Down-regulation of IL-4 gene transcription and control of Th2 cell differentiation by a mechanism involving NFAT1

Genetic deficiency of the transcription factor NFAT1 confers protection against fibrogenic responses independent of immune influx

Idiopathic pulmonary fibrosis (IPF) is marked by unremitting matrix deposition and architectural distortion. Multiple profibrotic pathways contribute to the persistent activation of mesenchymal cells (MCs) in fibrosis, highlighting the need to identify and target common signaling pathways. The transcription factor nuclear factor of activated T cells 1 (NFAT1) lies downstream of second messenger calcium signaling and has been recently shown to regulate key profibrotic mediator autotaxin (ATX) in lung MCs. Herein, we investigate the role of NFAT1 in regulating fibroproliferative responses during the development of lung fibrosis. Nfat1-/--deficient mice subjected to bleomycin injury demonstrated improved survival and protection from lung fibrosis and collagen deposition as compared with bleomycin-injured wild-type (WT) mice. Chimera mice, generated by reconstituting bone marrow cells from WT or Nfat1-/- mice into irradiated WT mice (WT→WT and Nfat1-/-→WT), demonstrated no difference in bleomycin-induced fibrosis, suggesting immune influx-independent fibroprotection in Nfat1-/- mice. Examination of lung tissue and flow sorted lineageneg/platelet-derived growth factor receptor alpha (PDGFRα)pos MCs demonstrated decreased MC numbers, proliferation [↓ cyclin D1 and 5-ethynyl-2'-deoxyuridine (EdU) incorporation], myofibroblast differentiation [↓ α-smooth muscle actin (α-SMA)], and survival (↓ Birc5) in Nfat1-/- mice. Nfat1 deficiency abrogated ATX expression in response to bleomycin in vivo and MCs derived from Nfat1-/- mice demonstrated decreased ATX expression and migration in vitro. Human IPF MCs demonstrated constitutive NFAT1 activation, and regulation of ATX in these cells by NFAT1 was confirmed using pharmacological and genetic inhibition. Our findings identify NFAT1 as a critical mediator of profibrotic processes, contributing to dysregulated lung remodeling and suggest its targeting in MCs as a potential therapeutic strategy in IPF.NEW & NOTEWORTHY Idiopathic pulmonary fibrosis (IPF) is a fatal disease with hallmarks of fibroblastic foci and exuberant matrix deposition, unknown etiology, and ineffective therapies. Several profibrotic/proinflammatory pathways are implicated in accelerating tissue remodeling toward a honeycombed end-stage disease. NFAT1 is a transcriptional factor activated in IPF tissues. Nfat1-deficient mice subjected to chronic injury are protected against fibrosis independent of immune influxes, with suppression of profibrotic mesenchymal phenotypes including proliferation, differentiation, resistance to apoptosis, and autotaxin-related migration.

Correlation of the transcription factors IRF4 and BACH2 with the abnormal NFATC1 expression in T cells from chronic myeloid leukemia patients

OBJECTIVE

T cell dysfunction is a common characteristic of patients with myeloid leukemia and is closely related to clinical efficacy and prognosis. In order to clarify the mechanisms leading to the T cell dysfunction, we characterized the gene expression profile of T cells from chronic myelogenous leukemia (CML) patients by microarray analysis and investigated the related regulating pathway.

METHODS

We employed gene expression profiling, bioinformatics and real-time quantitative reverse transcription PCR (RT-qPCR) to detect genes differentially expressed in CML patients versus healthy donors.

RESULTS

There were 1704 genes differentially expressed between CD3⁺ T cells from CML patients and healthy donors, including 868 up-regulated genes and 836 down-regulated genes, which mostly related to T cell functional pathways. In particular, lower expression of NFATC1, a member of the TCR signaling pathway, was detected in CD3⁺ T cells from CML patients. We further found that the expression of IRF4 and BACH2, transcription factors that potentially regulate NFATC1, in CD3⁺ T cells from CML patients was significantly lower than that in healthy donors.

CONCLUSION

We for the first time observed the altered gene expression profiles of CD3⁺ T cells from CML patients, and the results suggested that IRF4, BACH2 and NFATC1 may be involved in regulating T cell dysfunction in CML patients in the form of a transcriptional regulatory network. These findings may provide potential targets for tyrosine kinase inhibitors in combination with other targeted immunotherapies .

The role of NFAT2/miR-20a-5p signaling pathway in the regulation of CD8+ naïve T cells activation and differentiation

T cell dysfunction is a common characteristic in leukemia patients that significantly impacts clinical treatment and prognosis. However, the mechanism underlying T cell dysfunction and its reversal remains unclear. In this study, in accordance with our previous findings, we found that the expression of NFAT2 and pri-miR-17 ~ 92 are lower in peripheral blood CD3⁺ T cells from chronic myelogenous leukemia (CML) patients by gene expression analysis. We further demonstrate that the NFAT2-induced activation, differentiation, and expression of cytokines in human umbilical cord blood CD8⁺ naïve T cells are miR-20a-5p dependent. We also preliminarily explored the relationship between NFAT2 and miR-20a-5p in naive T cells. These results suggest that NFAT2 and miR-20a are crucial for regulating functional CD8⁺ T cells. Additionally, their alteration may be related to CD8⁺ T cell dysfunction in CML patients; thus, NFAT2 and miR-20a-5p may be considered potential targets for revising T cell function in leukemia immunotherapy.

Calcineurin inhibitors suppress acute graft-versus-host disease via NFAT-independent inhibition of T cell receptor signaling

Inhibitors of calcineurin phosphatase activity (CNIs) such as cyclosporin A (CsA) are widely used to treat tissue transplant rejection and acute graft-versus-host disease (aGVHD), for which inhibition of gene expression dependent on nuclear factor of activated T cells (NFAT) is the mechanistic paradigm. We recently reported that CNIs inhibit TCR-proximal signaling by preventing calcineurin-mediated dephosphorylation of LckS59, an inhibitory modification, raising the possibility of another mechanism by which CNIs suppress immune responses. Here we used T cells from mice that express LckS59A, which cannot accept a phosphate at residue 59, to initiate aGVHD. Although CsA inhibited NFAT-dependent gene upregulation in allo-aggressive T cells expressing either LckWT or LckS59A, it was ineffective in treating disease when the T cells expressed LckS59A. Two important NFAT-independent T cell functions were found to be CsA-resistant in LckS59A T cells: upregulation of the cytolytic protein perforin in tissue-infiltrating CD8+ T cells and antigen-specific T/DC adhesion and clustering in lymph nodes. These results demonstrate that effective treatment of aGVHD by CsA requires NFAT-independent inhibition of TCR signaling. Given that NFATs are widely expressed and off-target effects are a major limitation in CNI use, it is possible that targeting TCR-associated calcineurin directly may provide effective therapies with less toxicity.

