Proteome analysis reveals caspase activation in hyporesponsive CD4 T lymphocytes induced in vivo by the oral administration of antigen

Bridging the Gap: Modulatory Roles of the Grb2-Family Adaptor, Gads, in Cellular and Allergic Immune Responses

Antigen receptor signaling pathways are organized by adaptor proteins. Three adaptors, LAT, Gads, and SLP-76, form a heterotrimeric complex that mediates signaling by the T cell antigen receptor (TCR) and by the mast cell high affinity receptor for IgE (FcεRI). In both pathways, antigen recognition triggers tyrosine phosphorylation of LAT and SLP-76. The recruitment of SLP-76 to phospho-LAT is bridged by Gads, a Grb2 family adaptor composed of two SH3 domains flanking a central SH2 domain and an unstructured linker region. The LAT-Gads-SLP-76 complex is further incorporated into larger microclusters that mediate antigen receptor signaling. Gads is positively regulated by dimerization, which promotes its cooperative binding to LAT. Negative regulation occurs via phosphorylation or caspase-mediated cleavage of the linker region of Gads. FcεRI-mediated mast cell activation is profoundly impaired in LAT- Gads- or SLP-76-deficient mice. Unexpectedly, the thymic developmental phenotype of Gads-deficient mice is much milder than the phenotype of LAT- or SLP-76-deficient mice. This distinction suggests that Gads is not absolutely required for TCR signaling, but may modulate its sensitivity, or regulate a particular branch of the TCR signaling pathway; indeed, the phenotypic similarity of Gads- and Itk-deficient mice suggests a functional connection between Gads and Itk. Additional Gads binding partners include costimulatory proteins such as CD28 and CD6, adaptors such as Shc, ubiquitin regulatory proteins such as USP8 and AMSH, and kinases such as HPK1 and BCR-ABL, but the functional implications of these interactions are not yet fully understood. No interacting proteins or function have been ascribed to the evolutionarily conserved N-terminal SH3 of Gads. Here we explore the biochemical and functional properties of Gads, and its role in regulating allergy, T cell development and T-cell mediated immunity.

Bridging the Gap: Modulatory Roles of the Grb2-Family Adaptor, Gads, in Cellular and Allergic Immune Responses

Antigen receptor signaling pathways are organized by adaptor proteins. Three adaptors, LAT, Gads, and SLP-76, form a heterotrimeric complex that mediates signaling by the T cell antigen receptor (TCR) and by the mast cell high affinity receptor for IgE (FcεRI). In both pathways, antigen recognition triggers tyrosine phosphorylation of LAT and SLP-76. The recruitment of SLP-76 to phospho-LAT is bridged by Gads, a Grb2 family adaptor composed of two SH3 domains flanking a central SH2 domain and an unstructured linker region. The LAT-Gads-SLP-76 complex is further incorporated into larger microclusters that mediate antigen receptor signaling. Gads is positively regulated by dimerization, which promotes its cooperative binding to LAT. Negative regulation occurs via phosphorylation or caspase-mediated cleavage of the linker region of Gads. FcεRI-mediated mast cell activation is profoundly impaired in LAT- Gads- or SLP-76-deficient mice. Unexpectedly, the thymic developmental phenotype of Gads-deficient mice is much milder than the phenotype of LAT- or SLP-76-deficient mice. This distinction suggests that Gads is not absolutely required for TCR signaling, but may modulate its sensitivity, or regulate a particular branch of the TCR signaling pathway; indeed, the phenotypic similarity of Gads- and Itk-deficient mice suggests a functional connection between Gads and Itk. Additional Gads binding partners include costimulatory proteins such as CD28 and CD6, adaptors such as Shc, ubiquitin regulatory proteins such as USP8 and AMSH, and kinases such as HPK1 and BCR-ABL, but the functional implications of these interactions are not yet fully understood. No interacting proteins or function have been ascribed to the evolutionarily conserved N-terminal SH3 of Gads. Here we explore the biochemical and functional properties of Gads, and its role in regulating allergy, T cell development and T-cell mediated immunity.

Proteomic change of peripheral lymphocytes from scald injury and Pseudomonas aeruginosa sepsis in rabbits

BACKGROUND

Increased susceptibility to infection has been related to impairment of lymphocyte-regulated immune responses after severe burn. The aim of this study is to identify the differential expression of proteins in circulating lymphocytes from scald injury and Pseudomonas aeruginosa sepsis in rabbits to provide a basis for pathogenesis of burns and sepsis.

