Articles de revues : « Kinase Syk »

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Makhoul, Stephanie, Stephanie Dorschel, Stepan Gambaryan, Ulrich Walter et Kerstin Jurk. « Feedback Regulation of Syk by Protein Kinase C in Human Platelets ». International Journal of Molecular Sciences 21, n^o 1 (25 décembre 2019) : 176. http://dx.doi.org/10.3390/ijms21010176.

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The spleen tyrosine kinase (Syk) is essential for immunoreceptor tyrosine-based activation motif (ITAM)-dependent platelet activation, and it is stimulated by Src-family kinase (SFK)-/Syk-mediated phosphorylation of Y352 (interdomain-B) and Y525/526 (kinase domain). Additional sites for Syk phosphorylation and protein interactions are known but remain elusive. Since Syk S297 phosphorylation (interdomain-B) was detected in platelets, we hypothesized that this phosphorylation site regulates Syk activity via protein kinase C (PKC)-and cyclic adenosine monophosphate (cAMP)-dependent pathways. ADP, the GPVI-agonist convulxin, and the GPIbα-agonist echicetin beads (EB) were used to stimulate human platelets with/without effectors. Platelet aggregation and intracellular messengers were analyzed, along with phosphoproteins, by immunoblotting using phosphosite-specific antibodies or phos-tags. ADP, convulxin, and EB upregulated Syk S297 phosphorylation, which was inhibited by iloprost (cAMP pathway). Convulxin-stimulated Syk S297 phosphorylation was stoichiometric, transient, abolished by the PKC inhibitor GF109203X, and mimicked by the PKC activator PDBu. Convulxin/EB stimulated Syk S297, Y352, and Y525/526 phosphorylation, which was inhibited by SFK and Syk inhibitors. GFX and iloprost inhibited convulxin/EB-induced Syk S297 phosphorylation but enhanced Syk tyrosine (Y352/Y525/526) and substrate (linker adaptor for T cells (LAT), phospholipase γ2 (PLC γ2)) phosphorylation. GFX enhanced convulxin/EB-increases of inositol monophosphate/Ca2+. ITAM-activated Syk stimulates PKC-dependent Syk S297 phosphorylation, which is reduced by SFK/Syk/PKC inhibition and cAMP. Inhibition of Syk S297 phosphorylation coincides with enhanced Syk activation, suggesting that S297 phosphorylation represents a mechanism for feedback inhibition in human platelets.

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Zhang, Pengyu, Fiorella A. Solari, Johan W. M. Heemskerk, Marijke J. E. Kuijpers, Albert Sickmann, Ulrich Walter et Kerstin Jurk. « Differential Regulation of GPVI-Induced Btk and Syk Activation by PKC, PKA and PP2A in Human Platelets ». International Journal of Molecular Sciences 24, n^o 9 (24 avril 2023) : 7776. http://dx.doi.org/10.3390/ijms24097776.

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Bruton’s tyrosine kinase (Btk) and spleen tyrosine kinase (Syk) are major signaling proteins in human platelets that are implicated in atherothrombosis and thrombo-inflammation, but the mechanisms controlling their activities are not well understood. Previously, we showed that Syk becomes phosphorylated at S297 in glycoprotein VI (GPVI)-stimulated human platelets, which limits Syk activation. Here, we tested the hypothesis that protein kinases C (PKC) and A (PKA) and protein phosphatase 2A (PP2A) jointly regulate GPVI-induced Btk activation in platelets. The GPVI agonist convulxin caused rapid, transient Btk phosphorylation at S180 (pS180↑), Y223 and Y551, while direct PKC activation strongly increased Btk pS180 and pY551. This increase in Btk pY551 was also Src family kinase (SFK)-dependent, but surprisingly Syk-independent, pointing to an alternative mechanism of Btk phosphorylation and activation. PKC inhibition abolished convulxin-stimulated Btk pS180 and Syk pS297, but markedly increased the tyrosine phosphorylation of Syk, Btk and effector phospholipase Cγ2 (PLCγ2). PKA activation increased convulxin-induced Btk activation at Y551 but strongly suppressed Btk pS180 and Syk pS297. PP2A inhibition by okadaic acid only increased Syk pS297. Both platelet aggregation and PLCγ2 phosphorylation with convulxin stimulation were Btk-dependent, as shown by the selective Btk inhibitor acalabrutinib. Together, these results revealed in GPVI-stimulated platelets a transient Syk, Btk and PLCγ2 phosphorylation at multiple sites, which are differentially regulated by PKC, PKA or PP2A. Our work thereby demonstrated the GPVI–Syk–Btk signalosome as a tightly controlled protein kinase network, in agreement with its role in atherothrombosis.

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Xu, Rong, Rony Seger et Israel Pecht. « Cutting Edge : Extracellular Signal-Regulated Kinase Activates Syk : A New Potential Feedback Regulation of Fcε Receptor Signaling ». Journal of Immunology 163, n^o 3 (1 août 1999) : 1110–14. http://dx.doi.org/10.4049/jimmunol.163.3.1110.

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Abstract The protein tyrosine kinase Syk is an essential element in several cascades coupling Ag receptors to cell responses. Syk and the mitogen-activated protein kinase extracellular signal-regulated kinase 1 (ERK1) were found to form a tight complex in both resting and Ag-stimulated rat mucosal-type mast cells (rat basophilic leukemia 2H3 cell line RBL-2H3). A direct serine phosphorylation and activation of Syk by ERK was observed in in vitro experiments. Moreover the mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) kinase (MEK) inhibitors markedly decreased the Ag-induced phosphorylation of the tyrosyl residues of Syk and its activation as well as suppressed the degranulation of the cells. These results suggest a positive feedback regulation of Syk by ERK in the cascade coupling the type 1 Fcε receptor to the secretory response of mast cells; hence, the existence of a novel type of cross-talk between protein serine/threonine kinases and protein tyrosine kinases is suggested.

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Makhoul, Stephanie, Elena Kumm, Pengyu Zhang, Ulrich Walter et Kerstin Jurk. « The Serine/Threonine Protein Phosphatase 2A (PP2A) Regulates Syk Activity in Human Platelets ». International Journal of Molecular Sciences 21, n^o 23 (25 novembre 2020) : 8939. http://dx.doi.org/10.3390/ijms21238939.

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Distinct membrane receptors activate platelets by Src-family-kinase (SFK)-, immunoreceptor-tyrosine-based-activation-motif (ITAM)-dependent stimulation of spleen tyrosine kinase (Syk). Recently, we reported that platelet activation via glycoprotein (GP) VI or GPIbα stimulated the well-established Syk tyrosine (Y)-phosphorylation, but also stoichiometric, transient protein kinase C (PKC)-mediated Syk serine(S)297 phosphorylation in the regulatory interdomain-B, suggesting possible feedback inhibition. The transient nature of Syk S297 phosphorylation indicated the presence of an unknown Syk pS297 protein phosphatase. In this study, we hypothesize that the S-protein phosphatase 2A (PP2A) is responsible for Syk pS297 dephosphorylation, thereby affecting Syk Y-phosphorylation and activity in human washed platelets. Using immunoblotting, we show that specific inhibition of PP2A by okadaic acid (OA) alone leads to stoichiometric Syk S297 phosphorylation, as analyzed by Zn2+-Phos-tag gels, without affecting Syk Y-phosphorylation. Pharmacological inhibition of Syk by PRT060318 or PKC by GF109203X only minimally reduced OA-induced Syk S297 phosphorylation. PP2A inhibition by OA preceding GPVI-mediated platelet activation induced by convulxin extended Syk S297 phosphorylation but inhibited Syk Y-phosphorylation. Our data demonstrate a novel biochemical and functional link between the S-protein phosphatase PP2A and the Y-protein kinase Syk in human platelets, and suggest that PP2A represents a potential enhancer of GPVI-mediated Syk activity caused by Syk pS297 dephosphorylation.

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Coates, Matthew S., Eric W. F. W. Alton, Garth W. Rapeport, Jane C. Davies et Kazuhiro Ito. « Pseudomonas aeruginosa induces p38MAP kinase-dependent IL-6 and CXCL8 release from bronchial epithelial cells via a Syk kinase pathway ». PLOS ONE 16, n^o 2 (1 février 2021) : e0246050. http://dx.doi.org/10.1371/journal.pone.0246050.

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Pseudomonas aeruginosa (Pa) infection is a major cause of airway inflammation in immunocompromised and cystic fibrosis (CF) patients. Mitogen-activated protein (MAP) and tyrosine kinases are integral to inflammatory responses and are therefore potential targets for novel anti-inflammatory therapies. We have determined the involvement of specific kinases in Pa-induced inflammation. The effects of kinase inhibitors against p38MAPK, MEK 1/2, JNK 1/2, Syk or c-Src, a combination of a p38MAPK with Syk inhibitor, or a novel narrow spectrum kinase inhibitor (NSKI), were evaluated against the release of the proinflammatory cytokine/chemokine, IL-6 and CXCL8 from BEAS-2B and CFBE41o- epithelial cells by Pa. Effects of a Syk inhibitor against phosphorylation of the MAPKs were also evaluated. IL-6 and CXCL8 release by Pa were significantly inhibited by p38MAPK and Syk inhibitors (p<0.05). Phosphorylation of HSP27, but not ERK or JNK, was significantly inhibited by Syk kinase inhibition. A combination of p38MAPK and Syk inhibitors showed synergy against IL-6 and CXCL8 induction and an NSKI completely inhibited IL-6 and CXCL8 at low concentrations. Pa-induced inflammation is dependent on p38MAPK primarily, and Syk partially, which is upstream of p38MAPK. The NSKI suggests that inhibiting specific combinations of kinases is a potent potential therapy for Pa-induced inflammation.

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Yan, S. R., M. Huang et G. Berton. « Signaling by adhesion in human neutrophils : activation of the p72syk tyrosine kinase and formation of protein complexes containing p72syk and Src family kinases in neutrophils spreading over fibrinogen. » Journal of Immunology 158, n^o 4 (15 février 1997) : 1902–10. http://dx.doi.org/10.4049/jimmunol.158.4.1902.

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Abstract Src family kinases are implicated in signaling by integrins in polymorphonuclear neutrophils (PMN). To identify proteins present in complexes with Src family kinases, we subjected p58(c-fgr) or p53/56(lyn) immunoprecipitates from Triton X-100 lysates of PMN incubated on fibrinogen-coated surfaces to in vitro kinase assays. Assays on p58(c-fgr) or p53/56(lyn) immunoprecipitates from Triton lysates of PMN induced to spread over fibrinogen in response to TNF-alpha showed that several proteins form complexes with Src family kinases and can be phosphorylated in vitro. Immunoblot analysis showed that the p72(syk) tyrosine kinase is one of these proteins. Formation of protein complexes containing Src family kinases and p72(syk) required PMN spreading because p72(syk) was not detected in p58(c-fgr) or p53/56(lyn) immunoprecipitates from PMN, which were stimulated with TNF-alpha, in suspension. In addition, induction of PMN spreading with Mn2+ in the absence of TNF-alpha promoted the formation of protein complexes containing Src family kinases and p72(syk). We also found that p72(syk)-autophosphorylating kinase activity was enhanced, and a fraction of p72(syk) was translocated to a Triton-insoluble cytoskeletal fraction in PMN induced to spread over fibrinogen by TNF-alpha or Mn2+. In vitro kinase assays on CD18 (beta 2 integrin subunit) immunoprecipitates from Triton lysates of spread PMN showed that several proteins formed complexes with CD18 and could be phosphorylated in vitro. Immunoblot analysis of CD18 immunoprecipitates allowed us to identify p72(syk) as one of these proteins. These findings show that PMN spreading is accompanied by activation of p72(syk) and formation of multimolecular complexes in which Src family kinases and p72(syk) colocalize.