Role of host genetics and cytokines in Leishmania infection

Cytokines and chemokines are important regulators of innate and specific responses in leishmaniasis, a disease that currently affects 12 million people. We overviewed the current information about influences of genetically engineered mouse models of cytokine and chemokine on leishmaniasis. We found that genetic background of the host, parasite species and sub-strain, as well as experimental design often modify effects of genetically engineered cytokine genes. Next we analyzed genes and QTLs (quantitative trait loci) that control response to Leishmania species in mouse in order to establish relationship between genetic control of cytokine expression and organ pathology. These studies revealed a network-like complexity of the combined effects of the multiple functionally diverse QTLs and their individual specificity. Genetic control of organ pathology and systemic immune response overlap only partially. Some QTLs control both organ pathology and systemic immune response, but the effects of genes and loci with the strongest impact on disease are cytokine-independent, whereas several loci modify cytokines levels in serum without influencing organ pathology. Understanding this genetic control might be important in development of vaccines designed to stimulate certain cytokine spectrum.

Genetic inhibition of NFATC2 attenuates asparaginase hypersensitivity in mice

The family of nuclear factor of activated T cells (NFAT) transcription factors plays a critical role in mediating immune responses. Our previous clinical pharmacogenetic studies suggested that NFATC2 is associated with the risk of hypersensitivity reactions to the chemotherapeutic agent L-asparaginase (ASNase) that worsen outcomes during the treatment of pediatric acute lymphoblastic leukemia. We therefore hypothesized that the genetic inhibition of NFATC2 would protect against the development of anti-ASNase antibodies and ASNase hypersensitivity. Our study demonstrates that ASNase-immunized NFATC2-deficient mice are protected against ASNase hypersensitivity and develop lower antigen-specific and total immunoglobulin E (IgE) levels compared with wild-type (WT) controls. Furthermore, ASNase-immunized NFATC2-deficient mice develop more CD4+ regulatory T cells, fewer CD4+ interleukin-4-positive (IL-4+) cells, higher IL-10/TGF-β1 levels, and lower IL-4/IL-13 levels relative to WT mice. Basophils and peritoneal mast cells from ASNase-immunized, but not naïve, NFATC2-deficient mice had lower FcεRI expression and decreased IgE-mediated mast cell activation than WT mice. Furthermore, ASNase-immunized, but not naïve, NFATC2-deficient mice developed less severe shock than WT mice after induction of passive anaphylaxis or direct histamine administration. Thus, inhibition of NFATC2 protects against ASNase hypersensitivity by impairing T helper 2 responses, which may provide a novel strategy for attenuating hypersensitivity and the development of antidrug antibodies, including to ASNase.

All-trans-retinoic acid shifts Th1 towards Th2 cell differentiation by targeting NFAT1 signalling to ameliorate immune-mediated aplastic anaemia

Severe acquired aplastic anaemia (AA) is a serious disease characterised by autoreactive T cells attacking haematopoietic stem cells, leading to marrow hypoplasia and pancytopenia. Immunosuppressive therapy combined with antithymocyte globulin and ciclosporin can rescue most patients with AA. However, the relapse after ciclosporin withdrawal and the severe side effects of long-term ciclosporin administration remain unresolved. As such, new strategies should be developed to supplement current therapeutics and treat AA. In this study, the possibility of all-trans-retinoic acid (ATRA) as an alternative AA treatment was tested by using an immune-mediated mouse model of AA. Results revealed that ATRA inhibited T-cell proliferation, activation and effector function. It also restrained the Fas/Fasl pathway, shifted Th1 towards Th2 cell development, rebalanced T-cell subsets at a relatively high level and corrected the Th1/Th2 ratio by targeting NFAT1 signalling. In addition, ATRA inhibited Th17 cell differentiation and promoted regulatory T-cell development. Therefore, ATRA was an effective agent to improve AA treatment outcomes.

TCR Dependent Metabolic Programming Regulates Autocrine IL-4 Production Resulting in Self-Tuning of the CD8+ T Cell Activation Setpoint

The ability of T cells to sense and respond to environmental cues by altering their functional capabilities is critical for a safe and optimally protective immune response. One of the important properties that contributes to this goal is the activation set-point of the T cell. Here we report a new pathway through which TCR transgenic OT-I CD8⁺ T cells can self-tune their activation threshold. We find that in the presence of a strong TCR engagement event there is a shift in the metabolic programming of the cell where both glycolysis and oxidative phosphorylation are significantly increased. This diverges from the switch to a predominantly glycolytic profile that would be predicted following naïve T cell activation. Our data suggest this altered metabolic program results in the production of autocrine IL-4. Both metabolic pathways are required for this cytokine to be made. IL-4 signaling in the activated OT-I CD8⁺ T cell results in modulation of the sensitivity of the cell, establishing a higher activation setpoint that is maintained over time. Together these data demonstrate a novel mechanism for the regulation of IL-4 production in CD8⁺ T cells. Further, they reveal a new pathway for the self-tuning of peptide sensitivity. Finally, these studies uncover an unexpected role for oxidative phosphorylation in regulating differentiation in these cells.

Targeted deletion of NFAT-Interacting-Protein-(NIP) 45 resolves experimental asthma by inhibiting Innate Lymphoid Cells group 2 (ILC2)

Here we investigated the role of NFAT-interacting protein (NIP)-45, an Interleukin (IL)-4 inducing Transcription Factor, and its impact on the differentiation of Group 2 Innate -Lymphoid -Cells (ILC2s) in the pathogenesis of asthma. NIP45, a transcription factor regulating NFATc1 activity, mRNA was found to be induced in the Peripheral Blood mononuclear cells (PMBCs) of asthmatic pre-school children with allergies and in the peripheral blood CD4⁺ T cells from adult asthmatic patients. In PBMCs of asthmatic and control children, NIP45 mRNA directly correlated with NFATc1 but not with T-bet. Targeted deletion of NIP45 in mice resulted in a protective phenotype in experimental asthma with reduced airway mucus production, airway hyperresponsiveness and eosinophils. This phenotype was reversed by intranasal delivery of recombinant r-IL-33. Consistently, ILC2s and not GATA3⁺ CD4⁺ T-cells were decreased in the lungs of asthmatic NIP45^−/− mice. Reduced cell number spleen ILC2s could be differentiated from NIP45^−/− as compared to wild-type mice after in vivo injection of a microcircle-DNA vector expressing IL-25 and decreased cytokines and ILC2 markers in ILC2 differentiated from the bone marrow of NIP45^−/− mice. NIP45 thus emerges as a new therapeutic target for the resolution of the airway pathology, down-regulation of ILC2s and mucus production in asthma.

NFAT-Specific Inhibition by dNP2-VIVITAmeliorates Autoimmune Encephalomyelitisby Regulation of Th1 and Th17

Nuclear factor of activated T cells (NFATs) is an important transcription factor for T cell activation and proliferation. Recent studies have highlighted the role of NFATs in regulating the differentiation of effector CD4 T helper (Th) subsets including Th1 and Th17 cells. Because controlling the effector T cell function is important for the treatment of autoimmune diseases, regulation of NFAT functions in T cells would be an important strategy to control the pathogenesis of autoimmune diseases. Here, we demonstrated that an NFAT inhibitory peptide, VIVIT conjugated to dNP2 (dNP2-VIVIT), a blood-brain barrier-permeable peptide, ameliorated experimental autoimmune encephalomyelitis (EAE) by inhibiting Th1 and Th17 cells, but not regulatory T (T_reg) cells. dNP2-VIVIT negatively regulated spinal cord-infiltrating interleukin-17A (IL-17A) and interferon (IFN)-γ-producing CD4⁺ T cells without affecting the number of Foxp3⁺ CD4⁺ T_reg cells, whereas dNP2-VEET or 11R-VIVIT could not significantly inhibit EAE. In comparison with cyclosporin A (CsA), dNP2-VIVIT selectively inhibited Th1 and Th17 differentiation, whereas CsA inhibited the differentiation of all T cell subsets including that of Th2 and T_reg cells. Collectively, this study demonstrated the role of dNP2-VIVIT as a novel agent for the treatment of autoimmune diseases such as multiple sclerosis by regulating the functions of Th1 and Th17 cells.

