G-proteins are not directly involved in the CD3-antigen-mediated production of inositol phosphates in HPB-ALL T-leukaemia cells expressing phospholipase C isoforms gamma 1 and beta 3

Ovalbumin Antigen-Specific Activation of Human T Cell Receptor Closely Resembles Soluble Antibody Stimulation as Revealed by BOOST Phosphotyrosine Proteomics

Activation of the T cell receptor (TCR) leads to a network of early signaling predominantly orchestrated by tyrosine phosphorylation in T cells. The TCR is commonly activated using soluble anti-TCR antibodies, but this approach is not antigen-specific. Alternatively, activating the TCR using specific antigens of a range of binding affinities in the form of a peptide-major histocompatibility complex (pMHC) is presumed to be more physiological. However, due to the lack of wide-scale phosphotyrosine (pTyr) proteomic studies directly comparing anti-TCR antibodies and pMHC, a comprehensive definition of these activated states remains enigmatic. Elucidation of the tyrosine phosphoproteome using quantitative pTyr proteomics enables a better understanding of the unique features of these activating agents and the role of ligand binding affinity on signaling. Here, we apply the recently established Broad-spectrum Optimization Of Selective Triggering (BOOST) to examine perturbations in tyrosine phosphorylation of human TCR triggered by anti-TCR antibodies and pMHC. Our data reveal that high-affinity ovalbumin (OVA) pMHC activation of the human TCR triggers a largely similar, albeit potentially stronger, pTyr-mediated signaling regulatory axis compared to the anti-TCR antibody. The signaling output resulting from OVA pMHC variants correlates well with their weaker affinities, enabling affinity-tunable control of signaling strength. Collectively, we provide a framework for applying BOOST to compare pTyr-mediated signaling pathways of human T cells activated in an antigen-independent and antigen-specific manner.

Effects of cadmium and vanadium ions on antigen-induced signaling in CD4(+) T cells

Heavy metal environmental pollutants modulate antigen-directed responses by T lymphocytes, but the molecular mechanisms by which certain metal ions exert their effects are only poorly understood. We tested the hypothesis that cadmium and vanadium ions alter antigen-induced T cell signal transduction pathways in CD4(+) T helper cells. We used CD4(+) primary T lymphocytes and splenic T cells from DO.11.10 T cell receptor transgenic mice. We determined the effects of cadmium chloride and sodium orthovanadate at concentrations that did not induce apoptotic cell death, but affected cytokine or proliferation responses to antigenic stimulation. We used electrophoretic mobility shift assays to measure effects of cadmium and vanadium ions on antigen-induced activation of the nuclear transcriptional regulator proteins, nuclear factor-kappaB, cyclic AMP response element binding protein, nuclear factor of activated T cells, and activator protein-1. Different signaling pathways lead to activation of these transcription factors. Our results suggest that the two heavy metal ions differentially affect signaling pathways. This knowledge will help in the development of molecular epidemiological assays.

Mobilization of intracellular Ca2+ by adenine nucleotides in human T-leukaemia cells: evidence for ADP-specific and P2y-purinergic receptors

The expression of purinergic receptors on human T-cells was investigated and the receptors were shown to be functionally coupled to intracellular signals in two out of eight T-leukaemia cell-lines. Addition of adenine nucleotides resulted in mobilization of intracellular Ca2+ in HPB-ALL cells and a cell line (CB1) recently isolated from a patient with T-acute lymphoblastic leukaemia. Of a range of nucleotides tested only ADP and ATP elevated intracellular levels of Ca2+, with ADP being the more potent agonist. Ca2+ mobilization by ATP was accompanied by increased inositol phosphate production and was blocked by the purinergic receptor antagonist, Reactive Blue 2, indicating that ATP was interacting with a P2y receptor. Intracellular Ca2+ release triggered by ADP was independent of both inositol phosphate production and protein tyrosine phosphorylation. Expression of the transmembrane phosphotyrosine phosphatase, CD45, had no effect on ADP-stimulated Ca2+ mobilization. Our results show that functional P2y receptors can be expressed on T-cells, and also identify a novel T-cell ADP receptor. Signals mediated by these purinergic receptors could play important roles in modulating T-cell function.

Selective coupling of the T cell antigen receptor to phosphoinositide-derived diacylglycerol production in HPB-ALL T cells correlates with CD45-regulated p59fyn activity

In HPB-ALL T-cells the p59fyn tyrosine kinase is regulated by the CD45 phosphotyrosine phosphatase and plays a critical role in coupling the T cell receptor (TCR) to the generation of intracellular signals which include diacylglycerol (DAG) production and protein kinase C activation. The aim of this study was to determine the phospholipid pools from which the DAG is generated and to identify which phospholipase activities are regulated by the TCR. When CD45+ cells were pre-labeled with [3H]arachidonic acid, CD3-antigen cross-linking stimulated negligible increases in both [3H]DAG and [3H]phosphatidic acid (PA). However, CD3 monoclonal antibody (mAb) induced an increase of 300% in [3H]PA when the cells were permeabilized with streptolysin-O, and this correlated with increased levels of protein tyrosine phosphorylation. Stimulation of [3H]PA production upon CD3 cross-linking was 77% lower in permeabilized CD45- cells than in CD45+ cells, consistent with the reduced activity of p59fyn in CD45- cells. The stimulated production of PA was not mediated by activation of phospholipase D (PLD), although the presence of a G-protein-regulated PLD activity was established. The CD3-induced increase in total inositol phosphates (InsP) in permeabilized cells was similar to the stimulated production of [3H]PA production in both CD45+ and CD45- cells. Dose-response curves for InsP and PA production triggered by CD3 mAb were super-imposable and the production of InsP and PA over a range of Ca2+ concentrations was comparable. Differential labeling of phospholipids with 3H-labeled fatty acids revealed that CD3-induced PA production reflected incorporation of label into the phosphatidylinositol pool. Our data suggest that in HPB-ALL cells the production of DAG following CD3-antigen cross-linking can be fully accounted for by the selective coupling of the TCR to breakdown of phosphatidylinositol-(4,5)-bisphosphate as the result of phospholipase C gamma 1 activation. This event correlates with the activity of the CD45-regulated TCR-associated tyrosine kinase, p59fyn.