Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.10.2 (focal adhesion kinase)
 44,029 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Engagement of the TCR can induce different functional outcomes such as activation, proliferation, survival, or apoptosis. How the TCR-mediated signaling cascades generating these distinct cellular responses are organized on the molecular level is so far not completely understood. To obtain insight into this question, we analyzed TCR/CD8-mediated signaling events in mature OT-I TCR transgenic T cells under conditions of stimulation that lead to either proliferation or apoptosis. These experiments revealed major differences in the phosphorylation dynamics of LAT, ZAP70, protein kinase B, phospholipase C-gamma1, protein kinase D1, and ERK1/2. Moreover, input signals leading to apoptosis induced a strong, but transient activation of ERK1/2 mainly at sites of TCR-engagement. In contrast, stimuli promoting survival/proliferation generated a low and sustained activation of ERK1/2, which colocalizes with Ras in recycling endosomal vesicles. The transient activation of ERK1/2 under pro-apoptotic conditions of stimulation is at least partially due to the rapid polyubiquitination and subsequent degradation of ZAP70, whereas the sustained activation of ERK1/2 under survival promoting conditions is paralleled by the induction/phosphorylation of anti-apoptotic molecules such as protein kinase B and Bcl-x(L). Collectively, our data provide signaling signatures that are associated with proliferation or apoptosis of T cells.
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PMID:Dynamics of proximal signaling events after TCR/CD8-mediated induction of proliferation or apoptosis in mature CD8+ T cells. 1845 90

Phospho-site specific antibodies become increasingly available, enabling the study of signaling events by Western blotting (WB) or intracellular flow cytometry (Phospho-Flow). Here we compared data generated by WB or Phospho-Flow regarding the kinetics and degree of phosphorylation of membrane proximal TCR signaling molecules. Phosphorylation events in Jurkat T cells were triggered by anti-CD3 stimulation (OKT3) or by oxidative stress (H(2)O(2)) and were analyzed by Phospho-Flow or WB. Both techniques showed that OKT3- or H(2)O(2)-induced, transient phosphorylation of ZAP70 or LAT was dependent on functional Lck. Phospho-Flow data revealed differences in the kinetics and the degree of H(2)O(2)- or OKT3-mediated protein phosphorylation compared with WB data. In addition, using Phospho-Flow we discovered that H(2)O(2)-induced phosphorylation of TCR signaling proteins was inhibited by small molecular weight kinase inhibitors far more potently than OKT3-triggered protein phosphorylation, despite a superior induction of phosphorylation by H(2)O(2). This finding was confirmed by WB. Interestingly, we identified by Phospho-Flow that, in P116 Jurkat cells lacking ZAP70 protein expression, H(2)O(2) potently triggered the phosphorylation of ZAP70 residues Y493 and Y292 but not Y319. The phosphorylation of these ZAP70 tyrosine residues cells was blocked by an Lck inhibitor, suggesting the existence of an Lck-coupled truncated ZAP70 protein or a novel isoform of ZAP70 in P116 cells. Phospho-Flow is a largely quantitative technology with excellent throughput, highly suited in studying the function or inhibition of TCR signaling pathways and allowing the detection of novel pathway insights. It can serve as a good complement to Western blot analysis.
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PMID:Intracellular Phospho-Flow cytometry reveals novel insights into TCR proximal signaling events. A comparison with Western blot. 1854 11

