Delayed lymphoid repopulation with defects in IL-4-driven responses produced by inactivation of NF-ATc

Multifaceted control of T cell differentiation by STIM1

In T cells, stromal interaction molecule (STIM) and Orai are dispensable for conventional T cell development, but critical for activation and differentiation. This review focuses on novel STIM-dependent mechanisms for control of Ca2+ signals during T cell activation and its impact on mitochondrial function and transcriptional activation for control of T cell differentiation and function. We highlight areas that require further work including the roles of plasma membrane Ca2+ ATPase (PMCA) and partner of STIM1 (POST) in controlling Orai function. A major knowledge gap also exists regarding the independence of T cell development from STIM and Orai, despite compelling evidence that it requires Ca2+ signals. Resolving these and other outstanding questions ensures that the field will remain active for many years to come.

Formaldehyde exposure induces differentiation of regulatory T cells via the NFAT-mediated T cell receptor signalling pathway in Yucatan minipigs

The use of minipigs (Sus scrofa) as a platform for toxicological and pharmacological research is well established. In the present study, we investigated the effect of formaldehyde (FA) exposure on helper T cell-mediated splenic immune responses in Yucatan minipigs. The minipigs were exposed to different inhaled concentrations of FA (0, 2.16, 4.62, or 10.48 mg/m³) for a period of 2 weeks. Immune responses elicited by exposure to FA were determined by assessing physiological parameters, mRNA expression, and cytokine production. Additionally, the distribution of helper T cells and regulatory T (Treg) cells and expression of NFAT families, which are well-known T cell receptor signalling proteins associated with regulatory T cell development, were evaluated. Exposure to FA suppressed the expression of genes associated with Th1 and Th2 cells in minipigs in a concentration-dependent manner. The subsequent production of cytokines also declined post-FA exposure. Furthermore, exposure to FA induced the differentiation of CD4⁺ Foxp3⁺ Treg cells with divergent expression levels of NFAT1 and NFAT2. These results indicated that exposure to FA increased the Treg cell population via the NFAT-mediated T cell receptor signalling pathway, leading to suppression of effector T cell activity with a decline in T cell-related cytokine production.

The Role of Airway Epithelial Cell Alarmins in Asthma

The airway epithelium is the first line of defense for the lungs, detecting inhaled environmental threats through pattern recognition receptors expressed transmembrane or intracellularly. Activation of pattern recognition receptors triggers the release of alarmin cytokines IL-25, IL-33, and TSLP. These alarmins are important mediators of inflammation, with receptors widely expressed in structural cells as well as innate and adaptive immune cells. Many of the key effector cells in the allergic cascade also produce alarmins, thereby contributing to the airways disease by driving downstream type 2 inflammatory processes. Randomized controlled clinical trials have demonstrated benefit when blockade of TSLP and IL-33 were added to standard of care medications, suggesting these are important new targets for treatment of asthma. With genome-wide association studies demonstrating associations between single-nucleotide polymorphisms of the TSLP and IL-33 gene and risk of asthma, it will be important to understand which subsets of asthma patients will benefit most from anti-alarmin therapy.

Alcohol consumption induces murine osteoporosis by downregulation of natural killer T-like cell activity

Introduction

Chronic alcohol consumption (CAC) can induce several deleterious effects on the body, including the promotion of osteoporosis; however, the immunological mechanism underlying alcohol‐induced osteoporosis is still unclear.

Methods

We administered alcohol to mice for 4 weeks as the experimental CAC model and analyzed the bone and immune cells that are located in the vicinity of a bone.

Results

IL‐4 is known to be a suppressive factor for osteoclastogenesis, and we found that natural killer T (NKT)‐like cells, which showed NK1.1‐positive, CD3‐positive, and α‐galactosylceramide‐loaded CD1d tetramer‐negative, produced IL‐4 more effectively than CD4⁺ T and natural killer (NK) cells. The alcohol consumption facilitated a significant decrease of bone mineral density with the upregulation of nuclear factor of activated T cells 1 and receptor activator of NF‐κB ligand expression. Meanwhile, we confirmed that alcohol consumption suppressed the activity of antigen‐presenting cells (APCs) and NKT‐like cells, leading to decreased IL‐4 secretion. Moreover, these harmful effects of alcohol consumption were reduced by simultaneous treatment with a glycolipid antigen OCH.

