Inhibition of mast cell Fc epsilon R1-mediated signaling and effector function by the Syk-selective inhibitor, piceatannol

Identifying and testing potential new anti-asthma agents

INTRODUCTION

Inhaled corticosteroids alone or with long-acting beta-2 agonists (LABA) are the basic treatment for stable asthma. While the majority of patients are controllable, some patients retain chronic severe disease and develop permanent alterations in airway function. For patients such as these it is important to better understand the mechanisms of asthma so that alternative approaches can be developed.

AREA COVERED

Based on data from in vitro cell culture, animal models and clinical trials, this review discusses potential agents targeting either key effector cells, mediators and their receptors in asthma pathogenesis or their signaling cascade molecules.

EXPERT OPINION

As targeting single Th2 cytokines and their receptors has been shown to have limited clinical benefit, it is important to identify and test potential new therapeutic agents. Recent studies suggest that blockade of IgE synthesis, its interaction with its receptors and downstream signaling, identification of molecular targets in innate immune and airways structural cells, and fresh anti-neutrophil strategies should be prominent among these. Further studies are required to clarify the relationship between airways remodeling and asthma severity so that appropriate patients may be targeted.

Phospho-proteomic analysis of mantle cell lymphoma cells suggests a pro-survival role of B-cell receptor signaling

Background

Mantle cell lymphoma (MCL) is currently an incurable entity, and new therapeutic approaches are needed. We have applied a high-throughput phospho-proteomic technique to MCL cell lines to identify activated pathways and we have then validated our data in both cell lines and tumor tissues.

Methods

PhosphoScan analysis was performed on MCL cell lines. Results were validated by flow cytometry and western blotting. Functional validation was performed by blocking the most active pathway in MCL cell lines.

Results

PhosphoScan identified more than 300 tyrosine-phosporylated proteins, among which many protein kinases. The most abundant peptides belonged to proteins connected with B-cell receptor (BCR) signaling. Active BCR signaling was demonstrated by flow cytometry in MCL cells and by western blotting in MCL tumor tissues. Blocking BCR signaling by Syk inhibitor piceatannol induced dose/time-dependent apoptosis in MCL cell lines, as well as several modifications in the phosphorylation status of BCR pathway members and a collapse of cyclin D1 protein levels.

Conclusion

Our data support a pro-survival role of BCR signaling in MCL and suggest that this pathway might be a candidate for therapy. Our findings also suggest that Syk activation patterns might be different in MCL compared to other lymphoma subtypes.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-011-0019-7) contains supplementary material, which is available to authorized users.

Recognition and functional activation of the human IgA receptor (FcalphaRI) by C-reactive protein

C-reactive protein (CRP) is an important biomarker for inflammatory diseases. However, its role in inflammation beyond complement-mediated pathogen clearance remains poorly defined. We identified the major IgA receptor, FcαRI, as a ligand for pentraxins. CRP recognized FcαRI both in solution and on cells, and the pentraxin binding site on the receptor appears distinct from that recognized by IgA. Further competitive binding and mutational analysis showed that FcαRI bound to the effector face of CRP in a region overlapping with complement C1q and Fcγ receptor (FcγR) binding sites. CRP cross-linking of FcαRI resulted in extracellular signal-regulated kinase (ERK) phosphorylation, cytokine production, and degranulation in FcαRI-transfected RBL cells. In neutrophils, CRP induced FcαRI surface expression, phagocytosis, and TNF-α secretion. The ability of CRP to activate FcαRI defines a function for pentraxins in inflammatory responses involving neutrophils and macrophages. It also highlights the innate aspect of otherwise humoral immunity-associated antibody receptors.

Characterization of syk expression in human lung mast cells: relationship with function

BACKGROUND

Previous studies indicate that the protein tyrosine kinase, syk, is critical in transducing FcɛRI-mediated signals. In human basophils, 'releasability' has been linked to the extent of syk expression. Human lung mast cells, like basophils, are also found to be variably responsive to IgE-dependent activation.

OBJECTIVE

The aim of the present study was to determine whether the wide variability in human lung mast cell responses, following IgE-dependent activation, has a relationship with syk expression.

METHODS

Mast cells were isolated from human lung tissue and 'releasability' was determined by activating the cells with a maximal releasing concentration of anti-IgE. Syk levels in mast cells were determined by immunoblotting and flow cytometry.

RESULTS

Histamine release from mast cells, challenged with a maximal releasing concentration of anti-IgE, ranged from 0% to 69% (mean±SEM, 24±2%, n=53). A proportion of these preparations (nine out of 53) released very low levels of histamine (5%) in response to anti-IgE. Flow cytometry of a subset of preparations indicated that a weak response to anti-IgE was not related to a lack of surface IgE. Immunoblotting and flow cytometry studies demonstrated that, compared with mononuclear cells, human lung mast cells express low and variable levels of syk. However, there was no correlation between syk expression and mast cell releasability. Nonetheless, a number of putative inhibitors of syk including NVP-QAB205 (EC₅₀, 0.2 μm) effectively attenuated the IgE-dependent release of histamine from mast cells.

CONCLUSION AND CLINICAL RELEVANCE

These studies indicate that although syk may play an important role in mediating degranulation, the relative level of syk expression does not govern human lung mast cell releasability. Identification of the mechanisms that govern IgE-dependent activation of human lung mast cells is likely to be of wider clinical significance, given the central role that mast cells play in the development of allergic asthma.

Ubiquitination and endocytosis of the high affinity receptor for IgE

The high affinity receptor for IgE (FcvarepsilonRI) is constitutivelly expressed on the surface of mast cells and basophils as a multimeric complex. Upon antigen ligation to FcvarepsilonRI-bound IgE molecules, the receptor complex transduces intracellular signals leading to the release of preformed and newly synthesised pro-inflammatory mediators. FcvarepsilonRI engagement also generates negative intracellular signals involving the coordinated action of adapters, phosphatases and ubiquitin ligases that limits the intensity and duration of positive signals. Relevant to this, antigen-induced FcvarepsilonRI ubiquitination has become recognized as an important signal for the internalization and delivery of engaged receptor complexes to lysosomes for degradation. In this article, we review recent advances in our understanding of molecular mechanisms that guarantee the clearance of antigen-stimulated FcvarepsilonRI complexes from the cell surface. A particular emphasis will be given on how lipid rafts and the ubiquitin pathway cooperate to ensure receptor internalization and sorting along the endocytic compartments. A brief discussion regarding how ubiquitination regulates the endocytosis of Fc receptors other than FcvarepsilonRI will be included.

Nicotine inhibits Fc epsilon RI-induced cysteinyl leukotrienes and cytokine production without affecting mast cell degranulation through alpha 7/alpha 9/alpha 10-nicotinic receptors

Smokers are less likely to develop some inflammatory and allergic diseases. In Brown-Norway rats, nicotine inhibits several parameters of allergic asthma, including the production of Th2 cytokines and the cysteinyl leukotriene LTC(4). Cysteinyl leukotrienes are primarily produced by mast cells, and these cells play a central role in allergic asthma. Mast cells express a high-affinity receptor for IgE (FcepsilonRI). Following its cross-linking, cells degranulate and release preformed inflammatory mediators (early phase) and synthesize and secrete cytokines/chemokines and leukotrienes (late phase). The mechanism by which nicotine modulates mast cell activation is unclear. Using alpha-bungarotoxin binding and quantitative PCR and PCR product sequencing, we showed that the rat mast/basophil cell line RBL-2H3 expresses nicotinic acetylcholine receptors (nAChRs) alpha7, alpha9, and alpha10; exposure to exceedingly low concentrations of nicotine (nanomolar), but not the biologically inactive metabolite cotinine, for > or = 8 h suppressed the late phase (leukotriene/cytokine production) but not degranulation (histamine and hexosaminidase release). These effects were unrelated to those of nicotine on intracellular free calcium concentration but were causally associated with the inhibition of cytosolic phospholipase A(2) activity and the PI3K/ERK/NF-kappaB pathway, including phosphorylation of Akt and ERK and nuclear translocation of NF-kappaB. The suppressive effect of nicotine on the late-phase response was blocked by the alpha7/alpha9-nAChR antagonists methyllycaconitine and alpha-bungarotoxin, as well as by small interfering RNA knockdown of alpha7-, alpha9-, or alpha10-nAChRs, suggesting a functional interaction between alpha7-, alpha9-, and alpha10-nAChRs that might explain the response of RBL cells to nanomolar concentrations of nicotine. This "hybrid" receptor might serve as a target for novel antiallergic/antiasthmatic therapies.

