Role of caspases in dexamethasone-induced apoptosis and activation of c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase in human eosinophils

Strength in diversity: Understanding the pathways to herpes simplex virus reactivation

Herpes simplex virus (HSV) establishes a latent infection in peripheral neurons and can periodically reactivate to cause disease. Reactivation can be triggered by a variety of stimuli that activate different cellular processes to result in increased HSV lytic gene expression and production of infectious virus. The use of model systems has contributed significantly to our understanding of how reactivation of the virus is triggered by different physiological stimuli that are correlated with recrudescence of human disease. Furthermore, these models have led to the identification of both common and distinct mechanisms of different HSV reactivation pathways. Here, we summarize how the use of these diverse model systems has led to a better understanding of the complexities of HSV reactivation, and we present potential models linking cellular signaling pathways to changes in viral gene expression.

Differential regulation of cell death pathways by the microenvironment correlates with chemoresistance and survival in leukaemia

Glucocorticoids (GCs) and topoisomerase II inhibitors are used to treat acute lymphoblastic leukaemia (ALL) as they induce death in lymphoid cells through the glucocorticoid receptor (GR) and p53 respectively. Mechanisms underlying ALL cell death and the contribution of the bone marrow microenvironment to drug response/resistance remain unclear. The role of the microenvironment and the identification of chemoresistance determinants were studied by transcriptomic analysis in ALL cells treated with Dexamethasone (Dex), and Etoposide (Etop) grown in the presence or absence of bone marrow conditioned media (CM). The necroptotic (RIPK1) and the apoptotic (caspase-8/3) markers were downregulated by CM, whereas the inhibitory effects of chemotherapy on the autophagy marker Beclin-1 (BECN1) were reduced suggesting CM exerts cytoprotective effects. GCs upregulated the RIPK1 ubiquitinating factor BIRC3 (cIAP2), in GC-sensitive (CEM-C7-14) but not in resistant (CEM-C1-15) cells. In addition, CM selectively affected GR phosphorylation in a site and cell-specific manner. GR is recruited to RIPK1, BECN1 and BIRC3 promoters in the sensitive but not in the resistant cells with phosphorylated GR forms being generally less recruited in the presence of hormone. FACS analysis and caspase-8 assays demonstrated that CM promoted a pro-survival trend. High molecular weight proteins reacting with the RIPK1 antibody were modified upon incubation with the BIRC3 inhibitor AT406 in CEM-C7-14 cells suggesting that they represent ubiquitinated forms of RIPK1. Our data suggest that there is a correlation between microenvironment-induced ALL proliferation and altered response to chemotherapy.

Eosinophil resistance to glucocorticoid-induced apoptosis is mediated by the transcription factor NFIL3

The mainstay of asthma therapy, glucocorticoids (GCs) exert their therapeutic effects through the inhibition of inflammatory signaling and induction of eosinophil apoptosis. However, laboratory and clinical observations of GC-resistant asthma suggest that GCs' effects on eosinophil viability may depend on the state of eosinophil activation. In the present study we demonstrate that eosinophils stimulated with IL-5 show impaired pro-apoptotic response to GCs. We sought to determine the contribution of GC-mediated transactivating (TA) and transrepressing (TR) pathways in modulation of activated eosinophils' response to GC by comparing their response to the selective GC receptor (GR) agonist Compound A (CpdA) devoid of TA activity to that upon treatment with Dexamethasone (Dex). IL-5-activated eosinophils showed contrasting responses to CpdA and Dex, as IL-5-treated eosinophils showed no increase in apoptosis compared to cells treated with Dex alone, while CpdA elicited an apoptotic response regardless of IL-5 stimulation. Proteomic analysis revealed that both Nuclear Factor IL-3 (NFIL3) and Map Kinase Phosphatase 1 (MKP1) were inducible by IL-5 and enhanced by Dex; however, CpdA had no effect on NFIL3 and MKP1 expression. We found that inhibiting NFIL3 with specific siRNA or by blocking the IL-5-inducible Pim-1 kinase abrogated the protective effect of IL-5 on Dex-induced apoptosis, indicating crosstalk between IL-5 anti-apoptotic pathways and GR-mediated TA signaling occurring via the NFIL3 molecule. Collectively, these results indicate that (1) GCs' TA pathway may support eosinophil viability in IL-5-stimulated cells through synergistic upregulation of NFIL3; and (2) functional inhibition of IL-5 signaling (anti-Pim1) or the use of selective GR agonists that don't upregulate NFIL3 may be effective strategies for the restoring pro-apoptotic effect of GCs on IL-5-activated eosinophils.

Mitochondria in the center of human eosinophil apoptosis and survival

Eosinophils are abundantly present in most phenotypes of asthma and they contribute to the maintenance and exacerbations of the disease. Regulators of eosinophil longevity play critical roles in determining whether eosinophils accumulate into the airways of asthmatics. Several cytokines enhance eosinophil survival promoting eosinophilic airway inflammation while for example glucocorticoids, the most important anti-inflammatory drugs used to treat asthma, promote the intrinsic pathway of eosinophil apoptosis and by this mechanism contribute to the resolution of eosinophilic airway inflammation. Mitochondria seem to play central roles in both intrinsic mitochondrion-centered and extrinsic receptor-mediated pathways of apoptosis in eosinophils. Mitochondria may also be important for survival signalling. In addition to glucocorticoids, another important agent that regulates human eosinophil longevity via mitochondrial route is nitric oxide, which is present in increased amounts in the airways of asthmatics. Nitric oxide seems to be able to trigger both survival and apoptosis in eosinophils. This review discusses the current evidence of the mechanisms of induced eosinophil apoptosis and survival focusing on the role of mitochondria and clinically relevant stimulants, such as glucocorticoids and nitric oxide.

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.

Dexamethasone-loaded block copolymer nanoparticles induce leukemia cell death and enhance therapeutic efficacy: a novel application in pediatric nanomedicine

Nanotechnology approaches have tremendous potential for enhancing treatment efficacy with lower doses of chemotherapeutics. Nanoparticle (NP)-based drug delivery approaches are poorly developed for childhood leukemia. Dexamethasone (Dex) is one of the most common chemotherapeutic drugs used in the treatment of childhood leukemia. In this study, we encapsulated Dex in polymeric NPs and validated their antileukemic potential in vitro and in vivo. NPs with an average diameter of 110 nm were assembled from an amphiphilic block copolymer of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) bearing pendant cyclic ketals (ECT2). The blank NPs were nontoxic to cultured cells in vitro and to mice in vivo. Encapsulation of Dex into the NPs (Dex-NP) did not compromise the bioactivity of the drug. Dex-NPs induced glucocorticoid phosphorylation and showed cytotoxicity similar to the free Dex in leukemic cells. Studies using NPs labeled with fluorescent dyes revealed leukemic cell surface binding and internalization. In vivo biodistribution studies showed NP accumulation in the liver and spleen with subsequent clearance of the particles with time. In a preclinical model of leukemia, Dex-NPs significantly improved the quality of life and survival of mice as compared to the free drug. To our knowledge, this is the first report showing the efficacy of polymeric NPs to deliver Dex to potentially treat childhood leukemia and reveals that low doses of Dex should be sufficient for inducing cell death and improving survival.

Eosinophil apoptosis and clearance in asthma

Asthma is an increasingly common respiratory condition characterized by reversible airway obstruction, bronchial hyper-responsiveness and airway inflammation with a clear unmet need for more effective therapy. Eosinophilic asthma is a phenotype of the condition that features increased blood or sputum eosinophils whose numbers correlate with disease severity. Several lines of evidence are now emerging, which implicate increased persistence of eosinophils in the lungs of patients with asthma as a consequence of inhibition of and defects in the apoptotic process, together with impaired apoptotic cell removal mechanisms. This article will update our knowledge of the mechanisms controlling eosinophil apoptosis and clearance, together with evidence implicating defects in apoptosis and pro-inflammatory cell removal in asthma. Recent developments in novel therapies for asthma that target eosinophil apoptotic and/or clearance pathways will also be discussed.