Conclusions

Our results indicate that the inactivation of innate immune cells, APCs, and NKT‐like cells are likely to be crucial for alcohol‐induced osteoporosis and provide a new therapeutic approach for preventing osteoporosis.

Role of NFAT in Chronic Lymphocytic Leukemia and Other B-Cell Malignancies

In recent years significant progress has been made in the clinical management of chronic lymphocytic leukemia (CLL) as well as other B-cell malignancies; targeting proximal B-cell receptor signaling molecules such as Bruton Tyrosine Kinase (BTK) and Phosphoinositide 3-kinase (PI3Kδ) has emerged as a successful treatment strategy. Unfortunately, a proportion of patients are still not cured with available therapeutic options, thus efforts devoted to studying and identifying new potential druggable targets are warranted. B-cell receptor stimulation triggers a complex cascade of signaling events that eventually drives the activation of downstream transcription factors including Nuclear Factor of Activated T cells (NFAT). In this review, we summarize the literature on the expression and function of NFAT family members in CLL where NFAT is not only overexpressed but also constitutively activated; NFAT controls B-cell anergy and targeting this molecule using specific inhibitors impacts on CLL cell viability. Next, we extend our analysis on other mature B-cell lymphomas where a distinct pattern of expression and activation of NFAT is reported. We discuss the therapeutic potential of strategies aimed at targeting NFAT in B-cell malignancies not overlooking the fact that NFAT may play additional roles regulating the inflammatory microenvironment.

Isoform-Selective NFAT Inhibitor: Potential Usefulness and Development

Nuclear factor of activated T cells (NFAT), which is the pharmacological target of immunosuppressants cyclosporine and tacrolimus, has been shown to play an important role not only in T cells (immune system), from which their name is derived, but also in many biological events. Therefore, functional and/or structural abnormalities of NFAT are linked to the pathogenesis of diseases in various organs. The NFAT protein family consists of five isoforms, and each isoform performs diverse functions and has unique expression patterns in the target tissues. This diversity has made it difficult to obtain ideal pharmacological output for immunosuppressants that inhibit the activity of almost all NFAT family members, causing serious and wide-ranging side effects. Moreover, it remains unclear whether isoform-selective NFAT regulation can be achieved by targeting the structural differences among NFAT isoforms and whether this strategy can lead to the development of better drugs than the existing ones. This review summarizes the role of the NFAT family members in biological events, including the development of various diseases, as well as the usefulness of and problems associated with NFAT-targeting therapies, including those dependent on current immunosuppressants. Finally, we propose a novel therapeutic strategy based on the molecular mechanisms that enable selective regulation of specific NFAT isoforms.

Role of nuclear factor of activated T cells 2 (NFATc2) in allergic asthma

BACKGROUND

We recently described increased NFATc1, IRF4, and NIP45 messenger RNA (mRNA) expression in peripheral blood mononuclear cells (PBMCs) of asthmatic children and adults with multiple allergies.

OBJECTIVE

NFATc2 has been described to associate with IRF4 to induce interleukin-4, and to be inhibited by T-bet. Here, we analyzed the role of NFATc2 in asthmatic children and adults.

METHODS

PBMCs were isolated from the blood of control of asthmatics subjects. Some PBMCs were analyzed untreated and some cultured with and without phytohemagglutinin. Then, RNA was extracted from the cells and cytokines were measured in the supernatants via enzyme-linked immunosorbent assay or multiplex analysis. RNA was then reverse-transcribed and NFATc1, NFATC2, IRF4, and T-bet mRNA were analyzed by real-time polymerase chain reaction. In addition, in peripheral blood cells, NFATc2 expression was analyzed, in a population of asthmatic children and adults from the Asthma BRIDGE study.

