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

The engagement of activating FcgammaRs inhibits primate lentivirus replication in human macrophages

We previously reported that the stimulation of monocyte-derived macrophages (MDM) by plate-bound i.v. Igs inhibits HIV-1 replication. In this study, we show that IgG immune complexes also suppress HIV-1 replication in MDMs and that activating receptors for the Fc portion of IgG-FcgammaRI, FcgammaRIIA, and FcgammaRIII-are responsible for the inhibition. MDM stimulation through FcgammaRs induces activation signals and the secretion of HIV-1 modulatory cytokines, such as M-CSF, TNF-alpha, and macrophage-derived chemokine. However, none of these cytokines contribute to HIV-1 suppression. HIV-1 entry and postintegration steps of viral replication are not affected, whereas reduced levels of reverse transcription products and of integrated proviruses, as determined by real-time PCR analysis, account for the suppression of HIV-1 gene expression in FcgammaR-activated MDMs. We found that FcgammaR-dependent activation of MDMs also inhibits the replication of HIV-2, SIVmac, and SIVagm, suggesting a common control mechanism for primate immunodeficiency lentiviruses in activated macrophages.

Differing mechanisms of cAMP- versus seawater-induced oocyte maturation in marine nemertean worms II. The roles of tyrosine kinases and phosphatases

Instead of blocking oocyte maturation as it does in most animals, cAMP causes oocytes of marine nemertean worms to initiate maturation (=germinal vesicle breakdown, "GVBD"). To characterize cAMP-induced GVBD in nemerteans, inhibitors of tyrosine kinase signaling were tested on Cerebratulus sp. oocytes that had been incubated in cAMP-elevating drugs versus seawater (SW) alone. Such tests yielded similar results for Src-like tyrosine kinase blockers, as the inhibitors prevented mitogen-activated protein kinase (MAPK) activation without stopping either GVBD or maturation-promoting factor (MPF) activation in both SW and cAMP-elevating treatments. Alternatively, genistein, a general tyrosine kinase antagonist, and piceatannol, an inhibitor of the tyrosine kinase Syk, reduced GVBD and MAPK/MPF activities in SW-, but not cAMP-induced maturation. Similarly, inhibitors of the human epidermal growth factor receptor-2 (HER-2) tyrosine kinase prevented GVBD and MAPK/MPF activations in oocytes treated with SW, but not with cAMP-elevating drugs. Antagonists of either protein tyrosine phosphatases (PTPs) or the dual-specificity phosphatase Cdc25 also reduced GVBD and MAPK/MPF activities in SW-treated oocytes without generally affecting cAMP-induced maturation. Collectively, these data suggest cAMP triggers GVBD via pathways that do not require MAPK activation or several components of tyrosine kinase signaling. In addition, such differences in tyrosine kinase cascades, coupled with the dissimilar patterns of Ser/Thr kinase signaling described in the accompanying study, indicate that nemertean oocytes are capable of utilizing multiple mechanisms to activate MPF during GVBD.

Piceatannol stimulates osteoblast differentiation that may be mediated by increased bone morphogenetic protein-2 production

Piceatannol (3,3',4,5'-tetrahydroxy-trans-stilbene) is a polyphenol present in grapes and wine. By means of alkaline phosphatase activity and osteocalcin enzyme-linked immunosorbent assay (ELISA), we have shown that piceatannol exhibits a significant induction of differentiation in immortalized fetal osteoblasts (hFOB), and osteosarcoma cells (MG-63). Alkaline phosphatase and osteocalcin are phenotypic markers for early-stage differentiated osteoblasts and terminally differentiated osteoblasts, respectively, our results indicate that piceatannol stimulate osteoblast differentiation at various stages (from maturation to terminally differentiated osteoblasts). Induction of differentiation by piceatannol was associated with increased bone morphogenetic protein-2 (BMP-2) production. Addition of purified BMP-2 protein did not increase the upregulation of alkaline phosphatase activity and osteocalcin secretion by piceatannol, whereas the BMP-2 antagonist noggin blocked piceatannol and BMP-2-mediated alkaline phosphatase activity, and osteocalcin secretion enhancement, indicating that BMP-2 production is required in piceatannol-mediated osteoblast maturation and differentiation. In conclusion, piceatannol increased BMP-2 synthesis, and this effect may contribute to its action on the induction of osteoblasts maturation and differentiation, followed by an increase of bone mass. Decreases in new bone formation, followed by estrogen deficiency or various pathologic factors, may contribute to the mechanisms involved in postmenopausal osteoporosis.

Mutational analysis of the mechanism of negative regulation by SRC homology 2 domain-containing protein tyrosine phosphatase substrate-1 of phagocytosis in macrophages

Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) is a transmembrane protein predominantly expressed in macrophages. The binding of CD47 on RBCs to SHPS-1 on macrophages is implicated in inhibition of phagocytosis of the former cells by the latter. We have now shown that forced expression in mouse RAW264.7 macrophages of a mutant version (SHPS-1-4F) of mouse SHPS-1, in which four tyrosine phosphorylation sites are replaced by phenylalanine, markedly promoted Fc gammaR-mediated phagocytosis of mouse RBCs or SRBCs. Forced expression of another mutant form (SHPS-1-deltaCyto) of mouse SHPS-1, which lacks most of the cytoplasmic region, did not promote such phagocytosis. Similarly, forced expression of a rat version of SHPS-1-4F, but not that of rat wild-type SHPS-1 or SHPS-1-deltaCyto, in RAW264.7 cells enhanced Fc gammaR-mediated phagocytosis of RBCs. Tyrosine phosphorylation of endogenous SHPS-1 as well as its association with Src homology 2 domain-containing protein tyrosine phosphatase-1 were not markedly inhibited by expression of SHPS-1-4F. Furthermore, the attachment of IgG-opsonized RBCs to RAW264.7 cells was markedly increased by expression of SHPS-1-4F, and this effect did not appear to be mediated by the interaction between CD47 and SHPS-1. These data suggest that inhibition by SHPS-1 of phagocytosis in macrophages is mediated, at least in part, in a manner independent of the transinteraction between CD47 and SHPS-1. In addition, the cytoplasmic region as well as tyrosine phosphorylation sites in this region of SHPS-1 appear indispensable for this inhibitory action of SHPS-1. Moreover, SHPS-1 may regulate the attachment of RBCs to macrophages by an as yet unidentified mechanism.

FcR gamma presence in TCR complex of double-negative T cells is critical for their regulatory function

TCRalphabeta+CD4-CD8- double-negative (DN) T regulatory (Treg) cells have recently been shown to suppress Ag-specific immune responses mediated by CD8+ and CD4+ T cells in humans and mice. Our previous study using cDNA microarray analysis of global gene expression showed that FcRgamma was the most highly overexpressed gene in functional DN Treg cell clones compared with nonfunctional mutant clones. In this study, we demonstrate that FcRgamma-deficient DN T cells display markedly reduced suppressive activity in vitro. In addition, unlike FcRgamma-sufficient DN T cells, FcRgamma-deficient DN T cells were unable to prolong donor-specific allograft survival when adoptively transferred to recipient mice. Protein analyses indicate that in addition to FcRgamma, DN Treg cell clones also express higher levels of TCRbeta, while mutant clones expressed higher levels of Zap70 and Lck. Within DN Treg cells, we found that FcRgamma associates with the TCR complex and that both FcRgamma and Syk are phosphorylated in response to TCR cross-linking. Inhibition of Syk signaling and FcRgamma expression were both found to reduce the suppressive function of DN Treg cells in vitro. These results indicate that FcRgamma deficiency significantly impairs the ability of DN Treg cells to down-regulate allogeneic immune responses both in vitro and in vivo, and that FcRgamma plays a role in mediating TCR signaling in DN Treg cells.

Nonspecific desensitization, functional memory, and the characteristics of SHIP phosphorylation following IgE-mediated stimulation of human basophils

Previous studies of secretion from basophils have demonstrated the phenomenon called nonspecific desensitization, the ability of one IgE-mediated stimulus to alter the cell's response to other non-cross-reacting IgE-mediated stimuli, and a process that would modify phosphatidylinositol 3,4,5-phosphate levels was speculated to be responsible for nonspecific desensitization. The current studies examined the changes and characteristics of SHIP1 phosphorylation as a measure of SHIP1 participation in the reaction. Based on the earlier studies, two predictions were made that were not observed. First, the kinetics of SHIP1 phosphorylation were similar to reaction kinetics of other early signals and returned to resting levels while nonspecific desensitization remained. Second, in contrast to an expected exaggerated SHIP phosphorylation, cells in a state of nonspecific desensitization showed reduced SHIP phosphorylation (compared with cells not previously exposed to a non-cross-reacting Ag). Discordant with expectations concerning partial recovery from nonspecific desensitization, treatment of cells with DNP-lysine to dissociate bound DNP-HSA, either enhanced or had no effect on SHIP phosphorylation following a second Ag. These experiments also showed a form of desensitization that persisted despite dissociation of the desensitizing Ag. Recent studies and the results of these studies suggest that loss of early signaling components like syk kinase may account for some of the effects of nonspecific desensitization and result in a form of immunological memory of prior stimulation. Taken together, the various characteristics of SHIP phosphorylation were not consistent with expectations for a signaling element involved in nonspecific desensitization, but instead one which itself undergoes nonspecific desensitization.

