Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.10.2 (focal adhesion kinase)
44,029 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

T lymphocytes require two signals to be activated. The antigen-specific T-cell receptor can deliver the first signal, while ligation of the T-cell surface molecule CD28 by antibodies or its cognate ligands B7-1 (CD80) or B7-2 has been demonstrated to be sufficient for the delivery of the second signal. Signaling via CD28 and the T-cell receptor results (i) in their costimulation of T cells to produce numerous lymphokines including interleukin 2 and (ii) in the prevention of anergy induction. Little is known about the pathway by which CD28 mediates its signals except that protein-tyrosine phosphorylation is involved. We show here in human Jurkat cells that the Tec-family protein-tyrosine kinase ITK/EMT (p72ITK/EMT) is associated with CD28 and becomes tyrosine-phosphorylated and activated within seconds of CD28 ligation. This tyrosine phosphorylation of p72ITK/EMT is rapid (within 30 sec), occurs in the absence of LCK activation, and precedes tyrosine phosphorylation of the guanine nucleotide exchange factor VAV. Secondary crosslinking of CD28 is unnecessary for the induced tyrosine phosphorylation of p72ITK/EMT. Thus, tyrosine phosphorylation of p72ITK/EMT may represent one of the earliest events in CD28 signaling. This demonstrates that a member of the Tec family of protein tyrosine kinases, similar to members of the Src and Syk families, plays a role in the activation of T cells. Furthermore, the data demonstrate that p72ITK/EMT, and by analogy other members of the Tec family, responds to extracellularly generated signals.
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PMID:CD28 is associated with and induces the immediate tyrosine phosphorylation and activation of the Tec family kinase ITK/EMT in the human Jurkat leukemic T-cell line. 752 75

T-cell activation requires cooperative signals generated by the T-cell antigen receptor zeta-chain complex (TCR zeta-CD3) and the costimulatory antigen CD28. CD28 interacts with three intracellular proteins-phosphatidylinositol 3-kinase (PI 3-kinase), T cell-specific protein-tyrosine kinase ITK (formerly TSK or EMT), and the complex between growth factor receptor-bound protein 2 and son of sevenless guanine nucleotide exchange protein (GRB-2-SOS). PI 3-kinase and GRB-2 bind to the CD28 phosphotyrosine-based Tyr-Met-Asn-Met motif by means of intrinsic Src-homology 2 (SH2) domains. The requirement for tyrosine phosphorylation of the Tyr-Met-Asn-Met motif for SH2 domain binding implicates an intervening protein-tyrosine kinase in the recruitment of PI 3-kinase and GRB-2 by CD28. Candidate kinases include p56Lck, p59Fyn, zeta-chain-associated 70-kDa protein (ZAP-70), and ITK. In this study, we demonstrate in coexpression studies that p56Lck and p59Fyn phosphorylate CD28 primarily at Tyr-191 of the Tyr-Met-Asn-Met motif, inducing a 3- to 8-fold increase in p85 (subunit of PI 3-kinase) and GRB-2 SH2 binding to CD28. Phosphatase digestion of CD28 eliminated binding. In contrast to Src kinases, ZAP-70 and ITK failed to induce these events. Further, ITK binding to CD28 was dependent on the presence of p56Lck and is thus likely to act downstream of p56Lck/p59Fyn in a signaling cascade. p56Lck is therefore likely to be a central switch in T-cell activation, with the dual function of regulating CD28-mediated costimulation as well as TCR-CD3-CD4 signaling.
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PMID:p56Lck and p59Fyn regulate CD28 binding to phosphatidylinositol 3-kinase, growth factor receptor-bound protein GRB-2, and T cell-specific protein-tyrosine kinase ITK: implications for T-cell costimulation. 756 38

CD28 costimulatory signals are required for lymphokine production and T cell proliferation. CD28 signaling recruits the intracellular proteins PI 3-kinase, ITK, and GRB-2/SOS. PI 3-kinase and GRB-2/SOS bind the CD28 cytoplasmic pYMNM motif via SH2 domains. We generated CD28 pYMNM mutants and found that Y191 mutation (Y191CD28F) disrupted both PI 3-kinase and GRB-2 binding, while M194 mutation (M194CD28C) disrupted only PI 3-kinase binding. Both mutants still bound ITK. We have assessed the ability of these selective mutants to support IL-2 production upon TCR zeta/CD3 ligation in the presence of CHO-CD86 (B7-2) cells. Both Y191CD28F and M194CD28C mutants failed to generate IL-2. These data directly implicate PI 3-kinase in CD28-mediated costimulation leading to IL-2 secretion. Wortmannin, an inhibitor of PI 3-kinase, induced cell apoptosis and as such was unsuitable for use in this study.
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PMID:Selective CD28pYMNM mutations implicate phosphatidylinositol 3-kinase in CD86-CD28-mediated costimulation. 758 33