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Pasquet, Jean-Max, Romain Gioia, Claire Drullion, Valerie Lagarde, Cedric Leroy, Serge Roche, Bruno Cardinaud et Francois-Xavier Mahon. « Tyrosine Kinase Proteins profiling of Nilotinib Resistant Chronic Myelogenous Leukemia Cells Unravels a Tyrosine Kinase-Mediated Bypass. » Blood 114, n^o 22 (20 novembre 2009) : 2175. http://dx.doi.org/10.1182/blood.v114.22.2175.2175.

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Abstract Abstract 2175 Poster Board II-152 Targeting the tyrosine kinase activity of Bcr-Abl is an attractive therapeutic strategy in Chronic Myeloid Leukemia (CML) and in Bcr-Abl positive Acute Lymphoblastic Leukemia. Whereas imatinib, a selective inhibitor of Bcr-Abl tyrosine kinase, is now used in frontline therapy for CML, second generation inhibitors such as nilotinib or dasatinib have been developed for the treatment of imatinib-resistant or –intolerant disease. We have shown that one of the mechanisms of resistance to nilotinib is an increasing expression of the p53/56 Lyn kinase, both at mRNA and protein level in cell lines. This result was confirmed in vivo in nilotinib-resistant CML patients (Mahon et al. Cancer Res., 2008, 68(23):9809-16.). To elucidate Lyn mediated-nilotinib resistance, a phosphoproteomic study was performed by Stable Isotope Labelling with Amino acid in Cell culture (SILAC) which highlights the potential role of downstream tyrosine kinases. Among different candidate proteinsThe Spleen tyrosine kinase Syk and the UFO family receptor tyrosine kinase Axl were the most relevant in the nilotinib resistant cell line as compared to the sensitive counterpart. Syk hyperphosphorylation was confirmed in the nilotinib resistant cell line using western blot at least on tyrosine residues Y323 and Y525/526, two critical tyrosine residues respectively involved in Lyn-mediated Syk phosphorylation and autophosphorylation-associated Syk activation. Lyn interacts with Syk as detected in Syk immunoprecipitates in nilotinib resistant cells. Furthermore, Syk-Lyn interaction is inhibited by dasatinib suggesting the requirement of Lyn kinase activity and Syk phosphorylation. Targeting Syk expression in nilotinib resistant cells by siRNA or tyrosine kinase activity by pharmacological inhibitors leads respectively to a partial (35%) or to a full restoration of nilotinib sensitivity. Moreover, the identification of Axl by SILAC is correlated to a 9 fold increase of its level of expression in the resistant cell line and the inhibition of Axl tyrosine kinase activity decreases proliferation of both nilotinib sensitive and resistant CML cells. All together these results disclose a new pathway for tyrosine kinase inhibitors resistance in CML involving at least the two Lyn downstream tyrosine kinases Syk and Axl. Disclosures: Mahon: Amgen: Honoraria; Novartis Pharma: Consultancy, Honoraria, Research Funding; Alexion: Consultancy, Honoraria.

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MELANDER, Fredrik, Tommy ANDERSSON et Karim DIB. « Fgr but not Syk tyrosine kinase is a target for beta2 integrin-induced c-Cbl-mediated ubiquitination in adherent human neutrophils ». Biochemical Journal 370, n^o 2 (1 mars 2003) : 687–94. http://dx.doi.org/10.1042/bj20021201.

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An early and critical event in β2 integrin signalling during neutrophil adhesion is activation of Src tyrosine kinases and Syk. In the present study, we report Src kinase-dependent β2 integrin-induced tyrosine phosphorylation of Cbl occurring in parallel with increased Cbl-associated tyrosine kinase activity. These events concurred with activation of Fgr and, surprisingly, also with dissociation of this Src tyrosine kinase from Cbl. Moreover, the presence of the Src kinase inhibitor PP1 in an in vitro assay had only a limited effect on the Cbl-associated kinase activity. These results suggest that an additional active Src-dependent tyrosine kinase associates with Cbl. The following observations imply that Syk is such a kinase: (i) β2 integrins activated Syk in a Src-dependent manner, (ii) Syk was associated with Cbl much longer than Fgr was, and (iii) the Syk inhibitor piceatannol (3,4,3′,5′-tetrahydroxy-trans-stilbene) abolished the Cbl-associated kinase activity in an in vitro assay. Effects of the mentioned interactions between these two kinases and Cbl may be related to the finding that Cbl is a ubiquitin E3 ligase. Indeed, we detected β2 integrin-induced ubiquitination of Fgr that, similar to the phosphorylation of Cbl, was abolished in cells pretreated with PP1. However, the ubiquitination of Fgr did not cause any apparent degradation of the protein. In contrast with Fgr, Syk was not modified by the E3 ligase. Thus Cbl appears to be essential in β2 integrin signalling, first by serving as a matrix for a subsequent agonist-induced signalling interaction between Fgr and Syk, and then by mediating ubiquitination of Fgr which possibly affects its interaction with Cbl.

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Jiang, Aimin, Andrew Craxton, Tomohiro Kurosaki et Edward A. Clark. « Different Protein Tyrosine Kinases Are Required for B Cell Antigen Receptor–mediated Activation of Extracellular Signal–Regulated kinase, c-Jun NH2-terminal Kinase 1, and p38 Mitogen-activated Protein Kinase ». Journal of Experimental Medicine 188, n^o 7 (5 octobre 1998) : 1297–306. http://dx.doi.org/10.1084/jem.188.7.1297.

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B cell antigen receptor (BCR) cross-linking activates three distinct families of nonreceptor protein tyrosine kinases (PTKs): src-family kinases, Syk, and Btk; these PTKs are responsible for initiating downstream events. BCR cross-linking in the chicken DT40 B cell line also activates three distinct mitogen-activated protein kinases (MAPKs): extracellular signal–regulated kinase (ERK)2, c-jun NH2-terminal kinase (JNK)1, and p38 MAPK. To dissect the functional roles of these PTKs in MAPK signaling, activation of MAPKs was examined in various PTK-deficient DT40 cells. BCR-mediated activation of ERK2, although maintained in Lyn-deficient cells, was abolished in Syk-deficient cells and partially inhibited in Btk-deficient cells, indicating that BCR-mediated ERK2 activation requires Syk and that sustained ERK2 activation requires Btk. BCR-mediated JNK1 activation was maintained in Lyn-deficient cells but abolished in both Syk- and Btk-deficient cells, suggesting that JNK1 is activated via a Syk- and Btk-dependent pathway. Consistent with this, BCR-mediated JNK1 activation was dependent on intracellular calcium and phorbol myristate acetate–sensitive protein kinase Cs. In contrast, BCR-mediated p38 MAPK activation was detected in all three PTK-deficient cells, suggesting that no single PTK is essential. However, BCR-mediated p38 MAPK activation was abolished in Lyn/Syk double deficient cells, demonstrating that either Lyn or Syk alone may be sufficient to activate p38 MAPK. Our data show that BCR-mediated MAPK activation is regulated at the level of the PTKs.

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Dangelmaier, Carol A., Patricia G. Quinter, Jianguo Jin, Alexander Y. Tsygankov, Satya P. Kunapuli et James L. Daniel. « Rapid ubiquitination of Syk following GPVI activation in platelets ». Blood 105, n^o 10 (15 mai 2005) : 3918–24. http://dx.doi.org/10.1182/blood-2004-09-3689.

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AbstractSpleen tyrosine kinase (Syk) activation is a key intermediate step in the activation of platelets by the physiologic agonist collagen. We have found that Syk is rapidly ubiquitinated upon activation of platelets by collagen, collagen-related peptide (CRP), and convulxin. The Src family kinase inhibitors prevented Syk phosphorylation and its ubiquitination, indicating that the process is downstream of Src kinases. The ubiquitination of Syk did not cause degradation of the protein as evidenced by the lack of effect of proteasomal and lysosomal inhibitors. We separated ubiquitinated Syk from its nonubiquitinated counterpart and used an in vitro kinase assay to compare their activities. We found that the ubiquitinated Syk appeared to be about 5-fold more active. Using a phosphospecific antibody to Syk (Tyr525/Tyr526) that measures activated Syk, we found that most (60%-75%) of the active Syk is in the ubiquitinated fraction. This result explains the apparent high specific activity of ubiquitinated Syk. In c-Cbl–deficient mice, Syk is not ubiquitinated, implicating c-Cbl as the E3 ligase involved in Syk ubiquitination. Furthermore, Syk is not dephosphorylated in these mice. We propose that c-Cbl plays a regulatory role in glycoprotein VI (GPVI)/Fc receptor γ (FcRγ)-chain–dependent platelet activation through its interaction with Syk.

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Chen, Jin-Shuen, Li-Chien Chang, Shyh-Jer Huang et Chao-Wen Cheng. « Targeting Spleen Tyrosine Kinase-Bruton’s Tyrosine Kinase Axis for Immunologically Mediated Glomerulonephritis ». BioMed Research International 2014 (2014) : 1–6. http://dx.doi.org/10.1155/2014/814869.

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The importance of B-cell activation and immune complex-mediated Fc-receptor activation in the pathogenesis of immunologically mediated glomerulonephritis has long been recognized. The two nonreceptor tyrosine kinases, spleen tyrosine kinase (Syk) and Bruton’s tyrosine kinase (Btk), are primarily expressed by hematopoietic cells, and participate in B-cell-receptor- and Fc-receptor-mediated activation. Pharmacological inhibitors of Syk or Btk are undergoing preclinical development and clinical trials for several immune diseases; and Syk inhibitors have been shown to reduce disease activity in rheumatoid arthritis patients. However, the clinical therapeutic efficacies of these inhibitors in glomerulonephritis have not been evaluated. Herein, we review recent studies of Syk and Btk inhibitors in several experimental primary and secondary glomerulonephritis models. These inhibitors suppressed development of glomerular injury, and also ameliorated established kidney disease. Thus, targeting Syk and Btk signaling pathways is a potential therapeutic strategy for glomerulonephritis, and further evaluation is recommended.

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Castro, Rodrigo, Juan Zhang, Maria Jamur, Constance Oliver et Reuben Siraganian. « Tyrosines in the carboxy-terminal region regulate Syk function (86.18) ». Journal of Immunology 184, n^o 1_Supplement (1 avril 2010) : 86.18. http://dx.doi.org/10.4049/jimmunol.184.supp.86.18.

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Abstract The Syk tyrosine kinase family has an essential role in immunoreceptor tyrosine-based activation motif (ITAM) signaling. The binding of Syk to tyrosine phosphorylated ITAMs in the subunits of FcϵRI results in a conformational change, with an increase in the enzymatic activity of Syk. This conformational change exposes the COOH terminal region of Syk which has three conserved Tyr residues (Y623, Y624, Y625 of rat Syk). To understand the role of these residues in signaling, wild-type and mutant Syk with these three Tyr mutated to Phe were expressed in Syk-deficient mast cells. There was decreased FcϵRI induced degranulation, together with reduced phosphorylation of MAP kinases p38 and p42/44 ERK. There was a parallel decrease in NFAT and NFκB activation with the mutated Syk. In non-stimulated cells, there was increased tyrosine phosphorylation of the mutated Syk, however, this still increased after FcϵRI activation. In vitro mutated Syk had decreased ITAM-binding and reduced kinase activity. In testing Syk mutated singly at each one of the tyrosines, Y623F had minimal effect while Y624F but specially Y625F had the most reduction in these assays. Also, tyrosines Y624 and Y625 controlled Syk capacity for autophosphorylation. Therefore these tyrosines in the tail region of Syk regulate its kinase activity and their phosphorylation is important for Syk function in mast cell FcϵRI-mediated signaling.

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Borna, Simon, Matej Fabisik, Kristyna Ilievova, Tomas Dvoracek et Tomas Brdicka. « Mechanisms determining a differential threshold for sensing Src family kinase activity by B and T cell antigen receptors ». Journal of Biological Chemistry 295, n^o 37 (14 juillet 2020) : 12935–45. http://dx.doi.org/10.1074/jbc.ra120.013552.