Anti-inflammatory and anti-allergic activities of Pentaherb formula, Moutan Cortex (Danpi) and gallic acid

Pentaherb formula (PHF) has been proven to improve the quality of life of children with atopic dermatitis without side effects. The aim of this study was to elucidate the potential anti-inflammatory and anti-allergic activities of PHF, Moutan Cortex (Danpi/DP) and gallic acid (GA) using human basophils (KU812 cells), which are crucial effector cells in allergic inflammation. PHF, DP and GA could significantly suppress the expression of allergic inflammatory cytokine IL-33-upregulated intercellular adhesion molecule (ICAM)-1, and the release of chemokines CCL2, CCL5, CXCL8 and inflammatory cytokine IL-6 from KU812 cells (all p < 0.05). With the combined use of dexamethasone (0.01 μg/mL) and GA (10 μg/mL), the suppression of ICAM-1 expression and CCL5 and IL-6 release of IL-33-activated KU812 cells were significantly greater than the use of GA alone (all p < 0.05). The suppression of the IL-33-induced activation of intracellular signalling molecules p38 mitogen activated protein kinase, nuclear factor-kB and c-Jun amino-terminal kinase in GA-treated KU812 cells could be the underlying mechanism for the suppression on ICAM-1, chemokines and cytokines. The combined use of dexamethasone with the natural products PHF or DP or GA might therefore enhance the development of a novel therapeutic modality for allergic inflammatory diseases with high potency and fewer side effects.

Apaf-1 deficiency confers resistance to ultraviolet-induced apoptosis in mouse embryonic fibroblasts by disrupting reactive oxygen species amplification production and mitochondrial pathway

Apoptosis requires tightly regulated cell death pathways. The signaling pathways that trigger a cell to undergo apoptosis after UV radiation are cell type specific and are currently being defined. Here, we have used pharmacological and genetic tools to demonstrate the decisive part of the mitochondrial pathway in UVC-induced apoptosis in mouse embryo fibroblasts (MEFs). UVC-induced apoptosis proceeded independent of the activation of death receptor components. In contrast, soon after UV radiation, MAPK activation and generation of reactive oxygen species (ROS) increased, followed by a decline in mitochondrial membrane potential (MMP) and cytochrome c release, as well as activation of caspase-9 and -3 and the upregulation of p47-phox. Deficiency of apaf-1, a critical member of the apoptosome, dramatically abolished all the UV-induced signal deterioration and cell death. In parallel, UVC-induced apoptosis was largely attenuated by either DN-caspase-9 or Bcl-X(L) overexpression. Pretreatment of cells with N-acetylcysteine or catalase but not Tempol decreased UVC-induced MAPK activation and apoptosis. Inhibition of JNK and caspase attenuated p47-phox upregulation. Altogether, we have for the first time demonstrated the critical role of Apaf-1 in the regulation of MAPK, ROS, and MMP in UVC-radiated MEFs and propose that the amplification feedback loop among mitochondrial signal molecules culminates in the demise of the cell.

Targeting p53 via JNK pathway: a novel role of RITA for apoptotic signaling in multiple myeloma

The low frequency of p53 alterations e.g., mutations/deletions (∼10%) in multiple myeloma (MM) makes this tumor type an ideal candidate for p53-targeted therapies. RITA is a small molecule which can induce apoptosis in tumor cells by activating the p53 pathway. We previously showed that RITA strongly activates p53 while selectively inhibiting growth of MM cells without inducing genotoxicity, indicating its potential as a drug lead for p53-targeted therapy in MM. However, the molecular mechanisms underlying the pro-apoptotic effect of RITA are largely undefined. Gene expression analysis by microarray identified a significant number of differentially expressed genes associated with stress response including c-Jun N-terminal kinase (JNK) signaling pathway. By Western blot analysis we further confirmed that RITA induced activation of p53 in conjunction with up-regulation of phosphorylated ASK-1, MKK-4 and c-Jun. These results suggest that RITA induced the activation of JNK signaling. Chromatin immunoprecipitation (ChIP) analysis showed that activated c-Jun binds to the activator protein-1 (AP-1) binding site of the p53 promoter region. Disruption of the JNK signal pathway by small interfering RNA (siRNA) against JNK or JNK specific inhibitor, SP-600125 inhibited the activation of p53 and attenuated apoptosis induced by RITA in myeloma cells carrying wild type p53. On the other hand, p53 transcriptional inhibitor, PFT-α or p53 siRNA not only inhibited the activation of p53 transcriptional targets but also blocked the activation of c-Jun suggesting the presence of a positive feedback loop between p53 and JNK. In addition, RITA in combination with dexamethasone, known as a JNK activator, displays synergistic cytotoxic responses in MM cell lines and patient samples. Our study unveils a previously undescribed mechanism of RITA-induced p53-mediated apoptosis through JNK signaling pathway and provides the rationale for combination of p53 activating drugs with JNK activators in the treatment of MM.

The role of caspase activation and mitochondrial depolarisation in cultured human apoptotic eosinophils

Caspases are key intracellular molecules in the control of apoptosis, but little is known concerning their relative contribution to the cascade of events leading to eosinophil apoptosis. We examined caspase-3, -8, and -9 activities in receptor ligation dependent apoptosis induction in the cultured eosinophils (CE). CE cultured alone for 48 hours exhibited constitutive apoptosis (12% ± 1.2). Significant (P < 0.05) enhancement of eosinophil apoptosis was observed following monoclonal antibody (Mab) treatment with CD45 (40% ± 0.7), CD95 (36% ± 1.6), or CD69 (34% ± 0.2). Caspase activity was analysed using the novel CaspaTagTM technique and flow cytometry. CE ligated with CD45 (Bra55), CD95 (Fas) and CD69 Mab resulted in caspase-3 and -9 activation after 16 hours post-ligation. This trend in caspase-3 and -9 activation continued to increase significantly through to the 20 and 24 hours time points when compared to isotype control. Activated up-stream caspase-8 was detected 16 and 20 hours after treatment with CD45, CD95 and CD69 Mab followed by a trend toward basal levels at 24 hours. Ligation of CD95 was followed by mitochondrial permeabilization, as demonstrated by marked increase in mitochondrial transmembrane potential ([Formula: see text]) at all time points. However, ligation with CD45 and CD69 failed to induce a change in [Formula: see text] at 16 hours post-treatment compared to isotype control even though there was an alteration in mitochondrial downstream-caspase activity following ligation with these Mab(s) at this time point. At 20 and 24 hours post-ligation, CD45 or CD69 induce significantly altered levels of [Formula: see text]. Thus, the intrinsic and extrinsic caspase pathways are involved in controlling receptor ligation-mediated apoptosis induction in human eosinophils, findings that may aid the development of a more targeted, anti inflammatory therapy for asthma.

Dexamethasone-induced cardioprotection: a role for the phosphatase MKP-1?

AIMS

Previous studies suggested that p38 MAPK activation during sustained myocardial ischaemia and reperfusion was harmful. We hypothesize that attenuation of p38MAPK activity via dephosphorylation by the dual-specificity phosphatase MKP-1 should be protective against ischaemia/reperfusion injury. Since the glucocorticoid, dexamethasone, induces the expression of MKP-1, the aim of this study was to determine whether upregulation of this phosphatase by dexamethasone protects the heart against ischaemia/reperfusion injury.