Revisiting the Concept of Targeting NFAT to Control T Cell Immunity and Autoimmune Diseases

The nuclear factor of activated T cells (NFAT) family of transcription factors, which includes NFAT1, NFAT2, and NFAT4, are well-known to play important roles in T cell activation. Most of NFAT proteins are controlled by calcium influx upon T cell receptor and costimulatory signaling results increase of IL-2 and IL-2 receptor. NFAT3 however is not shown to be expressed in T cells and NFAT5 has not much highlighted in T cell functions yet. Recent studies demonstrate that the NFAT family proteins involve in function of lineage-specific transcription factors during differentiation of T helper 1 (Th1), Th2, Th17, regulatory T (Treg), and follicular helper T cells (Tfh). They have been studied to make physical interaction with the other transcription factors like GATA3 or Foxp3 and they also regulate Th cell signature gene expressions by direct binding on promotor region of target genes. From last decades, NFAT functions in T cells have been targeted to develop immune modulatory drugs for controlling T cell immunity in autoimmune diseases like cyclosporine A, FK506, etc. Due to their undesirable side defects, only limited application is available in human diseases. This review focuses on the recent advances in development of NFAT targeting drug as well as our understanding of each NFAT family protein in T cell biology. We also discuss updated detail molecular mechanism of NFAT functions in T cells, which would lead us to suggest an idea for developing specific NFAT inhibitors as a therapeutic drug for autoimmune diseases.

Transcriptional Programs Underlying Cd4 T Cell Differentiation and Functions

Understanding the basis of cellular differentiation is a fundamental issue in developmental biology but also for the comprehension of pathological processes. In fact, the palette of developmental decisions for naive CD4 T cells is a critical aspect of the development of appropriate immune responses which could control infectious processes or cancer growth. However, the current accumulation of data on CD4 T cells biology reveals a complex world with different helper populations. Naive CD4 T cells can differentiate into different subtypes in response to cytokine stimulation. This stimulation involves a complex transcriptional network implicating the activation of Signal Transducer and Activator of Transcription but also master regulator transcription factors allowing the functions of each helper T lymphocyte subtype. In this review, we will present an overview of the transcriptional regulation which controls process of helper T cells differentiation. We will focus on the role of initiator transcriptional factors and on master regulators but also on other nonspecific transcriptional factors which refine the T helper polarization to stabilize or modulate the differentiation program.

The Transcription Factor NFAT1 Participates in the Induction of CD4+ T Cell Functional Exhaustion during Plasmodium yoelii Infection

Repeated stimulation of T cells that occurs in the context of chronic infection results in progressively reduced responsiveness of T cells to pathogen-derived antigens. This phenotype, known as T cell exhaustion, occurs during chronic infections caused by a variety of pathogens, from persistent viruses to parasites. Unlike the memory cells that typically form after successful pathogen clearance following an acute infection, exhausted T cells secrete lower levels of effector cytokines, proliferate less in response to cognate antigen, and upregulate cell surface inhibitory molecules such as PD-1 and LAG-3. The molecular events that lead to the induction of this phenotype have, however, not been fully characterized. In T cells, members of the NFAT family of transcription factors not only are responsible for the expression of many activation-induced genes but also are crucial for the induction of transcriptional programs that inhibit T cell activation and maintain tolerance. Here we show that NFAT1-deficient CD4⁺ T cells maintain higher proliferative capacity and expression of effector cytokines following Plasmodium yoelii infection and are therefore more resistant to P. yoelii-induced exhaustion than their wild-type counterparts. Consequently, gene expression microarray analysis of CD4⁺ T cells following P. yoelii-induced exhaustion shows upregulation of effector T cell-associated genes in the absence of NFAT1 compared with wild-type exhausted T cells. Furthermore, adoptive transfer of NFAT1-deficient CD4⁺ T cells into mice infected with P. yoelii results in increased production of antibodies to cognate antigen. Our results support the idea that NFAT1 is necessary to fully suppress effector responses during Plasmodium-induced CD4⁺ T cell exhaustion.

Expression profiling of Sudanese visceral leishmaniasis patients pre- and post-treatment with sodium stibogluconate

Visceral leishmaniasis (VL) in Sudan caused by Leishmania donovani is fatal in susceptible individuals if untreated. Treatment with sodium stibogluconate (SSG) leads to post-kala-azar dermal leishmaniasis (PKDL) in 58% of patients. Here, Affymetrix microarrays were used to identify genes differentially expressed in lymph nodes (N=9 paired samples) pre- and post-treatment with SSG. Using the Bioconductor package limma, 438 genes from 28 869 post-quality-control probe sets were differentially expressed (P_nominal ≤.02) post- vs pretreatment. Canonical pathway analysis using Ingenuity Pathway Analysis™ identified "role of nuclear factor of activated T-cell in regulation of immune response" (P_nominal =1.35×10^-5 ; P_BH-adjusted =4.79×10^-3 ), "B-cell development" (P_nominal =2.04×10^-4 ; P_BH-adjusted =.024), "Fcγ receptor-mediated phagocytosis in macrophages and monocytes" (P_nominal =2.04×10^-4 ; P_BH-adjusted =.024) and "OX40 signalling" (P_nominal =2.82×10^-4 ; P_BH-adjusted =.025) as pathways differentially regulated post- vs pretreatment. Major network hub genes included TP53, FN1, MYC, BCL2, JUN, SYK, RUNX2, MMP1 and ACTA2. Top endogenous upstream regulators included IL-7 (P=2.28×10^-6 ), TNF (P=4.26×10^-6 ), Amyloid Precursor Protein (P=4.23×10^-5 ) and SPI1/PI.1 (P=1.17×10^-7 ). Top predicted chemical drug regulators included the flavonoid genistein (P=4.56×10^-7 ) and the quinoline alkaloid camptothecin (P=5.14×10^-5 ). These results contribute to our understanding of immunopathology associated with VL and response to SSG treatment. Further replication could identify novel therapeutic strategies that improve on SSG treatment and reduce the likelihood of progression to PKDL.

