T cells infiltrating non-Hodgkin's B cell lymphomas show altered tyrosine phosphorylation pattern even though T cell receptor/CD3-associated kinases are present

Although tumor infiltrating lymphocytes (T-TIL) from B cell non-Hodgkins lymphoma patients contain tumor-reactive T cells, they display poor proliferation and IFN-gamma production when stimulated through the TCR-CD3. To determine if there was altered signaling linked to TCR-CD3 ligation, tyrosine phosphorylation was examined in T-TIL because it represents an early and critical event in T cell activation. After stimulation with anti-CD3 Ab, Western blotting with anti-phosphotyrosine showed reduced phosphorylation in T-TIL when compared with peripheral blood-derived T cells from normal individuals. The altered phosphorylation was not due to the reduced expression of signaling elements linked to the TCR-CD3 complex. T-TIL expressed normal levels of CD3 epsilon, TCR zeta chain, and the three tyrosine kinases, p56lck (Lck), p59fyn, and ZAP-70. However, in T-TIL, anti-Lck Ab reacted with a 60-kDa protein, which appears to be the phosphorylated form of Lck. Binding of anti-Lck Ab to the 60-kDa protein was blocked by Lck peptide. In addition, anti-Lck Ab immunoprecipitated a phosphorylated 60-kDa protein from gamma-32P-labeled T-TIL that was not seen in normal resting T cells. In vitro kinase assay studies also demonstrated that TCR-CD3 engagement increased the kinase activity of Lck in normal T cells but not in T-TIL. These results suggest that although T-TIL from B cell non-Hodgkins lymphoma patients contain the signal transduction molecules associated with TCR-CD3 activation pathway, they are impaired in tyrosine phosphorylation and Lck activity, which may contribute to the functional defects of these cells.

The molecular chaperone calnexin is expressed on the surface of immature thymocytes in association with clonotype-independent CD3 complexes

Immature thymocytes express clonotype-independent CD3 complexes that, when engaged by anti-CD3 antibodies, can signal CD4-CD8- thymocytes to differentiate into CD4+CD8+ cells. Clonotype-independent CD3 complexes consist of CD3 components associated with an unknown 90 kDa surface protein. We now report the surprising finding that this 90 kDa surface protein is the molecular chaperone calnexin, an integral membrane protein previously thought to reside only in the endoplasmic reticulum (ER). We found that calnexin-CD3 complexes escaping to the cell surface utilize interchain associations distinct from those utilized by calnexin-CD3 complexes remaining within the ER. Specifically, we demonstrate that carbohydrate-mediated luminal domain interactions that are necessary for formation of most internal calnexin-CD3 complexes destined to be expressed on the cell surface, and we provide evidence that cytoplasmic domain interactions between calnexin and CD3 epsilon chains mask calnexin's ER retention signal, permitting calnexin and associated proteins to escape ER retention. Thus, the present study demonstrates that partial T cell antigen receptor complexes can escape the ER of immature thymocytes in association with their molecular chaperone to be expressed at low levels on the cell surface where they may function as a signaling complex to regulate thymocyte maturation.

Rapid turnover of the CD3 zeta chain independent of the TCR-CD3 complex in normal T cells

The function of CD3 zeta in the assembly and transport of the T cell receptor (TCR)-CD3 complex was analyzed in normal T cells. The zeta chain, but not other chains in the surface TCR complex, rapidly exchanged with newly synthesized zeta. Because zeta was expressed independently from the complex, the TCR complex may be transported to the surface along the zeta turnover pathway by association with zeta. These data suggest the dynamic nature of zeta metabolism and provide the evidence that a single component in a multisubunit receptor exhibits independent metabolism from the rest of the complex.

