The protein tyrosine kinase ZAP-70 can associate with the SH2 domain of proto-Vav

Stimulation of the T cell antigen receptor (TCR) leads to tyrosine phosphorylation of a number of cellular proteins, including the vav proto-oncogene product. We now report the detection of several phosphotyrosine proteins (80, 74, and 70 kDa) from TCR-stimulated T cells that bind to the Src homology 2 (SH2) domain of proto-Vav (Vav-SH2) and co-immunoprecipitate with the proto-Vav product. Their binding to Vav-SH2 differs from that observed with SH2 domains from other proteins. None of the Vav-SH2-associated phosphoproteins bind to either of the Src homology 3 (SH3) domains of proto-Vav or to mutant Vav-SH2 proteins. The association of the phosphoproteins with Vav-SH2 requires induction of tyrosine phosphorylation of cellular proteins since proteins from lysates of herbimycin A-treated TCR-activated T cells fail to associate with Vav-SH2. Among the proteins from T cells that co-immunoprecipitate with the proto-Vav product and bind to its SH2 domain, specific antibodies identified the 70-kDa tyrosine phosphoprotein as ZAP-70, a protein tyrosine kinase (PTK) involved in TCR signal transduction. Binding of this PTK to Vav-SH2 is inhibited by a ZAP-70-specific synthetic tyrosine phosphopeptide. We suggest that ZAP-70 may function as a PTK for proto-Vav.

ZAP-70 is constitutively associated with tyrosine-phosphorylated TCR zeta in murine thymocytes and lymph node T cells

Studies with T cell lines and clones have shown that engagement of the TCR results in the tyrosine phosphorylation of the TCR subunits. This leads to the recruitment of the ZAP-70 protein tyrosine kinase, an interaction involving the two SH2-domains of ZAP-70 with tyrosine-phosphorylated zeta and CD3. However, as previously described, murine thymocytes and lymph node T cells express a constitutively tyrosine-phosphorylated zeta subunit in the basal state. Here, we show that a fraction of ZAP-70 molecules are constitutively associated with tyrosine-phosphorylated zeta. TCR ligation promotes a large increase in the tyrosine phosphorylation of ZAP-70 as well as other TCR subunits. Genetic studies reveal that the constitutive ZAP-70 association with tyrosine-phosphorylated zeta does not absolutely require either TCR or coreceptor interactions with MHC molecules.

The role of protein kinase C in the regulation of extracellular signal-regulated kinase by the T cell antigen receptor

The aim of this study was to explore the role of protein kinase C (PKC) in the activation of mitogen-activated protein kinases (MAPK) in T lymphocytes. The MAPK extracellular signal-regulated kinase-2 (ERK2) is activated in response to phorbol esters which stimulate PKC, by transient expression of a constitutively active ras mutant by cell activation via the G protein-coupled type 1 muscarinic acetylcholine receptor (HM1R) or in response to triggering of the T cell antigen receptor (TCR). The relative contribution of PKC to TCR and HM1R regulation of ERK2 was explored by examining the effects of a PKC inhibitor (Ro 31-8425) on ERK2 activation. The data demonstrate that phorbol ester and HM1R regulation of ERK2 was prevented by the PKC inhibitor, but that the inhibitor had no effect on ERK2 activation induced by expression of a constitutively active ras mutant p21v-Ha-ras. Furthermore, the TCR stimulates both PKC and p21ras but TCR regulation of ERK2 was only weakly suppressed by the PKC inhibitor. These data indicate that PKC has a potential but not a predominant role in TCR regulation of ERK2.