Ectoadenylate Kinase and Plasma Membrane ATP Synthase Activities of Human Vascular Endothelial Cells

Formation of ATP from ADP on the external surface of vascular endothelial cells has been attributed to plasma membrane ATP synthase, ectoadenylate kinase (ecto-AK), and/or ectonucleoside diphosphokinase. These enzymes or their catalytic products have been causatively linked to the elaboration of vascular networks and the regulation of capillary function. The amount of ATP generated extracellularly is small, requiring sensitive analytical methods for quantification. Human umbilical vein endothelial cells were used to revisit extracellular ATP synthesis using a reliable tetrazolium reduction assay and multiwell plate cultures. Test conditions compatible with AK stability were established. Extracellular AK activity was found to be <1% of the total (intracellular and extracellular), raising the possibility that the external enzyme could have leaked from living cells and/or a few dying cells. To determine whether AK inadvertently leaked from the cells, the activity of another cytoplasmic enzyme, glucose-6-phosphate dehydrogenase (G6PD), was also measured. G6PD is present in the cytoplasm in similar abundance to AK. The activity ratio of G6PD (extracellular/total) was found to be similar to that of AK. Because G6PD in the medium was probably due to leakage, other cytoplasmic macromolecules, including AK, should be released proportionately from the cells. The role of plasma membrane ATP synthase in extracellular ATP formation was examined using Hanks' balanced salt solution with and without selective inhibitors of AK and ATP synthase activities. With P(1),P(5)-di(adenosine 5')-pentaphosphate (inhibitor of AK activity), no extracellular ATP synthesis was detected, whereas with oligomycin, piceatannol, and aurovertin (inhibitors of F(1)F(0)-ATP synthase and F(1)-ATPase activities), no inhibition of extracellular ATP synthesis was observed. AK activity alone could account for the observed extracellular ATP synthesis. The possible impact of ADP impurity in the assays is discussed.

Biosynthesis of plant-specific stilbene polyketides in metabolically engineered Escherichia coli

BACKGROUND

Phenylpropanoids are the precursors to a range of important plant metabolites such as the cell wall constituent lignin and the secondary metabolites belonging to the flavonoid/stilbene class of compounds. The latter class of plant natural products has been shown to function in a wide range of biological activities. During the last few years an increasing number of health benefits have been associated with these compounds. In particular, they demonstrate potent antioxidant activity and the ability to selectively inhibit certain tyrosine kinases. Biosynthesis of many medicinally important plant secondary metabolites, including stilbenes, is frequently not very well understood and under tight spatial and temporal control, limiting their availability from plant sources. As an alternative, we sought to develop an approach for the biosynthesis of diverse stilbenes by engineered recombinant microbial cells.

RESULTS

A pathway for stilbene biosynthesis was constructed in Escherichia coli with 4-coumaroyl CoA ligase 1 4CL1) from Arabidopsis thaliana and stilbene synthase (STS) cloned from Arachis hypogaea. E. coli cultures expressing these enzymes together converted the phenylpropionic acid precursor 4-coumaric acid, added to the growth medium, to the stilbene resveratrol (>100 mg/L). Caffeic acid, added in the same way, resulted in the production of the expected dihydroxylated stilbene, piceatannol (>10 mg/L). Ferulic acid, however, was not converted to the expected stilbene product, isorhapontigenin. Substitution of 4CL1 with a homologous enzyme, 4CL4, with a preference for ferulic acid over 4-coumaric acid, had no effect on the conversion of ferulic acid. Accumulation of tri- and tetraketide lactones from ferulic acid, regardless of the CoA-ligase expressed in E. coli, suggests that STS cannot properly accommodate and fold the tetraketide intermediate to the corresponding stilbene structure.

CONCLUSION

Phenylpropionic acids, such as 4-coumaric acid and caffeic acid, can be efficiently converted to stilbene compounds by recombinant E. coli cells expressing plant biosynthetic genes. Optimization of precursor conversion and cyclization of the bulky ferulic acid precursor by host metabolic engineering and protein engineering may afford the synthesis of even more structurally diverse stilbene compounds.

Suppression of the Phosphorylation of Receptor Tyrosine Phosphatase-α on the Src-Independent Site Tyrosine 789 by Reactive Oxygen Species

Oxidation of receptor protein tyrosine phosphatase-alpha (RPTPalpha) is emerging as an important yet poorly characterized regulatory mechanism for RPTPalpha signaling in cells. RPTPalpha has been shown to be reversibly oxidized and inhibited by reactive oxygen species. However, it is not known whether oxidative stress could regulate the phosphorylation of Tyr789, a critical tyrosine residue for RPTPalpha signaling that modulates the function of Grb2 and the activation of Src family kinases. In the present study, we have taken advantage of a phosphospecific antibody against Tyr789-phosphorylated RPTPalpha and characterized the phosphorylation of RPTPalpha Tyr789 in various cultured cells, including SYF cells lacking all three ubiquitously expressed members (Src, Yes, and Fyn) of Src family kinases. We have obtained substantial evidence indicating that the phosphorylation of RPTPalpha Tyr789 is regulated predominantly by an Src kinase inhibitor, protein phosphatase 1 (PP1)-sensitive but Src/Yes/Fyn-independent tyrosine kinase, in cells. We further reported a novel finding that, besides the inhibition of RPTPalpha's activity, H(2)O(2) at low to moderate concentrations (50-250 microM) markedly suppressed the phosphorylation of RPTPalpha Tyr789 and the association of RPTPalpha with Grb2 in cultured cells, which may result from inhibition of such a PP1-sensitive but Src/Yes/Fyn-independent tyrosine kinase. Because Tyr789 plays an important role in RPTPalpha signaling, our findings may provide new insights into the functional regulation of RPTPalpha by oxidative stress in cells.

Dissociation of recruitment and activation of the small G-protein Rac during Fcgamma receptor-mediated phagocytosis

Rho-family proteins play a central role in most actin-dependent processes, including the control and maintenance of cell shape, adhesion, motility, and phagocytosis. Activation of these GTP-binding proteins is tightly regulated spatially and temporally; however, very little is known of the mechanisms involved in their recruitment and activation in vivo. Because of its inducible, restricted signaling, phagocytosis offers an ideal physiological system to delineate the pathways linking surface receptors to actin remodeling via Rho GTPases. In this study, we investigated the involvement of early regulators of Fcgamma receptor signaling in Rac recruitment and activation. Using a combination of receptor mutagenesis, cellular, molecular, and pharmacological approaches, we show that Src family and Syk kinases control Rac and Vav function during phagocytosis. Importantly, both the immunoreceptor tyrosine-based activation motif within Fcgamma receptor cytoplasmic domain and Src kinase control the recruitment of Vav and Rac. However, Syk activity is dispensable for Vav and Rac recruitment. Moreover, we show that Rac and Cdc42 activities coordinate F-actin accumulation at nascent phagosomes. Our results provide new insights in the understanding of the spatiotemporal regulation of Rho-family GTPase function, and of Rac in particular, during phagocytosis. We believe they will contribute to a better understanding of more complex cellular processes, such as cell adhesion and migration.

The tyrosine kinase Syk regulates TPL2 activation signals

Tpl2/Cot is a serine/threonine kinase that plays a key physiological role in the regulation of immune responses to pro-inflammatory stimuli, including tumor necrosis factor-alpha (TNF-alpha). TNF-alpha stimulates the JNK, ERK, and p38 mitogen-activated protein kinases and the NF-kappaB pathway by recruiting RIP1 and TRAF2 to the TNF receptor 1. Here we showed that Tpl2 activation by TNF-alpha signals depends on the integrity of the Tpl2-interacting proteins RIP1 and TRAF2, which are required for the engagement of the ERK mitogen-activated protein kinase pathway. However, neither RIP1 nor TRAF2 overexpression was sufficient to activate Tpl2 and ERK. We also showed that Tpl2 activation by TNF-alpha depends on a tyrosine kinase activity that is detected in TNF-alpha-stimulated cells. Based on both genetic and biochemical evidence, we concluded that in a variety of cell types, Syk is the tyrosine kinase that plays an important role in the activation of Tpl2 upstream of ERK. These data therefore dissect the TNF receptor 1 proximal events that regulate Tpl2 and ERK and highlight a role for RIP1, TRAF2, and Syk in this pathway.

