- and interleukin-5-induced eosinophil shape change

Interleukin-5 (IL-5) and eotaxin are the most important cytokines/chemokines responsible for regulating eosinophil locomotion and are known to play a co-operative role in the selective recruitment of eosinophils to inflamed tissues. Following exposure to chemoattractants, eosinophils undergo a series of events, including reorganization of actin filaments and subsequent rapid shape changes, culminating in chemotaxis. In this study we examined the signalling pathways for eosinophil shape change regulated by eotaxin and IL-5, primarily using a gated autofluorescence/forward-scatter assay. Eotaxin and IL-5 were able to elicit shape change with peaks at 10 and 60 min, respectively, and IL-5 triggered the shape change more efficiently than eotaxin. The pharmacological inhibitors of mitogen-activated protein kinase (MAP kinase) and p38 blocked both eotaxin- and IL-5-induced eosinophil shape change in a dose-dependent manner. In addition, depletion of intracellular Ca2+ and inhibition of protein kinase A (PKA) strongly reduced eosinophil shape change. In contrast, even when used at high concentrations, protein tyrosine kinase (PTK) inhibitors caused only a slight reduction in the ability to change shape. However, treatment with protein kinase C (PKC) inhibitors, such as GF109203X and staurosporine, resulted in a striking inhibition of eosinophil shape change by IL-5, but not eotaxin. Data from the inhibition of activation and chemotaxis of the extracellular signal-regulated kinases (ERK1/2) by the PKC inhibitors were also consistent with findings from the experiments on shape change. Collectively, two eosinophil-selective cytokines/chemokines probably regulate eosinophil shape change via a largely overlapping signalling pathway, with involvement of PKC restricted to the IL-5 signal alone.

MDA-7/IL-24: novel cancer growth suppressing and apoptosis inducing cytokine

The melanoma differentiation-associated gene-7 (mda-7) was cloned by subtraction hybridization as a molecule whose expression is elevated in terminally differentiated human melanoma cells. Current information based on structural and sequence homology, has led to the recognition of MDA-7 as an IL-10 family cytokine member and its renaming as IL-24. Northern blot analysis revealed mda-7/IL-24 expression in human tissues associated with the immune system such as spleen, thymus, peripheral blood leukocytes and normal melanocytes. The MDA-7/IL-24 mouse counterpart, FISP, appears to be a Th2-specific protein and the rat counterpart, C49A/MOB-5, is associated with wound healing and is also induced as a consequence of ras-transformation. A notable property of MDA-7/IL-24 is its ability to induce apoptosis in a large spectrum of human cancer derived cell lines, in mouse xenografts and upon intratumoral injection in human tumors (phase I clinical trials). Various aspects of this intriguing molecule including its cytokine and anti-tumoral effects are described and discussed.

Platelet-activating factor activates two distinct effector pathways in human eosinophils

In granulocytes, platelet-activating factor (PAF) shares many of its biological effects with other chemotactic factors, such as FMLP, complement fragments, and lipid mediators. Two unique effects are that PAF is relatively resistant to pertussis toxin (PTX) and that PAF activates the inflammatory functions of eosinophils more strongly than it activates those of neutrophils. To investigate the molecular mechanisms of the responses of eosinophils to PAF, we analyzed superoxide anion production by a chemiluminescence method that provides real-time kinetic data for the cellular responses. We found that PAF induced bimodal superoxide anion production in human eosinophils, consisting of an intense, but transient, first phase and a larger and sustained second phase. In contrast, PAF induced essentially a transient unimodal response in human neutrophils. The two phases of eosinophil response were mediated by distinct cellular mechanisms: the second phase was highly dependent on cellular adhesion and beta(2) integrins, but the first phase was independent of both adhesion and beta(2) integrins. The upstream signaling mechanisms were also different: the second phase was mediated by PTX-resistant G-protein(s) and through activation of phosphatidylinositol 3-kinase, while the first phase was mediated by PTX-sensitive G-protein(s). Furthermore, the second-phase response was approximately 100-fold more resistant to inhibition by a competitive PAF receptor antagonist than the first phase. Thus, eosinophils and neutrophils react differently to PAF, and PAF activates two separate and distinct effector pathways in human eosinophils. These two activation pathways may explain the eosinophils' strong and diverse biological responses to PAF.