METHODS

Rabbits were subjected to sham burn (A), 30% scald (B), A+bacterial challenge (C) or B+bacterial challenge (D). Bacterial challenge was inflicted by an injection of 2.0x10(8) CFU P. aeruginosa (ATCC27853) in the auricular vein 22 h after the burn procedure. The animals were sacrificed 24 h later. Lymphocytes were isolated, and the differential proteins in the lymphocytes from the experimental and control animals were identified by two-dimensional electrophoresis (2-DE) coupled with matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), two of which were confirmed by Western blotting.

RESULTS

Nineteen differential protein spots were found by 2-DE and 12 spots (11 proteins) were identified. Differential expression of peroxiredoxin and annexin I was validated by Western blotting. Among the identified proteins, the expression levels of cofilin, cyclophilin A, ubiquitin, nucleoside diphosphate kinase, glutamate dehydrogenase and annexin I were down-regulated in group B, excessively down-regulated in group D, but mildly in group C, and peroxiredoxin was up-regulated in groups B and D.

CONCLUSIONS

Proteome changes in lymphocytes from P. aeruginosa sepsis in the scalded rabbits were revealed, which are related to immune suppression and the pathogenesis of sepsis after scald injury.

Targeted cleavage of signaling proteins by caspase 3 inhibits T cell receptor signaling in anergic T cells

T cell receptor (TCR) engagement in the absence of costimulation induces the calcium-dependent upregulation of a program of gene expression that leads to the establishment of T cell anergy. Casp3 is one of the genes activated during anergy induction. Here we show that caspase 3 is required for the induction of T cell unresponsiveness. Suboptimal T cell stimulation induced caspase 3 activation, which did not result in cell death. Furthermore, caspase 3-deficient T cells showed impaired responses to anergizing stimuli. In anergic T cells, activated caspase 3 associated to the plasma membrane, where it cleaved and inactivated proteins such as the Grb2-related adaptor downstream of shc (GADS) and the guanine-nucleotide exchange factor Vav1, causing a blockade in TCR signaling. Our results identify a role for caspase 3 in nonapoptotic T cells and support that caspase 3-dependent proteolytic inactivation of signaling proteins is essential to maintain T cell tolerance.

Identification of the genes specifically expressed in orally tolerized T cells

Oral tolerance is the systemic immunological unresponsiveness that occurs after feeding protein antigens. Its physiological role is thought to be the prevention of hypersensitivity to food antigens, and its therapeutic use to treat inflammatory diseases has been suggested. Although it has been shown that CD4(+) T cells mediate oral tolerance, the precise molecular mechanisms remain unclear. In the present study, we employed suppression subtractive hybridization and identified 10 genes specifically expressed in orally tolerized T cells. These included genes that were interesting in terms of their putative functions in the negative regulation of T cell activation, e.g. Culin 1, LAX, and Zfhx1b, as well as four genes that encoded unknown proteins. We further investigated the expression of these genes in hyporesponsive T cells induced in vitro (in vitro anergized T cells). We found that six of the 10 genes were highly expressed in these cells, and kinetic studies suggested that one was associated with the induction of anergy, while the other five were associated with the maintenance of anergy. The remaining 4 genes that were not expressed in in vitro anergized T cells are also of interest as they may play a specific role in in vivo T cell tolerance. Functional analysis of these genes should help to understand the complex mechanisms underlying the induction and maintenance of oral tolerance, and moreover, in vivo immune tolerance in general.

Contributions to our understanding of T cell physiology through unveiling the T cell proteome

Since the sequencing of the human genome was completed, attention has turned to examining the functionality of the molecular machinery, in particular of protein expression. Differential proteome analysis by two-dimensional electrophoresis has been adopted to study changes in T cell proteomes during T cell activation, and this work is increasing our understanding of the complexity of signals elicited across multiple pathways. The purpose of this review is to summarize the available evidence in the application of proteomic techniques and methodologies to understand T cell receptor activation from lipid raft and cytoskeletal rearrangements, through to signalling cascades, transcription factor modulation and changes in protein expression patterns. These include post-translational modifications, which are not encoded by the genome.

Molecular mechanisms of late endosome morphology, identity and sorting

Recent studies using electron microscopy, protein crystallography, classic biochemistry and novel live-cell imaging have provided numerous insights into the endocytic pathway, describing a dynamic system in which compartment morphology, molecular identity and the mechanics of cargo sorting are intimately connected. Current evidence supports a model of maturation in which the lipids, cargo proteins and Rab population at the endosome determine its competence to perform the functions of late endosomes, including the sorting of cargoes into lumenal vesicles and fusion with lysosomes.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.

