Role Of Spleen Tyrosine Kinase Research Articles

The Role of Spleen Tyrosine Kinase in Acute Renal Allograft Rejection in the Rat.

The Role of Spleen Tyrosine Kinase in Acute Renal Allograft Rejection in the Rat.

Exploring the role of SYK in respiratory in vivo models

Background Spleen Tyrosine Kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in Last cells downstream of the high-affinity IgE receptor (FceR1). Most studies evaluating SYK function in preclinical models have relied on poorly selective compounds, anti-sense oligonucleotides, or SYK knockout mice. Here we describe the characterization of SYK mechanism in multiple in vivo model settings.

Advances in basic and clinical immunology in 2012

Basic and clinical immunology articles published in the Journal in 2012 were mostly related to the expanding area of primary immunodeficiencies (PIDs). Novel forms of PID were identified by using whole-exome sequencing or after careful examination of flow cytometric data, as in the reports of lymphocyte-specific protein tyrosine kinase, CD27, and CD21 deficiencies. Absent IgG and IgA memory B cells were described in patients with hyper-IgE syndrome, which is consistent with defective antibody response and suggests a potential benefit of immunoglobulin replacement. Impaired production of antibodies to polysaccharide antigens by the human B-cell subset analog to murine B-1 cells was reported in a child with selective polysaccharide antibody deficiency. Increased production of inflammatory cytokines by monocyte-derived cells on Toll-like receptor activation was reported in patients with X-linked agammaglobulinemia, underscoring the important role of Bruton tyrosine kinase in modulation of inflammation. The mechanisms explaining susceptibility to yeast infections and development of chronic mucocutaneous candidiasis were extensively studied. Universal newborn screening for T-cell deficiencies is being implemented in several states, resulting in the diagnosis of a higher number of immunodeficient newborns than previously estimated. The use of laboratory testing to distinguish PIDs from HIV infection was clarified. In the management of PIDs, refinement of indication and strategies to hematopoietic stem cell transplantation resulted in improved outcomes. The use of anti-IL-6 mAbs showed promise as an alternative treatment in patients with Schnitzler syndrome.

Spleen tyrosine kinase mediates high glucose-induced transforming growth factor-β1 up-regulation in proximal tubular epithelial cells

The role of spleen tyrosine kinase (Syk) in high glucose-induced intracellular signal transduction has yet to be elucidated. We investigated whether Syk is implicated in high glucose-induced transforming growth factor-β1 (TGF-β1) up-regulation in cultured human proximal tubular epithelial cells (HK-2 cell).High glucose increased TGF-β1 gene expression through Syk, extracellular signal-regulated kinase (ERK), AP-1 and NF-κB. High glucose-induced AP-1 DNA binding activity was decreased by Syk inhibitors and U0126 (an ERK inhibitor). Syk inhibitors suppressed high glucose-induced ERK activation, whereas U0126 had no effect on Syk activation. High glucose-induced NF-κB DNA binding activity was also decreased by Syk inhibitors. High glucose increased nuclear translocation of p65 without serine phosphorylation of IκBα and without degradation of IκBα, but with an increase in tyrosine phosphorylation of IκBα that may account for the activation of NF-κB. Both Syk inhibitors and Syk-siRNA attenuated high glucose-induced IκBα tyrosine phosphorylation and p65 nuclear translocation. Depletion of p21-activated kinase 2 (Pak2) by transfection of Pak2-siRNA abolished high glucose-induced Syk activation.In summary, high glucose-induced TGF-β1 gene transcription occurred through Pak2, Syk and subsequent ERK/AP-1 and NF-κB pathways. This suggests that Syk might be implicated in the diabetic kidney disease.

