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Isoliquiritigenin (ISL) is a chalcone‐type flavonoid derived from the root of licorice with antioxidant, anti‐inflammatory, anti‐tumour and neuroprotective properties. ISL has been proven to downregulate the productions of IL‐1β, TNF‐α and IL‐6 by macrophages. However, detailed molecular mechanisms of this modulation remain elusive. Here, ISL suppressed Syk phosphorylation and CD80, CD86, IL‐1β, TNF‐α and IL‐6 expressions in lipopolysaccharide‐stimulated macrophages ex vivo. ApoC3‐transgenic (ApoC3TG) mice had more activated macrophages. ISL was also able to downregulate the inflammatory activities of macrophages from ApoC3TG mice. Administration of ISL inhibited Syk activation and inflammatory activities of macrophages in ApoC3TG mice in vivo. The treatment of ISL further alleviated MCD‐induced non‐alcoholic fatty liver disease (NAFLD) in wild‐type and ApoC3TG mice, accompanied by less recruitment and activation of liver macrophages. Due to the inhibition of Syk phosphorylation, ISL‐treated macrophages displayed less production of cytoplasmic ROS, NLRP3, cleaved‐GSDMD and cleaved‐IL‐1β, suggesting less inflammasome activation. Finally, the molecular docking study demonstrated that ISL bound to Syk directly with the Kd of 1.273 × 10−8 M. When the Syk expression was knocked down by its shRNA, the inhibitory effects of ISL on activated macrophages disappeared, indicating that Syk was at least one of key docking‐molecules of ISL. Collectively, ISL could alleviate MCD‐induced NAFLD in mice involved with the inhibition of macrophage inflammatory activity by the blockade of Syk‐induced inflammasome activation. [ABSTRACT FROM AUTHOR]

Prostate cancer (PCa), a prevalent malignancy among elderly males, exhibits a notable rate of advancement, even when subjected to conventional androgen deprivation therapy or chemotherapy. An effective progression prediction model would prove invaluable in identifying patients with a higher progression risk. Using bioinformatics strategies, we integrated diverse data sets of PCa to construct a novel risk model predicated on gene expression and progression‐free survival (PFS). The accuracy of the model was assessed through validation using an independent data set. Eight genes were discerned as independent prognostic factors and included in the prediction model. Patients assigned to the high‐risk cohort demonstrated a diminished PFS, and the areas under the curve of our model in the validation set for 1‐year, 3‐year, and 5‐year PFS were 0.9325, 0.9041 and 0.9070, respectively. Additionally, through the application of single‐cell RNA sequencing to two castration‐related prostate cancer (CRPC) samples and two hormone‐related prostate cancer (HSPC) samples, we discovered that luminal cells within CRPC exhibited an elevated risk score. Subsequent molecular biology experiments corroborated our findings, illustrating heightened SYK expression levels within tumour tissues and its contribution to cancer cell migration. We found that the knockdown of SYK could inhibit migration in PCa cells. Our progression‐related risk model demonstrated the potential prognostic value of SYK and indicated its potential as a target for future diagnosis and treatment strategies in PCa management. [ABSTRACT FROM AUTHOR]

Death due to severe influenza is usually a fatal complication of a dysregulated immune response more than the acute virulence of an infectious agent. Although spleen tyrosine kinase (SYK) as a critical immune signaling molecule and therapeutic target plays roles in airway inflammation and acute lung injury, the role of SYK in influenza virus infection is not clear. Here, we investigated the antiviral and anti‐inflammatory effects of SYK inhibitor R406 on influenza infection through a coculture model of human alveolar epithelial (A549) and macrophage (THP‐1) cell lines and mouse model. The results showed that R406 treatment increased the viability of A549 and decreased the pathogenicity and mortality of lethal influenza virus in mice with influenza A infection, decreased levels of intracellular signaling molecules under the condition of inflammation during influenza virus infection. Combination therapy with oseltamivir further ameliorated histopathological damage in the lungs of mice and further delayed the initial time to death compared with R406 treatment alone. This study demonstrated that phosphorylation of SYK is involved in the pathogenesis of influenza, and R406 has antiviral and anti‐inflammatory effects on the treatment of the disease, which may be realized through multiple pathways, including the already reported SYK/STAT/IFNs‐mediated antiviral pathway, as well as TNF‐α/SYK‐ and SYK/Akt‐based immunomodulation pathway. [ABSTRACT FROM AUTHOR]

Epigenetic alterations, especially DNA methylation, have been shown to play a role in the pathogenesis of diabetes mellitus (DM) and its complications, including diabetic kidney disease (DKD). Spleen tyrosine kinase (Syk) is known to be involved in immune and inflammatory disorders. We, therefore, investigated the possible involvement of Syk promoter methylation in DKD, and the mechanisms underlying this process. Kidney tissues were obtained from renal biopsies of patients with early and advanced DKD. A diabetic mouse model (ApoE−/− DM) was generated from ApoE knockout (ApoE−/−) mice using a high‐fat and high‐glucose diet combined with low‐dose streptozocin intraperitoneal injection. We also established an in vitro model using HK2 cells. A marked elevation in the expression levels of Syk, PKCβ, and P66shc in renal tubules was observed in patients with DKD. In ApoE−/− DM mice, Syk expression and the binding of Sp1 to the Syk gene promoter were both increased in the kidney. In addition, the promoter region of the Syk gene exhibited hypomethylation. Syk inhibitor (R788) intervention improved renal function and alleviated pathologic changes in ApoE−/− DM mice. Moreover, R788 intervention alleviated oxidative stress and apoptosis and downregulated the expression of PKCβ/P66shc signaling pathway proteins. In HK2 cells, oxLDL combined with high‐glucose stimulation upregulated Sp1 expression in the nucleus (compared with control and oxLDL groups), and this was accompanied by an increase in the binding of Sp1 to the Syk gene promoter. SP1 silencing downregulated the expression of Syk and inhibited the production of reactive oxygen species and cell apoptosis. Finally, PKC agonist intervention reversed the oxidative stress and apoptosis induced by Syk inhibitor (R406). In DKD, hypomethylation at the Syk gene promoter was accompanied by an increase in Sp1 binding at the promoter. As a consequence of this enhanced Sp1 binding, Syk gene expression was upregulated. Syk inhibitors could attenuate DKD‐associated oxidative stress and apoptosis via downregulation of PKCβ/P66shc signaling pathway proteins. Together, our results identify Syk as a promising target for intervention in DKD. [ABSTRACT FROM AUTHOR]

Mast cells have traditionally been associated with allergic inflammatory responses; however, they play important roles in cutaneous innate immunity and wound healing. The Hidradenitis Suppurativa tissue transcriptome is associated with alterations in innate immunity and wound healing‐associated pathways; however, the role of mast cells in the disease is unexplored. We demonstrate that mast cell‐associated gene expression (using whole tissue RNAseq) is upregulated, and in‐silico cellular deconvolution identifies activated mast cells upregulated and resting mast cells downregulated in lesional tissue. Tryptase/Chymase positive mast cells (identified using IHC) localize adjacent to epithelialized tunnels, fibrotic regions of the dermis and at perivascular sites associated with Neutrophil Extracellular Trap formation and TNF‐alpha production. Treatment with Spleen Tyrosine Kinase antagonist (Fostamatinib) reduces the expression of mast cell‐associated gene transcripts, associated biochemical pathways and the number of tryptase/chymase positive mast cells in lesional hidradenitis suppurativa tissue. This data indicates that although mast cells are not the most abundant cell type in Hidradenitis Suppurativa tissue, the dysregulation of mast cells is paralleled with B cell/plasma cell inflammation, inflammatory epithelialized tunnels and epithelial budding. This provides an explanation as to the mixed inflammatory activation signature seen in HS, the correlation with dysregulated wound healing and potential pathways involved in the development of epithelialized tunnels. [ABSTRACT FROM AUTHOR]

