Requirement of Lyn and Syk tyrosine kinases for the prevention of apoptosis by cytokines in human eosinophils

Protein kinase A inhibitors reverse histamine-mediated regulation of IL-5 secretion

Histamine and IL-5 are important autacoid mediators involved in the etiology of allergic diseases. IL-5 is the main factor of eosinophilic reactions in allergy. It has been suggested that the protein kinase A-dependent (PKA) pathway of signal transduction may play the main role in histamine-induced elevation of interleukin-5 production. This study was designed to investigate the effects of the inhibitors of regulatory and catalytic subunits of PKA on histamine-mediated elevation of IL-5 production. In our study, histamine at a concentration range of 10(-4)-10(-6) M enhanced IL-5 production in D10.G4.1 cells, a mouse Th2 helper cell line. Pretreatment of this cell line with histamine at a concentration of 10(-4) M for 6-9 h had the maximum stimulatory effects (226-420%) on IL-5 production. Other cAMP-elevating agents including forskolin and Bt2-cAMP produced similar effects. The PKA inhibitors N-[2-(methylaminoethyl]-5-isoquinoline-sulfonamide (H-8) and Rp-diastereomer of adenosine cyclic 3',5'-phosphorothioate (Rp-cAMPS) were used for the inhibition of catalytic and regulatory subunits of PKA, respectively. Pretreatment of D10.G4.1 cells with H-8 at a concentration of 10(-5) M completely prevented the effects of histamine at a concentration range of 10(-6)-10(-4) M. Rp-cAMPS at 10(-5) M also prevented histamine-induced stimulation. Neither inhibitor affected IL-5 production when tested alone. These observations suggest a role for PKA in histamine-mediated increase in IL-5 production.

Disruption of fas receptor signaling by nitric oxide in eosinophils

It has been suggested that Fas ligand-Fas receptor interactions are involved in the regulation of eosinophil apoptosis and that dysfunctions in this system could contribute to the accumulation of these cells in allergic and asthmatic diseases. Here, we demonstrate that nitric oxide (NO) specifically prevents Fas receptor-mediated apoptosis in freshly isolated human eosinophils. In contrast, rapid acceleration of eosinophil apoptosis by activation of the Fas receptor occurs in the presence of eosinophil hematopoietins. Analysis of the intracellular mechanisms revealed that NO disrupts Fas receptor-mediated signaling events at the level of, or proximal to, Jun kinase (JNK), but distal to sphingomyelinase (SMase) activation and ceramide generation. In addition, activation of SMase occurs downstream of an interleukin 1 converting enzyme-like (ICE-like) protease(s) that is not blocked by NO. However, NO prevents activation of a protease that targets lamin B1. These findings suggest a role for an additional NO-sensitive apoptotic signaling pathway that amplifies the proteolytic cascade initialized by activation of the Fas receptor. Therefore, NO concentrations within allergic inflammatory sites may be important in determining whether an eosinophil survives or undergoes apoptosis upon Fas ligand stimulation.

Cellular functions regulated by Src family kinases

Src family protein tyrosine kinases are activated following engagement of many different classes of cellular receptors and participate in signaling pathways that control a diverse spectrum of receptor-induced biological activities. While several of these kinases have evolved to play distinct roles in specific receptor pathways, there is considerable redundancy in the functions of these kinases, both with respect to the receptor pathways that activate these kinases and the downstream effectors that mediate their biological activities. This chapter reviews the evidence implicating Src family kinases in specific receptor pathways and describes the mechanisms leading to their activation, the targets that interact with these kinases, and the biological events that they regulate.

