T cell receptor for antigen induces linker for activation of T cell-dependent activation of a negative signaling complex involving Dok-2, SHIP-1, and Grb-2

Imaging of biphasic signalosomes constructed by checkpoint receptor 2B4 in conventional and chimeric antigen receptor-T cells

A co-signaling receptor, 2B4, has dual effects in immune cells, but its actual functions in T cells remain elusive. Here, using super-resolution imaging technology with an immunological synapse model, we showed that 2B4 forms "2B4 microclusters" immediately after 2B4-CD48 binding. A lipid phosphatase, SHIP-1, subsequently combined with 2B4 to form coinhibitory signalosomes, leading to the suppression of cytokine production. An activating adapter, SLAM-associated protein (SAP), attenuated the clustering of SHIP-1 and recruited a kinase, Fyn, enhancing the Vav1 signaling pathway as costimulatory signalosomes. Furthermore, we found that a chimeric antigen receptor with a 2B4 tail (2B4-CAR) retained the original signal transduction mechanism of 2B4. With endogenous levels of SAP expression, 2B4-CAR-T cells exposed sufficient antitumor efficacy in vivo without excess cytokine production. Our results may help explain the biphasic feature of 2B4 in T cell responses from the viewpoint of the signalosome and provide a new candidate for CAR development.

SHIP-1 regulates the differentiation and function of Tregs via inhibiting mTORC1 activity

Cell metabolism is crucial for orchestrating the differentiation and function of regulatory T cells (Tregs). However, the underlying mechanism that coordinates cell metabolism to regulate Treg activity is not completely understood. As a pivotal molecule in lipid metabolism, the role of SHIP-1 in Tregs remains unknown. In this study, we found SHIP-1 Treg KO mice (SHIP-1 specifically deleted in regulatory T cells) had severe autoimmunity with increased Tregs in the thymus and disrupted peripheral T cell homeostasis. Mechanistically, CD4Cre Ship-1flox/flox mice were found to have increased Treg precursors and SHIP-1 KO Tregs had reduced migration and stability, which caused decreased Tregs in the spleen. Additionally, the suppressive function of Tregs from SHIP-1 KO mice was diminished, along with their promotion of anti-tumor immunity. Interestingly, the PI3K-mTORC1, but not mTORC2, signaling axis was enhanced in SHIP-1 KO Tregs. In vivo treatment of SHIP-1 Treg KO mice with rapamycin rescued the abnormal Treg percentages and peripheral T cell homeostasis, as well as Treg suppressive function. Furthermore, the treatment of wild-type mice with SHIP-1 inhibitor enhanced anti-tumor activity. Our study highlights the SHIP-1-PI3K-mTORC1 axis that regulates Treg differentiation and function, and it is a potential target for cancer treatment.

DOK1 and DOK2 regulate CD8 T cell signaling and memory formation without affecting tumor cell killing

Targeting intracellular inhibiting proteins has been revealed to be a promising strategy to improve CD8+ T cell anti-tumor efficacy. Here, we are focusing on intracellular inhibiting proteins specific to TCR signaling: DOK1 and DOK2 expressed in T cells. We hypothesized that depletion of intracellular inhibition checkpoint DOK1 and DOK2 could improve CD8+ T-cell based cancer therapies. To evaluate the role of DOK1 and DOK2 depletion in physiology and effector function of CD8+ T lymphocytes and in cancer progression, we established a transgenic T cell receptor mouse model specific to melanoma antigen hgp100 (pmel-1 TCR Tg) in WT and Dok1/Dok2 DKO (double KO) mice. We showed that both DOK1 and DOK2 depletion in CD8+ T cells after an in vitro pre-stimulation induced a higher percentage of effector memory T cells as well as an up regulation of TCR signaling cascade- induced by CD3 mAbs, including the increased levels of pAKT and pERK, two major phosphoproteins involved in T cell functions. Interestingly, this improved TCR signaling was not observed in naïve CD8+ T cells. Despite this enhanced TCR signaling essentially shown upon stimulation via CD3 mAbs, pre-stimulated Dok1/Dok2 DKO CD8+ T cells did not show any increase in their activation or cytotoxic capacities against melanoma cell line expressing hgp100 in vitro. Altogether we demonstrate here a novel aspect of the negative regulation by DOK1 and DOK2 proteins in CD8+ T cells. Indeed, our results allow us to conclude that DOK1 and DOK2 have an inhibitory role following long term T cell stimulations.

Immunotherapeutic implications of negative regulation by protein tyrosine phosphatases in T cells: the emerging cases of PTP1B and TCPTP

In the context of inflammation, T cell activation occurs by the concerted signals of the T cell receptor (TCR), co-stimulatory receptors ligation, and a pro-inflammatory cytokine microenvironment. Fine-tuning these signals is crucial to maintain T cell homeostasis and prevent self-reactivity while offering protection against infectious diseases and cancer. Recent developments in understanding the complex crosstalk between the molecular events controlling T cell activation and the balancing regulatory cues offer novel approaches for the development of T cell-based immunotherapies. Among the complex regulatory processes, the balance between protein tyrosine kinases (PTK) and the protein tyrosine phosphatases (PTPs) controls the transcriptional and metabolic programs that determine T cell function, fate decision, and activation. In those, PTPs are de facto regulators of signaling in T cells acting for the most part as negative regulators of the canonical TCR pathway, costimulatory molecules such as CD28, and cytokine signaling. In this review, we examine the function of two close PTP homologs, PTP1B (PTPN1) and T-cell PTP (TCPTP; PTPN2), which have been recently identified as promising candidates for novel T-cell immunotherapeutic approaches. Herein, we focus on recent studies that examine the known contributions of these PTPs to T-cell development, homeostasis, and T-cell-mediated immunity. Additionally, we describe the signaling networks that underscored the ability of TCPTP and PTP1B, either individually and notably in combination, to attenuate TCR and JAK/STAT signals affecting T cell responses. Thus, we anticipate that uncovering the role of these two PTPs in T-cell biology may lead to new treatment strategies in the field of cancer immunotherapy. This review concludes by exploring the impacts and risks that pharmacological inhibition of these PTP enzymes offers as a therapeutic approach in T-cell-based immunotherapies.

IFN-γ-dependent interactions between tissue-intrinsic γδ T cells and tissue-infiltrating CD8 T cells limit allergic contact dermatitis

BACKGROUND

Elicitation of allergic contact dermatitis (ACD), an inflammatory type 4 hypersensitivity disease, induces skin infiltration by polyclonal effector CD8 αβ T cells and precursors of tissue-resident memory T (TRM) cells. Because TRM have long-term potential to contribute to body-surface immunoprotection and immunopathology, their local regulation needs a fuller understanding.

OBJECTIVE

We sought to investigate how TRM-cell maturation might be influenced by innate-like T cells pre-existing within many epithelia.

METHODS

This study examined CD8+ TRM-cell maturation following hapten-induced ACD in wild-type mice and in strains harboring altered compartments of dendritic intraepidermal γδ T cells (DETCs), a prototypic tissue-intrinsic, innate-like T-cell compartment that reportedly regulates ACD, but by no elucidated mechanism.

RESULTS

In addition to eliciting CD8 TRM, ACD induced DETC activation and an intimate coregulatory association of the 2 cell types. This depended on DETC sensing IFN-γ produced by CD8 cells and involved programmed death-ligand 1 (PD-L1). Thus, in mice lacking DETC or lacking IFN-γ receptor solely on γδ cells, ACD-elicited CD8 T cells showed enhanced proliferative and effector potentials and reduced motility, collectively associated with exaggerated ACD pathology. Comparable dysregulation was elicited by PD-L1 blockade in vitro, and IFN-γ-regulated PD-L1 expression was a trait of human skin-homing and intraepithelial γδ T cells.