Resistance of T cells to activation-induced cell death (AICD) is associated with autoimmunity and lymphoproliferation. We found that apigenin (4',5,7-trihydroxyflavone), a non-mutagenic dietary flavonoid, augmented both extrinsic and intrinsic pathways of apoptosis in recurrently activated, but not in primarily stimulated, human blood CD4+ T cells. Apigenin potentiated AICD by inhibiting NF-kappaB activation and suppressing NF-kappaB-regulated anti-apoptotic molecules, cFLIP, Bcl-x(L), Mcl-1, XIAP and IAP, but not Bcl-2. Apigenin suppressed NF-kappaB translocation to nucleus and inhibited IkappaBalpha phosphorylation and degradation in response to TCR stimulation in reactivated peripheral blood CD4 T cells, as well as in leukemic Jurkat T cell lines. Among the pathways that lead to NF-kappaB activation upon TCR stimulation, apigenin selectively inhibited PI3K-PKB/Akt, but not PKC-theta activation in the human T cells, and synergized with a PI3K inhibitor to markedly augment AICD. Apigenin also suppressed expression of anti-apoptotic cyclooxygenase 2 (COX-2) protein in activated human T cells, but it did not affect activation of Erk MAPKinase. Thus, in chronically activated human T cells, relatively non-toxic apigenin can suppress anti-apoptotic pathways involving NF-kappaB activation, and especially cFLIP and COX-2 expression that are important for functioning and maintenance of immune cells in inflammation, autoimmunity and lymphoproliferation.
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PMID:Apigenin, a dietary flavonoid, sensitizes human T cells for activation-induced cell death by inhibiting PKB/Akt and NF-kappaB activation pathway. 1881 89

In CD45-deficient animals, there is a severe defect in thymocyte-positive selection, resulting in an absence of mature T cells and the accumulation of thymocytes at the DP stage of development. However, the signaling defect(s) responsible for the block in development of mature single-positive T cells is not well characterized. Previous studies have found that early signal transduction events in CD45-deficient cell lines and thymocytes are markedly diminished following stimulation with anti-CD3. Nevertheless, there are also situations in which T cell activation and TCR signaling events can be induced in the absence of CD45. For example, CD45-independent TCR signaling can be recovered upon simultaneous Ab cross-linking of CD3 and CD4 compared with cross-linking of CD3 alone. These data suggest that CD45 may differentially regulate TCR signaling events depending on the nature of the signal and/or on the differentiation state of the cell. In the current study, we have assessed the role of CD45 in regulating primary thymocyte activation following physiologic stimulation with peptide. Unlike CD3-mediated stimulation, peptide stimulation of CD45-deficient thymocytes induces diminished, but readily detectable TCR-mediated signaling events, such as phosphorylation of TCR-associated zeta, ZAP70, linker for activation of T cells, and Akt, and increased intracellular calcium concentration. In contrast, phosphorylation of ERK, which is essential for positive selection, is more severely affected in the absence of CD45. These data suggest that CD45 has a selective role in regulating different aspects of T cell activation.
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PMID:Selective regulation of TCR signaling pathways by the CD45 protein tyrosine phosphatase during thymocyte development. 1894 Nov 97

Imatinib mesylate (Gleevec, STI571), a selective inhibitor of a restricted number of tyrosine kinases, has been effectively used for the treatment of Philadelphia chromosome-positive leukemias and gastrointestinal stromal tumors. Imatinib may also directly influence immune cells. Suppressive as well as stimulating effects of this drug on CD4(+) and CD8(+) T lymphocytes or dendritic cells have been reported. In the current study, we have investigated the influence of imatinib mesylate on CD4(+)CD25(+)FoxP3(+) regulatory T cells (Treg), a critical population of lymphocytes that contributes to peripheral tolerance. Used at concentrations achieved clinically, imatinib impaired Treg immunosuppressive function and FoxP3 expression but not production of IL-10 and TGF-beta in vitro. Imatinib significantly reduced the activation of the transcription factors STAT3 and STAT5 in Treg. Analysis of Treg TCR-induced signaling cascade indicated that imatinib inhibited phosphorylation of ZAP70 and LAT. Substantiating these observations, imatinib treatment of mice decreased Treg frequency and impaired their immunosuppressive function in vivo. Furthermore, imatinib mesylate significantly enhanced antitumor immune responses to dendritic cell-based immunization against an imatinib-resistant BCR-ABL negative lymphoma. The clinical applications of imatinib mesylate might thus be expanded with its use as a potent immunomodulatory agent targeting Treg in cancer immunotherapy.
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PMID:Imatinib mesylate inhibits CD4+ CD25+ regulatory T cell activity and enhances active immunotherapy against BCR-ABL- tumors. 1898 Nov 15