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Although signal transduction by immunoreceptors such as the T cell antigen receptor (TCR), B cell antigen receptor (BCR), and Fc receptors uses the same schematic and similar molecules, the threshold and the fine-tuning are set differently for each receptor. One manifestation of these differences is that inhibition of Src family kinases (SFK) blocks TCR but not BCR signaling. SFKs are key kinases phosphorylating immunoreceptor tyrosine-based activation motifs (ITAM) in both these receptors. However, it has been proposed that in B cells, downstream kinase SYK can phosphorylate ITAM sequences independently of SFK, allowing it to compensate for the loss of SFK activity, whereas its T cell paralog ZAP-70 is not capable of this compensation. To test this proposal, we examined signaling in SYK- and ZAP-70–deficient B and T cell lines expressing SYK or ZAP-70. We also analyzed signal transduction in T cells expressing BCR or B cells expressing part of the TCR complex. We show that when compared with ZAP-70, SYK lowered the threshold for SFK activity necessary to initiate antigen receptor signaling in both T and B cells. However, neither SYK nor ZAP-70 were able to initiate signaling independently of SFK. We further found that additional important factors are involved in setting this threshold. These include differences between the antigen receptor complexes themselves and the spatial separation of the key transmembrane adaptor protein LAT from the TCR. Thus, immunoreceptor sensing of SFK activity is a complex process regulated at multiple levels.

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Gioia, Romain, Cédric Leroy, Claire Drullion, Valérie Lagarde, Gabriel Etienne, Stéphanie Dulucq, Eric Lippert, Serge Roche, François-Xavier Mahon et Jean-Max Pasquet. « Quantitative phosphoproteomics revealed interplay between Syk and Lyn in the resistance to nilotinib in chronic myeloid leukemia cells ». Blood 118, n^o 8 (25 août 2011) : 2211–21. http://dx.doi.org/10.1182/blood-2010-10-313692.

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Abstract In this study, we have addressed how Lyn kinase signaling mediates nilotinib-resistance by quantitative phospho-proteomics using Stable Isotope Labeling with Amino acid in Cell culture. We have found an increased tyrosine phosphorylation of 2 additional tyrosine kinases in nilotinib-resistant cells: the spleen tyrosine kinase Syk and the UFO family receptor tyrosine kinase Axl. This increased tyrosine phosphorylation involved an interaction of these tyrosine kinases with Lyn. Inhibition of Syk by the inhibitors R406 or BAY 61-3606 or by RNA interference restored the capacity of nilotinib to inhibit cell proliferation. Conversely, coexpression of Lyn and Syk were required to fully induce resistance to nilotinib in drug-sensitive cells. Surprisingly, the knockdown of Syk also strongly decreased tyrosine phosphorylation of Lyn and Axl, thus uncovering interplay between Syk and Lyn. We have shown the involvement of the adaptor protein CDCP-1 in resistance to nilotinib. Interestingly, the expression of Axl and CDCP1 were found increased both in a nilotinib-resistant cell line and in nilotinib-resistant CML patients. We conclude that an oncogenic signaling mediated by Lyn and Syk can bypass the need of Bcr-Abl in CML cells. Thus, targeting these kinases may be of therapeutic value to override imatinib or nilotinib resistance in CML.

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Delaney, Suzanne, Uma Sinha, Nisha Nanda, Yibing Yan, Anjali Pandey, Stan Hollenbach, Whyte Owen, David Phillips et Patrick Andre. « Specific Pharmacological Targeting of the Syk Kinase Activity in Platelets : A Novel, Safe Anti-Thrombotic Strategy ». Blood 112, n^o 11 (16 novembre 2008) : 409. http://dx.doi.org/10.1182/blood.v112.11.409.409.

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Abstract Studies of the Syk −/− mouse have implicated spleen tyrosine kinase (Syk), a signaling protein with both kinase and scaffolding activities, in platelet signaling following engagement of GPVI and αIIbβ3 by collagen and fibrinogen, respectively. The present study was designed to determine whether specific inhibition of the kinase activity of Syk, without targeting the Syk scaffolding function, affected in vivo arterial thrombosis. In preliminary experiments, blood from wild-type and Syk−/− mice was perfused through collagen-coated capillaries under arterial shear rates to study ex vivo thrombosis. While blood from wild-type mice formed robust thrombi (37±4.7 μm3/μm2), none was observed in Syk−/− mice. Thrombi intermediate in size (16±3.9 μm3/μm2) developed in Syk+/− mice. To achieve specific pharmacological targeting of the kinase activity of Syk, P142-76, a potent (IC50 = 4 nM) and selective Syk kinase inhibitor was utilized. P142-76 was screened against a broad panel of 139 purified kinases at 50 nM. While Syk kinase was inhibited by 92%, all other kinases retained more than 70% of their activity. In washed human platelets, P142-76 inhibited convulxin (CVX)-induced phosphorylation of LAT (linker for activation of T-cells; IC50 = 111 nM) and intracellular calcium increases (IC50 = 31 nM). The GPVI/Syk-specificity of P142-76 activity was confirmed by its inability to inhibit intracellular calcium increases induced by the PAR1 thrombin receptor agonist TRAP. P142-76 also inhibited CVX-induced aggregation of both human washed platelets (IC50 = 87 nM) and platelet-rich plasma (IC50 = 2.5 μM). Considering the controversial data in respect to the participation of GPVI in arterial thrombosis in murine models, the dependence of arterial thrombosis on Syk function was studied in vivo in pigs. Cross-species activity of P142-76 was confirmed in vitro (CVX-induced PRP aggregation IC50= 350 nM; 5 μM P142-76 completely inhibited thrombosis triggered by collagen in the perfusion chamber assay). At a plasma concentration which abolished ex vivo CVX-induced but not ADP-induced pig platelet aggregation, P142-76 significantly inhibited the deposition of [111In]-labeled platelets in a carotid artery crush swine thrombosis model, without compromising primary hemostasis. % aggregation Swine (n=3) Platelet Deposition % inhibition Plasma Conc (ng/ml) Bleed Time (min) Activated Clotting Time (sec) ADP (20 μM) CVX (250 ng/ml) Control Artery 0 0 3±0.9 133±22 100 100 Treated Artery 76±6.5 1343±304 3.5±0.3 130±13 100 0 To clarify further the contribution of the kinase activity of Syk to arterial thrombosis, effects of P142-76 on human blood were evaluated in real time in the collagen-coated perfusion chamber. Low concentrations of P142-76 (0.3 μM) affected thrombus stability, while increasing concentrations (1–5 μM) delayed and then completely inhibited thrombus formation. Furthermore, P142-76 destabilized pre-formed thrombi, indicating a critical role for Syk in conferring strength to platelet-platelet interactions, i.e. αIIbβ3-mediated cohesion. Our data indicate that the kinase activity of Syk acts in arterial thrombosis through at least two distinct mechanisms. First, Syk kinase confers stability to platelet-platelet interactions downstream of αIIbβ3. Second, it initiates thrombus formation on collagen surfaces. This dual activity of the kinase activity of Syk makes it a preferred target for inhibition of arterial thrombosis, as it does not compromise primary hemostasis.

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Zhao, Xiaoxian, Andrew E. Schade et Eric Hsi. « Distinct Role of Src Family Kinase Inhibitors in Burkitt Lymphoma Cells Vs. Diffuse Large B-Cell Lymphoma Cells ». Blood 112, n^o 11 (16 novembre 2008) : 3765. http://dx.doi.org/10.1182/blood.v112.11.3765.3765.

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Abstract Introduction: The Non-Hodgkin lymphomas (NHLs) are a heterogeneous group of malignancies, with approximately 85% of NHL belonging to the B-cell lineage. Src family kinases (SFKs) are non-receptor intracellular tyrosine kinases which are important in the regulation of multiple signaling pathways including cell proliferation, tumor invasiveness, angiogenesis and apoptosis. Syk is another predominant tyrosine kinase expressed in B-cell lines in addition to SFKs. We attempted to correlate SFK and Syk inhibitor efficacy with the presence of phospho-SFK or phospho-Syk in lymphoma cell lines and tissues. Methods: Cell proliferation was measured with WST-1 reagent. Apoptotic assay was performed with Annexin-V and 7-AAD by flow cytometry (FC, FACSCalibur, BD Bioscience). Phospho-Src (Y416) antibody (cell signaling Technology, CSL) was used for immunoblotting and immunohistochemistry. (IHC, Discovery, Ventana Medical Systems). Phospho-Syk (Y525/526) antibody (CSL) was used for FC and immunoblotting. Results: In a screening for the effects of different kinases’ inhibitors on B-cell lymphoma lines, we observed that SFK inhibitors, PP2 and dasatinib (Sprycel, Bristol Myers Squibb), inhibited proliferation and caused dose-dependent apoptosis induction at 24 h (PP2: 31% at 10 mM; dasatinib: 39% at 100 nM) in Burkitt’s lymphoma cell line Raji. The apoptotic induction was associated with cleavage of caspase-3 and caspase-8. The ability of SFK inhibitors to induce apoptosis in Raji cells paralleled high level expression of constitutive phospho- SFK (Y416). In contrast to this Burkitt’s line, diffuse large B-cell lymphoma (DLBCL) lines (Sud-HL4, Sud-HL-6 and OCI-LY3, OCI-LY10) were less-sensitive to these SFK inhibitors but showed apoptosis induction upon exposure to the Syk inhibitor (piceatannol & syk inhibitor IV). Interestingly, the DLBCL lines that were resistant to SFK inhibitors had undectable or low levels of phospho-SFK (Y416); while their susceptibility to the Syk inhibitor-induced apoptosis paralleled detectable constitutive phospho-Syk (Y525/526). Immunohistochemical staining of burkitt’s lymphoma tissues and a tissue microarray panel of NHL indicated 13/20 (65%) of Burkitt’s lymphoma, 3/5 of small lymphocytic lymphoma, 2/5 of mantle cell lymphoma, 3/10 of follicular lymphoma, 2/5 of DLBCL, 2/5 of marginal zone lymphoma, 1/5 of lymphoblastic lymphoma are positive for phospho-Src (Y416). Staining of normal tonsil tissue showed germinal center cells are strong positive for phospho-Src (Y416), while marginal zone cells are weak positive and plasma cells are negative. We are currently testing the correlation of phospho-Src (Y416) expression in fresh NHL tissues and their sensitivity to Src family kinase inhibitors. Conclusion: These data suggest that rational application of molecularly targeted therapy for aggressive NHL is possible by directly examining key signaling nodes promoting survival and proliferation. For instance, the clinical SFK inhibitor dasatinib is currently being examined in a clinical trial for NHL (NCT00550615). Our results suggest that profiling patients’ lymphoma cells for phospho-SFK could optimize therapeutic efficacy and minimize unnecessary treatment-related side effects.

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Dangelmaier, Carol A., Patricia Quinter, Jianguo Jin, Alexander Y. Tysgankov, Satya P. Kunapuli et James L. Daniel. « Regulation of Syk Function by Ubiquitination in Human Platelets. » Blood 104, n^o 11 (16 novembre 2004) : 627. http://dx.doi.org/10.1182/blood.v104.11.627.627.