MAIN METHODS

Male Wistar rats were treated with dexamethasone (3 mg/kg/day ip) for 10 days, before removal of the hearts for Western blot (ip Dex-P) or perfusion in the working mode (ip Dex+P). Hearts were subjected to 20 min global or 35 min regional ischaemia (36.5 degrees C) and 30 or 120 min reperfusion. In a separate series, dexamethasone (1 microM) was added to the perfusate for 10 min (Pre+Dex) before or after (Rep+Dex) ischaemia.

KEY FINDINGS

Dexamethasone, administered intraperitoneally or added directly to the perfusate, significantly improved post-ischaemic functional recovery and reduced infarct size compared to untreated controls (p<0.05). These were associated with enhanced up-regulation of MKP-1 protein expression (arbitrary units (mean+/-SD): Untreated: 1; ip Dex-P: 2.59+/-0.22; ip Dex+P: 1.51+/-0.22; Pre+Dex: 4.11+/-0.73, Rep+15'Dex: 1.51+/-0.14; untreated vs. all groups, p<0.05) and attenuation of p38 MAPK activation (p<0.05) in all dexamethasone-treated groups, except for Rep+10'Dex. ERK and PKB/Akt activation were unchanged.

SIGNIFICANCE

Dexamethasone-induced cardioprotection was associated with upregulation of the phosphatase MKP-1 and inactivation of pro-apoptotic p38 MAPK.

IL-3 induces a Pim1-dependent antiapoptotic pathway in primary human basophils

The contribution of basophils in allergic disease and other Th2-type immune responses depends on their persistence at sites of inflammation, but the ligands and molecular pathways supporting basophil survival are largely unknown. The comparison of rates of apoptosis and of the expression of antiapoptotic proteins in different human granulocyte types revealed that basophils have a considerably longer spontaneous life span than neutrophils and eosinophils consistent with high levels of constitutive Bcl-2 expression. Interleukin-3 (IL-3) is the only ligand that efficiently protects basophils from apoptosis as evidenced by screening a large number of stimuli. IL-3 up-regulates the expression of the antiapoptotic proteins cIAP2, Mcl-1, and Bcl-X(L) and induces a rapid and sustained de novo expression of the serine/threonine kinase Pim1 that closely correlates with cytokine-enhanced survival. Inhibitor studies and protein transduction of primary basophils using wild-type and kinase-dead Pim1-Tat fusion-proteins demonstrate the functional importance of Pim1 induction in the IL-3-enhanced survival. Our data further indicate that the antiapoptotic Pim1-mediated pathway operates independently of PI3-kinase but involves the activation of p38 MAPK. The induction of Pim1 leading to PI3-kinase-independent survival as described here for basophils may also be a relevant antiapoptotic mechanism in other terminally differentiated leukocyte types.

Search for a functional glucocorticoid receptor in the mammalian lens

Prolonged glucocorticoid treatment of medical conditions such as rheumatoid arthritis or asthma can lead to the formation of a posterior subcapsular cataract as a negative side effect. Currently, the only treatment for this cataract is surgery because very little is known about the mechanism of glucocorticoid action in the mammalian lens. Understanding of a lens glucocorticoid response is essential for the treatment and prevention of a steroid induced cataract. It has been suggested that glucocorticoids exert their effects on the lens indirectly, non-specifically, or through non-classical mechanisms. While these modes of action may contribute to the formation of glucocorticoid induced posterior subcapsular cataract, the finding of a classical, specific, functional lens glucocorticoid receptor suggests that glucocorticoids target lens epithelial cells directly, specifically, and similar to what has been observed in other cells types. This review explores the discovery of the glucocorticoid receptor in humans lens epithelial cells and the lens specific glucocorticoid response. The distinct changes in lens epithelial cell signaling pathways (MAPK and PI3K-AKT) suggest that glucocorticoids modulate several cellular functions and may explain why a lens glucocorticoid response has been difficult to elucidate.

Glucocorticoids induce osteocyte apoptosis by blocking focal adhesion kinase-mediated survival. Evidence for inside-out signaling leading to anoikis

Bone fragility induced by chronic glucocorticoid excess is due, at least in part, to induction of osteocyte apoptosis through direct actions on these cells. However, the molecular mechanism by which glucocorticoids shorten osteocyte life span has remained heretofore unknown. We report that apoptosis of osteocytic MLO-Y4 cells induced by the synthetic glucocorticoid dexamethasone is abolished by the glucocorticoid receptor antagonist RU486, but not by inhibition of protein or RNA synthesis. Dexamethasone-induced apoptosis is preceded by a decrease in the number of cytoplasmic processes, an indicator of cell detachment. In addition, the focal adhesion kinase FAK prevents dexamethasone-induced apoptosis, whereas the FAK-related kinase Pyk2 increases the basal levels of apoptosis. Dexamethasone-induced apoptosis is also prevented in cells expressing kinase-deficient or phosphorylation-defective (Y402F) dominant negative mutants of Pyk2. Consistent with the requirement of tyrosine 402, dexamethasone induces rapid Pyk2 phosphorylation in this residue. Moreover, knocking down Pyk2 expression abolishes apoptosis and cell detachment induced by dexamethasone, and transfection with human Pyk2 rescues both responses. Furthermore, induction of apoptosis as well as cell detachment by dexamethasone is abolished by inhibiting the activity of JNK, a recognized downstream target of Pyk2 activation. These results demonstrate that glucocorticoids promote osteocyte apoptosis via a receptor-mediated mechanism that does not require gene transcription and that is mediated by rapid activation of Pyk2 and JNK, followed by inside-out signaling that leads to cell detachment-induced apoptosis or anoikis.

Effects of dexamethasone exposure on rat metanephric development: in vitro and in vivo studies

Maternal administration of dexamethasone (DEX) for 48 h early in rat kidney development results in offspring with a reduced nephron endowment. However, the mechanism through which DEX inhibits nephrogenesis is unknown. In this study, we hypothesized that DEX may indirectly inhibit nephrogenesis by inhibiting ureteric branching morphogenesis. Whole metanephroi from embryonic day 14.5 (E14.5) rat embryos were cultured in the presence of DEX. DEX (10(-5) M) exposure for 2 days significantly inhibited ureteric branching compared with metanephroi grown in control media or DEX (10(-7) M). Culturing metanephroi for a further 3 days (in control media only) reduced total glomerular number in metanephroi previously exposed to DEX (10(-5) M) or (10(-7) M) compared with control cultures. Expression of genes known to regulate ureteric branching morphogenesis was determined by real-time PCR in metanephroi after 2 days in culture. DEX exposure in vitro decreased expression of glial cell line-derived neurotrophic factor (GDNF) and increased expression of bone morphogenetic protein-4 (BMP-4) and transforming growth factor-beta1 (TGF-beta1). Similar gene expression changes were found in E16.5 metanephroi in which the dam had been exposed to 2 days of DEX (0.2 mg.kg(-1).day(-1)) at E14.5/15.5 in vivo. However, in kidneys collected at E20.5 after in vivo exposure for 2 days, GDNF expression was increased and BMP-4 and TGF-beta1 expression decreased suggesting a biphasic response in gene expression to DEX exposure. These results show for the first time that inhibition of ureteric branching morphogenesis may be a key mechanism through which DEX exposure results in a reduced nephron endowment.

Specific activation of the glucocorticoid receptor and modulation of signal transduction pathways in human lens epithelial cells

PURPOSE

Prolonged use of glucocorticoids (GCs) can lead to cataract formation. Lens GC responses have been difficult to elucidate. A previous study showed the presence of the glucocorticoid receptor (GR) in immortalized and primary human lens epithelial cells (hLECs) and GC-induced changes in gene expression. This study demonstrates specific GR activation and identifies the biological effect of GC-induced changes in gene expression in hLECs.