On their entry into the thymus, developing lymphocyte progenitors depend on signaling from the pre-T cell receptor (pre-TCR), which orchestrates differentiation, cell proliferation, and survival. The exact mechanism of pre-TCR-mediated suppression of T cell death remains unclear and controversial. Here, we identify Bim and Bid, 2 members of the BH3-only group of the BCL2 family, as important regulators of pre-T cell death. Both factors are highly expressed in proapoptotic thymocytes and their expression is suppressed on signaling through the pre-TCR. Their expression is directly regulated by the transcription factors FoxO3a and p53. Bid expression and p53 activity are related to the ongoing rearrangement of the TCR loci and induced DNA damage responses. Bim expression and FoxO3a nuclear translocation are directly controlled by the pre-TCR by means of its downstream kinase Akt/PKB. Interestingly, deletion of either gene on a pre-TCR(-/-) background rescues survival, but fails to induce further progenitor differentiation uncoupling the 2 processes.
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PMID:Regulation of lymphocyte progenitor survival by the proapoptotic activities of Bim and Bid. 1908 89

The highly homologous proteins ezrin, radixin, and moesin link proteins to the actin cytoskeleton. The two family members expressed in T cells, ezrin and moesin, are implicated in promoting T cell activation and polarity. To elucidate the contributions of ezrin and moesin, we conducted a systematic analysis of their function during T cell activation. In response to TCR engagement, ezrin and moesin were phosphorylated in parallel at the regulatory threonine, and both proteins ultimately localized to the distal pole complex (DPC). However, ezrin exhibited unique behaviors, including tyrosine phosphorylation and transient localization to the immunological synapse before movement to the DPC. To ask whether these differences reflect unique requirements for ezrin vs moesin in T cell signaling, we generated mice with conditional deletion of ezrin in mature T cells. Ezrin-/- T cells exhibited normal immunological synapse organization based upon localization of protein kinase C-theta, talin, and phospho-ZAP70. DPC localization of CD43 and RhoGDP dissociation inhibitor, as well as the novel DPC protein Src homology region 2 domain-containing phosphatase-1, was also unaffected. However, recruitment of three novel DPC proteins, ezrin binding protein of 50 kDa, Csk binding protein, and the p85 subunit of PI3K was partially perturbed. Biochemical analysis of ezrin-/- T cells or T cells suppressed for moesin using small interfering RNA showed intact early TCR signaling, but diminished levels of IL-2. The defects in IL-2 production were more pronounced in T cells deficient for both ezrin and moesin. These cells also exhibited diminished phospholipase C-gamma1 phosphorylation and calcium flux. We conclude that despite their unique movement and phosphorylation patterns, ezrin and moesin function together to promote T cell activation.
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PMID:Ezrin and moesin function together to promote T cell activation. 1912 45