Receptor-mediated gene transfer into human T lymphocytes via binding of DNA/CD3 antibody particles to the CD3 T cell receptor complex

Retrovirus-mediated gene transfer is currently the method of choice for the transfection of human T lymphocytes for applications in gene therapy. Use of retroviral vectors, however, is hampered by limits on the size of the genetic material to be transferred, the requirement of dividing target cells, and by potential safety questions. Synthetic peptide-enhanced or adenovirus-enhanced receptor-mediated transferrinfection of DNA (SPET and AVET, respectively) is a powerful method for the introduction of genetic material into mammalian cells. Although transferrin has proven to be a useful ligand for gene transfer in many cell types, gene expression in T cells with transferrin/DNA complexes is usually not satisfactory. To improve gene transfer to T cells, antibodies directed against the CD3-T cell receptor complex were tested for their ability to function as ligands for DNA delivery. In T cell lines, up to 50% of the cells expressed a beta-galactosidase reporter gene using anti-CD3 gene transfer complexes. Applying optimized conditions, prestimulated primary peripheral blood lymphocytes were also transfected successfully, although at a lesser efficiency (5%).

Analysis of the interaction of ZAP-70 and syk protein-tyrosine kinases with the T-cell antigen receptor by plasmon resonance

Tyrosine phosphorylation of a 17-amino acid immunoreceptor tyrosine-based activation motif (ITAM), conserved in each of the signaling subunits of the T-cell antigen receptor (TCR), mediates the recruitment of ZAP-70 and syk protein-tyrosine kinases (PTKs) to the activated receptor. The interaction between the two tandemly arranged Src-homology 2 (SH2) domains of this family of PTKs and each of the phosphotyrosine-containing ITAMs was examined by real-time measurements of kinetic parameters. The association rate and equilibrium binding constants for the ZAP-70 and syk SH2 domains were determined for the CD3 epsilon ITAM. Both PTKs bound with ka and Kd values of 5 x 10(6) M-1.sec-1 and approximately 25 nM, respectively. Bindings to the other TCR ITAMs (zeta 1, zeta 2, gamma, and delta ITAMs) were comparable, although the zeta 3 ITAM bound approximately 2.5-fold less well. Studies of the affinity of a single functional SH2 domain of ZAP-70 provided evidence for the cooperative nature of binding of the dual SH2 domains. Mutation of either single SH2 domain decreased the Kd by > 100-fold. Finally, the critical features of the ITAM for syk binding were found to be similar to those required for ZAP-70 binding. These data provide insight into the mechanism by which the multisubunit TCR interacts with downstream effector molecules.

HIV-1 glycoprotein gp120 disrupts CD4-p56lck/CD3-T cell receptor interactions and inhibits CD3 signaling

Using the CD4+ human T cell clone P28, we demonstrated that the HIV-1 glycoprotein gp120 inhibited CD3-induced inositol trisphosphate production, calcium influx and T cell proliferation. Additionally, gp120 was shown to dissociate the tyrosine kinase p56lck from CD4 in CEM cells, with a concommittant inhibition of CD4-linked kinase activity. We have addressed the question whether disruption of CD4/p56lck or CD4/CD3-T cell receptor interactions, or both, could account for the inhibitory effect of gp120 in P28 cells. By comparing the effects of various anti-CD4 monoclonal antibodies (mAb) with those of gp120, we show that gp120 and IOT4a modulate CD4 expression, and decrease CD4-associated p56lck and CD4-linked kinase activity at the plasma membrane. In contrast, OKT4A and OKT4 anti-CD4 mAb have no inhibitory effect. Interestingly, gp120 also inhibits CD3-induced Lck activation and cellular tyrosine phosphorylation, particularly of phosphoinositide-specific phospholipase C-gamma-1. Kinetic experiments reveal that the inhibitory effect of gp120 on CD3-induced tyrosine phosphorylation appears as early as 30 min, but culminate when CD4-p56lck complexes disappear from the cell surface after 4 h. These results suggest that a negative signal is triggered by gp120 that results, after a few hours, in down-modulation of CD4-p56lck complexes and the impairment of CD3 signaling. Supporting this hypothesis, gp120 inhibits CD3-linked kinase activity as shown by the inhibition of the phosphorylation of CD3 chains, leading to the inhibition of subsequent signal transduction.