CONCLUSIONS

The size and quality of the tissue-infiltrating CD8 T-cell response during ACD can be profoundly regulated by local innate-like T cells responding to IFN-γ and involving PD-L1. Thus, interindividual and tissue-specific variations in tissue-intrinsic lymphocytes may influence responses to allergens and other challenges and may underpin inflammatory pathologies such as those repeatedly observed in γδ T-cell-deficient settings.

Immune Checkpoint Receptors Signaling in T Cells

The characterization of the receptors negatively modulating lymphocyte function is rapidly advancing, driven by success in tumor immunotherapy. As a result, the number of immune checkpoint receptors characterized from a functional perspective and targeted by innovative drugs continues to expand. This review focuses on the less explored area of the signaling mechanisms of these receptors, of those expressed in T cells. Studies conducted mainly on PD-1, CTLA-4, and BTLA have evidenced that the extracellular parts of some of the receptors act as decoy receptors for activating ligands, but in all instances, the tyrosine phosphorylation of their cytoplasmatic tail drives a crucial inhibitory signal. This negative signal is mediated by a few key signal transducers, such as tyrosine phosphatase, inositol phosphatase, and diacylglycerol kinase, which allows them to counteract TCR-mediated activation. The characterization of these signaling pathways is of great interest in the development of therapies for counteracting tumor-infiltrating lymphocyte exhaustion/anergy independently from the receptors involved.

Introduction to DOK2 and its potential role in cancer

Cancer is a complex, multifactorial disease that modern medicine ultimately aims to overcome. Downstream of tyrosine kinase 2 (DOK2) is a well-known tumor suppressor gene, and a member of the downstream protein DOK family of tyrosine kinases. Through a search of original literature indexed in PubMed and other databases, the present review aims to extricate the mechanisms by which DOK2 acts on cancer, thereby identifying more reliable and effective therapeutic targets to promote enhanced methods of cancer prevention and treatment. The review focuses on the role of DOK2 in multiple tumor types in the lungs, intestines, liver, and breast. Additionally, we discuss the potential mechanisms of action of DOK2 and the downstream consequences via the Ras/MPAK/ERK or PI3K/AKT/mTOR signaling pathways.

The Clinical Aspect of Adaptor Molecules in T Cell Signaling: Lessons Learnt From Inborn Errors of Immunity

Adaptor molecules lack enzymatic and transcriptional activities. Instead, they exert their function by linking multiple proteins into intricate complexes, allowing for transmitting and fine-tuning of signals. Many adaptor molecules play a crucial role in T-cell signaling, following engagement of the T-cell receptor (TCR). In this review, we focus on Linker of Activation of T cells (LAT) and SH2 domain-containing leukocyte protein of 76 KDa (SLP-76). Monogenic defects in these adaptor proteins, with known roles in T-cell signaling, have been described as the cause of human inborn errors of immunity (IEI). We describe the current knowledge based on defects in cell lines, murine models and human patients. Germline mutations in Adhesion and degranulation adaptor protein (ADAP), have not resulted in a T-cell defect.

Inhibition of lipid phosphatase SHIP1 expands myeloid-derived suppressor cells and attenuates rheumatoid arthritis in mice

Rheumatoid arthritis (RA) is a debilitating autoimmune disease of unknown cause, characterized by infiltration and accumulation of activated immune cells in the synovial joints where cartilage and bone destructions occur. Myeloid-derived suppressor cells (MDSCs) are of myeloid origin and are able to suppress T cell responses. Src homology 2 domain containing inositol polyphosphate 5-phosphatase 1 (SHIP1) was shown to be involved in the regulation of MDSC differentiation. The purpose of the present study was to investigate the effect of inhibition of SHIP1 on expansion of MDSCs in RA using a collagen-induced inflammatory arthritis (CIA) mouse model. In DBA/1 mice treatment with a small molecule specific SHIP1 inhibitor 3α-aminocholestane (3AC) induced a marked expansion of MDSCs in vivo. Both pre-treatment with 3AC of DBA/1 mice prior to CIA induction and intervention with 3AC during CIA progression significantly reduced disease incidence and severity. Adoptive transfer of MDSCs isolated from 3AC-treated mice, but not naïve MDSCs from normal mice, into CIA mice significantly reduced disease incidence and severity, indicating that the 3AC-induced MDSCs were the cellular mediators of the observed amelioration of the disease. In conclusion, inhibition of SHIP1 expands MDSCs in vivo and attenuates development of CIA in mice. Small molecule specific inhibition of SHIP1 may therefore offer therapeutic benefit to patients with RA and other autoimmune diseases.

TRAF3 in T Cells Restrains Negative Regulators of LAT to Promote TCR/CD28 Signaling

The adaptor protein TNFR-associated factor 3 (TRAF3) is required for in vivo T cell effector functions and for normal TCR/CD28 signaling. TRAF3-mediated enhancement of TCR function requires engagement of both CD3 and CD28, but the molecular mechanisms underlying how TRAF3 interacts with and impacts TCR/CD28-mediated complexes to enhance their signaling remains an important knowledge gap. We investigated how TRAF3 is recruited to, and regulates, CD28 as a TCR costimulator. Direct association with known signaling motifs in CD28 was dispensable for TRAF3 recruitment; rather, TRAF3 associated with the CD28-interacting protein linker of activated T cells (LAT) in human and mouse T cells. TRAF3-LAT association required the TRAF3 TRAF-C domain and a newly identified TRAF2/3 binding motif in LAT. TRAF3 inhibited function of the LAT-associated negative regulatory protein Dok1, which is phosphorylated at an inhibitory tyrosine residue by the tyrosine kinase breast tumor kinase (Brk/PTK6). TRAF3 regulated Brk activation in T cells, limiting the association of protein tyrosine phosphatase 1B (PTP1B) with the LAT complex. In TRAF3-deficient cells, LAT complex-associated PTP1B was associated with dephosphorylation of Brk at an activating tyrosine residue, potentially reducing its ability to inhibit Dok1. Consistent with these findings, inhibiting PTP1B activity in TRAF3-deficient T cells rescued basal and TCR/CD28-mediated activation of Src family kinases. These results reveal a new mechanism for promotion of TCR/CD28-mediated signaling through restraint of negative regulation of LAT by TRAF3, enhancing the understanding of regulation of the TCR complex.

"Non-Essential" Proteins of HSV-1 with Essential Roles In Vivo: A Comprehensive Review

Viruses encode for structural proteins that participate in virion formation and include capsid and envelope proteins. In addition, viruses encode for an array of non-structural accessory proteins important for replication, spread, and immune evasion in the host and are often linked to virus pathogenesis. Most virus accessory proteins are non-essential for growth in cell culture because of the simplicity of the infection barriers or because they have roles only during a state of the infection that does not exist in cell cultures (i.e., tissue-specific functions), or finally because host factors in cell culture can complement their absence. For these reasons, the study of most nonessential viral factors is more complex and requires development of suitable cell culture systems and in vivo models. Approximately half of the proteins encoded by the herpes simplex virus 1 (HSV-1) genome have been classified as non-essential. These proteins have essential roles in vivo in counteracting antiviral responses, facilitating the spread of the virus from the sites of initial infection to the peripheral nervous system, where it establishes lifelong reservoirs, virus pathogenesis, and other regulatory roles during infection. Understanding the functions of the non-essential proteins of herpesviruses is important to understand mechanisms of viral pathogenesis but also to harness properties of these viruses for therapeutic purposes. Here, we have provided a comprehensive summary of the functions of HSV-1 non-essential proteins.

