Interleukin 5 signals through Shc and Grb2 in human eosinophils

The Impact of CC16 on Pulmonary Epithelial-Driven Host Responses during Mycoplasma pneumoniae Infection in Mouse Tracheal Epithelial Cells

Club Cell Secretory Protein (CC16) plays many protective roles within the lung; however, the complete biological functions, especially regarding the pulmonary epithelium during infection, remain undefined. We have previously shown that CC16-deficient (CC16-/-) mouse tracheal epithelial cells (MTECs) have enhanced Mp burden compared to CC16-sufficient (WT) MTECs; therefore, in this study, we wanted to further define how the pulmonary epithelium responds to infection in the context of CC16 deficiency. Using mass spectrometry and quantitative proteomics to analyze proteins secreted apically from MTECs grown at an air-liquid interface, we investigated the protective effects that CC16 elicits within the pulmonary epithelium during Mycoplasma pneumoniae (Mp) infection. When challenged with Mp, WT MTECs have an overall reduction in apical protein secretion, whereas CC16-/- MTECs have increased apical protein secretion compared to their unchallenged controls. Following Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) assessment, many of the proteins upregulated from CC16-/- MTECS (unchallenged and during Mp infection) were related to airway remodeling, which were not observed by WT MTECs. These findings suggest that CC16 may be important in providing protection within the pulmonary epithelium during respiratory infection with Mp, which is the major causative agent of community-acquired pneumoniae.

An integrated analysis of hypoxic-ischemic encephalopathy-related cell sequencing outcomes via genes network construction

Hypoxic-ischemic encephalopathy (HIE) is one of the main causes of morbidity and severe neurological deficits in neonates. This study aimed to find core genes and their potential roles in HIE with the help of single-cell sequencing (SCS) technology and genes network construction. We collected and screened an HIE genes data set from the Pubmed database to analyze differential expression, and the differential values of genes were ≥3 or ≤-3 in gene expression. We constructed a protein-protein interaction (PPI) network by the string, which was also verified by Cytoscape 3.8.2. Functional enrichment analysis was performed to determine the characteristics and pathways of the core genes. We examined two meaningful papers and integrated all genes by SCS, which were classified into 12,093 genes without duplicates, 217 shared genes, and 11,876 distinct genes. Among 217 genes, the signal transducer and activator of transcription (STAT) family was the most targeted gene in the PPI network. Moreover, Gene Ontology and Kyoto encyclopedia of genes and genome analysis showed that the process in response to virus and the JAK-STAT signaling pathway play significant roles in HIE. We also found that 54 screened genes were highly expressed, while three genes (B2M, VIM, and MRPS30) were different in the heat map and differential genes expression exhibition. VIM, as an essential portion of the brain's cytoskeleton, is closely linked to STAT and neurologic development. From the findings of SCS and bioinformatics predictive analytics model, our outcomes provided a better understanding of the roles of STAT, the JAK-STAT signaling pathway, and VIM, which can pave an alternative avenue for further studies on HIE progression.

Apoptosis of Eosinophil Granulocytes

Simple Summary

Eosinophil granulocytes (eosinophils) belong to the family of white blood cells that play important roles in the development of asthma and various types of allergy. Eosinophils are cells with a diameter of 12–17 µm and they originate from myeloid precursors. They were discovered by Paul Ehrlich in 1879 in the process of staining fixed blood smears with aniline dyes. Apoptosis (programmed cell death) is the process by which cells lose their functionality. Therefore, it is very important to study the apoptosis of eosinophils and their survival factors to understand how to develop new drugs based on the modulation of eosinophil apoptosis for the treatment of asthma and allergic diseases.

Abstract

In the past 10 years, the number of people in the Czech Republic with allergies has doubled to over three million. Allergic pollen catarrh, constitutional dermatitis and asthma are the allergic disorders most often diagnosed. Genuine food allergies today affect 6–8% of nursing infants, 3–5% of small children, and 2–4% of adults. These disorders are connected with eosinophil granulocytes and their apoptosis. Eosinophil granulocytes are postmitotic leukocytes containing a number of histotoxic substances that contribute to the initiation and continuation of allergic inflammatory reactions. Eosinophilia results from the disruption of the standard half-life of eosinophils by the expression of mechanisms that block the apoptosis of eosinophils, leading to the development of chronic inflammation. Glucocorticoids are used as a strong acting anti-inflammatory medicine in the treatment of hypereosinophilia. The removal of eosinophils by the mechanism of apoptosis is the effect of this process. This work sums up the contemporary knowledge concerning the apoptosis of eosinophils, its role in the aforementioned disorders, and the indications for the use of glucocorticoids in their related therapies.