Regulation of CD45 engagement by the B-cell receptor CD22

The B-cell receptor CD22 binds sialic acid linked alpha-2-6 to terminal galactose residues on N-linked oligosaccharides associated with several cell-surface glycoproteins. The first of these sialoglycoproteins to be identified was the receptor-linked phosphotyrosine phosphatase CD45, which is required for antigen/CD3-induced T-cell activation. In the present work, we examine the effect of interaction between the extracellular domain of CD45 and CD22 on T-cell activation. Using soluble CD22-immunoglobulin fusion proteins and T cells expressing wild-type and chimeric CD45 forms, we show that engagement of CD45 by soluble CD22 can modulate early T-cell signals in antigen receptor/CD3-mediated stimulation. We also show that addition of sialic acid by beta-galactoside alpha-2,6-sialyltransferase to the CD22 molecule abrogates interactions between CD22 and its ligands. Together, these observations provide direct evidence for a functional role of the interaction between the extracellular domain of CD45 and a natural ligand and suggest another regulatory mechanism for CD22-mediated ligand engagement.

The MEK kinase activity of the catalytic domain of RAF-1 is regulated independently of Ras binding in T cells

Deletion of the amino-terminal domain of Raf-1, which contains the Ras-binding region, results in the constitutive activation of the liberated Raf-1 catalytic domain in fibroblast cell lines. We demonstrate that the MEK kinase activity of the isolated Raf-1 catalytic domain, Raf-BXB, is not constitutively active, but is regulated in Jurkat T cells. Raf-BXB is activated by engaging the antigen receptor-CD3 complex, or treating cells with phorbol myristate acetate or okadaic acid. Increasing intracellular cAMP inhibits Raf-1 activation stimulated by phorbol myristate acetate, but not the activation of Raf-BXB. Serine 621, but not serine 499, is essential for Raf-BXB MEK kinase activity. Because Raf-BXB does not bind Ras, the data establishes a Ras-independent signal in directly regulating the activity of the Raf-1 catalytic domain.

Regulation and function of p21ras in T lymphocytes

T cell activation is triggered by antigen stimulation and is characterized by the production of a wide range of cytokines and other immunomodulators crucial for the growth and development of other haemopoietic cells. Activation also induces the T cells to express, on their cell surface, receptors that enable the T cell to respond to the various cytokines generated during an immune response. One well characterized event that occurs when mature T cells are activated is the production of the cytokine IL2 and the acquisition by the T cell of IL2 receptors. Interaction between IL2 and its cellular receptor then directs T cell growth. Expression of the IL2 gene in T cells is regulated by signalling pathways that originate from the T cell antigen receptor complex (TCR). This review discusses the role of p21ras in these events. The TCR regulates the activity of p21ras, and a range of experiments have shown that p21ras couples the TCR to an intracellular kinase cascade involving the serine/threonine kinase Raf-1 and the MAP kinase ERK2. Analysis of more distal receptor signals shows that p21ras controls a signalling pathway that cooperates with a calcium/calcineurin controlled signalling system to stimulate the transcriptional factor NFAT and hence the IL2 gene. These studies identify p21ras as a critical signalling molecule in immune cells.