Protein-tyrosine kinases have been implicated in signal transduction in T lymphocytes after stimulation of many cell-surface molecules, including the T-cell antigen receptor, CD4, CD8, CD2, CD5, and CD28. Yet the identities of many of these tyrosine kinases remain unknown. We have isolated a murine tyrosine kinase gene, called Tsk for T-cell-specific kinase, that appears to be exclusively expressed in T lymphocytes. The Tsk cDNA clone encodes a polypeptide of 70 kDa, which is similar in sequence to both the src and abl families of tyrosine kinases. Sequence comparisons also indicate that Tsk contains one src-homology region 2 domain and one src-homology 3 domain but lacks the negative regulatory tyrosine (src Tyr-527) common to src-family kinases. In addition, Tsk expression is developmentally regulated. Steady-state Tsk mRNA levels are 5- to 10-fold higher in thymocytes than in peripheral T cells and increase in the thymus during mouse development from neonate to adult. Furthermore, Tsk is expressed in day 14 fetal thymus, suggesting a role for Tsk in early T-lymphocyte differentiation.
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PMID:Developmental regulation of a murine T-cell-specific tyrosine kinase gene, Tsk. 842 4

Functional T lymphocyte activation requires concurrent stimulation of the TCR complex and an accessory molecule, most frequently CD28. We have previously demonstrated that the TEC family tyrosine kinase EMT/ITK/TSK (EMT) is activated following cross-linking of CD28. We demonstrate herein that cross-linking of the CD3 component of the TCR complex also leads to EMT activation as indicated by a rapid and transient increase in EMT tyrosine phosphorylation and kinase activity in anti-EMT immunoprecipitates. However, although concurrent cross-linking of the TCR and CD28 results in a marked increase in production of the T cell growth factor IL-2, it does not result in a significant alteration in the magnitude or duration of EMT activation. Somatic cell mutants of the Jurkat T cell line, which lack the SRC family kinase LCK (JCaM1.6), fail to produce IL-2 when stimulated through the TCR complex. EMT activation, as evidenced by increased EMT tyrosine phosphorylation and EMT-associated kinase activity, was also greatly reduced following stimulation of the TCR in the JCaM1.6 Jurkat T cell mutants that lack LCK. In support of a role for LCK in EMT activation, reconstitution of the LCK-negative Jurkat T cell line by enforced expression of LCK restored TCR-mediated EMT activation. Taken together, the data indicate that the EMT tyrosine kinase is activated following cross-linking of the TCR, a process in which LCK likely plays an important role.
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PMID:The EMT/ITK/TSK (EMT) tyrosine kinase is activated during TCR signaling: LCK is required for optimal activation of EMT. 860 88

Activation of CD28 on T lymphocytes initiates a cascade of intracellular events, which in concert with activation of the T cell receptor, culminates in production of cytokines and a functional immune response. One of the earliest biochemical changes observed following stimulation of CD28 is tyrosine phosphorylation. We have demonstrated that both the LCK and the EMT/ITK/TSK (EMT) intracellular tyrosine kinases are activated following cross-linking of CD28. Utilizing somatic cell mutants lacking LCK, we demonstrate that functional LCK is required for CD28-induced activation of EMT as evidenced by increased tyrosine phosphorylation and kinase activity. In support of a role for LCK in EMT activation, reconstitution of a LCK-negative Jurkat T cell line by transfection with normal LCK recreates CD28-mediated EMT activation. Furthermore, co-transfection of LCK and EMT into COS-7 cells showed that EMT becomes phosphorylated in the presence of LCK. In addition, increases in EMT association with CD28 were eliminated in a LCK-negative Jurkat cell line, but were restored following transfection of wild type LCK. The data are most compatible with a model in which LCK, either directly or indirectly, initiates EMT activation and association with CD28 following ligation of CD28.
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PMID:Functional LCK Is required for optimal CD28-mediated activation of the TEC family tyrosine kinase EMT/ITK. 863 41

CD80 (B7-1) and CD86 (B7-2) ligation of CD28 provide co-stimulatory signals required for optimal lymphokine production in response to TCR zeta-CD3 ligation. CD28 binds to several intracellular proteins including phosphatidylinositol 3-kinase (Pl3-kinase), the tyrosine kinase ITK and the growth factor receptor-bound protein/Son of Sevenless (GRB-2/SOS) complex. Previously, we showed that TCR zeta-CD3 and CD28 co-stimulation required Pl3-kinase binding to the pYMNM motif of the cytoplasmic domain of the co-receptor. In this study, we have investigated whether CD28-associated Pl3-kinase is required for CD80 and CD86 co-stimulation, as well as in co-signaling that involves different primary signals (i.e. TCR zeta-CD3 versus phorbol ester/lonomycin). In the presence of anti-CD3, ligation of CD28 by both CD80 and CD86 was found to induce Pl3-kinase recruitment and IL-2 production. Furthermore, mutations at Y-191 and M-194 within the pYMNM motif blocked the ability of both ligands to induce IL-2. CD80 and CD86 therefore share a common signaling pathway leading to IL-2 production. By contrast, CD28 mediated co-stimulation involving receptor ligation plus phorbol ester/lonomycin induced IL-2 independent of Pl3-kinase binding to CD28. These data indicate that TCR zeta-CD3-dependent CD80 and CD86 co-signaling requires Pl3-kinase binding to the CD28pYMNM motif, while phorbol ester and lonomycin can bypass this requirement in CD28 co-stimulation.
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PMID:CD28 co-stimulatory regimes differ in their dependence on phosphatidylinositol 3-kinase: common co-signals induced by CD80 and CD86. 892 41