CD5 signalosome coordinates antagonist TCR signals to control the generation of Treg cells induced by foreign antigens

CD5 is characterized as an inhibitory coreceptor with an important regulatory role during T cell development. The molecular mechanism by which CD5 operates has been puzzling and its function in mature T cells suggests promoting rather than repressing effects on immune responses. Here, we combined quantitative mass spectrometry and genetic studies to analyze the components and the activity of the CD5 signaling machinery in primary T cells. We found that T cell receptor (TCR) engagement induces the selective phosphorylation of CD5 tyrosine 429, which serves as a docking site for proteins with adaptor functions (c-Cbl, CIN85, CRKL), connecting CD5 to positive (PI3K) and negative (UBASH3A, SHIP1) regulators of TCR signaling. c-CBL acts as a coordinator in this complex enabling CD5 to synchronize positive and negative feedbacks on TCR signaling through the other components. Disruption of CD5 signalosome in mutant mice reveals that it modulates TCR signal outputs to selectively repress the transactivation of Foxp3 and limit the inopportune induction of peripherally induced regulatory T cells during immune responses against foreign antigen. Our findings bring insights into the paradigm of coreceptor signaling, suggesting that, in addition to providing dualistic enhancing or dampening inputs, coreceptors can engage concomitant stimulatory and inhibitory signaling events, which act together to promote specific functional outcomes.

Genome-Wide CRISPR Screen Identifies Host Factors Required by Toxoplasma gondii Infection

Toxoplasma gondii are obligate intracellular protoza, and due to their small genome and limited encoded proteins, they have to exploit host factors for entry, replication, and dissemination. Such host factors can be defined as host dependency factors (HDFs). Though HDFs are inessential for cell viability, they are critical for pathogen infection, and potential ideal targets for therapeutic intervention. However, information about these HDFs required by T. gondii infection is highly deficient. In this study, the genes of human foreskin fibroblast (HFF) cells were comprehensively edited using the lentiviral CRISPR-Cas9-sgRNA library, and then the lentivirus-treated cells were infected with T. gondii at multiplication of infection 1 (MOI = 1) for 10 days to identify HDFs essential for T. gondii infection. The survival cells were harvested and sent for sgRNA sequencing. The sgRNA sequence matched genes or miRNAs were potential HDFs. Some cells in the lentivirus-treated group could survive longer than those in the untreated control group after T. gondii infection. From a pool of 19,050 human genes and 1,864 human pri-miRNAs, 1,193 potential HDFs were identified, including 1,183 genes and 10 pri-miRNAs (corresponding with 17 mature miRNAs). Among them, seven genes and five mature miRNAs were validated with siRNAs, miRNA inhibitors, and mimics, respectively. Bioinformatics analysis revealed that, among the 1,183 genes, 53 potential HDFs were associated with regulation of host actin cytoskeleton and 23 potential HDFs coded immune negative regulators. This result indicated that actin dynamics were indispensable for T. gondii infection, and some host immune negative regulators may be involved in disarming host defenses. Our findings contribute to the current limited knowledge about host factors required by T. gondii infection and provide us with new targets for medication therapy and vaccine exploitation.

Prognostic role of DOK family adapters in acute myeloid leukemia

Acute myeloid leukemia (AML) is a genetically and clinically heterogeneous disease. Gene mutational and expressional profile can aid the identification of different prognostic subgroups. Downstream of tyrosine kinase (DOK) proteins are a multigenic family of adaptors; some of them are key negative regulators of immune cell signaling. However, the expression and clinical implication of DOK family in AML has rarely been investigated. A total of 155 AML patients with DOK family (DOK1-7) expression data from The Cancer Genome Atlas database were enrolled in the study. In patients who only received chemotherapy, those with high expressions of DOK4 or DOK5 had significantly shorter EFS and OS than patients with low expressions (all P < 0.001), whereas high DOK7 expressers had longer EFS and OS than the low expressers (all P < 0.05). In patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), however, all DOK members had no impact on EFS and OS. Multivariate analysis confirmed that high DOK5 expression was an independent risk factor for EFS and OS in untransplanted patients (all P < 0.05). Our study suggests that in AML, high expressions of DOK4 and DOK5 are adverse prognostic factors, high DOK7 expression is a good prognostic factor, but their effects can be overcome by allo-HSCT.

Expression of T-cell receptor signalling pathway components in extranodal NK/T-cell lymphoma

AIMS

Although the neoplastic cells of extranodal natural killer (NK)/T-cell lymphoma (ENKTL) usually do not express T-cell antigens, the T-cell receptor (TCR) gene might be rearranged and TCR protein expressed. The aim is to elucidate the expression of the downstream TCR pathway components and their importance in ENKTL.

METHODS AND RESULTS

We used formalin-fixed paraffin-embedded tissues from 91 ENKTL samples to immunohistochemically characterise the expression of TCR pathway components. The following proteins were variably expressed: ZAP70 (94%; 83/88), GRAP2/GADS (68%; 60/88), DOK2 (42%; 38/90), LCK (35%; 31/88), and ITK (10%; 9/90). When these tumours were classified as being of T lineage (16%), NK lineage (45%), or indeterminate lineage (38%), the GRAP2/GADS expression rate was higher in T lineage tumours (versus NK, P = 0.0073; versus indeterminate, P = 0.00082). GRAP2/GADS-positive NK lineage tumours more frequently expressed DOK2 (P = 0.0073), and were more often confined to the nasal areas (P = 0.014). Furthermore, when these tumours were immunophenotypically classified into a T signature (42%) or NK signature (58%), the expression rates of GRAP2/GADS and ITK were higher in T signature tumours (P = 0.00074 and P = 0.067, respectively), whereas that of LCK was higher in NK-signature tumours (P = 0.10).

CONCLUSIONS

Although some ENTKL cases were polyclonal for TCR rearrangement and others lacked TCR expression, we speculate that the TCR pathway might be functioning in ENKTLs. A T signature versus a NK signature might be better for delineating the physiology of ENKTL than cellular lineage. Furthermore, ITK may represent a potential therapeutic target for patients with ITK-expressing tumours.

Id3 Restricts γδ NKT Cell Expansion by Controlling Egr2 and c-Myc Activity

γδ NKT cells are neonatal-derived γδ T lymphocytes that are grouped together with invariant NKT cells based on their shared innate-like developmental program characterized by the transcription factor PLZF (promyelocytic leukemia zinc finger). Previous studies have demonstrated that the population size of γδ NKT cells is tightly controlled by Id3-mediated inhibition of E-protein activity in mice. However, how E proteins promote γδ NKT cell development and expansion remains to be determined. In this study, we report that the transcription factor Egr2, which also activates PLZF expression in invariant NKT cells, is essential for regulating γδ NKT cell expansion. We observed a higher expression of Egr family genes in γδ NKT cells compared with the conventional γδ T cell population. Loss of function of Id3 caused an expansion of γδ NKT cells, which is accompanied by further upregulation of Egr family genes as well as PLZF. Deletion of Egr2 in Id3-deficient γδ NKT cells prevented cell expansion and blocked PLZF upregulation. We further show that this Egr2-mediated γδ NKT cell expansion is dependent on c-Myc. c-Myc knockdown attenuated the proliferation of Id3-deficient γδ NKT cells, whereas c-Myc overexpression enhanced the proliferation of Id3/Egr2-double-deficient γδ NKT cells. Therefore, our data reveal a regulatory circuit involving Egr2-Id3-E2A, which normally restricts the population size of γδ NKT cells by adjusting Egr2 dosage and c-Myc expression.

Evolutionary and expression analyses reveal a pattern of ancient duplications and functional specializations in the diversification of the Downstream of Kinase (DOK) genes

Downstream of Kinase (DOK) proteins represent a multigenic family of adaptors that includes negative regulators of immune cell signaling. Using phylogenetics and intron/exon structure data, we show here that the seven human DOK genes (DOK1 to DOK7) form three highly divergent groups that emerged before the protostome-deuterostome split: DOK1/2/3, DOK4/5/6, and DOK7. For two of these three groups (DOK1/2/3 and DOK4/5/6), further gene duplications occurred in vertebrates and so while chordates only have three DOK genes, vertebrates have seven DOK genes over the three groups. From our expression analysis in humans, we show that each group of DOK genes has a distinct pattern of expression. The DOK1/2/3 group is immune specific, yet each of the three genes in the group has a distinct pattern of expression in immune cells. This immune specificity could thus be ancestral, with the DOK1/2/3 gene also being immune-related in protostomes. The DOK4/5/6 and DOK7 groups represent genes that are much less expressed in immune system than the DOK1/2/3 group. Interestingly, we identify a novel tyrosine based motif that is specific to the vertebrate DOK4/5/6 sequences. The evolution of the DOK genes is thus marked by a pattern of ancient duplications and functional specializations.