Papillary thyroid cancer (PTC) is a prevalent malignancy worldwide. Spleen tyrosine kinase (SYK) is a crucial enzyme that participates in various biological processes, including cancer progression. This study aims to uncover the biological function of SYK in PTC. SYK expression patterns in PTC were evaluated using quantitative real time polymerase chain reaction (qRT‐PCR), immunohistochemistry (IHC), and western blot. Cell function assays were performed to assess the effects of SYK on PTC. Bioinformatics analysis was conducted to identify intriguing microRNA (miRNA) and circular RNA (circRNA). Dual‐Luciferase Reporter or RNA immunoprecipitation assays were used to investigate the correlation among SYK, miR‐377‐3p, and hsa_circ_0006417. SYK was upregulated in PTC. Overexpression of SYK exhibited a positive correlation with tumor size, lymph node metastasis, and unfavorable disease‐free survival. Functional assays revealed that SYK exerted tumorigenic effect on PTC cells through mTOR/4E‐BP1 pathway. Mechanistically, hsa_circ_0006417 and miR‐377‐3p regulated SYK expression, offering modulating its tumor‐promoting effects. Collectively, SYK acts as an oncogene in PTC through mTOR/4E‐BP1 pathway, which is regulated by the hsa_circ_0006417/miR‐377‐3p axis, thereby providing a potential alternative for PTC treatment. [ABSTRACT FROM AUTHOR]

Aim: To elucidate the mechanism of miR‐128‐3p in peritoneal fibrosis (PF). Methods: Peritoneal mesothelial cells (PMCs) were dealt with high glucose (HG) for 3 days. The expressions of miR‐128‐3p, p21‐activated kinase 2 (PAK2), spleen tyrosine kinase (SyK), and transforming growth factor‐β1 (TGF‐β1) were detected with quantitative real‐time reverse transcription polymerase chain reaction. The levels of IL‐1β, TNF‐α, IL‐6, and monocyte chemotactic protein‐1 in supernatant were measured by ELISA. Proteins of TGF‐β1, SyK, PAK2, α‐SMA, collagen I, vimentin, ERK/AP‐1, and IκBα/NF‐κB pathway related proteins were measured by Western blot. The correlation between miR‐128‐3p and PAK2 was found by bioinformatics analysis and luciferase reporter gene analysis. Results: miR‐128‐3p was decreased while PAK2, SyK, and TGF‐β1 were increased in HG‐induced PMCs. Moreover, miR‐128‐3p inhibited HG‐induced fibrosis and inflammation in PMCs by targeting PAK2. PAK2 activated SyK, which induced TGF‐β1 expression through ERK/AP‐1 and IκBα/NF‐κB pathways to promote HG‐induced fibrosis of PMCs. Conclusion: miR‐128‐3p inhibited HG‐induced PMCs fibrosis via PAK2/SyK/TGF‐β1 axis. [ABSTRACT FROM AUTHOR]

Background: Metastasis of colorectal cancer (CRC) extremely affects the prognosis of CRC patients. Recently, the genetic methylation has been shown to associate with tumor metastasis. This research aimed to explore the Syk gene, which is frequently hypermethylated in different cancers, and its impact on the metastasis of CRC cells. Methods: We employed the UALCAN database for the detection of the methylation levels of Syk in different cancers. CIBERSORT, TIMER and TISIDB tools were employed to analyze the association of Syk expression with immune features of CRC. Treatment with decitabine has been noted to restore the expression of Syk in CRC cells. The invasion and migration abilities of CRC cell lines were determined using transwell and wound healing assays. The correlation between Syk and c‐Myc was established using the GEPIA2 database and Western blot assays. ​Results: Our results, based on UALCAN, revealed that the methylation level of Syk was altered in diverse cancers including colon adenocarcinoma. We found that expression profile and methylation level of Syk was correlated with immune features of colon adenocarcinoma. Decitabine can restore the expression of Syk in HCT116 and SW480 cells, hence affecting their migration and invasion. Results from GEPIA2 showed that Syk expression was correlated with c‐Myc, while Western blotting analysis revealed a negative association between the expression level of Syk and c‐Myc. ​Conclusions:​ ​This study demonstrates that the expression of Syk could be restored by decitabine in colorectal cancer, thus affecting the migration and invasion abilities of CRC cells. [ABSTRACT FROM AUTHOR]

Chemical compounds have recently been introduced as alternative and non‐integrating inducers of pluripotent stem cell fate. However, chemical reprogramming is hampered by low efficiency and the molecular mechanisms remain poorly characterized. Here, we show that inhibition of spleen tyrosine kinase (Syk) by R406 significantly promotes mouse chemical reprogramming. Mechanistically, R406 alleviates Syk / calcineurin (Cn) / nuclear factor of activated T cells (NFAT) signaling‐mediated suppression of glycine, serine, and threonine metabolic genes and dependent metabolites. Syk inhibition upregulates glycine level and downstream transsulfuration cysteine biosynthesis, promoting cysteine metabolism and cellular hydrogen sulfide (H2S) production. This metabolic rewiring decreased oxidative phosphorylation and ROS levels, enhancing chemical reprogramming. In sum, our study identifies Syk‐Cn‐NFAT signaling axis as a new barrier of chemical reprogramming and suggests metabolic rewiring and redox homeostasis as important opportunities for controlling cell fates. Synopsis: Chemically‐induced pluripotent stem cells (ciPSCs) hold great potential for regenerative medicine, but their induction efficiency remains low and the underlying molecular mechanisms unclear. Here, suppression of spleen tyrosine kinase (Syk) is shown to enhance murine ciPSC formation via modulation of amino acid metabolism and redox homeostasis, suggesting novel approaches for controlling cell fates. Syk inhibitor R406 promotes chemical reprogramming of mouse embryonic fibroblasts.Syk inhibition alleviates calcineurin/NFAT‐mediated suppression of glycine, serine and threonine metabolic gene expression and impacted metabolites.Syk inhibition enhances cysteine biosynthesis and cellular hydrogen sulfide (H2S) production.Increased H2S levels reduce oxidative phosphorylation and ROS levels, facilitating ciPSC induction. [ABSTRACT FROM AUTHOR]

Inflammatory bowel disease (IBD) has emerged a global disease and the ascending incidence and prevalence is accompanied by elevated morbidity, mortality, and substantial healthcare system costs. However, the current typical one-sizef-its-all therapeutic approach is suboptimal for a substantial proportion of patients due to the variability in the course of IBD and a considerable number of patients do not have positive response to the clinically approved drugs, so there is still a great, unmet demand for novel alternative therapeutic approaches. Spleen tyrosine kinase (Syk), a cytoplasmic nonreceptor protein tyrosine kinase, plays crucial roles in signal transduction and there are emerging data implicating that Syk participates in pathogenesis of several gut disorders, such as IBD. In this study, we observed the Syk expression in IBD patients and explored the effects of therapeutic Syk inhibition using small-molecule Syk inhibitor piceatannol in bone marrow--derived macrophages (BMDMs). In addition, due to the poor bioavailability and pharmacokinetics of small-molecule tyrosine kinase inhibitors and superiority of targeting nanoparticles-based drug delivery system,we herein prepared piceatannol-encapsulated poly(lactic-co-glycolic acid) nanoparticles that conjugated with chemokine C--C motif ligand 4 (P-NPs-C) and studied its therapeutic effects in vitro in BMDMs and in vivo in experimental colitis model. Our results indicated that in addition to alleviating colitis, oral administration of P-NPs-C promoted the restoration of intestinal barrier function and improved intestinal microflora dysbiosis, which represents a promising treatment for IBD. [ABSTRACT FROM AUTHOR]

Introduction: The atypical Sts phosphatases negatively regulate signaling pathways in diverse immune cell types, with two of their molecular targets being the related kinases Syk and Zap‐70. Mice lacking Sts expression (Sts−/−) are resistant to infection by the live vaccine strain (LVS) of Francisella tularensis. Although the mechanisms underlying the enhanced resistance of Sts−/− mice have not been definitively established, Sts−/− bone marrow‐derived monocytes (BMMs) demonstrate greater clearance of intracellular LVS following ex vivo infection, relative to wild type cells. To determine how the Sts proteins regulate monocyte bactericidal properties, we analyzed responses of infected cells. Methods: Monocyte bacterial clearance was assayed using ex vivo coculture infections followed by colony‐forming unit analysis of intracellular bacteria. Levels of gene expression were quantified by quantitative reverse‐transcription polymerase chain reaction, levels of Nos2 protein levels were quantified by Western blot analysis, and levels of nitric oxide (NO) were quantified directly using the Griess reagent. We characterized monocyte cytokine production via enzyme‐linked immunosorbent assay. Results: We demonstrate that Sts−/− monocyte cultures produce elevated levels of interferon‐γ (IFNγ) after infection, relative to wild type cultures. Sts−/− monocytes also demonstrate heightened responsiveness to IFNγ. Specifically, Sts−/− monocytes produce elevated levels of antimicrobial NO following IFNγ stimulation, and this NO plays an important role in LVS restriction. Additional IFNγ‐stimulated genes, including Ip10 and members of the Gbp gene family, also display heightened upregulation in Sts−/− cells. Both Sts‐1 and Sts‐2 contribute to the regulation of NO production, as evidenced by the responses of monocytes lacking each phosphatase individually. Finally, we demonstrate that the elevated production of IFNγ‐induced NO in Sts−/− monocytes is abrogated following chemical inhibition of Syk kinase. Conclusion: Our results indicate a novel role for the Sts enzymes in regulating monocyte antibacterial responses downstream of IFNγ. [ABSTRACT FROM AUTHOR]

