Activation of Zap-70 tyrosine kinase due to a structural rearrangement induced by tyrosine phosphorylation and/or ITAM binding

Advances in CD247

CD247, which is also known as CD3ζ, CD3H, CD3Q, CD3Z, IMD25, T3Z, and TCRZ, encodes CD3ζ protein, which is expressed primarily in natural killer (NK) and T cells. Since the discovery of the ζ peptide in 1986, it has been continuously investigated. In this paper, we review the composition, molecular mechanisms and regulatory factors of CD247 expression in T cells; and review the autoimmune diseases, tumors and inflammatory diseases associated with CD247, providing a detailed and comprehensive reference for further research on the mechanism of CD247 and related diseases.

Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

Induction/engineering, detection, selection, and expansion of clinical-grade human antigen-specific CD8 cytotoxic T cell clones for adoptive immunotherapy

Adoptive transfer of effector antigen-specific immune cells is becoming a promising treatment option in allogeneic transplantation, infectious diseases, cancer, and autoimmune disorders. Within this context, the important role of CD8+ cytotoxic T cells (CTLs) is objective of intensive studies directed to their in vivo and ex vivo induction, detection, selection, expansion, and therapeutic effectiveness. Additional questions that are being addressed by the scientific community are related to the establishment and maintenance of their longevity and memory state as well as to defining critical conditions underlying their transitions between discrete, but functionally different subtypes. In this article we review and comment latest approaches and techniques used for preparing large amounts of antigen-specific CTLs, suitable for clinical use.

The Src, Syk, and Tec family kinases: distinct types of molecular switches

The Src, Syk, and Tec family kinases are three of the most well characterized tyrosine kinase families found in the human genome. Members of these kinase families function downstream of antigen and F(c) receptors in hematopoietic cells and transduce signals leading to calcium mobilization, altered gene expression, cytokine production, and cell proliferation. Over the last several years, structural and biochemical studies have begun to uncover the molecular mechanisms regulating activation of these kinases. It appears that each kinase family functions as a distinct type of molecular switch. This review discusses the activation of the Src, Syk, and Tec kinases from the perspective of structure, phosphorylation, allosteric regulation, and kinetics. The multiple factors that regulate the Src, Syk, and Tec families illustrate the important role played by each of these kinases in immune cell signaling.

Synergistic inhibition of T-cell activation by a cell-permeable ZAP-70 mutant and ctCTLA-4

T-cell activation requires TcR-mediated and co-stimulatory signals. ZAP-70 participates in the initial step of TcR signal transduction, while a co-receptor, CTLA-4, inhibits T-cell activation. In previous studies, the overexpression of a ZAP-70 mutant (ZAP-70-Y319F) inhibited the TcR-induced activation of NFAT and IL-2 production, while Hph-1-ctCTLA-4 prevented allergic inflammation. To develop an effective immunosuppressive protein drug that blocks both TcR-mediated and co-stimulatory signaling pathways, a fusion protein of ZAP-70-Y319F and the Hph-1 protein transduction domain was generated. Hph-1-ZAP-70-Y319F inhibited the phosphorylation of ZAP-70-Tyr319, LAT-Tyr191, and p44/42 MAPK induced by TcR stimulation, NFAT- and AP-1-mediated gene transcription, and the induction of CD69 expression and IL-2 secretion. Hph-1-ZAP-70-Y319F and Hph-1-ctCTLA-4 synergistically inhibited signaling events during T-cell activation. This is the first report to demonstrate the synergistic inhibition of signals transmitted via TcR and its co-stimulatory receptor by cell-permeable forms of intracellular signal mediators.