Liquid crystal droplet-based amplification of microvesicles that are shed by mammalian cells

Membrane-derived microvesicles (MVs) shed by cells are being investigated for their role in intercellular communication and as potential biomarkers of disease, but facile and sensitive methods for their analysis do not exist. Here we demonstrate new principles for analysis of MVs that use micrometer-sized droplets of liquid crystals (LCs) to amplify MVs that are selectively captured via antibody-mediated interactions. The influence of the MVs on the micrometer-sized LC droplets is shown to be readily quantified via use of flow cytometry. The methodology was developed using MVs shed by epidermoid carcinoma A431 cells that contain epidermal growth factor receptor (EGFR) as an important and representative example of MVs containing signaling proteins that play a central role in cancer. The LC droplets were found to be sensitive to 10(6) MVs containing EGFR (relative to controls using isotype control antibody) and to possess a dynamic range of response across several orders of magnitude. Because the 100 nm-sized MVs captured via EGFR generate an optical response in the micrometer-sized LC droplets that can be readily detected by flow cytometry in light scattering mode, the approach possesses significant advantages over direct detection of MVs by flow cytometry. The LC droplets are also substantially more sensitive than techniques such as immunoblotting because the lipid-component of the MVs serves to amplify the antibody-mediated capture of the target proteins in the MVs. Other merits of the approach are defined and discussed in the paper.

Human airway eosinophils exhibit preferential reduction in STAT signaling capacity and increased CISH expression

Allergic asthma, a chronic respiratory disorder marked by inflammation and recurrent airflow obstruction, is associated with elevated levels of IL-5 family cytokines and elevated numbers of eosinophils (EOS). IL-5 family cytokines elongate peripheral blood EOS (EOS(PB)) viability, recruit EOS(PB) to the airways, and, at higher concentrations, induce degranulation and reactive oxygen species generation. Although airway EOS (EOS(A)) remain signal ready in that GM-CSF treatment induces degranulation, treatment of EOS(A) with IL-5 family cytokines no longer confers a survival advantage. Because the IL-5 family receptors have common signaling capacity, but are uncoupled from EOS(A) survival, whereas other IL-5 family induced endpoints remain functional, we tested the hypothesis that EOS(A) possess a JAK/STAT-specific regulatory mechanism (because JAK/STAT signaling is critical to EOS survival). We found that IL-5 family-induced STAT3 and STAT5 phosphorylation is attenuated in EOS(A) relative to blood EOS from airway allergen-challenged donors. However, IL-5 family-induced ERK1/2 phosphorylation is not altered between EOS(A) and EOS from airway allergen-challenged donors. These observations suggest EOS(A) possess a regulatory mechanism for suppressing STAT signaling distinct from ERK1/2 activation. Furthermore, we found, in EOS(PB), IL-5 family cytokines induce members of the suppressors of cytokine signaling (SOCS) genes, CISH and SOCS1. Additionally, following allergen challenge, EOS(A) express significantly more CISH and SOCS1 mRNA and CISH protein than EOS(PB) counterparts. In EOS(PB), long-term pretreatment with IL-5 family cytokines, to varying degrees, attenuates IL-5 family-induced STAT5 phosphorylation. These data support a model in which IL-5 family cytokines trigger a selective downregulation mechanism in EOS(A) for JAK/STAT pathways.

Identification of SRC as a potent drug target for asthma, using an integrative approach of protein interactome analysis and in silico drug discovery

Network-biology inspired modeling of interactome data and computational chemistry have the potential to revolutionize drug discovery by complementing conventional methods. We consider asthma, a complex disease characterized by intricate molecular mechanisms, for our study. We aim to integrate prediction of potent drug targets using graph-theoretical methods and subsequent identification of small molecules capable of modulating activity of the best target. In this work, we construct the protein interactome underlying this disease: Asthma Protein Interactome (API). Using a strategy based on network analysis of the interactome, we identify a set of potential drug targets for asthma. Topologically and dynamically, v-src sarcoma (Schmidt-Ruppin A-2) viral oncogene homolog (SRC) emerges as the most central target in API. SRC is known to play an important role in promoting airway smooth muscle cell growth and facilitating migration in airway remodeling. From interactome analysis, and with the reported role in respiratory mechanisms, SRC emerges as a promising drug target for asthma. Further, we proceed to identify leads for SRC from a public database of small molecules. We predict two potential leads for SRC using ligand-based virtual screening methodology.

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.

The PTB domain of ShcA couples receptor activation to the cytoskeletal regulator IQGAP1

Adaptor proteins respond to stimuli and recruit downstream complexes using interactions conferred by associated protein domains and linear motifs. The ShcA adaptor contains two phosphotyrosine recognition modules responsible for binding activated receptors, resulting in the subsequent recruitment of Grb2 and activation of Ras/MAPK. However, there is evidence that Grb2-independent signalling from ShcA has an important role in development. Using mass spectrometry, we identified the multidomain scaffold IQGAP1 as a ShcA-interacting protein. IQGAP1 and ShcA co-precipitate and are co-recruited to membrane ruffles induced by activated receptors of the ErbB family, and a reduction in ShcA protein levels inhibits the formation of lamellipodia. We used NMR to characterize a direct, non-canonical ShcA PTB domain interaction with a helical fragment from the IQGAP1 N-terminal region that is pTyr-independent. This interaction is mutually exclusive with binding to a more conventional PTB domain peptide ligand from PTP-PEST. ShcA-mediated recruitment of IQGAP1 may have an important role in cytoskeletal reorganization downstream of activated receptors at the cell surface.