Amplification of Toll-like receptor–mediated signaling through spleen tyrosine kinase in human B-cell activation

B cells are activated by combined signals through the B-cell receptor (BCR) and CD40. However, the underlying mechanisms by which BCR signals synergize with Toll-like receptor (TLR) signaling in human B cells remain unclear. We sought to elucidate a role of spleen tyrosine kinase (Syk), a key molecule of BCR signaling, in TLR-mediated activation of human B cells. Human naive and memory B cells were stimulated with combinations of anti-BCR, soluble CD40 ligand, and CpG. Effects of the Syk inhibitors on several B-cell functions and expression of TLR9, TNF receptor-associated factors (TRAFs), and phospho-nuclear factor κB in B cells were assessed. Activation of BCR synergized with CD40- and TLR9-mediated signals in driving robust proliferation, cell-cycle progression, expression of costimulatory molecules, cytokine production, and immunoglobulin production of human B-cell subsets, especially memory B cells. However, the Syk inhibitors remarkably abrogated these B-cell functions. Notably, after stimulation through all 3 receptors, B-cell subsets induced marked expression of TLR9, TRAF6, and phospho-nuclear factor κB, which was again significantly abrogated by the Syk inhibitors. Syk-mediated BCR signaling is a prerequisite for optimal induction of TLR9 and TRAF6, allowing efficient propagation of TLR9-mediated signaling in memory B cells. These results also underscore the role of Syk in aberrant B-cell activation in patients with autoimmune diseases.

Specific Inhibition of Spleen Tyrosine Kinase Suppresses Leukocyte Immune Function and Inflammation in Animal Models of Rheumatoid Arthritis

Based on genetic studies that establish the role of spleen tyrosine kinase (Syk) in immune function, inhibitors of this kinase are being investigated as therapeutic agents for inflammatory diseases. Because genetic studies eliminate both adapter functions and kinase activity of Syk, it is difficult to delineate the effect of kinase inhibition alone as would be the goal with small-molecule kinase inhibitors. We tested the hypothesis that specific pharmacological inhibition of Syk activity retains the immunomodulatory potential of Syk genetic deficiency. We report here on the discovery of (4-(3-(2H-1,2,3-triazol-2-yl)phenylamino)-2-((1R,2S)-2-aminocyclohexylamino) pyrimidine-5-carboxamide acetate (P505-15), a highly specific and potent inhibitor of purified Syk (IC50 1-2 nM). In human whole blood, P505-15 potently inhibited B cell antigen receptor-mediated B cell signaling and activation (IC50 0.27 and 0.28 μM, respectively) and Fcε receptor 1-mediated basophil degranulation (IC50 0.15 μM). Similar levels of ex vivo inhibition were measured after dosing in mice (Syk signaling IC50 0.32 μM). Syk-independent signaling and activation were unaffected at much higher concentrations, demonstrating the specificity of kinase inhibition in cellular systems. Oral administration of P505-15 produced dose-dependent anti-inflammatory activity in two rodent models of rheumatoid arthritis. Statistically significant efficacy was observed at concentrations that specifically suppressed Syk activity by ∼67%. Thus specific Syk inhibition can mimic Syk genetic deficiency to modulate immune function, providing a therapeutic strategy in P505-15 for the treatment of human diseases.

Spleen Tyrosine Kinase Modulates the Proliferation and Phenotypes of Vascular Smooth Muscle Cells Induced by Platelet-Derived Growth Factor

Platelet-derived growth factor BB (PDGF-BB) regulates vascular smooth muscle cells (VSMCs) by activating signaling cascades that promote vasoconstriction and growth, but the underlying mechanisms remain incompletely characterized. In this study, we aimed at investigating the role of spleen tyrosine kinase (Syk) in the proliferation and phenotypes in rat pulmonary arterial VSMCs. Our results demonstrate that PDGF-BB or Syk-adenovirus led to a substantial increase of proliferation of VSMCs and cytoskeleton rearrangement in rat VSMCs. Consistently, these cells underwent phenotype changes. Notably, Syk inhibitor piceatannol significantly inhibited those biological effects induced by PDGF-BB. Thus, we conclude that Syk plays an important role in vascular remodeling through the modulation of proliferation and phenotypes of VSMCs.