Acute kidney injury (AKI) is a highly prevalent clinical syndrome with high mortality and morbidity. Previous studies indicated that inflammation promotes tubular damage and plays a key role in AKI progress. Spleen tyrosine kinase (Syk) has been linked to macrophage‐related inflammation in AKI. Up to date, however, no Syk‐targeted therapy for AKI has been reported. In this study, we employed both cell model of LPS‐induced bone marrow‐derived macrophage (BMDM) and mouse model of ischemia/reperfusion injury (IRI)‐induced AKI to evaluate the effects of a Syk inhibitor, BAY61‐3606 (BAY), on macrophage inflammation in vitro and protection of kidney from AKI in vivo. The expression and secretion of inflammatory cytokines, both in vitro and in vivo, were significantly inhibited even back to normal levels by BAY. The upregulated serum creatinine and blood urea nitrogen levels in the AKI mice were significantly reduced after administration of BAY, implicating a protective effect of BAY on kidneys against IRI. Further analyses from Western blot, immunofluorescence staining and flow cytometry revealed that BAY inhibited the Mincle/Syk/NF‐κB signaling circuit and reduced the inflammatory response. BAY also inhibited the reactive oxygen species (ROS), which further decreased the formation of inflammasome and suppressed the mature of IL‐1β and IL‐18. Notably, these inhibitory effects of BAY on inflammation and inflammasome in BMDM were significantly reversed by Mincle ligand, trehalose‐6,6‐dibehenate. In summary, these findings provided compelling evidence that BAY may be an efficient inhibitor of the Mincle/Syk/NF‐κB signaling circuit and ROS‐induced inflammasome, which may help to develop Syk‐inhibitors as novel therapeutic agents for AKI. [ABSTRACT FROM AUTHOR]

Fostamatinib demonstrated efficacy in phase 3 trials of adults with immune thrombocytopenia (ITP). Post hoc analysis compared patients who received fostamatinib as second‐line therapy (after steroids ± immunoglobulins) versus third‐or‐later‐line therapy (after ≥2 prior lines of therapy including a second‐line agent). Platelet responses ≥50 000/µl were observed in 25/32 (78%) second‐line and 54/113 (48%) third‐or‐later‐line patients. Bleeding events were less frequent in second‐line (28%) versus third‐or‐later‐line (45%) patients. Responses once achieved tended to be durable in both groups. The safety profile was similar in both groups. In this post hoc analysis, fostamatinib was more effective as second‐line than third‐or‐later‐line therapy for ITP. [ABSTRACT FROM AUTHOR]

Recently, several targeted agents have been developed for specific subsets of patients with acute myeloid leukaemia (AML), including midostaurin, the first FDA‐approved FLT3 inhibitor for newly diagnosed patients with FLT3 mutations. However, in the initial Phase I/II clinical trials, some patients without FLT3 mutations had transient responses to midostaurin, suggesting that this multi‐targeted kinase inhibitor might benefit AML patients more broadly. Here, we demonstrate submicromolar efficacy of midostaurin in vitro and efficacy in vivo against wild‐type (wt) FLT3‐expressing AML cell lines and primary cells, and we compare its effectiveness with that of other FLT3 inhibitors currently in clinical trials. Midostaurin was found to synergize with standard chemotherapeutic drugs and some targeted agents against AML cells without mutations in FLT3. The mechanism may involve, in part, the unique kinase profile of midostaurin that includes proteins implicated in AML transformation, such as SYK or KIT, or inhibition of ERK pathway or proviability signalling. Our findings support further investigation of midostaurin as a chemosensitizing agent in AML patients without FLT3 mutations. [ABSTRACT FROM AUTHOR]

The low‐grade, chronic inflammation initiated by TLR4‐triggered innate immune responses has a central role on early osteoarthritis. Amurensin H is a resveratrol dimer with anti‐inflammatory and anti‐apoptotic effects, while its effects on TLR‐4 signals to inhibit osteoarthritis are still unclear. In the present study, treatment with amurensin H for 2 weeks in monosodium iodoacetate‐induced mice significantly slows down cartilage degeneration and inflammation using macroscopic evaluation, haematoxylin and eosin (HE) staining and micro‐magnetic resonance imaging. In IL‐1β‐stimulated rat chondrocytes, amurensin H suppresses the production of inflammatory mediators including nitric oxide, IL‐6, IL‐17, PGE2 and TNF‐α using Greiss and ELISA assay. Amurensin H inhibits matrix degradation via decreasing levels of MMP‐9 and MMP‐13 using Western blot assay, promotes synthesis of type II collagen and glycosaminoglycan using immunostaining and safranin O staining, respectively. Amurensin H inhibits intracellular and mitochondrial reactive oxygen species (ROS) generation, and mitochondrial membrane depolarization using DCFH‐DA, MitoSOX Red and JC‐1 assay as well. IL‐1β stimulates TLR4 activation and Syk phosphorylation in chondrocytes, while amurensin H inhibits TLR4/Syk signals and downstream p65 phosphorylation and translocation in a time and dose‐dependent manner. Together, these results suggest that amurensin H exerts chondroprotective effects by attenuating oxidative stress, inflammation and matrix degradation via the TLR4/Syk/NF‐κB pathway. [ABSTRACT FROM AUTHOR]

Summary: We have previously demonstrated that the activation of the spleen tyrosine kinase (Syk)/inhibitory‐κB (IκB)‐α/nuclear factor‐κB (NF‐κB) p65 signalling pathway contributes to hypotension and inflammatory response in a rat models of zymosan (ZYM)‐induced non‐septic shock. The purpose of this study was to further examine the possible mechanism underlying the effect of inhibition of Syk by BAY61‐3606 via NF‐κB activity at the level of nuclear translocation regarding the production of vasodilator and proinflammatory mediators in lipopolysaccharide (LPS) (septic)‐ and ZYM (non‐septic)‐induced shock. Administration of LPS (10 mg/kg, ip) or ZYM (500 mg/kg, ip) to male Wistar rats decreased mean arterial pressure and increased heart rate that was associated with an increase in the activities of cyclooxygenase and nitric oxide synthase, tumour necrosis factor‐α, and interleukin‐8 levels, and NF‐κB activation and nuclear translocation in sera and/or cardiovascular and renal tissues. BAY61‐3606 (3 mg/kg, ip), the selective Syk inhibitor, given 1 hour after LPS‐ or ZYM injection reversed all the above‐mentioned effects. These results suggest that Syk contributes to the LPS‐ or ZYM‐induced hypotension and inflammation associated with transactivation of NF‐κB in septic and non‐septic shock. [ABSTRACT FROM AUTHOR]