Piceatannol inhibits phorbol ester-induced NF-kappa B activation and COX-2 expression in cultured human mammary epithelial cells

There are multiple lines of evidence supporting that inflammation is causally linked to carcinogenesis. Abnormal upregulation of cyclooxygenase-2 (COX-2), a rate-limiting enzyme in the prostaglandin biosynthesis, has been implicated in carcinogenesis. Trans-3,4,3',5'-tetrahydroxystilbene (piceatannol), a naturally occurring hydroxylated stilbene with potent anti-inflammatory and antioxidative activities, has been shown to inhibit the proliferation of several cancer cells by inducing apoptosis or blocking cell cycle progression. In this study, we examined the effect of piceatannol on activation of the nuclear transcription factor NF-kappa B, one of the major transcription factors that regulate proinflammatory COX-2 gene transcription, in human mammary epithelial (MCF-10A) cells treated with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). When pretreated to MCF-10A cells, piceatannol markedly inhibited TPA-induced NF-kappa B DNA binding to a greater extent than resveratrol and oxyresveratrol, stilbene analogs structurally related to piceatannol. Piceatannol also inhibited TPA-induced phosphorylation and degradation of Ikappa Balpha as well as nuclear translocation of the phosphorylated form of p65, the functionally active subunit of NF-kappa B. Likewise, TPA-induced expression of COX-2 was abrogated by piceatannol pretreatment. The thiol reducing agent dithiothreitol abolished the inhibitory effects of piceatannol on NF-kappa B DNA binding activity, suggesting that piceatannol may directly modify NF-kappa B or its regulator through reaction with the cysteine thiol(s).

Analysis of FcgammaRIIA cytoplasmic tail requirements in signaling for serotonin secretion: evidence for an ITAM-dependent, PI3K-dependent pathway

The human Fc receptor, FcgammaRIIA, is known to mediate phagocytosis and endocytosis, yet the greatest numbers of these receptors are expressed on the surface of non-phagocytic platelets, where they are involved in serotonin secretion. FcgammaRIIA harbours three tyrosine (Y) residues within its cytoplasmic domain. Y1 is upstream of both Y2 and Y3, which are contained within an immunoreceptor tyrosine-based activation motif (ITAM), required for many signaling events. We have demonstrated that the two ITAM tyrosines are required for phagocytic signaling and that mutation of a single ITAM tyrosine decreases but does not abolish phagocytic signaling. Furthermore, we have identified that the YMTL motif is required for endocytosis. These observations suggest that FcgammaRIIA utilizes different sequences for various signaling events. Therefore, we investigated the sequence requirements for another important FcgammaRIIA-mediated signaling event, serotonin secretion, using Rat Basophilic Leukemia (RBL-2H3) cells transfected with wildtype (WT) FcgammaRIIA or mutant FcgammaRIIA. Stimulation of cells expressing WT FcgammaRIIA induced release of serotonin at a level 7-fold greater than that in nonstimulated WT FcgammaRIIA-transfected cells or nontransfected RBL cells. Mutation of either ITAM tyrosine (Y2 or Y3) to phenylalanine was sufficient to abolish serotonin secretion. Further, while inhibition of Syk with piceatannol blocked phagocytosis as expected, it did not inhibit serotonin secretion. Additionally, inhibition of phosphoinositol-3-kinase (PI3K) with wortmannin only had a partial effect on serotonin signaling, despite the fact that the concentrations used completely abolished phagocytic signaling. These data suggest that the requirements for serotonin secretion differ from those for phagocytosis mediated by FcgammaRIIA.

Schistosoma mansoni: signal transduction processes during the development of the reproductive organs

Among the topics of considerable interest concerning our understanding of the unusual biology of schistosomes is the sexual maturation of the female. The identification of genes coding for signal transduction proteins controlling essential steps of the pairing-dependent differentiation of the reproductive organs, vitellarium and ovary will help to substantiate our knowledge about this unique parasite. Furthermore, such signalling proteins could be potential targets to interfere with the development of this parasite to combat schistosomiasis since its pathology is caused by the eggs. This review summarises first post-genomic steps to elucidate the function of gonad-specific signalling molecules which were identified by homology-based cloning strategies, by in silico identification or by yeast two-hybrid interaction analyses, using a combination of novel techniques. These include the in vitro culture of adult schistosomes, their treatment with chemical inhibitors to block enzyme activity, the use of RNAi to silence gene function post-transcriptionally, and confocal laser scanning microscopy to study the morphological consequences of these experimental approaches. Finally, we propose a first model of protein networks that are active in the ovary regulating mitogenic activity and differentiation. Some of these molecules are also active in the testes of males, probably fulfilling similar roles as in the ovary.

The Syk kinase SmTK4 of Schistosoma mansoni is involved in the regulation of spermatogenesis and oogenesis

The signal transduction protein SmTK4 from Schistosoma mansoni belongs to the family of Syk kinases. In vertebrates, Syk kinases are known to play specialized roles in signaling pathways in cells of the hematopoietic system. Although Syk kinases were identified in some invertebrates, their role in this group of animals has not yet been elucidated. Since SmTK4 is the first Syk kinase from a parasitic helminth, shown to be predominantly expressed in the testes and ovary of adult worms, we investigated its function. To unravel signaling cascades in which SmTK4 is involved, yeast two-/three-hybrid library screenings were performed with either the tandem SH2-domain, or with the linker region including the tyrosine kinase domain of SmTK4. Besides the Src kinase SmTK3 we identified a new Src kinase (SmTK6) acting upstream of SmTK4 and a MAPK-activating protein, as well as mapmodulin acting downstream. Their identities and colocalization studies pointed to a role of SmTK4 in a signaling cascade regulating the proliferation and/or differentiation of cells in the gonads of schistosomes. To confirm this decisive role we performed biochemical and molecular approaches to knock down SmTK4 combined with a novel protocol for confocal laser scanning microscopy for morphological analyses. Using the Syk kinase-specific inhibitor Piceatannol or by RNAi treatment of adult schistosomes in vitro, corresponding phenotypes were detected in the testes and ovary. In the Xenopus oocyte system it was finally confirmed that Piceatannol suppressed the activity of the catalytic kinase domain of SmTK4. Our findings demonstrate a pivotal role of SmTK4 in gametogenesis, a new function for Syk kinases in eukaryotes.

Formation of a mast cell synapse: Fc epsilon RI membrane dynamics upon binding mobile or immobilized ligands on surfaces

Fc epsilonRI on mast cells form a synapse when presented with mobile, bilayer-incorporated Ag. In this study, we show that receptor reorganization within the contacting mast cell membrane is markedly different upon binding of mobile and immobilized ligands. Rat basophilic leukemia mast cells primed with fluorescent anti-DNP IgE were engaged by surfaces presenting either bilayer-incorporated, monovalent DNP-lipid (mobile ligand), or chemically cross-linked, multivalent DNP (immobilized ligand). Total internal reflection fluorescence imaging and electron microscopy methods were used to visualize receptor reorganization at the contact site. The spatial relationships of Fc epsilonRI to other cellular components at the synapse, such as actin, cholesterol, and linker for activation of T cells, were also analyzed. Stimulation of mast cells with immobilized polyvalent ligand resulted in typical levels of degranulation. Remarkably, degranulation also followed interaction of mast cells, with bilayers presenting mobile, monovalent ligand. Receptors engaged with mobile ligand coalesce into large, cholesterol-rich clusters that occupy the central portion of the contacting membrane. These data indicate that Fc epsilonRI cross-linking is not an obligatory step in triggering mast cell signaling and suggest that dense populations of mobile receptors are capable of initiating low-level degranulation upon ligand recognition.