Cutting Edge: Check Your Mice-A Point Mutation in the Ncr1 Locus Identified in CD45.1 Congenic Mice with Consequences in Mouse Susceptibility to Infection

B6.SJL-Ptprc^a Pepc^b /Boy (CD45.1) mice have been used in hundreds of congenic competitive transplants, with the presumption that they differ from C57BL/6 mice only at the CD45 locus. In this study, we describe a point mutation in the natural cytotoxicity receptor 1 (Ncr1) locus fortuitously identified in the CD45.1 strain. This point mutation was mapped at the 40th nucleotide of the Ncr1 locus causing a single amino acid mutation from cysteine to arginine at position 14 from the start codon, resulting in loss of NCR1 expression. We found that these mice were more resistant to CMV due to a hyper innate IFN-γ response in the absence of NCR1. In contrast, loss of NCR1 increased susceptibility to influenza virus, a result that is consistent with the role of NCR1 in the recognition of influenza Ag, hemagglutinin. This work sheds light on potential confounding experimental interpretation when this congenic strain is used as a tool for tracking lymphocyte development.

Dual enhancement of T and NK cell function by pulsatile inhibition of SHIP1 improves antitumor immunity and survival

The success of immunotherapy in some cancer patients has revealed the profound capacity for cytotoxic lymphocytes to eradicate malignancies. Various immunotherapies work by blocking key checkpoint proteins that suppress immune cell activity. The phosphatase SHIP1 (SH2-containing inositol polyphosphate 5-phosphatase) limits signaling from receptors that activate natural killer (NK) cells and T cells. However, unexpectedly, genetic ablation studies have shown that the effector functions of SHIP1-deficient NK and T cells are compromised in vivo. Because chronic activation of immune cells renders them less responsive to activating signals (a host mechanism to avoid autoimmunity), we hypothesized that the failure of SHIP1 inhibition to induce antitumor immunity in those studies was caused by the permanence of genetic ablation. Accordingly, we found that reversible and pulsatile inhibition of SHIP1 with 3-α-aminocholestane (3AC; "SHIPi") increased the antitumor response of NK and CD8⁺ T cells in vitro and in vivo. Transient SHIP1 inhibition in mouse models of lymphoma and colon cancer improved the median and long-term tumor-free survival rates. Adoptive transfer assays showed evidence of immunological memory to the tumor in hematolymphoid cells from SHIPi-treated, long-term surviving mice. The findings suggest that a pulsatile regimen of SHIP1 inhibition might be an effective immunotherapy in some cancer patients.

Herpes simplex virus 1 infection of T cells causes VP11/12-dependent phosphorylation and degradation of the cellular protein Dok-2

Previous studies have shown that HSV-1 infection of lymphocytes induces the tyrosine phosphorylation of several proteins that might correspond to viral or host proteins. VP11/12, a viral tegument protein, is the major HSV-induced tyrosine phosphorylated protein identified thus far. In this report, we demonstrated that the cellular adaptor proteins Dok-2 and Dok-1 are tyrosine phosphorylated upon HSV-1 infection. In addition, HSV-1 induced the selective degradation of Dok-2. Finally, we provide evidence that Dok-2 interacts with VP11/12, and that HSV-induced tyrosine phosphorylation and degradation of Dok-2 require VP11/12. Inactivation of either the Src Family Kinases binding motifs or the SHC binding motif of VP11/12 eliminated the interaction of Dok-2 with VP11/12. Elimination of the binding of Dok-2 to VP11/12 prevented Dok-2 phosphorylation and degradation. We propose that HSV-induced Dok phosphorylation and Dok-2 degradation is an immune evasion mechanism to inactivate T cells that might play an important role in HSV pathogenesis.

Regulation of immune cell signaling by SHIP1: A phosphatase, scaffold protein, and potential therapeutic target

The phosphoinositide phosphatase SHIP is a critical regulator of immune cell activation. Despite considerable study, the mechanisms controlling SHIP activity to ensure balanced cell activation remain incompletely understood. SHIP dampens BCR signaling in part through its association with the inhibitory coreceptor Fc gamma receptor IIB, and serves as an effector for other inhibitory receptors in various immune cell types. The established paradigm emphasizes SHIP's inhibitory receptor-dependent function in regulating phosphoinositide 3-kinase signaling by dephosphorylating the phosphoinositide PI(3,4,5)P₃ ; however, substantial evidence indicates that SHIP can be activated independently of inhibitory receptors and can function as an intrinsic brake on activation signaling. Here, we integrate historical and recent reports addressing the regulation and function of SHIP in immune cells, which together indicate that SHIP acts as a multifunctional protein controlled by multiple regulatory inputs, and influences downstream signaling via both phosphatase-dependent and -independent means. We further summarize accumulated evidence regarding the functions of SHIP in B cells, T cells, NK cells, dendritic cells, mast cells, and macrophages, and data suggesting defective expression or activity of SHIP in autoimmune and malignant disorders. Lastly, we discuss the biological activities, therapeutic promise, and limitations of small molecule modulators of SHIP enzymatic activity.

Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4

The adapter protein Dok-4 (downstream of kinase-4) has been reported as both an activator and inhibitor of Erk and Elk-1, but lack of knowledge about the identity of its partner molecules has precluded any mechanistic insight into these seemingly conflicting properties. We report that Dok-4 interacts with the transactivation domain of Elk-4 through an atypical phosphotyrosine-binding domain-mediated interaction. Dok-4 possesses a nuclear export signal and can relocalize Elk-4 from nucleus to cytosol, whereas Elk-4 possesses two nuclear localization signals that restrict interaction with Dok-4. The Elk-4 protein, unlike Elk-1, is highly unstable in the presence of Dok-4, through both an interaction-dependent mechanism and a pleckstrin homology domain-dependent but interaction-independent mechanism. This is reversed by proteasome inhibition, depletion of endogenous Dok-4 or lysine-to-arginine mutation of putative Elk-4 ubiquitination sites. Finally, Elk-4 transactivation is potently inhibited by Dok-4 overexpression but enhanced by Dok-4 knockdown in MDCK renal tubular cells, which correlates with increased basal and EGF-induced expression of Egr-1, Fos and cylcinD1 mRNA, and cell proliferation despite reduced Erk activation. Thus, Dok-4 can target Elk-4 activity through multiple mechanisms, including binding of the transactivation domain, nuclear exclusion and protein destabilization, without a requirement for inhibition of Erk.

Hydrogen Peroxide Triggers a Dual Signaling Axis To Selectively Suppress Activated Human T Lymphocyte Migration

H₂O₂ is an early danger cue required for innate immune cell recruitment to wounds. To date, little is known about whether H₂O₂ is required for the migration of human adaptive immune cells to sites of inflammation. However, oxidative stress is known to impair T cell activity, induce actin stiffness, and inhibit cell polarization. In this study, we show that low oxidative concentrations of H₂O₂ also impede chemokinesis and chemotaxis of previously activated human T cells to CXCL11, but not CXCL10 or CXCL12. We show that this deficiency in migration is due to a reduction in inflammatory chemokine receptor CXCR3 surface expression and cellular activation of lipid phosphatase SHIP-1. We demonstrate that H₂O₂ acts through an Src kinase to activate a negative regulator of PI3K signaling, SHIP-1 via phosphorylation, providing a molecular mechanism for H₂O₂-induced chemotaxis deficiency. We hypothesize that although H₂O₂ serves as an early recruitment trigger for innate immune cells, it appears to operate as an inhibitor of T lymphocyte immune adaptive responses that are not required until later in the repair process.