The catalytic activity of the CD45 membrane-proximal phosphatase domain is required for TCR signaling and regulation

Cell surface expression of CD45, a receptor-like protein tyrosine phosphatase (PTPase), is required for T cell antigen receptor (TCR)-mediated signal transduction. Like the majority of transmembrane PTPases, CD45 contains two cytoplasmic phosphatase domains, whose relative in vivo function is not known. Site-directed mutagenesis of the individual catalytic residues of the two CD45 phosphatase domains indicates that the catalytic activity of the membrane-proximal domain is both necessary and sufficient for restoration of TCR signal transduction in a CD45-deficient cell. The putative catalytic activity of the distal phosphatase domain is not required for proximal TCR-mediated signaling events. Moreover, in the context of a chimeric PTPase receptor, the putative catalytic activity of the distal phosphatase domain is not required for ligand-induced negative regulation of PTPase function. We also demonstrate that the phosphorylation of the C-terminal tyrosine of Lck, a site of negative regulation, is reduced only when CD45 mutants with demonstrable in vitro phosphatase activity are introduced into the CD45-deficient cells. These results demonstrate that the phosphatase activity of CD45 is critical for TCR signaling, and for regulating the levels of C-terminal phosphorylated Lck molecules.

[Therapeutic interventional sonography]

By means of a review of the literature and basing on own results the possibilities of sonographically guided ontarget therapeutic interventions are disumed. Puncture of pleura, pericardium and in ascites can be performed with maximum safety. Therapeutic drainage of the effusions succeeds to practically 100 per cent. Punctures of custsare performed only if the lesions are symptomatic; sclerosing of renal cysts has a success rate of 65-80%, that of hepatic cysts up to 96%, ovarial and pancreatic cysts up to 90%. Since, however, the latter recur rapidly, permanent success can be rated as amounting to only 7%. Abscesses are punctured in installments or drained, depending on their size, shape and extension. Here, too, success rates achieved via on-target therapy guided by ultrasound are between 80 and 95%. First results obtained with ultrasound-guided on-target cholecystotomy in cases of colecystitis are encouraging; the disease pattern can be improved in at least 63% to 94% of cases, although the rate of complications is 8-12% and hence relatively high. Other techniques are also discussed, such as gastrostomy, nephrostomy, cholangiography and pancreaticography. Local on-target ultrasound-guided tumour therapy, especially of the primary hepatic cell carcinoma using highly concentrated alcohol results in a definitely longer survival period of the treated patients.

GRB2 and phospholipase C-gamma 1 associate with a 36- to 38-kilodalton phosphotyrosine protein after T-cell receptor stimulation

GRB2, a 25-kDa protein comprising a single SH2 domain flanked by two SH3 domains, has been implicated in linking receptor protein tyrosine kinases (PTKs) to the Ras pathway by interacting with the guanine nucleotide exchange protein SOS. Previous studies have demonstrated that GRB2 directly interacts with Shc, a proto-oncogene product that is tyrosine phosphorylated upon receptor and nonreceptor PTK activation. In this report, we detected low levels of tyrosine phosphorylation of Shc and induced association with GRB2 upon T-cell receptor (TCR) stimulation. Instead, a prominent 36- to 38-kDa tyrosine phosphoprotein (pp36-38) associated with the SH2 domain of GRB2 and formed a stable complex with GRB2/SOS upon TCR stimulation. Cellular fractionation studies showed that whereas both GRB2 and SOS partitioned to the soluble and particulate fractions, pp36-38 was present exclusively in the particulate fraction. This phosphoprotein had the same apparent mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as the phosphoprotein that associates with phospholipase C-gamma 1 (PLC-gamma 1). Furthermore, following partial immunodepletion of GRB2 and of the associated pp36-38, there was a significant reduction in the amount of the 36-kDa phosphoprotein associated with PLC-gamma 1, suggesting that a trimeric PLC-gamma 1/pp36-38/GRB2 complex could form. In support of this notion, we have also been able to detect low levels of PLC-gamma 1 in GRB2 immunoprecipitates. We suggest that pp36-38 may be a bridging protein, coupling different signalling molecules to cytoplasmic PTKs regulated by the TCR.

