The T cell antigen receptor tyrosine kinase pathway.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
L E Samelson
Publications and source records attributed to L E Samelson.
The protein tyrosine kinase inhibitor herbimycin A, but not genistein, specifically inhibits signal transduction by the T cell antigen receptor.
Several lines of evidence implicate a regulatory tyrosine phosphorylation in the activation of phospholipase C (PLC) by the T cell antigen receptor (TCR). These include studies using inhibitors of protein tyrosine kinases (PTKs). In Jurkat T cells expressing the heterologous human muscarinic receptor (HM1), PLC activity can be induced by either the TCR or HM1. HM1 activates PLC via a guanine nucleotide binding protein. We have studied the selectivity of the effects of the PTK inhibitors, herbimycin A and genistein, in this system. The results indicate that these inhibitors have different mechanisms of action, and suggest that herbimycin A, but not genistein, is a specific inhibitor of PTKs in T cells. Herbimycin A markedly inhibited both the resting and induced levels of phosphotyrosine-containing proteins, including the gamma 1 isozyme of PLC and the zeta chain of the TCR, and prevented activation of PLC by anti-TCR mAb. Herbimycin A did not inhibit activation of PLC by HM1. Genistein had a much less pronounced effect than herbimycin A on the appearance of tyrosine phosphoproteins. Moreover, genistein inhibited activation of PLC by both the TCR and HM1, and inhibition was only partial. Genistein was cytotoxic and markedly inhibited protein synthesis in both Jurkat cells and human peripheral lymphocytes. Herbimycin A was not cytotoxic. These findings confirm the role of a regulatory tyrosine phosphorylation in activation of PLC by the TCR. Herbimycin A was a selective inhibitor of a subclass of PTKs in Jurkat cells. In contrast, inhibition of signal transduction and later events in T cells by genistein may be due to effects other than direct inhibition of PTK activity.
Benzoquinones↗
Characterization of the T cell antigen receptor--p60fyn protein tyrosine kinase association by chemical cross-linking.
Engagement of the TCR by specific antigen results in activation of a tyrosine kinase pathway. A candidate for the kinase responsible for the rapid tyrosine phosphorylation detected with T cell activation is p60fyn, a member of the src kinase family. In an earlier study [Samelson et al. (1990) Proc. Natl Acad. Sci. USA 87:4358] this enzyme was co-immunoprecipitated with the TCR from T cells solubilized in digitonin. In that study a sensitive in vitro kinase assay was used to detect the associated p60fyn. It was subsequently found that the reproducibility of the interaction depended on lot-to-lot variations in digitonin. To eliminate the possibility that the association of antigen receptor and kinase is an artifact of solubilization with ill-defined digitonin preparations, a cross-linking protocol was developed to stabilize the interaction between the TCR and p60fyn. T cells were permeabilized with tetanolysin and proteins were cross-linked with the water soluble chemical cross-linker, 3,3' dithiobis(sulfosuccinimidylpropionate). These experiments allowed the confirmation of the interaction between the TCR, p60fyn, and several additional proteins. The cross-linking studies also enabled the mapping of the interaction of p60fyn and associated proteins to the TCR zeta-chain. This technique should have a general use in stabilizing interactions between other receptors and molecules required for intracellular signaling.
Animals↗
p59fyn tyrosine kinase associates with multiple T-cell receptor subunits through its unique amino-terminal domain.
Several lines of evidence link the protein tyrosine kinase p59fyn to the T-cell receptor. The molecular basis of this interaction has not been established. Here we show that the tyrosine kinase p59fyn can associate with chimeric proteins that contain the cytoplasmic domains of CD3 epsilon, gamma, zeta (zeta), and eta. Mutational analysis of the zeta cytoplasmic domain demonstrated that the membrane-proximal 41 residues of zeta are sufficient for p59fyn binding and that at least two p59fyn binding domains are present. The association of p59fyn with the zeta chain was specific, as two closely related Src family protein tyrosine kinases, p60src and p56lck, did not associate with a chimeric protein that contained the cytoplasmic domain of zeta. Mutational analysis of p59fyn revealed that a 10-amino-acid sequence in the unique amino-terminal domain of p59fyn was responsible for the association with zeta. These findings support evidence that p59fyn is functionally and structurally linked to the T-cell receptor. More importantly, these studies support a critical role for the unique amino-terminal domains of Src family kinases in the coupling of tyrosine kinases to the signalling pathways of cell surface receptors.
