Phosphorylation of Syk activation loop tyrosines is essential Syk function: An in vivo study using a specific anti-Syk activation loop phosphotyrosine antibody
ABSTRACT Syk is an important protein-tyrosine kinase in immunoreceptor signaling. FcepsilonRI aggregation in mast cells induces tyrosine phosphorylation and increased enzymatic activity of Syk. The two adjacent tyrosines in the Syk activation loop are thought to be important for the propagation of FcepsilonRI signaling. To evaluate the phosphorylation of these tyrosines in vivo and further understand the relationship of Syk tyrosine phosphorylation with its function, an antibody was developed specific for phosphorylated tyrosines in the activation loop of Syk. FcepsilonRI aggregation on mast cells induced the phosphorylation of both tyrosine residues of the activation loop. The kinase activity of Syk played the major role in phosphorylating its activation loop tyrosines both in vivo and in vitro. In FcepsilonRI-stimulated mast cells, the total Syk tyrosine phosphorylation paralleled the phosphorylation of its activation loop tyrosines and downstream propagation of signals for histamine release. In contrast, the cell surface binding of anti-ganglioside monoclonal antibody AA4 induced only strong general tyrosine phosphorylation of Syk and minimal histamine release and weak phosphorylation of activation loop tyrosines. These results demonstrate that phosphorylation of the activation loop tyrosines is important for mediating receptor signaling and is a better marker of Syk function than is total Syk tyrosine phosphorylation.
- SourceAvailable from: Maria Célia Jamur
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- "FcεRI signaling relies on Lyn-dependent phosphorylation of ITAMs on the cytoplasmic portion of the β and γ receptor subunits. The protein kinase Syk is recruited to the phosphorylated ITAMs where it becomes activated and autophosphorylated (Zhang et al. 2000; de Castro et al. 2010 "
ABSTRACT: Since first described by Paul Ehrlich in 1878, mast cells have been mostly viewed as effectors of allergy. It has been only in the past two decades that mast cells have gained recognition for their involvement in other physiological and pathological processes. Mast cells have a widespread distribution and are found predominantly at the interface between the host and the external environment. Mast cell maturation, phenotype and function are a direct consequence of the local microenvironment and have a marked influence on their ability to specifically recognize and respond to various stimuli through the release of an array of biologically active mediators. These features enable mast cells to act as both first responders in harmful situations as well as to respond to changes in their environment by communicating with a variety of other cells implicated in physiological and immunological responses. Therefore, the critical role of mast cells in both innate and adaptive immunity, including immune tolerance, has gained increased prominence. Conversely, mast cell dysfunction has pointed to these cells as the main offenders in several chronic allergic/inflammatory disorders, cancer and autoimmune diseases. This review summarizes the current knowledge of mast cell function in both normal and pathological conditions with regards to their regulation, phenotype and role.Acta histochemica et cytochemica official journal of the Japan Society of Histochemistry and Cytochemistry 07/2014; 62(10). DOI:10.1369/0022155414545334 · 1.22 Impact Factor
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- "Src and Fyn are regulated by phosphorylation on two sites: one at tyrosine 416 which is activatory, and the other at tyrosine 527 which is inhibitory (reviewed by Hunter, 1987). Similar phosphorylation sites are found in other SFK members: activation of phosphorylation are at tyrosines 394 for Lck, at tyrosines 323 and 352 for Syk, and inhibition of phosphorylation are at tyrosines 505 for Lck, and at tyrosines 525 and 526 for Syk (Chow et al., 1993; Law et al., 1996; Deckert et al., 1998; Zhang et al., 2000; Rao et al., 2001). Activating phosphorylation often results from autophosphorylation (Chiang and Sefton, 2000; reviewed by Roskoski, 2004; reviewed by Roskoski, 2005). "
ABSTRACT: Tau phosphorylation is regulated by a balance between tau kinase and phosphatase activities. Disruption of this equilibrium was suggested to be at the origin of abnormal tau phosphorylation and thereby might contribute to tau aggregation. Thus, understanding the regulation modes of tau phosphorylation is of high interest in determining the possible causes at the origin of the formation of tau aggregates in order to elaborate protection strategies to cope with these lesions in Alzheimer's disease. Among the possible and specific interventions that reverse tau phosphorylation is the inhibition of certain tau kinases. Here, we extensively reviewed tau protein kinases, their physiological roles and regulation, their involvement in tau phosphorylation and their relevance to AD. We also reviewed the most common inhibitory compounds acting on each tau kinase.Ageing research reviews 06/2012; 12(1):289-309. DOI:10.1016/j.arr.2012.06.003 · 7.63 Impact Factor
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- "Immunoblotting (Fig 4) showed that all the cell lines expressed Syk. JeKo-1 had very high expression of Syk, in accordance with arrayCGH, gene expression and FISH data. The protein was phosphorylated in all the four cell lines on the activation sites TYR 525/526 (Zhang et al, 2000). To assess the relevance of this observation on clinical samples, we performed immunohistochemistry for Syk and FISH analysis on an independent series of MCLs. "
ABSTRACT: Among B-cell lymphomas mantle cell lymphoma (MCL) has the worst prognosis. By using a combination of genomic and expression profiling (Affymetrix GeneChip Mapping 10k Xba131 and U133 set), we analysed 26 MCL samples to identify genes relevant to MCL pathogenesis and that could represent new therapeutic targets. Recurrent genomic deletions and gains were detected. Genes were identified as overexpressed in regions of DNA gain on 3q, 6p, 8q, 9q, 16p and 18q, including the cancer genes BCL2 and MYC. Among the transcripts with high correlation between DNA and RNA, we identified SYK, a tyrosine kinase involved in B-cell receptor signalling. SYK was amplified at DNA level, as validated by fluorescence in situ hybridisation (FISH) analysis, and overexpressed at both RNA and protein levels in the JeKo-1 cell line. Low-level amplification, with protein overexpression of Syk was demonstrated by FISH in a small subset of clinical samples. After treatment with low doses of the Syk inhibitor piceatannol, cell proliferation arrest and apoptosis were induced in the cell line overexpressing Syk, while cells expressing low levels of Syk were much less sensitive. A combination of genomic and expression profiling suggested Syk inhibition as a new therapeutic strategy to be explored in lymphomas.British Journal of Haematology 03/2006; 132(3):303-16. DOI:10.1111/j.1365-2141.2005.05883.x · 4.96 Impact Factor