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Abstract Platelets have an integral function in maintaining hemostasis. Signaling pathways are strictly regulated to ensure the cessation of bleeding without precipitating a thrombotic episode. An important initial physiological step in this process is the interaction of platelets with freshly exposed subendothelial collagen after vascular injury. A major platelet receptor involved is the GPVI/FcRγ-chain complex. Upon activation of this receptor, the immunoreceptor tyrosine-based activation motif (ITAM) present in the FcRγ-chain is phosphorylated by Src family kinases. This causes the tyrosine kinase Syk to bind to the ITAM where it is autophosphorylated, initializing a signaling cascade that activates a number of proteins including PLCγ2, PI-3 kinase and small G proteins. Syk appears to play an early pivotal role in GPVI/FcRγ-chain signal transduction and its regulation is crucial. Recent studies have shown that platelet aggregation, in response to collagen-related peptide (CRP), is potentiated in c-Cbl knockout mice. c-Cbl, a protein containing an E3 ligase responsible for substrate recognition for ubiquitin, appears to regulate numerous cytoplasmic kinases in other cell systems. This protein modification has emerged as one of the most common regulatory processes in all eukaryotes, second only to possibly phosphorylation. It appears to target proteins for proteosomal degradation although recently other mechanisms have been described, ranging from protein kinase activation to translation control. In the work presented here, we demonstrate that Syk associates with c-Cbl after GPVI/FcRγ-chain activation and therefore explored the possibility that Syk is ubiquitinated during GPVI/FcRγ-chain stimulation in human platelets. We have found that Syk is rapidly ubiquitinated upon activation by collagen, CRP and the snake venom protein convulxin, but not thrombin. PP2 and SU6656, two Src kinase inhibitors, prevented Syk phosphorylation and its ubiquitination, indicating that the process is downstream of Src kinases and probably requires Syk phosphorylation. The ubiquitination of Syk did not cause any apparent degradation of the protein as evidenced by the lack of effect of proteosomal and lysosomal inhibitors. We have been able to separate ubiquitinated Syk from its non-ubiquitinated counterpart. We have used an in vitro kinase assay to compare the activity of ubiquitinated Syk to non-ubiquitinated Syk. Surprisingly, when we compared the specific activity of the two Syk fractions, we found that the ubiquitinated Syk appeared to be about five-fold more active. Using a phosphospecific antibody to Syk (Tyr525/Tyr526) that measures activated Syk, we found that the majority (75%) of the active Syk is in the ubiquitinated fraction. In addition we found that Syk is not ubiquitinated in c-Cbl deficient mice. We therefore propose that c-Cbl plays a regulatory role in GPVI/FcRγ-chain stimulation through ubiquitination of Syk. The fact that 75% of active Syk is ubiquitinated suggests that ubiquitination plays an essential role in the regulation of its function. A possible function of ubiquitination may be targeting Syk to appropriate signaling molecules.

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Fernandez, Rosemarie, et Suzanne J. Suchard. « Syk Activation Is Required for Spreading and H2O2 Release in Adherent Human Neutrophils ». Journal of Immunology 160, n^o 10 (15 mai 1998) : 5154–62. http://dx.doi.org/10.4049/jimmunol.160.10.5154.

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Abstract Chemoattractant-stimulated polymorphonuclear leukocytes (PMNs) that are adherent to extracellular matrix proteins exhibit a massive, sustained respiratory burst that requires cell spreading. However, the signaling pathways culminating in PMN spreading are not well characterized. Studies showing that protein tyrosine phosphorylation increases with PMN spreading suggest that phosphorylation is critical for this process. In the present study, we observed increased tyrosine phosphorylation of both focal adhesion kinase and Syk in FMLP-activated PMNs that had been plated onto fibrinogen; an increase in Syk activity, but not focal adhesion kinase activity, was apparent. The time course of Syk phosphorylation correlated with the initiation of cell spreading and H2O2 release. Pretreatment of PMNs with piceatannol, a Syk-selective inhibitor, blocked Syk activity, cell spreading, and H2O2 release, indicating that Syk activity was required for the activation of adherent PMNs. Paxillin is a cytoskeletally associated protein that is also tyrosine phosphorylated during PMN spreading and H2O2 release. Paxillin phosphorylation is kinetically slower than Syk phosphorylation and is inhibited with piceatannol, suggesting that paxillin is a substrate for Syk. An analysis of Syk immunoprecipitates indicated that Syk and paxillin associate during PMN spreading. This interaction is not mediated by the src kinases Lyn and Fgr, since neither kinase coprecipitated with Syk. Syk from FMLP-activated, adherent PMNs phosphorylated paxillin-glutathione S-transferase, suggesting that paxillin is a substrate for Syk in vivo. These results indicate that PMN spreading and H2O2 release require a Syk-dependent signaling pathway leading to paxillin phosphorylation.

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Crowley, Mary T., Patrick S. Costello, Cheryl J. Fitzer-Attas, Martin Turner, Fanying Meng, Clifford Lowell, Victor L. J. Tybulewicz et Anthony L. DeFranco. « A Critical Role for Syk in Signal Transduction and Phagocytosis Mediated by Fcγ Receptors on Macrophages ». Journal of Experimental Medicine 186, n^o 7 (6 octobre 1997) : 1027–39. http://dx.doi.org/10.1084/jem.186.7.1027.

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Receptors on macrophages for the Fc region of IgG (FcγR) mediate a number of responses important for host immunity. Signaling events necessary for these responses are likely initiated by the activation of Src-family and Syk-family tyrosine kinases after FcγR cross-linking. Macrophages derived from Syk-deficient (Syk−) mice were defective in phagocytosis of particles bound by FcγRs, as well as in many FcγR-induced signaling events, including tyrosine phosphorylation of a number of cellular substrates and activation of MAP kinases. In contrast, Syk− macrophages exhibited normal responses to another potent macrophage stimulus, lipopolysaccharide. Phagocytosis of latex beads and Escherichia coli bacteria was also not affected. Syk− macrophages exhibited formation of polymerized actin structures opposing particles bound to the cells by FcγRs (actin cups), but failed to proceed to internalization. Interestingly, inhibitors of phosphatidylinositol 3-kinase also blocked FcγR-mediated phagocytosis at this stage. Thus, PI 3-kinase may participate in a Syk-dependent signaling pathway critical for FcγR-mediated phagocytosis. Macrophages derived from mice deficient for the three members of the Src-family of kinases expressed in these cells, Hck, Fgr, and Lyn, exhibited poor Syk activation upon FcγR engagement, accompanied by a delay in FcγR-mediated phagocytosis. These observations demonstrate that Syk is critical for FcγR-mediated phagocytosis, as well as for signal transduction in macrophages. Additionally, our findings provide evidence to support a model of sequential tyrosine kinase activation by FcγR's analogous to models of signaling by the B and T cell antigen receptors.

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Gioia, Romain, Cedric Leroy, Claire Drullion, Valérie Lagarde, Serge Roche, Francois-Xavier Mahon et jean-Max Pasquet. « Quantitative Phosphoproteomics Identified a New Syk-Lyn-Axl Signalling Pathway Involved In Resistance to Nilotinib In Chronic Myeloid Leukemia Cells. » Blood 116, n^o 21 (19 novembre 2010) : 3376. http://dx.doi.org/10.1182/blood.v116.21.3376.3376.

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Abstract Abstract 3376 Nilotinib has been developed to overcome resistance to imatinib, the first line treatment of chronic myeloid leukemia (CML). To anticipate resistance to nilotinib, we generate nilotinib resistant CML cell lines in vitro to characterize mechanisms and signaling pathways that may contribute to resistance. Among the different mechanisms of resistance identified, the overexpression of the Src-kinase Lyn was involved in resistance both in vitro, in a K562 cell line (K562-rn), and in vivo, in nilotinib-resistant CML patients. To characterize how Lyn mediates resistance, we performed a phosphoproteomic study using SILAC (Stable Isotope Labelling with Amino acid in Cell culture). Quantification and identification of phosphotyrosine proteins in the nilotinib resistant cells point out two tyrosine kinases, the spleen tyrosine kinase Syk and the UFO receptor Axl. The two tyrosine kinase Syk and Axl interact with Lyn as seen by coimmunopreciptation. Syk is phosphorylated on tyrosine 323 and 525/526 in Lyn dependent manner in nilotinib resistant cells. The inhibition of Syk tyrosine kinase by R406 or BAY31-6606 restores sensitivity to nilotinib in K562-rn cells. In parallel, the inhibition of Syk expression by ShRNA in K562-rn cells abolishes Lyn and Axl phosphorylation and then interaction between Lyn and Axl leading to a full restoration of nilotinib efficacy. In the opposite, the coexpression of Lyn and Syk in nilotinib sensitive K562 cells induced resistance to nilotinib whereas a Syk kinase dead mutant did not. These results highlight for the first time the critical role of Syk in resistance to tyrosine kinase inhibitors in CML disease emphasizing the therapeutic targeting of this tyrosine kinase. Moreover, Axl, which is already a target in solid tumor, will be also an interesting pathway to target in CML. Disclosures: No relevant conflicts of interest to declare.

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Zoller, K. E., I. A. MacNeil et J. S. Brugge. « Protein tyrosine kinases Syk and ZAP-70 display distinct requirements for Src family kinases in immune response receptor signal transduction. » Journal of Immunology 158, n^o 4 (15 février 1997) : 1650–59. http://dx.doi.org/10.4049/jimmunol.158.4.1650.

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Abstract Engagement of immunoreceptors in hemopoietic cells leads to activation of Src family tyrosine kinases as well as Syk or ZAP-70. Current models propose that Src family kinases are critical in immune response signal transduction through their role in phosphorylation of tyrosine residues within immunoreceptor tyrosine activation motifs (ITAMs; which recruit the SH2 domains of Syk or ZAP-70) and by direct phosphorylation of Syk and ZAP-70. Several lines of evidence suggest that Syk may not show the same dependence on activation by Src family kinases as ZAP-70. In this report, we used COS cells transiently transfected with components of the Fc epsilon RI complex (Lyn, Syk, and a chimeric CD8 receptor containing the cytoplasmic domain of the gamma subunit of Fc epsilon RI (CD8-gamma)) to examine the regulation of Syk activity. Syk was activated and phosphorylated in COS cells cotransfected with Lyn; however, in cells expressing CD8-gamma, activation of Syk and phosphorylation of CD8-gamma did not require coexpression of Lyn. Additional experiments indicate that gamma phosphorylation is dependent on Syk kinase activity and is independent of endogenous COS cell kinases. In parallel experiments, ZAP-70 was not activated by cotransfection with CD8-gamma, nor was CD8-gamma phosphorylated when coexpressed with ZAP-70 alone. Taken together, these studies indicate that Syk can be distinguished from ZAP-70 in its ability to be activated by coexpression with an ITAM-containing receptor without coexpression of a Src family kinase, and that Syk is capable of phosphorylating ITAM tyrosines under certain experimental conditions.

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Law, C. L., K. A. Chandran, S. P. Sidorenko et E. A. Clark. « Phospholipase C-gamma1 interacts with conserved phosphotyrosyl residues in the linker region of Syk and is a substrate for Syk. » Molecular and Cellular Biology 16, n^o 4 (avril 1996) : 1305–15. http://dx.doi.org/10.1128/mcb.16.4.1305.

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Antigen receptor ligation on lymphocytes activates protein tyrosine kinases and phospholipase C-gamma (PLC-gamma) isoforms. Glutathione S-transferase fusion proteins containing the C-terminal Src-homology 2 [SH2(C)] domain of PLC-gamma1 bound to tyrosyl phosphorylated Syk. Syk isolated from antigen receptor-activated B cells phosphorylated PLC-gamma1 on Tyr-771 and the key regulatory residue Tyr-783 in vitro, whereas Lyn from the same B cells phosphorylated PLC-gamma1 only on Tyr-771. The ability of Syk to phosphorylate PLC-gamma1 required antigen receptor ligation, while Lyn was constitutively active. An mCD8-Syk cDNA construct could be expressed as a tyrosyl-phosphorylated chimeric protein tyrosine kinase in COS cells, was recognized by PLC-gamma1 SH2(C) in vitro, and induced tyrosyl phosphorylation of endogenous PLC-gamma1 in vivo. Substitution of Tyr-525 and Tyr-526 at the autophosphorylation site of Syk in mCD8-Syk substantially reduced the kinase activity and the binding of this variant chimera to PLC-gamma1 SH2(C) in vitro; it also failed to induce tyrosyl phosphorylation of PLC-gamma1 in vivo. In contrast, substitution of Tyr-348 and Tyr-352 in the linker region of Syk in mCD8-Syk did not affect the kinase activity of this variant chimera but almost completely eliminated its binding to PLC-gamma1 SH(C) and completely eliminated its ability to induce tyrosyl phosphorylation of PLC-gamma1 in vivo. Thus, an optimal kinase activity of Syk and an interaction between the linker region of Syk with PLC-gamma1 are required for the tyrosyl phosphorylation of PLC-gamma1.