Molecular mechanism of the Syk activation switch

Many immune signaling pathways require activation of the Syk tyrosine kinase to link ligation of surface receptors to changes in gene expression. Despite the central role of Syk in these pathways, the Syk activation process remains poorly understood. In this work we quantitatively characterized the molecular mechanism of Syk activation in vitro using a real time fluorescence kinase assay, mutagenesis, and other biochemical techniques. We found that dephosphorylated full-length Syk demonstrates a low initial rate of substrate phosphorylation that increases during the kinase reaction due to autophosphorylation. The initial rate of Syk activity was strongly increased by either pre-autophosphorylation or binding of phosphorylated immune tyrosine activation motif peptides, and each of these factors independently fully activated Syk. Deletion mutagenesis was used to identify regions of Syk important for regulation, and residues 340-356 of the SH2 kinase linker region were identified to be important for suppression of activity before activation. Comparison of the activation processes of Syk and Zap-70 revealed that Syk is more readily activated by autophosphorylation than Zap-70, although both kinases are rapidly activated by Src family kinases. We also studied Syk activity in B cell lysates and found endogenous Syk is also activated by phosphorylation and immune tyrosine activation motif binding. Together these experiments show that Syk functions as an "OR-gate" type of molecular switch. This mechanism of switch-like activation helps explain how Syk is both rapidly activated after receptor binding but also sustains activity over time to facilitate longer term changes in gene expression.

3D structure of Syk kinase determined by single-particle electron microscopy

The cytoplasmic Syk kinase plays key roles in immune responses and comprises two N-terminal regulatory Src homology 2 (SH2) domains followed by a catalytic region. Atomic structures of these domains have only been solved in isolation. To gain insights into the three-dimensional structure of full-length Syk, we have used single-particle electron microscopy. Syk acquires a closed conformation resembling the inhibited structure of Zap-70, another member of the Syk family. Such configuration suggests an inhibition of the N-terminal domains on its catalytic activity. The phosphotyrosine binding pockets of both SH2 domains are not occluded and they could interact with other phosphoproteins.

TCR-Dependent Cell Response Is Modulated by the Timing of CD43 Engagement

Binding of Ag by the Ag receptor in combination with other stimuli provided by costimulatory receptors triggers the expansion and differentiation of T lymphocytes. However, it is unclear whether the time when costimulatory molecules interact with their counterreceptors with regards to Ag recognition leads to different T cell responses. Provided that the coreceptor molecule CD43 is a very abundant molecule evenly distributed on the membrane of T cell surface protruding 45 nm from the cell, we hypothesized that CD43 is one of the first molecules that interacts with the APC and thus modulates TCR activation. We show that engaging CD43 before or simultaneously with the TCR inhibited Lck-Src homology 2 domain containing phosphatase-1 interaction, preventing the onset of a negative feedback loop on TCR signals, favoring high levels of IL-2, cell proliferation, and secretion of proinflammatory cytokines and chemokines. In contrast, the intracellular signals resulting of engaging the TCR before CD43 were insufficient to induce IL-2 production and cell proliferation. Interestingly, when stimulated through the TCR and CD28, cells proliferated vigorously, independent of the order with which molecules were engaged. These results indicate that CD43 induces a signaling cascade that prolongs the duration of TCR signaling and support the temporal summation model for T cell activation. In addition to the strength and duration of intracellular signals, our data underscore temporality with which certain molecules are engaged as yet another mechanism to fine tune T cell signal quality, and ultimately immune function.

Determination of regulatory phosphorylation sites in nanogram amounts of a synthetic fragment of ZAP-70 using microprobe NMR and on-line coupled capillary HPLC-NMR

The protein kinase ZAP-70 is involved in T-cell activation and interacts with tyrosine-phosphorylated peptide sequences known as immunoreceptor tyrosine activation motifs (ITAMs). We have studied the regulatory phosphorylation sites in the tryptic fragment containing amino acids 485-496 (ALGADDSYYTAR). The four possible peptides with phosphorylation at none, one, or both of the Y-492 and Y-493 tyrosines were specifically synthesized and analyzed by (1)H/(13)C-NMR at 600 MHz using a capillary HPLC-NMR microprobe. Unambiguous discrimination of the peptides was possible via effect of chemical shifts of phosphorylation on the aromatic tyrosine protons. With the microprobe and the detection volume of 1.5 microl, it was possible to perform structure elucidation with the very small amounts available for the various peptides. For the syringe injection, 15 microg of the analyte were used (corresponding to ca 2 mg in classical 5-mm tubes). Capillary HPLC-NMR spectra were recorded in the stopped-flow mode from less than 400 ng of each peptide, using 1D and 2D techniques ((1)H,(1)H-COSY-90, (1)H/(13)C-HSQC, and (1)H/(13)C-HMBC).