Dok-1 and Dok-2 Regulate the Formation of Memory CD8+ T Cells

Diverse signals received by CD8⁺ T cells are integrated to achieve the required magnitude of cell expansion and the appropriate balance of effector/memory CD8⁺ T cell generation. Notably, the strength and nature of TCR signaling influence the differentiation and functional capacity of effector and memory CD8⁺ T cells. Dok-1 and Dok-2, the two members of the Dok family expressed in T cells, negatively regulate TCR signaling in vitro. However, the role of Dok proteins in modulating T cell function in vivo has not yet studied. We studied the function of Dok-1 and Dok-2 proteins in the regulation of the CD8⁺ T cell response to vaccinia virus infection. Comparison of responses to vaccinia virus expressing OVA peptide SIINFEKL by wild-type and Dok-1/2^-/- CD8⁺ OT-I cells showed that the absence of Dok-1 and Dok-2 slightly reduced the magnitude of virus-specific effector CD8⁺ T cell expansion. This was not due to reduced proliferation or enhanced apoptosis of effector CD8⁺ T cells. Dok-1/2-deficient effector CD8⁺ T cells showed increased cell surface TCR expression following virus infection in vivo and increased expression of granzyme B and TNF upon stimulation with peptide Ag ex vivo. Finally, Dok-1/2-deficient effector CD8⁺ T had a severe defect in survival that resulted in impaired generation of memory CD8⁺ T cells. These results reveal the critical involvement of Dok-1 and Dok-2 in a negative-feedback loop that prevents overactivation of CD8⁺ T cells and promotes memory formation.

Role of SHIP1 in Invariant NKT Cell Development and Functions

SHIP1 is a 5'-inositol phosphatase known to negatively regulate the signaling product of the PI3K pathway, phosphatidylinositol (3-5)-trisphosphate. SHIP1 is recruited to a large number of inhibitory receptors expressed on invariant NK (iNKT) cells. We hypothesized that SHIP1 deletion would have major effects on iNKT cell development by altering the thresholds for positive and negative selection. Germline SHIP1 deletion has been shown to affect T cells as well as other immune cell populations. However, the role of SHIP1 on T cell function has been controversial, and its participation on iNKT cell development and function has not been examined. We evaluated the consequences of SHIP1 deletion on iNKT cells using germline-deficient mice, chimeric mice, and conditionally deficient mice. We found that T cell and iNKT cell development are impaired in germline-deficient animals. However, this phenotype can be rescued by extrinsic expression of SHIP1. In contrast, SHIP1 is required cell autonomously for optimal iNKT cell cytokine secretion. This suggests that SHIP1 calibrates the threshold of iNKT cell reactivity. These data further our understanding of how iNKT cell activation is regulated and provide insights into the biology of this unique cell lineage.

Identification of SHIP-1 and SHIP-2 homologs in channel catfish, Ictalurus punctatus

Src homology domain 2 (SH2) domain-containing inositol 5'-phosphatases (SHIP) proteins have diverse roles in signal transduction. SHIP-1 and SHIP-2 homologs were identified in channel catfish, Ictalurus punctatus, based on sequence homology to murine and human SHIP sequences. Full-length cDNAs for catfish SHIP-1 and SHIP-2 (IpSHIP-1 and IpSHIP-2) were obtained using 5' and 3' RACE protocols. Catfish SHIP molecules share a high degree of sequence identity to their respective SHIP sequences from diverse taxa and both are encoded by single copy genes. IpSHIP-1 and IpSHIP-2 transcripts were expressed in all catfish tissues analyzed except for skin, and IpSHIP-1 message was more abundant than IpSHIP-2 message in lymphoid tissues. Catfish clonal B, cytotoxic T, and macrophage cell lines also expressed message for both molecules. IpSHIP-1 and IpSHIP-2 SH2 domains were expressed as recombinant proteins and were both found to be bound by cross-reacting rabbit anti-mouse SHIP-1 pAb. The anti-mouse SHIP-1 pAb also reacted with cell lysates from the cytotoxic T cell lines, macrophages and stimulated PBL. SHIP-1 is also phosphorylated at a conserved tyrosine residue, as shown by immunoprecipitation studies.

The signaling symphony: T cell receptor tunes cytokine-mediated T cell differentiation

T cell development, differentiation, and maintenance are orchestrated by 2 key signaling axes: the antigen-specific TCR and cytokine-mediated signals. The TCR signals the recognition of self- and foreign antigens to control T cell homeostasis for immune tolerance and immunity, which is regulated by a variety of cytokines to determine T cell subset homeostasis and differentiation. TCR signaling can synergize with or antagonize cytokine-mediated signaling to fine tune T cell fate; however, the latter is less investigated. Murine models with attenuated TCR signaling strength have revealed that TCR signaling can function as regulatory feedback machinery for T cell homeostasis and differentiation in differential cytokine milieus, such as IL-2-mediated Treg development; IL-7-mediated, naïve CD8(+) T cell homeostasis; and IL-4-induced innate memory CD8(+) T cell development. In this review, we discuss the symphonic cross-talk between TCR and cytokine-mediated responses that differentially control T cell behavior, with a focus on the negative tuning by TCR activation on the cytokine effects.

A THEMIS:SHP1 complex promotes T-cell survival

THEMIS is critical for conventional T-cell development, but its precise molecular function remains elusive. Here, we show that THEMIS constitutively associates with the phosphatases SHP1 and SHP2. This complex requires the adapter GRB2, which bridges SHP to THEMIS in a Tyr-phosphorylation-independent fashion. Rather, SHP1 and THEMIS engage with the N-SH3 and C-SH3 domains of GRB2, respectively, a configuration that allows GRB2-SH2 to recruit the complex onto LAT. Consistent with THEMIS-mediated recruitment of SHP to the TCR signalosome, THEMIS knock-down increased TCR-induced CD3-ζ phosphorylation, Erk activation and CD69 expression, but not LCK phosphorylation. This generalized TCR signalling increase led to augmented apoptosis, a phenotype mirrored by SHP1 knock-down. Remarkably, a KI mutation of LCK Ser59, previously suggested to be key in ERK-mediated resistance towards SHP1 negative feedback, did not affect TCR signalling nor ligand discrimination in vivo. Thus, the THEMIS:SHP complex dampens early TCR signalling by a previously unknown molecular mechanism that favours T-cell survival. We discuss possible implications of this mechanism in modulating TCR output signals towards conventional T-cell development and differentiation.

Integrative biology of T cell activation

The activation of T cells mediated by the T cell antigen receptor (TCR) requires the interaction of dozens of proteins, and its malfunction has pathological consequences. Our major focus is on new developments in the systems-level understanding of the TCR signal-transduction network. To make sense of the formidable complexity of this network, we argue that 'fine-grained' methods are needed to assess the relationships among a few components that interact on a nanometric scale, and those should be integrated with high-throughput '-omic' approaches that simultaneously capture large numbers of parameters. We illustrate the utility of this integrative approach with the transmembrane signaling protein Lat, which is a key signaling hub of the TCR signal-transduction network, as a connecting thread.