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Raeder, Evelin M. B., Pamela J. Mansfield, Vania Hinkovska-Galcheva, James A. Shayman et Laurence A. Boxer. « Syk Activation Initiates Downstream Signaling Events During Human Polymorphonuclear Leukocyte Phagocytosis ». Journal of Immunology 163, n^o 12 (15 décembre 1999) : 6785–93. http://dx.doi.org/10.4049/jimmunol.163.12.6785.

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Abstract We investigated the requirement for Syk activation to initiate downstream signaling events during polymorphonuclear leukocyte (PMN) phagocytosis of Ab-coated erythrocytes (EIgG). When PMN were challenged with EIgG, Syk phosphorylation increased in a time-dependent manner, paralleling the response of PMN phagocytosis. Pretreatment of PMN with piceatannol, a Syk-selective inhibitor, blocked EIgG phagocytosis and Syk phosphorylation. We found that piceatannol inhibited protein kinase Cδ (PKCδ) and Raf-1 translocation from cytosol to plasma membrane by >90%. Extracellular signal-regulated protein kinase-1 and -2 (ERK1 and ERK2) phosphorylation was similarly blocked. We also investigated phosphatidylinositide 3-kinase (PI 3-kinase) activity and Syk phosphorylation using piceatannol, wortmannin, and LY294002, inhibitors of PI 3-kinase. The phosphorylation of Syk preceded the activation of PI 3-kinase. Both wortmannin and piceatannol inhibited PI 3-kinase, but only piceatannol inhibited Syk. In contrast to piceatannol, wortmannin did not inhibit PKCδ and Raf-1 translocation. To elucidate signaling downstream of Syk activation, we assessed whether the cell-permeable diacylglycerol analogue didecanoylglycerol could normalize PMN phagocytosis, PKCδ and Raf-1 translocation, and ERK1 and ERK2 phosphorylation inhibited by piceatannol. The addition of didecanoylglycerol to the Syk-inhibited phagocytosing PMN normalized all three without a concomitant effect on PI 3-kinase activity and Syk phosphorylation. We conclude that Syk activation following Fcγ receptor engagement initiates downstream signaling events leading to mitogen-activated protein kinase activation independent of PI 3-kinase activation.

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SACI, Abdelhafid, Francine RENDU et Christilla BACHELOT-LOZA. « Platelet αIIb-β3 integrin engagement induces the tyrosine phosphorylation of Cbl and its association with phosphoinositide 3-kinase and Syk ». Biochemical Journal 351, n^o 3 (24 octobre 2000) : 669–76. http://dx.doi.org/10.1042/bj3510669.

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Agonist-induced platelet activation triggers ‘inside-out’signalling which activates αIIb-β3, the most abundant integrin in platelet membranes. The engagement of activated αIIb-β3 integrin by linking fibrinogen is necessary for platelet aggregation, and this induces subsequent outside-in signalling, which enhances platelet activation. Here we studied the involvement of Cbl during αIIb-β3-integrin-mediated signal transduction. During thrombin-induced platelet activation, Cbl was tyrosine phosphorylated, and phosphoinositide 3-kinase (PI 3-kinase) activity measured in Cbl immunoprecipitates was increased. Both Cbl phosphorylation and its association with PI 3-kinase were dependent on αIIb-β3 engagement by linking fibrinogen. The P256 and anti-LIBS6 (ligand-induced binding site 6) antibodies, which activate platelets directly through αIIb-β3, induced Cbl phosphorylation and increased the PI 3-kinase activity associated with Cbl. Both thrombin and antibodies to αIIb-β3 induced association of Cbl with the tyrosine kinase, Syk. Experiments performed with inhibitors of tyrosine kinases indicated that both Src-family kinases and Syk contribute to phosphorylation of Cbl and its consequent association with PI 3-kinase. The results show that, following integrin αIIb-β3 engagement, Cbl is tyrosine phosphorylated, recruits PI 3-kinase to this integrin signalling pathway and possibly enhances PI 3-kinase activity, downstream of Src-family tyrosine kinases and Syk activation.

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Kurosaki, T., M. Takata, Y. Yamanashi, T. Inazu, T. Taniguchi, T. Yamamoto et H. Yamamura. « Syk activation by the Src-family tyrosine kinase in the B cell receptor signaling. » Journal of Experimental Medicine 179, n^o 5 (1 mai 1994) : 1725–29. http://dx.doi.org/10.1084/jem.179.5.1725.

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Signaling through the B cell antigen receptor (BCR) results in rapid increases in tyrosine phosphorylation on a number of proteins. The BCR associates with two classes of tyrosine kinase: Src-family kinase (Src-protein-tyrosine kinase [PTK]; Lyn, Fyn, Blk, or Lck) and Syk kinase. We have investigated the interaction between the Src-PTK and the Syk kinase in the BCR signaling. In contrast to wild-type B cells, BCR-mediated tyrosine phosphorylation of Syk and activation of its in vitro kinase activity were profoundly reduced in lyn-negative cells. The requirement of the Src-PTK to induce tyrosine phosphorylation and activation of Syk was also demonstrated by cotransfection of syk and src-PTK cDNAs into COS cells. These results suggest that the Src-PTK associated with BCR phosphorylates the tyrosine residue(s) of Syk upon receptor stimulation, enhancing the activity of Syk.

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Van Ziffle, Jessica A., et Clifford A. Lowell. « Neutrophil-specific deletion of Syk kinase results in reduced host defense to bacterial infection ». Blood 114, n^o 23 (26 novembre 2009) : 4871–82. http://dx.doi.org/10.1182/blood-2009-05-220806.

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Abstract Leukocyte-specific CD18 integrins are critical in mediating cell recruitment and activation during host defense responses to bacterial infection. The signaling pathways downstream of CD18 integrins are dependent on the spleen tyrosine kinase, Syk. To investigate the role integrin signaling plays in host defense, we examined the responses of Syk-deficient neutrophils to bacterial challenge with serum-opsonized Staphylococcus aureus and Escherichia coli. Syk-conditional knockout mice lacking this kinase specifically in myeloid cells or just neutrophils were also used to investigate host responses in vivo. Syk-deficient neutrophils manifested impaired exocytosis of secondary and tertiary granules, reduced cytokine release, and very poor activation of the NADPH oxidase in response to serum-opsonized S aureus and E coli. These functional defects correlated with impaired activation of c-Cbl, Pyk2, Erk1/2, and p38 kinases. Bacterial phagocytosis, neutrophil extracellular trap formation, and killing were also reduced in Syk-deficient cells, with a more profound effect after S aureus challenge. In vivo, loss of Syk in myeloid cells or specifically in neutrophils resulted in reduced clearance of S aureus after subcutaneous or intraperitoneal infection, despite normal recruitment of inflammatory cells. These results indicate that loss of Syk kinase-mediated integrin signaling impairs leukocyte activation, leading to reduced host defense responses.

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Miah, S. M. Shahjahan, Kiyonao Sada, Polygena T. Tuazon, Jun Ling, Koichiro Maeno, Shinkou Kyo, Xiujuan Qu, Yumi Tohyama, Jolinda A. Traugh et Hirohei Yamamura. « Activation of Syk Protein Tyrosine Kinase in Response to Osmotic Stress Requires Interaction with p21-Activated Protein Kinase Pak2/γ-PAK ». Molecular and Cellular Biology 24, n^o 1 (1 janvier 2004) : 71–83. http://dx.doi.org/10.1128/mcb.24.1.71-83.2004.

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ABSTRACT The p21-activated serine/threonine protein kinase Pak2/γ-PAK and the nonreceptor type of protein tyrosine kinase Syk are known to be activated when the cells are exposed to osmotic stress. The purpose of the present study was to examine whether Pak2 and Syk functionally cooperate in cellular signaling. Cotransfection studies revealed that Pak2 associates with Syk in COS cells. The constitutively active form of Cdc42 increases the association of Pak2 with Syk. Pak2 coexpressed with an inactive form of Cdc42 or kinase-inactive Pak2 interacts to a lesser extent with Syk, suggesting that Pak2-Syk association is enhanced by Pak2 activation. Interaction with Pak2 enhances the intrinsic kinase activity of Syk. This is supported by in vitro studies showing that Pak2 phosphorylates and activates Syk. Treatment of cells with sorbitol to induce hyperosmolarity results in the translocation of Pak2 and Syk to the region surrounding the nucleus and in dramatic enhancement of their association. Furthermore, cotransfection of Pak2 and Syk leads to the activation of c-Jun N-terminal kinase (JNK) under hyperosmotic conditions. Pak2 short interfering RNA suppresses sorbitol-mediated activation of endogenous Syk and JNK, thus identifying a novel pathway for JNK activation by Cdc42. These results demonstrate that Pak2 and Syk positively cooperate to regulate cellular responses to stress.

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Althubiti, Mohammad. « Spleen Tyrosine Kinase Inhibition Modulates p53 Activity ». Journal of Cell Death 10 (1 janvier 2017) : 117906601773156. http://dx.doi.org/10.1177/1179066017731564.

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Spleen tyrosine kinase (SYK) is a cytoplasmic enzyme that promotes survival and proliferation of B cells. SYK inhibition has shown promising results in the treatment of arthritis and chronic lymphocytic leukemia (CLL). However, in other context, it has been shown that SYK overexpression in epithelial cancer cells induced senescence in p53-dependent mechanism, which underscored its antineoplastic activity in vitro. Here, we show that SYK was induced in response of DNA damage in parallel with p53 levels. In addition, using chemical inhibitors of SYK reduced p53 levels in HCT116 and HT1080 cell lines, which underlines the role of SYK inhibition on p53 activity. Furthermore, SYK inhibition modulated the cell growth, which resulted in a decreasing in cell death. Interestingly, SYK expression showed a positive prognosis in patients with solid tumors in correlations with their survival rates, as expected negative correlation was seen between SYK expression and survival rate of patients with CLL. In conclusion, these findings demonstrate that SYK inhibition modulates p53 expression and activity in HCT116 and HT1080 cells. Reconsidering using of SYK inhibitors in clinical setting in the future should be evaluated carefully in accordance with these findings to prevent the formation of secondary malignancies.

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Jiang, Kun, Bin Zhong, Connie Ritchey, Danielle L. Gilvary, Elizabeth Hong-Geller, Sheng Wei et Julie Y. Djeu. « Regulation of Akt-dependent cell survival by Syk and Rac ». Blood 101, n^o 1 (1 janvier 2003) : 236–44. http://dx.doi.org/10.1182/blood-2002-04-1251.

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Abstract 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-2Rβ 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.

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Ghosh, Debjani, Katalin Kis-Toth, Yuang-Taung Juang et George Tsokos. « Activation of the protein kinase A pathway down regulates spleen tyrosine kinase in human T cells (63.30) ». Journal of Immunology 186, n^o 1_Supplement (1 avril 2011) : 63.30. http://dx.doi.org/10.4049/jimmunol.186.supp.63.30.

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Abstract Cyclic adenosine monophosphate (cAMP)-mediated activation of the protein kinase A (PKA) pathway has an overall negative impact on T cell proliferation and down regulates or neutralizes signaling pathways of many genes. Spleen tyrosine kinase (SYK) is an important gene expressed differentially during T cell development and functions by phosphorylating downstream effector molecules in both T and B lymphocytes. We report here that PKA inhibitors promoted, whereas cAMP analogues suppressed SYK expression. Overexpression of a catalytic subunit of PKA significantly abrogated SYK protein and mRNA expression as well as the levels of phosphorylated SYK. A complete cAMP response element (CRE) site on SYK promoter was found functional and capable of binding CREMα and CREB as detected by EMSA and chromatin immunoprecipitation. CREMα overexpression reduced, while disruption of the CRE site enhanced the basal promoter activity of SYK. Collectively, the cAMP-mediated PKA pathway functions as the negative regulator of SYK expression by promoting direct binding of a repressor element to the SYK promoter.