B Cell-Activating Factor (BAFF)-Targeted B Cell Therapies in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) involve dysregulated immune responses to gut antigens in genetically predisposed individuals. While a better elucidation of IBD pathophysiology has considerably increased the number of treatment options, the need for more effective therapeutic strategies remains a pressing priority. Defects of both non-hematopoietic (epithelial and stromal) and hematopoietic (lymphoid and myeloid) cells have been described in patients with IBD. Within the lymphoid system, alterations of the T cell compartment are viewed as essential in the pathogenesis of IBD. However, growing evidence points to the additional perturbations of the B cell compartment. Indeed, the intestinal lamina propria from IBD patients shows an increased presence of antibody-secreting plasma cells, which correlates with enhanced pro-inflammatory immunoglobulin G production and changes in the quality of non-inflammatory IgA responses. These B cell abnormalities are compounded by the emergence of systemic antibody responses to various autologous and microbial antigens, which predates the clinical diagnosis of IBD and identifies patients with complicated disease. It is presently unclear whether such antibody responses play a pathogenetic role, as B cell depletion with the CD20-targeting monoclonal antibody rituximab did not ameliorate ulcerative colitis in a clinical trial. However, it must be noted that unresponsiveness to rituximab is also observed also in some patients with autoimmune disorders usually responsive to B cell-depleting therapies. In this review, we discussed mechanistic aspects of B cell-based therapies and their potential role in IBD with a special interest on BAFF and BAFF-targeting therapies buoyed by the success of anti-BAFF treatments in rheumatologic disorders.

Inhibition of G-Protein βγ Signaling Decreases Levels of Messenger RNAs Encoding Proinflammatory Cytokines in T Cell Receptor-Stimulated CD4(+) T Helper Cells

Background: Inhibition of G-protein βγ (Gβγ) signaling was found previously to enhance T cell receptor (TCR)-stimulated increases in interleukin 2 (IL-2) mRNA in CD4⁺ T helper cells, suggesting that Gβγ might be a useful drug target for treating autoimmune diseases, as low dose IL-2 therapy can suppress autoimmune responses. Because IL-2 may counteract autoimmunity in part by shifting CD4⁺ T helper cells away from the Type 1 T helper cell (TH1) and TH17 subtypes towards the TH2 subtype, the purpose of this study was to determine if blocking Gβγ signaling affected the balance of TH1, TH17, and TH2 cytokine mRNAs produced by CD4⁺ T helper cells.

Methods: Gallein, a small molecule inhibitor of Gβγ, and siRNA-mediated silencing of the G-protein β₁ subunit (Gβ₁) were used to test the effect of blocking Gβγ on mRNA levels of cytokines in primary human TCR-stimulated CD4⁺ T helper cells.

Results: Gallein and Gβ₁ siRNA decreased interferon-γ (IFN-γ) and IL-17A mRNA levels in TCR-stimulated CD4⁺ T cells grown under TH1-promoting conditions. Inhibiting Gβγ also decreased mRNA levels of STAT4, which plays a positive role in TH1 differentiation and IL-17A production. Moreover, mRNA levels of the STAT4-regulated TH1-associated proteins, IL-18 receptor β chain (IL-18Rβ), mitogen-activated protein kinase kinase kinase 8 (MAP3K8), lymphocyte activation gene 3 (LAG-3), natural killer cell group 7 sequence (NKG7), and oncostatin M (OSM) were also decreased upon Gβγ inhibition. Gallein also increased IL-4, IL-5, IL-9, and IL-13 mRNA levels in TCR-stimulated memory CD4⁺ T cells grown in TH2-promoting conditions.

Conclusions: Inhibiting Gβγ to produce these shifts in cytokine mRNA production might be beneficial for patients with autoimmune diseases such as rheumatoid arthritis (RA), Crohn’s disease (CD), psoriasis, multiple sclerosis (MS), and Hashimoto’s thyroiditis (HT), in which both IFN-γ and IL-17A are elevated.

Impact on antibody responses of B-cell-restricted transgenic expression of a viral gene inhibiting activation of NF-κB and NFAT

In this work, we have assessed the impact in vivo of the evasion gene A238L of African swine fever virus, an inhibitor of both NF-κB- and NFAT-mediated transcription. The A238L gene was selectively expressed in mouse B lymphocytes using the promoter and enhancer sequences of the mouse Ig μ heavy chain. The IgM primary and IgG2b secondary serological responses and the number of splenic germinal centres in response to the TD antigens DNP-keyhole limpet hemocyanin and sheep red blood cells, respectively, were both lower in the transgenic mice, whereas the response to the TI type-1 and type-2 antigens DNP-Ficoll and DNP-LPS, respectively, were normal, except for the increased levels of IgG3 at day 14 in the DNP-LPS-immunized mice. Thus, it appears that neither p65 (NF-κB) nor NFAT is essential for B-cell development but, in a manner that is still unclear, may be relevant for their function.

Transcriptional regulatory networks for CD4 T cell differentiation

CD4(+) T cells play a central role in controlling the adaptive immune response by secreting cytokines to activate target cells. Naïve CD4(+) T cells differentiate into at least four subsets, Th1Th1 , Th2Th2 , Th17Th17 , and inducible regulatory T cellsregulatory T cells , each with unique functions for pathogen elimination. The differentiation of these subsets is induced in response to cytokine stimulation, which is translated into Stat activation, followed by induction of master regulator transcription factorstranscription factors . In addition to these factors, multiple other transcription factors, both subset specific and shared, are also involved in promoting subset differentiation. This review will focus on the network of transcription factors that control CD4(+) T cell differentiation.

NFATc2 mediates epigenetic modification of dendritic cell cytokine and chemokine responses to dectin-1 stimulation

The transcription factor NFATc2 regulates dendritic cell (DC) responses to microbial stimulation through the C-type lectin receptor dectin-1. But the genetic targets of NFATc2 and their effects on DC function remain largely unknown. Therefore we used ChIP-seq to conduct genome-wide mapping of NFATc2 target sites in dectin-1-activated DCs. By combining binding-site data with a comprehensive gene expression profile, we found that NFATc2 occupancy regulates the expression of a subset of dectin-1-activated genes. Surprisingly, NFATc2 targeted an extensive range of DC-derived cytokines and chemokines, including regulatory cytokines such as IL2, IL23a and IL12b. Furthermore, we demonstrated that NFATc2 binding is required to induce the histone 3 lysine 4 trimethylation (H3K4me3) epigenetic mark, which is associated with enhanced gene expression. Together, these data show that the transcription factor NFATc2 mediates epigenetic modification of DC cytokine and chemokine genes leading to activation of their expression.

6-Methoxyflavone inhibits NFAT translocation into the nucleus and suppresses T cell activation

NFAT plays a crucial role in the immune system by regulating the transcription of inducible genes during immune responses. In T cells, NFAT proteins govern various cellular events related to T cell development, activation, tolerance induction, and differentiation. We previously reported the NFAT1-dependent enhancer activity of conserved noncoding sequence (CNS)-9, a distal cis-acting element, in the regulation of IL-10 transcription in T cells. In this study, we developed a T cell-based reporter system to identify compounds that modulate the regulatory activity of CNS-9. Among the identified candidates, 6-methoxyflavone (6-MF) significantly inhibited the enhancer activity of CNS-9, thereby reducing IL-10 expression in T cells without affecting cell viability. 6-MF also downregulated the transcription of NFAT1 target genes such as IL-4, IL-13, and IFN-γ. Treatment of 6-MF inhibited the translocation of NFAT1 into the nucleus, which consequently interrupted NFAT1 binding to the target loci, without affecting the expression or dephosphorylation of NFAT1. Treatment of 6-MF to CD4(+) T cells or B cells isolated from mice with atopic dermatitis significantly reduced disease-associated cytokine production, as well as the levels of IgE. In addition, oral administration of 6-MF to atopic dermatitis mice ameliorated disease symptoms by reducing serum IgE levels and infiltrating lymphocytes. Conclusively, our results suggest that 6-MF can be a potential candidate for the development of an effective immunomodulator via the suppression of NFAT-mediated T cell activation.