Abstract 3496: SYK inhibition results in increased sensitivity of OVCAR-3 cells to paclitaxel

Abstract In order to identify novel drug targets in ovarian cancers, we examined our ovarian cancer gene expression microarray data for expression of genes in the tyrosine kinase family. The spleen tyrosine kinase (SYK) gene was expressed in 73% of 55 ovarian cancer specimens, compared to 26% of 60 breast cancer specimens. Previous studies established the role of SYK in lymphocyte development, immune cell activation, and tumor progression. We found SYK to be expressed in 6 of 10 ovarian carcinoma cell lines. Among its many targets, SYK can bind microtubules and other molecules associated with the cytoskeleton. Because of this ability, we studied the relationship of SYK expression to cellular sensitivity to taxanes. We focused on the OVCAR-3 cell line, which was one of the highest SYK-expressing cell lines, to elucidate the potential effects of SYK on taxane sensitivity. Our results demonstrate that knockdown of SYK expression by siRNA resulted in a one log-fold increased sensitivity of OVCAR-3 cells to the taxane, paclitaxel. Furthermore, this effect was durable, as knockdown of SYK and sensitization to paclitaxel persisted over 128 hours. The potential effects of SYK on tubulin polymerization are currently being investigated. We will evaluate potential upstream and downstream targets to elucidate the pathway(s) responsible for SYK effects and determine whether SYK levels contribute to tumor resistance to chemotherapeutic agents. Understanding the growth signals in drug sensitive and resistant ovarian cancer cell lines and tumor samples may eventually lead to new therapeutic approaches for ovarian cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3496.

The tyrosine kinase Syk regulates the survival of chronic lymphocytic leukemia B cells through PKCδ and proteasome-dependent regulation of Mcl-1 expression

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by accumulation of mature monoclonal CD5+ B cells. The disease results mainly from a failure of cells to undergo apoptosis, a process largely influenced by the existence of constitutively activated components of B-cell receptor signaling and the deregulated expression of anti-apoptotic molecules. Recent evidence pointing to a critical role of spleen tyrosine kinase (Syk) in ligand-independent BCR signaling prompted us to examine its role in primary B-CLL cell survival. We demonstrate that pharmacological inhibition of constitutive Syk activity and silencing by siRNA led to a dramatic decrease of cell viability in CLL samples (n=44), regardless of clinical and biological status and induced typical apoptotic cell death with mitochondrial failure followed by caspase 3-dependent cell death. We also provide functional and biochemical evidence that Syk regulated B-CLL cell survival through a novel pathway involving PKCdelta and a proteasome-dependent regulation of the anti-apoptotic protein Mcl-1. Together, our observations are consistent with a model wherein PKCdelta downstream of Syk stabilizes Mcl-1 through inhibitory phosphorylation of GSK3 by Akt. We conclude that Syk constitutes a key regulator of B-CLL cell survival, emphasizing the clinical utility of Syk inhibition in hematopoietic malignancies.

The tyrosine kinase Syk regulates survival of chronic lymphocytic leukemia B cells through PKCδ phosphorylation and proteasome-dependent regulation of Mcl-1 expression (88.22)

Abstract B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of mature monoclonal CD5+ B cells. The disease results mainly from a failure of cells to undergo apoptosis, a process largely influenced by the existence of constitutively activated components of BCR signaling and the deregulated expression of anti-apoptotic molecules. Recent evidence pointing to a critical role of spleen tyrosine kinase (Syk) in ligand-independent BCR signaling prompted us to examine its role in CLL cells survival. Using primary leukemic cells, we show that pharmacologic inhibition of constitutive Syk activity and depletion of its expression by siRNAs led to a dramatic decrease of cell viability in all tested CLL samples (n=44/44), regardless of clinical and biological status, and induced typical apoptotic cell death, with mitochondrial failure followed by caspase 3-dependent cell death. These events were accompanied by a decreased phosphorylation of PKCδ, but not PKCα/β, and by a down-regulation of Mcl-1, but not XIAP. Moreover, the degradation of Mcl-1 following Syk inhibition relied on a caspase-independent, but proteasome-dependent process, and was rescued by the expression of a proteasome-resistant Mcl-1 mutant. Together, our results show that Syk is a key regulator of B-CLL cell viability, and represents an attractive therapeutic target.