METHODS

HLE B-3 (B-3) and primary cultures of hLECs were transfected with pGRE.Luc and treated with or without dexamethasone (Dex), RU-486, spironolactone, or vehicle. mRNA and protein expression were examined by real-time PCR and Western blot analysis, respectively. Cell proliferation and apoptosis were examined by WST-1 and flow cytometry, respectively.

RESULTS

Dex treatment of B-3 and primary cultures demonstrated specific GR, but not mineralocorticoid receptor (MR), activation and phosphorylation. Pathway analysis revealed GC-induced changes in expression of MAPK regulators. Increased expression of GILZ mRNA and MKP-1 mRNA and protein was observed in immortalized and donor hLECs. This corresponded with a decrease in the phosphorylated forms of RAF, ERK, p38, and AKT, but not in JNK. No net change in LEC proliferation or apoptosis was observed with Dex treatment.

CONCLUSIONS

GC treatment of hLECs activates the GR to modulate the expression of MAPK and PI3K/AKT regulators. This is the first demonstration of GC signaling in hLECs. GCs, MAPK, and PI3K/AKT are involved in cell processes implicated in steroid-induced cataractogenesis. The absence of a net change in cell activity with acute steroid treatment is consistent with the possibility that chronic treatment leads to prolonged modulation of these pathways and steroid-induced cataract.

Excretory-secretory products from Fasciola hepatica induce eosinophil apoptosis by a caspase-dependent mechanism

Eosinophils (Eo) are known to be important effector cells in the host defense against helminth parasites. Excretory-secretory products (ESP) released by helminths have shown wide immunomodulatory properties, such as the induction of cellular apoptosis. We investigated the ability of ESP from Fasciola hepatica to induce Eo apoptosis. In this work, we observed that ESP induced an early apoptosis of rat peritoneal eosinophils and that this phenomenon was time- and concentration-dependent. Furthermore, we demonstrated that activation of protein tyrosine kinases (TyrK) and caspases were necessary to mediate the Eo apoptosis induced by the ESP, and that carbohydrate components present in these antigens were involved in this effect. We have described for the first time the ability of ESP from F. hepatica to modify the viability of Eo by apoptosis induction. Besides that, we have observed Eo apoptosis in the liver of rats 21 days after F. hepatica infection. The diminution in Eo survival in early infection could be a parasite strategy in order to prevent a host immune response.

Rapid selective priming of FcalphaR on eosinophils by corticosteroids

Preactivation or priming of eosinophils by (proinflammatory) cytokines is important in the pathogenesis of allergic diseases. Several priming-dependent eosinophil responses, such as migration and adhesion, are reduced by treatment with corticosteroids. Many inhibitory effects of corticosteroids are mediated by the glucocorticoid receptor via genomic mechanisms, which are evident only after prolonged interaction (>30 min). However, also faster actions of corticosteroids have been identified, which occur in a rapid, nongenomic manner. In this study, fast effects of corticosteroids were investigated on the function of eosinophil opsonin receptors. Short term corticosteroid treatment of eosinophils for maximal 30 min with dexamethasone (Dex) did not influence eosinophil cell surface CD11b/CD18 expression, adhesion, and/or chemokinesis. In marked contrast, incubation with Dex resulted in a rapid increase in binding of IgA-coated beads to human eosinophils, showing that Dex can up-regulate the activation of FcalphaR (CD89). This priming response by Dex was dose dependent and optimal between 10(-8) and 10(-6) M and was mediated via the glucocorticoid receptor as its selective antagonist RU38486 (10(-6) M) blocked the priming effect. In contrast to FcalphaR, eosinophil FcgammaRII (CD32) was not affected by Dex. Further characterization of the Dex-induced inside-out regulation of FcalphaR revealed p38 MAPK as the central mediator. Dex dose dependently enhanced p38 MAPK phosphorylation and activation in situ as measured by phosphorylation of its downstream target mitogen-activated protein kinase-activated protein kinase 2. The dose responses of the Dex-induced activation of these kinases were similar as seen for the priming of FcalphaR. This work demonstrates that corticosteroids selectively activate the FcalphaR on eosinophils by activation of p38 MAPK.

Dependence on p38 MAPK signalling in the up-regulation of TLR2, TLR4 and TLR9 gene expression in Trichomonas vaginalis-treated HeLa cells

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that recognize conserved pathogen-associated molecular patterns (PAMPs) synthesized by micro-organisms. Despite the essential requirement for TLRs in prokaryotic infection, the pattern and regulation of TLR gene expression by Trichomonas vaginalis in the mucocutaneous barrier are still unknown. Our hypothesis is that T. vaginalis-infected epithelial cells are major effector cells in the skin barrier. These cells function as a central regulator of TLR gene expression, thus accelerating the process of barrier dysfunction via increased release of chemokines and proinflammatory cytokines. To test this hypothesis, RT-PCR was performed on TLRs, interleukin (IL)-8 and tumour necrosis factor (TNF)-alpha. Stimulation of HeLa cells by T. vaginalis was observed to up-regulate TLR2, 4 and 9 mRNA expression as well as that of IL-8 and TNF-alpha. To further clarify the molecular mechanism of barrier devastation triggered by these up-regulatory stimuli, we examined the profiles of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-kappaB activation in HeLa cells using specific inhibitors. Interestingly, pretreatment of HeLa cells with the p38 MAPK inhibitor SB203580 demonstrated inhibition of T. vaginalis-induced up-regulation of TLR2, 4, and 9 mRNA expression. By contrast, inhibition of ERK or NF-kappaB activation failed to block T. vaginalis-induced up-regulation of TLR9 mRNA expression or TLR2 and TLR4 mRNA expression, respectively. In addition, pretreatment with SB203580 reduced epithelium-derived IL-8 and TNF-alpha release evoked by T. vaginalis. Our results show that T. vaginalis infection of the mucocutaneous barrier could up-regulate TLR2, 4 and 9 gene expression via the p38 MAPK signalling pathway in epithelial cells; this process then leads to modulation of p38 MAPK-dependent IL-8 and TNF-alpha release from the epithelium.

The glucocorticoid RU24858 does not distinguish between transrepression and transactivation in primary human eosinophils

Background

Glucocorticoids are used to treat chronic inflammatory diseases such as asthma. Induction of eosinophil apoptosis is considered to be one of the main mechanisms behind the anti-asthmatic effect of glucocorticoids. Glucocorticoid binding to its receptor (GR) can have a dual effect on gene transcription. Activated GR can activate transcription (transactivation), or by interacting with other transcription factors such as NF-κB suppress transcription (transrepression). RU24858 has been reported to transrepress but to have little or no transactivation capability in other cell types. The dissociated properties of RU24858 have not been previously studied in non-malignant human cells. As the eosinophils have a very short lifetime and many of the modern molecular biological methods cannot be used, a "dissociated steroid" would be a valuable tool to evaluate the mechanism of action of glucocorticoids in human eosinophils. The aim of this study was to elucidate the ability of RU24858 to activate and repress gene expression in human eosinophils in order to see whether it is a dissociated steroid in human eosinophils.

Methods

Human peripheral blood eosinophils were isolated under sterile conditions and cultured in the presence and/or absence RU24858. For comparison, dexamethasone and mometasone were used. We measured chemokine receptor-4 (CXCR4) and Annexin 1 expression by flow cytometry and cytokine production by ELISA. Apoptosis was measured by DNA fragmentation and confirmed by morphological analysis.