Anti-apoptotic signals of granulocyte-macrophage colony-stimulating factor are transduced via Jak2 tyrosine kinase in eosinophils

Cytokine-mediated inhibition of eosinophil apoptosis is a mechanism causing tissue eosinophilia. Previously published work suggested that activation of the Lyn-Ras-Raf-1-MAP kinase pathway is obligatory for prevention of eosinophil apoptosis by eosinophil hematopoietins. We demonstrate herein that activation of freshly isolated human blood eosinophils by granulocyte-macrophage colony-stimulating factor (GM-CSF) is associated with increased tyrosine phosphorylation of Jak2. The tyrosine kinase blocker, tyrphostin B42, prevented activation of Jak2 but not Lyn, suggesting that Jak2 is the specific target for tyrphostin B42 in eosinophils. In addition, since Lyn remained unaffected by tyrphostin B42, it is unlikely that Jak2 is required for Lyn activation in this model. To test whether tyrosine phosphorylation of Jak2 is linked to GM-CSF-mediated prolonged eosinophil survival, we determined the effect of tyrphostin B42 on eosinophil viability and apoptosis. Prevention of Jak2 activation by tyrphostin B42 was associated with the inability of GM-CSF to prevent eosinophil apoptosis. These data suggest that disruption of not only the Lyn-Ras-Raf-1-MAP kinase but also the Jak-STAT pathway blocks the ability of eosinophil survival factors to prevent apoptosis in eosinophils.

Increased Enzymatic Activity of the T-Cell Antigen Receptor-Associated Fyn Protein Tyrosine Kinase in Asymptomatic Patients Infected With the Human Immunodeficiency Virus

The immune system of patients infected with human immunodeficiency virus (HIV) is in a state of chronic activation; however, the nature of HIV-related immune activation is unknown. As normal T-cell activation involves early tyrosine phosphorylation induced by the T-cell antigen receptor-associated src-family protein tyrosine kinase p59fyn(T) (Fyn), we examined a potential role for this kinase in HIV-related immune dysfunction. We determined the relative specific kinase activity of Fyn in lysates of peripheral blood mononuclear cells from 47 normal control individuals tested negative for HIV-1 and -2, human T-cell lymphotropic virus Type I, hepatitis B virus (HBV), hepatitis C virus (HCV), and syphilis; 14 asymptomatic HIV-infected patients having near-normal CD4+ T-cell counts (350 to 980 CD4+ cells/μL); 4 patients with symptomatic acquired immunodeficiency syndrome (AIDS) (<30 CD4+ cells/μL); 13 patients having chronic infection with HBV (6 patients) or HCV (7 patients); and 6 patients with systemic lupus erythematosis (SLE). All patients with asymptomatic HIV disease were shown to have a profound increase (mean increase of 19-fold; range threefold to 56-fold increase; p = 1.33 × 10−9) in the relative specific kinase activity of Fyn compared to uninfected controls or patients with hepatitis or SLE. In contrast, patients with AIDS had an Fyn-specific kinase activity that was much less affected (mean increase of threefold; range onefold to sevenfold increase; p = 1.30 × 10−5). It was further shown that HIV infection affects the Fyn-specific kinase activity in CD8+-enriched cells, suggesting abnormal Fyn activity in both CD8+ as well as CD4+ T lymphocytes. Initial results implicate a role for the CSK protein tyrosine kinase as responsible for the abnormal Fyn kinase activity observed in HIV-infected patients. These data indicate early and chronic activation of Fyn as a unique HIV-related effect that has the potential to be diagnostic for early HIV infection and/or may serve as a prognostic indicator for advancement to full-blown AIDS. More importantly, sustained activation of the protein tyrosine kinase associated with T-cell antigen receptor function may result in, or contribute to, the immunopathogenic effects associated with HIV infection.

Interleukin-10 Counterregulates Proinflammatory Cytokine-Induced Inhibition of Neutrophil Apoptosis During Severe Sepsis