Extracellular signal-regulated kinase mediates granulocyte-macrophage colony-stimulating factor messenger RNA stabilization in tumor necrosis factor-alpha plus fibronectin-activated peripheral blood eosinophils

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is critical for promoting the long-term survival of lung- or airway-based eosinophils. Previously, we have shown that fibronectin and tumor necrosis factor alpha induced autocrine production of GM-CSF that markedly enhanced eosinophil survival. Cytokine release was preceded by and dependent on messenger RNA (mRNA) stabilization. Here, we show that mitogen-activated protein kinase (MAPK) activation is responsible for GM-CSF mRNA stabilization in peripheral blood eosinophils (pbeos). Activation of extracellular signal-regulated kinase (ERK) but not p38 correlated with GM-CSF mRNA stability. Although ERK inhibition completely prevented GM-CSF mRNA stabilization, p38 inhibition had a partial effect. To establish which MAPK was crucial, we transduced pbeos with dominant-active TatMEK1(E) or TatMKK3b(E) proteins that selectively phosphorylate ERK or p38, respectively. These studies showed that ERK but not p38 was sufficient for GM-CSF mRNA stabilization. These data are in contradistinction to the c-Jun NH(2)-terminal kinase-mediated regulation of interleukin 2 and 3 mRNAs and suggest unique regulatory features for GM-CSF mRNA in eosinophils.

Translocation of the tetraspanin CD63 in association with human eosinophil mediator release

The tetraspanin CD63 (also known as LAMP-3) has been implicated in phagocytic and intracellular lysosome-phagosome fusion events. It is also present in eosinophils, with predominant expression on crystalloid granule membrane. However, its role in eosinophil function is obscure. We hypothesized that CD63 is associated with intracellular events involved in eosinophil activation and mediator release. We used a combination of confocal immunofluorescence microscopy, flow cytometry, and secretion assays, including beta-hexosaminidase, eosinophil peroxidase, and RANTES, to examine CD63 expression, intracellular localization, and its association with cell activation and mediator release. In resting eosinophils, CD63 immunoreactivity was localized to plasma and crystalloid granule membranes. In interferon-gamma (IFN-gamma)- or C5a/CB-stimulated cells (10 minutes), intracellular CD63 appeared to shift to the cell periphery and plasma membrane, while stimulation with a cocktail of interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor induced the appearance of discrete intracellular clusters of CD63 immunoreactivity. IFN-gamma induced mobilization of CD63 to the cell periphery, which coincided with selective mobilization of RANTES prior to its release, implying CD63 association with piecemeal degranulation. Agonist-induced CD63 mobilization and cell surface up-regulation was associated with beta-hexosaminidase, eosinophil peroxidase, and RANTES release. Dexamethasone as well as genistein (a broad-spectrum inhibitor of tyrosine kinases) inhibited agonist-induced intracellular mobilization of CD63 and RANTES together with cell surface up-regulation of CD63 and mediator release. This is the first report of an association between CD63 mobilization and agonist-induced selective mediator release, which may imply the involvement of CD63 in eosinophil activation and piecemeal degranulation.

JAKs, STATs and Src kinases in hematopoiesis

Hematopoiesis is the cumulative result of intricately regulated signal transduction cascades that are mediated by cytokines and their cognate receptors. Proper culmination of these diverse signaling pathways forms the basis for an orderly generation of different cell types and aberrations in these pathways is an underlying cause for diseases such as leukemias and other myeloproliferative and lymphoproliferative disorders. Over the past decade, downstream signal transduction events initiated upon cytokine/growth factor stimulation have been a major focus of basic and applied biomedical research. As a result, several key concepts have emerged allowing a better understanding of the complex signaling processes. A group of transcription factors, termed signal transducers and activators of transcription (STATs) appear to orchestrate the downstream events propagated by cytokine/growth factor interactions with their cognate receptors. Similarly, cytoplasmic Janus protein tyrosine kinases (JAKs) and Src family of kinases seem to play a critical role in diverse signal transduction pathways that govern cellular survival, proliferation, differentiation and apoptosis. Accumulating evidence suggests that STAT protein activation may be mediated by members of both JAK and Src family members following cytokine/growth factor stimulation. In addition, JAK kinases appear to be essential for the phosphorylation of the cytokine receptors which results in the creation of docking sites on the receptors for binding of SH2-containing proteins such as STATs, Src-kinases and other signaling intermediates. Cell and tissue-specificity of cytokine action appears to be determined by the nature of signal transduction pathways activated by cytokine/receptor interactions. The integration of these diverse signaling cues from active JAK kinases, members of the Src-family kinases and STAT proteins, leads to cell proliferation, cell survival and differentiation, the end-point of the cytokine/growth factor stimulus.

