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Previously we demonstrated that human glioblastoma cell lines induce apoptosis in peripheral blood T cells through partial involvement of secreted gangliosides. Here we show that GBM-derived gangliosides induce apoptosis through involvement of the TNF receptor and activation of the caspase cascade. Culturing T lymphocytes with GBM cell line derived gangliosides (10-20 μg/ml) demonstrated increased ROS production as early as 18 hrs as indicated by increased uptake of the dye H2DCFDA while western blotting demonstrated mitochondrial damage as evident by cleavage of Bid to t-Bid and by the release of cytochrome-c into the cytosol. Within 48-72 hrs apoptosis was evident by nuclear blebbing, trypan blue positivity and annexinV/7AAD staining. GBM-ganglioside induced activation of the effector caspase-3 along with both initiator caspases (-9 and -8) in T cells while both the caspase-8 and -9 inhibitors were equally effective in blocking apoptosis (60% protection) confirming the role of caspases in the apoptotic process. Ganglioside-induced T cell apoptosis did not involve production of TNF-α since anti-human TNFα antibody was unable to protect T cells from nuclear blebbing and subsequent cell death. However, confocal microscopy demonstrated co-localization of GM2 ganglioside with the TNF receptor and co-immunoprecipitation experiments showed recruitment of death domains FADD and TRADD with the TNF receptor post ganglioside treatment, suggesting direct interaction of gangliosides with the TNF receptor. Further confirmation of the interaction between GM2 and TNFR1 was obtained from confocal microscopy data with wild type and TNFR1 KO (TALEN mediated) Jurkat cells, which clearly demonstrated co-localization of GM2 and TNFR1 in the wild type cells but not in the TNFR1 KO clones. Thus, GBM-ganglioside can mediate T cell apoptosis by interacting with the TNF receptor followed by activation of both the extrinsic and the intrinsic pathway of caspases.

Genetically susceptible rodents exposed to low nontoxic levels of inorganic mercury (Hg(2+)) develop idiosyncratic autoimmune disease associated with defective T-cell function. However, the molecular mechanisms underlying this phenomenon remain mostly unexplained. Brief exposure of T cells to micromolar concentrations of Hg(2+) leads to physiologically relevant nontoxic cellular mercury burdens, and as we have previously reported, attenuates T-cell receptor (TCR) signal strength by approximately 50%. We have found this to be the result of an inadequate activation of the tyrosine kinase ZAP-70, which is hypophosphorylated following TCR stimulation in Hg(2+) burdened cells when compared to untreated controls. In T cells, ZAP-70 phosphorylation is dependent on lymphocyte-specific protein tyrosine kinase (Lck) activity, which in turn is either positively or negatively regulated by the phosphorylation of specific Lck tyrosine residues. In particular, the general belief is that Lck is negatively regulated by phosphorylation of tyrosine 192 (Y192). We now demonstrate by Western blotting that, in Jurkat T cells, TCR signal transduction (and ZAP-70 phosphorylation) was positively associated with a rapid transient phosphorylation of Y192, which was inhibited in cells that were briefly (5 min) exposed to 5 microM Hg(2+). Thus, Hg(2+) inhibits a critical activating role played by Lck Y192 during the most proximal events of the TCR-induced cell signaling.

