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)

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an important regulator of T cell homeostasis. Ligation of this receptor leads to prominent downregulation of T cell proliferation, mainly as a consequence of interference with IL-2 production. We here report that CTLA-4 engagement strikingly selectively shuts off activation of downstream T cell receptor (TCR)/CD28 signaling events, i.e., activation of the microtubule-associated protein kinase (MAPKs) ERK and JNK. In sharp contrast, proximal TCR signaling events such as ZAP70 and TCR-zeta chain phosphorylation are not affected by CTLA-4 engagement on activated T cells. Since activation of the ERK and JNK kinases is required for stimulation of interleukin (IL)-2 transcription, these data provide a molecular explanation for the block in IL-2 production imposed by CTLA-4.
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PMID:Cytotoxic T lymphocyte antigen 4 (CTLA-4) interferes with extracellular signal-regulated kinase (ERK) and Jun NH2-terminal kinase (JNK) activation, but does not affect phosphorylation of T cell receptor zeta and ZAP70. 936 25

The co-stimulatory antigen CD28 has been shown to bind to several intracellular proteins including phosphatidylinositol 3-kinase, growth factor receptor-bound protein 2 (Grb2), and ITK. Paradoxically, Grb2 and phosphatidylinositol 3-kinase binding has been mapped to a similar pYMNM motif within the CD28 cytoplasmic tail. Given the importance of CD28 co-signaling to T cell function, questions exist regarding the mechanism by which Grb2 binds to CD28, and whether the interaction plays a role in co-stimulation. To biochemically characterize Grb2/CD28 binding, we initially utilized glutathione S-transferase-Grb2 fusion proteins carrying inactivating mutations within the SH2 and SH3 domains of Grb2, and assessed their ability to bind to CD28. In vitro binding experiments indicated that the Grb2 SH2 domain is critical for the association, while the SH3 domain plays an additional role in facilitating optimal binding. Enhanced binding via the SH3 domains was not observed when the C-terminal PXXP motif within CD28 was disrupted, thereby indicating that both SH2 and SH3 domains contribute to CD28 binding. Mutations that alter Grb2 binding were found to block the CD28-dependent interleukin-2 production. Further, tyrosine phosphorylation of Vav and the costimulation-dependent activation of Jun N-terminal kinase was blocked in cells defective in CD28/Grb2 binding. These results provide evidence for an alternate CD28-mediated signaling process involving Grb2 binding to the co-receptor.
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PMID:Growth factor receptor-bound protein 2 SH2/SH3 domain binding to CD28 and its role in co-signaling. 941 79

Optimal T cell activation requires crosslinking of the T cell receptor (TCR) concurrently with an accessory receptor, most efficiently CD28. Crosslinking of CD28 leads to increased interleukin 2 (IL2) production, inhibition of anergy and prevention of programmed cell death. Crosslinking of CD28 leads to rapid increases in tyrosine phosphorylation of specific intracellular substrates including CD28 itself. Since CD28 does not encode an intrinsic tyrosine kinase domain, CD28 must activate an intracellular tyrosine kinase(s). Indeed, crosslinking of CD28 increases the activity of the intracellular tyrosine kinases EMT/ITK and LCK. The phosphatidylinositol 3-kinase (PI3K) and GRB2 binding site in CD28 is dispensable for optimal IL2 production in Jurkat T cells. We demonstrate herein that murine Y170 (equivalent to human Y173) in CD28 is also dispensable for activation of the SRC family tyrosine kinase LCK and the TEC family tyrosine kinase EMT/ITK. In contrast, the distal three tyrosines in CD28 are required for optimal IL2 production as well as for optimal activation of the LCK and EMT/ITK tyrosine kinases. The distal three tyrosines of CD28, however, are not required for recruitment of PI3K to CD28. Furthermore, PI3K is recruited to CD28 in JCaM1 cells which lack LCK and in which EMT/ITK is not activated by ligation of CD28. Thus optimal activation of LCK or EMT/ITK is not obligatory for recruitment of PI3K to CD28 and thus is also not required for tyrosine phosphorylation of the YMNM motif in CD28. Taken together the data indicate that the distal three tyrosines in CD28 are integral to the activation of LCK and EMT/ITK and for subsequent IL2 production.
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PMID:Efficient CD28 signalling leads to increases in the kinase activities of the TEC family tyrosine kinase EMT/ITK/TSK and the SRC family tyrosine kinase LCK. 949 76