Bone marrow stromal cells (BMSCs) are multipotent cells that can differentiate into adipocytes and osteoblasts. Inadequate BMSC differentiation is occasionally implicated in chronic bone metabolic disorders. However, specific signaling pathways directing BMSC differentiation have not been elucidated. Here, we explored the roles of spleen tyrosine kinase (Syk) in BMSC differentiation into adipocytes and osteoblasts. We found that Syk phosphorylation was increased in the early stage, whereas its protein expression was gradually decreased during the adipogenic and osteogenic differentiation of two mouse mesenchymal stromal cell lines, ST2 and 10T(1/2), and a human BMSC line, UE6E-7-16. Syk inactivation with either a pharmacological inhibitor or Syk-specific siRNA suppressed adipogenic differentiation, characterized by decreased lipid droplet appearance and the gene expression of fatty acid protein 4 ( Fabp4), peroxisome proliferator-activated receptor γ2 (Pparg2), CCAAT/enhancer binding proteins α (C/EBPα), and C/EBPβ. In contrast, Syk inhibition promoted osteogenic differentiation, represented by increase in matrix mineralization and alkaline phosphatase (ALP) activity, as well as the expression levels of osteocalcin, runt-related transcription factor 2 (Runx2), and distal-less homeobox 5 (Dlx5) mRNAs. We also found that Syk-induced signals are mediated by phospholipase C γ1 (PLCγ1) in osteogenesis and PLCγ2 in adipogenesis. Notably, Syk-activated PLCγ2 signaling was partly modulated through B-cell linker protein (BLNK) in adipogenic differentiation. On the other hand, growth factor receptor-binding protein 2 (Grb2) was involved in Syk-PLCγ1 axis in osteogenic differentiation. Taken together, these results indicate that Syk-PLCγ signaling has a dual role in regulating the initial stage of adipogenic and osteogenic differentiation of BMSCs. [ABSTRACT FROM AUTHOR]

The spleen tyrosine kinase (SYK) regulates immune cell activation in response to engagement of a variety of receptors, making it an intriguing target for the treatment of inflammatory and autoimmune disorders as well as certain B-cell malignancies. We have previously reported on the discovery and preclinical characterization of PRT062607, a potent and highly selective inhibitor of SYK that exhibits robust anti-inflammatory activity in a variety of animal models. Here we present data from our first human studies aimed at characterizing the pharmacokinetics (PK), pharmacodynamics (PD), and safety of PRT062607 in healthy volunteers following single and multiple oral administrations. PRT062607 demonstrated a favorable PK profile and the ability to completely inhibit SYK activity in multiple whole-blood assays. The PD half-life in the more sensitive assays was approximately 24 hours and returned to predose levels by 72 hours. Selectivity for SYK was observed at all dose levels tested. Analysis of the PK/PD relationship indicated an IC50 of 324 nM for inhibition of B-cell antigen receptor-mediated B-cell activation and 205 nM for inhibition of FcεRI-mediated basophil degranulation. PRT062607 was safe and well tolerated across the entire range of doses. Clinical PK/PD was related to in vivo anti-inflammatory activity of PRT062607 in the rat collagen-induced arthritis model, which predicts that therapeutic concentrations may be safely achieved in humans for the treatment of autoimmune disease. PRT062607 has a desirable PK profile and is capable of safely, potently, and selectively suppressing SYK kinase function in humans following once-daily oral dosing. [ABSTRACT FROM AUTHOR]

Exposure to arsenic is a global health concern. We previously documented an inhibitory effect of inorganic Arsenite on IgE-mediated degranulation of RBL-2H3 mast cells (Hutchinson et al., 2011; J. Appl. Toxicol. 31: 231-241). Mast cells are tissue-resident cells that are positioned at the host-environment interface, thereby serving vital roles in many physiological processes and disease states, in addition to their well-known roles in allergy and asthma. Upon activation, mast cells secrete several mediators from cytoplasmic granules, in degranulation. The present study is an investigation of Arsenite's molecular target(s) in the degranulation pathway. Here, we report that arsenic does not affect degranulation stimulated by either the Ca2+ ionophore A23187 or thapsigargin, which both bypass early signaling events. Arsenic also does not alter degranulation initiated by another non-IgE-mediated mast cell stimulant, the G-protein activator compound 48/80. However, arsenic inhibits Ca2+ influx into antigen-activated mast cells. These results indicate that the target of arsenic in the degranulation pathway is upstream of the Ca2+ influx. Phospho-Syk and phospho-p85 phosphoinositide 3-kinase enzyme-linked immunosorbent assays data show that arsenic inhibits early phosphorylation events. Taken together, this evidence indicates that the mechanism underlying arsenic inhibition of mast cell degranulation occurs at the early tyrosine phosphorylation steps in the degranulation pathway. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Trichophyton infection is highly prevalent and tends to be recurrent. Therefore, it is important to develop new therapeutic agents. Previously, we established a mouse model of Trichophyton-induced contact hypersensitivity ( CHS) and demonstrated that dectin-1 was involved in inflammation induced by trichophytin, the Trichophyton antigen. Here, we used that model to investigate glycyrrhetinic acid ( GA) from plants of the genus Glycyrrhiza as a potential anti-inflammatory agent against superficial mycoses. GA suppressed swelling and the expression of inflammatory cytokines, including macrophage inflammatory protein ( MIP)-2, interleukin ( IL)-6, tumor necrosis factor ( TNF)- α and interferon ( IFN)- γ mRNA. Anti- MIP-2 antibody suppressed trichophytin-induced inflammation, and antidectin-1 antibody suppressed zymosan-induced MIP-2 production in keratinocyte cells. These results suggest that MIP-2 is produced by dectin-1 activation and is involved in inflammation associated with CHS to trichophytin. GA also suppressed zymosan-induced MIP-2 and interleukin ( IL)-8, production in mouse and human macrophages and keratinocytes. Furthermore, GA suppressed the phosphorylation of spleen tyrosine kinase (Syk) and inhibitor of nuclear factor-kappa B (I κB α) and the degradation of I κB α in zymosan-simulated RAW264.7 cells. The results of this study suggest that GA suppresses inflammation induced by trichophytin, partly by the downregulation of Syk phosphorylation. [ABSTRACT FROM AUTHOR]

Off-target pharmacology may contribute to both adverse and beneficial effects of a new drug. In vitro pharmacological profiling is often applied early in drug discovery; there are fewer reports addressing the relevance of broad profiles to clinical adverse effects. Here, we have characterized the pharmacological profile of the active metabolite of fostamatinib, R406, linking an understanding of drug selectivity to the increase in blood pressure observed in clinical studies. R406 was profiled in a broad range of in vitro assays to generate a comprehensive pharmacological profile and key targets were further investigated using functional and cellular assay systems. A combination of traditional literature searches and text-mining approaches established potential mechanistic links between the profile of R406 and clinical side effects. R406 was selective outside the kinase domain, with only antagonist activity at the adenosine A3 receptor in the range relevant to clinical effects. R406 was less selective in the kinase domain, having activity at many protein kinases at therapeutically relevant concentrations when tested in multiple in vitro systems. Systematic literature analyses identified KDR as the probable target underlying the blood pressure increase observed in patients. While the in vitro pharmacological profile of R406 suggests a lack of selectivity among kinases, a combination of classical searching and text-mining approaches rationalized the complex profile establishing linkage between off-target pharmacology and clinically observed effects. These results demonstrate the utility of in vitro pharmacological profiling for a compound in late-stage clinical development. [ABSTRACT FROM AUTHOR]

Fostamatinib is a tyrosine kinase inhibitor with activity against spleen tyrosine kinase which has completed clinical trials for patients with rheumatoid arthritis. In clinical studies fostamatinib treatment was associated with a small elevation of systemic arterial blood pressure (BP), a similar finding to that seen with other kinase inhibitors, especially those that inhibit VEGFR2 signaling. We have investigated the link between fostamatinib-induced blood pressure elevation and plasma levels of the fostamatinib-active metabolite R940406 in conscious rats and found the time course of the BP effect correlated closely with changes in R940406 plasma concentration, indicating a direct pharmacological relationship. Free plasma levels of R940406 produced in these studies (up to 346 nmol/ L) span the clinically observed mean peak free plasma concentration of 49 nmol/L. We have demonstrated that the blood pressure elevation induced by fostamatinib dosing can be successfully controlled by a variety of methods, notably simple drug withdrawal or codosing with a range of standard antihypertensive agents such as atenolol, captopril, and nifedipine. These findings support potential methods of maintaining patient safety while on fostamatinib therapy. Furthermore, we have demonstrated, using nifedipine as an example agent, that this blood pressure control was not achieved by reduction in plasma exposure of R940406, suggesting that potential benefits from the pharmacology of the investigational drug can be maintained while blood pressure control is managed by use of standard comedications. [ABSTRACT FROM AUTHOR]