Cellular and molecular aspects of organotin-induced thymus atrophy

1. Organotin compounds, di-n-butyltin dichloride (DBTC) in particular, have been shown to cause thymus atrophy in the rat. 2. DBTC-induced thymus atrophy results from a depletion of small CD4+CD8+ thymocytes which is caused by a diminished production of immature CD4-CD8+ and CD4+CD8+ thymoblasts. 3. DBTC inhibits the activation, but not the differentiation of immature CD4-CD8+ thymocytes in vitro and in vivo suggesting a selective antiproliferative activity of DBTC. 4. DBTC inhibits the adhesion molecule-mediated binding of thymocytes to thymic epithelial cells. 5. DBTC enhances the Ca2+ release elicited by cross-linking of the T cell receptor complex (TcR alpha beta-CD3) on thymocytes and moreover delays cap formation of the TcR alpha beta-CD3 receptor. 6. It is concluded that DBTC possibly interferes with the functioning of the cytoskeleton. The relation of the in vitro findings to the inhibition of immature CD4-CD8+ thymocyte activation and the induction of thymus atrophy is unknown as yet.

Activation-induced cell death in proliferating T cells is associated with altered tyrosine phosphorylation of TCR/CD3 subunits

The first signaling event that occurs after stimulation of the TCR is an increase in the tyrosine phosphorylation of a number of proteins including the TCR-zeta chain and CD3 subunits. It is known that proliferating T cells respond differently to TCR stimulation when compared with naive T cells. Stimulation of the TCR on proliferating T cells has been shown to result in cell death by apoptosis, a process referred to as activation-induced cell death (AICD). In this study we have determined the pattern of tyrosine phosphorylation of TCR-zeta and the CD3 subunits of naive and proliferating CD4- CD8+ T cells that express a transgenic TCR that is specific for the male Ag presented by Db class I molecules after TCR stimulation. AICD in proliferating T cells was mediated by stimulation with anti-TCR/CD3, but not anti-Thy-1, anti-CD8, or anti-Db mAbs. When compared with naive T cells, tyrosine phosphorylation of TCR-zeta was dramatically decreased in proliferating cells. Furthermore, whereas CD3 delta, CD3 epsilon, and CD3 gamma of naive T cells were phosphorylated in a 1:2:1 ratio after TCR stimulation, these subunits in proliferating T cells were tyrosine phosphorylated in a 1:1:0 ratio after TCR stimulation. Altered phosphorylation of these subunits was not caused by the lack of synthesis or amount of these proteins in proliferating cells. This is the first study implicating altered tyrosine phosphorylation of TCR/CD3 subunits in AICD.

Retention of unassembled components of integral membrane proteins by calnexin

Quality control mechanisms prevent the cell surface expression of incompletely assembled multisubunit receptors such as the T cell receptor (TCR). The molecular chaperone function of calnexin (IP90, p88), a 90-kilodalton protein that resides in the endoplasmic reticulum (ER), in the retention of representative chains of the TCR-CD3 complex in the ER was tested. Truncation mutants of calnexin, when transiently expressed in COS cells, were exported from the ER and either accumulated in the Golgi or progressed to the cell surface. CD3 epsilon chains cotransfected with the forms of calnexin that were not retained in the ER exited the ER and colocalized with calnexin. Since engineered calnexin determined the intracellular localization of the proteins associated with it, it is concluded that calnexin interacts with incompletely assembled TCR components and retains them in the ER.

Location of cAMP-dependent protein kinase type I with the TCR-CD3 complex

Selective activation of cyclic adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase type I (cAKI), but not type II, is sufficient to mediate inhibition of T cell replication induced through the antigen-specific T cell receptor-CD3 (TCR-CD3) complex. Immunocytochemistry and immunoprecipitation studies of the molecular mechanism by which cAKI inhibits TCR-CD3-dependent T cell replication demonstrated that regulatory subunit I alpha, along with its associated kinase activity, translocated to and interacted with the TCR-CD3 complex during T cell activation and capping. Regulatory subunit II alpha did not. When stimulated by cAMP, the cAKI localized to the TCR-CD3 complex may release kinase activity that, through phosphorylation, might uncouple the TCR-CD3 complex from intracellular signaling systems.