The T-cell antigen receptor utilizes Lck, Raf-1, and MEK-1 for activating mitogen-activated protein kinase. Evidence for the existence of a second protein kinase C-dependent pathway in an Lck-negative Jurkat cell mutant

T-cell antigen receptor (TCR) ligation of an Lck-deficient Jurkat mutant, J.CaM1, with anti-CD3 or anti-TCR beta monoclonal antibodies failed to induce tyrosine phosphorylation and activation of p42MAPK. The same stimuli activated mitogen-activated protein (MAP) kinase in J.CaM1 cells transfected with Lck, demonstrating that Lck plays a critical role in MAP kinase activation. Utilizing immunocomplex kinase assays, we demonstrated that TCR/CD3 ligation activated a MAP kinase kinase kinase (Raf-1) as well as a MAP kinase kinase (MEK-1) in Jurkat but not in J.CaM1 cells. It was possible, however, to activate Raf-1, MEK-1, and p42MAPK in J.CaM1 cells during treatment with the phorbol ester phorbol 12-myristate 13-acetate, which activates protein kinase C (PKC). This demonstrates the presence of a PKC-dependent pathway which functions independently from Lck in MAP kinase activation. Stimulation of Jurkat cells with either anti-TCR beta or anti-CD3 monoclonal antibody failed to induce substantial tyrosine phosphorylation of Shc proteins or their association with Grb2 which forms a complex with the guanine nucleotide exchange factor hSOS. However, the same stimuli induced tyrosine phosphorylation of another putative guanine nucleotide exchange factor, p95Vav, in Jurkat but not J.CaM1 cells. Moreover, Lck was reversibly co-immunoprecipitated with p95Vav, and the stoichiometry of binding increased in anti-CD3-treated Jurkat cells. Phorbol 12-myristate 13-acetate did not induce tyrosine phosphorylation of p95Vav. These data show that the TCR activates MAP kinase by way of a signaling cascade, which depends upon Lck, and may be mediated by downstream events involving PKC or p95Vav which act on Raf-1 and MEK-1.

ZAP-70 deficiency in an autosomal recessive form of severe combined immunodeficiency

Protein tyrosine kinases (PTKs) play an integral role in T cell activation and differentiation. Defects in the Src-family PTKs in mice and in T cell lines have resulted in variable defects in thymic development and in T cell antigen receptor (TCR) signal transduction. Here, three siblings are described with an autosomal recessive form of severe combined immunodeficiency disease (SCID) in which ZAP-70, a non-Src PTK, is absent as a result of mutations in the ZAP-70 gene. This absence is associated with defects in TCR signal transduction, suggesting an important functional role for ZAP-70.

Human severe combined immunodeficiency due to a defect in ZAP-70, a T cell tyrosine kinase

A homozygous mutation in the kinase domain of ZAP-70, a T cell receptor-associated protein tyrosine kinase, produced a distinctive form of human severe combined immunodeficiency. Manifestations of this disorder included profound immunodeficiency, absence of peripheral CD8+ T cells, and abundant peripheral CD4+ T cells that were refractory to T cell receptor-mediated activation. These findings demonstrate that ZAP-70 is essential for human T cell function and suggest that CD4+ and CD8+ T cells depend on different intracellular signaling pathways to support their development or survival.

Differential expression of ZAP-70 and Syk protein tyrosine kinases, and the role of this family of protein tyrosine kinases in TCR signaling