NFAT1 transcription factor in dendritic cells is required to modulate T helper cell differentiation

The NFAT family of transcription factors plays a central role in the regulation of cytokine gene expression during the immune response. NFAT functions have been extensively explored in lymphocyte activation and differentiation, but the involvement of NFAT proteins in dendritic cells (DCs) is still not well known. Here, we investigated the role of the NFAT1 transcription factor in murine DCs. Initially, we demonstrated by western blot that the NFAT1 protein is present in splenic DCs and is rapidly activated upon calcium influx. We then used NFAT1-deficient mice (NFAT1-/-) to investigate whether NFAT1 influences the ability of DCs to induce Th differentiation. Our data demonstrated that NFAT1-/- DCs showed an increased capacity to differentiate CD4 T cells to the Th1 phenotype. CD4 cells that were primed in vitro with NFAT1-/- DCs had increased IFN-γ production. The same results were observed when the CD4 cells were primed in vivo through the sensitization of NFAT1-/- mice with ovalbumin. Furthermore, our results demonstrated that the cytokine IL-12 is one of the factors involved in this process because its production is increased in NFAT1-/- mice, and neutralizing anti-IL-12 antibodies almost completely eliminated the IFN-γ production. These results demonstrated that the NFAT1 transcription factor regulates specific functions in DCs that are involved in CD4 differentiation, suggesting that the inhibition of NFAT1 in DCs may be used as a therapy to modulate specific immune responses.

The studies of chlorogenic Acid antitumor mechanism by gene chip detection: the immune pathway gene expression

Persistently increasing incident of cancer in human beings has served to emphasize the importance of studies on mechanism of antitumor substances. Chlorogenic acid (CA), extracted from folium cortex eucommiae, has been confirmed to have lots of biological activities encompassing inhibition of tumor. However, the anticancer mechanism of CA remains unclear. Here, we have utilized a whole mouse genome oligo microarray (4∗44K) to analyze gene expression level of female BALB/c mice (implanted with EMT-6 sarcoma cells) after treatment with low, medium, and high-dose CA (5 mg/kg, 10 mg/kg, and 20 mg/kg), docetaxel, interferon, and normal saline separately at 6 time points (3rd, 6th, 9th, 12th, 15th, and 18th days after administration). Differentially expressed genes screened out by time-series analysis, GO analysis, and pathway analysis, and four immune-related genes were selected for further confirmation using RT-qPCR. The results demonstrated that CA is able to change gene expression and that the responsive genes (CaN, NFATC2, NFATC2ip, and NFATC3) involved in immune pathways had been significantly upregulated by CA. Expression of immune factors such as IL-2R and IFN- γ can be improved by CA to promote activation and proliferation of T cells, macrophages, and NK cells, thus enhancing their surveillance and killing abilities, further suppressing the growth rate of tumor cells.

Functional T cell immunodeficiencies (with T cells present)

Severe combined immunodeficiency (SCID) comprises a group of disorders that are fatal owing to genetic defects that abrogate T cell development. Numerous related defects have recently been identified that allow T cell development but that compromise T cell function by affecting proximal or distal steps in intracellular signaling. These functional T cell immunodeficiencies are characterized by immune dysregulation and increased risk of malignancies, in addition to infections. The study of patients with these rare conditions, and of corresponding animal models, illustrates the importance of intracellular signaling to maintain T cell homeostasis.

p38α protein negatively regulates T helper type 2 responses by orchestrating multiple T cell receptor-associated signals

Mitogen-activated protein kinase p38α is a critical regulator of certain inflammatory diseases. However, its role in T helper type 2 (Th2) responses and allergic inflammation remains unknown. Here we show an increase in the production of interleukin-4 (IL-4) in p38α(-/-) CD4(+) T cells in response to antigen stimulation. p38α-deficient naïve CD4(+) T cells preferentially differentiate into Th2 cells through increased endogenous production of IL-4. Consistent with those results, we also observed decreased expression of p38α during T helper cell differentiation. Furthermore, deficiency of p38α alters the balance in the expression of NFATc1 and NFATc2 under steady-state conditions and enhances the expression and nuclear translocation of NFATc1 in CD4(+) T cells upon antigen stimulation. Knockdown of NFATc1 significantly inhibits Th2 differentiation in p38α(-/-) T cells but not in p38α(+/-) T cells. p38α deficiency also inhibits the activation of Akt but enhances the activation of ERK in response to T cell receptor engagement without impacting IL-2/Stat5 signaling. In a model of ovalbumin-induced acute allergic airway inflammation, mice with induced deletion of p38α show elevated serum ovalbumin-specific IgE level, increased infiltration of eosinophils, and higher concentrations of Th2 cytokines including IL-4 and IL-5 in the bronchoalveolar lavage fluid relative to control mice. Taken together, p38α regulates multiple T cell receptor-associated signals and negatively influences Th2 differentiation and allergic inflammation.

The transcription factor NFATp plays a key role in susceptibility to TB in mice

In T cells, the transcription factor nuclear factor of activated T cells p (NFATp) is a key regulator of the cytokine genes tumor necrosis factor (TNF) and interferon-γ (IFN-γ). Here, we show that NFATp-deficient (NFATp(-/-)) mice have a dramatic and highly significant increase in mortality after Mycobacterium tuberculosis (MTb) infection as compared to mortality of control animals after MTb infection. Animals deficient in NFATp have significantly impaired levels of TNF and IFN-γ transcription and protein expression in naïve or total CD4(+) T cells, but display wild-type levels of TNF mRNA or protein from MTb-stimulated dendritic cells (DC). The rapid mortality and disease severity observed in MTb-infected NFATp(-/-) mice is associated with dysregulated production of TNF and IFN-γ in the lungs, as well as with increased levels of TNF, in their serum. Furthermore, global blocking of TNF production by injection of a TNF neutralizaing agent at 6 weeks, but not 12 weeks, post-MTb-infection further decreased the survival rate of both wild-type and NFATp(-/-) mice, indicating an early role for TNF derived from cells from the monocyte lineage in containment of infection. These results thus demonstrate that NFATp plays a critical role in immune containment of TB disease in vivo, through the NFATp-dependent expression of TNF and IFN-γ in T cells.

NFAT control of innate immunity

The calcineurin/nuclear factor of activated T cells (NFAT) signaling pathway mediates multiple adaptive T-cell functions, but recent studies have shown that calcineurin/NFAT signaling also contributes to innate immunity and regulates the homeostasis of innate cells. Myeloid cells, including granulocytes and dendritic cells, can promote inflammation, regulate adaptive immunity, and are essential mediators of early responses to pathogens. Microbial ligation of pattern-recognition receptors, such as TLR4, CD14, and dectin 1, is now known to induce the activation of calcineurin/NFAT signaling in myeloid cells, a finding that has provided new insights into the molecular pathways that regulate host protection. Inhibitors of calcineurin/NFAT binding, such as cyclosporine A and FK506, are broadly used in organ transplantation and can act as potent immunosuppressive drugs in a variety of different disorders. There is increasing evidence that these agents influence innate responses as well as inhibiting adaptive T-cell functions. This review focuses on the role of calcineurin/NFAT signaling in myeloid cells, which may contribute to the various unexplained effects of immunosuppressive drugs already being used in the clinic.