The development and function of B lymphocytes is regulated by numerous signaling pathways, some emanating from the B-cell antigen receptor ( BCR). The spleen tyrosine kinase (Syk) plays a central role in the activation of the BCR, but less is known about its contribution to the survival and maintenance of mature B cells. We generated mice with an inducible and B-cell-specific deletion of the Syk gene and found that a considerable fraction of mature Syk-negative B cells can survive in the periphery for an extended time. Syk-negative B cells are defective in BCR, RP105 and CD38 signaling but still respond to an IL-4, anti- CD40, CpG or LPS stimulus. Our in vivo experiments show that Syk-deficient B cells require BAFF receptor and CD19/ PI3K signaling for their long-term survival. These studies also shed a new light on the signals regulating the maintenance of the normal mature murine B-cell pool. [ABSTRACT FROM AUTHOR]

Background: Syk, an immune regulatory tyrosine kinase, plays a role in inflammatory disease processes. We recently reported a role for epithelial expression of Syk in the airways hyper-responsiveness in response to air pollution in a mouse model of asthma. The aim of this study was to further investigate the role of Syk in airway contractility in response to methacholine (MCh) and particulate matter (PM) air pollutants, in the absence of underlying inflammation. Methods: We used Sykflox/flox//rosa26CreERT2 conditional Syk knockout mice to evaluate respiratory mechanics and MCh responsiveness following PM exposure in vivo using the ventilator-based flexiVent® system. Results: While total and differential cell counts in bronchoalveolar lavage fluid were similar between the Sykflox/flox and Sykdel/del mice, central airways respiratory resistance (RN) to MCh was significantly augmented following PM exposure between Syk-intact (Sykflox/flox) and Syk-deficient (Sykdel/del) mice (RN(max): 2.06 ± 0.29 vs. 1.29 ± 0.10, respectively; p < 0.05, n = 8-10/group). We employed live videomicroscopy to investigate changes in airway luminal diameter using ex vivo lung slices, which were devoid of circulating leukocytes. MCh reduced the airway luminal area of Sykflox/flox mice to 81.1 ± 1.4% of baseline, which was virtually abrogated in Sykdel/del mice (luminal area = 93.2 ± 0.5%, n = 5/group, p < 0.05). In response to PM exposure, Sykflox/flox airways contracted to 73.8 ± 2.7% of baseline luminal diameter, whereas Sykdel/del airways exhibited minimal contractility to PM and MCh (90.0 ± 1.3% of baseline, n = 5/group, p < 0.05). Conclusions: These observations suggest that Syk mediates airway contractility in the normal and allergic airways, independent of its role and function in leukocytes, and supports a paracrine role for airway epithelial Syk in modulating airway smooth muscle activity. [ABSTRACT FROM AUTHOR]

Kidney allografts induce strong T-cell and antibody responses which mediate acute rejection. Spleen tyrosine kinase ( Syk) is expressed by most leucocytes, except mature T cells, and is involved in intracellular signalling following activation of the Fcγ-receptor, B-cell receptor and some integrins. A role for Syk signalling has been established in antibody-dependent native kidney disease, but little is known of Syk in acute renal allograft rejection. Sprague- Dawley rats underwent bilateral nephrectomy and received an orthotopic Wistar renal allograft. Recipient rats were treated with a Syk inhibitor ( CC0482417, 30 mg/kg/bid), or vehicle, from 1 h before surgery until being killed 5 days later. Vehicle-treated recipients developed severe allograft failure with marked histologic damage in association with dense leucocyte infiltration ( T cells, macrophages, neutrophils and NK cells) and deposition of Ig M, Ig G and C3. Immunostaining identified Syk expression by many infiltrating leucocytes. CC0482417 treatment significantly improved allograft function and reduced histologic damage, although allograft injury was still clearly evident. CC0482417 failed to prevent T-cell infiltration and activation within the allograft. However, CC0482417 significantly attenuated acute tubular necrosis, infiltration of macrophages and neutrophils and thrombosis of peritubular capillaries. In conclusion, this study identifies a role for Syk in acute renal allograft rejection. Syk inhibition may be a useful addition to T-cell-based immunotherapy in renal transplantation. [ABSTRACT FROM AUTHOR]

Toll-like receptors (TLRs) can recognize microbial patterns and utilize adaptor molecules, such as-MyD88 or (TRIF TIR-domain-containing adapter-inducing interferon-β), to initiate downstream signaling that ultimately affects the initiation of adaptive immunity. In addition to this inflammatory role, TLR5 expression on dendritic cells can favor antigen presentation of flagellin peptides and thus increase the sensitivity of flagellin-specific T-cell responses in vitro and in vivo. Here, we examined the role of alternative signaling pathways that might regulate flagellin antigen presentation in addition to MyD88. These studies suggest a requirement for spleen tyrosine kinase, a noncanonical TLR-signaling adaptor molecule, and its downstream molecule CARD9 in regulating the sensitivity of flagellin-specific CD4+ T-cell responses in vitro and in vivo. Thus, a previously unappreciated signaling pathway plays an important role in regulating the dominance of flagellin-specific T-cell responses. [ABSTRACT FROM AUTHOR]

Syk and Zap-70 constitute a closely related nonreceptor protein tyrosine kinase family, of which both members are functionally indispensable for conferring their respective antigen receptors with enzymatic activity. In this study, we analyze the impact of altering BCR signaling output on B-cell germinal center (GC) fate selection by constitutive, as well as inducible, monoallelic Syk kinase loss in the presence of a Zap-70 knock-in rescue allele. Cre-mediated Syk deletion in Sykflox/Zap-70 B cells lowers pErk, but not pAkt-mediated signaling. Surprisingly, the use of a B-cell-specific constitutive mb1-cre deleter mouse model showed that a small cohort of peripheral Sykflox/Zap-70;mb1-cre B cells efficiently circumvents deletion, which ultimately favors these Syk-sufficient cells to contribute to the GC reaction. Using a developmentally unbiased Sykflox/Zap-70;mb1-creERT2 approach in combination with an inducible tdRFP allele, we further demonstrate that this monoallelic deletion escape is not fully explained by leakiness of Cre expression, but is possibly the result of differential Syk locus accessibility in maturing B cells. Altogether, this underscores the importance of proper Syk kinase function not only during central and peripheral selection processes, but also during GC formation and maintenance. [ABSTRACT FROM AUTHOR]

Although being a normal part of the skin flora, yeasts of the genus Malassezia are associated with several common dermatologic conditions including pityriasis versicolour, seborrhoeic dermatitis ( SD), folliculitis, atopic eczema/dermatitis ( AE/ AD) and dandruff. While Malassezia spp. are aetiological agents of pityriasis versicolour, a causal role of Malassezia spp. in AE/ AD and SD remains to be established. Previous reports have shown that fungi such as Candida albicans and Aspergillus fumigatus are able to efficiently activate the NLRP3 inflammasome leading to robust secretion of the pro-inflammatory cytokine IL-1 β. To date, innate immune responses to Malassezia spp. are not well characterized. Here, we show that different Malassezia species could induce NLRP3 inflammasome activation and subsequent IL-1 β secretion in human antigen-presenting cells. In contrast, keratinocytes were not able to secrete IL-1 β when exposed to Malassezia spp. Moreover, we demonstrate that IL-1 β secretion in antigen-presenting cells was dependent on Syk-kinase signalling. Our results identify Malassezia spp. as potential strong inducers of pro-inflammatory responses when taken up by antigen-presenting cells and identify C-type lectin receptors and the NLRP3 inflammasome as crucial actors in this process. [ABSTRACT FROM AUTHOR]

Angiopoietin-like protein 2 ( ANGPTL2) plays an important role in inflammatory carcinogenesis and tumor metastasis by activating tumor angiogenesis and tumor cell chemotaxis and invasiveness. However, it is unclear whether ANGPTL2 expression has an effect on tumor cell survival. Here, we explored that possibility by determining whether ANGPTL2 expression altered survival of human colorectal cancer cell lines treated with antineoplastic drugs. To do so, we generated SW480 cells expressing ANGPTL2 ( SW480/ ANGPTL2) and control ( SW480/ Ctrl) cells. Apoptosis induced by antineoplastic drug treatment was significantly decreased in SW480/ ANGPTL2 compared to control cells. Expression of anti-apoptotic BCL-2 family genes was upregulated in SW480/ ANGPTL2 compared to SW480/ Ctrl cells. To assess signaling downstream of ANGPTL2 underlying this effect, we carried out RNA sequencing analysis of SW480/ ANGPTL2 and SW480/ Ctrl cells. That analysis, combined with in vitro experiments, indicated that Syk- PI3 K signaling induced expression of BCL-2 family genes in SW480/ ANGPTL2 cells. Furthermore, ANGPTL2 increased its own expression in a feedback loop by activating the spleen tyrosine kinase-nuclear factor of activated T cells ( Syk- NFAT) pathway. Finally, we observed a correlation between higher ANGPTL2 expression in primary unresectable tumors from colorectal cancer patients who underwent chemotherapy with a lower objective response rate. These findings suggest that attenuating ANGPTL2 signaling in tumor cells may block tumor cell resistance to antineoplastic therapies. [ABSTRACT FROM AUTHOR]