TCR stimulation results in the tyrosine phosphorylation of a number of cellular substrates. We have recently identified a 70-kDa protein tyrosine kinase, ZAP-70, which associates with the human TCR zeta-chain after TCR stimulation. We report here the isolation and sequence of a cDNA clone that encodes murine ZAP-70. Murine and human ZAP-70 share 93% amino acid identity and are homologous to the 72-kDa protein tyrosine kinase Syk. Syk has been implicated in the signal transduction pathways of the B cell membrane Ig and high affinity IgE receptors, Fc epsilon RI. In addition, we examined the tissue distribution of ZAP-70 and Syk in human and murine thymocyte subsets, B cells, and peripheral T cell subsets. ZAP-70 protein is expressed in all major thymocyte populations, with the level of expression being comparable to that found in both CD4+ and CD8+ peripheral T cells. Although Syk protein is also present in all thymocyte subsets, expression of Syk protein is down-regulated threefold to fourfold in peripheral T cells. In contrast to ZAP-70, expression of Syk is 12- to 15-fold higher in peripheral B cells when compared with peripheral T cells. In addition, whereas T cell stimulation results in down-regulation of Lck, no significant change in ZAP-70 or Syk protein is detected. Finally, we provide evidence that both ZAP-70 and Syk can associate with the TCR after TCR stimulation. With the use of a heterologous expression system, we show that, like ZAP-70, Syk is dependent upon a Src-family protein tyrosine kinase for association with the phosphorylated zeta-chain. Thus, the differential expression of these kinases suggests the possibility of different roles for ZAP-70 and Syk in TCR signaling and thymic development.

Differential expression of ZAP-70 and Syk protein tyrosine kinases, and the role of this family of protein tyrosine kinases in TCR signaling

TCR stimulation results in the tyrosine phosphorylation of a number of cellular substrates. We have recently identified a 70-kDa protein tyrosine kinase, ZAP-70, which associates with the human TCR zeta-chain after TCR stimulation. We report here the isolation and sequence of a cDNA clone that encodes murine ZAP-70. Murine and human ZAP-70 share 93% amino acid identity and are homologous to the 72-kDa protein tyrosine kinase Syk. Syk has been implicated in the signal transduction pathways of the B cell membrane Ig and high affinity IgE receptors, Fc epsilon RI. In addition, we examined the tissue distribution of ZAP-70 and Syk in human and murine thymocyte subsets, B cells, and peripheral T cell subsets. ZAP-70 protein is expressed in all major thymocyte populations, with the level of expression being comparable to that found in both CD4+ and CD8+ peripheral T cells. Although Syk protein is also present in all thymocyte subsets, expression of Syk protein is down-regulated threefold to fourfold in peripheral T cells. In contrast to ZAP-70, expression of Syk is 12- to 15-fold higher in peripheral B cells when compared with peripheral T cells. In addition, whereas T cell stimulation results in down-regulation of Lck, no significant change in ZAP-70 or Syk protein is detected. Finally, we provide evidence that both ZAP-70 and Syk can associate with the TCR after TCR stimulation. With the use of a heterologous expression system, we show that, like ZAP-70, Syk is dependent upon a Src-family protein tyrosine kinase for association with the phosphorylated zeta-chain. Thus, the differential expression of these kinases suggests the possibility of different roles for ZAP-70 and Syk in TCR signaling and thymic development.

The cytoplasmic domain of CD28 is both necessary and sufficient for costimulation of interleukin-2 secretion and association with phosphatidylinositol 3'-kinase

T-cell activation requires two signaling events. One is provided by the engagement of the T-cell antigen receptor, and the second represents a costimulatory signal provided by antigen-presenting cells. CD28 mediates a costimulatory signal by binding its ligands, B7-1 and B7-2, on antigen-presenting cells, but the signaling pathway activated by CD28 has not been identified. A homologous molecule, CTLA-4, expressed on activated T cells, also binds to B7-1 and B7-2, but whether it has a signaling function is not known. We performed a structure-function analysis of CD28 to identify the functional domain which activates signal transduction. Truncation of the 40-amino-acid CD28 cytoplasmic tail abrogated costimulatory signaling. Chimeric constructs containing the extracellular and transmembrane regions of CD8 linked to the cytoplasmic region of CD28 had a costimulatory signaling function. Similar chimeras containing the cytoplasmic tail of CTLA-4 did not signal. Thus, the cytoplasmic region of CD28, but not CTLA-4, is sufficient to mediate costimulatory signaling. In addition, after CD28 stimulation, the p85 subunit of phosphatidylinositol 3'-kinase and phosphatidylinositol 3'-kinase activity were found in CD28 immunoprecipitates. The CD8-CD28 chimera, which has a costimulatory signaling function, associates with p85, while the nonfunctioning CD8-CTLA-4 chimera and a CD8-zeta chimera do not associate with p85. These results suggest that phosphatidylinositol 3'-kinase is specifically activated by CD28 and may mediate proximal events in the costimulatory signaling pathway regulated by CD28.