TRPV4 mediates pain-related behavior induced by mild hypertonic stimuli in the presence of inflammatory mediator

The ligand-gated ion channel, TRPV4, functions as a transducer of hypotonic stimuli in primary afferent nociceptive neurons and contributes to inflammatory and neuropathic pain. Hypertonic saline also stimulates primary afferent nociceptors and the injection of mild hypertonic saline (2-5%) is widely used as an experimental model of pain in humans. Therefore, we tested whether TRPV4 participates in the transduction of hypertonic stimuli. Intradermal injection of 2% (607 mOsm) or 10% (3,250 mOsm) saline solution in the hind paw of rats induced a concentration-dependent pain-related behavior, flinching. Sensitization with prostaglandin E(2) (PGE(2)) caused a 7-fold increase in the number of flinches induced by 2% saline but failed to increase those caused by 10% saline. Spinal administration of antisense oligodeoxynucleotides to TRPV4 caused a 46% decrease in the number of flinches induced by 2% saline, but there was no change in flinching induced by 10% saline. Similarly, only the nociceptive behavior caused by 2% saline was reduced in TRPV4(-/-) knockout mice. The TRPV4-mediated nociceptive behaviors induced by hyper- and hypotonic stimuli were dependent on Src tyrosine kinase. We suggest TRPV4 is a transducer in primary afferents that mediates nociceptive behavior induced by small increases or decreases in osmolarity. Such changes in osmolarity might contribute to pain in inflammatory and neuropathic states.

The initiation of antigen-induced B cell antigen receptor signaling viewed in living cells by fluorescence resonance energy transfer

Binding of antigen to the B cell antigen receptor (BCR) triggers signaling that ultimately leads to B cell activation. Using quantitative fluorescence resonance energy transfer imaging, we provide evidence here that the BCR is a monomer on the surface of resting cells. Binding of multivalent antigen clustered the BCR, resulting in the simultaneous phosphorylation of and a conformational change in the BCR cytoplasmic domains from a closed to an open form. Notably, the open conformation required immunoreceptor tyrosine-activation motif and continuous Src family kinase activity but not binding of the kinase Syk. Thus, the initiation of BCR signaling is a very dynamic process accompanied by reversible conformational changes induced by Src family kinase activity.

Inhibitor of p42/44 mitogen-activated protein kinase, but not p38 MAPK, attenuated antigen challenge of guinea pig airways in vitro

Upon cross-linking of the high-affinity IgE receptors on mast cells, a family of mitogen-activated protein kinases (MAPKs) is activated. The present study examined the effects of p42/44 MAPK kinase inhibitor U0126 and p38 MAPK inhibitors SB220025 and PD169316 on ovalbumin (OVA)-induced anaphylactic contraction of isolated guinea pig bronchi and release of histamine and peptidoleukotrienes from lung fragments. Guinea pigs were actively sensitized by OVA. OVA induced anaphylactic bronchial contractions, and release of histamine and peptidoleukotrienes from lung fragments. U0126 (0.3-30 microM), but not SB220025 and PD169316 (3-30 microM), slightly suppressed peak OVA-induced bronchial contraction but markedly reduced anaphylactical contraction over a 50-min period in a dose-dependent manner. U0126 did not inhibit bronchial contractions induced by KCl, histamine or leukotriene D4. U0126 produced a slight reduction in OVA-induced release of histamine but a significant inhibition on the release of peptidoleukotrienes from lung fragments. Exogenous arachidonic acid-induced release of peptidoleukotrienes was not blocked by U0126. SB220025 and PD169316 had no effect on OVA-induced release of histamine and peptidoleukotrienes. Our data indicate that inhibitor of p42/44 MAPK kinase, but not p38 MAPK, can reduce antigen-induced release of peptidoleukotrienes leading to a rapid resolution of anaphylactic bronchial contraction, and may have therapeutic potential for allergic asthma.

In situ measurement of degranulation as a biosensor based on RBL-2H3 mast cells

A direct degranulation assay has been developed to enable the use of RBL mast cells as a biosensor for screening chemical libraries for drug discovery and environmental toxicity evaluation. Release of beta-hexosaminidase into the extracellular milleu is widely used to characterize cellular components and mechanisms involved in stimulated exocytosis, including those initiated by crosslinking of IgE receptors on mast cells. To adapt this versatile assay for high throughput screening, we developed a direct, in situ method in which beta-hexosaminidase detection is carried out in a single step, convenient for multi-sample processing and thus for biosensor applications. This direct assay is efficient for measuring exocytosis in antigen-stimulated RBL mast cells, detecting antigen concentrations as low as 1 pM. We also demonstrate its utility in detecting inhibition of degranulation by a known pharmacologic inhibitor that blocks Syk tyrosine kinase activity critical for cell activation.

Effects of resveratrol, piceatannol, tri-acetoxystilbene, and genistein on the inflammatory response of human peripheral blood leukocytes

Inflammatory processes are involved in the etiology of diseases. We analyzed the effect of resveratrol, piceatannol, synthetic tri-acetoxystilbene (TAS), and genistein (Bonistein(TM)) on the production of inflammatory mediators including prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha), interleukins, and chemokines, which participate in the progression of inflammation. In order to induce inflammatory responses, human peripheral blood mononuclear and/or polymorphonuclear leukocytes were stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN(gamma)) and the production of PGE2, interleukin-8 (IL-8), and TNF-alpha was determined. In response to the stimuli, genes were substantially activated within < 2 h (e. g., TNF-alpha, IL-1alpha), or at a later stage, (e. g., COX-2, IL-6, IL-8). Unlike genistein, resveratrol and related compounds dose-dependently reduced PGE2 production. Genistein, piceatannol, and TAS diminished secretion of TNF-alpha, and IL-8. TAS reduced mRNA levels of COX-2, TNF-alpha, IL-8, IL-6, and IL-1alpha, while resveratrol impaired early expression of IL-8 and TNF-alpha. Piceatannol out-performed resveratrol, yet without matching TAS. Genistein downregulated TNF-alpha and IL-8 expression. These substances altered the LPS/IFNgamma-induced gene expression in mononuclear cells rather than in polymorphonuclear leukocytes. Immunoblot analyses corroborated the distinct activity pattern of resveratrol and genistein. In conclusion, resveratrol and their derivatives attenuated the inflammatory response of PBLs at several levels, whereas genistein acts on cytokines and pro-inflammatory interleukins.

Negative regulation of phagocytosis in macrophages by the CD47-SHPS-1 system

Src homology 2 domain-containing protein tyrosine phosphatase (SHP) substrate-1 (SHPS-1) is a transmembrane protein that is expressed predominantly in macrophages. Its extracellular region interacts with the transmembrane ligand CD47 expressed on the surface of adjacent cells, and its cytoplasmic region binds the protein tyrosine phosphatases SHP-1 and SHP-2. Phagocytosis of IgG- or complement-opsonized RBCs by peritoneal macrophages derived from mice that express a mutant SHPS-1 protein that lacks most of the cytoplasmic region was markedly enhanced compared with that apparent with wild-type macrophages. This effect was not observed either with CD47-deficient RBCs as the phagocytic target or in the presence of blocking Abs to SHPS-1. Depletion of SHPS-1 from wild-type macrophages by RNA interference also promoted FcgammaR-mediated phagocytosis of wild-type RBCs. Ligation of SHPS-1 on macrophages by CD47 on RBCs promoted tyrosine phosphorylation of SHPS-1 and its association with SHP-1, whereas tyrosine phosphorylation of SHPS-1 was markedly reduced in response to cross-linking of FcgammaRs. Treatment with inhibitors of PI3K or of Syk, but not with those of MEK or Src family kinases, abolished the enhancement of FcgammaR-mediated phagocytosis apparent in macrophages from SHPS-1 mutant mice. In contrast, FcgammaR-mediated tyrosine phosphorylation of Syk, Cbl, or the gamma subunit of FcR was similar in macrophages from wild-type and SHPS-1 mutant mice. These results suggest that ligation of SHPS-1 on macrophages by CD47 promotes the tyrosine phosphorylation of SHPS-1 and thereby prevents the FcgammaR-mediated disruption of the SHPS-1-SHP-1 complex, resulting in inhibition of phagocytosis. The inhibition of phagocytosis by the SHPS-1-SHP-1 complex may be mediated at the level of Syk or PI3K signaling.