Antiviral and regulatory T cell immunity in a patient with stromal interaction molecule 1 deficiency

Stromal interaction molecule 1 (STIM1) deficiency is a rare genetic disorder of store-operated calcium entry, associated with a complex syndrome including immunodeficiency and immune dysregulation. The link from the molecular defect to these clinical manifestations is incompletely understood. We report two patients with a homozygous R429C point mutation in STIM1 completely abolishing store-operated calcium entry in T cells. Immunological analysis of one patient revealed that despite the expected defect of T cell proliferation and cytokine production in vitro, significant antiviral T cell populations were generated in vivo. These T cells proliferated in response to viral Ags and showed normal antiviral cytotoxicity. However, antiviral immunity was insufficient to prevent chronic CMV and EBV infections with a possible contribution of impaired NK cell function and a lack of NKT cells. Furthermore, autoimmune cytopenia, eczema, and intermittent diarrhea suggested impaired immune regulation. FOXP3-positive regulatory T (Treg) cells were present but showed an abnormal phenotype. The suppressive function of STIM1-deficient Treg cells in vitro, however, was normal. Given these partial defects in cytotoxic and Treg cell function, impairment of other immune cell populations probably contributes more to the pathogenesis of immunodeficiency and autoimmunity in STIM1 deficiency than previously appreciated.

Enhanced chromatin accessibility and recruitment of JUNB mediate the sustained IL-4 expression in NFAT1 deficient T helper 2 cells

Nuclear factor of activated T cells (NFAT) is a family of transcription factors composed of five proteins. Among them, NFAT1 is a predominant NFAT protein in CD4(+) T cells. NFAT1 positively regulates transcription of a large number of inducible cytokine genes including IL-2, IL-4, IL-5 and other cytokines. However, disruption of NFAT1 results in an unexpected increase of IL-4. In this study, we have investigated the role of NFAT1 in regulation of IL-4 gene expression in T helper 2 cells (Th2) from an epigenetic viewpoint. NFAT1 deficient Th2 cells showed a sustained IL-4 expression while wild type (WT) cells reduced its expression. We tested whether epigenetic maintenance and changes in the chromatin architecture of IL-4 promoter locus play a role in differential IL-4 transcription between in WT and NFAT1 deficient Th2 cells. Compared with WT, NFAT1 deficient CD4(+) Th2 cells exhibited enhanced chromatin accessibility with permissive histone modification and DNA demethylation in the IL-4 promoter region. Transcription factors bound to IL-4 promoter region in the absence of NFAT1 were identified by Micro-LC/LC-MS/MS analysis. Among the candidates, preferential recruitment of JUNB to the IL-4 promoter was confirmed by chromatin immunoprecipitation analysis. Overexpression of JUNB together with SATB1 synergistically upregulated IL-4 promoter activity, while knockdown JUNB significantly reduced IL-4 expression. Our results suggest that the prolonged IL-4 expression in NFAT1 deficient Th2 cells is mediated by preferential binding of JUNB/SATB1 to the IL-4 promoter with permissive chromatin architecture.

Osteomyelosclerosis, anemia and extramedullary hematopoiesis in mice lacking the transcription factor NFATc2

BACKGROUND

Nuclear factors of activated T cells (NFAT) are transcription factors that are central to cytokine production in activated T cells and regulate the development and differentiation of various tissues. NFATc2 is expressed in hematopoietic stem cells and regulated during myeloid commitment in a lineage-specific manner. The biological role of NFATc2 in hematopoiesis is, however, unclear.

DESIGN AND METHODS

In the present study, we analyzed steady-state hematopoiesis in young (<3 months) and old (>12 months) mice lacking NFATc2. Complete blood counts were performed in the peripheral blood, bone marrow and spleen. Using cytological and histological analyses, the blood cell differential was determined. Colony-formation assays were used to determine the differentiation potential of hematopoietic cells. Bone cell cultures were derived from the bone marrow, and bone remodeling markers were determined in the serum.

RESULTS

NFATc2(-/-) mice older than 12 months were anemic and thrombocytopenic. The bone marrows of these mice showed a markedly reduced number of hematopoietic cells, of which megakaryocytic and erythroid lineages were most affected. While the number of hematopoietic progenitor cells in NFATc2-deficent bone marrow was reduced, the myeloid differentiation potential of these cells remained intact. Aged NFATc2(-/-) mice showed ossification of their bone marrow space and developed extramedullary hematopoiesis in the spleen. Ex vivo differentiation assays revealed an intrinsic defect of NFATc2-deficient stromal cells, in which NFATc2(-/-) osteoblasts differentiated more efficiently than wild-type cells, whereas osteoclast differentiation was impaired.

CONCLUSIONS

Our data suggest that NFATc2 may play a role in the maintenance of steady-state hematopoiesis and bone remodeling in adult organisms.

Interferon regulatory factor 2 binding protein 2 is a new NFAT1 partner and represses its transcriptional activity

The nuclear factor of activated T cells (NFAT) family of transcription factors is expressed in a wide range of cell types and regulates genes involved in cell cycle, differentiation, and apoptosis. NFAT proteins share two well-conserved regions, the regulatory domain and the DNA binding domain. The N- and C-terminal ends are transactivation sites and show less sequence similarity, whereas their molecular functions remain poorly understood. Here, we identified a transcriptional repressor, interferon regulatory factor 2 binding protein 2 (IRF-2BP2), which specifically interacts with the C-terminal domain of NFAT1 among the NFAT family members. IRF-2BP2 was described as a corepressor by inhibiting both enhancer-activated and basal transcription. Gene reporter assays demonstrated that IRF-2BP2 represses the NFAT1-dependent transactivation of NFAT-responsive promoters. The ectopic expression of IRF-2BP2 in CD4 T cells resulted in decreased interleukin-2 (IL-2) and IL-4 production, supporting a repressive function of IRF-2BP2 for NFAT target genes. Furthermore, NFAT1 and IRF-2BP2 colocalized in the nucleus in activated cells, and the mutation of a newly identified nuclear localization signal in the IRF-2BP2 rendered it cytoplasmic, abolishing its repressive effect on NFAT1 activity. Collectively, our data demonstrate that IRF-2BP2 is a negative regulator of the NFAT1 transcription factor and suggest that NFAT1 repression occurs at the transcriptional level.

NFATc3 regulates the transcription of genes involved in T-cell activation and angiogenesis

The nuclear factor of activated T cells (NFAT) family of transcription factors plays important roles in many biologic processes, including the development and function of the immune and vascular systems. Cells usually express more than one NFAT member, raising the question of whether NFATs play overlapping roles or if each member has selective functions. Using mRNA knock-down, we show that NFATc3 is specifically required for IL2 and cyclooxygenase-2 (COX2) gene expression in transformed and primary T cells and for T-cell proliferation. We also show that NFATc3 regulates COX2 in endothelial cells, where it is required for COX2, dependent migration and angiogenesis in vivo. These results indicate that individual NFAT members mediate specific functions through the differential regulation of the transcription of target genes. These effects, observed on short-term suppression by mRNA knock-down, are likely to have been masked by compensatory effects in gene-knockout studies.