Intracellular signal transduction in eosinophils and its clinical significance

The incidence and prevalence of allergic diseases such as asthma and allergic rhinitis have recently been increasing worldwide. Eosinophils are the principal effector cells for the pathogenesis of allergic inflammation via the secretion of highly cytotoxic granular proteins including eosinophil cationic protein, major basic protein and eosinophil protein X. Blood and tissue eosinophilia is a common manifestation of late-phase allergic inflammation causing tissue damage. The development of eosinophilia correlates with the production of haematopoietic cytokines including interleukin (IL)-3. IL-5 and granulocyte macrophage colony stimulating factor (GM-CSF), and eosinophil-specific chemoattractant, eotaxin, from T-lymphocytes and the epithelium respectively. Elucidation of intracellular mechanisms that control the activation, apoptosis and recruitment of eosinophils to tissues is therefore fundamental in understanding these disease processes and provides targets for novel drug therapy. Over the past decade, there has been intensive investigation for the intracellular signal transduction regulating various biological functions of eosinophils and their roles in the pathogenesis of eosinophil-related diseases. This review will emphasize on the cytokine and chemokine-mediated signal transductions including the RAS-RAF-mitogen-activated protein kinases (MAPK), Janus kinases (JAK)-signal transducers and activators of transcription (STAT), phosphatidylinositol 3-kinase (PI3K) and nuclear factor-kappa B (NF-kappaB), and various antagonists of receptors and inhibitors of intracellular signaling molecules as potential therapeutic agents of allergic diseases.

Interleukin-15 inhibits spontaneous apoptosis in human eosinophils via autocrine production of granulocyte macrophage-colony stimulating factor and nuclear factor-kappaB activation

Prolonged eosinophil survival, i.e., reduced apoptosis, is implicated in the pathogenesis of chronic allergic inflammation. Here we demonstrate that interleukin (IL)-15, in the presence or absence of tumor necrosis factor (TNF)-alpha, reduces spontaneous apoptosis in freshly isolated human eosinophils. The prosurvival effect of IL-15 was abrogated by neutralizing antibody to granulocyte macrophage-colony stimulating factor (GM-CSF), although GM-CSF was not detected in conditioned media by ELISA. Additionally, the effect of IL-15 on spontaneous eosinophil apoptosis appeared to require nuclear factor-kappaB (NF-kappaB) activation based on evidence for NF-kappaB nuclear translocation and abrogation of the effect by the NF-kappaB inhibitor, Bay 11- 7082. Finally, the data demonstrate that IL-15 expression is higher in the submucosa of endobronchial tissues from subjects with moderate to severe asthma when compared with control subjects. Thus, our results suggest that IL-15, either alone or in combination with TNF-alpha, may perpetuate allergic inflammation by reduction of spontaneous eosinophil apoptosis through autocrine production of GM-CSF and NF-kappaB activation.

Lyn tyrosine kinase is important for IL-5-stimulated eosinophil differentiation

IL-5 plays a pivotal role in growth and differentiation of eosinophils. The signal transduction mechanism of IL-5Ralpha is largely unknown. We have demonstrated that IL-5 induces tyrosine phosphorylation of IL-5Ralpha in eosinophils. To identify IL-5Ralpha-associated tyrosine kinases, we have examined the expression of Src family tyrosine kinases in eosinophils. Among the Src family members, Lyn, Hck, Fgr, and Lck are present in eosinophils, and, among these four kinases, only Lyn is associated with the IL-5Ralpha under basal conditions. We also confirm the association of Janus kinase (Jak)2 with IL-5Ralpha. Lyn kinase phosphorylates both IL-5Ralpha and betacR in vitro. The importance of Lyn kinase for eosinophil differentiation was studied using antisense oligodeoxynucleotides. Lyn antisense oligodeoxynucleotide blocks eosinophil differentiation from stem cells in a dose-dependent manner. The Jak2 inhibitor tyrphostin AG490 also inhibits eosinophil differentiation. The importance of Lyn for eosinophil differentiation was further studied using Lyn knockout mice. The IL-5-stimulated eosinophil differentiation from bone marrow cells is significantly inhibited in Lyn(-/-) mice as compared with that in control mice. We conclude that both Lyn and Jak2 play an essential role in IL-5Ralpha signaling, leading to eosinophil differentiation. The effect of Lyn appears to be relatively specific for the eosinophilic lineage.