Distinct role of spleen tyrosine kinase in the early phosphorylation of inhibitor of κBα via activation of the phosphoinositide-3-kinase and Akt pathways

Nuclear factor (NF)-κB activation is a critical step in the triggering of inflammatory responses by macrophages. Although numerous investigations have been reported, the precise regulatory mechanisms controlling inflammatory responses mediated by NF-κB remain unclear. In this study, we investigated the early signaling events responsible for modulating NF-κB activation using various parameters, such as the expression of pro-inflammatory genes and the phosphorylation levels of inhibitor of κBα (IκBα) and its upstream kinases. Lipopolysaccharide (LPS) treatment biphasically induced activation of IκBα phosphorylation at 5 and 30min, which induced subsequent pro-inflammatory gene expression that was maximized at 45 and 90min. Of the intracellular signals tested, a series of signaling cascades composed of spleen tyrosine kinase (Syk), phosphoinositide-3-kinase (PI3K), and Akt (protein kinase B) were involved in regulating early phosphorylation of IκBα, according to biochemical and pharmacological analyses. Therefore, our data suggests that Syk-mediated activation of intracellular signaling in response to LPS may play an important role in LPS-induced inflammatory signaling events. Thus, Syk may be a potential target for the development of potent anti-inflammatory drugs.

Spleen tyrosine kinase: a novel target for therapeutic intervention of rheumatoid arthritis

Background: In the last few years, significant progress has been made in understanding the pathogenic mechanisms and in defining the role of relevant cells and molecules in the pathophysiology of rheumatoid arthritis (RA). Various therapies, both biological (anti-TNF, anti-interleukins [e.g., IL-1]) and small molecule inhibitors have been explored for the treatment of RA. Objective: To date, no single signaling pathway inhibitor as wide acting as the corticosteroids, is known. However, treatment with corticosteroids is also associated with allied side effects. Despite a lot of efforts in the category of small molecule inhibitors, no inhibitor is available to deal with RA at both fronts (inflammation and tissue damage), without causing immense side effects. Method: This present review explores the role of spleen tyrosine kinase (Syk) in the pathogenesis of RA and also discusses how it may meet the present day therapeutic requirements for the treatment of RA. This review gives an in-depth discussion on the role of Syk signaling in RA, the possibilities of using Syk as a target and also discusses the possible side effects that could be associated with its inhibition. Conclusion: We propose Syk inhibition as a potential therapeutic approach for the treatment of RA.

Syk contributes to PDGF-BB-mediated migration of rat aortic smooth muscle cells via MAPK pathways

Here we investigated the role of spleen tyrosine kinase (Syk) in the migration induced by platelet-derived growth factor (PDGF) in rat aortic smooth muscle cells (RASMC). Cell migration was determined using a Boyden chamber, by wound-healing, and by aortic ring assays. Activity of Syk, mitogen-activated protein kinase (MAPK), and heat shock protein 27 (HSP27) were tested using immunoblotting with kinase inhibitors and small interference RNAs. PDGF-BB induced binding of Syk to the PDGFbeta receptor and increased the phosphorylation of Syk and migration in RASMC. These effects of PDGF-BB were inhibited by piceatannol, an inhibitor of Syk. PDGF-BB increased the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, p38 MAPK, and HSP27, which were significantly inhibited by piceatannol and in Syk-knockdown cells. The p38 MAPK inhibitor SB203580 and ERK1/2 inhibitor PD98059 inhibited the migration, which was further inhibited by the combination of these inhibitors. SB203580, but not PD98059, inhibited the phosphorylation of HSP27 induced by PDGF-BB in RASMC. PDGF-BB-induced migration was attenuated in HSP27-knockdown cells. Kinase inhibitors and Syk-knockdown diminished PDGF-BB-induced sprout outgrowth in the aortic ring assay. These results imply that Syk is an upstream signal of the p38 MAPK/HSP27 and ERK1/2 pathways that contributes to PDGF-BB-mediated migration in RASMC.