Therapeutic prospect of Syk inhibitors

BACKGROUND

The non-receptor spleen tyrosine kinase (Syk; EC 2.7.10.2) is involved in signal transduction in a variety of cell types. In particular, it is a key mediator of immune receptors signaling in host inflammatory cells (B cells, mast cells, macrophages and neutrophils), important for both allergic and antibody-mediated autoimmune diseases. Deregulated Syk kinase activity also allows growth factor-independent proliferation and transforms bone marrow-derived pre-B cells that are able to induce leukemia. Consequently, the development of Syk kinase inhibitors could conceivably treat these disorders and so they have became a major focus in the pharmaceutical and biotech industry.

OBJECTIVE

In this review, we analyze the structure and role of Syk kinase, the use of small molecules, interacting with ATP-binding site, as inhibitors of kinase activity and finally the potential of using inhibitors of Syk kinase expression to attenuate pathological conditions.

CONCLUSION

Syk kinase inhibition is suggested as a powerful tool for the therapy of different pathologies.

B-cell anergy is maintained in anti-DNA transgenic NZB/NZW mice

Clonal anergy has been well recognized as an important mechanism of B cell immunologic tolerance. However, the properties of anergic B cells and especially their role in the development of autoimmune disease in susceptible animals have been controversial. Here we show that low-affinity anti-DNA anergic B cells populate the mature B-cell compartment in the mouse spleen in excessive numbers and display paradoxical behavior in response to a combined B-cell receptor/TLR9 activation. Surprisingly, B-cell anergy was maintained in aged NZB/NZW F1 mice that develop a systemic lupus erythematosus (SLE)-like autoimmune disease. In several parameters of anergy, such as calcium mobilization and antibody secretion, the lupus-prone mice appeared more anergic than their non-autoimmune counterparts. We conclude that low-affinity anergic B cells are unlikely to serve as precursors for the high-affinity autoreactive B cells that give rise to pathogenic anti-DNA auto-antibodies in SLE.

Lyn-mediated mitochondrial tyrosine phosphorylation is required to preserve mitochondrial integrity in early liver regeneration

Functional alterations in mitochondria such as overproduction of ROS (reactive oxygen species) and overloading of calcium, with subsequent change in the membrane potential, are traditionally regarded as pro-apoptotic conditions. Although such events occur in the early phases of LR (liver regeneration) after two-thirds PH (partial hepatectomy), hepatocytes do not undergo apoptosis but continue to proliferate until the mass of the liver is restored. The aim of the present study was to establish whether tyrosine phosphorylation, an emerging mechanism of regulation of mitochondrial function, participates in the response to liver injury following PH and is involved in contrasting mitochondrial pro-apoptotic signalling. Mitochondrial tyrosine phosphorylation, negligible in the quiescent liver, was detected in the early phases of LR with a trend similar to the events heralding mitochondrial apoptosis and was attributed to the tyrosine kinase Lyn, a member of the Src family. Lyn was shown to accumulate in an active form in the mitochondrial intermembrane space, where it was found to be associated with a multiprotein complex. Our results highlight a role for tyrosine phosphorylation in accompanying, and ultimately counteracting, mitochondrial events otherwise leading to apoptosis, hence conveying information required to preserve the mitochondrial integrity during LR.

Comparison of the anti-allergic activity of Syk inhibitors with optimized Syk siRNAs in FcepsilonRI-activated RBL-2H3 basophilic cells

Spleen tyrosine kinase (Syk) binds ITAM-bearing receptors in a wide variety of cell types. One such example is the activation of mast cells, basophils and eosinophils via the stimulation of the FcepsilonRI receptor by IgE/allergen complexes. The possible role of Syk in inflammatory signaling cascades has led to the development of pharmacological agents designed to block the Syk catalytic domain as potential novel therapeutics. Whilst the enzymatic activity of Syk lends towards the design of small-molecule inhibitors, other attention has focused on the possibility of targeting Syk expression using anti-sense oligonucleotides as an alternate means of anti-inflammatory therapy. In this study, we compared the ability of multiple optimized Syk siRNA sequences and small-molecule Syk inhibitors to block FcepsilonRI-mediated signal transduction, degranulation and TNFalpha secretion in the basophilic cell line RBL-2H3. We also characterized the specificity of each siRNA sequence with regards to off-target induction of the interferon-inducible gene IFIT1. We identified a single siRNA sequence, which displayed a favorable profile of efficient Syk knockdown, blockage of FcepsilonRI-mediated signal transduction, degranulation and TNFalpha secretion and a lack of IFIT1 induction. The effect of this siRNA was comparable to that of the Syk kinase domain inhibitors BAY61-3606 and R406. The identification of an active and specific Syk siRNA could be a basis for the development of therapeutic Syk siRNAs against inflammatory diseases.

Fcgamma receptor cross-linking stimulates cell proliferation of macrophages via the ERK pathway

Macrophage proliferation can be stimulated by phagocytosis and by cross-linking of Fcgamma receptors (FcgammaR). In this study, we investigated the role of FcgammaR and the signaling cascades that link FcgammaR activation to cell cycle progression. This effect was mediated by the activating FcgammaR, including FcgammaRI and III, via their Fcgamma subunit. Further investigation revealed that the cell cycle machinery was activated by FcgammaR cross-linking through downstream signaling events. Specifically, we identified the extracellular signal-regulated kinase (ERK) signaling pathway as a mediator of signals from FcgammaR activation to cyclin D1 expression, because cyclin D1 expression associated with FcgammaR cross-linking was attenuated by specific inhibitors of the ERK1/2 signaling pathway, PD98059 and U0126 and the spleen tyrosine kinase (Syk) inhibitor, Piceatannol. Our findings establish a link between the ERK activation and cell cycle signaling pathways, thus providing a causal mechanism by which FcgammaR activation produces a mitogenic effect that stimulates macrophage proliferation. Macrophage mitosis following FcgammaR activation could potentially affect the outcome of macrophage interactions with intracellular pathogens. In addition, our results suggest the possibility of new treatment options for certain infectious diseases, chronic inflammatory diseases, and leukemias based on interference with FcgammaR-stimulated macrophage cell proliferation.

Expression of activated STAT5 in neoplastic mast cells in systemic mastocytosis: subcellular distribution and role of the transforming oncoprotein KIT D816V

Recent data suggest that the signal transducer and activator of transcription (STAT)5 contributes to differentiation and growth of mast cells. It has also been described that constitutively phosphorylated STAT5 (pSTAT5) plays a pro-oncogenic role in various myeloid neoplasms. We examined the expression of pSTAT5 in neoplastic mast cells in systemic mastocytosis and asked whether the disease-related oncoprotein KIT D816V is involved in STAT5 activation. As assessed by immunohistochemistry using the anti-pSTAT5 antibody AX1, neoplastic mast cells were found to display pSTAT5 in all SM patients examined (n = 40). Expression of pSTAT5 was also demonstrable in the KIT D816V-positive mast cell leukemia cell line HMC-1. Using various staining-protocols, pSTAT5 was found to be located in both the cytoplasmic and nuclear compartment of mast cells. To define the functional role of KIT D816V in STAT5-activation, Ba/F3 cells with doxycycline-inducible expression of KIT D816V were used. In these cells, induction of KIT D816V resulted in an increased expression of pSTAT5 without substantial increase in total STAT5. Moreover, the KIT D816V-targeting kinase-inhibitor PKC412 was found to counteract expression of pSTAT5 in HMC-1 cells as well as doxycycline-induced expression of pSTAT5 in Ba/F3 cells. Finally, a dominant negative STAT5-construct was found to inhibit growth of HMC-1 cells. Together, our data show that neoplastic mast cells express cytoplasmic and nuclear pSTAT5, that KIT D816V promotes STAT5-activation, and that STAT5-activation contributes to growth of neoplastic mast cells.