T lymphocytes express a range of tyrosine kinases that are involved in signalling processes driving cell activation, proliferation and differentation. Two tyrosine kinases expressed only in T cells, the Itk/Emt and Txk gene products, are members of the Tec family of kinases. The role of Tec kinases in cellular function is poorly understood, although a Tec kinase specific to B cells, Btk, is essential for B-cell development. To explore the contribution of the T-cell-specific Tec kinases to lymphocyte function, we have expressed human Txk in the baculovirus system and conducted the first characterization of its activity. We find that Txk exhibits a substrate preference in vitro quite distinct from that of the major T-cell kinases Lck and ZAP70, suggesting that Tec-family kinases might act on a distinct range of substrates. We also investigated the interactions of Txk with the cytoplasmic domains of the key signalling molecules CD3zeta, CD28 and CTLA4 and find that none of these are phosphorylated by Txk, nor are they ligands for the SH2 or SH3 domains of Txk. We conclude that it is unlikely that Txk has a role in the early signal transduction events associated with these key pathways controlling T-cell activation.
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PMID:Functional analysis of the T-cell-restricted protein tyrosine kinase Txk. 976 24

CTLA-4 and CD28 are differentially expressed on T-cells. They bind to a common ligand B71/2 (CD80/86), however with different avidities. Unlike CD28 which augments the T-cell response, CTLA-4 operates predominately as a negative regulator of T-cell proliferation. The mechanism by which CTLA-4 can generate these intracellular signals is unclear. Little is known regarding the identity of the protein-tyrosine kinase(s) responsible for CTLA-4 phosphorylation and thus creating conditions for the reported binding to PI 3-kinase and the protein tyrosine phosphatase SHP-2. In this study, we demonstrate that Rlk (resting lymphocyte kinase) is capable of phosphorylating CTLA-4 at the YVKM motif. Consistent with this finding, Rlk is capable of providing conditions for the binding of the SH2 domains of PI 3-kinase to the receptor. CTLA-4 is therefore the first known substrate for Rlk suggesting the possibility that this kinase may participate in CTLA-4 function.
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PMID:Resting lymphocyte kinase (Rlk/Txk) phosphorylates the YVKM motif and regulates PI 3-kinase binding to T-cell antigen CTLA-4. 981 38

Ligation of the TCR or CD28 induces activation of phosphatidylinositol 3-kinase (PI3K), the TEC family protein tyrosine kinase, EMT/ITK/TSK (EMT), and the SRC family tyrosine kinase, LCK. LCK is required for the activation and phosphorylation of EMT induced by ligation of the TCR or CD28 placing LCK upstream of EMT in T cell signaling cascades. We report herein that inhibition of PI3K activity with the specific inhibitors LY294002 and wortmannin markedly decreased EMT activation induced by CD28 cross-linking but not by CD3 cross-linking. Further, inhibition of PI3K markedly decreased EMT in vitro autokinase activity induced by activated LCK. In contrast, PI3K inhibitors did not alter CD28 or CD3 cross-linking or LCK-induced EMT phosphorylation. Consistent with the requirement of PI3K activity for CD28 but not CD3-induced stimulation of the EMT in vitro autokinase activity, a small but significant portion of cellular EMT associates with PI3K following CD28 cross-linking but not following CD3 cross-linking. CD28-induced association of EMT with PI3K also requires functional expression of LCK. Fusion proteins containing the SRC homology 2 domain of EMT interact with PI3K or a PI3K-associated molecule in a tyrosine phosphorylation-dependent manner. Taken together, the data suggest that EMT is differentially regulated and recruited to different signaling complexes following ligation of CD28 or the TCR complex, perhaps contributing to the disparate roles that EMT appears to play downstream of CD28 and the TCR.
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PMID:Phosphatidylinositol 3-kinase is required for CD28 but not CD3 regulation of the TEC family tyrosine kinase EMT/ITK/TSK: functional and physical interaction of EMT with phosphatidylinositol 3-kinase. 982 May 15

Beta1 integrins can provide T cell co-stimulation, but little is known concerning their downstream signaling pathways. We found that Pyk2, a focal adhesion kinase-related tyrosine kinase, is regulated by beta1 integrin signaling in human T cells. Stimulation of Jurkat T cells with the alpha4beta1 integrin ligand VCAM-1 results in Pyk2 tyrosine phosphorylation, and combined stimulation with VCAM-1 and anti-CD3 mAb induces rapid and sustained synergistic Pyk2 phosphorylation. Studies with mAb suggest that in synergistic CD3- and alpha4beta1 integrin-mediated Pyk2 tyrosine phosphorylation, a major contribution of CD3-derived signals is independent of their effects on regulating integrin adhesion. Analysis of resting human CD4+ T cells confirmed the ability of CD3-derived signals to synergize with beta1 integrin-dependent signals in the induction of Pyk2 tyrosine phosphorylation. In addition, although CD28-mediated co-stimulatory signals were able to synergize with CD3-mediated signals in inducing ERK and JNK activation and secretion of IL-2 in the primary T cells, they did not contribute to the induction of Pyk2 phosphorylation. Taken together, these results indicate a potential role for Pyk2 in T cell co-stimulation mediated specifically by beta1 integrins.
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PMID:Pyk2 is differentially regulated by beta1 integrin- and CD28-mediated co-stimulation in human CD4+ T lymphocytes. 984 30