Background Rhinovirus and IgE act in concert to promote asthma exacerbations. While basophils are the principal cell type in the blood that is activated by IgE, their role in virus-induced asthma episodes remains elusive. Objective To monitor IgE responsiveness in circulating basophils of rhinovirus-infected atopic asthmatics during acute infection and convalescence. Methods The capacity for basophils to respond to IgE was assessed by testing the effects of allergen, or cross-linking anti-Fcε RI and anti-IgE antibodies, on surface TSLP receptor in 24-hour PBMC cultures. Activation profiles of basophils from atopic asthmatics challenged intranasally with human rhinovirus 16 were monitored directly ex vivo or else in 24-hour cultures, at baseline (day 0), and then at days 4 and 21 post-challenge. Results Basophils in atopic asthmatics, but not in non-atopic controls, upregulated TSLP receptor upon IgE receptor ligation. The magnitude of this response was correlated with the proportion of serum total IgE that was allergen-specific ( r = 0.615, P < 0.05). Following rhinovirus infection, all subjects developed nasal symptoms that peaked 3-5 days after viral challenge. Basophils displayed maximal IgE responsiveness 3 weeks post-challenge as judged by TSLP receptor levels in 24-hour cultures. No significant change in total IgE or specific IgE antibodies was detected during rhinovirus infection. By contrast, levels of IgE receptor-associated spleen tyrosine kinase, Syk, were increased on day 4 ( P < 0.05), and elevated levels were also detected three weeks post-challenge. Conclusions and Clinical Relevance Circulating basophils display increased IgE responsiveness 3 weeks after rhinovirus infection in atopic asthmatics. This observation, coupled with increased expression of Syk, implicates basophils in promoting, or else prolonging, rhinovirus-induced inflammation in atopic asthmatics. [ABSTRACT FROM AUTHOR]

Background Mast cells play important roles in allergic inflammatory responses because they produce leukotrienes ( LTs), prostaglandins ( PGs), and a variety of inflammatory cytokines. Thus, pharmacological interventions for allergies have focused on inhibiting mast cell activation. Homoisoflavanone ( HIF), isolated from Cremastra appendiculata Makino, has anti-angiogenic activities; however, its effects on allergic reactions have not been determined. The aim of this study was to assess the inhibitory effects of HIF on mast cell activation, which is critical for anti-allergic reaction and the underlying mechanisms. Methods Enzyme-linked immunosorbent assays, quantitative real-time PCR, western blot analyses, and degranulation assay were performed to measure pro-inflammatory and allergic mediators in PMA/A23187- or IgE/antigen-stimulated mouse bone marrow-derived mast cells ( BMMCs), HMC-1, RBL-1, or human PBMC-derived mast cells treated with or without HIF. The anti-allergic effects of HIF were determined in mouse models using dinitrophenol-immunoglobulin E-induced passive cutaneous anaphylaxis ( PCA) and compound 48/80-induced ear swelling. Results Homoisoflavanone down-regulated PGD2, LTB4, and LTC4 production and inhibited the production of pro-inflammatory cytokines, such as interleukin-6 and tumor necrosis factor-α in PMA/A23187- or IgE/antigen-stimulated mast cells. The molecular mechanisms by which HIF caused these inhibitory effects were determined to be the inactivation of spleen tyrosine kinase (Syk) signaling and the concurrent suppression of cPLA2. HIF inhibited IgE-mediated PCA and compound 48/80-induced ear swelling in mouse. Conclusions Homoisoflavanone inhibited mast cell activation through the suppression of Syk pathway together with the inhibition of cPLA2. Thus, it might be a good candidate molecule for allergic diseases. [ABSTRACT FROM AUTHOR]

Background Clinical desensitization of patients to drugs involves progressive exposure to escalating doses of drug over a period of 24 h. In prior studies, this method was re-capitulated in vitro to also demonstrate loss of mast cell or basophil responsiveness. However, most signalling studies of human basophils have identified changes in signalling by using other methods of inducing cellular desensitization. Objective This study examined two well-described endpoints of basophil desensitization, loss of syk or Fcε RI expression, under conditions of subthreshold desensitization. Methods The loss of Fcε RI and syk was examined in human basophils. Results It was shown that both loss of syk and Fcε RI/IgE occurred during an escalating series of stimulation (anti-IgE Ab) and that expression loss occurred despite the presence of little histamine release. If basophils were first cultured for 3 days in 10 ng/mL IL-3, the concentration-dependence of histamine release shifted to 100-fold lower concentrations of stimulus. However, loss of syk did not show any change in its EC50 while loss of Fcε RI also shifted 100-fold. From the perspective of early signal element activation, the marked shift in the EC50 for histamine release was not accompanied by similar shifts in the EC50s for several signalling elements. The EC50s for phospho-Src, phospho- SHIP1, phospho-Syk, or phospho-Cbl did not change while the EC50s for phospho-Erk and the cytosolic calcium response did shift 100-fold. Conclusions These studies show that under normal conditions, subthreshold desensitization leads to loss of two critical signalling molecules (Fcε RI and syk) but under at least one condition, treatment with IL-3, it is possible to markedly blunt the loss of syk, but not Fcε RI, while executing a proper subthreshold titration. These data also suggest that IL-3 modifies only the sensitivity of signalling elements that are downstream of syk activation. [ABSTRACT FROM AUTHOR]

Treatment for systemic lupus erythematosus (SLE) has traditionally been restricted to broad-based immunosuppression, with glucocorticoids being central to care. Recent insights into lupus pathogenesis promise new, selective therapies with more favorable side effect profiles. The best example of this is belimumab, which targets the B cell cytokine BLyS and has now received Food and Drug Administration (FDA) approval for its use in SLE. Strategies targeting other cytokines, such as interleukin 6 (IL-6) and interferon (IFN)-α, are also on the horizon. Blockade of costimulatory interactions between immune cells offers another opportunity for therapeutic intervention, as do small molecule inhibitors that interfere with cell signaling pathways. We review here the current strategies for SLE treatment, with particular focus on therapies now in active pharmaceutical development. We will also discuss new understandings in lupus pathogenesis that may lead to future advances in therapy. [ABSTRACT FROM AUTHOR]

Background Previous studies indicate that the protein tyrosine kinase, syk, is critical intransducing FceRI-mediated signals. In human basophils, ‘releasability’ has been linked to the extent of syk expression. Human lung mast cells, like basophils, are also found to be variably responsive to IgE-dependent activation. Objective The aim of the present study was to determine whether the wide variability in human lung mast cell responses, following IgE-dependent activation, has a relationship with syk expression. Methods Mast cells were isolated from human lung tissue and ‘releasability’ was determined by activating the cells with a maximal releasing concentration of anti-IgE. Syk levels in mast cells were determined by immunoblotting and flow cytometry. Results Histamine release from mast cells, challenged with a maximal releasing concentration of anti-IgE, ranged from 0% to 69% (mean± SEM, 24± 2%, n = 53). A proportion of these preparations (nine out of 53) released very low levels of histamine (45%) in response to anti-IgE. Flow cytometry of a subset of preparations indicated that a weak response to anti-IgE was not related to a lack of surface IgE. Immunoblotting and flow cytometry studies demonstrated that, compared with mononuclear cells, human lung mast cells express low and variable levels of syk. However, there was no correlation between syk expression and mast cell releasability. Nonetheless, a number of putative inhibitors of syk including NVP-QAB205 (EC50, 0.2 mM) effectively attenuated the IgE-dependent release of histamine from mast cells. Conclusion and clinical relevance These studies indicate that although syk may play an important role in mediating degranulation, the relative level of syk expression does not govern human lung mast cell releasability. Identification of the mechanisms that govern IgEdependent activation of human lung mast cells is likely to be of wider clinical significance, given the central role that mast cells play in the development of allergic asthma. [ABSTRACT FROM AUTHOR]

Abstract: The aggregation by antigen of the IgE bound to its high affinity receptor on mast cells initiates a complex series of biochemical events that result in the release of inflammatory mediators. The essential role of the protein tyrosine kinase Syk has been appreciated for some time, and newer results have defined the mechanism of its activation. The use of siRNA has defined the relative contribution of Syk, Fyn and Gab2 to signaling and has made possible a screening study to identify previously unrecognized molecules that are involved in these pathways. [ABSTRACT FROM AUTHOR]

The article discusses the study on the presence of activating mutations in spleen tyrosine kinase (SYK) that contribute to improved B-cell receptor (BCR) signaling in patients with chronic lymphocytic leukemia (CLL). It states that the investigation describe mutations in the region of protein coding of SYK that could contribute to the pathogenesis of CLL. It mentions that the gain-of-function point mutation was not the caused of improved SYK kinase activity.