Phosphoinositide 3-kinase is a novel target of piceatannol for inhibiting PDGF-BB-induced proliferation and migration in human aortic smooth muscle cells

AIMS

Abnormal migration and proliferation of human aortic smooth muscle cells (HASMCs) to the intima causes intimal thickening of the aorta, which is strongly related to the development of atherosclerosis. Previous studies have suggested that red wine polyphenols, particularly resveratrol, have great protective effects against cardiovascular diseases. Here, we compared the anti-atherosclerotic effect of piceatannol, a metabolite of resveratrol, and its underlying mechanisms.

METHODS AND RESULTS

We demonstrated that piceatannol inhibited platelet-derived growth factor (PDGF)-BB-induced cell migration using a modified Boyden chamber assay and wound healing assay. Western blot analysis showed that PDGF-BB-induced phosphorylation of Akt, p70S6K, and p38 was inhibited by piceatannol, but not resveratrol. In vitro and ex vivo phosphoinositide 3-kinase (PI3K) assays demonstrated that piceatannol suppressed PI3K activity more effectively than resveratrol. PDGF-BB-induced migration and proliferation of HASMCs were inhibited by treatment with a commercial PI3K inhibitor, LY294002. Both in vitro and ex vivo pull-down assays revealed that piceatannol directly binds with sepharose 4B-PI3K beads in an ATP-competitive manner.

CONCLUSION

The results of the present study demonstrate that piceatannol directly binds with PI3K in an ATP-competitive manner and suppresses PI3K activity with anti-atherosclerotic effects.

Developmental switch in NF-kappaB signalling required for neurite growth

For a given cell type, particular extracellular signals generate characteristic patterns of activity in intracellular signalling networks that lead to distinctive cell-type specific responses. Here, we report the first known occurrence of a developmental switch in the intracellular signalling network required for an identical cellular response to the same extracellular signal in the same cell type. We show that although NF-kappaB signalling is required for BDNF-promoted neurite growth from both foetal and postnatal mouse sensory neurons, there is a developmental switch between these stages in the NF-kappaB activation mechanism and the phosphorylation status of the p65 NF-kappaB subunit required for neurite growth. Shortly before birth, BDNF activates NF-kappaB by an atypical mechanism that involves tyrosine phosphorylation of IkappaBalpha by Src family kinases, and dephosphorylates p65 at serine 536. Immediately after birth, BDNF-independent constitutive activation of NF-kappaB signalling by serine phosphorylation of IkappaBalpha and constitutive dephosphorylation of p65 at serine 536 are required for BDNF-promoted neurite growth. This abrupt developmental switch in NF-kappaB signalling in a highly differentiated cell type illustrates an unsuspected plasticity in signalling networks in the generation of identical cellular responses to the same extracellular signal.

The lymphoma-associated fusion tyrosine kinase ITK-SYK requires pleckstrin homology domain-mediated membrane localization for activation and cellular transformation

ITK-SYK, a novel fusion tyrosine kinase (FTK) resulting from a recurrent t(5;9)(q33;q22), was recently identified in a poorly understood subset of peripheral T-cell lymphomas. However, the biochemical and functional properties of ITK-SYK are unknown. Here we demonstrate that ITK-SYK is a catalytically active tyrosine kinase that is sensitive to an established inhibitor of SYK. The expression of ITK-SYK, but not SYK, transformed NIH3T3 cells, inducing loss of contact inhibition and formation of anchorage-independent colonies in soft agar, in a kinase activity-dependent manner. ITK-SYK is unusual among FTKs in having an N-terminal phosphatidylinositol 3,4,5-trisphosphate-binding pleckstrin homology (PH) domain. Introduction of a well characterized loss-of-function mutation (R29C) into the PH domain of ITK-SYK inhibited its phosphorylation, markedly reduced its catalytic activity, and abrogated its ability to activate the ERK signaling pathway and to transform NIH3T3 cells. Although ITK-SYK was membrane-associated, ITK-SYK-R29C was not. However, each of these properties could be recovered by retargeting ITK-SYK-R29C back to the plasma membrane by the addition of an N-terminal myristylation sequence. Consistent with a model in which ITK-SYK requires PH domain-mediated binding to phosphatidylinositol 3,4,5-trisphosphate generated by phosphatidylinositol 3-kinase (PI3K), ITK-SYK activity was reduced by pharmacological inhibition of PI3K and increased by co-expression with a constitutively active form of PI3K. Together, these findings identify ITK-SYK as an active, transforming FTK dependent upon PH domain-mediated membrane localization, identify a novel mechanism for activation of an oncogenic FTK, and suggest ITK-SYK as a rational therapeutic target for t(5;9)(q33;q22)-positive lymphomas.

Role of the protein tyrosine kinase Syk in regulating cell-cell adhesion and motility in breast cancer cells

The expression of the Syk protein tyrosine kinase in breast cancer cells is inversely correlated with invasive growth and metastasis. The expression of Syk inhibits cell motility while supporting the formation of cell clusters by enhancing cell-cell contacts and promoting the redistribution of the adhesion proteins cortactin and vinculin to these contacts. Syk associates physically with cortactin and catalyzes its phosphorylation on tyrosine. The clustering of integrins leads to the phosphorylation of Syk and of numerous cellular proteins in a manner dependent on the activity of the kinase and on the presence of tyrosine 342 located in the linker B region. The ability of Syk to participate in integrin-mediated protein tyrosine phosphorylation correlates well with its ability to inhibit cell motility.

Phosphoproteomic analysis of Syk kinase signaling in human cancer cells reveals its role in cell-cell adhesion

The spleen tyrosine kinase Syk has predominantly been studied in hematopoietic cells in which it is involved in immunoreceptor-mediated signaling. Recently, Syk expression was evidenced in numerous nonhematopoietic cells and shown to be involved in tumor formation and progression. The Syk downstream signaling effectors in nonhematopoietic cells remain, however, to be uncovered, and were investigated using MS-based quantitative phosphoproteomics. Two strategies, based on the inhibition of the Syk catalytic activity and on the loss of Syk expression were employed to identify phosphotyrosine-dependent complexes. Quantitative measurements were obtained on 350 proteins purified with phosphotyrosine affinity columns using the SILAC method. Forty-one proteins are dependent on both Syk expression and catalytic activity and were selected as signaling effectors. They are involved in a variety of biological processes such as signal transduction, cell-cell adhesion and cell polarization. We investigated the functional involvement of Syk in cell-cell adhesion and demonstrated the phosphorylation of E-cadherin and alpha-catenin. In addition, Syk is localized at cell-cell contacts, and Syk-mediated phosphorylation of E-cadherin seems to be important for the proper localization of p120-catenin at adherens junctions. Identification of the biochemical pathways regulated by Syk in human cancer cells will help to uncover its role in tumor formation and progression.

Piceatannol, a derivative of resveratrol, moderately slows I(Na) inactivation and exerts antiarrhythmic action in ischaemia-reperfused rat hearts

BACKGROUND AND PURPOSE

Piceatannol is more potent than resveratrol in free radical scavenging in association with antiarrhythmic and cardioprotective activities in ischaemic-reperfused rat hearts. The present study aimed to investigate the antiarrhythmic efficacy and the underlying ionic mechanisms of piceatannol in rat hearts.

EXPERIMENTAL APPROACH

Action potentials and membrane currents were recorded by the whole-cell patch clamp techniques. Fluo-3 fluorimetry was used to measure cellular Ca2+ transients. Antiarrhythmic activity was examined from isolated Langendorff-perfused rat hearts.