Intracellular TCR-signaling pathway: novel markers for lymphoma diagnosis and potential therapeutic targets

Despite the immunologic functions of T-cell receptor signaling molecules being extensively investigated, their potential as immunohistochemical markers has been poorly explored. With this background, we evaluated the expression of 5 intracellular proteins-GADS, DOK2, SKAP55, ITK, and PKCα-involved in T-cell receptor signaling in normal and neoplastic hematologic tissue samples, using antibodies raised against fixation-resistant epitopes of the 5 molecules. All 5 antibodies were associated with normal T-cell differentiation. GADS, DOK2, SKAP55, and ITK turned out to be T-cell lineage-specific markers in the setting of lymphoid and myeloid precursor neoplasms but showed differential expression in peripheral T-cell lymphoma (PTCL) subtypes, being detected in PTCL/not otherwise specified (NOS) and angioimmunoblastic T-cell lymphoma but negative in anaplastic large cell lymphoma (ALCL). Peripheral B-cell lymphomas were consistently negative for ITK, with occasional cases showing expression of DOK2 and SKAP55, and a proportion (47%) of hairy cell leukemias were GADS. Notably, PKCα highlighted a defective antigen in both PTCL/NOS (6%) and angioimmunoblastic T-cell lymphoma (10%), mostly negative in ALCL, and was aberrantly expressed in classical Hodgkin lymphoma (65%), Burkitt lymphoma (48%), and plasma cell myeloma (48%). In conclusion, all five molecules evaluated play a role in T-cell differentiation in normal and neoplastic tissues. They can be applied confidently to routine sections contributing primarily to assignment of T-lineage differentiation in the setting of hematopoietic precursor neoplasms (GADS/DOK2/SKAP55/ITK) and for the differential diagnosis between ALCL and PTCL/NOS (GADS/DOK2/SKAP55/ITK) or classical Hodgkin lymphoma (PKCα). Finally, association with specific tumor subtypes may have therapeutic potential.

Adaptor regulation of LFA-1 signaling in T lymphocyte migration: Potential druggable targets for immunotherapies?

The integrin lymphocyte function associated antigen-1 (LFA-1) plays a key role in leukocyte trafficking and in adaptive immune responses through interactions with adhesive ligands, such as ICAM-1. Specific blockade of these interactions has validated LFA-1 as a therapeutic target in many chronic inflammatory diseases, however LFA-1 antagonists have not been clinically successful due to the development of a general immunosuppression, causing fatal side effects. Growing evidence has now established that LFA-1 mediates an array of intracellular signaling pathways by triggering a number of downstream molecules. In this context, a class of multimodular domain-containing proteins capable of recruiting two or more effector molecules, collectively known as "adaptor proteins," has emerged as important mediators in LFA-1 signal transduction. Here, we provide an overview of the adaptor proteins involved in the intracellular signaling cascades by which LFA-1 regulates T-cell motility and immune responses. The complexity of the LFA-1-associated signaling delineated in this review suggests that it may be an important and challenging focus for future research, enabling the identification of "tunable" targets for the development of immunotherapies.

Dok1 and Dok2 proteins regulate natural killer cell development and function

Natural killer (NK) cells are involved in immune responses against tumors and microbes. NK-cell activation is regulated by intrinsic and extrinsic mechanisms that ensure NK tolerance and efficacy. Here, we show that the cytoplasmic signaling molecules Dok1 and Dok2 are tyrosine phosphorylated upon NK-cell activation. Overexpression of Dok proteins in human NK cells reduces cell activation induced by NK-cell-activating receptors. Dok1 and Dok2 gene ablation in mice induces an NK-cell maturation defect and leads to increased IFN-γ production induced by activating receptors. Taken together, these results reveal that Dok1 and Dok2 proteins are involved in an intrinsic negative feedback loop downstream of NK-cell-activating receptors in mouse and human.

Enhanced response of T cells from murine gammaherpesvirus 68-infected mice lacking the suppressor of T cell receptor signaling molecules Sts-1 and Sts-2

The human gammaherpesviruses establish life-long infections that are associated with the development of lymphomas and neoplasms, especially in immunocompromised individuals. T cells play a crucial role in the control of gammaherpesvirus infection through multiple functions, including the direct killing of infected cells, production of cytokines such as interferon-γ (IFN-γ), and costimulation of B cells. Impaired T cell function in mice infected with murine gammaherpesvirus 68 (MHV68) leads to increased reactivation and pathologies, including a higher incidence of lymphoid hyperplasia. Here we report that the absence of Suppressor of TCR signaling −1 and −2 (Sts-1^-/-/2^-/-) during MHV68 infection leads to the generation of T cells with significantly heightened responses. Transient differences in the T and B cell response of infected Sts-1^-/-/2^-/- (Sts dKO) mice were also observed when compared to WT mice. However, these alterations in the immune response and the overall absence of Sts-1 and Sts-2 did not impact viral pathogenesis or lead to pathology. Acute lytic replication in the lungs, establishment of latency in the spleen and reactivation from latency in the spleen in the Sts dKO mice were comparable to WT mice. Our studies indicate that Sts-1 and Sts-2 are not required for the immune control of MHV68 in a normal course of gammaherpesvirus infection, but suggest that interference with negative regulators of T cell responses might be further explored as a safe and efficacious strategy to improve adoptive T cell therapy.

Dok-2 adaptor protein regulates the shear-dependent adhesive function of platelet integrin αIIbβ3 in mice

The Dok proteins are a family of adaptor molecules that have a well defined role in regulating cellular migration, immune responses, and tumor progression. Previous studies have demonstrated that Doks-1 to 3 are expressed in platelets and that Dok-2 is tyrosine-phosphorylated downstream of integrin αIIbβ3, raising the possibility that it participates in integrin αIIbβ3 outside-in signaling. We demonstrate that Dok-2 in platelets is primarily phosphorylated by Lyn kinase. Moreover, deficiency of Dok-2 leads to dysregulated integrin αIIbβ3-dependent cytosolic calcium flux and phosphatidylinositol(3,4)P2 accumulation. Although agonist-induced integrin αIIbβ3 affinity regulation was unaltered in Dok-2(-/-) platelets, Dok-2 deficiency was associated with a shear-dependent increase in integrin αIIbβ3 adhesive function, resulting in enhanced platelet-fibrinogen and platelet-platelet adhesive interactions under flow. This increase in adhesion was restricted to discoid platelets and involved the shear-dependent regulation of membrane tethers. Dok-2 deficiency was associated with an increased rate of platelet aggregate formation on thrombogenic surfaces, leading to accelerated thrombus growth in vivo. Overall, this study defines an important role for Dok-2 in regulating biomechanical adhesive function of discoid platelets. Moreover, they define a previously unrecognized prothrombotic mechanism that is not detected by conventional platelet function assays.

Proteomic analysis of the SH2 domain-containing leukocyte protein of 76 kDa (SLP76) interactome in resting and activated primary mast cells [corrected]

We report the first proteomic analysis of the SLP76 interactome in resting and activated primary mouse mast cells. This was made possible by a novel genetic approach used for the first time here. It consists in generating knock-in mice that express signaling molecules bearing a C-terminal tag that has a high affinity for a streptavidin analog. Tagged molecules can be used as molecular baits to affinity-purify the molecular complex in which they are engaged, which can then be studied by mass spectrometry. We examined first SLP76 because, although this cytosolic adapter is critical for both T cell and mast cell activation, its role is well known in T cells but not in mast cells. Tagged SLP76 was expressed in physiological amounts and fully functional in mast cells. We unexpectedly found that SLP76 is exquisitely sensitive to mast cell granular proteases, that Zn(2+)-dependent metalloproteases are especially abundant in mast cells and that they were responsible for SLP76 degradation. Adding a Zn(2+) chelator fully protected SLP76 in mast cell lysates, thereby enabling an efficient affinity-purification of this adapter with its partners. Label-free quantitative mass spectrometry analysis of affinity-purified SLP76 interactomes uncovered both partners already described in T cells and novel partners seen in mast cells only. Noticeably, molecules inducibly recruited in both cell types primarily concur to activation signals, whereas molecules recruited in activated mast cells only are mostly associated with inhibition signals. The transmembrane adapter LAT2, and the serine/threonine kinase with an exchange factor activity Bcr were the most recruited molecules. Biochemical and functional validations established the unexpected finding that Bcr is recruited by SLP76 and positively regulates antigen-induced mast cell activation. Knock-in mice expressing tagged molecules with a normal tissue distribution and expression therefore provide potent novel tools to investigate signalosomes and to uncover novel signaling molecules in mast cells.