Orally tolerized T cells can form conjugates with APCs but are defective in immunological synapse formation

Oral tolerance is systemic immune hyporesponsiveness induced by the oral administration of soluble Ags. Hyporesponsiveness of Ag-specific CD4 T cells is responsible for this phenomenon. However, the molecular mechanisms underlying the hyporesponsive state of these T cells are not fully understood. In the present study, we investigated the ability of orally tolerized T cells to form conjugates with Ag-bearing APCs and to translocate TCR, protein kinase C-theta (PKC-theta), and lipid rafts into the interface between T cells and APCs. Orally tolerized T cells were prepared from the spleens of OVA-fed DO11.10 mice. Interestingly, the orally tolerized T cells did not show any impairment in the formation of conjugates with APCs. The conjugates were formed in a LFA-1-dependent manner. Upon antigenic stimulation, the tolerized T cells could indeed activate Rap1, which is critical for LFA-1 activation and thus cell adhesion. However, orally tolerized T cells showed defects in the translocation of TCR, PKC-theta, and lipid rafts into the interface between T cells and APCs. Translocation of TCR and PKC-theta to lipid raft fractions upon antigenic stimulation was also impaired in the tolerized T cells. Ag-induced activation of Vav, Rac1, and cdc42, which are essential for immunological synapse and raft aggregation, were down-regulated in orally tolerized T cells. These results demonstrate that orally tolerized T cells can respond to specific Ags in terms of conjugate formation but not with appropriate immunological synapse formation. This may account for the hyporesponsive state of orally tolerized T cells.

Signal role for activation of caspase-3-like protease and burst of superoxide anions during Ce4+-induced apoptosis of cultured Taxus cuspidata cells

The signal events of 1 mM Ce4+ (Ce(NH4)2(NO3)6)-induced apoptosis of cultured Taxus cuspidata cells were investigated. The percentage of apoptotic cells increased from 0.82% to 51.32% within 6 days. Caspase-3-like protease activity became notable during the second day of Ce4+-treatment, and the maximum activity was 5-fold higher than that of control cells at the fourth day. When the experiment system was pretreated with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) at 100 microM, caspase-3-like activity resulted in distinct inhibition by 70% and 77.3% after 3 and 4 days of induction. Furthermore, 100 microM Ac-DEVD-CHO partially reduced the apoptotic cells by 58.6% and 60.8% at day 4 and 5 respectively. Ce4+ induced superoxide anions (O2*-) transient burst, and the first peak appeared at around 3.7-4 h, the second appeared at about 7 h. Both O2*- burst and cell apoptosis were effectively suppressed by application of diphenyl iodonium (NADPH oxidase inhibitor). Inhibition of O2*- production attenuated caspase-3-like activation by 49% and 53.6% during day 3 and 4 respectively. In addition, a total of 15 protein spots changed in response to caspase-3-like protease activation were identified by two-dimensional gel electrophoresis. These results suggest that Ce4+ of 1 mM induces apoptosis in suspension cultures of T. cuspidata through O2*- burst as well as caspase-3-like protease activation. The burst of O2*- exerts its activity as an upstream of caspase-3-like activation. Our results also implicate that other signal pathways independent of an O2*- burst possibly participate in mediating caspase-3-like protease activation.

Sodium nitroprusside affects the level of photosynthetic enzymes and glucose metabolism in Phaseolus aureus (mung bean)

Nitric oxide (NO) is an important signaling molecule in plants. The present study aims to investigate the downstream signaling pathways of NO in plants using a proteomic approach. Phaseolus aureus (mung bean) leaf was treated with sodium nitroprusside (SNP), which releases nitric oxide in the form of nitrosonium cation (NO+) upon light irradiation. Changes in protein expression profiles of the SNP treated mung bean leaf were analyzed by two-dimensional gel electrophoresis (2-DE). Comparison of 2-DE electropherograms revealed seven down-regulated and two up-regulated proteins after treatment with 0.5 mM SNP for 6 h. The identities of these proteins were analyzed by a combination of peptide mass fingerprinting and post-source decay using a matrix-assisted-laser-desorption-ionisation-time-of-flight (MALDI-TOF) mass spectrometer. Six out of these nine proteins found are involved in either photosynthesis or cellular metabolism. We have taken our investigation further by studying the effect of NO+ on glucose contents in mung bean leaves. Our results clearly demonstrated that NO+ rapidly and drastically decrease the amount of glucose in mung bean leaves. Moreover, four out of nine of these proteins are chloroplastic isoforms. These results suggested that chloroplasts might be one of the main sub-cellular targets of NO in plants.