The Tec protein-tyrosine kinase family includes Btk, Itk/Tsk/Emt, Tec, Rlk/Txk, and Bmx which are involved in signals mediated by various cytokines or antigen receptors. Itk is expressed primarily in T cells and activated by TCR/CD3, CD28, and CD2. However, the defect in T cell signaling in itk-deficient mice is very modest. Thus, we looked for other Tec family kinases that could be expressed in lymphoid cells and involved in T cell signal transduction. Here, we demonstrate that Tec, expressed in T cells, is activated following TCR/CD3 or CD28 ligation and interacts with CD28 receptor in an activation-dependent manner. This interaction involves the Tec SH3 domain and the proline-rich motifs in CD28. We also show that Tec can phosphorylate p62(dok), one CD28-specific substrate, whereas Itk cannot. Overexpression of Tec but not Itk can enhance the interleukin-2 promoter activity mediated by TCR/CD3 or CD28 stimulation and introduction of a kinase-dead Tec but not Itk can suppress interleukin-2 expression, indicating that Tec is directly involved in T cell activation. Altogether, these data demonstrate that Tec kinase is an integral component of T cell signaling and that the two Tec family kinases, Tec and Itk, have distinct roles in T cell activation.
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PMID:The role of Tec protein-tyrosine kinase in T cell signaling. 987 94

Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4) is a cell surface receptor expressed on activated T cells that can inhibit T cell responses induced by activation of the TCR and CD28. Studies with phosphorylated peptides based on the CTLA-4 intracellular domain have suggested that tyrosine phosphorylation of CTLA-4 may regulate its interactions with cytoplasmic proteins that could determine its intracellular trafficking and/or signal transduction. However, the kinase(s) that phosphorylate CTLA-4 remain uncharacterized. In this report, we show that CTLA-4 can associate with the Src kinases Fyn and Lck and that transfection of Fyn or Lck, but not the unrelated kinase ZAP70, can induce tyrosine phosphorylation of CTLA-4 on residues Y201 and Y218. A similar pattern of tyrosine phosphorylation was found in pervanadate-treated Jurkat T cells stably expressing CTLA-4. Phosphorylation of CTLA-4 Y201 in Jurkat cells correlated with cell surface accumulation of CTLA-4. CTLA-4 phosphorylation induced the association of CTLA-4 with the tyrosine phosphatase SHP-2, but not with phosphatidylinositol 3-kinase. In contrast, Lck-induced phosphorylation of CD28 resulted in the recruitment of phosphatidylinositol 3-kinase, but not SHP-2. These findings suggest that phosphorylation of CD28 and CTLA-4 by Lck activates distinct intracellular signaling pathways. The association of CTLA-4 with Src kinases and with SHP-2 results in the formation of a CTLA-4 complex with the potential to regulate T cell activation.
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PMID:Regulation of cytotoxic T lymphocyte-associated molecule-4 by Src kinases. 997 79

Protein tyrosine kinases are critical for the function of CD28 in T cells. We examined whether the tyrosine kinases Pyk2 and Fak (members of the focal adhesion kinase family) are involved in CD28 signaling. We found that ligating CD28 in Jurkat T cells rapidly increases the tyrosine phosphorylation of Pyk2 but not of Fak. Paxillin, a substrate for Pyk2 and Fak, was not tyrosine-phosphorylated after CD28 ligation. CD28-induced tyrosine phosphorylation of Pyk2 was markedly reduced in the absence of external Ca2+. Previous studies have shown that the T cell antigen receptor (TCR) induces tyrosine phosphorylation of Pyk2. In this report, the concurrent ligation of CD28 and TCR increased tyrosine phosphorylation of Pyk2; however, the extent of phosphorylation by both receptors was equivalent to the sum of that induced by each receptor alone. The Syk/Zap inhibitor piceatannol blocked CD28, and TCR induced tyrosine phosphorylation of Pyk2, suggesting that Syk/Zap is involved in Pyk2 phosphorylation. In contrast, the phosphatidylinositol 3-kinase inhibitor wortmannin blocked TCR- but not CD28-induced phosphorylation of Pyk2, suggesting that CD28 and TCR activate distinct pathways to induce tyrosine phosphorylation of Pyk2. Notably, depleting phorbol 12-myristate 13-acetate-sensitive protein kinase C did not block CD28- and CD3-induced tyrosine phosphorylation of Pyk2. These data provide evidence for the involvement of Pyk2 in the CD28 signaling cascade and suggest that neither Fak nor paxillin is involved in the signaling pathways of CD28.
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PMID:CD28 ligation induces tyrosine phosphorylation of Pyk2 but not Fak in Jurkat T cells. 1003 72


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