Background: Local anesthetics, especially lidocaine, can lead to persistent cauda equina syndrome after spinal anesthesia. Recently, lidocaine has been reported to trigger apoptosis, although the underlying mechanisms remain unknown. To elucidate the pathway of lidocaine-induced apoptosis, the authors used genetically modified cells with overexpression or deficiencies of key regulators of apoptosis., Methods: Human Jurkat T-lymphoma cells overexpressing the antiapoptotic protein B-cell lymphoma 2 as well as cells deficient of caspase 9, caspase 8, or Fas-associated protein with death domain were exposed to lidocaine and compared with parental cells. The authors evaluated cell viability, mitochondrial alterations, cytochrome c release, caspase activation, and early apoptosis. Apoptosis was in addition investigated in neuroblastoma cells., Results: In Jurkat cells, lidocaine reduced viability, associated with a loss of the mitochondrial membrane potential. At low concentrations (3-6 mm) of lidocaine, caspase 3 was activated and release of cytochrome c was detected, whereas at higher concentrations (10 mm), no caspase activation was found. Apoptosis by lidocaine was strongly reduced by B-cell lymphoma-2 protein overexpression or caspase-9 deficiency, whereas cells lacking the death receptor pathway components caspase 8 and Fas-associated protein with death domain were not protected and displayed similar apoptotic alterations as the parental cells. Lidocaine also induced apoptotic caspase activation in neuroblastoma cells., Conclusions: Apoptosis is triggered by concentrations of lidocaine occurring intrathecally after spinal anesthesia, whereas higher concentrations induce necrosis. The data indicate that death receptors are not involved in lidocaine-induced apoptosis. In contrast, the observation that B-cell lymphoma-2 protein overexpression or the lack of caspase 9 abolished apoptosis clearly implicates the intrinsic mitochondrial death pathway in lidocaine-induced apoptosis.

We have developed a multiplexed reverse phase protein (RPP) microarray platform for simultaneous monitoring of site-specific phosphorylation of numerous signaling proteins using nanogram amounts of lysates derived from stimulated living cells. We first show the application of RPP microarrays to the study of signaling kinetics and pathway delineation in Jurkat T lymphocytes. RPP microarrays were used to profile the phosphorylation state of 62 signaling components in Jurkat T cells stimulated through their membrane CD3 and CD28 receptors, identifying a previously unrecognized link between CD3 crosslinking and dephosphorylation of Raf-1 at Ser259. Finally, the potential of this technology to analyze rare primary cell populations is shown in a study of differential STAT protein phosphorylation in interleukin (IL)-2-stimulated CD4(+)CD25(+) regulatory T cells. RPP microarrays, prepared using simple procedures and standard microarray equipment, represent a powerful new tool for the study of signal transduction in both health and disease.

Human ENX-2 is a homologue of Drosophila Enhancer of zeste, which is a member of Polycomb-group proteins regulating the expression of homeotic genes as chromatin-associated proteins. In this study, we demonstrate that ENX-2 plays an important role as a signaling molecule involved in T cell receptor-mediated signaling pathway. In immunoprecipitation experiments, ENX-2 and zeta associated protein-70 (ZAP-70) were co-precipitated from T cell lysate. When probed with an anti-phospho-tyrosine antibody, ENX-2 was found to be phosphorylated on tyrosine. On the other hand, ENX-2 was not phosphorylated on tyrosine in the mutant Jurkat cell, J.Cam1.6 lacking the activity of lymphocyte protein tyrosine kinase p56(lck). The interaction between ENX-2 and ZAP-70 was abolished in the mutant cell. Furthermore, in-vitro kinase assay using purified p56(lck) demonstrated that ENX-2 became tyrosine phosphorylated by this kinase. These findings show that the phosphorylation of ENX-2 is responsible for the interaction between ENX-2 and ZAP-70.

p62(dok) belongs to a newly identified family of adaptor proteins. In T cells, the two members that are predominantly expressed, p56(dok) and p62(dok), are tyrosine phosphorylated upon CD2 or CD28 stimulation, but not upon CD3 ligation. Little is known about the biological role of Dok proteins in T cells. In this study, to evaluate the importance of p62(dok) in T cell function, we generated Jurkat clones overexpressing p62(dok). Our results demonstrate that overexpression of p62(dok) in Jurkat cells has a dramatic negative effect on CD2-mediated signaling. The p62(dok)-mediated inhibition affects several biochemical events initiated by CD2 ligation, such as the increase of intracellular Ca(2+), phospholipase C gamma 1 activation, and extracellular signal-regulated kinase 1/2 activation. Importantly, these cellular events are not affected in the signaling cascade induced by engagement of the CD3/TCR complex. However, both CD3- and CD2-induced NF-AT activation and IL-2 secretion are impaired in p62(dok)-overexpressing cells. In addition, we show that CD2 but not CD3 stimulation induces p62(dok) and Ras GTPase-activating protein recruitment to the plasma membrane. These results suggest that p62(dok) plays a negative role at multiple steps in the CD2 signaling pathway. We propose that p62(dok) may represent an important negative regulator in the modulation of the response mediated by the TCR.