Qualitatively differential regulation of T cell activation and apoptosis by T cell receptor zeta chain ITAMs and their tyrosine residues

The issue of whether three ITAMs in the TCR zeta chain can transmit qualitatively distinct signals or redundantly amplify TCR-mediated activation signals was extensively investigated using stable hCD8-zeta Jurkat transfectants which contain stepwise deletions of each ITAM or mutations of tyrosine residues in each ITAM of TCR zeta chain. The influence of mutations of each tyrosine residue on reduction of the amount and species of tyrosine phosphorylated proteins recruited to zeta chain was quite distinctive, but they were roughly proportional to the number of functionally intact ITAMs. However, the first N-terminal ITAM had a signaling potential to trigger most intracellular signaling events for T cell activation and apoptosis similar to wild-type CD8-zeta, but this level was substantially reduced in the presence of the first and second N-terminal ITAM together. Mutations of tyrosine residues in first and second N-terminal ITAM significantly impaired most signaling events leading to T cell activation and activation-induced cell death, but phosphorylation of mitogen-activated protein kinases (MAPKs) was differentially impaired in each mutant. The mutation of the first tyrosine residue in C-terminal ITAM did not show any impairment in induction of surface antigens and cell death, but rather increased IL-2 secretion and MAPK phosphorylation. Therefore, in this study we demonstrated that the ITAMs and their tyrosine residues of TCR zeta chain can transmit qualitatively differential intracellular signals upon TCR stimulation through distinctive regulation of recruitment of tyrosine phosphorylated proteins to zeta chain and activation of various MAPKs.

The three-dimensional structure of the ZAP-70 kinase domain in complex with staurosporine: implications for the design of selective inhibitors

The ZAP-70 tyrosine kinase plays a critical role in T cell activation and the immune response and therefore is a logical target for immunomodulatory therapies. Although the crystal structure of the tandem Src homology-2 domains of human ZAP-70 in complex with a peptide derived from the zeta subunit of the T cell receptor has been reported (Hatada, M. H., Lu, X., Laird, E. R., Green, J., Morgenstern, J. P., Lou, M., Marr, C. S., Phillips, T. B., Ram, M. K., Theriault, K., Zoller, M. J., and Karas, J. L. (1995) Nature 377, 32-38), the structure of the kinase domain has been elusive to date. We crystallized and determined the three-dimensional structure of the catalytic subunit of ZAP-70 as a complex with staurosporine to 2.3 A resolution, utilizing an active kinase domain containing residues 327-606 identified by systematic N- and C-terminal truncations. The crystal structure shows that this ZAP-70 kinase domain is in an active-like conformation despite the lack of tyrosine phosphorylation in the activation loop. The unique features of the ATP-binding site, identified by structural and sequence comparison with other kinases, will be useful in the design of ZAP-70-selective inhibitors.

Identification of a novel isoform of ZAP-70, truncated ZAP kinase

We identified a novel cDNA encoding truncated ZAP-70, which lacked the SH2 domain and a part of interdomain B, and named it truncated ZAP kinase (TZK). TZK was expressed in the thymus, spleen, and lymph nodes with ZAP-70. TZK was expressed in CD44+CD25- thymocytes up to mature T cells, but ZAP-70 was not expressed in CD44+CD25- or CD44+CD25+ thymocytes. ZAP-70 or TZK was transfected into P116 cells derived from a Jurkat T-cell line deficient in ZAP-70. The P116 cells with ZAP-70 induced the T-cell receptor-mediated signal transduction, but the cells expressing TZK did not. While ZAP-70 was accumulated at the immune synapse, TZK was not. Meanwhile, impaired phosphorylation of SLP-76, one of the substrates of ZAP-70, in P116 cells upon pervanadate stimulation was rescued in the cells expressing TZK. These findings show that TZK is a novel isoform of ZAP-70, which is expressed in pre-T-cell receptor-minus thymocytes and functions as a kinase not associated with T-cell receptor.

Changes in actin dynamics at the T-cell/APC interface: implications for T-cell anergy?

Over the past 20 years the role of the actin cytoskeleton in the formation of the immunological synapse and in T-cell activation has been the subject of intense scrutiny. T-cell receptor (TCR) signaling leads to tyrosine phosphorylation of numerous adapter proteins whose function is to relay signals to downstream components of the TCR signaling pathway and, in particular, to molecules implicated in remodeling the actin cytoskeleton. Here, we discuss how signals from the TCR converge on two key regulators of the actin cytoskeleton, Ena/vasodilator-stimulated phosphoproteins (VASPs) and the actin-related protein (ARP2/3) complex. We also discuss the implications of TCR signaling in the process of T-cell anergy with particular emphasis on the actin remodeling and molecules involved in the control of T-cell proliferation.