Results

RU24858 (1 μM) increased CXCR4 and Annexin 1 expression on eosinophils to a similar extent as mometasone (1 μM) and dexamethasone (1 μM). Like dexamethasone and mometasone, RU24858 did suppress IL-8 and MCP-1 production in eosinophils. RU24858 also increased spontaneous eosinophil apoptosis to a similar degree as dexamethasone and mometasone, but unlike dexamethasone and mometasone it did not reverse IL-5- or GM-CSF-induced eosinophil survival.

Conclusion

Our results suggest that in human eosinophils RU24858 acts as transactivator and transrepressor like classical glucocorticoids. Thus, RU24858 seems not to be a "dissociated steroid" in primary human eosinophils in contrast to that reported in animal cells. In addition, functionally RU24858 seems to be a less potent glucocorticoid as it did not reverse IL-5- and GM-CSF-afforded eosinophil survival similarly to dexamethasone and mometasone.

c-Jun N-terminal kinase mediates constitutive human eosinophil apoptosis

Eosinophils are considered to play an important role in the pathogenesis of asthma. Glucocorticoids are potent anti-inflammatory agents for the treatment of chronic inflammatory diseases and they have been shown to increase the rate of eosinophil apoptosis. c-Jun N-terminal kinase (JNK) has been suggested to participate in the signaling pathways of apoptosis. The aims of the present study were to examine whether JNK is involved in the regulation of constitutive eosinophil apoptosis and whether it mediates dexamethasone-induced apoptosis of human eosinophils. Isolated human eosinophils were cultured with and without dexamethasone and the JNK inhibitor L-JNKI-1. Apoptosis was assessed by measuring the relative DNA content of propidium iodide-stained cells and confirmed by Annexin V-binding and morphological analysis with bright field microscopy. The phosphorylation of both JNK and c-Jun were measured by Western blotting. During a 40h culture, dexamethasone (1muM) enhanced human eosinophil apoptosis by 10-30%. Culture with L-JNKI1 (10muM) inhibited apoptosis in dexamethasone-treated cells by 53%. Furthermore, L-JNKI1 decreased the rate of constitutive eosinophil apoptosis by 64%. However, the enhancement of eosinophil apoptosis by dexamethasone was not reversed by L-JNKI1. Slow activation of JNK in constitutive apoptosis as well as a similar tendency in dexamethasone-induced eosinophil apoptosis could be observed by Western blot analyses. c-Jun was found to be active both in the presence and absence of dexamethasone. However, no further phosphorylation of the serine residue 63 of c-Jun could be seen. Taken together, our present results suggest that JNK is active during apoptosis of human eosinophils both in the presence and absence of glucocorticoids. JNK seems to mediate constitutive human eosinophil apoptosis. However, the activity of JNK is not enhanced by glucocorticoids and the effects of glucocorticoids cannot be reversed by JNK inhibition. JNK therefore seems not to mediate glucocorticoid-induced human eosinophil apoptosis.

Genomic and non-genomic effects of different glucocorticoids on mouse thymocyte apoptosis

Glucocorticoids, widely used therapeutic agents for several pathologies, act upon diverse cells and tissues, including the lympho-haemopoietic system. Glucocorticoid-mediated apoptosis has been described as one of the mechanisms underlying their pharmacological and physiological effects. Glucocorticoids induce apoptosis in thymocytes through genomic and non-genomic signals. We tested thymocyte apoptosis rates as induced by a panel of glucocorticoids. Using four glucocorticoids that are widely adopted in clinical practice we compared their induction of thymocyte apoptosis and activation of non-genomic and genomic signals, including phosphatidylinositol-specific phospholipase C (PI-PLC), caspase-8, -9 and -3, and Glucocorticoid-Induced Leucine Zipper (GILZ). GILZ is a protein that is rapidly induced by glucocorticoids treatment and involved in apoptosis modulation. Results indicate different glucocorticoids have different apoptotic activity which is related to their ability to induce both genomic, evaluated as caspases activation and GILZ expression, and non-genomic effects, evaluated as PI-PLC phosphorylation.

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.

Dexamethasone-induced and estradiol-induced CREB activation and annexin 1 expression in CCRF-CEM lymphoblastic cells: evidence for the involvement of cAMP and p38 MAPK

AIMS

Annexin 1 (ANXA1), a member of the annexin family of calcium-binding and phospholipid-binding proteins, is a key mediator of the anti-inflammatory actions of steroid hormones. We have previously demonstrated that, in the human lymphoblastic CCRF-CEM cell line, both the synthetic glucocorticoid hormone, dexamethasone (Dex), and the estrogen hormone, 17beta-estradiol (E2beta), induce the synthesis of ANXA1, by a mechanism independent of the activation of their nuclear receptors. Recently, it was reported that the gene coding for ANXA1 contains acAMP-responsive element (CRE). In this work, we investigated whether Dex and E2beta were able to induce the activation of CRE binding proteins (CREB) in the CCRF-CEM cells. Moreover, we studied the intracellular signalling pathways involved in CREB activation and ANXA1 synthesis in response to Dex and E2beta; namely, the role of cAMP and the p38 mitogen activated protein kinase (MAPK).

RESULTS

The results show that Dex and E2beta were as effective as the cAMP analogue, dBcAMP, in inducing CREB activation. On the contrary, dBcAMP induced ANXA1 synthesis as effectively as these steroid hormones. Furthermore, the cAMP antagonist, Rp-8-Br-cAMPS, and the specific p38 MAPK inhibitor,SB203580, effectively prevented both Dex-induced, E2beta-induced and dBcAMP-induced CREB activation and ANXA1 synthesis.

CONCLUSIONS

Taken together, our results suggest that,in CCRF-CEM cells, Dex-induced and E2beta-inducedANXA1 expression requires the activation of the transcription factor CREB, which in turn seems to be mediated by cAMP and the p38 MAPK. These findings also suggest that, besides the nuclear steroid hormone receptors, other transcription factors, namely CREB, may play important roles in mediating the anti-inflammatory actions of glucocorticoids and oestrogen hormones.

Membrane receptor-mediated apoptosis and caspase activation in the differentiated EoL-1 eosinophilic cell line

Caspases are key molecules in the control of apoptosis, but relatively little is known about their contribution to eosinophil apoptosis. We examined caspase-3, -8, and -9 activities in receptor ligation-dependent apoptosis induction in the differentiated human eosinophilic cell line EoL-1. Differentiated EoL-1 exhibited bi-lobed nuclei, eosinophil-associated membrane receptors, and basic granule proteins. Annexin-V fluorescein isothiocyanate binding to EoL-1 revealed significant (P<0.01) apoptosis induction in cells cultured for 20 h with monoclonal antibodies (mAb) specific for CD45 (71%+/-4.3), CD45RA (58%+/-2.3), CD45RB (68%+/-2.4), CD95 (47%+/-2.6), and CD69 (52%+/-2.1) compared with control (23%+/-1.6) or CD45RO mAb (27%+/-3.9). The pan-caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone (fmk) and inhibitors of caspase-8 (Z-Ile-Glu-Thr-Asp-fmk) and caspase-9 (Z-Leu-Glu-His-Asp-fmk) significantly inhibited mAb-induced apoptosis of EoL-1 but had no effect on constitutive (baseline) apoptosis at 16 and 20 h. Caspase activity was analyzed using the novel CaspaTag trade mark technique and flow cytometry. EoL-1 treated with pan-CD45, CD45RA, CD45RB, and CD95 mAb exhibited caspase-3 and -9 activation at 12 h post-treatment, which increased at 16 and 20 h. Activated caspase-8 was detected 12 and 16 h after ligation with CD45, CD45RA, CD45RB, and CD95 mAb followed by a trend toward basal levels at 20 h. CD69 ligation resulted in caspase-3 activation, a modest but significant activation of caspase-8, and a loss in mitochondrial transmembrane potential but had no significant effect on activation of caspase-9. Thus, the intrinsic and extrinsic caspase pathways are involved in controlling receptor ligation-mediated apoptosis induction in human eosinophils, findings that may aid the development of a more targeted, anti-inflammatory therapy for asthma.