Molecular cloning of human Syk. A B cell protein-tyrosine kinase associated with the surface immunoglobulin M-B cell receptor complex

B cell antigen receptors are multicomponent complexes consisting of the surface immunoglobulin and accessory molecules with associating protein-tyrosine kinases. A spleen tyrosine kinase, Syk, in porcine B cells and a 72-kDa protein-tyrosine kinase, PTK72, in murine B cells associate with the B cell antigen receptor. Herein, we report the isolation of a full-length cDNA encoding the human homologue of Syk. This cDNA predicted a polypeptide consisting of two NH2-terminal SH2 domains and a COOH-terminal tyrosine kinase domain. Syk is highly conserved between human and swine and is homologous to the T cell-associated protein-tyrosine kinase ZAP-70. Both Syk mRNA and protein were detected in cells derived from multiple hematopoietic lineages. Within the B cell compartment, Syk was expressed from pro-B cells to plasma cells. In vitro kinase assays conducted on the human Syk protein isolated from B cells revealed the presence of autophosphorylation activity on Syk tyrosine residues. Tyrosine phosphorylation of Syk associating with the B cell receptor complex in human was augmented rapidly after surface immunoglobulin cross-linking. The human SYK locus was mapped to chromosome 9 at band q22.

Production and characterization of monoclonal antibodies specific for the murine T cell receptor zeta chain

The T cell receptor (TCR) comprises an antigen-specific alpha beta heterodimer non-covalently associated with the CD3 gamma delta epsilon and TCR zeta subunits. Both the CD3 and TCR zeta subunits are proposed to be responsible for the intracellular signal-transduction events. We report here the production of eight monoclonal antibodies (mAbs) that bind in an ELISA assay to a 113 amino acid synthetic peptide corresponding to the cytoplasmic domain of TCR zeta. Western blot analysis of anti-CD8 precipitates of lysates of transfectants expressing chimeric CD8/zeta constructs encoding increasing COOH-terminal truncations of TCR zeta indicates that four of these mAbs recognized the region of TCR zeta chain comprising the last 29 COOH-terminal residues. Thus, this region of TCR theta may encode an immunodominant epitope. Furthermore, one of these mAbs, G3, is capable of precipitating both non-phosphorylated and tyrosine phosphorylated TCR zeta. The G3 mAb should be useful for elucidating the structural and signalling characteristics of the TCR zeta chain.

The role of protein tyrosine kinases and protein tyrosine phosphatases in T cell antigen receptor signal transduction

Engagement of the T cell antigen receptor (TCR) by peptide antigen bound to the major histocompatibility complex (MHC) molecules initiates a biochemical cascade involving protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPases). Recent biochemical and genetic evidence has implicated at least three cytoplasmic protein tyrosine kinases (PTKs), Lck, Fyn, and ZAP-70, that are involved in the initiation of TCR signal transduction. In addition, genetic evidence has demonstrated the requirement of the transmembrane PTPase, CD45, for TCR function. Activation of T cells through the TCR represents an alteration in the dynamic equilibrium between PTKs and PTPases. The TCR is a multi-subunit complex composed of at least six different gene products. Dissection of the TCR utilizing chimeric receptors and TCR mutants has demonstrated that the multi-subunit receptor is composed of at least two signal transducing modules, the CD3 and the zeta chain subunits. These two modules have in common peptide sequences within their cytoplasmic domains termed antigen recognition activation motifs (ARAMs) that are responsible for transducing signaling events. Moreover, the ARAM sequence is also found in subunits associated with a variety of other hematopoietic cell antigen receptors and is likely to form the basis for interactions with effector molecules within the signaling cascades of these receptors. Here we review the mechanism by which the ARAM sequences interact with PTKs and the cascades of PTKs and PTPases that are involved in mediating TCR function.