Neutrophils play a key role in the pathophysiology of septic multiple organ dysfunction syndrome (MODS) through excessive release of toxic granule components and reactive oxygen metabolites with consequent tissue destruction. The increase of senescent neutrophils during sepsis indicates a potential breakdown of autoregulatory mechanisms including apoptotic processes to remove activated neutrophils from inflammatory sites. Therefore, neutrophil apoptosis of patients with severe sepsis and its regulatory mechanisms were investigated. Spontaneous neutrophil apoptosis from patients with severe sepsis was significantly reduced in comparison to healthy individuals. Cytokines detected in the circulation during sepsis (tumor necrosis factor-α [TNF-α], interferon-γ [IFN-γ], granulocyte colony-stimulating factor [G-CSF], granulocyte-macrophage colony-stimulating factor [GM-CSF]) inhibited neutrophil apoptosis in both groups, though the effect was more distinct in neutrophils from healthy humans. Addition of lipopolysaccharide (LPS) to neutrophils from healthy humans markedly (P < .05) reduced apoptosis which was partially restored through addition of anti–TNF-antibody. Interleukin-10 (IL-10) counteracted (P < .05) inhibition of neutrophil apoptosis induced by LPS, recombinant human (rh) TNF-α, rhIFN-γ, rhG-CSF, and rhGM-CSF, whereas rhIL-4 or rhIL-13 were ineffective. Reduced neutrophil apoptosis during sepsis was concomitant with increased tyrosine phosphorylation, while IL-10 markedly inhibited tyrosine phosphorylation in LPS-stimulated neutrophils. These results identify proinflammatory cytokines and IL-10 as strong regulators of spontaneous neutrophil apoptosis during sepsis. Inhibition as well as acceleration of neutrophil apoptosis seems to be associated with alterations of signal transduction pathways.

The GM-CSF analogue E21R induces apoptosis of normal and activated eosinophils

There is evidence that eosinophils have an important role in the pathogenesis of allergy and asthma. These cells are regulated by two classes of polypeptides, the colony-stimulating factors, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), and the chemokines, such as RANTES and eotaxin. GM-CSF is involved in the production, survival, and functional activation of eosinophils. RANTES and eotaxin regulate the migration of eosinophils to inflammatory sites, but any effect of these chemokines on eosinophil survival is not known. In this study we demonstrate that although GM-CSF promoted eosinophil survival, the specific GM-CSF analogue E21R induced apoptosis of eosinophils. Apoptosis was observed with unstimulated as well as with chemokine (RANTES and eotaxin)-activated eosinophils. Neither RANTES nor eotaxin supported eosinophil survival, and a RANTES antagonist did not affect either cell survival or apoptosis. E21R also induced apoptosis of eosinophils from asthmatic patients. These findings suggest that the GM-CSF receptor may actively control the death as well as the survival of eosinophils, and thus precisely regulate their numbers and activities. Our data also indicate that chemokines are not involved in regulating the lifespan of eosinophils. The introduction of the GM-CSF analogue E21R may offer a novel therapy in inflammatory diseases associated with eosinophil infiltration of different etiologies.

Interleukin-3 activates Syk in a human myeloblastic leukemia cell line, AML193

Protein-tyrosine kinases and phosphatases play an important role in cytokine-mediated cell growth. The proliferation of a human myeloid leukemia cell line, AML193, is dependent on interleukin-3 (IL-3) or granulocyte colony-stimulating factor. In the current study, we demonstrated that a non-receptor-type protein-tyrosine kinase, Syk, was immediately activated by the stimulation with IL-3 or granulocyte colony-stimulating factor in AML193 cells. We further investigated the relation of Syk with IL-3-mediated signaling and found that the IL-3 receptor beta subunit was immunoprecipitated with Syk. Since the IL-3 receptor beta subunit is known to mediate growth signaling, our results indicate that Syk may be involved in the proliferation of myeloid cells.

Facilitation of apoptosis by cyclosporins A and H, but not FK506 in mouse bronchial eosinophils