The T cell antigen receptor alpha and beta chains interact via distinct regions with CD3 chains

Selective pairwise interactions between CD3 chains and the clonotypic T cell antigen receptor (TCR)-alpha, -beta chains has recently been established. In this study, the region of interaction between clonotypic and CD3 chains involved with assembly was examined. To determine the site of protein interaction a variety of genetically altered TCR chains were constructed. These included: truncated proteins, lacking transmembrane and or cytosolic domains; chimeric proteins, in which extracellular, transmembrane or cytosolic domains were replaced with similar domains derived from either the Tac antigen or CD4; and point mutagenized TCR chains. COS-1 cells were transfected with cDNA, metabolically labeled, and immunoprecipitates analyzed using non-equilibrium pH gel electrophoresis (NEPHGE)-SDS/PAGE. The results demonstrated that assembly between TCR-alpha and TCR-beta chains occurred at the extracellular level. Assembly of the TCR-alpha chain with CD3-delta, and CD3-epsilon was localized to an eight-amino acid motif within the transmembrane domain of TCR-alpha. Site-specific mutations of the TCR-alpha charged residues within this motif (arginine, lysine) to leucine and similar point mutations of the transmembrane CD3-epsilon and CD3-delta charge groups resulted in the abrogation of assembly. In contrast, TCR-beta and CD3-epsilon binary complexes interacted via their extracellular domain. Analogous to TCR-alpha, the site of TCR-beta and CD3-delta assembly was at the transmembrane region. Despite multiple genetic manipulations on CD3-gamma and zeta these proteins failed to assemble with TCR-alpha. Similarly, there was no interaction between TCR-beta and zeta. These findings when coupled with the information on pairwise interactions and formation of higher order subcomplexes extend our model for the structure of the TCR complex.

A 72-kilodalton fyn-related polypeptide (p72fyn-R) binds to the antigen-receptor/CD3 (TcR/CD3) complex

Protein-tyrosine kinases play crucial roles in the activation and transformation of T lymphocytes. In this study, we have identified a variant of the fyn kinase at 70-72 kDa (termed p72fyn-R) that can preferentially associate with the TcR/CD3 complex in certain T cells. Phosphoamine acid analysis revealed that the CD3-associated p72fyn-R is labeled on both tyrosine and serine/threonine residues. TcR/CD3-associated p72fyn-R could be specifically reprecipitated using anti-fyn antisera to both the N and C terminus of p59fyn. In addition, two-dimensional phosphotryptic peptide map patterns of TcR/CD3-associated p72fyn and anti-fyn-precipitable p72 were identical. By contrast, a comparison of p72fyn-R and p62fyn showed similarities and differences. p72fyn-R possesses a peptide corresponding to the autophosphorylation site that migrates in the same position as found for p59/62fyn. However, p72fyn-R possessed at least four novel phosphorylated sites labeled on serine and threonine residues that are absent in the p62fyn pattern. Phosphatase digestion experiments indicated that p72fyn-R is more resistant to dephosphorylation than p59/62fyn. Two-dimensional phosphotryptic analysis indicated that the novel serine/threonine phosphorylation sites were responsible for the resistance to phosphatase digestion. Although the exact nature of the relationship between p72fyn-R and p59/62fyn remains undetermined, these data indicate that TcR/CD3 may utilize novel variants of src-related kinases in the generation of signals which regulate T-cell growth.

Covalent binding of guanine nucleotides to the CD3-gamma chain of the T cell receptor/CD3 complex