Pharmacological comparison of LTB(4)-induced NADPH oxidase activation in adherent and non-adherent guinea-pig eosinophils

1. Leukotriene B(4) (LTB(4)) stimulation of guinea-pig peritoneal eosinophils, induced a biphasic activation of the NADPH oxidase composed of a rapid (<3 min) phase mediated by non-adherent cells and a sustained (3 - 120 min) phase mediated by CD11b/CD18 adherent eosinophils. Studies were undertaken to compare the intracellular mechanism that mediate these responses. 2. SB 203580 and PP1, inhibitors of p38 mitogen-activated protein (MAP) kinase and the src-family protein tyrosine kinases, respectively caused concentration-dependent attenuation of both the rapid (SB203580: pD(2)=-6.31; PP1: pD(2)=-5.50) and sustained (SB203580: pD(2)=-6.50; PP1: pD(2)=-5.73) phases. Similarly, the MAP kinase kinase-1 inhibitor, PD098059 produced partial inhibition of the both phases of superoxide generation. 3. The protein kinase C (PKC) inhibitors Ro-31 8220, GF 109203X and Gö 6976 attenuated the rapid NADPH oxidase response (pD(2)s=-6.10, -6.72, -6.15 respectively) and, to a lesser extent, (pD(2)s=-5.54, -6.02, -6.51 respectively) the sustained phase. 4. An inhibitor of phosphatidylinositol 3-kinase (PtdIns 3-kinase), wortmannin caused concentration dependent attenuation of the sustained (pD(2)=-8.68) but not rapid phase of superoxide generation. In contrast, the syk kinase inhibitor, piceatannol abolished the rapid (pD(2)=-6.43) but not sustained respiratory responses. 5. This study demonstrates that LTB(4)-induced superoxide generation from adherent and non-adherent eosinophils is mediated via both common (p38 MAP kinase, MEK-1, PKC and the src kinases) and divergent intracellular pathways (syk kinases and PtdIns 3-kinase). This suggests the possibility of therapeutic intervention to selective attenuate activation of adherent tissue eosinophils.

Transduction of a dominant-negative H-Ras into human eosinophils attenuates extracellular signal-regulated kinase activation and interleukin-5-mediated cell viability

Inhibition of eosinophil apoptosis by exposure to interleukin-5 (IL-5) is associated with the development of tissue eosinophilia and may contribute to the inflammation characteristic of asthma. Analysis of the signaling events associated with this process has been hampered by the inability to efficiently manipulate eosinophils by the introduction of active or inhibitory effector molecules. Evidence is provided, using a dominant-negative N17 H-Ras protein (dn-H-Ras) and MEK inhibitor U0126, that activation of the Ras-Raf-MEK-ERK pathway plays a determining role in the prolongation of eosinophil survival by IL-5. For these studies, a small region of the human immunodeficiency virus Tat protein, a protein transduction domain known to enter mammalian cells efficiently, was fused to the N-terminus of dn-H-Ras. The Tat-dn-H-Ras protein generated from this construct transduced isolated human blood eosinophils at more than 95% efficiency. When Tat-dn-H-Ras-transduced eosinophils were treated with IL-5, they exhibited a time- and dosage-dependent reduction in extracellular regulated kinase 1 and 2 activation and an inhibition of p90 Rsk1 phosphorylation and IL-5-mediated eosinophil survival in vitro. In contrast, Tat-dn-H-Ras did not inhibit CD11b up-regulation or STAT5 tyrosine phosphorylation. These data demonstrate that Tat dominant-negative protein transduction can serve as an important and novel tool in studying primary myeloid cell signal transduction in primary leukocytes and can implicate the Ras-Raf-MEK-ERK pathway in IL-5-initiated eosinophil survival.