RESULTS

In addition to NFATc1 and NIP45, also NFATc2 was found upregulated in PBMCs and peripheral blood cells from asthmatic children and adults with allergic asthma. Moreover, NFATc1 directly correlated with lymphocytes number whereas NFATc2 correlated with peripheral eosinophilia in asthma.

CONCLUSIONS

In addition to NFATc1 and NIP45, NFATc2 was found upregulated in asthma. Moreover, NFATc1 mRNA correlated with lymphocytes both in control and asthma, and NFATC1 and NFATc2 mRNA showed a direct correlation with eosinophils in controls but not in asthma, indicating that NFATc1 is associated with lymphocytes and not eosinophils in asthma.

CLINICAL SIGNIFICANCE

Targeting NFATc2 in T lymphocytes might ameliorate the allergic phenotype in asthmatic subjects.

Formaldehyde exposure induces regulatory T cell-mediated immunosuppression via calcineurin-NFAT signalling pathway

In this study, we investigated the effects of Formaldehyde (FA) exposure on splenic immune responses wherein helper T cells become activated and differentiate into effector T and regulatory T cells. BALB/c mice were exposed to two FA concentrations (1.38 mg/m3 and 5.36 mg/m3) for 4 h/day and 5 days/week for 2 weeks. FA-induced immune responses were examined by the production of cytokines, expression of mRNAs, and distributions of helper T cells and regulatory T cells. Moreover, expression of calcineurin and NFATs, regulatory T cell-related signalling proteins, were evaluated. FA exposure suppressed Th2-, Th1-, and Th17-related splenic cytokines in a dose-dependent manner. mRNA expression of splenic cytokines was also decreased by FA exposure, which correlated with decreased cytokine expression. In parallel, FA exposure promoted T cell differentiation into regulatory T cells in a dose-dependent manner supported by the expression of calcineurin and NFAT1. Taken together, our results indicated that FA exposure increases the number of regulatory T cells via calcineurin-NFAT signalling, thereby leading to effector T cell activity suppression with decreased T cell-related cytokine secretion and mRNA expression. These findings provide insight into the mechanisms underlying the adverse effects of FA and accordingly have general implications for human health, particularly in occupational settings.

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.

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.

Identification of novel interacting regions involving calcineurin and nuclear factor of activated T cells

Nuclear factor of activated T cells (NFAT) leads to the transcription of diverse inducible genes involved in many biological processes; therefore, aberrant NFAT expression is responsible for the development and exacerbation of various disorders. Since five isoforms of NFAT (NFATc1-c4, NFAT5) exhibit distinct and overlapping functions, selective control of a part, but not all, of NFAT family members is desirable. By comparing the binding activity of each NFATc1-c4 with its regulatory enzyme, calcineurin (CN), using a quantitative immunoprecipitation assay, we found a new CN-binding region (CNBR) selectively functioning in NFATc1 and NFATc4. This region, termed CNBR3, is located between two preexisting CNBR1 and CNBR2, within the Ca²⁺ regulatory domain. The nuclear translocation of NFATc1 but not NFATc2 in T cells was suppressed by ectopic expression of CNBR3 and, accordingly, NFATc1-dependent cytokine expression was downregulated. Through competition assays using NFATc1-derived partial peptides and mass spectrometry with photoaffinity technology, we identified 18 amino acids in NFATc1 (Arg²⁵⁸ to Pro²⁷⁵ ) and 13 amino acids in CN catalytic subunit (CNA) (Asn⁷⁷ to Gly⁸⁹ ) responsible for CNA/CNBR3 binding in which Cys²⁶³ and Asp⁸² , respectively, played crucial roles. The possible selective regulation of NFAT-mediated biological processes by targeting this new CN/NFAT-binding region is suggested.