KEY RESULTS

In rat ventricular cells, piceatannol (3-30 micromol.L(-1)) prolonged the action potential durations (APDs) and decreased the maximal rate of upstroke (V(max)) without altering Ca2+ transients. Piceatannol decreased peak I(Na) and slowed I(Na) inactivation, rather than induced a persistent non-inactivating current, which could be reverted by lidocaine. Resveratrol (100 micromol.L(-1)) decreased peak I(Na) without slowing I(Na) inactivation. The inhibition of peak I(Na) or V(max) was associated with a negative shift of the voltage-dependent steady-state I(Na) inactivation curve without altering the activation threshold. At the concentrations more than 30 micromol.L(-1), piceatannol could inhibit I(Ca,L), I(to), I(Kr), Ca2+ transients and Na+-Ca2+ exchange except I(K1). Piceatannol (1-10 micromol.L(-1)) exerted antiarrhythmic activity in isolated rat hearts subjected to ischaemia-reperfusion injury.

CONCLUSIONS AND IMPLICATIONS

The additional hydroxyl group on resveratrol makes piceatannol possessing more potent in I(Na) inhibition and uniquely slowing I(Na) inactivation, which may contribute to its antiarrhythmic actions at low concentrations less than 10 micromol.L(-1).

Differential expression and molecular associations of Syk in systemic lupus erythematosus T cells

Diminished expression of TCR zeta and reciprocal up-regulation and association of FcRgamma with the TCR/CD3 complex is a hallmark of systemic lupus erythematosus (SLE) T cells. In this study we explored whether differential molecular associations of the spleen tyrosine kinase Syk that preferentially binds to FcRgamma contribute to pathological amplification of signals downstream of this "rewired TCR" in SLE. We detected higher amounts of Syk expression and activity in SLE compared with normal T cells. Selective inhibition of the activity of Syk reduced the strength of TCR-induced calcium responses and slowed the rapid kinetics of actin polymerization exclusively in SLE T cells. Syk and ZAP-70 also associated differently with key molecules involved in cytoskeletal and calcium signaling in SLE T cells. Thus, while Vav-1 and LAT preferentially bound to Syk, phospholipase C-gamma1 bound to both Syk and ZAP-70. Our results show that differential associations of Syk family kinases contribute to the enhanced TCR-induced signaling responses in SLE T cells. Thus, we propose molecular targeting of Syk as a measure to control abnormal T cell responses in SLE.

Endosomal trafficking of the ligated FcvarepsilonRI receptor

In addition to initiating signaling cascades leading to mast cell mediator release, aggregation of the high affinity IgE receptor (FcvarepsilonRI) leads to rapid internalization of the cross-linked receptor. However, little is known about the trafficking of the internalized FcvarepsilonRI. Here we demonstrate that in RBL-2H3 cells, aggregated FcvarepsilonRI appears in the early endosomal antigen 1 (EEA1(+)) domains of the early endosomes within 15min after ligation. Minimal co-localization of FcvarepsilonRI with Rab5 was observed by 30min, followed by its appearance in the Rab7(+) late endosomes and lysosomes at later time points. During endosomal sorting, FcvarepsilonRIalpha and gamma subunits remain associated. In Syk-deficient RBL-2H3 cells, the rate of transport to lysosomes is markedly increased. Taken together, our data demonstrate time-dependent sorting of aggregated FcvarepsilonRI within the endosomal-lysosomal network, and that Syk may play an essential role in regulating the trafficking and retention of FcvarepsilonRI in endosomes.

Piceatannol, a stilbene present in grapes, attenuates dextran sulfate sodium-induced colitis

Piceatannol (3,5,3',4'-tetrahydroxy-trans-stilbene; PIC) is a polyphenol found in grapes. It is known as a protein kinase inhibitor that modifies multiple cellular targets, exerting immunosuppressive and antitumorigenic activities in several cell lines. The purpose of the present work was to evaluate the anti-inflammatory effect of PIC on dextran sulfate sodium (DSS)-induced colitis. Experimental colitis was induced in BALB/c mice by dissolving 5% DSS in their drinking water for 7 days. PIC (1, 2.5, 5, or 10 mg/kg body weight) was administrated daily per oral route for 7 days. A significant blunting of weight loss and clinical signs was observed in DSS-exposed, PIC-treated mice when compared to vehicle-treated mice. This was associated with a remarkable amelioration of the disruption of the colonic architecture, a significant reduction in colonic myeloperoxidase (MPO) activity, and a decrease in production of inflammatory mediators such as nitric oxide (NO), prostaglandin (PG) E2, and pro-inflammatory cytokines. The present data indicate that further evaluation of the potential of PIC as an agent for the prevention and/or treatment of inflammatory bowel diseases in human clinical studies is warranted.

Platelets undergo phosphorylation of Syk at Y525/526 and Y352 in response to pathophysiological shear stress

Atherosclerotic plaques can lead to partial vascular occlusions that produce abnormally high levels of arterial wall shear stress. Such pathophysiological shear stress can promote shear-induced platelet aggregation (SIPA), which has been linked to acute myocardial infarction, unstable angina, and stroke. This study investigated the role of the tyrosine kinase Syk in shear-induced human platelet signaling. The extent of Syk tyrosine phosphorylation induced by pathophysiological levels of shear stress (100 dyn/cm(2)) was significantly greater than that resulting from physiological shear stress (10 dyn/cm(2)). With the use of phospho-Syk specific antibodies, these data are the first to show that key regulatory sites of Syk at tyrosines 525/526 (Y525/526) and tyrosine 352 (Y352) were phosphorylated in response to pathophysiological shear stress. Increased phosphorylation at both sites was attenuated by pharmacological inhibition of Syk using two different Syk inhibitors, piceatannol and 3-(1-methyl-1H-indol-3-yl-methylene)-2-oxo-2,3-dihydro-1H-indole-5-sulfonamide (OXSI-2), and by inhibition of upstream Src-family kinases (SFKs). Shear-induced response at the Syk 525/526 site was ADP dependent but not contingent on glycoprotein (GP) IIb-IIIa ligation or the generation of thromboxane (Tx) A(2). Pretreatment with Syk inhibitors not only reduced SIPA and Syk phosphorylation in isolated platelets, but also diminished, up to 50%, the platelet-mediated thrombus formation when whole blood was perfused over type-III collagen. In summary, this study demonstrated that Syk is a key molecule in both SIPA and thrombus formation under flow. Pharmacological regulation of Syk may prove efficacious in treating occlusive vascular disease.

Mast cell-fibroblast interactions induce matrix metalloproteinase-9 release from fibroblasts: role for IgE-mediated mast cell activation

Mast cells adhere to fibroblasts, but the biological effects of adhesion are not well understood. We hypothesized that these adhesive interactions are important for tissue remodeling through the release of matrix metalloproteinases (MMP). Murine bone marrow cultured mast cells (BMCMC) were cocultured with NIH-3T3 fibroblasts or murine lung fibroblasts (CCL-206) and supernatants analyzed for MMP-9 release by gelatin zymography. Coculture of BMCMC for 24 h with NIH-3T3 or CCL-206 fibroblasts increased the release of MMP-9 from fibroblasts by 1.7+/-0.2 and 2.0+/-0.7-fold, respectively. Coculture of BMCMC and fibroblasts in the presence of IgE increased further MMP-9 release, which was released by fibroblasts. MMP-9 release was dependent on TNF released from IgE activated BMCMC and on adhesive interactions between BMCMC and fibroblasts. Increased MMP-9 release was also p44/42-dependent, as was MMP-9 up-regulation during coculture of fibroblasts with resting BMCMC. Finally, IgE injection into the mouse ear increased MMP-9 content of the ear tissue in the absence of Ag, indicating that IgE-mediated remodeling may play a pathogenic role in allergic conditions even in the absence of exposure to allergens. In conclusion, mast cell-fibroblast interactions induce the release of proteases important for tissue remodeling, such as MMP-9. MMP-9 release was further increased in the presence of IgE during coculture, suggesting a role for mast cell-fibroblast interactions in atopic conditions.