In a search for proteins involved in signal transduction through the T cell receptor (TcR/CD3 complex), a recently developed highly efficient method for labeling of nucleotide binding proteins in permeabilized cells was applied. Here, we report that human CD3-gamma could be labeled by periodate-oxidized [alpha-32P] GTP (GTPoxi). In contrast to GTPoxi labeling of CD3-zeta (Peter, M. E., Hall, C., Rühlmann, A., Sancho, J. and Terhorst, C., EMBO J. 1992. 11:933), GTP-specific labeling of CD3-gamma reached a maximum when nucleotides were added 60 min prior to the cross-linking reaction. As CD3-gamma did not contain a known consensus sequence for nucleotide binding and since labeling kinetics of CD3-gamma coincided with those of cytosolic GTP-binding proteins, labeling may have been caused by a GTP-binding protein. This putative protein was not T cell specific because labeling of CD3-gamma could also be achieved when expressed in the endoplasmic reticulum of Chinese hamster ovary (CHO) cells. In CHO cells, labeling by GTPoxi took place only when CD3-gamma was associated with CD3-epsilon, whereas labeling could not be established upon association of CD3-gamma with CD3-delta or TcR alpha. The observation that CD3-gamma was labeled without leaving the endoplasmic reticulum led to the hypothesis that the association of CD3-gamma with a GTP-binding protein might be involved in an early step of the TcR/CD3 complex formation or transport.

Characterization of T cell receptor assembly and expression in a Ti gamma delta-positive cell line

T cell antigen receptor (TcR) heterodimers of both the Ti-alpha beta and Ti-gamma delta types are expressed at the surface of T cells noncovalently associated with the CD3 complex composed of the monomorphic chains gamma, delta, epsilon and zeta. The structural relationship and assembly of the various components of this multimeric protein complex is still not fully understood. In this report, the human leukemic T cell line Lyon which expresses a Ti-gamma delta/CD3 complex, was characterized and compared to another human leukemic T cell line Jurkat (Ti-alpha beta/CD3). Membrane TCR-/CD3- variants of the T cell Lyon were induced and found to produce all of the Ti/CD3 components, with the exception of Ti-delta. Biochemical analysis indicated that: (1) Ti-gamma/CD3 gamma, delta, epsilon complexes were formed in the endoplasmic reticulum in the absence of Ti-delta; (2) the CD3-zeta chain did not associate with the Ti-gamma/CD3 gamma delta epsilon complex and (3) the Ti-delta chain was required for cell surface expression of the Ti-gamma delta/CD3 complex. Introduction of Jurkat wild-type Ti-alpha cDNA into Lyon T cells resulted in Ti-alpha beta/CD3 expression and abrogated Ti-gamma delta/CD3 expression. In contrast, the expression of the Ti-gamma delta/CD3 complex was not affected by transfection of a mutated Ti-alpha cDNA into Lyon cells. The mutated Ti-alpha chain formed complexes with Ti-beta and CD3 gamma delta epsilon, but the CD3-zeta chain did not associate with these complexes. Taken together analysis of Lyon cells transfected with either wild-type or mutated Ti-alpha suggested that the CD3-zeta chain may have higher affinity for Ti-alpha beta/CD3 complexes than for Ti-gamma delta/CD3 complexes.

Does uremic environment down-regulate T cell activation via TCR/CD3 antigen receptor complex?

TCR/CD3 receptor complex plays a central role in antigen recognition and T cell activation. Therefore, the present study investigates TCR alpha/beta (TCR-1) and CD3 receptor density (RD, number of receptors per cell) on uremic CD4 T lymphocytes in relation to T cell proliferative response induced by anti-CD3 monoclonal antibodies (mAb). The influence of uremic serum on TCR/CD3 receptor expression of normal and uremic CD4 T lymphocytes was evaluated as well. We found, that: a) percentage of TCR-1 and CD3 positive cells of freshly isolated CD4 T lymphocytes is the same in controls and ESRD-patients, but the TCR/CD3 RD is lower on uremic CD4 T lymphocytes, b) Incubation for 24 h with uremic serum lowers TCR/CD3 RD on normal and uremic CD4 T cells, c) There is positive correlation between TCR/CD3 RD and anti-CD3 induced lymphocyte proliferation. These data might also support the hypothesis that blunted T-cell response to antigen in uremia is due to down-regulation of the TCR/CD3 receptor complex by uremic milieu.