Enhancer jungles establish robust tissue-specific regulatory control in the human genome

An increasing number of studies suggest that functionally redundant enhancers safeguard development via buffering gene expression against environmental and genetic perturbations. Here, we identified over-represented clusters of enhancers (enhancer jungles or EJs) in human B lymphoblastoid cells. We found that EJs tend to associate with genes involved in the activation of the immune system response. Although spanning multiple genes, the enhancers within an EJ tend to collaborate with each other on regulating a single gene. The employment of homotypic transcription factor binding sites (TFBSs) in EJ enhancers and heterotypic TFBSs between constituent enhancers within an EJ may safeguard a robust transcriptional output of the target gene. EJ enhancers evolve under a weaker selective pressure compared to regular enhancers (REs), and approximately 35% of EJs do not have orthologues in the mouse genome. In GM12878, these human-specific EJs appear to regulate genes associated with the adaptive immune system response, while the conserved EJs are associated with innate immunity. Recently acquired human EJs are associated with the higher level of target gene expression compared with conserved EJs, thus facilitating the environmental adaptation of the organism during evolution. In short, the existence of EJs is a common regulatory architecture conferring a robust regulatory control for key lineage genes.

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.

STIM- and Orai-mediated calcium entry controls NF-κB activity and function in lymphocytes

The central role of Ca²⁺ signaling in the development of functional immunity and tolerance is well established. These signals are initiated by antigen binding to cognate receptors on lymphocytes that trigger store operated Ca²⁺ entry (SOCE). The underlying mechanism of SOCE in lymphocytes involves TCR and BCR mediated activation of Stromal Interaction Molecule 1 and 2 (STIM1/2) molecules embedded in the ER membrane leading to their activation of Orai channels in the plasma membrane. STIM/Orai dependent Ca²⁺ signals guide key antigen induced lymphocyte development and function principally through direct regulation of Ca²⁺ dependent transcription factors. The role of Ca²⁺ signaling in NFAT activation and signaling is well known and has been studied extensively, but a wide appreciation and mechanistic understanding of how Ca²⁺ signals also shape the activation and specificity of NF-κB dependent gene expression has lagged. Here we discuss and interpret what is known about Ca²⁺ dependent mechanisms of NF-kB activation, including what is known and the gaps in our understanding of how these signals control lymphocyte development and function.

Developments in the field of allergy mechanisms in 2015 through the eyes of Clinical & Experimental Allergy

In the first of two papers we described the development in the field of allergy mechanisms as described by Clinical and Experimental Allergy in 2015. Experimental models of allergic disease, basic mechanisms, clinical mechanisms and allergens are all covered. A second paper will cover clinical aspects.

Identification of a Novel Alternatively Spliced Form of Inflammatory Regulator SWAP-70-Like Adapter of T Cells

Activation of naive CD4⁺ T cells results in the development of several distinct subsets of effector Th cells, including Th2 cells that play a pivotal role in allergic inflammation and helminthic infections. SWAP-70-like adapter of T cells (SLAT), also known as Def6 or IBP, is a guanine nucleotide exchange factor for small GTPases, which regulates CD4⁺ T cell inflammatory responses by controlling Ca²⁺/NFAT signaling. In this study, we have identified a novel alternatively spliced isoform of SLAT, named SLAT2, which lacks the region encoded by exons 2-7 of the Def6 gene. SLAT2 was selectively expressed in differentiated Th2 cells after the second round of in vitro stimulation, but not in differentiated Th1, Th17, or regulatory T (Treg) cells. Functional assays revealed that SLAT2 shared with SLAT the ability to enhance T cell receptor- (TCR-) mediated activation of NFAT and production of IL-4 but was unable to enhance TCR-induced adhesion to ICAM-1. Ectopic expression of SLAT2 or SLAT in Jurkat T cells resulted in the expression of distinct forms of filopodia, namely, short versus long ones, respectively. These results demonstrate that modulating either SLAT2 or SLAT protein expression could play critical roles in cytokine production and actin reorganization during inflammatory immune responses.