Identification of caspase-3 degradome by two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight analysis

The activation of caspases is a critical event for the execution phase of programmed cell death. Caspases are highly specific in their ability to activate or inhibit many crucial proteins in the cell via site-specific cleavage. To date, more than 60 proteins have been shown to be substrates of one or more caspases in mammalian cells, and the list is still growing. In this study, to identify human caspase-3 substrates, we digested lysates obtained from a caspase-3-deficient MCF-7 cell line with purified caspase-3 and analyzed eliminated or decreased spots by 2-DE. Proteins degraded by caspase-3, termed as caspase-3 degradome, are involved in a variety of cellular functions, such as stress-responsive proteins, signaling molecules, structural proteins, and unclassified proteins. Interestingly, the cellular level of vinculin, a caspase-3 substrate, was dramatically reduced during the apoptotic process, where the expression level of caspase-3 was increased. This degradomic approach could provide a powerful tool in finding physiological substrates of many proteolytic enzymes whose functions remain to be determined.

Hyporesponsiveness of CD4 T cells induced in oral tolerance is maintained by selective impairment in the TCR-induced calcium/NFAT signaling pathway resulting from caspase activation

We examined intracellular signaling of hyporesponsive CD4 T cells induced by continuous feeding with high-dose antigen in a TCR transgenic mouse system. The results demonstrated a selective impairment in their TCR-induced calcium/NFAT-signaling pathway. Proteomic analysis revealed caspase activation in these cells, which resulted in cleavage of GADS. Further analysis of the TCR-signaling complex showed that GADS-LAT-SLP-76-associated PLC-gamma1 was decreased in both phosphorylation and association. Thus, as a consequence of caspase activation, orally tolerant CD4 T cells could not form normal TCR signaling complexes associated with GADS and showed downregulated PLC-gamma1 activation, which resulted in impairment of TCR-induced calcium signaling.

Proteomics in the chicken: tools for understanding immune responses to avian diseases

The entire chicken genome sequence will be available by the time this review is in press. Chickens will be the first production animal species to enter the "postgenomic era." This fundamental structural genomics achievement allows, for the first time, complete functional genomics approaches for understanding the molecular basis of chicken normo- and pathophysiology. The functional genomics paradigm, which contrasts with classical functional genetic investigations of one gene (or few) in isolation, is the systematic holistic genetic analyses of biological systems in defined contexts. Context-dependent gene interactions are the fundamental mechanics of all life. Functional genomics uses high-throughput large-scale experimental methods combined with statistical and computational analyses. Projects with expressed sequence tags in chickens have already allowed the creation of cDNA microarrays for large-scale context-dependant mRNA analysis (transcriptomics). However, proteins are the functional units of almost all biological processes, and protein expression very often bears no correlation to mRNA expression. Proteomics, a discipline within functional genomics, is the context-defined analysis of complete complements of proteins. Proteomics bridges the "sequence-to-phenotype gap;" it complements structural and other functional genomics approaches. Proteomics requires high capital investment but has ubiquitous biological applications. Although currently the fastest-growing human biomedical discipline, new paradigms may need to be established for production animal proteomics research. The prospective promise and potential pitfalls of using proteomics approaches to improve poultry pathogen control will be specifically highlighted. The first stage of our recently established proteomics program is global protein profiling to identify differentially expressed proteins in the context of the commercially important pathogens. Our trials and tribulations in establishing our proteomics program, as well some of our initial data to understand chicken immune system function, will be discussed.

Calcineurin imposes T cell unresponsiveness through targeted proteolysis of signaling proteins

Sustained calcium signaling induces a state of anergy or antigen unresponsiveness in T cells, mediated through calcineurin and the transcription factor NFAT. We show here that Ca(2+)-induced anergy is a multistep program that is implemented at least partly through proteolytic degradation of specific signaling proteins. Calcineurin increased mRNA and protein of the E3 ubiquitin ligases Itch, Cbl-b and GRAIL and induced expression of Tsg101, the ubiquitin-binding component of the ESCRT-1 endosomal sorting complex. Subsequent stimulation or homotypic cell adhesion promoted membrane translocation of Itch and the related protein Nedd4, resulting in degradation of two key signaling proteins, PKC-theta and PLC-gamma1. T cells from Itch- and Cbl-b-deficient mice were resistant to anergy induction. Anergic T cells showed impaired calcium mobilization after TCR triggering and were unable to maintain a mature immunological synapse, instead showing late disorganization of the outer ring containing lymphocyte function-associated antigen 1. Our results define a complex molecular program that links gene transcription induced by calcium and calcineurin to a paradoxical impairment of signal transduction in anergic T cells.