Screening of proteins that interact with human thrombopoietin receptor c-Mpl using yeast two-hybrid system

Thrombopoietin (TPO) is the major cytokine involved in platelet production and exerts its effects via the receptor c-Mpl. The yeast two-hybrid system has been used to screen the proteins interacting with c-Mpl. First, the cDNA fragment of c-Mpl intracellular domain was cloned into two-hybrid vector pAS2, and the resulting plasmid is designated as pASMM. Then a human placenta cDNA library was screened using the pASMM as a target plasmid. Seven positive clones were isolated from 150 000 independent transformants. Sequence analysis of one of the positive clones demonstrates that a part of coding sequence of vimentin from 611 bp to 3' end and flanking non-translation region was obtained. Therefore, there is an interaction between vimentin and TPO receptor. The results suggest that cytoskeletal protein may play an important role in TPO signal transduction pathway.

Separate endocytic pathways regulate IL-5 receptor internalization and signaling

Eosinophils are critically dependent on IL-5 for their activation, differentiation, survival, and augmentation of cytotoxic activity. We previously showed that the cytoplasmic domain of the hematopoietic receptor, betac, which is shared by IL-5, IL-3, and GM-CSF, is directly ubiquitinated and degraded by the proteasomes in a JAK2-dependent manner. However, studies describing the spatial distribution, endocytic regulation, and trafficking of betac-sharing receptors in human eosinophils are currently lacking. Using deconvolution microscopy and biochemical methods, we clearly demonstrate that IL-5Rs reside in and are internalized by clathrin- and lipid raft-dependent endocytic pathways. Microscopy analyses in TF1 cells and human eosinophils revealed significant colocalization of betac, IL-5Ralpha, and Cy3-labeled IL-5 with transferrin- (clathrin) and cholera toxin-B- (lipid raft) positive vesicles. Moreover, whereas internalized IL-5Rs were detected in both clathrin- and lipid raft-positive vesicles, biochemical data revealed that tyrosine phosphorylated, ubiquitinated, and proteasome-degraded IL-5Rs partitioned to the soluble, nonraft fractions (clathrin-containing). Lastly, we show that optimal IL-5-induced signaling requires entry of activated IL-5Rs into the intracellular compartment, as coimmunoprecipitation of key signaling molecules with the IL-5R was completely blocked when either endocytic pathway was inhibited. These data provide the first evidence that IL-5Rs segregate and traffic into two distinct plasma membrane compartments, and they further establish that IL-5R endocytosis regulates signaling both positively and negatively.

A protein interaction network associated with asthma

Identifying candidate genes related to complex diseases or traits and mapping their relationships require a system-level analysis at a cellular scale. The objective of the present study is to systematically analyze the complex effects of interrelated genes and provide a framework for revealing their relationships in association with a specific disease (asthma in this case). We observed that protein-protein interaction (PPI) networks associated with asthma have a power-law connectivity distribution as many other biological networks have. The hub nodes and skeleton substructure of the result network are consistent with the prior knowledge about asthma pathways, and also suggest unknown candidate target genes associated with asthma, including GNB2L1, BRCA1, CBL, and VAV1. In particular, GNB2L1 appears to play a very important role in the asthma network through frequent interactions with key proteins in cellular signaling. This network-based approach represents an alternative method for analyzing the complex effects of candidate genes associated with complex diseases and suggesting a list of gene drug targets. The full list of genes and the analysis details are available in the following online supplementary materials: http://biosoft.kaist.ac.kr:8080/resources/asthma_ppi.

Generation of Th1 and Th2 chemokines by human eosinophils: evidence for a critical role of TNF-alpha

Emerging evidence suggests a role for eosinophils in immune regulation of T cells. Thus, we sought to determine whether human eosinophils may exert their effect via differential generation of Th1 and Th2 chemokines depending on cytokines in their microenvironment and, if so, to establish the conditions under which these chemokines are produced. Eosinophils cultured with TNF-alpha plus IL-4 had increased mRNA expression and protein secretion of the Th2-type chemokines, CCL17 (thymus and activation-regulated chemokine) and CCL22 (macrophage-derived chemokine). Conversely, the Th1-type chemokines, CXCL9 (monokine induced by IFN-gamma) and CXCL10 (IFN-gamma-inducible protein-10), were expressed after stimulation with TNF-alpha plus IFN-gamma. Addition of TNF-alpha appeared to be essential for IFN-gamma-induced release of Th1-type chemokines and significantly enhanced IL-4-induced Th2-type chemokines. Inhibition of NF-kappaB completely blocked the production of both Th1 and Th2 chemokines. Activation of NF-kappaB, STAT6, and STAT1 was induced in eosinophils by TNF-alpha, IL-4, and IFN-gamma, respectively. However, there was no evidence for enhancement of these signaling events when eosinophils were stimulated with the combination of TNF-alpha plus IL-4 or TNF-alpha plus IFN-gamma. Thus, independently activated signaling cascades appear to lead to activation of NF-kappaB, STAT1, and STAT6, which may then cooperate at the promoter level to increase gene transcription. Our data demonstrate that TNF-alpha is a vital component for eosinophil chemokine generation and that, depending on the cytokines present in their microenvironment, eosinophils can promote either a Th2 or a Th1 immune response, supporting an immunoregulatory role for eosinophils.