This study was undertaken to clarify whether or not binding to cyclophilin is a prerequisite for cyclosporin A-induced modulation of apoptotic cell death in eosinophils. Eosinophils were isolated from bronchoalveolar lavage fluid of mice challenged with inhaled allergen after sensitization. Apoptosis was determined by analysing the DNA content. At 72 h, 99% of the cells had died without addition of cytokines, whereas 55-60% of the cells survived in the presence of 10 U/ml recombinant murine interleukin 5 or recombinant murine granulocyte macrophage-colony stimulation factor (GM-CSF). Apoptotic cell death at 72 h in the presence of 10 U/ml interleukin 5 was increased by addition of cyclosporin H, an analogue of cyclosporin A without cyclophilin binding activity, in a concentration-dependent (0.3 to 3 microM) manner. The increase in apoptosis elicited by cyclosporin A and cyclosporin H took place also in the presence of 10 U/ml GM-CSF but to a lesser extent. There was a significant augmentation of apoptosis in eosinophils cultured in the presence of each cytokine for 72 h or longer. Tacrolimus (FK506) failed to augment apoptotic cell death. Thus, it is unlikely that binding of cyclosporin A to cyclophilin accounts for the increased apoptosis induced by cyclosporin A and its analogue in eosinophils. The increase in apoptosis induced by cyclosporin A, but not FK506, in activated eosinophils from the airways may be attributed to the anti-asthmatic effects of cyclosporin A.

Src homology 2 protein tyrosine phosphatase (SHPTP2)/Src homology 2 phosphatase 2 (SHP2) tyrosine phosphatase is a positive regulator of the interleukin 5 receptor signal transduction pathways leading to the prolongation of eosinophil survival

Interleukin-5 (IL-5) regulates the growth and function of eosinophils. It induces rapid tyrosine phosphorylation of Lyn and Jak2 tyrosine kinases. The role of tyrosine phosphatases in IL-5 signal transduction has not been investigated. In this study, we provide first evidence that SH2 protein tyrosine phosphatase 2 (SHPTP2) phosphotyrosine phosphatase plays a key role in prevention of eosinophil death by IL-5. We found that IL-5 produced a rapid activation and tyrosine phosphorylation of SHPTP2 within 1 min. The tyrosine phosphorylated SHPTP2 was complexed with the adapter protein Grb2 in IL-5-stimulated eosinophils. Furthermore, SHPTP2 appeared to physically associate with beta common (betac) chain of the IL-5 receptor (IL-5betacR). The association of SHPTP2 with IL-5betacR was reconstituted using a synthetic phosphotyrosine-containing peptide, betac 605-624, encompassing tyrosine (Y)612. The binding to the phosphotyrosine-containing peptide increased the phosphatase activity of SHPTP2, whereas the same peptide with the phosphorylated Y612--> F mutation did not activate SHPTP2. Only SHPTP2 antisense oligonucleotides, but not sense SHPTP2, could inhibit tyrosine phosphorylation of microtubule-associated protein kinase, and reverse the eosinophil survival advantage provided by IL-5. Therefore, we conclude that the physical association of SHPTP2 with the phosphorylated betac receptor and Grb2 and its early activation are required for the coupling of the receptor to the Ras signaling pathway and for prevention of eosinophil death by IL-5.

Up-regulation of Syk activity during HL60 cell differentiation into granulocyte but not into monocyte/macrophage-lineage

Following induction of cell differentiation in vitro, an increase in Syk activity was observed only in HL60 cells differentiation into granulocytes induced by all trans retinoic acid (RA) but not into macrophages induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) or monocytes induced by sodium butyrate. This elevation of Syk activity was the specific increase in kinase activity because the Syk amount was not altered before and after differentiation. Anti-phosphotyrosine blot revealed that tyrosine phosphorylation of Syk was significantly increased as the function of induction time by RA, but not by TPA and sodium butyrate, suggesting that tyrosine phosphorylation might account for Syk activation. More importantly, Syk tyrosine phosphorylation and Syk activity were not altered in U937 and K562 cells which undergo monocyte differentiation and no differentiation, respectively, in response to RA induction. Taken together, Syk might exert a unique role in directing HL60 cells toward granulocyte differentiation.