The in vitro influence of different culture conditions on the potential of sheep rib perichondrium to form hyaline-like cartilage. Evaluation of gluing materials used for in vivo graft fixation

The effectiveness of autologous rib perichondrium for repair of full-thickness hyaline cartilage defects has been shown experimentally and clinically in various reports. The purpose of this study was to examine the behaviour of sheep rib perichondrial tissue under in vitro conditions and the influence of different culture matrices in order to evaluate possible stimulating effects. Rib perichondrium was obtained from sheep used for an experimental in vivo trial. After removal of adjacent cartilage remnants the tissue was divided and specimens cultured for 14 days in different ways. Explants cultured on collagen sponges (group A), fibrin glue (group B) and cellulose acetate filter (group C) were examined histologically, histochemically, histomorphometrically and autoradiographically. Clear differentiation of perichondrial cells towards a chondrocyte-like cell shape, particularly in the proliferation zone, was noticed on all matrices. These cells synthesized new matrix substances comparable to the ground substance normally present in hyaline cartilage. Morphometric comparison of tissue differentiation on different culture matrices revealed no significant differences in proliferation rates.

Sequential interactions of the TCR with two distinct cytoplasmic tyrosine kinases

The T cell antigen receptor (TCR) initiates signals by interacting with cytoplasmic protein tyrosine kinases (PTKs) through a 17-residue sequence motif [called the antigen recognition activation motif (ARAM)] that is contained in the TCR zeta and CD3 chains. TCR stimulation induces the tyrosine phosphorylation of several cellular substrates, including the ARAMs. Lck kinase activity is required for phosphorylation of two conserved tyrosine residues in an ARAM. This phosphorylation leads to the recruitment of a second cytoplasmic PTK, ZAP-70, through both of the ZAP-70 Src homology 2 domains and its phosphorylation. Thus, TCR signal transduction is initiated by the sequential interaction of two PTKs with TCR ARAMs.

V beta gene repertoires in T cells expanded in local self-healing and lethal systemic murine cutaneous leishmaniasis

Inbred mice infected with Leishmania major promastigotes display two different courses of leishmaniasis: resistant strains develop self-healing local sores, while susceptible strains show progressive systemic disease with lethal outcome. Resistance predominantly correlates with the production of T helper type 1 (TH1) lymphokines and susceptibility with production of TH2-type lymphokines. Here, we analyzed whether this TH phenotype difference correlates with expression of particular T cell receptor V beta chains. Our results show that T cells expand strongly during infection in all groups of mice and invariantly express the same V beta gene families as prior to infection. Our data indicate that TH1 and TH2 cells use similar V beta gene families, and argue against the engagement of a restricted set of V beta by dominant determinants associated with L. major.

Signal transduction by lymphocyte antigen receptors

Despite the differences in the antigens that they recognize and in the effector functions they carry out, B and T lymphocytes utilize remarkably similar signal transduction components to initiate responses. They both use oligomeric receptors that contain distinct recognition and signal transduction subunits. Antigen receptors on both cells interact with at least two distinct families of PTKs via common sequence motifs, ARAMs, in the cytoplasmic tails of their invariant chains, which have likely evolved from a common evolutionary precursor. Coreceptors appear to serve to increase the sensitivity of both of these receptor systems through events that influence ligand binding and signal transduction. The critical role of tyrosine phosphorylation of downstream signaling components, such as phospholipase C, is the net result of changes in the balance of the action of antigen receptor-regulated PTKs and PTPases. The identification of downstream effectors, including calcineurin and Ras, that regulate cellular responses, such as lymphokine gene expression, promises the future possibility of connecting the complex pathway from the plasma membrane to the nucleus in lymphocytes. Insight gained from studies of the signaling pathways downstream of TCR and BCR stimulation is likely to contribute significantly to future understanding of mechanisms responsible for lymphocyte differentiation and for the discrimination of self from nonself in developing and mature cells.