The CD28 cell surface receptor provides an important costimulatory signal for T cells necessary for their response to Ag. Early events in CD28 signaling include recruitment and activation of phosphatidylinositol 3-kinase (PI3-kinase) and activation of the protein tyrosine kinases (PTKs), LCK and EMT. Recruitment and activation of PI3-kinase is known to be dependent upon phosphorylation of tyrosine 173 of the CD28 cytoplasmic tail contained within a YMNM motif. By contrast, little is known of which residues of the CD28 tail, including tyrosines, are required for the activation of PTKs. To address this we studied the ability of truncation mutants and tyrosine to phenylalanine substitution mutants of the CD28 cytoplasmic tail to activate LCK and EMT in Jurkat T leukemia cells. Our results indicate that 1) activation of EMT is partially dependent upon tyrosine 173 of the CD28 tail, although it does not require PI3-kinase activation; 2) activation of LCK is independent of CD28 cytoplasmic tail tyrosine residues; and 3) elements sufficient for the activation of both kinases are contained within the first half of the tail. In addition we studied the CD28 tail as a substrate for both PTKs in in vitro kinase assays. We demonstrate that EMT can phosphorylate all four tyrosines of the CD28 tail, in contrast to LCK, which phosphorylates only tyrosine 173. Together with evidence that in vivo, tyrosines other than tyrosine 173 become phosphorylated following CD28 stimulation, this finding suggests that, like LCK, one function of EMT during CD28 signaling is phosphorylation of the receptor.
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PMID:Analysis of CD28 cytoplasmic tail tyrosine residues as regulators and substrates for the protein tyrosine kinases, EMT and LCK. 899 71

Development of IgE-mediated allergic conditions is dependent on the secretion of a Th2 cytokine pattern, including IL-4, IL-5, and IL-13. The induction of anergy would be one mechanism to abrogate cytokine secretion by Th2 cells, which may be pivotal to the allergic response. We demonstrate here that incubation of cloned human CD4+ phospholipase A2 (PLA)-specific Th2 cells with antigenic peptide, in the absence of professional APC, results in a state of nonresponsiveness. The anergic T cells failed to proliferate or secrete IL-4 in response to optimal stimulation with PLA and autologous, professional APC. Secretion of IL-5 and IL-13, however, was only partially inhibited. The anergic state of the Th2 cells was not associated with CD3 or CD28 down-regulation. However, anergy did appear to be closely related to alterations in signaling pathways, mediated through the TCR, of the cells. In contrast to untreated Th2 cells, anergized Th2 cells failed to respond to anti-CD3 mAb with either increased tyrosine kinase activity or increased levels of tyrosine phosphorylation of p56(lck) or ZAP70. A strong and sustained intracellular calcium flux, observed in untreated Th2 cells in response to anti-CD3 mAb, was absent in anergic Th2 cells. Furthermore, the induction of anergy seems to represent an active process, associated with increased levels of basal tyrosine kinase activity, cytokine production, and CD25 up-regulation in anergic Th2 cells. Together, our results indicate that anergy in Th2 cells is associated with defective transmembrane signaling through the TCR.
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PMID:Defective TCR stimulation in anergized type 2 T helper cells correlates with abrogated p56(lck) and ZAP-70 tyrosine kinase activities. 920 Apr 38

The Tec family of tyrosine kinases are involved in signals emanating from cytokine receptors, antigen receptors, and other lymphoid cell surface receptors. One family member, ITK (inducible T cell kinase), is involved in T cell activation and can be activated by the T cell receptor and the CD28 cell surface receptor. This stimulation of tyrosine phosphorylation and activation of ITK can be mimicked by the Src family kinase Lck. We have explored the mechanism of this requirement for Src family kinases in the activation of ITK. We found that coexpression of ITK and Src results in increased membrane association, tyrosine phosphorylation and activation of ITK, which could be blocked by inhibitors of the lipid kinase phosphatidylinositol 3-kinase (PI 3-kinase) as well as overexpression of the p85 subunit of PI 3-kinase. Removal of the Pleckstrin homology domain (PH) of ITK resulted in a kinase that could no longer be induced to localize to the membrane or be activated by Src. The PH of ITK was also able to bind inositol phosphates phosphorylated at the D3 position. Membrane targeting of ITK without the PH recovered its ability to be activated by Src. These results suggest that ITK can be activated by a combination of Src and PI 3-kinase.
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PMID:Src-induced activation of inducible T cell kinase (ITK) requires phosphatidylinositol 3-kinase activity and the Pleckstrin homology domain of inducible T cell kinase. 932 91


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