Immunomodulation of human B cells following treatment with intravenous immunoglobulins involves increased phosphorylation of extracellular signal-regulated kinases 1 and 2

In the treatment of autoimmune diseases, intravenous Igs (IVIg) are assumed to modulate immune cells through the binding of surface receptors. IVIg act upon definite human B cell populations to modulate Ig repertoire, and such modulation might proceed through intracellular signaling. However, the heterogeneity of human B cell populations complicates investigations of the intracellular pathways involved in IVIg-induced B cell modulation. The aim of this study was to establish a model allowing the screening of IVIg signal transduction in human B cell lines and to attempt transposing observations made in cell lines to normal human B lymphocytes. Nine human B cell lines were treated with IVIg with the goal of selecting the most suitable model for human B lymphocytes. The IgG(+) DB cell line, whose response was similar to that of human B lymphocytes, showed reduced IVIg modulation following addition of PD98059, an inhibitor of extracellular signal-regulated protein kinase 1/2 (ERK1/2). The IVIg-induced ERK1/2 phosphorylation was indeed proportional to the dosage of monomeric IVIg used when tested on DB cells as well as Pfeiffer cells, another IgG(+) cell line. In addition, two other intermediates, Grb2-associated binder 1 (Gab1) and Akt, showed increased phosphorylation in IVIg-treated DB cells. IVIg induction of ERK1/2 phosphorylation was finally observed in peripheral human B lymphocytes, specifically within the IgG(+) B cell population. In conclusion, IVIg immunomodulation of human B cells can thus be linked to intracellular transduction pathways involving the phosphorylation of ERK1/2, which in combination with Gab1 and Akt, may be related to B cell antigen receptor signaling.

Stimulus dependence of the action of small-molecule inhibitors in the CD3/CD28 signalling network

Cells in the body are exposed simultaneously to a multitude of various signals. Inside a cell, molecular signalling networks integrate this information into a physiologically meaningful response. Interestingly, in the cellular testing of drug candidates, this complexity is largely ignored. Compounds are tested for cells that are challenged with one stimulus only. The activation of T lymphocytes through engagement of the T cell receptor (TCR)-CD3 complex and CD28 coreceptor is a prominent example for a cellular response that depends on the integration of signals. We investigated the cellular response characteristics of this network at different strengths of receptor and coreceptor activation. A novel cellular microarray-based approach, in which various combinations of antibodies directed against the CD3 complex and CD28 were spotted, was employed for analysing the stimulus dependence of activation of the transcription factor NFAT and actin reorganisation. For both responses, quantitative differences in inhibitor activity were observed. Remarkably, for IL-2 expression, which was detected by standard ELISA, low doses of the Src-family kinase inhibitor PP2 strongly potentiated IL-2 expression at high-level, but not at low-level, CD28 co-engagement. Therefore, for a physiologically highly relevant signalling network, the cellular response might vary qualitatively with only quantitative variations of a stimulus. This level of complexity should be considered in early cellular drug testing.

Paw paw and cancer: annonaceous acetogenins from discovery to commercial products

Extracts of paw paw ( Asimina triloba, Annonaceae) are among the most potent of the 3500 species of higher plants screened for bioactive compounds in our laboratories at Purdue University. The paw paw is a small tree native to eastern North America; its edible fruits (sometimes referred to as "Indiana Bananas") have nurtured mankind for centuries. Activity-directed fractionation of the paw paw extracts, using the brine shrimp lethality bioassay, led to the isolation and molecular characterization of over 50 unique annonaceous acetogenins. Fractionation of extracts from related species resulted in the identification of over 150 additional acetogenins. The annonaceous acetogenins are derivatives of long-chain (C32 or C34) fatty acids. They are potent inhibitors of mitochondrial (complex I) as well as cytoplasmic (anaerobic) production of adenosine triphosphate (ATP) and the related nucleotides. The powerful cytotoxicity, in vivo antitumor, pesticidal, antimalarial, anthelmintic, piscicidal, antiviral, and antimicrobial effects indicated a myriad of potentially useful applications. Commercial development of these compounds uses natural mixtures of active components, incorporated into pesticidal, topical, and dietary supplement products. Successful applications and commercial products include a shampoo, highly effective in treating infestations of head lice, fleas, and ticks; a series of pesticidal sprays, which protects host plants against a diversity of pests; and an ointment for treatment of oral herpes (HSV-1) and other skin afflictions. The extract (in capsule form) enhances a mixture of natural anthelmintics. In addition, an encapsulated extract has been effectively used by certain cancer patients as a botanical supplement product.

Anaplasma phagocytophilum PSGL-1-independent infection does not require Syk and leads to less efficient AnkA delivery

Anaplasma phagocytophilum is an obligate intracellular bacterium that infects neutrophils to cause granulocytic anaplasmosis in humans and mammals. P-selectin glycoprotein ligand-1 (PSGL-1) and the tetrasaccharide sialyl Lewis x (sLe(x)), which caps the PSGL-1 N-terminus, are confirmed A. phagocytophilum receptors. A. phagocytophilum is capable of sLe(x)-modified PSGL-1-dependent and -independent infection. PSGL-1 N-terminus-mediated entry is dependent on spleen tyrosine kinase (Syk). Here, we determined that PSGL-1-independent entry does not alter bacterial replication and investigated whether it involves Syk using NCH-1A2, an enriched subpopulation of A. phagocytophilum NCH-1 obtained through cultivation in a sLe(x)-deficient HL-60 cell line, HL-60 A2. Pharmacological inhibition of Syk nearly abolishes NCH-1 infection, but does not alter NCH-1A2 invasion and only marginally reduces NCH-1A2 propagation. This phenomenon was confirmed by a competitive infection assay using PSGL-1-dependent and -independent A. phagocytophilum organisms transformed to express mCherry or green fluorescent protein respectively. We also assayed for delivery and tyrosine phosphorylation of the A. phagocytophilum effector, AnkA, following NCH-1or NCH-1A2 incubation with HL-60 or HL-60 A2 cells in the presence of PSGL-1 blocking antibody. PSGL-1 N-terminus recognition promotes optimal AnkA delivery while binding to sLe(x) or the unknown receptor is comparably less important for this process.

Quantitative time-resolved phosphoproteomic analysis of mast cell signaling

Mast cells play a central role in type I hypersensitivity reactions and allergic disorders such as anaphylaxis and asthma. Activation of mast cells, through a cascade of phosphorylation events, leads to the release of mediators of the early phase allergic response. Understanding the molecular architecture underlying mast cell signaling may provide possibilities for therapeutic intervention in asthma and other allergic diseases. Although many details of mast cell signaling have been described previously, a systematic, quantitative analysis of the global tyrosine phosphorylation events that are triggered by activation of the mast cell receptor is lacking. In many cases, the involvement of particular proteins in mast cell signaling has been established generally, but the precise molecular mechanism of the interaction between known signaling proteins often mediated through phosphorylation is still obscure. Using recently advanced methodologies in mass spectrometry, including automation of phosphopeptide enrichments and detection, we have now substantially characterized, with temporal resolution as short as 10 s, the sites and levels of tyrosine phosphorylation across 10 min of FcepsilonRI-induced mast cell activation. These results reveal a far more extensive array of tyrosine phosphorylation events than previously known, including novel phosphorylation sites on canonical mast cell signaling molecules, as well as unexpected pathway components downstream of FcepsilonRI activation. Furthermore, our results, for the first time in mast cells, reveal the sequence of phosphorylation events for 171 modification sites across 121 proteins in the MCP5 mouse mast cell line and 179 modification sites on 117 proteins in mouse bone marrow-derived mast cells.