Thrombin-induced tyrosine phosphorylation of HS1 in human platelets is sequentially catalyzed by Syk and Lyn tyrosine kinases and associated with the cellular migration of the protein

Thrombin stimulation of platelets triggers Tyr phosphorylation of several signaling proteins, most of which remain unidentified. In this study, we demonstrate for the first time that hematopoietic lineage cell-specific protein 1 (HS1) undergoes a transient Tyr phosphorylation in human platelets stimulated with thrombin. The protein is synergistically phosphorylated by Syk and Lyn tyrosine kinases according to a sequential phosphorylation mechanism. By means of specific inhibitors (PP2, SU6656, and piceatannol) and phosphopeptide-specific antibodies, as well as by coimmunoprecipitation and binding competition experiments, we show that Syk acts as the primary kinase that phosphorylates HS1 at Tyr397 and that Syk phosphorylation is required for HS1 interaction with the Lyn SH2 domain. Upon docking to Syk-phosphorylated HS1, Lyn catalyzes the secondary phosphorylation of the protein at Tyr222. Once the secondary Tyr phosphorylation of HS1 is accomplished the protein dissociates from Lyn and undergoes a dephosphorylation process. HS1 Tyr phosphorylation does not occur when thrombin-induced actin assembly is inhibited by cytochalasin D even under conditions in which Syk and Lyn are still active. Immunofluorescence microscopic analysis shows that the agonist promotes HS1 migration to the plasma membrane and that the inhibition of Lyn-mediated secondary phosphorylation of HS1 abrogates the subcellular translocation of the protein. All together these results indicate that HS1 Tyr phosphorylation catalyzed by Syk and Lyn plays a crucial role in the translocation of the protein to the membrane and is involved in the cytoskeleton rearrangement triggered by thrombin in human platelets.

Anti-allergic activity of stilbenes from Korean rhubarb (Rheum undulatum L.): structure requirements for inhibition of antigen-induced degranulation and their effects on the release of TNF-alpha and IL-4 in RBL-2H3 cells

Stilbenes isolated from the rhizomes of Rheum undulatum (Korean rhubarb) and the related compounds were investigated on their anti-allergic activities. The results revealed that 3,5,4'-trimethylpiceatannol exhibited the most potent inhibition against beta-hexosaminidase release as a marker of degranulation in RBL-2H3 cells with IC(50) of 2.1 microM, followed by trimethylresveratrol (IC(50)=5.1 microM). Structural requirements of stilbenes for the activity are as follows: (1) The oxygen functions (-OCH(3), -OH), especially methoxyl groups, are essential and their positions on aromatic rings are important for the activity; (2) the alpha-beta double bond increased the activity; (3) the glycoside moiety dramatically decreased the activity; and (4) the substitution group at the 3'-position in trimethylresveratrol (3,5,4'-trimethoxystilbene) was preferably OH>H>OCH(3) for the activity. Several active stilbenes (piceatannol, 3,5,4'-trimethylpiceatannol, resveratrol, trimethylresveratrol) also inhibited ionomycin-induced beta-hexosaminidase release, suggesting that inhibition of Ca(2+) influx or degranulation mechanisms after Ca(2+) influx is important for their activities. Piceatannol, 3,5,4'-trimethylpiceatannol, resveratrol, and trimethylresveratrol also significantly inhibited antigen-induced release of TNF-alpha and IL-4 in RBL-2H3 cells.

Oncostatin M causes VEGF release from human airway smooth muscle: synergy with IL-1beta

Vascular endothelial growth factor (VEGF), a potent angiogenesis factor, likely contributes to airway remodeling in asthma. We sought to examine the effects and mechanism of action of IL-6 family cytokines on VEGF release from human airway smooth muscle (HASM) cells. Oncostatin M (OSM), but not other IL-6 family cytokines, increased VEGF release, and IL-1beta enhanced OSM-induced VEGF release. OSM increased VEGF mRNA expression and VEGF promoter activity, whereas IL-1beta had no effect. IL-1beta did not augment the effects of OSM on VEGF promoter activity but did augment OSM-induced VEGF mRNA expression and mRNA stability. The STAT3 inhibitor piceatannol decreased both OSM-induced VEGF release and synergy between OSM and IL-1beta, without affecting responses to IL-1beta alone. Piceatannol also inhibited OSM-induced VEGF mRNA expression. In contrast, inhibitors of MAPK pathway had no effect on OSM or OSM plus IL-1beta-induced VEGF release. OSM increased type 1 IL-1 receptor (IL-1R1) mRNA expression, as measured by real-time PCR, and piceatannol attenuated this response. Consistent with the increase in IL-1R1 expression, OSM markedly augmented IL-1beta-induced VEGF, MCP-1, and IL-6 release. In summary, our data indicate OSM causes VEGF expression in HASM cells by a transcriptional mechanism involving STAT3. IL-1beta also synergizes with OSM to increase VEGF release, likely as a result of effects of IL-1beta on VEGF mRNA stability as well as effects of OSM on IL-1R1 expression. This is the first description of a role for OSM on IL-1R1 expression in any cell type. OSM may contribute to airway remodeling observed in chronic airway disease.

Activation of Src kinase Lyn by the Kaposi sarcoma-associated herpesvirus K1 protein: implications for lymphomagenesis

The K1 gene of Kaposi sarcoma-associated herpesvirus (KSHV) encodes a transmembrane glycoprotein bearing a functional immunoreceptor tyrosine-based activation motif (ITAM). Previously, we reported that the K1 protein induced plasmablastic lymphomas in K1 transgenic mice, and that these lymphomas showed enhanced Lyn kinase activity. Here, we report that systemic administration of the nuclear factor kappa B (NF-kappaB) inhibitor Bay 11-7085 or an anti-vascular endothelial growth factor (VEGF) antibody significantly reduced K1 lymphoma growth in nude mice. Furthermore, in KVL-1 cells, a cell line derived from a K1 lymphoma, inhibition of Lyn kinase activity by the Src kinase inhibitor PP2 decreased VEGF induction, NF-kappaB activity, and the cell proliferation index by 50% to 75%. In contrast, human B-cell lymphoma BJAB cells expressing K1, but not the ITAM sequence-deleted mutant K1, showed a marked increase in Lyn kinase activity with concomitant VEGF induction and NF-kappaB activation, indicating that ITAM sequences were required for the Lyn kinase-mediated activation of these factors. Our results suggested that K1-mediated constitutive Lyn kinase activation in K1 lymphoma cells is crucial for the production of VEGF and NF-kappaB activation, both strongly implicated in the development of KSHV-induced lymphoproliferative disorders.

The non-receptor tyrosine kinase Syk regulates lamellipodium formation and site-directed migration of human leukocytes

The tyrosine kinase Syk is associated with CD18, the beta-subunit of the leukocyte adhesion molecules of the beta(2) integrin family (CD11/CD18), and becomes activated upon beta(2) integrin-mediated adhesion. In this study, we elucidated the role of Syk in polarization and site-directed migration of neutrophil-like differentiated HL-60 cells and monocytic THP-1 cells. By means of confocal microscopy, we detected a homogenous distribution of Syk in unstimulated cells in suspension. The stimulation of HL-60 cells by formyl-methionyl-leucyl-phenylalanine (fMLP, 100 nM) or the activation of THP-1 cells by monocyte chemoattractant protein-1 (10 ng/ml) induced beta(2) integrin-mediated cell adhesion and polarization on immobilized fibrinogen which was associated with an enrichment of Syk at the lamellipodium forming site. This effect was abolished by function blocking anti-CD18 antibody or by treatment of the cells with the Syk inhibitor piceatannol (30 microM) suggesting that the redistribution of Syk required both, beta(2) integrin-mediated adhesion and Syk activation. Moreover, the inhibition of Syk by piceatannol or the downregulation of Syk by antisense technique resulted in an excessive formation of lamellipodia indicating that Syk may act as a negative regulator that limits lamellipodium formation. The analysis of chemotaxis revealed that the inhibition of Syk impaired the ability of the cells to follow a chemotactic gradient whereas random migration was intact. Taken together, our data suggest a novel role for Syk in the maintenance of a bipolar phenotype by regulating lamellipodium formation, which is a critical prerequisite for site-directed migration of leukocytes.

Transient transfection of human peripheral blood basophils

The human basophil has resisted previous attempts at transient transfection. Basophils were transfected by nucleoporation and to test whether there was sufficient expression to modify cell function, the cells were transfected with a syk kinase tandem SH2 construct linked to GFP. This approach was taken because in RBL cells and murine mast cells syk kinase is known to play a very early role in signal transduction and previous studies in RBL cells demonstrated that expression of the tandem SH2 domains of syk would inhibit signaling, presumably by competition with endogenous syk for binding to ITAMs. Results from basophil transfections with SH2syk were compared to an empty construct. Basophils were stimulated with anti-IgE antibody and analyzed for single cell changes in cytosolic calcium levels. Basophils expressing the empty GFP construct showed a cytosolic calcium response similar to non-expressing cells. In contrast, basophils expressing the GFP-tandem SH2syk construct, on average, showed an anti-IgE-induced calcium response that was completely ablated. The transfection frequency was 8% (median), with an average viable recovery of 12% (n=18). While the procedure is not benign and is not always successful, these studies indicate that with gating techniques, the human basophil, a non-dividing primary leukocyte, can be transiently transfected to express high enough levels of an inhibitory protein to alter an IgE-mediated response.