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Taylor, Naomi, Thomas Jahn, Susan Smith, Thomas Lamkin, Lisa Uribe, Yenbou Liu, Donald L. Durden et Kenneth Weinberg. « Differential Activation of the Tyrosine Kinases ZAP-70 and Syk After FcγRI Stimulation ». Blood 89, n^o 2 (15 janvier 1997) : 388–96. http://dx.doi.org/10.1182/blood.v89.2.388.

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Abstract Engagement of the high-affinity IgG Fc receptor (FcγRI) activates a signal transduction pathway involving tyrosine phosphorylation of associated kinases. We compared the activation of the related protein tyrosine kinases (PTKs), Syk and ZAP-70, in FcγRI-mediated signaling. Cross-linking of the FcγRI multimeric receptor in monocytic cells results in tyrosine phosphorylation of the FcεRIγ subunit and association of Syk with this complex. We stably introduced ZAP-70 via a retroviral vector into two monocytic cell lines, U937 and THP-1, which normally do not express ZAP-70. Neither Syk nor MAP kinase activation was affected by the presence of ZAP-70. Although transduced ZAP-70 had in vitro kinase activity and associated with FcεRIγ after receptor aggregation, it was not tyrosine phosphorylated. In contrast, both ZAP-70 and Syk were phosphorylated in a T-cell line in which their respective levels of expression were similar to those detected in U937/ZAP-70 cells. Therefore, these results suggest that requirements for Syk and ZAP-70 phosphorylation are distinct in a monocytic cell context.

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LOPEZ, Isabelle, Véronique DUPREZ, Josiane MELLE, François DREYFUS, Sylviane LÉVY-TOLÉDANO et Michaëla FONTENAY-ROUPIE. « Thrombopoietin stimulates cortactin translocation to the cytoskeleton independently of tyrosine phosphorylation ». Biochemical Journal 356, n^o 3 (8 juin 2001) : 875–81. http://dx.doi.org/10.1042/bj3560875.

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Cortactin is an F-actin-binding protein expressed in platelets. During aggregation by thrombin, cortactin associates with Src, is tyrosine phosphorylated, and then translocates to the cytoskeleton. It is also found to associate with Syk during platelet shape change. Since cortactin undergoes tyrosine phosphorylation in platelets activated by thrombopoietin (TPO) that exhibit neither shape change nor aggregation, we investigated whether it could also relocalize to the detergent-insoluble fraction. We demonstrate that cortactin was present as a tyrosine-phosphorylated protein and co-localized with Syk in the Triton X-100-insoluble fraction of TPO-activated platelets. TPO stimulated Syk activation and association with cortactin. Conversely, cortactin associated with the kinases, Syk and Src. Cortactin tyrosine phosphorylation was blocked by Syk kinase inhibitor, piceatannol or Src family kinase inhibitor, PP2, suggesting that it depends on these two kinases. However, piceatannol or PP2 did not prevent cortactin translocation to the detergent-insoluble fraction. These data suggest that tyrosine phosphorylation is not required for cortactin translocation to the detergent-insoluble compartment. Furthermore, TPO activates, through its receptor c-Mpl, a signalling pathway to the cytoskeleton.

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Alshafie, Walaa, Maryam Fotouhi, Riham Ayoubi, Kathleen Southern et Carl Laflamme. « Identification of high-performing antibodies for tyrosine-protein kinase SYK for use in Western Blot, immunoprecipitation and immunofluorescence ». F1000Research 12 (9 octobre 2023) : 1222. http://dx.doi.org/10.12688/f1000research.140456.2.

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Tyrosine-protein kinase SYK, encoded by the SYK gene, is a non-receptor type protein kinase which mediates immune signal transduction through immunoreceptors. Tyrosine-protein kinase SYK expression has been associated with the development of various inflammatory diseases, cancer and neurodegenerative conditions. The reproducibility of tyrosine-protein kinase SYK research would help elucidate the mechanism in which it causes neuroinflammation as well as its potential as a novel target to treat Alzheimer’s disease. This would be facilitated with the availability of high-quality tyrosine-protein kinase SYK. In this study, we characterized thirteen tyrosine-protein kinase SYK commercial antibodies for Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many high-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

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Alshafie, Walaa, Maryam Fotouhi, Riham Ayoubi, Kathleen Southern et Carl Laflamme. « Identification of high-performing antibodies for tyrosine-protein kinase SYK for use in Western Blot, immunoprecipitation and immunofluorescence ». F1000Research 12 (27 septembre 2023) : 1222. http://dx.doi.org/10.12688/f1000research.140456.1.

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Tyrosine-protein kinase SYK, encoded by the SYK gene, is a non-receptor type protein kinase which mediates immune signal transduction through immunoreceptors. Tyrosine-protein kinase SYK expression has been associated with the development of various inflammatory diseases, cancer and neurodegenerative conditions. The reproducibility of tyrosine-protein kinase SYK research would help elucidate the mechanism in which it causes neuroinflammation as well as its potential as a novel target to treat Alzheimer’s disease. This would be facilitated with the availability of high-quality tyrosine-protein kinase SYK. In this study, we characterized thirteen tyrosine-protein kinase SYK commercial antibodies for Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many high-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

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Alshafie, Walaa, Maryam Fotouhi, Riham Ayoubi, Kathleen Southern et Carl Laflamme. « Identification of high-performing antibodies for tyrosine-protein kinase SYK for use in Western Blot, immunoprecipitation and immunofluorescence ». F1000Research 12 (11 juin 2024) : 1222. http://dx.doi.org/10.12688/f1000research.140456.3.

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Tyrosine-protein kinase SYK, encoded by the SYK gene, is a non-receptor type protein kinase which mediates immune signal transduction through immunoreceptors. Tyrosine-protein kinase SYK expression has been associated with the development of various inflammatory diseases, cancer and neurodegenerative conditions. The reproducibility of tyrosine-protein kinase SYK research would help elucidate the mechanism in which it causes neuroinflammation as well as its potential as a novel target to treat Alzheimer’s disease. This would be facilitated with the availability of high-quality tyrosine-protein kinase SYK. In this study, we characterized thirteen tyrosine-protein kinase SYK commercial antibodies for Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many high-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

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Bauer, Markus, Petra Maschberger, Lynn Quek, Stephen Briddon, Debabrata Dash, Michael Weiss, Steve Watson et Wolfgang Siess. « Genetic and Pharmacological Analyses of Involvement of Src-family, Syk and Btk Tyrosine Kinases in Platelet Shape Change ». Thrombosis and Haemostasis 85, n^o 02 (2001) : 331–40. http://dx.doi.org/10.1055/s-0037-1615689.

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SummaryPlatelet shape change was found to be associated with an increase in protein tyrosine phosphorylation upon stimulation of thrombin-, ADPand thromboxane A2-G-protein coupled receptors in human platelets and thromboxane A2 receptors in mouse platelets. By using PP1 and PD173956, two structurally unrelated specific inhibitors of Src-family tyrosine kinases, and mouse platelets deficient in the Src-kinase Fyn or Lyn, we show that Src-family kinases cause the increase in protein tyrosine phosphorylation. We further detected that the non-Src tyrosine kinase Syk was activated during shape change in a manner dependent on Src-family kinaseactivation. The pharmacological experiments and the studies on Fyn-, Lyn- and Syk-deficient mouse platelets showed that neither Src-family kinases nor Syk are functionally involved in shape change. Also human platelets deficient of the tyrosine kinase Btk showed a normal shape change. Binding of PAC-1 that recognizes activated integrin αIIb β3 complexes on the platelet surface was enhanced during shape change and blocked by inhibition of Src-kinases. We conclude that the activation of Src-kinases and the subsequent Syk stimulation upon activation of G-protein coupled receptors are not involved in the cytoskeletal changes underlying shape change of human and mouse platelets, but that the stimulation of this evolutionary conserved pathway leads to integrin αIIb β3 exposure during shape change.

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Yamamoto, Noriyuki, Haruki Hasegawa, Hitomi Seki, Karl Ziegelbauer et Takahiro Yasuda. « Development of a high-throughput fluoroimmunoassay for Syk kinase and Syk kinase inhibitors ». Analytical Biochemistry 315, n^o 2 (avril 2003) : 256–61. http://dx.doi.org/10.1016/s0003-2697(03)00026-5.

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Ghazizadeh, S., J. B. Bolen et H. B. Fleit. « Tyrosine phosphorylation and association of Syk with FcγRII in monocytic THP-1 cells ». Biochemical Journal 305, n^o 2 (15 janvier 1995) : 669–74. http://dx.doi.org/10.1042/bj3050669.

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Although the cytoplasmic portion of the low-affinity receptor for immunoglobulin G, Fc gamma RII, does not contain a kinase domain, rapid tyrosine phosphorylation of intracellular substrates occurs in response to aggregation of the receptor. The use of specific tyrosine kinase inhibitors has suggested that these phosphorylations are required for subsequent cellular responses. We previously demonstrated the coprecipitation of a tyrosine kinase activity with Fc gamma RII, suggesting that non-receptor tyrosine kinases might associate with the cytoplasmic domain of Fc gamma RII. Anti-receptor immune complex kinase assays revealed the coprecipitation of several phosphoproteins, most notably p56/53lyn, an Src-family protein tyrosine kinase (PTK), and a 72 kDa phosphoprotein. Here we identify the 72 kDa Fc gamma RII-associated protein as p72syk (Syk), a member of a newly described family of non-receptor PTKs. A rapid and transient tyrosine phosphorylation of Syk was observed following Fc gamma RII activation. Syk was also tyrosyl-phosphorylated following aggregation of the high-affinity Fc gamma receptor, Fc gamma RI. The Fc gamma RI activation did not result in association of Syk with Fc gamma RII, implying that distinct pools of Syk are activated upon aggregation of each receptor in a localized manner. These results demonstrate a physical association between Syk and Fc gamma RII and suggest that the molecules involved in Fc gamma RII signalling are very similar to the ones utilized by multichain immune recognition receptors such as the B-cell antigen receptor and the high-affinity IgE receptor.

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Zhang, Juan, Teruaki Kimura et Reuben P. Siraganian. « Mutations in the Activation Loop Tyrosines of Protein Tyrosine Kinase Syk Abrogate Intracellular Signaling But Not Kinase Activity ». Journal of Immunology 161, n^o 8 (15 octobre 1998) : 4366–74. http://dx.doi.org/10.4049/jimmunol.161.8.4366.

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Abstract The protein tyrosine kinase Syk plays a pivotal role in mediating the high-affinity IgE receptor (FcεRI)-induced degranulation of mast cells. To examine the mechanism of Syk regulation, the two tyrosine residues at 519 and 520 in the putative activation loop of rat Syk were mutated to phenylalanine either singly or in combination. The various mutants were expressed in a Syk-negative variant of the RBL-2H3 (rat basophilic leukemia 2H3) mast cell line. In these transfected cell lines, mutant Syk did show increased tyrosine phosphorylation in vivo and increased enzymatic activity in vitro after FcεRI aggregation. There were conformational changes detected by an Ab when the wild-type and mutant Syk were either tyrosine phosphorylated or bound to tyrosine-phosphorylated immunoreceptor tyrosine-based activation motif peptides. However, these mutant Syk were incapable of transducing FcεRI signaling. In cells in which the expression level of mutant Syk was similar to that of the wild-type Syk, FcεRI cross-linking induced no increase in cellular protein tyrosine phosphorylation, no increase in tyrosine phosphorylation of phospholipase C-γ2 and mitogen-activated protein kinase, and no histamine release. Overexpression of Y519F or Y520F Syk mutants partially reconstituted the signaling pathways. These results indicate that these tyrosines in the putative activation loop are not essential for the enzymatic activity of Syk or for the conformational changes induced by binding of tyrosine-phosphorylated immunoreceptor tyrosine-based activation motif peptides. However, these tyrosines are necessary for Syk-mediated propagation of FcεRI signaling.