Amplification of B cell antigen receptor signaling by a Syk/ITAM positive feedback loop

We have established a protocol allowing transient and inducible coexpression of many foreign genes in Drosophila S2 Schneider cells. With this powerful approach of reverse genetics, we studied the interaction of the protein tyrosine kinases Syk and Lyn with the B cell antigen receptor (BCR). We find that Lyn phosphorylates only the first tyrosine whereas Syk phosphorylates both tyrosines of the BCR immunoreceptor tyrosine-based activation motif (ITAM). Furthermore, we show that Syk is a positive allosteric enzyme, which is strongly activated by the binding to the phosphorylated ITAM tyrosines, thus initiating a positive feedback loop at the receptor. The BCR-dependent Syk activation and signal amplification is efficiently counterbalanced by protein tyrosine phosphatases, the activity of which is regulated by H(2)O(2) and the redox equilibrium inside the cell.

Tyrosine 315 determines optimal recruitment of ZAP-70 to the T cell antigen receptor

Recruitment of ZAP-70 protein tyrosine kinase to the T cell antigen receptor (TCR) is mediated by the binding of the SH2 domains of this enzyme to phosphorylated ITAM motifs in the CD3 and TCRzeta subunits. We have previously shown that the efficiency of both positive and negative thymocyte selection was decreased in knock-in mice expressing ZAP-70 mutated at Tyr315 (ZAP-70-Y315F), a residue laying in the interdomain B of this protein. Surprisingly, in these cells the amount of phosphorylated TCRzeta chain co-precipitating with ZAP-70-Y315F was significantly reduced compared to control mice. We report now that the binding affinity of ZAP-70-Y315F to phosphorylated ITAM is reduced as compared to the wild-type protein, whereas the intrinsic catalytic activity is untouched. Consequently, phosphorylated ITAM appear to be more accessible to protein tyrosine phosphatases (PTP) and can be readily dephosphorylated. We provide evidence suggesting that the defective ITAM binding induced by Tyr315 mutation is independent of the putative role of this residue as a binding site for Vav-1. Finally, we found that the extracellular signal-regulated kinase pathway is impaired in ZAP-70-Y315F-expressing mice. Collectively, these results demonstrate that Tyr315 has an unsuspected structural role in ZAP-70 and may allosterically regulate the function of the nearby SH2 domains.

T cell development and T cell responses in mice with mutations affecting tyrosines 292 or 315 of the ZAP-70 protein tyrosine kinase

After stimulation of the T cell receptor (TCR), the tyrosine residues 292 and 315 in interdomain B of the protein tyrosine kinase ZAP-70 become phosphorylated and plausibly function as docking sites for Cbl and Vav1, respectively. The two latter proteins have been suggested to serve as substrates for ZAP-70 and to fine-tune its function. To address the role of these residues in T cell development and in the function of primary T cells, we have generated mice that express ZAP-70 molecules with Tyr to Phe substitution at position 292 (Y292F) or 315 (Y315F). When analyzed in a sensitized TCR transgenic background, the ZAP-70 Y315F mutation reduced the rate of positive selection and delayed the occurrence of negative selection. Furthermore, this mutation unexpectedly affected the constitutive levels of the CD3-zeta p21 phosphoisoform. Conversely, the ZAP-70 Y292F mutation upregulated proximal events in TCR signaling and allowed more T cells to produce interleukin 2 and interferon gamma in response to a given dose of antigen. The observation that ZAP-70 Y292F T cells have a slower rate of ligand-induced TCR downmodulation suggests that Y292 is likely involved in regulating the duration activated TCR reside at the cell surface. Furthermore, we showed that Y292 and Y315 are dispensable for the TCR-induced tyrosine phosphorylation of Cbl and Vav1, respectively. Therefore, other molecules present in the TCR signaling cassette act as additional adaptors for Cbl and Vav1. The present in vivo analyses extend previous data based on transformed T cell lines and suggest that residue Y292 plays a role in attenuation of TCR signaling, whereas residue Y315 enhances ZAP-70 function.