Screening for PTB domain binding partners and ligand specificity using proteome-derived NPXY peptide arrays

Modular interaction domains that recognize peptide motifs in target proteins can impart selectivity in signaling pathways. Phosphotyrosine binding (PTB) domains are components of cytoplasmic docking proteins that bind cell surface receptors through NPXY motifs. We have employed a library of human proteome-derived NXXY sequences to explore PTB domain specificity and function. SPOTS peptide arrays were used to create a comprehensive matrix of receptor motifs that were probed with a set of 10 diverse PTB domains. This approach confirmed that individual PTB domains have selective and distinct recognition properties and provided a means to explore over 2,500 potential PTB domain-NXXY interactions. The results correlated well with previously known associations between full-length proteins and predicted novel interactions, as well as consensus binding data for specific PTB domains. Using the Ret, MuSK, and ErbB2 receptor tyrosine kinases, we show that interactions of these receptors with PTB domains predicted to bind by the NXXY arrays do occur in cells. Proteome-based peptide arrays can therefore identify networks of receptor interactions with scaffold proteins that may be physiologically relevant.

IL-5 and granulocyte-macrophage colony-stimulating factor activate STAT3 and STAT5 and promote Pim-1 and cyclin D3 protein expression in human eosinophils

Allergic inflammation is characterized by elevated eosinophil numbers and by the increased production of the cytokines IL-5 and GM-CSF, which control several eosinophil functions, including the suppression of apoptosis. The JAK/STAT pathway is important for several functions in hemopoietic cells, including the suppression of apoptosis. We report in this study that STAT3, STAT5a, and STAT5b are expressed in human eosinophils and that their signaling pathways are active following IL-5 or GM-CSF treatment. However, in airway eosinophils, the phosphorylation of STAT5 by IL-5 is reduced, an event that may be related to the reduced expression of the IL-5Ralpha on airway eosinophils. Furthermore, IL-5 and GM-CSF induced the protein expression of cyclin D3 and the kinase Pim-1, both of which are regulated by STAT-dependent processes in some cell systems. Pim-1 is more abundantly expressed in airway eosinophils than in blood eosinophils. Because Pim-1 reportedly has a role in the modulation of apoptosis, these results suggest that Pim-1 action is linked to the suppression of eosinophil apoptosis by these cytokines. Although cyclin D3 is known to be critical for cell cycle progression, eosinophils are terminally differentiated cells that do not proceed through the cell cycle. Thus, this apparent cytokine regulation of cyclin D3 suggests that there is an alternative role(s) for cyclin D3 in eosinophil biology.

Tyrosine kinase inhibitors: a new approach for asthma

The pathogenesis of allergic asthma involves the interplay of inflammatory cells and airway-resident cells, and of their secreted mediators including cytokines, chemokines, growth factors and inflammatory mediators. Receptor tyrosine kinases are important for the pathogenesis of airway remodeling. Activation of epidermal growth factor (EGF) receptor kinase and platelet-derived growth factor (PDGF) receptor kinase leads to hyperplasia of airway smooth muscle cells, epithelial cells and goblet cells. Stimulation of non-receptor tyrosine kinases (e.g. Lyn, Lck, Syk, ZAP-70, Fyn, Btk, Itk) is the earliest detectable signaling response upon antigen-induced immunoreceptor activation in inflammatory cells. Cytokine receptor dimerization upon ligand stimulation induces activation of Janus tyrosine kinases (JAKs), leading to recruitment and phosphorylation of signal transducer and activator of transcription (STAT) for selective gene expression regulation. Activation of chemokine receptors can trigger JAK-STAT pathway, Lck, Fyn, Lyn, Fgr, and Syk/Zap-70 to induce chemotaxis of inflammatory cells. Inhibitors of tyrosine kinases have been shown in vitro to block growth factor-induced hyperplasia of airway-resident cells; antigen-induced inflammatory cell activation and cytokine synthesis; cytokine-mediated pro-inflammatory gene expression in inflammatory and airway cells; and chemokine-induced chemotaxis of inflammatory cells. Recently, anti-inflammatory effects of tyrosine kinase inhibitors (e.g. genistein, tyrphostin AG213, piceatannol, tyrphostin AG490, WHI-P97, WHI-P131, Syk antisense) in animal models of allergic asthma have been reported. Therefore, development of inhibitors of tyrosine kinases can be a very attractive strategy for the treatment of asthma.

Expression of interleukin-5- and granulocyte macrophage-colony-stimulating factor-responsive genes in blood and airway eosinophils

Because interleukin (IL)-5 family cytokines are critical regulators of eosinophil development, recruitment, and activation, this study was initiated to identify proteins induced by these cytokines in eosinophils. Using oligonucleotide microarrays, numerous transcripts were identified as responsive to both IL-5 and granulocyte macrophage-colony-stimulating factor (GM-CSF), but no transcripts were markedly affected by one cytokine and not the other. Expression of several gene products were seen to be increased following in vitro stimulation of human blood eosinophils, including the IL-3 receptor alpha subunit, lymphotoxin beta, Pim-1, and cyclin D3. Given that eosinophils recovered from the bronchoalveolar lavage fluid of allergic patients after antigen challenge are exposed to IL-5 or GM-CSF in the airway prior to isolation, the hypothesis was tested that selected IL-5- and GM-CSF-responsive genes are upregulated in airway eosinophils relative to the expression in blood cells. Airway eosinophils displayed greater cell surface expression of the IL-3 receptor alpha subunit, CD44, CD25, and CD66e, suggesting that these proteins may be markers of eosinophil activation by IL-5 family cytokines in airway eosinophils. Other genes that were induced by both IL-5 and GM-CSF showed protein expression at similar or decreased levels in airway eosinophils relative to their circulating counterparts (i.e., lymphotoxin beta and CD24). These studies have identified several transcriptional targets of IL-5 and GM-CSF in human eosinophils and suggest that a number of protein products are critical to the responsiveness of airway eosinophils.