Phospholipase Cγ1 is required for pre-TCR signal transduction and pre-T cell development

Pre-T cell receptor (TCR) signaling is required for pre-T cell survival, proliferation, and differentiation from the CD4 and CD8 double negative (DN) to the double positive (DP) stage. However, the pre-TCR signal transduction pathway is not fully understood and the signaling molecules involved have not been completely identified. Phospholipase Cγ (PLCγ) 1 is an important signaling molecule that generates two second messengers, diacylglycerol and inositol 1,4,5-trisphosphate, that are important to mediate PKC activation and intracellular Ca²⁺ flux in many signaling pathways. Previously, we have shown that PLCγ1 is important for TCR-mediated signaling, development and T-cell activation, but the role of PLCγ1 in pre-TCR signal transduction and pre-T cell development is not known. In this study, we demonstrated that PLCγ1 expression level in pre-T cells was comparable to that in mature T cells. Deletion of PLCγ1 prior to the pre-TCR signaling stage partially blocked the DN3 to DN4 transition and reduced thymic cellularity. We also demonstrated that deletion of PLCγ1 impaired pre-T cell proliferation without affecting cell survival. Further study showed that deficiency of PLCγ1 impaired pre-TCR mediated Ca²⁺ flux and Erk activation. Thus our studies demonstrate that PLCγ1 is important for pre-TCR mediated signal transduction and pre-T cell development.

NFAT2 Regulates Generation of Innate-Like CD8+ T Lymphocytes and CD8+ T Lymphocytes Responses

Nuclear factor of activated T cells (NFAT) 2 null mutant mice die in utero of cardiac failure, precluding analysis of the role of NFAT2 in lymphocyte responses. Only the NFAT2^-/-/Rag-1^-/- chimeric mice model gave insight into the role of NFAT2 transcription factor in T lymphocyte development, activation, and differentiation. As reports are mainly focused on the role of NFAT2 in CD4⁺ T lymphocytes activation and differentiation, we decided to investigate NFAT2's impact on CD8⁺ T lymphocyte responses. We report that NFAT2 is phosphorylated and inactive in the cytoplasm of naive CD8⁺ T cells, and upon TCR stimulation, it is dephosphorylated and translocated into the nucleus. To study the role of NFAT2 in CD8⁺ T responses, we employed NFAT2^fl/flCD4-Cre mice with NFAT2 deletion specifically in T cells. Interestingly, the absence of NFAT2 in T cells resulted in increased percentage of non-conventional innate-like CD8⁺ T cells. These cells were CD122⁺, rapid producer of interferon gamma (IFN-γ) and had characteristics of conventional memory CD8⁺ T cells. We also observed an expansion of PLZF⁺ expressing CD3⁺ thymocyte population in the absence of NFAT2 and increased IL-4 production. Furthermore, we found that CD8⁺ T lymphocytes deficient in NFAT2 had reduced activation, proliferation, and IFN-γ and IL-2 production at suboptimal TCR strength. NFAT2 absence did not significantly influence differentiation of CD8⁺ T cells into cytotoxic effector cells but reduced their IFN-γ production. This work documents NFAT2 as a negative regulator of innate-like CD8⁺ T cells development. NFAT2 is required for complete CD8⁺ T cell responses at suboptimal TCR stimulation and regulates IFN-γ production by cytotoxic CD8⁺ T cells in vitro.

NFATC3 promotes IRF7 transcriptional activity in plasmacy--toid dendritic cells

The transcription factor NFATC3 binds to IRF7 and to type 1 IFN promoters, regulating IRF7-mediated IFN expression in pDCs.

Plasmacytoid dendritic cells (pDCs) rapidly produce large amounts of type 1 interferon (IFN) after Toll-like receptor 7 and 9 engagements. This specialized function of type 1 IFN production is directly linked to the constitutive expression of IRF7, the master transcription factor for type 1 IFN production. However, the IRF7 regulatory network in pDCs remains largely unknown. In this study, we identify that the transcription factor NFATC3 specifically binds to IRF7 and enhances IRF7-mediated IFN production. Furthermore, knockout of NFATC3 greatly reduced the CpG DNA–induced nuclear translocation of IRF7, which resulted in impaired type 1 IFN production in vitro and in vivo. In addition, we found that NFATC3 and IRF7 both bound to type 1 IFN promoters and that the NFAT binding site in IFN promoters was required for IRF7-mediated IFN expression. Collectively, our study shows that the transcription factor NFATC3 binds to IRF7 and functions synergistically to enhance IRF7-mediated IFN expression in pDCs.