Bacterial GroEL-like heat shock protein 60 protects epithelial cells from stress-induced death through activation of ERK and inhibition of caspase 3

Bacterial heat shock proteins (hsps) can have various effects on human cells. We investigated whether bacterial hsp60s can protect epithelial cells from cell death by affecting the mitogen-activated protein kinase (MAPK) signal pathways. Cell protection was studied by adding bacterial hsp60s to skin keratinocyte cultures (HaCaT cell line) before UV radiation. The results show that hsp60 significantly protected against UV radiation-induced cell death. Effects of UV radiation and exogenous hsp60 on phosphorylation of MAPKs and on activation of caspase 3 were examined by Western blot analysis. UV radiation strongly induced phosphorylation of p38 MAPK and formation of active caspase 3. A p38 inhibitor, SB 203580, totally blocked UV radiation-mediated activation of caspase 3. Preincubation with hsp60 strongly induced phosphorylation of ERK1/2 and inhibited UV radiation-mediated activation of caspase 3. PD 98059, a specific inhibitor of the ERK1/2 pathway, blocked this inhibitory effect of exogenous hsp60. Studies on the association between activity of MAPKs or caspase 3 and cell death showed that the ERK1/2 pathway inhibitor reversed protective effect of hsp60 while specific inhibition of p38 and caspase 3 reduced cell death. These results indicate that in HaCaT cells UV radiation mediates cell death through activation of p38 followed by caspase 3 activation. Exogenous hsp60 partially protects against UV radiation-mediated epithelial cell death through activation of ERK1/2, which inhibits caspase 3 activation.

Suppression of Extracellular Signal-related Kinase and Activation of p38 MAPK Are Two Critical Events Leading to Caspase-8- and Mitochondria-mediated Cell Death in Phytosphingosine-treated Human Cancer Cells

We previously demonstrated that the phytosphingosine-induced apoptosis was accompanied by the concomitant induction of both the caspase-8-mediated and mitochondrial activation-mediated apoptosis pathways. In the present study, we investigated the role of mitogen-activated protein kinases (MAPKs) in the activation of these two distinct cell death pathways induced by phytosphingosine in human cancer cells. Phytosphingosine caused strong induction of caspase-8 activity and caspase-independent Bax translocation to the mitochondria. A rapid decrease of phosphorylated ERK1/2 and a marked increase of p38 MAPK phosphorylation were observed within 10 min after phytosphingosine treatment. Activation of ERK1/2 by pretreatment with phorbol 12-myristate 13-acetate or forced expression of ERK1/2 attenuated phytosphingosine-induced caspase-8 activation. However, Bax translocation and caspase-9 activation was unaffected, indicating that down-regulation of the ERK activity is specifically required for the phytosphingosine-induced caspase-8-dependent cell death pathway. On the other hand, treatment with SB203580, a p38 MAPK-specific inhibitor, or expression of a dominant negative form of p38 MAPK suppressed phytosphingosine-induced translocation of the proapoptotic protein, Bax, from the cytosol to mitochondria, cytochrome c release, and subsequent caspase-9 activation but did not affect caspase-8 activation, indicating that activation of p38 MAPK is involved in the mitochondrial activation-mediated cell death pathway. Our results suggest that phytosphingosine can utilize two different MAPK signaling pathways for amplifying the apoptosis cascade, enhancing the understanding of the molecular mechanisms utilized by naturally occurring metabolites to regulate cell death. Molecular dissection of the signaling pathways that activate the apoptotic cell death machinery is critical for both our understanding of cell death events and development of cancer therapeutic agents.

Regulation of eosinophil apoptosis by nitric oxide: Role of c-Jun-N-terminal kinase and signal transducer and activator of transcription 5

BACKGROUND

Reduced eosinophil apoptosis is considered to be a key mechanism for eosinophilia in allergic diseases such as asthma, rhinitis, and eczema.

OBJECTIVE

The aim of our study was to investigate the possible modulatory effect of nitric oxide (NO) in human eosinophils.

METHODS

Apoptosis in isolated eosinophils was assessed by relative DNA fragmentation assay, annexin-V binding, and morphologic analysis. The activation of c-Jun-N-terminal kinase (JNK) and signal transducer and activator of transcription 5 (STAT5) was assessed by immunoblot analysis.

RESULTS

The NO donor S-nitroso-N -acetylpenicillamine (SNAP) reversed the survival-prolonging effect of IL-5 by inducing apoptosis. This effect was blocked by the NO scavenger (2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide.potassium salt), indicating that reversal of IL-5-mediated eosinophil survival was due to NO. The effect of NO on IL-5-afforded cell survival was not mediated by cyclic guanosine 3': 5'-monophosphate (cGMP), because neither an inhibitor of guanylyl cyclase nor inhibitors of phosphodiesterases had any effect on SNAP-induced eosinophil apoptosis in IL-5-treated cells. SNAP induced a time-dependent increase in the activity of JNK, and an inhibitor peptide specific for JNK, L-JNKI1, completely reversed SNAP-induced apoptosis in IL-5-treated eosinophils. In contrast, SNAP did not inhibit IL-5-induced STAT5 activation. Inhibition of the activity of caspases by Z-Asp-CH(2)-DCB reversed the effect of SNAP, suggesting that NO promotes apoptosis in IL-5-treated human eosinophils in a caspase-dependent manner. However, this effect of NO was not mediated by means of activation of caspases 3, 8, or 9.

CONCLUSIONS

Our results suggest that exogenous NO reverses IL-5-mediated eosinophil survival by inducing apoptosis, and this is mediated by means of activation of JNK in a cGMP-independent manner.

Interleukin-3, -5, and granulocyte macrophage colony-stimulating factor-induced adhesion molecule expression on eosinophils by p38 mitogen-activated protein kinase and nuclear factor-[kappa] B

We investigated the intracellular signaling mechanisms for cytokine interleukin (IL)-3, IL-5, or granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced expression of adhesion molecules including very late antigen 4 (CD49 d), macrophage antigen-1 (CD11b), leukocyte function-associated antigen-1 (CD11a/CD18), intercellular adhesion molecule (ICAM)-1, and ICAM-3 on eosinophils. The expression of adhesion molecules and nuclear factor (NF)-kappaB pathway was measured by flow cytometry and cDNA expression array, respectively. The phosphorylation of inhibitor kappaB-alpha and p38 mitogen-activated protein kinase (MAPK) was detected by Western blot, whereas NF-kappaB activity was measured by electrophoretic mobility shift assay. IL-3, IL-5, and GM-CSF could enhance p38 MAPK and NF-kappaB activity and induce ICAM-1, CD11b, and CD18 expressions on eosinophils. They could suppress ICAM-3 expression, but had no effect on CD49 d expression. Either SB 203580 or MG-132 was able to offset the cytokine-induced expression of ICAM-1. Only SB 203580 could reverse the effect on CD11b, CD18, and ICAM-3 expressions. Therefore, the expression of ICAM-1 might involve both p38 MAPK and NF-kappaB activities, whereas the regulation of CD11b, CD18, and ICAM-3 expressions might be mediated through p38 MAPK but not NF-kappaB. These cytokines therefore play a crucial role, via the p38 MAPK and NF-kappaB pathways, in the expression of important adhesion molecules on eosinophils in allergic inflammation.