Role of inositol poly-phosphatases and their targets in T cell biology

T lymphocytes play a critical role in host defense in all anatomical sites including mucosal surfaces. This not only includes the effector arm of the immune system, but also regulation of immune responses in order to prevent autoimmunity. Genetic targeting of PI3K isoforms suggests that generation of PI(3,4,5)P3 by PI3K plays a critical role in promoting effector T cell responses. Consequently, the 5'- and 3'-inositol poly-phosphatases SHIP1, SHIP2, and phosphatase and tensin homolog capable of targeting PI(3,4,5)P3 are potential genetic determinants of T cell effector functions in vivo. In addition, the 5'-inositol poly-phosphatases SHIP1 and 2 can shunt PI(3,4,5)P3 to the rare but potent signaling phosphoinositide species PI(3,4)P2 and thus these SHIP1/2, and the INPP4A/B enzymes that deplete PI(3,4)P2 may have precise roles in T cell biology to amplify or inhibit effectors of PI3K signaling that are selectively recruited to and activated by PI(3,4)P2. Here we summarize recent genetic and chemical evidence that indicates the inositol poly-phosphatases have important roles in both the effector and regulatory functions of the T cell compartment. In addition, we will discuss future genetic studies that might be undertaken to further elaborate the role of these enzymes in T cell biology as well as potential pharmaceutical manipulation of these enzymes for therapeutic purposes in disease settings where T cell function is a key in vivo target.

A physical interaction between the adaptor proteins DOK3 and DAP12 is required to inhibit lipopolysaccharide signaling in macrophages

DNAX-activating protein of 12 kD (DAP12) is an immunoreceptor tyrosine-based activation motif (ITAM)-containing adaptor protein found in myeloid cells and natural killer cells, and it couples to various receptors that mediate either cellular activation or inhibition. DAP12 inhibits Toll-like receptor (TLR) signaling, such as that of TLR4 in response to its ligand lipopolysaccharide (LPS), as well as cytokine responses by coupling to TREM2 (triggering receptor expressed on myeloid cells 2) at the plasma membrane. Understanding the mechanisms that inhibit inflammatory responses in macrophages is important for the development of therapies to treat inflammatory diseases. We show that inhibition of LPS responses by DAP12 is mediated by the adaptor protein DOK3 (downstream of kinase 3). DOK3 physically associated with the ITAM of DAP12 through its phosphotyrosine-binding domain. In response to LPS, DOK3 was phosphorylated in a DAP12- and Src-dependent manner, which led to translocation of phosphorylated DOK3 to the plasma membrane. DOK3-deficient cells exhibited increased production of proinflammatory cytokines and activation of extracellular signal-regulated kinase (ERK). Compared to wild-type mice, DOK3-deficient mice had increased susceptibility to challenge with a sublethal dose of LPS and produced increased serum concentrations of the inflammatory cytokine tumor necrosis factor-α (TNF-α). Together, these data suggest the mechanism by which DAP12 and TREM2 inhibit LPS signaling in macrophages to prevent inflammation.

Triptolide ameliorates ileocolonic anastomosis inflammation in IL-10 deficient mice by mechanism involving suppression of miR-155/SHIP-1 signaling pathway

The model of ileocaecal resection (ICR) in IL-10(-/-) mice provides us a new way to investigate the postsurgical inflammation of intestinal anastomosis. As an extracts isolated from Tripterygium wilfordii Hook F (TWHF), triptolide has been used to treat Crohn's disease for years. Several mechanisms have been interpreted in previous studies. MiR-155, which can be inhibited by triptolide, has a powerful ability in regulating immune cells. As a target of miR-155, SHIP-1 is a potent inhibitor of many inflammatory pathways. MiR-155/SHIP-1 pathway plays an important role in the inflammatory conditions. We hypothesized that triptolide would ameliorate the postsurgical intestine inflammation especially the anastomosis inflammation by inhibition of miR-155/SHIP-1 pathway. Histological examination, as well as examination of calprotectin and MPO, demonstrated triptolide significantly reduced the severity of postsurgical intestine inflammation. Our data also suggested triptolide could suppress miR-155/SHIP-1 signaling pathway and attenuated expression of inflammatory cytokines in IL-10(-/-) mice performed ICR.

ERK positive feedback regulates a widespread network of tyrosine phosphorylation sites across canonical T cell signaling and actin cytoskeletal proteins in Jurkat T cells

Competing positive and negative signaling feedback pathways play a critical role in tuning the sensitivity of T cell receptor activation by creating an ultrasensitive, bistable switch to selectively enhance responses to foreign ligands while suppressing signals from self peptides. In response to T cell receptor agonist engagement, ERK is activated to positively regulate T cell receptor signaling through phosphorylation of Ser⁵⁹ Lck. To obtain a wide-scale view of the role of ERK in propagating T cell receptor signaling, a quantitative phosphoproteomic analysis of 322 tyrosine phosphorylation sites by mass spectrometry was performed on the human Jurkat T cell line in the presence of U0126, an inhibitor of ERK activation. Relative to controls, U0126-treated cells showed constitutive decreases in phosphorylation through a T cell receptor stimulation time course on tyrosine residues found on upstream signaling proteins (CD3 chains, Lck, ZAP-70), as well as downstream signaling proteins (VAV1, PLCγ1, Itk, NCK1). Additional constitutive decreases in phosphorylation were found on the majority of identified proteins implicated in the regulation of actin cytoskeleton pathway. Although the majority of identified sites on T cell receptor signaling proteins showed decreases in phosphorylation, Tyr⁵⁹⁸ of ZAP-70 showed elevated phosphorylation in response to U0126 treatment, suggesting differential regulation of this site via ERK feedback. These findings shed new light on ERK’s role in positive feedback in T cell receptor signaling and reveal novel signaling events that are regulated by this kinase, which may fine tune T cell receptor activation.

T cell receptor signalling networks: branched, diversified and bounded

Engagement of antigen-specific T cell receptors (TCRs) is a prerequisite for T cell activation. Acquisition of appropriate effector T cell function requires the participation of multiple signals from the T cell microenvironment. Trying to understand how these signals integrate to achieve specific functional outcomes while maintaining tolerance to self is a major challenge in lymphocyte biology. Several recent publications have provided important insights into how dysregulation of T cell signalling and the development of autoreactivity can result if the branching and integration of signalling pathways are perturbed. We discuss how these findings highlight the importance of spatial segregation of individual signalling components as a way of regulating T cell responsiveness and immune tolerance.

Phosphatase regulation of immunoreceptor signaling in T cells, B cells and mast cells

Recent progress has begun to reveal the often complex and changing roles of phosphotyrosine and phosphoinositide phosphatases in regulation of immunoreceptor signaling. The resultant confusion has been further increased by discoveries of new players. Here we provide a review of recent progress in defining the roles of these enzymes in immunoreceptor-dependent mast cell, T cell and B cell activation.

Inositol polyphosphate phosphatases in human disease

Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.

TCR activation kinetics and feedback regulation in primary human T cells

BACKGROUND

Signaling through the TCR is crucial for the generation of different cellular responses including proliferation, differentiation, and apoptosis. A growing body of evidence indicates that differences in the magnitude and the duration of the signal are critical determinants in eliciting cellular responses.

RESULTS

Here, we have analyzed signaling dynamics correlating with either unresponsiveness or proliferation induced upon TCR/CD28 ligation in primary human T cells. We used two widely employed methods to stimulate T cells in vitro, antibodies either cross-linked in solution (sAbs) or immobilized on microbeads (iAbs). A comparative analysis of the signaling properties of iAbs and sAbs revealed that, under proliferation-inducing conditions, feedback regulation is markedly different from that leading to an unresponsive state. In fact, upon iAbs stimulation TCR-mediated signaling is prolonged by a positive feedback loop involving Erk, whereas sAbs strongly activate inhibitory molecules that likely terminate signaling. We additionally found that, by enhancing the phosphorylation of Src family kinases under proliferation-inducing conditions, signaling and T-cell activation are terminated.

CONCLUSIONS

In summary, our analysis documents TCR signaling kinetics and feedback regulation under conditions of stimulation inducing either unresponsiveness or proliferation.