Amino Acid Sequence↗
The T cell antigen receptor: biochemical aspects of signal transduction.
Explore the source record for details and available documents.
Animals↗
Ligand-stimulated signaling events in immature CD4+CD8+ thymocytes expressing competent T-cell receptor complexes.
During thymic selection of the developing T-cell repertoire, the fate of individual CD4+CD8+ thymocytes is determined by the specificity of the T-cell antigen receptors (TCRs) they express. Paradoxically, most CD4+CD8+ thymocytes express few TCR molecules, and those they express are essentially incapable of transducing intracellular signals as measured by intracellular calcium mobilization. However, both TCR number and calcium-signaling capability are significantly induced in CD4+CD8+ thymocytes when the cells are released from intrathymic inhibitory signals that are mediated by their CD4 molecules. Here, the response to ligand engagement of TCR on "induced" CD4+CD8+ thymocytes that have been released from CD4-mediated inhibition was examined and was found to result in internalization of surface TCR complexes and rephosphorylation of zeta chains of the TCR complex. In addition, a proportion of induced CD4+CD8+ thymocytes were found to fragment their DNA upon ligand engagement. Thus, this study describes early events in immature CD4+CD8+ thymocytes resulting from TCR-mediated signals.
Animals↗
T cell antigen receptor activation pathways: the tyrosine kinase connection.
Explore the source record for details and available documents.
Animals↗
Expression of v-src in a murine T-cell hybridoma results in constitutive T-cell receptor phosphorylation and interleukin 2 production.
Ligand binding to the T-cell antigen receptor results in phosphatidylinositol hydrolysis and the resultant activation of protein kinase C, as well as the activation of a receptor-coupled protein-tyrosine kinase. As a model for tyrosine kinase activation in T cells, we used retroviral gene transfer to express the v-src oncogene in an antigen-specific murine T-cell hybridoma. Clones that expressed v-src mRNA demonstrated constitutive tyrosine phosphorylation of several cellular substrates, including the zeta chain of the T-cell receptor, and constitutive interleukin 2 production. Thus, expression of a constitutively active protein-tyrosine kinase such as pp60v-src appears to be sufficient to induce the expression of at least one gene critical to the process of T-cell activation.
Animals↗
Surface immunoglobulin crosslinking activates a tyrosine kinase pathway in B cells that is independent of protein kinase C.
It has been found that the principal biochemical pathway activated in B cells stimulated by antigen- or anti-immunoglobulin-mediated crosslinking of surface immunoglobulin is that resulting in hydrolysis of phosphatidylinositol bisphosphate with generation of diacylglycerol and inositol trisphosphate. Recent evidence suggests that surface immunoglobulin-mediated B-cell activation can proceed without detectable increases in the concentration of either diacylglycerol or intracellular Ca2+ concentration, implicating involvement of other non-protein-kinase-C/Ca2(+)-dependent signal-transduction pathways. Therefore, we sought evidence for activation of a signaling pathway that is associated with growth regulation in other cell types--i.e., the protein-tyrosine kinases. We now show that crosslinking of membrane immunoglobulin by mitogenic antibodies leads to rapid tyrosine phosphorylation of several cellular substrates, consistent with the induction of a tyrosine kinase activity. This increase in tyrosine phosphorylation is weakly (if at all) stimulated by other B-cell mitogens, including phorbol esters and ionophores, and does not require the presence of detectable protein kinase C. Furthermore, inhibition of anti-immunoglobulin-stimulated phosphatidylinositol bisphosphate hydrolysis does not inhibit activation of this tyrosine kinase-dependent pathway. These findings suggest that occupancy of the membrane immunoglobulin receptor may induce multiple pathways of activation.
Animals↗
Identification of a murine monoclonal antibody specific for an allotypic determinant on mouse CD3.