IgD-receptor (IgD-R) cross-linking partially protects murine T cells from dexamethasone-induced apoptosis

Based on our previous findings that immunoglobulin D (IgD) receptor (IgD-R) cross-linking with oligomeric IgD (IgD-R-xL) led to T cell activation, we examined the effect of IgD-R-xL on the expression of Fas antigen and apoptosis induction. In splenic T cells, IgD-R-xL followed by dexamethasone (dex) treatment resulted in a decreased percentage of Fas-positive cells as well as a decreased mean fluorescence intensity (P<0.05) when compared with cells treated with dex alone. There are significant differences in annexin-fluorescein isothiocyanate (FITC) and phosphatidylinositol (PI) staining between samples treated with dex alone and IgD-R-xL followed by dex-treated samples (P<0.05), suggesting a protective role for IgD-R-xL. No significant differences are seen in Fas antigen expression, annexin-FITC staining, and/or PI staining in murine T hybridoma (7C5) cells cultured under similar conditions (P<0.07). We hypothesize that ligation of IgD-R may predispose antigen-specific T lymphocytes for survival during primary immune responses when IgD-positive B cells serve as antigen-presenting cells.

Interleukin-6 enhances whereas tumor necrosis factor alpha and interferons inhibit integrin expression and adhesion of human mast cells to extracellular matrix proteins

Integrins are expressed on mast cells and constitute an essential prerequisite for the accumulation of the cells at sites of inflammation. In order to clarify a potential contribution of inflammatory cytokines to this process, we have studied the modulation of integrin expression and adhesion of immature human mast cells (HMC-1) to extracellular matrix proteins by interleukin-6, tumor necrosis factor alpha, interferon-alpha and interferon-gamma. Corticosteroids were used for comparison. On fluorescence-activated cell sorter analysis, preincubation of cells for 48 h with different concentrations of interleukin-6 induced a significant, up to 40%, increase of alpha v alpha 5, CD49b (alpha 2), CD49e (alpha 5), CD49f (alpha 6), and CD51 (alpha v). In contrast, different concentrations of tumor necrosis factor alpha, interferon-alpha, interferon-gamma, and dexamethasone (10-8-10-10 M) inhibited expression of adhesion receptors by up to 60%, reaching significance for some but not all integrins. On semiquantitative polymerase chain reaction analysis, interleukin-6, the other cytokines, and corticosteroids significantly modulated expression of alpha1, alpha v and alpha 5 integrin chains at mRNA level. Functional significance of these findings was proven in adhesion assays using fibronectin, laminin, and vitronectin, with interleukin-6 causing significant enhancement of adhesion in all cases, tumor necrosis factor alpha and dexamethasone inducing significant reduction of adhesion to fibronectin and laminin, and interferon-gamma significantly inhibiting adhesion to fibronectin only. Specificity of interleukin-6-induced changes was demonstrated using antibodies against alpha1 and alpha 5 integrins in unstimulated and interleukin-6-prestimulated cells. These data show that interleukin-6 stimulates mast cell adhesion to extracellular matrix and thus allows for the accumulation of the cells at tissue sites by enhancing integrin expression, whereas tumor necrosis factor alpha, interferon-alpha, interferon-gamma, and dexamethasone downmodulate this process.

Oxidant-mediated mitochondrial injury in eosinophil apoptosis: enhancement by glucocorticoids and inhibition by granulocyte-macrophage colony-stimulating factor

The mainstay of asthma therapy, glucocorticosteroids (GCs) have among their therapeutic effects the inhibition of inflammatory cytokine production and induction of eosinophil apoptosis. In the absence of prosurvival cytokines (e.g., GM-CSF), eosinophils appear to be short-lived, undergoing apoptosis over 96 h in vitro. In a dose-dependent manner, GC further enhances apoptosis, while prosurvival cytokines inhibit apoptosis and antagonize the effect of GC. The mechanisms of eosinophil apoptosis, its enhancement by GC, and antagonism of GC by GM-CSF are not well-understood. As demonstrated in this study, baseline apoptosis of eosinophils resulted from oxidant-mediated mitochondrial injury that was significantly enhanced by GC. Mitochondrial injury was detected by early and progressive loss of mitochondrial membrane potential and the antioxidant protein, Mn superoxide dismutase (SOD). Also observed was the activation/translocation of the proapoptotic protein, Bax, to mitochondria. Underscoring the role of oxidants was the inhibition of mitochondrial changes and apoptosis with culture in hypoxia, or pretreatment with a flavoprotein inhibitor or a SOD mimic. GCs demonstrated early (40 min) and late (16 h) activation of proapoptotic c-Jun NH2-terminal kinase (JNK) and decreased the antiapoptotic protein X-linked inhibitor of apoptosis, a recently demonstrated inhibitor of JNK activation. Similarly, inhibition of JNK prevented GC-enhanced mitochondrial injury and apoptosis. Importantly, GM-CSF prevented GC-induced loss of X-linked inhibitor of apoptosis protein, late activation of JNK, and mitochondrial injury even in the face of unchanged oxidant production, loss of MnSOD, and early JNK activation. These data demonstrate that oxidant-induced mitochondrial injury is pivotal in eosinophil apoptosis, and is enhanced by GC-induced prolonged JNK activation that is in turn inhibited by GM-CSF.

Cell-specific regulation of apoptosis by glucocorticoids: implication to their anti-inflammatory action

Glucocorticoids play a major role in attenuation of the inflammatory response. These steroid hormones are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages, and T lymphocytes that are involved in the inflammation reaction. In contrast, it was discovered recently that in glandular cells such as the mammary gland epithelia, hepatocytes, ovarian follicular cells, and in fibroblasts glucocorticoids protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors, and death genes. The anti-apoptotic effect of glucocorticoids is exerted by modulation of several survival genes such as Bcl-2, Bcl-x(L), and NFkB, in a cell-specific manner. Moreover, upregulation or downregulation of the same gene product can occur in a cell-dependent manner following stimulation by glucocorticoids. This phenomenon is probably due to composite regulatory cross-talk among multiple nuclear coactivators or corepressors, which mediate the transcription regulation of the genes, by their interaction with the glucocorticoid receptor. These observations suggest that the anti-inflammatory action of glucocorticoids is exerted by two complementary mechanisms: on one hand, they induce death of the cells that provoke the inflammation, and on the other hand they protect the resident cells of the inflamed tissue by arresting apoptotic signals. Moreover, the complementary action of glucocorticoids provides a new insight to the therapeutic potential of these hormones.

Activation of p38 mitogen-activated protein kinase and nuclear factor-kappaB in tumour necrosis factor-induced eotaxin release of human eosinophils

The CC chemokine eotaxin is a potent eosinophil-specific chemoattractant that is crucial for allergic inflammation. Allergen-induced tumour necrosis factor (TNF) has been shown to induce eotaxin synthesis in eosinophils. Nuclear factor-kappaB (NF-kappaB) and mitogen-activated protein kinases (MAPK) have been found to play an essential role for the eotaxin-mediated eosinophilia. We investigated the modulation of NF-kappaB and MAPK activation in TNF-induced eotaxin release of human eosinophils. Human blood eosinophils were purified from fresh buffy coat using magnetic cell sorting. NF-kappaB pathway-related genes were evaluated by cDNA expression array system. Degradation of IkappaBalpha and phosphorylation of MAPK were detected by Western blot. Activation of NF-kappaB was determined by electrophoretic mobility shift assay. Eotaxin released into the eosinophil culture medium was measured by ELISA. TNF was found to up-regulate the gene expression of NF-kappaB and IkappaBalpha in eosinophils. TNF-induced IkappaBalpha degradation was inhibited by the proteasome inhibitor N-cbz-Leu-Leu-leucinal (MG-132) and a non-steroidal anti-inflammatory drug sodium salicylate (NaSal). Using EMSA, both MG-132 and NaSal were found to suppress the TNF-induced NF-kappaB activation in eosinophils. Furthermore, TNF was shown to induce phosphorylation of p38 MAPK time-dependently but not extracellular signal-regulated kinases (ERK). Inhibition of NF-kappaB activation and p38 MAPK activity decreased the TNF-induced release of eotaxin from eosinophils. These results indicate that NF-kappaB and p38 MAPK play an important role in TNF-activated signalling pathway regulating eotaxin release by eosinophils. They have also provided a biochemical basis for the potential of using specific inhibitors of NF-kappaB and p38 MAPK for treating allergic inflammation.