NFAT1 transcription factor is central in the regulation of tissue microenvironment for tumor metastasis

Members of the nuclear factor of activated T cell (NFAT) family of transcription factors were originally described in T lymphocytes but later shown to be expressed in several immune and non-immune cell types. NFAT proteins can modulate cellular transformation intrinsically, and NFAT-deficient (NFAT1-/-) mice are indeed more susceptible to transformation than wild-type counterparts. However, the contribution of an NFAT1-/- microenvironment to tumor progression has not been studied. We have addressed this question by inoculating NFAT1-/- mice with B16F10 melanoma cells intravenously, an established model of tumor homing and growth. Surprisingly, NFAT1-/- animals sustained less tumor growth in the lungs after melanoma inoculation than wild-type counterparts. Even though melanoma cells equally colonize NFAT1-/- and wild-type lungs, tumors do not progress in the absence of NFAT1 expression. A massive mononuclear perivascular infiltrate and reduced expression of TGF-β in the absence of NFAT1 suggested a role for tumor-infiltrating immune cells and the cytokine milieu. However, these processes are independent of an IL-4-induced regulatory tumor microenvironment, since lack of this cytokine does not alter the phenotype in NFAT1-/- animals. Bone marrow chimera experiments meant to differentiate the contributions of stromal and infiltrating cells to tumor progression demonstrated that NFAT1-induced susceptibility to pulmonary tumor growth depends on NFAT1-expressing parenchyma rather than on bone marrow-derived cells. These results suggest an important role for NFAT1 in radio-resistant tumor-associated parenchyma, which is independent of the anti-tumor immune response and Th1 versus Th2 cytokine milieu established by the cancer cells, but able to promote site-specific tumor growth.

Nuclear factor of activated T cells negatively regulates expression of the tumor necrosis factor receptor-related 2 gene in T cells

Tumor necrosis factor receptor-related 2 (TR2, HVEM or TNFRSF-14) plays an important role in immune responses, however, the mechanisms regulating its expression are unclear. To understand the control of TR2 gene expression, we studied the upstream region of the gene. Gel supershift assays revealed inducible binding of nuclear factor of activated T cells (NFAT) to a putative NFAT site within the TR2 promoter. Furthermore, cotransfection of a dominant negative NFAT construct, or siRNA for NFAT, resulted in increased expression of a TR2 reporter gene. Our findings demonstrate that NFAT negatively regulates TR2 expression in activated T cells.

Ethyl acetate extract of Psidium guajava inhibits IgE-mediated allergic responses by blocking FcεRI signaling

Psidium guajava (P. guajava) is an important food crop and medicinal plant with antioxidant, anti-inflammatory, and anti-allergic activities, supporting its traditional uses. However, its precise effects remain unknown. We investigated the effects of P. guajava ethyl acetate extract (PGEA) on IgE-mediated allergic responses in rat mast RBL-2H3 cells. PGEA reduced antigen (DNP-BSA)-induced release of β-hexosaminidase and histamine in IgE-sensitized RBL-2H3 cells. In addition, it inhibited antigen-induced IL-4 and TNF-α mRNA expression and protein production in IgE-sensitized RBL-2H3 cells. PGEA also suppressed antigen-induced COX-2 mRNA and protein expression in these cells, as well as antigen-induced activation of NFAT and reactive oxygen species. Moreover, it inhibited antigen-induced activation of NF-κB and degradation of IκB-α. To identify the mechanisms underpinning the inhibition of degranulation and cytokine production by PGEA, we examined the activation of intracellular FcεRI signaling molecules. PGEA suppressed antigen-induced phosphorylation of Syk, LAT, Gab2, and PLCγ2 but not Lyn, and inhibited antigen-induced phosphorylation of downstream signaling intermediates including MAP kinases and Akt. Collectively, the anti-allergic effects of PGEA in vitro suggest its possible therapeutic application to inflammatory allergic diseases, in which its inhibition of inflammatory cytokine production and FcεRI-dependent signaling events in mast cells may be hugely beneficial.

Hyperactivation of nuclear factor of activated T cells 1 (NFAT1) in T cells attenuates severity of murine autoimmune encephalomyelitis

Nuclear factor of activated T cells (NFAT) proteins are a group of Ca(2+)-regulated transcription factors residing in the cytoplasm of resting cells. Dephosphorylation by calcineurin results in nuclear translocation of NFAT and subsequent expression of target genes; rephosphorylation by kinases, including casein kinase 1 (CK1), restores NFAT to its latent state in the cytoplasm. We engineered a hyperactivable version of NFAT1 with increased affinity for calcineurin and decreased affinity for casein kinase 1. Mice expressing hyperactivable NFAT1 in their T-cell compartment exhibited a dramatically increased frequency of both IL-17- and IL-10-producing cells after differentiation under Th17 conditions-this was associated with direct binding of NFAT1 to distal regulatory regions of Il-17 and Il-10 gene loci in Th17 cells. Despite higher IL-17 production in culture, the mice were significantly less prone to myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis than controls, correlating with increased production of the immunomodulatory cytokine IL-10 and enhanced accumulation of regulatory T cells within the CNS. Thus, NFAT hyperactivation paradoxically leads to decreased susceptibility to experimental autoimmune encephalomyelitis, supporting previous observations linking defects in Ca(2+)/NFAT signaling to lymphoproliferation and autoimmune disease.

Trpm4 differentially regulates Th1 and Th2 function by altering calcium signaling and NFAT localization

Th cell subsets have unique calcium (Ca(2+)) signals when activated with identical stimuli. The regulation of these Ca(2+) signals and their correlation to the biological function of each T cell subset remains unclear. Trpm4 is a Ca(2+)-activated cation channel that we found is expressed at higher levels in Th2 cells compared with Th1 cells. Inhibition of Trpm4 expression increased Ca(2+) influx and oscillatory levels in Th2 cells and decreased influx and oscillations in Th1 cells. This inhibition of Trpm4 expression also significantly altered T cell cytokine production and motility. Our experiments revealed that decreasing Trpm4 levels divergently regulates nuclear localization of NFATc1. Consistent with this, gene profiling did not show Trpm4-dependent transcriptional regulation, and T-bet and GATA-3 levels remain identical. Thus, Trpm4 is expressed at different levels in Th cells and plays a distinctive role in T cell function by differentially regulating Ca(2+) signaling and NFATc1 localization.

NIP45 controls the magnitude of the type 2 T helper cell response

Nuclear factor of activated T cell (NFAT) transcription factors are key regulators of gene transcription within immune cells. The NFAT-interacting protein, (NIP45), augments NFAT-driven IL-4 expression by a mechanism that relies on arginine methylation. To establish the function of NIP45 in vivo, we generated mice with a targeted deletion of the gene encoding this cofactor. NIP45-deficient T helper cells displayed profound defects in the expression of NFAT-regulated cytokine genes, including IL-4. Whereas NIP45 deficiency does not interfere with T helper cell NFAT activation or lineage-specific transcription-factor expression, NIP45 acts as an enhancer for the assembly of protein arginine methyltransferase 1 and the protein arginine methyltransferase 1-linked histone 4 arginine 3 methylation with the IL-4 promoter. Our study reveals an essential role for NIP45 in promoting robust cytokine expression in vivo, which is required for the efficient handling of parasites. We propose that NIP45 acts as a molecular rheostat serving to amplify the type-2 immune response.