Label-free, real-time monitoring of IgE-mediated mast cell activation on microelectronic cell sensor arrays

Immunoglobulin E (IgE)-mediated mast cell activation is involved in the immediate phase of allergic reactions and plays a central role in the onslaught and persistence of allergic diseases. IgE-mediated mast cell activation includes two important events: cell sensitization resulting from IgE binding to Fc (FcepsilonRI) receptor and cell activation triggered by allergen-mediated oligomerization of membrane-bound IgE. Real-time monitoring of these events is needed to dissect the molecular mechanisms underlying IgE-mediated mast cell activation. Existing technologies are limited to label-based end-point assay formats, which detect either early signaling or final phase of mast cell activation. We describe a microelectronic cell sensor-based technology allowing dynamic monitoring of IgE-mediated mast cell sensitization and activation in real-time without any labeling steps. RBL-2H3 mast cells were cultured onto the surface of microelectronic cell sensor arrays integrated into the bottom of microtiter plates, which record electric properties, such as impedance between cell membrane and sensor surface. In the presence of the allergen, dinitrophenyl (DNP)-bovine serum albumin (BSA), anti-DNP IgE-sensitized cells were activated within 5 min and the entire activation process was quantitatively and continuously recorded. Impedance measurements correlate with morphological dynamics and mediator release as measured by beta-hexosaminidase activity, and can be blocked by pharmacological agents, inhibiting IgE-mediated signaling. The assay on microelectronic cell sensor arrays can be scaled up for high-throughput screening of pharmacological inhibitors of IgE-mediated mast cell activation and other cell-based receptor-ligand assays.

TNF activates Syk protein tyrosine kinase leading to TNF-induced MAPK activation, NF-kappaB activation, and apoptosis

Spleen tyrosine kinase (Syk), a nonreceptor protein kinase initially found to be expressed only in hemopoietic cells, has now been shown to be expressed in nonhemopoietic cells and to mediate signaling of various cytokines. Whether Syk plays any role in TNF signaling was investigated. Treatment of Jurkat T cells with TNF activated Syk kinase but not ZAP70, another member of Syk kinase family, and the optimum activation occurred at 10 s and with 1 nM TNF. TNF also activated Syk in myeloid and epithelial cells. TNF-induced Syk activation was abolished by piceatannol (Syk-selective inhibitor), which led to the suppression of TNF-induced activation of c- JNK, p38 MAPK, and p44/p42 MAPK. Jurkat cells that did not express Syk (JCaM1, JCaM1/lck) showed lack of TNF-induced Syk, JNK, p38 MAPK, and p44/p42 MAPK activation, as well as TNF-induced IkappaBalpha phosphorylation, IkappaBalpha degradation, and NF-kappaB activation. TNF-induced NF-kappaB activation was enhanced by overexpression of Syk by Syk-cDNA and suppressed when Syk expression was down-regulated by expression of Syk-small interfering RNA (siRNA-Syk). The apoptotic effects of TNF were reduced by up-regulation of NF-kappaB by Syk-cDNA, and enhanced by down-regulation of NF-kappaB by siRNA-Syk. Immunoprecipitation of cells with Syk Abs showed TNF-dependent association of Syk with both TNFR1 and TNFR2; this association was enhanced by up-regulation of Syk expression with Syk-cDNA and suppressed by down-regulation of Syk using siRNA-Syk. Overall, our results demonstrate that Syk activation plays an essential role in TNF-induced activation of JNK, p38 MAPK, p44/p42 MAPK, NF-kappaB, and apoptosis.

Positive Regulation of Phagocytosis by SIRPβ and Its Signaling Mechanism in Macrophages

SIRPbeta (signal-regulatory protein beta) is a transmembrane protein that is expressed in hematopoietic cells but whose functions are unknown. We have now cloned mouse SIRPbeta cDNA and have shown that the gene is expressed in various tissues in addition to cells of the macrophage lineage. Engagement of SIRPbeta by specific monoclonal antibodies promoted Fcgamma receptor-dependent or -independent phagocytosis in mouse peritoneal macrophages. It also induced marked activation of MAPK and the upstream kinase MEK but weak activation of Akt. MEK inhibitors markedly blocked the promotion of phagocytosis by SIRPbeta, whereas an inhibitor of phosphoinositide 3-kinase partly blocked such response. In addition, inhibitors of myosin light chain kinase or of myosin ATPase blocked the promotion of phagocytosis by SIRPbeta. Furthermore, SIRPbeta induced the formation of filopodia and lamellipodia in macrophages as well as the translocation of activated MAPK to these structures. It also elicited tyrosine phosphorylation of DAP12, Syk, and SLP-76, and a Syk inhibitor blocked the promotion of phagocytosis and activation of MAPK by SIRPbeta. Our results suggest that engagement of SIRPbeta promotes phagocytosis in macrophages by inducing the tyrosine phosphorylation of DAP12, Syk, and SLP-76 and the subsequent activation of a MEK-MAPK-myosin light chain kinase cascade.

The monocyte Fcgamma receptors FcgammaRI/gamma and FcgammaRIIA differ in their interaction with Syk and with Src-related tyrosine kinases

There are important differences in signaling between the Fc receptor for immunoglobulin G (IgG) FcgammaRIIA, which uses the Ig tyrosine-activating motif (ITAM) within its own cytoplasmic domain, and FcgammaRI, which transmits signals by means of an ITAM located within the cytoplasmic domain of its associated gamma-chain. For example, in transfected epithelial cells and COS-1 cells, FcgammaRIIA mediates phagocytosis of IgG-coated red blood cells more efficiently than does FcgammaRI/gamma, and enhancement of phagocytosis by Syk kinase is more pronounced for FcgammaRI/gamma than for FcgammaRIIA. In addition, structure/function studies indicate that the gamma-chain ITAM and the FcgammaRIIA ITAM have different requirements for mediating the phagocytic signal. To study the differences between FcgammaRIIA and FcgammaRI/gamma, we examined the interaction of FcgammaRIIA and the FcgammaRI/gamma chimera FcgammaRI-gamma-gamma (extracellular domain-transmembrane domain-cytoplasmic domain) with Syk kinase and with the Src-related tyrosine kinases (SRTKs) Hck and Lyn in transfected COS-1 cells. Our data indicate that FcgammaRIIA interacts more readily with Syk than does FcgammaRI-gamma-gamma and suggest that one consequence may be the greater phagocytic efficiency of FcgammaRIIA compared with FcgammaRI/gamma. Furthermore, individual SRTKs affect the efficiency of phagocytosis differently for FcgammaRI-gamma-gamma and FcgammaRIIA and also influence the ability of these receptors to interact with Syk kinase. Taken together, the data suggest that differences in signaling by FcgammaRIIA and FcgammaRI-gamma-gamma are related in part to interaction with Syk and Src kinases and that individual SRTKs play different roles in FcgammaR-mediated phagocytosis.

Tyrosine kinase inhibitors: a new approach for asthma

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

Fc epsilon RI signaling of mast cells activates intracellular production of hydrogen peroxide: role in the regulation of calcium signals

Earlier studies, including our own, revealed that activation of mast cells is accompanied by production of reactive oxygen species (ROS) that help to mediate the release of the inflammatory mediators, including histamine and eicosanoids. However, little is known about the mechanisms of ROS production, including the species of oxidants produced. In this study we show that in both the RBL-2H3 mast cell line and bone marrow-derived mast cells, FcepsilonRI cross-linking stimulates intracellular oxidative burst, including hydrogen peroxide (H(2)O(2)) production, as defined with the oxidant-sensitive dyes dichlorofluorescein and scopoletin and the selective scavenger ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). The oxidative burst was observed immediately after stimulation and was most likely due to an NAD(P)H oxidase. Experiments using selective pharmacological inhibitors demonstrated that activation of tyrosine kinases and phosphatidylinositol-3-kinase is required for induction of the oxidative burst. Blockade of the oxidative burst by diphenyleneiodonium impaired the release of preformed granular mediators, such as histamine and beta-hexosaminidase, and the secretion of newly synthesized leukotriene C(4), whereas selective scavenging H(2)O(2) by ebselen impaired leukotriene C(4) secretion, but not degranulation. Sustained elevation of cytosolic calcium through store-operated calcium entry was totally abolished when ROS production was blocked. In contrast, selective depletion of H(2)O(2) caused a considerable decrease and delay of the calcium response. Finally, tyrosine phosphorylation of phospholipase Cgamma and the linker for activation of T cells, an event required for calcium influx, was suppressed by diphenyleneiodonium and ebselen. These studies demonstrate that activation of the intracellular oxidative burst is an important regulatory mechanism of mast cell responses.