A murine monoclonal antibody (mAb; 7D6) that was mitogenic for T cells was derived from 129/Sv animals immunized with a T helper clone from C57BL/6 origin. Fluoresceinated 7D6 labeled T cells from most common mouse strains but not from 129/Sv and LP/J animals, and this labeling was inhibited by the anti-CD3 epsilon mAb 145-2C11. The mitogenicity of 7D6 for T cells had a similar strain specificity. The antibody immunoprecipitated the T cell receptor (TcR) complex from a T cell hybridoma. After dissociation of this immunoprecipitate with detergents, the CD3 gamma and epsilon chains were retained by the 7D6 antibody. Immunoprecipitation data were also obtained with COS cells transfected with the CD3 gamma, delta or epsilon chains alone, in pairs or together. They confirmed that 7D6 bound the CD3 gamma epsilon pair, suggesting that the antibody recognizes a conformational epitope formed by gamma epsilon pairing, whereas 145-2C11 bound both gamma epsilon and delta epsilon pairs. These results, therefore, add to current information about TcR structure and subunit stoichiometry. We have demonstrated that the 7D6 mAb specifically binds to a CD3 dimer comprised of gamma and epsilon chains. We thus provide additional evidence that indicates that two CD3 epsilon chains are found within the receptor, one linked to CD3 gamma and the other to CD3 delta.
Animals↗
Multiple signal transduction pathways activated through the T cell receptor for antigen.
The T cell receptor for antigen (TCR) is a multichain complex on the surface of T lymphocytes which binds peptide antigen and transduces a transmembrane signal leading to IL-2 secretion. Engagement of the TCR leads to activation of a tyrosine phosphorylation pathway and a phospholipase C (PLC) pathway leading to activation of protein kinase C (PCK). Currently available data suggest that the primary event in signal transduction is tyrosine kinase activation, since when this pathway is inhibited, PLC activation is blocked and there is no production of IL-2. The nature of the tyrosine kinase which initiates the signaling cascade is currently unknown. The CD4/CD8 associated kinase p56lck clearly plays a role in tyrosine phosphorylation, but it is clearly not the only tyrosine kinase involved. Studies demonstrating physical association of p59lyn with the TCR implicate fyn as an important candidate for the TCR tyrosine kinase. The protein tyrosine phosphatase CD45 also plays a critical early role in signal transduction since in cells where it is deficient, neither tyrosine kinase activation nor later signaling events are seen. The importance of the PLC/PKC pathway is illustrated by the fact that activation of this pathway alone may lead to IL-2 production. However, there may also be other mechanisms which can generate an IL-2 response. Two proteins known to be involved in growth regulation--p21ras and c-raf--have now been shown to be downstream targets of the PLC/PKC pathway.
Animals↗
T cell antigen receptor engagement stimulates c-raf phosphorylation and induces c-raf-associated kinase activity via a protein kinase C-dependent pathway.
The c-raf kinase has been shown to be activated following stimulation of several tyrosine kinase growth factor receptors. We examined changes in c-raf following engagement of the T cell receptor for antigen (TCR), a stimulus which activates both a non-receptor tyrosine kinase and protein kinase C (PKC). We found that activation of the T-cell receptor on the T cell hybridoma 2B4 causes a rapid and stoichiometric hyperphosphorylation of c-raf and an increase in c-raf-associated kinase activity. Phosphoamino acid analysis showed that the phosphorylation was entirely on serine residues. High-resolution phosphopeptide mapping showed the appearance of a single major new phosphopeptide with TCR stimulation. That phosphopeptide was shown to comigrate with the major new phosphopeptide induced in response to phorbol ester. When cells were depleted of PKC by pretreatment with high concentrations of phorbol ester, TCR stimulation was no longer capable of inducing c-raf-associated kinase activity. To determine whether activation of the tyrosine kinase alone would activate c-raf, we examined the 2B4 variant cell line FL.8. In response to Thy-1 stimulation, these cells activate the tyrosine kinase but not protein kinase C due to a deficiency in TCR eta chain expression. We found that in contrast to Thy-1 stimulation of 2B4 cells, stimulation of FL.8 cells does not lead to the induction of c-raf-associated kinase activity, although phorbol ester activates the kinase to an equivalent degree in both cells. We conclude that T cell receptor activation of c-raf occurs via phosphorylation by the serine/threonine kinase PKC. Activation of c-raf through PKC represents a mechanism distinct from that reported for tyrosine kinase growth factor receptors.
Animals↗
Activation of tyrosine phosphorylation in human T cells via the CD2 pathway. Regulation by the CD45 tyrosine phosphatase.