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Chu, David H., Nicolai S. C. van Oers, Marie Malissen, Jeff Harris, Melissa Elder et Arthur Weiss. « Pre-T Cell Receptor Signals Are Responsible for the Down-Regulation of Syk Protein Tyrosine Kinase Expression ». Journal of Immunology 163, n^o 5 (1 septembre 1999) : 2610–20. http://dx.doi.org/10.4049/jimmunol.163.5.2610.

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Abstract Thymocyte development proceeds through two critical checkpoints that involve signaling events through two different receptors, the TCR and the pre-TCR. These receptors employ two families of protein tyrosine kinases to propagate their signals, the Src and Syk families. Genetic and biochemical evidence has shown that the Src family kinases are critical for normal T cell maturation. ZAP-70, a Syk family kinase, has similarly been implicated as a critical component in thymocyte development. Although genetic evidence has suggested that Syk is involved during thymocyte development, a definitive study of Syk expression has not been performed. In this paper we report our reanalysis of Syk expression in subpopulations of murine and human thymocytes by intracellular staining and flow cytometry using anti-Syk mAbs. Syk is expressed at increased levels during the stages in which pre-TCR signaling occurs. Furthermore, Syk is down-regulated after the pre-TCR checkpoint has been passed. Syk may play an important role in thymic development during pre-TCR signal transduction. Finally, incomplete down-regulation of Syk expression was noted in human thymocytes, offering a possible explanation for the distinct phenotypes of mice and humans deficient in ZAP-70.

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Sadras, Teresa, Jevon Cutler, Julia Aguade-Gorgorio, Zhengshan Chen, Kadriye Nehir Cosgun, Akhilesh Pandey et Markus Muschen. « Cooperation between SYK and ZAP70 Kinases As a Driver of Oncogenic BCR-Signaling in B-Cell Malignancies ». Blood 132, Supplement 1 (29 novembre 2018) : 3922. http://dx.doi.org/10.1182/blood-2018-99-116954.

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Abstract The spleen tyrosine kinase (SYK) and ζ-associated protein of 70 kD (ZAP70) tyrosine kinases play critical roles in proximal signal transduction of B-cell (BCR) and T-cell receptors (TCR), respectively. The highly similar SYK and ZAP70 kinases share a common structure composed of two tandem SH2 domains and a carboxy-terminal kinase domain. A linker region, termed interdomain B, connects the SH2 domains to the kinase domain and is important for kinase activation. Despite their conserved structure, SYK and ZAP70 are expressed in a largely mutually exclusive manner and play analogous roles in BCR- and TCR-signaling. Cross-lineage activation of ZAP70 in B cells was previously identified in chronic lymphocytic leukemia (CLL), which is characterized by clonal accumulation of malignant CD5+ B-cell cells that retain dependency on the BCR for survival signals. Nearly half of CLL cases show co-expression of SYK and ZAP70, and these patients have an aggressive disease course and a poor prognosis. Our analysis shows that in addition to CLL, aberrant ZAP70 expression occurs in other B-cell malignancies, e.g. TCF3-PBX1 pre-B ALL and B-cell lymphoma subsets that depend on survival signals from a functional (pre-) BCR. These findings suggest that interactions between SYK and ZAP70 may function to fine-tune strength of oncogenic BCR-signaling. To test this hypothesis, we have used a combination of molecular and proteomic approaches. We studied mechanisms by which ZAP70 integrates into BCR-mediated signals, and how the function of ZAP70 in B-cells differs from its native role downstream of the TCR. We demonstrate that ectopically expressed SYK and ZAP70 proteins are constitutively phosphorylated in BCR-ABL1+ B-ALL cells, but these induce distinctive signaling thresholds. CRISPR-mediated deletion of SYK or ZAP70 in leukemic cells further revealed that SYK and ZAP70 regulate unique signaling pathways in B-cells. We also demonstrate that ZAP70 is activated following BCR stimulation of lymphoma cells, and SYK/ZAP70 co-expressing cells display enhanced BCR signaling. Interestingly, enhanced BCR signaling was also observed in cells engineered to express an alternative splice variant of SYK (SYK-S). This shorter isoform of SYK, lacks a 23 amino-acid insert in the interdomain-B linker region, which is also absent in ZAP70, and may define unique protein-interactions that modulate signaling outcome. To elucidate the differential interactome of SYK, SYK-S, and ZAP70 we performed proximity-dependent biotin identification (BioID) experiments in B-cells following BCR-activation to capture the core signalling networks of these kinases in leukemic cells. In addition to expected BCR components including BLNK, PTPN6 and CBL we identified novel SYK and ZAP70 associated molecules including IKZF3, LAT2 and WAS which may play important roles in the survival of BCR-dependent malignancies. Importantly our findings highlight a role for ZAP70 in oncogenic BCR-signaling and suggest that ZAP70 promotes oncogenic BCR-signaling by limiting the ability of the BCR to induce negative B-cell selection and cell death. Disclosures No relevant conflicts of interest to declare.

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Oh, Hyunju, Elif Ozkirimli, Kavita Shah, Marietta L. Harrison et Robert L. Geahlen. « Generation of an Analog-sensitive Syk Tyrosine Kinase for the Study of Signaling Dynamics from the B Cell Antigen Receptor ». Journal of Biological Chemistry 282, n^o 46 (3 octobre 2007) : 33760–68. http://dx.doi.org/10.1074/jbc.m704846200.

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The Syk protein-tyrosine kinase is an essential component of the signaling machinery that couples the B cell receptor for antigen to multiple downstream signal transduction pathways. Syk is phosphorylated and activated rapidly and transiently following receptor engagement, but many signaling events, such as the activation of transcription factors occur over the course of several minutes or hours. To investigate a role for the continued activation of Syk in these processes, we generated an analog-sensitive mutant with an engineered ATP-binding pocket to render the kinase uniquely sensitive to an orthogonal inhibitor. Mutation of the gatekeeper residue in Syk yielded an enzyme with very low activity. Second-site mutations, selected based on structural comparisons between Syk and Src, were introduced that restored catalytic activity to the mutant Syk. Syk-deficient DT40 B cells were prepared expressing the analog-sensitive Syk (Syk-AQL). Inhibition of the activity of Syk prior to, concomitant with or shortly following receptor engagement led to the rapid inhibition of receptor-mediated tyrosine phosphorylation and blocked the activation of extracellular signal-regulated kinase, NF-κB, and NFAT. The receptor-mediated activation of NF-κB required active Syk for a relatively short period of time, whereas the activation of NFAT required active kinase for a prolonged (>1 h) period. Receptor cross-linking led to the recruitment of Syk to the clustered receptor. Retention of these receptor-kinase complexes on the cell surface was dependent on the continued activity of Syk. Thus, despite the apparent transient nature of the activation of Syk, the catalytic activity of the Syk was required for sustained signaling from ligated receptors.

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Matsuda, M., J. G. Park, D. C. Wang, S. Hunter, P. Chien et A. D. Schreiber. « Abrogation of the Fc gamma receptor IIA-mediated phagocytic signal by stem-loop Syk antisense oligonucleotides. » Molecular Biology of the Cell 7, n^o 7 (juillet 1996) : 1095–106. http://dx.doi.org/10.1091/mbc.7.7.1095.

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The role of Syk kinase in Fc gamma receptor (Fc gamma R) IIA-mediated phagocytosis was examined with two forms of antisense oligodeoxynucleotides (ODNs) designed to hybridize to human Syk mRNA. Monocytes were incubated with linear and stem-loop antisense ODNs targeted to Syk mRNA. When complexed with cationic liposomes, stem-loop Syk antisense ODN with phosphorothioate modification exhibited stability in fetal bovine and human serum. The stem-loop Syk antisense ODN at a concentration of 0.2 microM inhibited Fc gamma RIIA-mediated phagocytosis by 90% and completely eliminated Syk mRNA and protein in monocytes, whereas scrambled-control ODNs had no effect. The Syk antisense ODNs did not change beta-actin mRNA levels and Fc gamma RII cell-surface expression. In addition, stem-loop Syk antisense ODN inhibited Fc gamma RI and Fc gamma RIIIA-mediated phagocytosis. These data indicate the efficacy of stem-loop Syk antisense ODN for targeting and degrading Syk mRNA and protein and the importance of Syk kinase in Fc gamma receptor-mediated phagocytosis. Immunoblotting assay demonstrated that Fc gamma RII tyrosine phosphorylation after Fc gamma RII cross-linking did not change in the absence of Syk protein. These results indicate that Syk kinase is required for Fc gamma RIIA-mediated phagocytic signaling and that Fc gamma RII cross-linking leads to tyrosine phosphorylation of Fc gamma RII independent of Syk kinase.

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Biswas, Partha, Dipta Dey, Atikur Rahman, Md Aminul Islam, Tasmina Ferdous Susmi, Md Abu Kaium, Md Nazmul Hasan et al. « Analysis of SYK Gene as a Prognostic Biomarker and Suggested Potential Bioactive Phytochemicals as an Alternative Therapeutic Option for Colorectal Cancer : An In-Silico Pharmaco-Informatics Investigation ». Journal of Personalized Medicine 11, n^o 9 (6 septembre 2021) : 888. http://dx.doi.org/10.3390/jpm11090888.

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Background: SYK gene regulates the expression of SYK kinase (Spleen tyrosine kinase), an important non-receptor protein-tyrosine kinase for immunological receptor-mediated signaling, which is also considered a tumor growth metastasis initiator. An onco-informatics analysis was adopted to evaluate the expression and prognostic value of the SYK gene in colorectal cancer (CRC), the third most fatal cancer type; of late, it may be a biomarker as another targeted site for CRC. In addition, identify the potential phytochemicals that may inhibit the overexpression of the SYK kinase protein and minimize the human CRC. Materials & Methods: The differential expression of the SYK gene was analyzed using several transcriptomic databases, including Oncomine, UALCAN, GENT2, and GEPIA2. The server cBioPortal was used to analyze the mutations and copy number alterations, whereas GENT2, Gene Expression Profiling Interactive Analysis (GEPIA), Onco-Lnc, and PrognoScan were used to examine the survival rate. The protein-protein interaction network of SYK kinase and its co-expressed genes was conducted via Gene-MANIA. Considering the SYK kinase may be the targeted site, the selected phytochemicals were assessed by molecular docking using PyRx 0.8 packages. Molecular interactions were also observed by following the Ligplot+ version 2.2. YASARA molecular dynamics simulator was applied for the post-validation of the selected phytochemicals. Results: Our result reveals an increased level of mRNA expression of the SYK gene in colorectal adenocarcinoma (COAD) samples compared to those in normal tissues. A significant methylation level and various genetic alterations recurrence of the SYK gene were analyzed where the fluctuation of the SYK alteration frequency was detected across different CRC studies. As a result, a lower level of SYK expression was related to higher chances of survival. This was evidenced by multiple bioinformatics platforms and web resources, which demonstrated that the SYK gene can be a potential biomarker for CRC. In this study, aromatic phytochemicals, such as kaempferol and glabridin that target the macromolecule (SYK kinase), showed higher stability than the controls, and we have estimated that these bioactive potential phytochemicals might be a useful option for CRC patients after the clinical trial. Conclusions: Our onco-informatics investigation suggests that the SYK gene can be a potential prognostic biomarker of CRC. On the contrary, SYK kinase would be a major target, and all selected compounds were validated against the protein using in-silico drug design approaches. Here, more in vitro and in vivo analysis is required for targeting SYK protein in CRC.

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Palacios, Emil H., et Arthur Weiss. « Distinct roles for Syk and ZAP-70 during early thymocyte development ». Journal of Experimental Medicine 204, n^o 7 (2 juillet 2007) : 1703–15. http://dx.doi.org/10.1084/jem.20070405.