Suppression of the immune system by oral glucocorticoid therapy in bronchial asthma

The effect of systemic glucocorticoid therapy on immune parameters was studied in patients with bronchial asthma. Patients were divided into two groups: 1) those receiving oral glucocorticoid; 2) control patients who did not receive systemic glucocorticoid treatment. The glucocorticoid dose varied between 5 and 70 mg per day. Patients had been taking oral therapy for at least 1 year. Glucocorticoid treatment was associated with an increased frequency of respiratory tract infections. Therefore, we need to define immune parameters which may predict an increased risk of infections. In this study, we analyzed several surface markers on lymphocytes and monocytes by flow cytometry. A significant reduction of the ratio of peripheral blood CD4+ to CD8+ T cells was associated with the administration of oral glucocorticoids. Furthermore, the expression of the HLA-DR molecule on monocytes was reduced in patients with systemic glucocorticoid therapy compared to control patients. Moreover, the capacity to elaborate cytokines by peripheral blood mononuclear cells upon stimulation was greatly reduced after exposure to glucocorticoids in vivo and in vitro. In addition, the humoral immune response was affected, because reduced IgG, IgM, and IgA levels were observed in patients receiving oral glucocorticoids. These results indicate that systemic glucocorticoid treatment in patients with bronchial asthma is associated with cellular and humoral immunosuppression which results in an increased risk of bacterial and viral infections.

Activation of 12-O-tetradecanoylphorbol-13-acetate response element- and dyad symmetry element-dependent transcription by interleukin-5 is mediated by Jun N-terminal kinase/stress-activated protein kinase kinases

Interleukin-5 (IL-5) is one of the major regulators of eosinophilic granulocytes in vivo. IL-5 exerts its pleiotropic effects by binding to the IL-5 receptor, which is composed of an IL-5-specific alpha chain and a common betac chain shared with the receptors for IL-3 and granulocyte-macrophage colony-stimulating factor. Previous studies have shown that binding of IL-5 to its receptor triggers the activation of multiple signaling cascades, including the Ras/mitogen-activated protein kinase, the phosphatidyl -3'-kinase, and the Janus kinase/signal transducer and activator of transcription pathways. Here we describe that IL-5 activates the serine/threonine protein kinase Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) pathway. We show that IL-5 activates TPA response element (TRE)-dependent transcription in transfection experiments. TRE activation by IL-5 is mediated by a region of the betac (577-581) that is also responsible for activation of JNK/SAPK and for activation of dyad symmetry element (DSE)-dependent transcription. Dominant-negative SAPK or ERK kinase-1 was used to demonstrate that JNK/SAPK activation is necessary for induction of DSE- and TRE-dependent transcription by IL-5, whereas extracellular signal-regulated kinase 2 was not essential for TRE- and DSE-dependent transcription. By contrast, IL-5-induced activation of the tyrosine kinase Janus kinase 2 seems to be a prerequisite for TRE- and DSE-dependent transcription. Taken together, we show for the first time that IL-5 activates kinases of the JNK/SAPK family, and that this activation is linked to IL-5-induced TRE- and DSE-dependent transcription.

Expression and function of the Fas receptor on human blood and tissue eosinophils

The interaction between activated T cells and eosinophils has been proposed to play an important role in the pathogenesis of allergic diseases. T cell-derived cytokines such as interleukin-5 and granulocyte/macrophage colony-stimulating factor inhibit eosinophil apoptosis and may therefore contribute to the development of tissue and blood eosinophilia in these disorders. Withdrawal of these cytokines leads to eosinophil apoptosis in vitro. In contrast, the mechanisms which actively induce apoptosis in eosinophils are at present not completely understood. In this study, we demonstrate that freshly isolated human eosinophils express mRNA and protein for the Fas receptor. Using anti-Fas monoclonal antibody (mAb), we show that Fas activation accelerates apoptotic eosinophil death in vitro. Moreover, treatment of nasal polyps ex vivo with anti-Fas mAb decreased eosinophilic tissue inflammation. However, we observed that blood as well as tissue eosinophils derived from some eosinophilic donors do not express functional Fas receptors, although Fas protein is normally expressed in these cells. This implies that the susceptibility of the Fas receptor is a matter of regulation in eosinophils as previously observed in other systems. These data suggest that Fas ligand/Fas interactions are involved in the regulation of eosinophil apoptosis and that defects in this system could contribute to the accumulation of these cells in allergic and asthmatic diseases.