Different dendritic cell (DC) subsets have distinct specialized functions contributed in part by their differential expression of pattern recognition receptors (PRRs). C-type lectin receptors (CLRs) are a group of PRRs expressed by DCs and other myeloid cells that can recognize endogenous ligands as well as a wide range of exogenous structures present on pathogens. Dual roles in homeostasis and immunity have been demonstrated for some members of this receptor family. Largely due to their endocytic ability and subset specific expression, DC-expressed CLRs have been the focus of significant antigen-targeting studies. A number of CLRs function on the basis of signaling via association with immunoreceptor tyrosine-based activation motif (ITAM)-containing adapter proteins. Others contain ITAM-related motifs or immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in their cytoplasmic tails. Here we review CLRs that induce intracellular signaling via a single tyrosine-based ITAM-like motif and highlight their relevance in terms of DC function. [ABSTRACT FROM AUTHOR]

β-Glucans are naturally occurring carbohydrates that possess immune-modulating activities, but their mechanisms of action are largely unknown. Recent discoveries, however, including identification of β-glucan receptors, such as dectin-1, have started to shed some light on the mechanisms underlying the properties of these carbohydrates. The characterization of dectin-1, in particular, has revealed some of the processes involved in β-glucan sensing, intracellular signaling, and induction of cellular responses and has provided new insights into the role of β-glucans in immunity and disease. Here we review both β-glucans and their receptor, dectin-1. [ABSTRACT FROM AUTHOR]

A common signaling pathway is known to operate downstream of immunoreceptors, such as the T-cell, B-cell, or Fc receptors, following engagement by their respective ligands. This pathway involves Src family kinase-mediated tyrosine phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) that recruit and activate spleen tyrosine kinase (Syk) or Zap70 (ζ-associated protein of 70 kDa) kinases, which in turn activate a variety of downstream signals. Evidence has been building from a variety of sources, particularly mouse models, that molecules involved in the immunoreceptor signaling pathway are also required for signals initiated by integrins. Integrins are the major cell surface receptors that mediate adhesion of leukocytes to a variety of extracellular matrix proteins and counter-receptors expressed on endothelial cells. Integrin ligation is a critical step in the activation of leukocyte effector functions (such as neutrophil degranulation or lymphocyte proliferation). Integrin signaling through pathways common to those utilized by immunoreceptors provides a mechanism by which leukocyte adhesion can regulate activation of cellular responses. In animal models, integrin-mediated signal transduction plays a critical role in inflammatory disease. In this review, we discuss the convergence of immunoreceptor and integrin signaling, focusing on how these pathways modulate leukocyte activation. [ABSTRACT FROM AUTHOR]

Toll-like receptor 4 (TLR4) induces an innate immune response in mammals by recognizing lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria. In this study, we show that tyrosine kinase Syk constitutively associates with TLR4 in THP-1 cells. As previously reported in peripheral blood mononuclear cells, TLR4 gets inducibly tyrosine phosphorylated upon LPS engagement in THP-1 cells. Piceatannol, a pharmacological inhibitor of the tyrosine kinase Syk, abrogates TLR4 tyrosine phosphorylation at low doses. The kinetics of TLR4 tyrosine phosphorylation in THP-1 cells coincides with an early wave of Syk tyrosine phosphorylation. Additionally, serine threonine kinase interleukin-1 (IL1) receptor-associated kinase 1 (IRAK-1) is transiently recruited to the complex containing adaptor molecule MyD88, TLR4 and Syk within 1 min of LPS engagement and dissociates by 30 min. Finally, the inhibition of Syk with piceatannol has no effect on LPS-mediated release of cytokines IL6, IL1β, tumor necrosis factor-α, neither on chemokines macrophage inhibitory protein (MIP)1α, MIP1β, monocyte chemoattractant protein -1, IL8, Groα and RANTES. However, IL10 and IL12p40 releases are significantly inhibited. Our findings implicate Syk as a novel modulator of LPS-mediated TLR4 responses in human monocytic cells and shed insight into the kinetics of early complex formation upon LPS engagement.Immunology and Cell Biology (2007) 85, 249–256. doi:10.1038/sj.icb.7100030; published online 16 January 2007 [ABSTRACT FROM AUTHOR]

Phagocytosis is a central event in the innate immune responses that are triggered by the association between ligands on the surface of pathogens and receptors on the membrane of phagocytes. Particularly, complement-mediated phagocytosis is accomplished by specific recognition of bound complement components by the corresponding complement receptors on the phagocytes. The protein-tyrosine kinase, Syk, plays a central role in Fcγ receptor-mediated phagocytosis in the adaptive immune system. From recent studies using a macrophage-like differentiated cell line and serum-treated zymosan, it was found that Syk also plays an essential role in complement-mediated phagocytosis in innate immunity. Serum-treated zymosan particles promptly attached to the cells and were subsequently engulfed via complement receptor3. During this process, Syk became tyrosine-phosphorylated and accumulated around the nascent phagosomes. The transfer of Syk-siRNA or dominant-negative Syk (DN-Syk) into macrophages resulted in impaired engulfment of pathogen. Collectively, Syk is required for the engulfment of pathogen in complement-mediated phagocytosis. iubmb Life , 58: 304–308, 2006 [ABSTRACT FROM AUTHOR]

Among B-cell lymphomas mantle cell lymphoma (MCL) has the worst prognosis. By using a combination of genomic and expression profiling (Affymetrix GeneChip Mapping 10k Xba131 and U133 set), we analysed 26 MCL samples to identify genes relevant to MCL pathogenesis and that could represent new therapeutic targets. Recurrent genomic deletions and gains were detected. Genes were identified as overexpressed in regions of DNA gain on 3q, 6p, 8q, 9q, 16p and 18q, including the cancer genes BCL2 and MYC. Among the transcripts with high correlation between DNA and RNA, we identified SYK, a tyrosine kinase involved in B-cell receptor signalling. SYK was amplified at DNA level, as validated by fluorescence in situ hybridisation (FISH) analysis, and overexpressed at both RNA and protein levels in the JeKo-1 cell line. Low-level amplification, with protein overexpression of Syk was demonstrated by FISH in a small subset of clinical samples. After treatment with low doses of the Syk inhibitor piceatannol, cell proliferation arrest and apoptosis were induced in the cell line overexpressing Syk, while cells expressing low levels of Syk were much less sensitive. A combination of genomic and expression profiling suggested Syk inhibition as a new therapeutic strategy to be explored in lymphomas. [ABSTRACT FROM AUTHOR]

The non-receptor protein tyrosine kinase Syk is widely expressed and plays an important role in intracellular signal transduction in haematopoietic cells including B cells, mast cells, eosinophils, platelets, macrophages, neutrophils and T cells. We found that Syk is expressed in human nasal polyp tissue-derived fibroblasts and plays a critical role in chemokine production and activation of c-Jun N-terminal kinase 1 stimulated with lipopolysaccharide or IL-1. In mast cells, cross-linking FcℇRI via IgE bound to multivalent antigen induces tyrosine phosphorylation of immunoreceptor tyrosine-based activation motifs, and binds and modifies the activity of Syk, thereby initiating downstream signalling. In eosinophils, Syk is essential for activating the antiapoptotic pathway and generating reactive oxygen intermediates in response to Fcγ receptor engagement. In nasal polyps, Syk inhibition might influence the levels and function of specific IgE to Staphylococcus aureus enterotoxins that are thought to drive local eosinophilic inflammation therein. The regulation of Syk expression may prove to be a useful strategy in the treatment of airway diseases. [ABSTRACT FROM AUTHOR]