TEL-Syk fusion constitutively activates PI3-K/Akt, MAPK and JAK2-independent STAT5 signal pathways

We previously reported the fusion of the TEL gene to the Syk gene in myelodysplastic syndrome with t(9;12)(q22;p12). TEL-Syk fusion transformed interleukin-3 (IL-3)-dependent murine hematopoietic cell line BaF3 to growth factor independence. Here, we investigate the intracellular signal transduction of the stable transfectants. TEL-Syk fusion protein was associated with the p85 subunit of phosphatidyl inositol 3 kinase (PI3-K) followed by the activation of Akt in the absence of IL-3. Vav, phospholipase C-gamma2 and mitogen-activated protein kinase (MAPK) were also constitutively activated. TEL-Syk also activated the signal transducer and activator of transcription 5 (STAT5) in the absence of Janus kinase 2 activation. None of these kinases were phosphorylated in the BaF3 cells transfected with TELDeltaPNT-Syk in which the oligomerization domain of TEL was deleted. Inhibitor analysis showed that the MAPK pathway was important in TEL-Syk-mediated cell proliferation. The immunofluorescence technique revealed that the TEL-Syk fusion protein was located in the cytoplasm. These data suggest that TEL-Syk fusion protein in the cytoplasm leads to the constitutive activation of PI3-K/Akt, MAPK and STAT5 signal pathways, which are closely involved in IL-3-independent cell proliferation of BaF3 cells.

Integrins and cytokines activate nuclear transcription factor-kappaB in human neutrophils

Neutrophil adhesion to extracellular matrix is necessary for an effective inflammatory response. Adhesion may accelerate neutrophil activation by affecting intracellular signaling pathways. The nuclear transcription factor kappaB (NF-kappaB) controls several cellular functions, including inflammation, proliferation, and cell survival. We explored the role of adhesion in NF-kappaB activation in human neutrophils. Cells were stimulated with tumor necrosis factor-alpha (TNF-alpha), granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin-8 (IL-8), and formyl-methionyl-leucyl-phenylalanine (fMLP). All four initiated neutrophil adherence to and spreading on fibronectin. GM-CSF and IL-8 did not activate NF-kappaB in suspended neutrophils but rapidly activated NF-kappaB under adherent conditions on matrix, as shown by IkappaB kinase activity assay, IkappaBalpha degradation, electromobility shift assay, and quantitative reverse transcriptase-PCR. In contrast, TNF-alpha activated NF-kappaB both in suspended cells and adherent cells. fMLP did not activate NF-kappaB in either suspended or adherent cells. Specific beta(2) integrin blockade prevented NF-kappaB activation by GM-CSF and IL-8 on fibronectin. Co-stimulating CD18 and CD11b with activating antibodies resulted in NF-kappaB activation by GM-CSF and IL-8 in suspended cells. We inhibited actin polymerization with cytochalasin and blocked the non-receptor kinase Syk with piceatannol. Both maneuvers prevented the co-stimulatory NF-kappaB-activating signal by beta(2) integrins. Thus, in addition to beta(2) integrin ligand binding, NF-kappaB activation depended on the formation of the receptor-associated intracellular focal adhesion complex. We conclude that beta(2) integrins may provide co-stimulatory signals allowing some soluble mediators to activate the NF-kappaB pathway even when they are not capable of doing so in suspension. This effect may become important when human neutrophils leave the circulating blood and migrate through extracellular matrix during inflammation.

Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan

In diverse organisms, calorie restriction slows the pace of ageing and increases maximum lifespan. In the budding yeast Saccharomyces cerevisiae, calorie restriction extends lifespan by increasing the activity of Sir2 (ref. 1), a member of the conserved sirtuin family of NAD(+)-dependent protein deacetylases. Included in this family are SIR-2.1, a Caenorhabditis elegans enzyme that regulates lifespan, and SIRT1, a human deacetylase that promotes cell survival by negatively regulating the p53 tumour suppressor. Here we report the discovery of three classes of small molecules that activate sirtuins. We show that the potent activator resveratrol, a polyphenol found in red wine, lowers the Michaelis constant of SIRT1 for both the acetylated substrate and NAD(+), and increases cell survival by stimulating SIRT1-dependent deacetylation of p53. In yeast, resveratrol mimics calorie restriction by stimulating Sir2, increasing DNA stability and extending lifespan by 70%. We discuss possible evolutionary origins of this phenomenon and suggest new lines of research into the therapeutic use of sirtuin activators.

Activation of Epstein-Barr virus/C3d receptor (gp140, CR2, CD21) on human cell surface triggers pp60src and Akt-GSK3 activities upstream and downstream to PI 3-kinase, respectively

We previously demonstrated that CR2 activation on human B lymphocyte surface specifically triggered tyrosine phosphorylation of the 95-kDa nucleolin, this leading to its binding on SH2 domains of p85 sub-unit of PI 3-kinase and to activation of this enzyme. The specificity of CR2 pathway was clearly demonstrated as neither CD19 nor BCR could induce tyrosine phosphorylation of nucleolin in normal B lymphocytes. These data led us to investigate herein additional molecular events, which were triggered by CR2 activation, upstream and downstream to PI 3-kinase activation. Upstream, we demonstrated that pp60src, a tyrosine kinase of the src family, was involved in tyrosine phosphorylation of nucleolin, while syk tyrosine kinase was not. We also demonstrated a direct protein-protein interaction of pp60src with nucleolin in a CR2-dependent and CD19-independent pathway. Downstream, we demonstrated that CR2 activation also triggered Akt and GSK3 enzyme activation, this pathway being under the control of pp60src tyrosine kinase activation. These regulatory functions of activated CR2 were specific as independent of syk tyrosine kinase and of CD19 and BCR activation. Thus, CR2 activation recruits a specific mechanism to activate PI 3-kinase and its subsequent pathways, this mechanism being different to those recruited by CD19 and BCR.

A role for Syk-kinase in the control of the binding cycle of the beta2 integrins (CD11/CD18) in human polymorphonuclear neutrophils

A fine control of beta(2) integrin (CD11/CD18)-mediated firm adhesion of human neutrophils to the endothelial cell monolayer is required to allow ordered emigration. To elucidate the molecular mechanisms that control this process, intracellular protein tyrosine signaling subsequent to beta(2) integrin-mediated ligand binding was studied by immunoprecipitation and Western blotting techniques. The 72-kDa Syk-kinase, which was tyrosine-phosphorylated upon adhesion, was found to coprecipitate with CD18, the beta-subunit of the beta(2) integrins. Moreover, inhibition of Syk-kinase by piceatannol enhanced adhesion and spreading but diminished N-formyl-Met-Leu-Phe-induced chemotactic migration. The enhancement of adhesiveness was associated with integrin clustering, which results in increased integrin avidity. In contrast, piceatannol had no effect on the surface expression or on the affinity of beta(2) integrins. Altogether, this suggests that Syk-kinase controls alternation of beta(2) integrin-mediated ligand binding with integrin detachment.

G-protein-coupled receptor signaling in Syk-deficient neutrophils and mast cells

The Syk tyrosine kinase is essential for immunoreceptor and multiple integrin functions as well as being implicated in signaling from G-protein-coupled receptors (GPCR) in cell lines, transfection systems, and pharmacologic studies. In contrast, using Syk-deficient primary cells, we show here that Syk does not play a major functional role in chemoattractant/chemokine signaling in neutrophils and mast cells. syk(-/-) neutrophils showed normal respiratory burst and degranulation in response to the bacterial peptide formyl-Met-Leu-Phe (fMLP). The migration of neutrophils toward fMLP was similarly not affected by the syk(-/-) mutation. fMLP initiated normal Ca(2+)-signal, activation of the extracellular signal-related kinase (ERK) and p38 mitogen-activated protein (MAP) kinase cascades, and polymerization of cellular actin in the absence of Syk. syk(-/-) and wild-type neutrophils also responded similarly to LTB(4), C5a, and the chemokines macrophage inflammatory protein-1 (MIP-1)alpha or MIP-2, both in functional assays and in intracellular signaling mechanisms. Furthermore, bone marrow-derived syk(-/-) mast cells showed normal activation of the Akt, ERK, and p38 MAP kinase pathways when stimulated by the GPCR ligand adenosine. We conclude that, in contrast to previous reports, Syk does not play a major role in GPCR signaling.

The inhibitory effect of anti-CD33 monoclonal antibodies on AML cell growth correlates with Syk and/or ZAP-70 expression

OBJECTIVES

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that can function as a downregulator of cell growth, mediating growth arrest and apoptosis. The protein kinase Syk is an essential element in several cascades coupling certain antigen receptors to cell responses. Recently we reported that CD33 recruits Syk for its signaling in AML cell lines. In this study, we further investigated the mechanism(s) of Syk engagement in CD33 signaling in primary AML samples.