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.

Caspase activation in the absence of mitochondrial changes in granulocyte apoptosis

Eosinophils and neutrophils are two different types of granulocytes evolved from a common haematopoetic precursor in the bone marrow. Eosinophils are mainly involved in parasitic infection and allergic inflammation while neutrophils mainly participate in the defence against bacterial infections. Prolongation of granulocyte life span by inhibition of apoptosis may lead to tissue load of cells, and this has been detected in different inflammatory reactions. The molecular mechanisms and the potential role of the mitochondria in granulocyte apoptosis are poorly understood. In the present study we have characterized further the role of the mitochondria in granulocyte-apoptosis by studying the sequence of mitochondrial permeability transition (MPT) induction, loss of mitochondrial membrane potential (Deltapsim) and release of cytochrome c. This was made possible by applying tributyltin (TBT), a well-characterized apoptotic stimulus and MPT-inducer. We also studied potential differences in apoptosis-susceptibility between eosinophils and neutrophils. Ten minutes of TBT-exposure resulted in a substantial caspase-3 activity in both eosinophils and neutrophils, followed by phosphatidylserine (PS)-exposure after 30-120 min. Interestingly, caspase-3 activity was not preceded by MPT-induction, loss of Deltapsim or by cytochrome c-release in either eosinophils or neutrophils. In conclusion, we have demonstrated an extremely rapid induction of caspase-3 activity and apoptosis in human blood granulocytes without prior mitochondrial changes, including loss of mitochondrial membrane potential and release of cytochrome c. Our results open the possibility for a mitochondrial-independent activation of caspase 3 and subsequent apoptosis in granulocytes.

Critical role of mitochondria, but not caspases, during glucocorticosteroid-induced human eosinophil apoptosis

Glucocorticosteroids are potent anti-inflammatory drugs used in the treatment of eosinophilic disorders. These molecules directly promote eosinophil apoptosis, yet the molecular mechanisms regulating this process remain ill-defined. We show here that stimulation of human peripheral blood eosinophils with dexamethasone induced DNA fragmentation, chromatin and cytoplasm condensation, and caspase-3 activation, as assessed by the proteolysis of its zymogen form and by the increase of caspase-3-like activity in eosinophil lysates. These phenomena were accompanied by a reduced uptake of the mitochondrial potential-sensitive marker DiOC(6)(3), suggestive of mitochondrial membrane permeabilization. Eosinophil incubation with the caspase-3 inhibitor, Z-Asp-Glu-Val-Asp-fluromethylketone, or with the broad spectrum caspase inhibitor, Z-Val-Ala-Asp-fluromethylketone, inhibited caspase-3-like activity generation but failed to modify dexamethasone-mediated loss in mitochondrial transmembrane potential and eosinophil apoptosis. In contrast, bongkrekic acid, a ligand of the mitochondrial permeability transition pore component, adenine nucleotide translocator, prevented both dexamethasone-induced mitochondrial disruption and apoptosis. We conclude that the mitochondrial permeability transition pore, rather than the caspase cascade, plays a critical role in the propagation of glucocorticosteroid-mediated apoptotic signals in human eosinophils.

The anti-inflammatory action of glucocorticoids is mediated by cell type specific regulation of apoptosis

Glucocorticoids play a major role in attenuation of the inflammatory response. These steroid hormones are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages and T-lymphocytes that are involved in the inflammation reaction. In contrast, it was discovered recently that in glandular cells such as the mammary gland epithelia, hepatocytes, ovarian follicular cells and in fibroblasts glucocorticoids protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors and death genes. The anti-apoptotic effect of glucocorticoids is exerted by modulation of several survival genes such as Bcl-2, Bcl-x(L) and NFkappaB, in a cell type-specific manner. Moreover, up regulation or down regulation of the same gene product can occur in a cell type-dependent manner following stimulation by glucocorticoids. This phenomenon is probably due to composite regulatory cross-talk among multiple nuclear coactivators or corepressors, which mediate the transcriptional regulation of the genes, by their interaction with the glucocorticoid receptor (GR). These observations suggest that the anti-inflammatory action of glucocorticoids is exerted by two complementary mechanisms: on the one hand, they induce death of the cells that provoke the inflammation, and on the other hand, they protect the resident cells of the inflamed tissue by arresting apoptotic signals.

Interleukin-5 inhibits translocation of Bax to the mitochondria, cytochrome c release, and activation of caspases in human eosinophils

The apoptosis and subsequent clearance of eosinophils without histotoxic mediator release is thought to be crucial in the resolution of airway inflammation in asthma. Interleukin-5 (IL-5) is a potent suppressor of eosinophil apoptosis. The mechanism by which IL-5 inhibits spontaneous eosinophil apoptosis was investigated. Freshly isolated eosinophils constitutively expressed the conformationally active form of Bax in the cytosol and nucleus. During spontaneous and staurosporine-induced apoptosis, Bax underwent a caspase-independent translocation to the mitochondria, which was inhibited by IL-5. Eosinophil apoptosis was associated with the release of cytochrome c from the mitochondria, which was also inhibited by IL-5. IL-5 and the cell-permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-(OMe) fluoromethyl ketone (z-VAD.fmk), prevented phosphatidylserine (PS) externalization, although only IL-5 inhibited loss of mitochondrial membrane potential (DeltaPsim). Peripheral blood eosinophils endogenously expressed "initiator" caspase-8 and -9, and "effector" caspase-3, -6, and -7. Spontaneous eosinophil apoptosis was associated with processing of caspase-3, -6, -7, -8, and -9. IL-5 and z-VAD.fmk prevented caspase activation in spontaneous apoptosis. The results suggest that spontaneous eosinophil apoptosis involves Bax translocation to the mitochondria, cytochrome c release, caspase-independent perturbation of the mitochondrial membrane, and subsequent activation of caspases. IL-5 inhibits spontaneous eosinophil apoptosis at a site upstream of Bax translocation.

Dexamethasone destabilizes cyclooxygenase 2 mRNA by inhibiting mitogen-activated protein kinase p38

The stability of cyclooxygenase 2 (Cox-2) mRNA is regulated positively by proinflammatory stimuli acting through mitogen-activated protein kinase (MAPK) p38 and negatively by anti-inflammatory glucocorticoids such as dexamethasone. A tetracycline-regulated reporter system was used to investigate mechanisms of regulation of Cox-2 mRNA stability. Dexamethasone was found to destabilize beta-globin-Cox-2 reporter mRNAs by inhibiting p38. This inhibition occurred at the level of p38 itself: stabilization of reporter mRNA by a kinase upstream of p38 was blocked by dexamethasone, while stabilization by a kinase downstream of p38 was insensitive to dexamethasone. Inhibition of p38 activity by dexamethasone was observed in a variety of cell types treated with different activating stimuli. Furthermore, inhibition of p38 was antagonized by the anti-glucocorticoid RU486 and was delayed and actinomycin D sensitive, suggesting that ongoing glucocorticoid receptor-dependent transcription is required.