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The spleen tyrosine kinase (Syk) and ζ-associated protein of 70 kD (ZAP-70) tyrosine kinases are both expressed during early thymocyte development, but their unique thymic functions have remained obscure. No specific role for Syk during β-selection has been established, and no role has been described for ZAP-70 before positive selection. We show that Syk and ZAP-70 provide thymocytes with unique and separable fitness advantages during early development. Syk-deficient, but not ZAP-70–deficient, thymocytes are specifically impaired in initial pre-TCR signaling at the double-negative (DN) 3 β selection stage and show reduced cell-cycle entry. Surprisingly, and despite overlapping expression of both kinases, only ZAP-70 appears to promote sustained pre-TCR/TCR signaling during the DN4, immature single-positive, and double-positive stages of development before thymic selection occurs. ZAP-70 promotes survival and cell-cycle progression of developing thymocytes before positive selection, as also shown by in vivo anti-CD3 treatment of recombinase-activating gene 1–deficient mice. Our results establish a temporal separation of Syk family kinase function during early thymocyte development and a novel role for ZAP-70. We propose that pre-TCR signaling continues during DN4 and later stages, with ZAP-70 dynamically replacing Syk for continued pre-TCR signaling.

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Chan, A. C., N. S. van Oers, A. Tran, L. Turka, C. L. Law, J. C. Ryan, E. A. Clark et A. Weiss. « Differential expression of ZAP-70 and Syk protein tyrosine kinases, and the role of this family of protein tyrosine kinases in TCR signaling. » Journal of Immunology 152, n^o 10 (15 mai 1994) : 4758–66. http://dx.doi.org/10.4049/jimmunol.152.10.4758.

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Abstract TCR stimulation results in the tyrosine phosphorylation of a number of cellular substrates. We have recently identified a 70-kDa protein tyrosine kinase, ZAP-70, which associates with the human TCR zeta-chain after TCR stimulation. We report here the isolation and sequence of a cDNA clone that encodes murine ZAP-70. Murine and human ZAP-70 share 93% amino acid identity and are homologous to the 72-kDa protein tyrosine kinase Syk. Syk has been implicated in the signal transduction pathways of the B cell membrane Ig and high affinity IgE receptors, Fc epsilon RI. In addition, we examined the tissue distribution of ZAP-70 and Syk in human and murine thymocyte subsets, B cells, and peripheral T cell subsets. ZAP-70 protein is expressed in all major thymocyte populations, with the level of expression being comparable to that found in both CD4+ and CD8+ peripheral T cells. Although Syk protein is also present in all thymocyte subsets, expression of Syk protein is down-regulated threefold to fourfold in peripheral T cells. In contrast to ZAP-70, expression of Syk is 12- to 15-fold higher in peripheral B cells when compared with peripheral T cells. In addition, whereas T cell stimulation results in down-regulation of Lck, no significant change in ZAP-70 or Syk protein is detected. Finally, we provide evidence that both ZAP-70 and Syk can associate with the TCR after TCR stimulation. With the use of a heterologous expression system, we show that, like ZAP-70, Syk is dependent upon a Src-family protein tyrosine kinase for association with the phosphorylated zeta-chain. Thus, the differential expression of these kinases suggests the possibility of different roles for ZAP-70 and Syk in TCR signaling and thymic development.

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Shimoyama, Tadashi, Yoshiaki Okano, Yukiteru Fujishima, Tatsuo Oyake, Shugo Kowata, Kazunori Murai, Shigeki Ito et Yoji Ishida. « Dasatinib Is Effective in the Treatment of Mice Models with Immune Thrombocytopenia ». Blood 124, n^o 21 (6 décembre 2014) : 1456. http://dx.doi.org/10.1182/blood.v124.21.1456.1456.

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Abstract Background: Immune thrombocytopenia (ITP) is an autoimmune disease in which anti-platelet antibody (APA) is produced. APA-coated platelets are captured and phagocytized by macrophages in the spleen. Recent study revealed that spleen tyrosine kinase (Syk) inhibitor is effective in the treatment of ITP, because Syk phosphorylation is the key step of the phagocytosis by macrophages. Activated Fc receptor signal transduction is initiated by phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) tyrosine residues by SRC family kinases. Recruitment of Syk to dually phosphorylated ITAMs triggers the activation of Syk. To prove the hypothesis that the inhibition of SRC family kinase induces the decreased phosphorylation of Syk, resulting in decreased phagocytosis by macrophages, a SRC family kinase inhibitor, dasatinib, was used in the experiments. Methods, Results and Discussion: In vitro study; Murine macrophage cell line, RAW, was incubated with APA coated murine platelets for 30 minutes. Phagocytosis by RAW was significantly decreased with dasatinib (100nM, p<0.01), indicating SRC family kinase activity is required for efficient phagocytosis. Phosphorylated Syk was decreased in RAW, incubated with anti-Fc receptor antibody (rat IgG) and anti-rat IgG antibody with dasatinib (100nM), shown in the Western blot analysis (Figure 1). These results suggest that Syk phosphorylation is the key step in phagocytosis. In vivo study; (1) Three hours before APA intra-peritoneal injection, dasatinib (2.5mg/kg) was oral-administrated. Six hours after APA injection, platelet counts were measured. The platelet counts were 366 ± 164 x109/L with dasatinib (n=4, mean ± SD) and 114 ± 51 x109/L without dasatinib (n=4)(P=0.026)(Figure 2). (2) Osmotic pump, filled with APA, were inserted in murine intra-peritoneal cavity and dasatinib (2.5mg/kg) was oral-administered once daily for 7 days. The platelet counts were 499 ± 98 x109/L with dasatinib (n=4, mean ± SD) and 82 ± 131 x109/L without dasatinib (n=4) at day 7 (p<0.0022) (Figure 3). These results strongly suggest that dasatinib inhibit the phagocytosis in vivo. Conclusion: Dasatinib inhibits phosphorylation of Syk, inducing decreased phagocytosis of APA-coated platelets via decreased SRC family kinase activity. These findings reveal that SRC family kinase controls the efficiency of phagocytosis in part through the regulation of Syk function. Dasatinib might be effective in the treatment of ITP. Disclosures No relevant conflicts of interest to declare.

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Forns, Pilar, Cristina Esteve, Lorena Taboada, Juan Antonio Alonso, Adelina Orellana, Mónica Maldonado, Cristina Carreño et al. « Pyrazine-based Syk kinase inhibitors ». Bioorganic & ; Medicinal Chemistry Letters 22, n^o 8 (avril 2012) : 2784–88. http://dx.doi.org/10.1016/j.bmcl.2012.02.087.

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Yago, Tadayuki, Bojing Shao, Jonathan J. Miner, Longbiao Yao, Arkadiusz G. Klopocki, Kenichiro Maeda, K. Mark Coggeshall et Rodger P. McEver. « E-selectin engages PSGL-1 and CD44 through a common signaling pathway to induce integrin αLβ2-mediated slow leukocyte rolling ». Blood 116, n^o 3 (22 juillet 2010) : 485–94. http://dx.doi.org/10.1182/blood-2009-12-259556.

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Abstract In inflamed venules, neutrophils rolling on E-selectin induce integrin αLβ2-dependent slow rolling on intercellular adhesion molecule-1 by activating Src family kinases (SFKs), DAP12 and Fc receptor-γ (FcRγ), spleen tyrosine kinase (Syk), and p38. E-selectin signaling cooperates with chemokine signaling to recruit neutrophils into tissues. Previous studies identified P-selectin glycoprotein ligand-1 (PSGL-1) as the essential E-selectin ligand and Fgr as the only SFK that initiate signaling to slow rolling. In contrast, we found that E-selectin engagement of PSGL-1 or CD44 triggered slow rolling through a common, lipid raft–dependent pathway that used the SFKs Hck and Lyn as well as Fgr. We identified the Tec kinase Bruton tyrosine kinase as a key signaling intermediate between Syk and p38. E-selectin engagement of PSGL-1 was dependent on its cytoplasmic domain to activate SFKs and slow rolling. Although recruiting phosphoinositide-3-kinase to the PSGL-1 cytoplasmic domain was reported to activate integrins, E-selectin–mediated slow rolling did not require phosphoinositide-3-kinase. Studies in mice confirmed the physiologic significance of these events for neutrophil slow rolling and recruitment during inflammation. Thus, E-selectin triggers common signals through distinct neutrophil glycoproteins to induce αLβ2-dependent slow rolling.

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Coffey, Greg, DeGuzman Francis, Mayuko Inagaki, Yvonne Pak, Suzanne Delaney, Andreas Betz, Zhaozhong J. Jia et al. « Specific Inhibition of Syk Suppresses Leukocyte Immune Function and Alleviates Inflammation In Rodent Models of Rheumatoid Arthritis ». Blood 116, n^o 21 (19 novembre 2010) : 1727. http://dx.doi.org/10.1182/blood.v116.21.1727.1727.

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Abstract Abstract 1727 Genetic ablation of Syk in hematopoietic cells blocks various leukocyte immune functions, and protects mice from immune-complex mediated inflammation. These data have helped to identify Syk as an important therapeutic target for immune-mediated diseases. The next step is to test the hypothesis that low level, and specific, pharmacological inhibition of Syk retains the immunomodulatory potential observed with Syk genetic deficiency. With this goal in mind, we provide an update on the development of P505-15, a highly specific and potent small molecule Syk inhibitor which suppresses signaling and activation of primary human and rodent leukocyte immune function. The specificity of P505-15 was tested in a panel of 270 independent purified kinase assays at 300nM. At this concentration, Syk and 8 other kinases were inhibited by ≥ 80%. Subsequent analysis demonstrated a Syk IC50 of 1nM, whereas the next most potently inhibited kinase required an IC50 of 81nM. In a variety of cellular assays we observed potent inhibition of B cell receptor (BCR) induced Syk signaling, but not of Lyn, phorbol 12-myristate 13-acetate (PMA) induced protein kinase C, T cell receptor induced Zap70, or cytokine induced JAK1 (IL6), JAK2 (GM-CSF), or JAK1/3 (IL4) dependent STAT phosphorylation. Consistently, in Ba/F3 cell lines transformed by various kinases, P505-15 only inhibited proliferation of those cells transformed by Syk (IC50 = 0.12μM), and not by Zap70 or JAK family members (IC50 > 6μM). In human whole blood, P505-15 suppressed BCR-induced Syk signaling and cellular activation with IC50's of 0.383μM and 0.362μM, respectively. FceR1-induced basophil degranulation was similarly suppressed with an IC50 of 0.171μM. Importantly, Syk-independent signaling and cellular activation in human whole blood via PMA (B cell assays) or fMLP (basophil degranulation) was unaffected by this compound at 4μM and 1μM, respectively (the highest concentrations tested), again demonstrating its specificity of action. Oral administration of P505-15 in mice led to a reversible inhibition of Syk, with an IC50 of 0.282μM as determined by an ex vivo whole blood BCR stimulation assay. Finally, we tested the immunomodulatory potential of specific Syk inhibition in vivo using rodent models of rheumatoid arthritis. Oral administration of P505-15 resulted in statistically significant and dose-dependent anti-inflammatory activity in both the mouse collagen antibody-induced arthritis and rat collagen induced arthritis models. In each case, anti-inflammatory effects were achieved at sub-micromolar plasma concentrations in which Syk specificity was maintained. These data support the hypothesis that specific Syk inhibition can modulate immune function in vivo, and provide a therapeutic strategy for the treatment of human inflammatory disease by inhibition of this kinase. P505-15 is currently being evaluated in phase I clinical trials. Disclosures: Coffey: Portola Pharmaceuticals: Employment. Francis:Portola Pharmaceuticals: Employment. Inagaki:Portola Pharmaceuticals: Employment. Pak:Portola Pharmaceuticals: Employment. Delaney:Portola Pharmaceuticals: Employment. Betz:Portola Pharmaceuticals: Employment. Jia:Portola Pharmaceuticals: Employment. Xu:Portola Pharmaceuticals: Employment. Bauer:Portola Pharmaceuticals: Employment. Song:Portola Pharmaceuticals: Employment. Pandey:Portola Pharmaceuticals: Employment. Baker:Portola Pharmaceuticals: Employment. Hollenbach:Portola Pharmaceuticals: Employment. Phillips:Portola Pharmaceuticals: Employment. Sinha:Portola Pharmaceuticals: Employment.

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