A detailed proteomic analysis of rhodocytin-activated platelets reveals novel clues on the CLEC-2 signalosome: implications for CLEC-2 signaling regulation

C-type lectin-like receptor 2 (CLEC-2) is an essential platelet-activating receptor in hemostasis and thrombosis that is activated by the snake venom rhodocytin. We present here a differential proteomic analysis of basal and rhodocytin-activated platelets with the aim of providing novel clues on CLEC-2 signaling regulation. Proteome analysis was based on 2D-DIGE, phosphotyrosine immunoprecipitations followed by 1D SDS-PAGE and mass spectrometry. Protein-protein interactions were studied by coimmunoprecipitations and a systems biology approach. Overall, we identified 132 proteins differentially regulated after CLEC-2 platelet activation, including most of the major players reported so far in the signaling cascade. In addition, we identified various proteins not previously known to participate in CLEC-2 signaling, such as the adapters Dok-2 and ADAP, tyrosine kinase Fer, and tyrosine phosphatase SHIP-1. We also report an increased association between Dok-2 and SHIP-1 in rhodocytin-stimulated platelets, which might negatively regulate CLEC-2 signaling. Moreover, we also present a comparative analysis of proteomic data for CLEC-2 and glycoprotein VI signaling. We think that our data provide thrombosis-relevant information on CLEC-2 signaling regulation, contributing to a better understanding of this important signaling cascade.

Pharmacological targeting of phosphoinositide lipid kinases and phosphatases in the immune system: success, disappointment, and new opportunities

The predominant expression of the γ and δ isoforms of PI3K in cells of hematopoietic lineage prompted speculation that inhibitors of these isoforms could offer opportunities for selective targeting of PI3K in the immune system in a range of immune-related pathologies. While there has been some success in developing PI3Kδ inhibitors, progress in developing selective inhibitors of PI3Kγ has been rather disappointing. This has prompted the search for alternative targets with which to modulate PI3K signaling specifically in the immune system. One such target is the SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1) which de-phosphorylates PI(3,4,5)P₃ at the D5 position of the inositol ring to create PI(3,4)P₂. In this article, we first describe the current state of PI3K isoform-selective inhibitor development. We then focus on the structure of SHIP-1 and its function in the immune system. Finally, we consider the current state of development of small molecule compounds that potently and selectively modulate SHIP activity and which offer novel opportunities to manipulate PI3K mediated signaling in the immune system.

The inositol phosphatase SHIP-1 inhibits NOD2-induced NF-κB activation by disturbing the interaction of XIAP with RIP2

SHIP-1 is an inositol phosphatase predominantly expressed in hematopoietic cells. Over the ten past years, SHIP-1 has been described as an important regulator of immune functions. Here, we characterize a new inhibitory function for SHIP-1 in NOD2 signaling. NOD2 is a crucial cytoplasmic bacterial sensor that activates proinflammatory and antimicrobial responses upon bacterial invasion. We observed that SHIP-1 decreases NOD2-induced NF-κB activation in macrophages. This negative regulation relies on its interaction with XIAP. Indeed, we observed that XIAP is an essential mediator of the NOD2 signaling pathway that enables proper NF-κB activation in macrophages. Upon NOD2 activation, SHIP-1 C-terminal proline rich domain (PRD) interacts with XIAP, thereby disturbing the interaction between XIAP and RIP2 in order to decrease NF-κB signaling.

Dok-1 overexpression promotes development of γδ natural killer T cells

In T cells, two members of the Dok family, Dok-1 and Dok-2, are predominantly expressed. Recent evidence suggests that they play a negative role in T-cell signaling. In order to define whether Dok proteins regulate T-cell development, we have generated transgenic mice overexpressing Dok-1 in thymocytes and peripheral T cells. We show that overexpression of Dok-1 retards the transition from the CD4(-) CD8(-) to CD4(+) CD8(+) stage. Moreover, there is a specific expansion of PLZF-expressing Vγ1.1(+) Vδ6.3(+) T cells. This subset of γδ T cells acquires innate characteristics including rapid IL-4 production following stimulation and requiring SLAM-associated adaptor protein (SAP) for their development. Moreover, Dok-1 overexpression promotes the generation of an innate-like CD8(+) T-cell population that expresses Eomesodermin. Altogether, these findings identify a novel role for Dok-1 in the regulation of thymic differentiation and in particular, in the development of PLZF(+) γδ T cells.

An essential regulatory role of downstream of kinase-1 in the ovalbumin-induced murine model of asthma

The downstream of kinase (DOK)-1 is involved in the protein tyrosine kinase (PTK) pathway in mast cells, but the role of DOK-1 in the pathogenesis of asthma has not been defined. In this study, we have demonstrated a novel regulatory role of DOK-1 in airway inflammation and physiologic responses in a murine model of asthma using lentiviral vector containing DOK-1 cDNA or DOK-1-specific ShRNA. The OVA-induced inflammatory cells, airway hyperresponsiveness, Th2 cytokine expression, and mucus response were significantly reduced in DOK-1 overexpressing mice compared to OVA-challenged control mice. The transgenic introduction of DOK-1 significantly stimulated the activation and expression of STAT-4 and T-bet, while impressively inhibiting the activation and expression of STAT-6 and GATA-3 in airway epithelial cells. On the other hand, DOK-1 knockdown mice enhanced STAT-6 expression and its nuclear translocation compared to OVA-challenged control mice. When viewed in combination, our studies demonstrate DOK-1 regulates allergen-induced Th2 immune responses by selective stimulation and inhibition of STAT-4 and STAT-6 signaling pathways, respectively. These studies provide a novel insight on the regulatory role of DOK-1 in allergen-induced Th2 inflammation and airway responses, which has therapeutic potential for asthma and other allergic diseases.

The inositol 5-phosphatase SHIP-1 and adaptors Dok-1 and 2 play central roles in CD4-mediated inhibitory signaling

CD4 functions to enhance the sensitivity of T cells to antigenic peptide/MHC class II. However, if aggregated in isolation, e.g. in the absence of T cell receptor (TCR), CD4 can transduce yet undefined signals that lead to T cell unresponsiveness to antigen and apoptosis. In Human Immunodeficiency Virus-1 (HIV-1) disease, CD4(+) T cell loss can result from gp120-induced CD4 signaling in uninfected cells. We show here that CD4 aggregation leads to Lck-dependent phosphorylation of the RasGAP adaptors Downstream of kinase-1/2 (Dok-1/2) and the inositol 5-phosphatase-1 (SHIP-1) and association of the two molecules. Studies using SHIP-1 shRNA, knockout mice and decoy inhibitors further indicate that CD4-mediated inhibition of TCR-mediated T cell activation is SHIP-1 and Dok-1/2 dependent, and involves SHIP-1 hydrolysis of Phosphatidylinositol 3,4,5-trisphosophate (PI(3,4,5)P3) needed for TCR signaling. Our studies provide evidence for a novel mechanism by which ill-timed CD4-mediated signals activated by ligands such as HIV-1 gp120 lead to disarmament of the immune system.

A negatively charged domain of LAT mediates its interaction with the active form of Lck

We have shown previously that in T cells, LAT co-immunoprecipitates with the active but not the inactive-'closed' form of Lck, and that this interaction impacts negatively on Lck activity. Here we confirm that activation of T cells induced a transient LAT/Lck association within 4 min after stimulation, returning to basal levels by 30 min. Interestingly, autoimmune T cells isolated from patients with systemic lupus erythematosus, which contain a larger pool of active Lck and LAT, exhibited increased LAT/Lck association compared to healthy controls. To identify the domain of LAT responsible for its interaction with active Lck, a series of LAT truncation mutants were constructed and tested in co-immunoprecipitation experiments. We found that the segment comprising residues 112-126 of human LAT is required for its interaction with Lck. This domain is rich in negatively charged amino acids and is conserved among different species. Therefore, in addition to the conserved tyrosines, the 112-126 domain identified here could be important for certain functions of LAT in T cells.