Endo Y, Ishikawa O, Negishi I. Zeta-chain-associated protein-70 molecule is essential for the proliferation and the final maturation of dendritic epidermal T cells.Adult murine epidermis contains members of the epithelialγδ T-cell family called dendritic epidermal T cells (DETCs). Their development and maturation have been the subjects of investigations, but the details are still unclear. T-cell receptor (TCR) zeta-chain-associated protein-70 (ZAP-70), one of the protein tyrosine kinases required for TCR signaling, plays a pivotal role in the development ofαβ T cells. In mice lacking ZAP-70, thymic development ofαβ T cells was completely arrested at the immature CD4+CD8+ TCRlow stage. Here, we examined whether or not the development and maturation of DETCs were altered in ZAP-70-deficient mice. Immunohistochemical analyses of epidermal sheets revealed that the number of DETCs was reduced and their characteristic dendrites were lost or markedly shortened in ZAP-70–/– mice. In flow cytometric analyses, the expression levels ofγδ TCR and Thy-1.2 on the ZAP-70–/– DETCs were lower than those on ZAP-70+/– DETCs. The expression of a very early activation antigen, CD69, was not detected on ZAP-70–/– DETCs, whereas CD69 was expressed on ZAP-70+/– DETCs. Furthermore, ZAP-70–/– DETCs showed markedly reduced proliferation and no IL-2 gene expression in response to anti-CD3ε or concanavalin A stimulation. These results suggest that ZAP-70 is essential for TCR signaling which induces the proliferation and the final maturation of DETCs in the epidermis. [ABSTRACT FROM AUTHOR]

Hck is a member of the Src-family of protein tyrosine kinases that appears to function in mature leukocytes to communicate a number of extracellular signals including various cytokines. In this study we show that the thiol-reactive heavy metal, mercuric chloride (HgCl2 ) induces rapid and robust activation of tyrosine phosphorylation within human myelomonocytic cells. This increase in tyrosine-phosphorylated proteins requires the activity of Hck because both kinase inactive alleles of Hck and pharmacological inhibitors selective for the Src-family kinases are able to abrogate the cellular response to HgCl2 . Furthermore, ectopic expression of Hck in murine fibroblasts is able to confer HgCl2 responsiveness, as indicated by an increase in tyrosine-phosphorylated proteins to a normally nonresponsive cell line. Concomitant with the activation of Hck, there is a physical association of Hck with another cytoplasmic protein tyrosine kinase, Syk. The ability of HgCl2 to activate Src-family kinases such as Hck in hematopoietic cells may help explain why exposure to the heavy metal is associated with immune system dysfunction in rodents as well as humans. [ABSTRACT FROM AUTHOR]

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

The Syk protein-tyrosine kinase is expressed in many hematopoietic cells and is involved in signaling from various receptors for antigen and Fc portions of IgG and lgE. After cross-linking of these receptors, Syk is rapidly phosphorylated on tyrosine residues. We have previously reported that Syk expressed in COS cells is predominantly phosphorylated at both Tyr518 and Tyr519 at its putative autophosphorylation site. In this study, we have examined the role of each of these two residues for the catalytic activity of Syk in vitro and for the Syk-induced phosphorylation of cellular proteins in intact cells. Mutation of either residue had minor effects on the catalytic activity of Syk, and even the double mutant [F518, F519]Syk was about 60% as active as the wild-type enzyme, in intact cells, however, all three mutants consistently failed to induce the extensive tyrosine phosphorylation of cellular proteins typically observed with wild-type Syk. We have recently shown that the doubly phosphorylated Y518/Y519 site is also the site for association of Syk with the SH2 domain of the Lck kinase, which suggests that although phosphates at Y518/Y519 may enhance the catalytic activity of Syk, its interaction with Src family proteintyrosine kinases is at least equally important for the induction of downstream substrate phosphorylation. [ABSTRACT FROM AUTHOR]

The two related protein-tyrosine kinases Syk and Zap are rapidly phosphorylated on tyrosine residues and enzymatically activated upon crossiinking of the T cell antigen receptor. We have previously reported that the activation of Syk is less dependent on the Src family kinase Lck than the activation of Zap. Here we report that overexpression of Syk in the Lck-negative JCaM1 cells enabled the T cell antigen receptor/CD3 complex to induce a normal activation of the mitogen-activated protein kinase (MAPK) pathway and expression of a nuclear factor of activated T cells reporter construct. In contrast, Zap and other protein-tyrosine kinases were unable to reconstitute these signaling pathways when expressed at the same levels. In parallel, Syk was phosphorylated on tyrosine, while Zap was not. The Syk-mediated T cell antigen receptor-induced MAPK activation was detectable within 1 min of receptor stimulation and peaked at 3–5 rain. The capacity of Syk to reconstitute the MAPK response required the catalytic activity of Syk, an intact autophosphorylation site (Y518 and Y519), both Src homology 2 domains and it was blocked by the inhibitory N17-mutated dominant-negative Ras construct. A Y341→F mutant of Syk, which is deficient in its interaction with phospholipase Cγ,1 and Vav, was less efficient than wild-type Syk. Our results suggest that Syk, in contrast to Zap, can transduce signals from the T cell antigen receptor independently of Lck. [ABSTRACT FROM AUTHOR]

Accumulating data indicate that the ‘linker’ region of Syk, which lies between its tandem Src homology 2 (SH2) domains and kinase region, provides a critical function for the biological activity of Syk. This importance has been ascribed to the presence of tyrosine phosphorylation sites capable of mediating the recruitment of cellular effectors. We and others previously identified an alternatively spliced variant of Syk, termed SykB, which lacks a 23 amino acid sequence in the linker domain. As this ‘linker insert’ is also not present in the closely related enzyme Zap-70, it seems plausible that Syk possesses this unique sequence for functional reasons. To understand its role better, we have compared the abilities of Syk and SykB to participate in immunoreceptor-triggered signal transduction. The results of our experiments revealed that, unlike Syk, SykB was inefficient at coupling stimulation of FceRI on basophils or the antigen receptor on T cells to the early and late events of cellular activation. Further studies showed that the functional defect in SykB was not caused by the absence of crucial tyrosine phosphorylation sites, or by a reduced intrinsic kinase activity. Rather, it correlated with the reduced ability of SykB to bind phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) in vitro and in vivo. In combination, these results demonstrated that the unique insert in the linker domain of Syk is crucial for its capacity to participate in immunoreceptor signalling. Furthermore, they provided evidence that the linker region can regulate the ability of Syk to bind ITAMs, thus identifying a novel function for this domain. [ABSTRACT FROM AUTHOR]

Bruton's tyrosine kinase (Btk) is essential for B-lineage development and represents an emerging family of non-receptor tyrosine kinases implicated in signal transduction events initiated by a range of cell surface receptors. Increased dosage of Btk in normal B cells resulted in a striking enhancement of extracellular calcium influx following B-cell antigen receptor (BCR) cross-linking. Ectopic expression of Btk, or related Btk/Tec family kinases, restored deficient extracellular Ca2+ influx in a series of novel Btk-deficient human B-cell lines. Btk and phospholipase Cγ (PLCγ) co-expression resulted in tyrosine phosphorylation of PLCγ and required the same Btk domains as those for Btk-dependent calcium influx. Receptor-dependent Btk activation led to enhanced peak inositol trisphosphate (IP3) generation and depletion of thapsigargin (Tg)-sensitive intracellular calcium stores. These results suggest that Btk maintains increased intracellular calcium levels by controlling a Tg-sensitive, IP3-gated calcium store(s) that regulates store-operated calcium entry. Overexpression of dominant-negative Syk dramatically reduced the initial phase calcium response, demonstrating that Btk/Tec and Syk family kinases may exert distinct effects on calcium signaling. Finally, co-cross-linking of the BCR and the inhibitory receptor, FcγRIIb1, completely abrogated Btk-dependent IP3 production and calcium store depletion. Together, these data demonstrate that Btk functions at a critical crossroads in the events controlling calcium signaling by regulating peak IP3 levels and calcium store depletion. [ABSTRACT FROM AUTHOR]