Syk tyrosine kinase is linked to cell motility and progression in squamous cell carcinomas of the head and neck

Syk, a non-receptor tyrosine kinase, is an important component of immunoreceptor signaling in hematopoietic cells. It has been implicated in key regulatory pathways including phosphoinositide 3-kinase and phospholipase Cgamma (PLCgamma) activation in B cells and integrin signaling in platelets and bronchial epithelial cells. Recently, potential roles in cancer have been reported. In breast cancers, reduced Syk expression was associated with invasion, and its overexpression in cell lines was shown to inhibit cell motility. In contrast, Syk has been shown to mediate chemomigration in nasopharyngeal carcinoma cells. Its role in squamous cell carcinomas of the head and neck (SCCHN) has not yet been investigated. Syk mRNA and protein expression was detected in 6 of 10 SCCHN cell lines. When Syk was transfected into Syk-negative cells (SIHN-011A), chemomigration was enhanced in vitro and this was associated with activation of PLCgamma1. Conversely, abrogation of Syk activity by pharmacologic inhibition or small interfering RNA in HN6 cells with high levels of endogenous expression inhibited migration, haptotaxis, and engagement with matrix proteins; this was accompanied by decreased levels of phosphorylated AKT. Similar effects were seen in Syk-positive CAL 27 cells but not in Syk-negative SIHN-011A cells. Immunoprecipitation suggested co-association of Syk with epidermal growth factor receptor and GRB-2. Syk expression in SCCHN patient tissues was examined by semiquantitative real-time PCR (n = 45) and immunohistochemistry (n = 38) in two independent cohorts. Higher levels of Syk expression were observed in tumors and lymph node metastases relative to normal tissues. High Syk expression significantly correlated with worse survival and may be of prognostic value in SCCHN due to its potential role in cell migration and invasion.

The adaptor molecule CIN85 regulates Syk tyrosine kinase level by activating the ubiquitin-proteasome degradation pathway

Triggering of mast cells and basophils by IgE and Ag initiates a cascade of biochemical events that lead to cell degranulation and the release of allergic mediators. Receptor aggregation also induces a series of biochemical events capable of limiting FcepsilonRI-triggered signals and functional responses. Relevant to this, we have recently demonstrated that Cbl-interacting 85-kDa protein (CIN85), a multiadaptor protein mainly involved in the process of endocytosis and vesicle trafficking, regulates the Ag-dependent endocytosis of the IgE receptor, with consequent impairment of FcepsilonRI-mediated cell degranulation. The purpose of this study was to further investigate whether CIN85 could alter the FcepsilonRI-mediated signaling by affecting the activity and/or expression of molecules directly implicated in signal propagation. We found that CIN85 overexpression inhibits the FcepsilonRI-induced tyrosine phosphorylation of phospholipase Cgamma, thus altering calcium mobilization. This functional defect is associated with a substantial decrease of Syk protein levels, which are restored by the use of selective proteasome inhibitors, and it is mainly due to the action of the ubiquitin ligase c-Cbl. Furthermore, coimmunoprecipitation experiments demonstrate that CIN85 overexpression limits the ability of Cbl to bind suppressor of TCR signaling 1 (Sts1), a negative regulator of Cbl functions, while CIN85 knockdown favors the formation of Cbl/Sts1 complexes. Altogether, our findings support a new role for CIN85 in regulating Syk protein levels in RBL-2H3 cells through the activation of the ubiquitin-proteasome pathway and provide a mechanism for this regulation involving c-Cbl ligase activity.

Elf-1 Binds to GGAA Elements on the FcRγ Promoter and Represses Its Expression

The Fc receptor (FcR) gamma-chain has been shown to be up-regulated in T cells when the TCR zeta-chain is decreased. We demonstrate that Elf-1, but not other Ets family transcription factors, bind to a cluster of GGAA sites located within the 200 bp upstream from the transcription initiation site of the FcRgamma promoter. Forced expression of Elf-1 results in the suppression of FcRgamma expression, whereas silencing its expression with small interfering RNA Elf-1 results in increased FcRgamma expression. Elf-1 represents the first transcription factor identified to be involved in the transcriptional regulation of FcRgamma, and cells that fail to express Elf-1, as is the case with human systemic lupus erythematosus T cells, will express FcRgamma-chain.

The Cbl-b RING finger domain has a limited role in regulating inflammatory cytokine production by IgE-activated mast cells

The RING finger type E3 ubiquitin ligase, Cbl-b, is abundantly expressed in bone marrow-derived mast cells (BMMCs) and functions as a potent negative regulator of signalling responses from the high-affinity IgE receptor (FcvarepsilonRI). To determine the contribution of Cbl-b E3 ligase activity we generated knockin mice with a loss-of-function mutation in the RING finger domain. We find the mice to be healthy and, unlike equivalent c-Cbl RING finger mutant mice, produce homozygous offspring at the expected frequency. Comparative analyses of BMMCs from Cbl-b knockout and Cbl-b RING finger mutant mice revealed that both showed similarly enhanced FcvarepsilonRI signalling compared to wild-type cells for most parameters examined. A notable exception was a markedly higher level of activation of IkappaB kinase (IKK) in Cbl-b knockout BMMC compared to RING finger mutant-derived cells. In addition BMMCs from the Cbl-b RING finger mutant did not retard FcvarepsilonRI internalization to the extent observed for knockout cells. Most striking however was the finding that RING finger mutant mast cells do not produce the very high levels of TNF-alpha, IL-6, and MCP-1 evident in Cbl-b knockout cultures following FcvarepsilonRI activation. Thus the ability of Cbl-b to function as a negative regulator of FcvarepsilonRI signalling that promotes inflammatory cytokine production is largely independent of the RING finger domain.

Dual role of mitochondrial reactive oxygen species in hypoxia signaling: activation of nuclear factor-{kappa}B via c-SRC and oxidant-dependent cell death

Hypoxia is a prominent feature of solid tumor development and is known to stimulate mitochondrial ROS (mROS), which, in turn, can activate hypoxia-inducible transcription factor-1alpha and nuclear factor-kappaB (NF-kappaB). Because NF-kappaB plays a central role in carcinogenesis, we examined the mechanism of mROS-mediated NF-kappaB activation and the fate of cancer cells during hypoxia after mitochondrial reduced glutathione (mGSH) depletion. Hypoxia generated mROS in hepatoma (HepG2, H35), neuroblastoma (SH-SY5Y), and colon carcinoma (DLD-1) cells, leading to hypoxia-inducible transcription factor-1alpha-dependent gene expression and c-Src activation that was prevented in cells expressing a redox-insensitive c-Src mutant (C487A). c-Src stimulation activated NF-kappaB without IkappaB-alpha degradation due to IkappaB-alpha tyrosine phosphorylation that was inhibited by rotenone/TTFA or c-Src antagonism. The c-Src-NF-kappaB signaling contributed to the survival of cells during hypoxia as c-Src inhibition or p65 down-regulation by small interfering RNA-sensitized HepG2 cells to hypoxia-induced cell death. Moreover, selective mGSH depletion resulted in an accelerated and enhanced mROS generation by hypoxia that killed SH-SY5Y and DLD-1 cells without disabling the c-Src-NF-kappaB pathway. Thus, although mROS promote cell survival by NF-kappaB activation via c-Src, mROS overgeneration may be exploited to sensitize cancer cells to hypoxia.

Crystal-induced neutrophil activation. IX. Syk-dependent activation of class Ia phosphatidylinositol 3-kinase

The deposition of monosodium urate (MSU) crystals in the joints of humans leads to an extremely acute, inflammatory reaction, commonly known as gout, characterized by a massive infiltration of neutrophils. Direct interactions of MSU crystals with human neutrophils and inflammatory mediators are crucial to the induction and perpetuation of gout attacks. The intracellular signaling events initiated by the physical interaction between MSU crystals and neutrophils depend on the activation of specific tyrosine kinases (Src and Syk, in particular). In addition, PI-3Ks may be involved. The present study investigates the involvement of the PI-3K family in the mediation of the responses of human neutrophils to MSU crystals. The results obtained indicate that the interaction of MSU crystals with human neutrophils leads to the stimulation of class Ia PI-3Ks by a mechanism that is dependent on the tyrosine kinase Syk. We also found an increase in the amount of p85 associated with the Nonidet P-40-insoluble fraction derived from MSU crystal-stimulated human neutrophils. Furthermore, MSU crystals induce the formation of a complex containing p85 and Syk, which is mediated by the Src family kinases. Finally, evidence is also obtained indicating that the activation of PI-3Ks by MSU crystals is a critical element regulating phospholipase D activation and degranulation of human neutrophils. The latter response is likely to be involved in the joint and tissue damage that occurs in gouty patients.