METHODS

We investigated 25 primary AML samples for their proliferative response (3H-thymidine incorporation) and biochemical changes (Western blot analysis) to anti-CD33 mAb treatment.

RESULTS

Proliferation studies demonstrated that 14 (56%) of AML samples were responsive (R) while 11 (44%) were nonresponsive (n-R) to inhibitory antibody activity. Seven of 25 AML samples (28%) expressed undetectable levels of Syk. However, cells from two of these patients expressed the ZAP-70 protein kinase. In Syk/ZAP-70(+) samples, CD33 ligation inhibited proliferation in 70% of cases, while none of the Syk/ZAP-70(-) samples was responsive. There were significant biochemical differences between responder and nonresponder AML populations. In responder samples, CD33 ligation induced phosphorylation of CD33 andSyk and formation of the CD33/Syk complex. In nonresponder samples, CD33 was not phosphorylated, and Syk was in complex with the SHP-1 protein phosphatase constitutively.

CONCLUSIONS

Syk is an important component in the regulation of proliferation in AML cells. The differential response of AML cells to CD33 ligation is associated with the level of the Syk expression.

Discovery and SAR of novel Naphthyridines as potent inhibitors of spleen tyrosine kinase (SYK)

The discovery of novel 5,7-disubstituted[1,6]naphthyridines as potent inhibitors of Spleen Tyrosine Kinase (SYK) is discussed. The SAR reveals the necessity for a 7-aryl group with preference towards para substitution and that this in combination with 5-aminoalkylamino substituents further improved the potency of the compounds. The initial SAR as well as a survey of the other positions is discussed in detail.

Regulation of a transient receptor potential (TRP) channel by tyrosine phosphorylation. SRC family kinase-dependent tyrosine phosphorylation of TRPV4 on TYR-253 mediates its response to hypotonic stress

The recently identified transient receptor potential (TRP) channel family member, TRPV4 (formerly known as OTRPC4, VR-OAC, TRP12, and VRL-2) is activated by hypotonicity. It is highly expressed in the kidney as well as blood-brain barrier-deficient hypothalamic nuclei responsible for systemic osmosensing. Apart from its gating by hypotonicity, little is known about TRPV4 regulation. We observed that hypotonic stress resulted in rapid tyrosine phosphorylation of TRPV4 in a heterologous expression model and in native murine distal convoluted tubule cells in culture. This tyrosine phosphorylation was sensitive to the inhibitor of Src family tyrosine kinases, PP1, in a dose-dependent fashion. TRPV4 associated with Src family kinases by co-immunoprecipitation studies and confocal immunofluorescence microscopy, and this interaction required an intact Src family kinase SH2 domain. One of these kinases, Lyn, was activated by hypotonic stress and phosphorylated TRPV4 in an immune complex kinase assay and an in vitro kinase assay using recombinant Lyn and TRPV4. Transfection of wild-type Lyn dramatically potentiated hypotonicity-dependent TRPV4 tyrosine phosphorylation whereas dominant negative-acting Lyn modestly inhibited it. Through mutagenesis studies, the site of tonicity-dependent tyrosine phosphorylation was mapped to Tyr-253, which is conserved across all species from which TRPV4 has been cloned. Importantly, point mutation of Tyr-253 abolished hypotonicity-dependent channel activity. In aggregate, these data indicate that hypotonic stress results in Src family tyrosine kinase-dependent tyrosine phosphorylation of the tonicity sensor TRPV4 at residue Tyr-253 and that this residue is essential for channel function in this context. This is the first example of direct regulation of TRP channel function through tyrosine phosphorylation.

Forced expression of the Fc receptor gamma-chain renders human T cells hyperresponsive to TCR/CD3 stimulation

High level expression of Fc epsilon RI gamma chain replaces the deficient TCR zeta-chain and contributes to altered TCR/CD3-mediated signaling abnormalities in T cells of patients with systemic lupus erythematosus. Increased responsiveness to Ag has been considered to lead to autoimmunity. To test this concept, we studied early signaling events and IL-2 production in fresh cells transfected with a eukaryotic expression vector encoding the Fc epsilon RI gamma gene. We found that the overexpressed Fc epsilon RI gamma chain colocalizes with the CD3 epsilon chain on the surface membrane of T cells and that cross-linking of the new TCR/CD3 complex leads to a dramatic increase of intracytoplasmic calcium concentration, protein tyrosine phosphorylation, and IL-2 production. We observed that overexpression of Fc epsilon RI gamma is associated with increased phosphorylation of Syk kinase, while the endogenous TCR zeta-chain is down-regulated. We propose that altered composition of the CD3 complex leads to increased T cell responsiveness to TCR/CD3 stimulation and sets the biochemical grounds for the development of autoimmunity.

Antigen-stimulated trafficking from the recycling compartment to the plasma membrane in RBL mast cells

Binding of fluorescein isothiocyanate (FITC)-conjugated cholera toxin B subunit to ganglioside GM1 on RBL-2H3 cells at 37 degrees C results in labeling of the plasma membrane as well as a pool of perinuclear intracellular membranes identified as the endosomal recycling compartment. Antigen-mediated activation of IgE receptor signaling causes rapid, sustained outward trafficking of these labeled endosomes, that is monitored as an increase in FITC fluorescence due to relief of quenching in the acidic endosomes upon delivery to the plasma membrane. Stimulation of this process depends on the integrity of cholesterol-dependent lipid rafts and occurs in response to Ca2+-mobilizing thapsigargin as well as antigen. Inhibitors of some early signaling enzymes stimulated by FcepsilonRI, including Syk tyrosine kinase and phosphoinositide 3-kinase, have little or no effect on this trafficking response. Other signaling pathways, including activation of phospholipase C and Ca2+ influx, do not appear to be necessary for the initiation of the outward trafficking response, but they contribute to maintaining the sustained phase of this process. Consistent with this, antigen-stimulated ruffles are labeled with FITC-cholera toxin B in a Ca2+-dependent manner. Thus, this trafficking response provides a mechanism by which an internal membrane pool can contribute to plasma membrane remodeling during stimulated membrane ruffling, cell motility, and phagocytosis.

SWAP-70-like adapter of T cells, an adapter protein that regulates early TCR-initiated signaling in Th2 lineage cells

We describe the isolation of a protein, SWAP-70-like adapter of T cells (SLAT), which is expressed at high levels in thymocytes and differentiated Th2 cells. SLAT expression was upregulated in differentiating Th2 cells and downregulated in Th1 cells. Ectopic SLAT expression exerted positive or negative effects on IL-4 versus IFNgamma induction, respectively. TCR signaling induced translocation of SLAT to the immunological synapse and its association with ZAP-70 kinase. SLAT reduced the association of ZAP-70 with TCR-zeta and interfered with ZAP-70 but not Lck signaling. Consistent with these results, pharmacological inhibition of ZAP-70 also induced Th2 skewing. Thus, SLAT is a protein which plays a role in Th2 development and/or activation, perhaps by interfering with ZAP-70 signaling.

Treatment of human T cells with bisperoxovanadium phosphotyrosyl phosphatase inhibitors leads to activation of cyclooxygenase-2 gene

Protein-tyrosine phosphatase (PTP) inhibitors are potent activators of T lymphocytes, most likely by affecting the early steps of T cell receptor (TCR) signaling. We have analyzed the effect of the PTP inhibitor bisperoxovanadium (bpV) on expression of the human cyclooxygenase 2 (COX-2) gene, which is induced following TCR triggering. Here we show that COX-2 promoter activity is markedly up-regulated following exposure of Jurkat T cells to bpV(pic). Interestingly enough, treatment of Jurkat cells with cyclic AMP-elevating agents such as forskolin, in combination with bpV, resulted in a more important COX-2 transcriptional activation. Such activation is inhibited by the immunosuppressive drugs FK506 and cyclosporin A. The two nuclear factor of activated T cells (NFAT) binding sites located within the COX-2 promoter region are involved in bpV-mediated positive effect on COX-2 promoter. Electromobility shift assays showed that NFAT1 and activator protein-1 are both translocated to the nucleus following bpV treatment. The active participation of p56(lck), ZAP-70, p36(LAT), and calcium in the bpV-dependent signaling cascade leading to COX-2 transcriptional activation was demonstrated using deficient cell lines and specific inhibitors. Although several PTPs are most likely targeted by bpV, our data suggest that the bpV-mediated signaling cascade is initiated by inhibition of SHP-1, which leads to phosphorylation of p56(lck) and ZAP-70 and, ultimately, to NFAT and activator protein-1 nuclear translocation. These results suggest that PTP inhibitors can activate COX-2 gene expression in a manner very similar to the stimulation induced by TCR triggering.