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.

Role of tyrosine kinases and the tyrosine phosphatase SptP in the interaction of Salmonella with host cells

Salmonella has evolved an intimate functional interface with its host. Central to this interface is a battery of bacterial proteins delivered into host cells via a specialized organelle termed the type III secretion system. A subset of these bacterial proteins stimulates cellular responses by activating the Rho family GTPases Cdc42 and Rac. Stimulation of these responses leads to actin cytoskeleton reorganization and the activation of cellular transcription factors that result in bacterial uptake and proinflammatory cytokine production. Remarkably, the cellular responses stimulated by Salmonella are quickly reversed by another bacterial protein, SptP, which exerts its function as a GTPase-activating protein (GAP) for Cdc42 and Rac. In addition to its GAP activity located within its amino-terminus, the carboxy-terminal domain of SptP possesses potent tyrosine phosphatase activity. We show here that the tyrosine phosphatase activity of SptP is involved in reversing the MAP kinase activation that results from Salmonella infection. We also demonstrate an important role for tyrosine kinases, including ACK, in the cellular responses induced by Salmonella. We also found that a potential target for the tyrosine phosphatase activity of SptP is the intermediate filament protein vimentin, which is recruited to the membrane ruffles stimulated by Salmonella.

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.

Interleukin-5: a novel target for asthma therapy

Eosinophilic airway inflammation is the main histologic correlate of airway hyper-responsiveness (AHR) and tissue injury in the pathogenesis of bronchial asthma. There is strong evidence for a central role of CD4+ T-cells secreting pro-allergic Th2-cytokines, such as IL-4 and IL-5, in the induction of airway eosinophilia and AHR. IL-5 appears to be one of the main pro-inflammatory mediators among a growing number of cytokines and chemokines that induce, regulate and sustain eosinophilic airway inflammation. Animal studies provide confirmatory evidence for the important role of IL-5 in the induction and maintenance of eosinophilic airway infiltration leading to altered airway function. Interfering with the action of IL-5 represents one of the new immunomodulatory therapeutic strategies in the treatment of bronchial asthma. Compared to established immunosuppressive agents like steroids, a major advantage of this strategy is the specificity of reducing eosinophilic inflammation, thus possibly acting nearly without side effects. There are several possible ways to inhibit the effects of IL-5 including alteration of the signalling pathway in the IL-5 producing cell by inhibition or modification of transcription factors or the use of antisense oligonucleotides and blocking of the IL-5 protein itself by monoclonal antibodies, soluble IL-5 receptor or antagonists of the IL-5 receptor expressed on the surface of eosinophils. Although preliminary data from the first clinical trials gave rise to skepticism about the efficacy of anti-IL-5 treatment regarding the improvement of lung function of asthmatic patients, further studies with a better defined profile of the target population may provide encouraging results, allowing the introduction of this truly new therapeutic concept.

Granulocyte macrophage colony-stimulating factor and interleukin-5 activate STAT5 and induce CIS1 mRNA in human peripheral blood eosinophils

In these studies, we examined signaling through the transcription factor STAT5 in human peripheral blood eosinophils after treatment with granulocyte macrophage colony-stimulating factor (GM-CSF) or interleukin (IL)-5. In response to either cytokine, STAT5 was rapidly tyrosine phosphorylated and acquired interferon gamma activation site (GAS) DNA binding activity. Tyrosine-phosphorylated STAT5 was associated with both cytosolic and nuclear cell fractions. Consistent with activation, the transcription of a STAT5-dependent gene, cytokine inducible, SH2-containing protein (CIS1), was enhanced after cytokine stimulation. This is the first report of IL-5 regulation of CIS1 gene expression in any cell type. Given its role in cytokine signaling, CIS1 upregulation may serve to attenuate IL-5 and GM-CSF modulation of eosinophil function. These data suggest that active nuclear STAT5 participates in the regulation of IL-5 and GM-CSF--inducible genes in stimulated human peripheral blood eosinophils.

Matrix assisted laser desorption/ionization-time of flight-mass spectrometry analysis of proteins detected by anti-phosphotyrosine antibody on two-dimensional-gels of fibrolast cell lysates after tumor necrosis factor-alpha stimulation