The Mycobacterium tuberculosis early secreted Ag of 6 kDa (ESAT-6) is a potent Ag for human T cells and is a putative vaccine candidate. However, ESAT-6 also contributes to virulence in animal models, mediates cellular cytolysis, and inhibits IL-12 production by mononuclear phagocytes. We evaluated the effects of ESAT-6 and its molecular chaperone, culture filtrate protein of 10 kDa (CFP10), on the capacity of human T cells to produce IFN-gamma and proliferate in response to TCR activation. Recombinant ESAT-6, but not CFP10, markedly inhibited IFN-gamma production by T cells stimulated with M. tuberculosis or with the combination of anti-CD3 and anti-CD28, in a dose-dependent manner. ESAT-6 also inhibited T cell production of IL-17 and TNF-alpha but not IL-2. Preincubation of ESAT-6 with CFP10 under conditions that favor dimer formation did not affect inhibition of IFN-gamma. ESAT-6 decreased IFN-gamma transcription and reduced expression of the transcription factors, ATF-2 and c-Jun, which normally bind to the IFN-gamma proximal promoter and stimulate mRNA expression. ESAT-6 inhibited T cell IFN-gamma secretion through mechanisms that did not involve cellular cytotoxicity or apoptosis. ESAT-6, but not CFP10, bound to T cells and inhibited expression of early activation markers without reducing activation of ZAP70. We conclude that ESAT-6 directly inhibits human T cell responses to mycobacterial Ags by affecting TCR signaling pathways downstream of ZAP70.
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PMID:ESAT-6 inhibits production of IFN-gamma by Mycobacterium tuberculosis-responsive human T cells. 1926 45

Pertussis toxin (PTx) has been shown to exert a variety of effects on immune cells independent of its ability to ADP-ribosylate G proteins. Of these effects, the binding subunit of PTx (PTxB) has been shown to block signaling via the chemokine receptor CCR5, but the mechanism involved in this process is unknown. Here, we show that PTxB causes desensitization of a related chemokine receptor, CXCR4, and explore the mechanism by which this occurs. CXCR4 is the receptor for the chemokine stromal cell-derived factor 1alpha (SDF-1alpha) and elicits a number of biological effects, including stimulation of T cell migration. PTxB treatment causes a decrease in CXCR4 surface expression, inhibits G protein-associated signaling, and blocks SDF-1alpha-mediated chemotaxis. We show that PTxB mediates these effects by activating the TCR signaling network, as the effects are dependent on TCR and ZAP70 expression. Additionally, the activation of the TCR with anti-CD3 mAb elicits a similar set of effects on CXCR4 activity, supporting the idea that TCR signaling leads to cross-desensitization of CXCR4. The inhibition of CXCR4 by PTxB is rapid and transient; however, the catalytic activity of PTx prevents CXCR4 signaling in the long term. Thus, the effects of PTx holotoxin on CXCR4 signaling can be divided into two phases: short term by the B subunit, and long term by the catalytic subunit. These data suggest that TCR crosstalk with CXCR4 is likely a normal cellular process that leads to cross-desensitization, which is exploited by the B subunit of PTx.
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PMID:Pertussis toxin signals through the TCR to initiate cross-desensitization of the chemokine receptor CXCR4. 1938 Aug 20

Translocations of proto-oncogenes to the B-cell or T-cell antigen receptor loci in acute T- or B-cell leukemia and lymphoma have been, in most cases, accredited to V(D)J or switch recombination depending on the location of the breakpoint at the receptor locus. Only in rare instances, the reports take into account mechanistic characteristics of the translocation mechanism. To assess the functional ability of several sites implicated in supposedly V(D)J-mediated translocations, we tested five sites at four proto-oncogene loci in an ex vivo recombination substrate assay for their potential to act as direct target for V(D)J recombination. Our results show that the LMO2/RBTN2/TTG2 site and one LCK/P56 site readily engage in recombination with a genuine TCR element with the majority of breakpoint junctions showing the characteristics of V(D)J recombination, which strongly supports the involvement of this mechanism in the pathogenesis of the corresponding translocations in vivo. The site at the TLX1/HOX11 locus yielded 0.8% V(D)J-specific junctions. Sites at the LCK/P56 and TCF3/E2A proto-oncogenes resulted in exclusively unspecific breakpoints scattered over part of or the entire proto-oncogene region tested, marking them as unlikely V(D)J recombination targets. Our data suggest that, while being a potentially dangerous mechanism due to the introduction of DNA breaks, V(D)J recombination is a tightly controlled mechanism allowing for only few direct mistakes.
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PMID:V(D)J targeting mistakes occur at low frequency in acute lymphoblastic leukemia. 1945 8


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