Antiinflammatory effects of genistein, a tyrosine kinase inhibitor, on a guinea pig model of asthma

Protein tyrosine kinase signaling cascade plays a pivotal role in the activation of inflammatory cells. The purpose of this study was to investigate the effects of genistein, a broad-spectrum protein tyrosine kinase inhibitor, on airway inflammation in an in vivo guinea pig model of asthma. Guinea pigs were actively sensitized by intraperitoneal injections of ovalbumin. Aerosolized ovalbumin induced acute bronchoconstriction in conscious animals in a dose-dependent manner. Genistein (15 mg/kg given intraperitoneally) markedly inhibited ovalbumin-induced, but not histamine- and methacholine-induced, acute bronchoconstriction. In addition, genistein significantly reduced ovalbumin-induced increases in total cell counts and eosinophils recovered in bronchoalveolar lavage fluid, airway eosinophilia, and eosinophil peroxidase activity in cell-free bronchoalveolar lavage fluid and markedly attenuated ovalbumin-induced airway hyperresponsiveness to inhaled methacholine. Immunoblot analysis of lung lysates isolated from genistein-pretreated animals showed that epidermal growth factor-induced tyrosine phosphorylation in lung tissues was inhibited by genistein. These results implicate that inhibition of tyrosine kinase signaling cascade may have therapeutic potential for allergic airway inflammation.

Regulation of Akt-dependent cell survival by Syk and Rac

Interleukin-2 (IL-2) prevents cell apoptosis and promotes survival, but the involved mechanisms have not been completely defined. Although phosphatidylinositide 3-kinase (PI 3-kinase) has been implicated in IL-2-mediated survival mechanisms, none of the 3 chains of the IL-2 receptor (IL-2R) expresses a binding site for PI 3-kinase. However, IL-2Rbeta does express a Syk-binding motif. By using an IL-2-dependent natural killer (NK) cell line, followed by validation of the results in fresh human NK cells, we identified Syk as a critical effector essential for IL-2-mediated prosurvival signaling in NK cells. Down-regulation of Syk by piceatannol treatment impaired NK cellular viability and induced prominent apoptosis as effectively as suppression of PI 3-kinase function by LY294002. Expression of kinase-deficient Syk or pretreatment with piceatannol markedly suppressed IL-2-stimulated activation of PI 3-kinase and Akt, demonstrating that Syk is upstream of PI 3-kinase and Akt. However, constitutively active PI 3-kinase reversed this loss of Akt function caused by kinase-deficient Syk or piceatannol. Thus, Syk appears to regulate PI 3-kinase, which controls Akt activity during IL-2 stimulation. More important, we observed Rac1 activation by IL-2 and found that it mediated PI 3-kinase activation of Akt. This conclusion came from experiments in which dominant-negative Rac1 significantly decreased IL-2-induced Akt activation, whereas constitutively active Rac1 reelevated Akt activity not only in Syk-impaired but also in PI 3-kinase-impaired NK cells. These results constitute the first report of a Syk --> PI3K --> Rac1 --> Akt signal cascade controlled by IL-2 that mediates NK cell survival.

Piceatannol in combination with low doses of cyclosporine A prolongs kidney allograft survival in a stringent rat transplantation model

BACKGROUND

The discovery of new immunosuppressive agents has enhanced short-term graft survival. However, current immunosuppressants often induce toxicities that limit their clinical use. Thus, there is a need for new immunosuppressants for use in clinical transplantation. Piceatannol blocks Syk and ZAP-70, tyrosine kinases involved in immune cell activation. We examined whether piceatannol prolongs kidney allograft survival in the stringent ACI-to-Lewis rat model.

METHODS

Kidney recipients were divided into four groups. Group 1 (n=8) received piceatannol 30 mg/kg per day intravenously and cyclosporine A (CsA) 2 mg/kg per day intramuscularly from day -3 to day 7 after transplantation. At day 8, piceatannol was reduced to 10 mg/kg per day and the combined treatment continued until day 60. Group 2 (n=9) received 2 mg/kg per day CsA alone from day -3 to day 60. Group 3 (n=4) received piceatannol alone as in group 1. Group 4 (n=2) received only the vehicle dimethyl sulfoxide from day -3 to day 60. Graft rejection was defined as either a serum creatinine level more than 2 mg/dL or animal death.

RESULTS

Group 1 animals survived for at least 115 days (n=8, P<0.05), with several animals maintaining their grafts for more than 200 days. In contrast, 8 of 9 animals in group 2 rejected their grafts within 10 days of transplantation; one animal survived for 71 days. Excellent graft function was maintained in group 1 animals despite withdrawal of immunosuppression.

CONCLUSIONS

These results are the first to show that piceatannol, when combined with subtherapeutic dosages of CsA, prevents graft rejection, suggesting that targeting Syk and Zap could be useful for preventing graft rejection.

Piceatannol inhibits TNF-induced NF-kappaB activation and NF-kappaB-mediated gene expression through suppression of IkappaBalpha kinase and p65 phosphorylation

Piceatannol is an anti-inflammatory, immunomodulatory, and anti-proliferative stilbene that has been shown to interfere with the cytokine signaling pathway. Previously, we have shown that resveratrol suppresses the activation of the nuclear transcription factor NF-kappaB. Piceatannol, previously reported as a selective inhibitor of protein tyrosine kinase Syk, is structurally homologous to resveratrol. Whether piceatannol can also suppress NF-kappaB activation was investigated. The treatment of human myeloid cells with piceatannol suppressed TNF-induced DNA binding activity of NF-kappaB. In contrast, stilbene or rhaponticin (another analog of piceatannol) had no effect, suggesting the critical role of hydroxyl groups. The effect of piceatannol was not restricted to myeloid cells, as TNF-induced NF-kappaB activation was also suppressed in lymphocyte and epithelial cells. Piceatannol also inhibited NF-kappaB activated by H(2)O(2), PMA, LPS, okadaic acid, and ceramide. Piceatannol abrogated the expression of TNF-induced NF-kappaB-dependent reporter gene and of matrix metalloprotease-9, cyclooxygenase-2, and cyclin D1. When examined for the mechanism, we found that piceatannol inhibited TNF-induced IkappaBalpha phosphorylation, p65 phosphorylation, p65 nuclear translocation, and IkappaBalpha kinase activation, but had no significant effect on IkappaBalpha degradation. Piceatannol inhibited NF-kappaB in cells with deleted Syk, indicating the lack of involvement of this kinase. Overall, our results clearly demonstrate that hydroxyl groups of stilbenes are critical and that piceatannol, a tetrahydroxystilbene, suppresses NF-kappaB activation induced by various inflammatory agents through inhibition of IkappaBalpha kinase and p65 phosphorylation.

Thrombin induces mast cell adhesion to fibronectin: evidence for involvement of protease-activated receptor-1

Thrombin activates mast cells to release inflammatory mediators through a mechanism involving protease-activated receptor-1 (PAR-1). We hypothesized that PAR-1 activation would induce mast cell adhesion to fibronectin (FN). Fluorescent adhesion assay was performed in 96-well plates coated with FN (20 microg/ml). Murine bone marrow cultured mast cells (BMCMC) were used after 3-5 wk of culture (>98% mast cells by flow cytometry for c-Kit expression). Thrombin induced beta-hexosaminidase, IL-6, and matrix metalloproteinase-9 release from BMCMC. Thrombin and the PAR-1-activating peptide AparafluoroFRCyclohexylACitY-NH(2) (cit) induced BMCMC adhesion to FN in a dose-dependent fashion, while the PAR-1-inactive peptide FSLLRY-NH(2) had no effect. Thrombin and cit induced also BMCMC adhesion to laminin. Thrombin-mediated adhesion to FN was inhibited by anti-alpha(5) integrin Ab (51.1 +/- 6.7%; n = 5). The combination of anti-alpha(5) and anti-alpha(4) Abs induced higher inhibition (65.7 +/- 7.1%; n = 5). Unlike what is known for FcepsilonRI-mediated adhesion, PAR-1-mediated adhesion to FN did not increase mediator release. We then explored the signaling pathways involved in PAR-1-mediated mast cell adhesion. Thrombin and cit induced p44/42 and p38 phosphorylation. Pertussis toxin inhibited PAR-1-mediated BMCMC adhesion by 57.3 +/- 7.3% (n = 4), indicating that G(i) proteins are involved. Wortmannin and calphostin almost completely inhibited PAR-1-mediated mast cell adhesion, indicating that PI-3 kinase and protein kinase C are involved. Adhesion was partially inhibited by the mitogen-activated protein kinase kinase 1/2 inhibitor U0126 (24.5 +/- 3.3%; n = 3) and the p38 inhibitor SB203580 (25.1 +/- 10.4%; n = 3). The two inhibitors had additive effects. Therefore, thrombin mediates mast cell adhesion through the activation of G(i) proteins, phosphoinositol 3-kinase, protein kinase C, and mitogen-activated protein kinase pathways.