Objective: To study the intracellular signaling events associated with ligation of the surface receptor CD95., Methods: A mutant clone of Jurkat T cells, DD3, which fails to transmit apoptotic signals through CD95, was selected for study. Surface expression of CD95 and the primary nucleotide sequence of CD95, as well as the functional effects of a mutant CD95 molecule found in DD3, were examined., Results: DD3, while exhibiting impaired ability to undergo apoptosis after CD95 ligation, retained the ability to die after ultraviolet light stimulation. A CD95 complementary DNA (cDNA) cloned from DD3 encoded a mutant transmembrane protein lacking the carboxy-terminal "death domain." Western blotting confirmed the presence of both wild-type and mutant CD95 protein in DD3. Transfection of the mutant CD95 cDNA into parental Jurkat cells conferred protection from CD95-mediated apoptosis., Conclusion: A mutant CD95 receptor lacking the cytoplasmic "death domain" can interfere with wild-type receptor function in T cells.

beta-Endorphin (beta-EP) and delta opioid receptor (DOR) agonists affect immune functions such as lymphocyte chemotaxis, proliferation, and cytokine production. Recent studies indicate that both neuronal DOR and novel G-protein-coupled receptors with high affinity for beta-EP and DOR agonists are expressed by mononuclear cells. In addition, proenkephalin A mRNA and enkephalin-related peptides are expressed by lymphocytes. These investigations were conducted to identify signal transduction pathways that mediate the effects of beta-EP and DOR agonists on T cells. Calcium mobilization was studied because it is central to T-cell activation initiated by antigen presentation to the T-cell receptor (TCR). Using the calcium-sensitive dye Fluo-3 and flow cytofluorometry to determine the concentration of free intracellular calcium, physiological concentrations of beta-EP were shown to enhance concanvalin. A (con A)-stimulated calcium mobilization by murine splenic T cells (p < 0.01). The DOR antagonist, naltrindole, inhibited this, whereas CTAP, a selective mu OR antagonist, was ineffective. In addition, N-Ac-beta-EP and the mu OR agonist DAMGO, failed to mimic the effects of beta-EP. Although it was less potent than beta-EP, DADLE, a DOR agonist, also enhanced Con-A-induced calcium mobilization (p < 0.01). A DOR-transfected human T-cell line (DOR-Jul.1) was developed to study signal transduction. Both DADLE and the selective DOR agonist, deltorphin, rapidly increased intracellular free calcium concentrations; ED50s were 10(-9) M. Pertussis toxin prevented the response, and EGTA significantly reduced it. In addition, DADLE inhibited forskolin-stimulated cAMP production (ED50: 10(-11) M). These findings with normal splenic T cells and DOR-transfected T-cell line indicate that beta-EP and DOR agonists affect calcium mobilization. This is likely to modulate downstream pathways that regulate T-cell activation and function.

CD38 is a multifunctional membrane surface glycoprotein expressed by different cells and tissues, including T cells at certain stages of their development. Besides its involvement in transmembrane signaling, CD38 play a role in cell adhesion processes. Structurally, membrane CD38 was reported as presenting lateral associations with molecules involved in recognition and signaling, namely with the TCR/CD3 complex in T cells. Here we report that ligation of CD38 by agonistic and non-agonistic monoclonal antibodies exerts different effects on T cells, the former inducing down-modulation of the associated molecules, probably through a protein kinase C-dependent mechanism. This observation supports the view that the reduced expression of TCR/CD3 is secondary to interplay with CD38-mediated signaling, which partially overlaps with the CD3-mediated pathway. CD3 ligation by monoclonal antibodies leads not only to the expected internalization of the TCR/CD3 complex but also to down-modulation of surface CD38. The results obtained indicate that CD38 is closely associated with the CD3/TCR complex and that co-modulation of CD38 with TCR/CD3 is a critical step in signaling processes on T lymphocytes.