We describe efficient methods for using functional proteomics analysis to study signal transduction pathways in murine fibroblast L929 cells following stimulation with tumor necrosis factor (TNF)-alpha. After stimulation with TNF-alpha, cellular proteins of L929 cells were extracted with a lysis buffer containing 0.3% sodium dodecyl sulfate (SDS) for 10-30 min time intervals, and were separated by two-dimensional (2-D) electrophoresis followed by immunoblot analysis with anti-phosphotyrosine antibody and alkaline phosphatase-anti IgG antibody conjugate. To improve detection sensitivity by immunoblot analysis we used a chemifluorescent substrate for alkaline phosphatase. One hundred protein spots were detected in the TNF-alpha stimulated L929 cell extract by immunoblot analysis. The use of chemifluorescence allowed us to quantitate immunoblotted spots with fluoroscanner so that we were able to detect time-dependent changes of a number of immunoblotted spots. Protein spots on a silver-stained 2-D gel corresponding to those detected by immunoblot analysis were subjected to in-gel trypsin digestion- matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-mass spectrometry analysis, respectively. Twenty-one proteins detected by immunoblot analysis were identified by MS-Fit database search analysis. Among them, the proteins that show time-dependent changes in staining intensity include vimentin, tubulin beta-chain, eukaryotic translation initiation factor 1A, chromatin assembly factor 1 (P48 subunit), probable protein disulfide isomerase P5, and several other proteins. Vimentin and tubulin beta-chain have been reported to be phosphorylated at tyrosine residues and involved in the signal transduction pathway induced by TNF-alpha. However, the other proteins have no previously known function in the signal transduction pathway. Thus, the methods used in this study seem to be suitable for the identification of time-dependent changes in many proteins that are involved in signal transduction. Usefulness of the method for comprehensive analysis of the proteins involved in signal transduction pathway and the limitations of the method are discussed.

ERK1 and ERK2 activation by chemotactic factors in human eosinophils is interleukin 5-dependent and contributes to leukotriene C(4) biosynthesis

Eosinophils, the major immune effector cells contributing to allergic inflammation and asthma, are profoundly affected by interleukin (IL) 5 with respect to their differentiation, viability, recruitment, and cytotoxic effector functions. IL-5 enhances eosinophil responsiveness to a variety of chemotactic factors via a process called priming, although the molecular mechanism is unknown. In this study, we report that, following IL-5 priming of eosinophils, chemotactic agents including fMet-Leu-Phe, IL-8, and RANTES, promote vigorous transient activation of ERK1 and ERK2. In contrast, these chemotactic factors stimulate weak or indiscernible ERK activation in unprimed eosinophils. Furthermore, this intracellular marker of priming is selective for IL-5-related cytokines, in that it is observed following exposure to IL-5 and granulocyte macrophage-colony stimulating factor but not to interferon-gamma, stem cell factor, tumor necrosis factor alpha, or IL-4. Interestingly, priming of chemoattractant-induced ERK activation is accompanied by an increase in association of tyrosine-phosphorylated proteins with the adapter protein Grb2. The biological relevance of ERK activation to IL-5 priming is supported by the observation that inhibition of ERK activity by treatment with the MEK inhibitors PD98059 or U0126 inhibited the release of leukotriene C(4) stimulated by fMet-Leu-Phe in IL-5-primed eosinophils. These data provide evidence for a previously undescribed fundamental mechanism by which stimulation of IL-5 family receptors induces a rapid phenotypic alteration in the signal transduction pathways of chemotactic receptors, enabling their activation of the ERK1 and ERK2 pathway and contributing to the capacity of these cells to synthesize LTC(4).

Epidermal growth factor-stimulated tyrosine phosphorylation of caveolin-1. Enhanced caveolin-1 tyrosine phosphorylation following aberrant epidermal growth factor receptor status

Caveolin-1 is the major coat protein of caveolae and has been reported to interact with various intracellular signaling molecules including the epidermal growth factor (EGF) receptor. To investigate the involvement of caveolin-1 in EGF receptor action, we used mouse B82L fibroblasts transfected with (a) wild type EGF receptor, (b) a C-terminally truncated EGF receptor at residue 1022, (c) a C-terminally truncated EGF receptor at residue 973, or (d) a kinase-inactive EGF receptor (K721M). Following EGF treatment, there was a distinct electrophoretic mobility shift of the caveolin-1 present in cells expressing the truncated forms of the EGF receptor, but this shift was not detectable in cells bearing either normal levels of the wild type EGF receptor or a kinase-inactive receptor. This mobility shift was also not observed following the addition of other cell stimuli, such as platelet-derived growth factor, insulin, basic fibroblast growth factor, or phorbol 12-myristate 13-acetate. Analysis of caveolin-1 immunoprecipitates from EGF-stimulated or nonstimulated cells demonstrated that the EGF-induced mobility shift of caveolin-1 was associated with its tyrosine phosphorylation in cells expressing truncated EGF receptors. Maximal caveolin-1 phosphorylation was achieved within 5 min after exposure to 10 nM EGF and remained elevated for at least 2 h. Additionally, several distinct phosphotyrosine-containing proteins (60, 45, 29, 24, and 20 kDa) were co-immunoprecipitated with caveolin-1 in an EGF-dependent manner. Furthermore, the Src family kinase inhibitor, PP1, does not affect autophosphorylation of the receptor, but it does inhibit the EGF-induced mobility shift and phosphorylation of caveolin-1. Conversely, the MEK inhibitors PD98059 and UO126 could attenuate EGF-induced mitogen-activated protein kinase activation, they do not affect the EGF-induced mobility shift of caveolin-1. Because truncation and overexpression of the EGF receptor have been linked to cell transformation, these results provide the first evidence that the tyrosine phosphorylation of caveolin-1 occurs via an EGF-sensitive signaling pathway that can be potentiated by an aberrant activity or expression of various forms of the EGF receptor.