In this study we compare the effect of CD3 and CD2 ligation on tyrosine kinase activation in human peripheral blood T cells. Using antiphosphotyrosine antibody to detect tyrosine phosphorylation of cellular substrates, we demonstrate that mAb stimulation of either CD3 or CD2 results in tyrosine phosphorylation of the TCR-zeta chain and 135- and 100-kDa proteins. However, differences are observed between CD3 and CD2 ligation; only the former results in rapid tyrosine phosphorylation of 72-, 65-, and 40-kDa substrates. Co-aggregation of CD2 and CD45, a tyrosine phosphatase, results in inhibition of intracellular calcium elevation and T cell proliferation. We demonstrate in this study that this manipulation also inhibits polyphosphoinositide hydrolysis and tyrosine phosphorylation of the 100-kDa substrate. The failure of tyrosine phosphorylation of the 100-kDa substrate is specific in that phosphorylation of the 135-kDa protein is not inhibited. Similar results are observed when CD2 and CD45 are independently cross-linked rather than co-aggregated. The observation that CD45 cross-linking alters tyrosine phosphorylation of T cell substrates and effects polyphosphoinositide hydrolysis is further evidence that tyrosine phosphorylation regulates early events in T cell activation including, perhaps, phospholipase C activity.
Antigens, CD↗
Inhibition of T cell receptor expression and function in immature CD4+CD8+ cells by CD4.
Most immature CD4+CD8+ thymocytes express only a small number of T cell receptor (TCR) molecules on their surface, and the TCR molecules they do express are only marginally capable of transducing intracellular signals. TCR expression and function was not intrinsically low in immature CD4+CD8+ thymocytes, but was found to be actively inhibited by CD4-mediated signals. Indeed, release of CD4+CD8+ thymocytes from CD4-mediated signals resulted in significant increases in both TCR expression and signaling function. These results suggest that, in CD4+CD8+ cells developing in the thymus, increased TCR expression and function requires release from CD4-mediated inhibition.
Animals↗
Increases in tyrosine phosphorylation are detectable before phospholipase C activation after T cell receptor stimulation.
Antiphosphotyrosine immunoblots were used to characterize tyrosine phosphorylated proteins after stimulation of the human TCR. Increased tyrosine phosphorylation was evident on at least 12 substrates within 2 min after ligation of the TCR with mAb. Analysis of the time course for increased tyrosine phosphorylation revealed distinct patterns. Increased phosphorylation of 135-kDa and 100-kDa substrates was evident within 5 s, whereas increased phosphorylation of the TCR-zeta-chain required several minutes after treatment with anti-CD3 mAb. This rapid cellular tyrosine phosphorylation occurred independent of the cell cycle, as it occurred after stimulation of resting T cells, T cell blasts, and the Jurkat T cell leukemia line. When the TCR complex was cross-linked together with the CD4 receptor by heteroconjugate anti-CD3/CD4 mAb, an increased magnitude of tyrosine phosphorylation occurred, although no new substrates could be detected. The increased tyrosine phosphorylation of the 135-kDa and 100-kDa substrates was specific in that anti-HLA class I, anti-CD6, anti-CD7, and anti-CD28 antibodies did not cause increased tyrosine phosphorylation. Anti-CD4 stimulation of resting T cells did not cause increased tyrosine phosphorylation of pp100 and pp135, suggesting that the CD4-associated kinase, lck, does not account for the tyrosine phosphorylation observed after TCR stimulation. Similarly, pharmacologic treatment of cells with phorbol ester and calcium ionophore did not cause increased tyrosine phosphorylation of these substrates, indicating that activation of protein kinase C or phospholipase C does not account for these early increases in tyrosine phosphorylation. The time of onset of pp100 phosphorylation, and the magnitude of phosphorylation correlated with the magnitude of calcium mobilization when cells were stimulated with different forms of TCR stimulation. When cells were labeled with [3H]myoinositol and analyzed after stimulation by anti-CD3 mAb, increased tyrosine phosphorylation of the 135-kDa and 100-kDa substrates preceded the activation of phospholipase C, as measured by the appearance of inositol 1,4,5-trisphosphate. This occurred in both T cell blasts and in the Jurkat T cell line. Thus, these findings show that increased tyrosine phosphorylation is the earliest yet detected signal observed after ligation of the TCR complex, and furthermore suggest that tyrosine phosphorylation might link the TCR to the phosphatidylinositolbisphosphate hydrolysis signaling pathway.