FcRγ chain does not replace CD3ζ chain in CD3ζ-deficient T lymphocytes of patients with gastric adenocarcinoma

Defective CD3zeta chain expression has been reported in T lymphocytes of patients with inflammatory diseases, such as systemic lupus erythematosus or osteoarthritis, and with cancer. In lupus, the absent CD3zeta chain is replaced by the FcRgamma chain, rendering the T cells hyper responsive. However, there are no data on T lymphocytes from patients with cancer. In this study, the presence of the FcRgamma chain and its associated kinase, Syk, was analysed in patients with gastric adenocarcinoma and healthy subjects. Western blot and immunoprecipitation experiments were carried out with total cell or lipid raft extracts from fresh peripheral blood mononuclear cells or T lymphocytes, and Herpesvirus saimiri-derived T-cell lines (of blood or tissue origin). Our results revealed that the absent CD3zeta chain in cancer T lymphocytes was not replaced by FcRgamma either in fresh T cells or T-cell lines, in contrast to lupus T cells. This altered expression of signalling molecules in T lymphocytes of cancer patients, would explain their low proliferative capacity. Our T-cell lines represent tools to unveil the signalling abnormalities of cancer T lymphocytes.

Proximal signaling events in FcɛRI-mediated mast cell activation

Mast cells are central mediators of allergic diseases. Their involvement in allergic reactions is largely dependent on activation through the specific receptor for IgE (Fc epsilon RI). Cross-linking of Fc epsilon RI on mast cells initiates a cascade of signaling events that eventually results in degranulation, cytokine/chemokine production, and leukotriene release, contributing to allergic symptomology. Because of the importance of IgE in allergy, much focus has been placed on deciphering the signaling events that take place downstream of Fc epsilon RI. Studies have identified spleen tyrosine kinase as a key proximal regulator of Fc epsilon RI-mediated signaling. In this review, we discuss the multiple pathways that diverge from spleen tyrosine kinase with emphasis on the role of adapter molecules to orchestrate these signaling events. Understanding the molecular mechanisms underlying mast cell activation ideally will provide insights into the development of novel therapeutics to control allergic disease.

Functional and structural requirements for the internalization of distinct BCR-ligand complexes

Antigen (Ag) binding to the BCR rapidly initiates two important events: a phosphorylation cascade that results in the production of secondary signaling intermediaries and the internalization of Ag-BCR complexes. Previous studies using anti-BCR antibodies (Ab) have suggested that BCR signaling is an essential requirement for BCR endocytosis and have further implicated lipid rafts as essential platforms for both BCR functions. However, published data from our laboratory indicate that lipid rafts and consequently raft-mediated signaling are dispensable for BCR-mediated internalization of Ag-specific BCR. Therefore, we investigated the relationship between BCR signaling and endocytosis by defining the role of early kinase signaling in the BCR-mediated internalization of a model Ag (haptenated protein). The results demonstrate that Src kinases and Syk-mediated BCR signaling are not essential for BCR-mediated Ag internalization. Moreover, by comparing Ag and Ab, it was determined that while both localize to clathrin-coated pits, the internalization of Ab-BCR complexes is more susceptible to inhibition of signaling and highly sensitive to disruption of lipid rafts and the actin cytoskeleton compared to Ag-BCR complexes. Thus, these results demonstrate that the nature of the ligand ultimately determines the functional requirements and relative contribution of lipid rafts and other membrane structures to the internalization of BCR-ligand complexes.

Spleen tyrosine kinase (Syk) as a novel target for allergic asthma and rhinitis

Allergic asthma and rhinitis are prevalent diseases in the modern world, both marked by inflammation of the airways. The spleen tyrosine kinase (Syk) plays a critical role in the regulation of such immune and inflammatory responses. Although Syk is best known as a key component of immunoreceptor signalling complexes in leukocytes, recent studies demonstrated Syk expression in cells outside the haematopoietic lineage. Moreover, in recent years, it has been established that Syk is involved in various signalling cascades including those originating from integrin and cytokine receptors. Thus, Syk likely has a much wider biological role than previously recognised. Specific inhibition of Syk using aerosolised antisense oligonucleotides in liposome complexes significantly decreased lung inflammatory responses in experimental asthma and acute lung injury models. In addition, pharmacological inhibitors of Syk have been recently developed with potential for use as therapeutics. However, in the development and the rational delivery of drugs targeting Syk, it is important to consider the multiple cell types that express this kinase and the potential effects of its inhibition on various physiological functions. This review focuses on the recent data and the emerging ideas about Syk as a therapeutic target.

CXCR3-mediated T-cell chemotaxis involves ZAP-70 and is regulated by signalling through the T-cell receptor

The chemokine receptor CXCR3 is critical for the function of activated T cells. We studied the molecular mechanisms of CXCR3 signalling. The addition of CXCR3 ligands to normal human T cells expressing CXCR3 led to the tyrosine phosphorylation of multiple proteins. Addition of the same ligands to Jurkat T cells engineered to express CXCR3 induced tyrosine phosphorylation of proteins with molecular weights similar to those in normal cells. Immunoblotting with phosphotyrosine-specific antibodies identified Zeta-associated protein of 70,000 molecular weight (ZAP-70), linker for the activation of T cells (LAT), and phospholipase-C-gamma1 (PLCgamma1) to be among the proteins that become phosphorylated upon CXCR3 activation. ZAP-70 was phosphorylated on tyrosine 319, LAT on tyrosines 171 and 191, and PLCgamma1 on tyrosine 783. The ZAP-70 inhibitor piceatannol reduced CXCR3-mediated tyrosine phosphorylation of ZAP-70, LAT, PLCgamma1 and mitogen-activated protein kinase Erk and it reduced CXCL10-mediated chemotaxis of both CXCR3-transfected Jurkat T cells and normal T cells expressing CXCR3. These results are consistent with the involvement of ZAP-70 in CXCR3-mediated protein tyrosine phosphorylation and CXCR3-induced T-cell chemotaxis. Studies with the Lck-deficient Jurkat T-cell line, JCAM1.6, demonstrated that phosphorylation of ZAP-70 after CXCR3 activation is a Lck-dependent process. Finally, stimulating CXCR3-expressing Jurkat T cells and normal T cells expressing CXCR3 through the T-cell receptor attenuated CXCR3-induced tyrosine phosphorylation and CXCR3-mediated T-cell migration, indicating the occurrence of cross-talk between T-cell receptor and CXCR3-signalling pathways. These results shed light on the mechanisms of CXCR3 signalling. Such information could be useful when designing therapeutic strategies to regulate T-cell function.

Tyrosine kinase Syk associates with toll-like receptor 4 and regulates signaling in human monocytic cells

Toll-like receptor 4 (TLR4) induces an innate immune response in mammals by recognizing lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria. In this study, we show that tyrosine kinase Syk constitutively associates with TLR4 in THP-1 cells. As previously reported in peripheral blood mononuclear cells, TLR4 gets inducibly tyrosine phosphorylated upon LPS engagement in THP-1 cells. Piceatannol, a pharmacological inhibitor of the tyrosine kinase Syk, abrogates TLR4 tyrosine phosphorylation at low doses. The kinetics of TLR4 tyrosine phosphorylation in THP-1 cells coincides with an early wave of Syk tyrosine phosphorylation. Additionally, serine threonine kinase interleukin-1 (IL1) receptor-associated kinase 1 (IRAK-1) is transiently recruited to the complex containing adaptor molecule MyD88, TLR4 and Syk within 1 min of LPS engagement and dissociates by 30 min. Finally, the inhibition of Syk with piceatannol has no effect on LPS-mediated release of cytokines IL6, IL1beta, tumor necrosis factor-alpha, neither on chemokines macrophage inhibitory protein (MIP)1alpha, MIP1beta, monocyte chemoattractant protein -1, IL8, Groalpha and RANTES. However, IL10 and IL12p40 releases are significantly inhibited. Our findings implicate Syk as a novel modulator of LPS-mediated TLR4 responses in human monocytic cells and shed insight into the kinetics of early complex formation upon LPS engagement.