Advances in the immunobiology of eosinophils and their role in disease

Eosinophils play a protective role in host immunity to infections by parasitic worms and, detrimentally, are involved in the pathophysiology of asthma and other allergic diseases. Airway inflammation is central to the pathology of asthma and is characterized by infiltration of the bronchial mucosa by large numbers of proinflammatory cells, amongst which the eosinophil is prominent despite being a minority constituent of circulating leukocytes. Crucial steps in eosinophilic inflammation include augmented production of eosinophils in the bone marrow, their increased release into the circulation, and their selective accumulation in the conducting airways. The eosinophil has a potent armory of proinflammatory mediators, including cytotoxic granule proteins, cytokines and lipid mediators with considerable potential to initiate and sustain an inflammatory response. Thus there is much interest in the elucidation of the mechanisms responsible for eosinophil accumulation, persistence, activation and ultimate fate. This article reviews our current understanding of the role of the eosinophil in human disease and the immunobiology of this important proinflammatory cell.

Inhibition of T cell apoptosis by IFN-beta rapidly reverses nuclear translocation of protein kinase C-delta

Type I interferons rescue activated human T cells from cytokine deprivation-induced apoptosis. Our data now show that IFN-beta also rapidly inhibits apoptotic signals induced through the Fas receptor (CD95) in human T cells. To identify upstream signaling elements that could be targets of IFN-beta, we have studied protein kinase C (PKC). PKC-delta is actively involved in the regulation of apoptosis and immunofluorescence staining revealed that early in apoptosis PKC-delta accumulated in the nucleus. Addition of IFN-beta to T cells already deprived of survival factors or treated with anti-Fas antibody caused a rapid retranslocation of PKC-delta away from the nucleus. Furthermore, the generation of a constitutively active catalytic fragment by cleavage of PKC-delta by caspase 3 occurred only after translocation of full-length PKC-delta to the nucleus. IFN-beta also inhibited caspase 3 and the proteolytic activation of PKC-delta. We conclude from these studies that nuclear translocation of PKC-delta is an early event in T cell apoptosis and that IFN-beta rapidly reverses this process.

Interleukin-5 and the regulation of eosinophil production

Eosinophils play important roles in adaptive immune responses, inflammatory processes, and disease states. Recently, considerable research has been devoted to better defining the normal and abnormal biology of these cells, specifically their origin and mechanisms of stimulation, chemotaxis, regulation, and activation. Interleukin-5 has been identified as a major regulator of eosinophil development and function. This review highlights current literature on interleukin-5 and eosinophil production. Areas covered include molecular signaling, physiologic sources of interleukin-5, and interactions between interleukin-5, eosinophils, and the bone marrow microenvironment. Clinical correlates are also presented.

Biology of IL-5 in health and disease

LEARNING OBJECTIVES

Reading this article will increase the readers' knowledge of the biology of interleukin-5 (IL-5), an important cytokine. The immune and inflammatory responses of any organism are the basis of the defense mechanism ensuring its survival. The role of IL-5 in these processes, as well as in the pathogenesis of various diseases has been discussed along with the effects of various pharmacologic agents on the production and function of IL-5.

DATA SOURCES

A detailed literature search was performed. Studies considered relevant and important, in all languages, which involved humans and animals were used.

STUDY SELECTION

Information was obtained only from peer reviewed journals.

RESULTS

Interleukin-5 is normally produced by T-cells, mast cells, and eosinophils while Reed Sternberg and Epstein Barr virus (EBV) transformed cells also produce IL-5. Monoclonal antibodies (mAb) to IL-5 are potent inhibitors of IL-5 mediated tissue damage, secondary to eosinophil infiltration. The majority of the studies on IL-5 are preliminary, often the information is obtained from animal studies or in vitro systems and occasionally from pathologic tissue analysis. This along with the absence of confirmatory studies is a limiting factor. Nonetheless, the role of IL-5 in allergic and immunologic disease and asthma may be central to their pathogenesis.

CONCLUSIONS

Interleukin-5 is an important molecule that is participant to many processes that maintain health and are involved directly or indirectly in the pathogenesis of disease. Some pharmacologic agents can modify IL-5 production in vivo. Development of selective inhibitors of IL-5 may have a potential use for specific therapy of certain autoimmune, inflammatory, and neoplastic diseases.

The gene structure of the human growth factor bound protein GRB2

The growth factor bound protein GRB2, a 25-kDa cytosolic protein, plays a key role in two separate pathways of the insulin signal transduction system leading from the insulin receptor to the Ras proteins and thus affecting mitogenic signaling. GRB2 regulates Ras activation through association with the guanine nucleotide exchange factor Sos. The GRB2/Sos complex can connect with insulin receptor substrate 1 (IRS-1), which is one of the primary targets of the insulin and insulin-like growth factor receptors. In a second pathway, independent of IRS-1, GRB2 links the insulin receptor to Ras signaling through another adapter protein, called Shc. In protooncogenic and other noninsulin signaling systems, GRB2 appears to link receptor tyrosine kinases to Ras in similar pathways as well. This study presents the exon-intron organization of the human GRB2 gene. After primers were placed across the known mRNA sequence, Long PCR products spanning introns and their adjacent splice sites were amplified and adequately sequenced to establish the splice sites and flanking regions. The gene was found to consist of five exons (ranging from 78 to 186 bp) and of four introns (from approximately 1 to approximately 7 kb). Intron primers for the respective exons were generated using the newly found flanking sequences. All exons were successfully amplified and sequenced, and the data obtained from Long PCR sequencing were confirmed.