Animals↗
Association of the fyn protein-tyrosine kinase with the T-cell antigen receptor.
Activation of the T-cell antigen receptor (TCR) results in tyrosine phosphorylation of the TCR zeta chain and other intracellular substrates. Two other T-cell integral membrane proteins, CD4 and CD8, are associated with the protein-tyrosine kinase (PTK), lck. Despite evidence that activation of this enzyme results in TCR-zeta chain phosphorylation, it has not been shown that the TCR activates lck. We have sought evidence that the TCR is associated with a PTK. In this study we use digitonin to solubilize a murine T-cell hybridoma and demonstrate that antibodies binding extracellular but not intracellular domains of the TCR specifically coprecipitate only the fyn PTK and not lck or yes, two other kinases found in these cells. The association of the fyn PTK with the TCR might enable the T cell to independently regulate two PTKs through surface receptors.
Animals↗
Inhibition of tyrosine phosphorylation prevents T-cell receptor-mediated signal transduction.
The binding of antigen to the multicomponent T-cell receptor (TCR) activates several signal transduction pathways via coupling mechanisms that are poorly understood. One event that follows antigen receptor engagement is the activation of inositol phospholipid-specific phospholipase C (PLC). TCR activation by antigen, lectins, or anti-TCR monoclonal antibody has also been shown to cause increases in tyrosine phosphorylation of TCR-zeta and other substrates, suggesting stimulation of protein tyrosine kinase (PTK) activity. A critical question is whether these two pathways, PLC and PTK, are independently activated or whether one initiates and/or regulates the other. In the former case, PLC activation could be coupled to the TCR via a GTP-binding protein (G protein). We have reported, however, that tyrosine phosphorylation of intracellular substrates precedes detection of PLC activation and intracellular calcium elevation, suggesting that inositol phospholipid turnover in T cells is initiated by a PTK pathway. In this study, we test this hypothesis by treating T cells with the drug herbimycin A. We demonstrate that this agent inhibits substrate tyrosine phosphorylation, TCR-mediated inositol phospholipid hydrolysis, and calcium elevation. In contrast, under these conditions G-protein-mediated PLC activity, as tested by addition of aluminum fluoride, remains intact. Furthermore, whereas herbimycin treatment prevents TCR-mediated interleukin 2 production and interleukin 2 receptor expression, phorbol ester-induced effects are substantially resistant to herbimycin. The drug thus appears to abrogate TCR-mediated signaling without affecting distal signaling mechanisms.
Antifungal Agents↗
Tyrosine phosphorylation in T cells is regulated by phosphatase activity: studies with phenylarsine oxide.
Activation of T cells induces rapid tyrosine phosphorylation on the T-cell receptor zeta chain and other substrates. These phosphorylations can be regulated by a number of protein-tyrosine kinases (ATP: protein-tyrosine O-phosphotransferase, EC 2.7.1.112) and protein-tyrosine-phosphatases (protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48). In this study, we demonstrate that phenylarsine oxide can inhibit tyrosine phosphatases while leaving tyrosine kinase function intact. We use this reagent to investigate the effect of tyrosine phosphatase inhibition in a murine T-cell hybridoma. Increasing concentrations of phenylarsine oxide result in an increase in tyrosine phosphate on a number of intracellular substrates in unstimulated T cells, suggesting that a protein-tyrosine kinase is constitutively active in these cells. The effect of phenylarsine oxide on T cells stimulated with an anti-Thy 1 monoclonal antibody is more complex. At low concentrations of drug, there is a synergistic increase in the level of tyrosine phosphate on certain cellular substrates. At higher concentrations, anti-Thy 1-stimulated tyrosine phosphorylation is inhibited. These results indicate that tyrosine phosphorylation in T cells is tightly regulated by tyrosine phosphatases. Partial inhibition of these enzymes results in enhanced substrate phosphorylation. Inhibition of all stimulated tyrosine phosphorylation by high doses of phenylarsine oxide suggests that tyrosine kinase activity is regulated by tyrosine phosphatases.
Animals↗