Differentiation of effector CD4 T cell populations (*)

CD4 T cells play critical roles in mediating adaptive immunity to a variety of pathogens. They are also involved in autoimmunity, asthma, and allergic responses as well as in tumor immunity. During TCR activation in a particular cytokine milieu, naive CD4 T cells may differentiate into one of several lineages of T helper (Th) cells, including Th1, Th2, Th17, and iTreg, as defined by their pattern of cytokine production and function. In this review, we summarize the discovery, functions, and relationships among Th cells; the cytokine and signaling requirements for their development; the networks of transcription factors involved in their differentiation; the epigenetic regulation of their key cytokines and transcription factors; and human diseases involving defective CD4 T cell differentiation.

Regulation of T-cell tolerance by calcium/NFAT signaling

Cells that escape negative selection in the thymus must be inactivated or eliminated in the periphery through a series of mechanisms that include the induction of anergy, dominant suppression by regulatory T cells, and peripheral deletion of self-reactive T cells. Calcium signaling plays a central role in the induction of anergy in T cells, which become functionally inactivated and incapable of proliferating and expressing cytokines following antigen re-encounter. Suboptimal stimulation of T cells results in the activation of a calcium/calcineurin/nuclear factor of activated T cells-dependent cell-intrinsic program of self-inactivation. The proteins encoded by those genes are required to impose a state of functional unresponsiveness through different mechanisms that include downregulation of T-cell receptor signaling and inhibition of cytokine transcription.

Impaired NFAT transcriptional activity in antigen-stimulated CD8 T cells linked to defective phosphorylation of NFAT transactivation domain

NFAT transcription factors play critical roles in CD4 T cell activation and differentiation. Their function in CD8 T cell is, however, unknown. We show in this study that, in contrast to CD4 T cells, Ag-stimulated CD8 T cells do not demonstrate NFAT transcriptional activity despite normal regulation of NFAT nuclear shuttling. Further analysis of the signaling defect shows that phosphorylation of the (53)SSPS(56) motif of the NFAT transactivation domain is essential for NFAT-mediated transcription in primary T cells. Although Ag stimulation induces in CD4 T cells extensive phosphorylation of this motif, it does so only minimally in CD8 T cells. Although Ag stimulation triggers only modest activation of the p38 MAPK in CD8 T cells as opposed to CD4 T cells, p38 MAPK is not the upstream kinase that directly or indirectly phosphorylates the NFAT (53)SSPS(56) motif. These findings reveal an unsuspected difference between CD4 and CD8 T cells in the TCR downstream signaling pathway. Therefore, whereas in CD4 T cells TCR/CD28 engagement activates a yet unknown kinase that can phosphorylate the NFAT (53)SSPS(56) motif, this pathway is only minimally triggered in CD8 T cells, thus limiting NFAT transcriptional activity.

Transcriptional complexes formed by NFAT dimers regulate the induction of T cell tolerance

In T cells, anergy can be induced after T cell receptor engagement in the absence of costimulation. Under these conditions, the expression of a specific set of anergy-associated genes is activated. Several lines of evidence suggest that nuclear factor of activated T cells (NFAT) proteins may regulate the expression of many of those genes; however, the nature of the complexes responsible for the induction of this new program of gene expression is unknown. Here, we show that transcriptional complexes formed by NFAT homodimers are directly responsible for the activation of at least two anergy-inducing genes, Grail and Caspase3. Our data shows that Grail expression is activated by direct binding of NFAT dimers to the Grail promoter at two different sites. Consequently, a mutant NFAT protein with impaired ability to dimerize is not able to induce an unresponsive state in T cells. Our results not only identify a new biological function for NFAT dimers but also reveal the different nature of NFAT-containing complexes that induce anergy versus those that are activated during a productive immune response. These data also establish a basis for the design of immunomodulatory strategies that specifically target each type of complex.

CD4 cell-secreted, posttranslationally modified cytokine GIF suppresses Th2 responses by inhibiting the initiation of IL-4 production

T helper 2 (Th2) cells are critical to the induction of IgE antibody and allergic inflammation, but how the pathological pathways are controlled in nonallergic individuals remains unclear. Here we report that glycosylation-inhibiting factor (GIF) suppresses Th2 effector generation. GIF is a cytokine encoded by the same gene that codes for macrophage migration inhibitory factor (MIF). GIF-deficient mice demonstrated enhanced T-dependent antibody formation especially of IgE isotype and allergic airway inflammation with the generation of regulatory T cells unaffected. GIF-deficient macrophages and dendritic cells revealed normal responsiveness to toll-like receptor (TLR) ligands. GIF undergoes a unique posttranslational modification, cysteinylation. The modified GIF, mainly secreted by activated T cells derived from CD4(+)CD25(-) cells, inhibited IL-4 production by the same cells whereas the unmodified GIF showed no effect. Bone marrow chimera experiment demonstrated that T cell-derived GIF suppressed the generation of Th effectors that secrete IL-4. During the first 24 h of CD3/CD28 stimulation in vitro, GIF secreted from naïve CD4 cells acted on the same cells, maintained nuclear factor of activated T cells (NFAT)c2 in the nucleus, and repressed IL-4 mRNA levels. Thus, GIF represents a self-regulatory mechanism of Th2 cell generation from naïve CD4 cells, in which the posttranslational modification plays a crucial role.

Regulation of Down Syndrome Critical Region 1 expression by Nuclear Factor of Activated T cells in megakaryocytes

As precursors of platelets, megakaryocytes must fulfil the complex tasks of protein synthesis and platelet assembly. Megakaryocytic dysfunction can lead to neoplastic disorders, such as acute megakaryoblastic leukaemia, an entity with a 500-fold increased incidence in children with Down syndrome (DS). Down Syndrome Critical Region 1 (DSCR1), a member of the calcipressin family of calcineurin inhibitors, is overexpressed in DS, and destabilization of the calcineurin/Nuclear Factor of Activated T cells (NFAT) pathway by overexpression of DSCR1 has been implicated in some of the pathophysiological features of the disease. The roles of NFAT and DSCR1 in megakaryocyte signalling and gene expression, however, are unknown. In this study, we show that calcineurin and NFAT are components of a calcium-induced signalling cascade in megakaryocytes. NFAT activation in megakaryocytes was induced by fibrillar collagen type I and was completely sensitive to the calcineurin inhibitor cyclosporin A. We established DSCR1 as a calcium-induced NFAT target gene in these cells and show that overexpression of DSCR1 in megakaryocytes strongly inhibits NFAT activation as well as NFAT-dependent expression of the Fas ligand gene (FASLG). These results suggest that DSCR1 acts as an endogenous feedback inhibitor of NFAT signalling in megakaryocytes, and may have implications for megakaryocytic gene expression in DS.