Activation of Vav and Ras through the nerve growth factor and B cell receptors by different kinases

Engagement of the B-cell antigen receptor (BCR) or the nerve growth factor receptor (NGFR/TrkA) induces activation of multiple tyrosine kinases, resulting in phosphorylation of numerous intracellular substrates. We show that addition of NGF or anti-IgM antibody leads to the early tyrosine phosphorylation of p95(vav), which is expressed exclusively in hematopoietic cells; NGF, similar to crosslinking the BCR, also results in the rapid activation of Ras. The phosphorylation of Vav and activation of Ras triggered by NGF is mediated through Trk tyrosine kinase, whereas signaling through the BCR uses a different tyrosine kinase. We also show that NGF induces tyrosine phosphorylation of Shc and its association with Grb2. Vav and Ras with the adaptor proteins Shc and Grb2 appear to serve as a link between different receptor-mediated signaling pathways and, in human B cells, may play an important regulatory role in neuroimmune interactions.

Activation of the Jak-STAT-signaling pathway in embryonic lens cells

Previous studies showed that lens epithelial cells proliferate rapidly in the embryo and that a lens mitogen, most likely derived from the blood, is present in the anterior chamber of the embryonic eye (Hyatt, G. A., and Beebe, D. C., Development 117, 701-709, 1993). Messenger RNAs for several growth factor receptors have been identified in embryonic lens epithelial cells. We tested several growth factors that are ligands for these receptors for their ability to maintain lens cell proliferation. Embryo serum, PDGF, GM-CSF, and G-CSF maintained lens cell proliferation, but NGF, VEGF, and HGF did not. This and a previous study (Potts, J. D., Harocopos, G. J., and Beebe, D. C., Curr. Eye Res. 12, 759-763, 1993) detected members of the Janus kinase family (Jaks) in the developing lens. Because Jaks are central players in the Jak-STAT-signaling pathway, we identified STAT proteins in the lens and tested whether they were phosphorylated in response to mitogens. STAT1 and STAT3, but not STAT 5 were detected in chicken embryo lens epithelial cells. Only STAT3 was found in terminally differentiated lens fiber cells. STAT1 and STAT3 were phosphorylated in lens cells analyzed immediately after removal from the embryo and when lens epithelial explants were treated with embryo serum, PDGF, or GM-CSF, but not with NGF. Chicken embryo vitreous humor or IGF-1, factors that stimulate lens cell differentiation, but not proliferation, did not cause STAT phosphorylation. When lens epithelial cells were cultured for 4 h in unsupplemented medium, STAT1 and STAT3 declined to nearly undetectable levels. Treatment with PDGF or embryo serum for an additional 15 min restored STAT1 and -3 levels. This recovery was blocked by cycloheximide, but not actinomycin D, suggesting that STAT levels are regulated at the level of translation. STAT levels were maintained in epithelial explants by lens mitogens, but not by factors that stimulated lens fiber differentiation. Both factors that stimulated lens cell proliferation and those that caused fiber differentiation protected cultured lens epithelial cells from apoptosis. These data suggest that the factor(s) responsible for lens cell proliferation in vivo activates the Jak-STAT-signaling pathway. They also indicate that growth factors maintain STAT protein levels in lens epithelial cells by promoting the translation of STAT mRNA, an aspect of STAT regulation that has not been described previously. Signaling by most of the growth factors and cytokines known to activate the Jak-STAT pathway has been disrupted in mice by mutation or targeted deletion. Consideration of the phenotypes of these mice suggests that the factor responsible for lens cell proliferation in vivo may be a growth factor or cytokine that has not yet been described.

The mechanism of IL-5 signal transduction

Cytokines are important regulators of hematopoiesis. They exert their actions by binding to specific receptors on the cell surface. Interleukin-5 (IL-5) is a critical cytokine that regulates the growth, activation, and survival of eosinophils. Because eosinophils play a seminal role in the pathogenesis of asthma and allergic diseases, an understanding of the signal transduction mechanism of IL-5 is of paramount importance. The IL-5 receptor is a heterodimer of alpha- and beta-subunits. The alpha-subunit is specific, whereas the beta-subunit is common to IL-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF) receptors and is crucial for signal transduction. It has been shown that there are two major signaling pathways of IL-5 in eosinophils. IL-5 activates Lyn, Syk, and JAK2 and propagates signals through the Ras-MAPK and JAK-STAT pathways. Studies suggest that Lyn, Syk, and JAK2 tyrosine kinases and SHP-2 tyrosine phosphatase are important for eosinophil survival. In contrast to their survival-promoting activity, Lyn and JAK2 appear to have no role in eosinophil degranulation or expression of surface adhesion molecules. Raf-1 kinase, on the other hand, is critical for eosinophil degranulation and adhesion molecule expression. Btk is involved in IL-5 stimulation of B cell function. However, it does not appear to be important for eosinophil function. Thus a clear segregation of signaling molecules based on their functional importance is emerging. This review describes the signal transduction mechanism of the IL-3/GM-CSF/IL-5 receptor system and compares and contrasts IL-5 signaling between eosinophils and B cells.