NFAT1 transcription factor regulates cell cycle progression and cyclin E expression in B lymphocytes

The NFAT family of transcription factors has been primarily related to T cell development, activation, and differentiation. Further studies have shown that these ubiquitous proteins are observed in many cell types inside and outside the immune system, and are involved in several biological processes, including tumor growth, angiogenesis, and invasiveness. However, the specific role of the NFAT1 family member in naive B cell proliferation remains elusive. Here, we demonstrate that NFAT1 transcription factor controls Cyclin E expression, cell proliferation, and tumor growth in vivo. Specifically, we show that inducible expression of NFAT1 inhibits cell cycle progression, reduces colony formation, and controls tumor growth in nude mice. We also demonstrate that NFAT1-deficient naive B lymphocytes show a hyperproliferative phenotype and high levels of Cyclin E1 and E2 upon BCR stimulation when compared to wild-type B lymphocytes. NFAT1 transcription factor directly regulates Cyclin E expression in B cells, inhibiting the G1/S cell cycle phase transition. Bioinformatics analysis indicates that low levels of NFAT1 correlate with high expression of Cyclin E1 in different human cancers, including Diffuse Large B-cell Lymphomas (DLBCL). Together, our results demonstrate a repressor role for NFAT1 in cell cycle progression and Cyclin E expression in B lymphocytes, and suggest a potential function for NFAT1 protein in B cell malignancies.

Cell cycle and apoptosis regulation by NFAT transcription factors: new roles for an old player

The NFAT (nuclear factor of activated T cells) family of transcription factors consists of four Ca²⁺-regulated members (NFAT1–NFAT4), which were first described in T lymphocytes. In addition to their well-documented role in T lymphocytes, where they control gene expression during cell activation and differentiation, NFAT proteins are also expressed in a wide range of cells and tissue types and regulate genes involved in cell cycle, apoptosis, angiogenesis and metastasis. The NFAT proteins share a highly conserved DNA-binding domain (DBD), which allows all NFAT members to bind to the same DNA sequence in enhancers or promoter regions. The same DNA-binding specificity suggests redundant roles for the NFAT proteins, which is true during the regulation of some genes such as IL-2 and p21. However, it has become increasingly clear that different NFAT proteins and even isoforms can have unique functions. In this review, we address the possible reasons for these distinct roles, particularly regarding N- and C-terminal transactivation regions (TADs) and the partner proteins that interact with these TADs. We also discuss the genes regulated by NFAT during cell cycle regulation and apoptosis and the role of NFAT during tumorigenesis.

NFATc1 deletion in T lymphocytes inhibits the allergic trait in a murine model of asthma

BACKGROUND

NFATc1 isoforms are highly regulated in peripheral T cells where they contribute to the effector function and cell homeostasis.

OBJECTIVE

Here, we investigated the role of NFATc1 in asthma and in T cells.

METHODS

In a murine model of allergic asthma, we analysed differences in T-cell development in this allergic disease model, between wild-type and NFATc1 conditional knockout mice. Thus, we performed quantitative real-time PCR to investigate the mRNA expression of Th2-associated genes as well as genes that are involved in IgE immunoglobulin class-switch. Additionally, we used ELISA, Western blot and flow cytometry (FACS) to analyse protein concentrations of Th1-, Th2- and Th17-specific transcription factors and cytokines and the Th2 chemokine, thymus and activation-regulated chemokine/chemokine ligand 17 (TARC/CCL17) by ELISA.

RESULTS

Mice lacking NFATc1 in CD4(+) T cells display a significant reduction in lung Th2 and Th17 as well as an increase of Th1 cells in an experimental asthma model. Additionally, Batf gene, a recently described transcription factor of the Th2 and Th17 cell differentiation as well as a key T and B transcription factor involved in the IgE immunoglobulin class-switch, was found decreased in the lungs of these mice. As a consequence, serum OVA-specific IgE and IgG1 levels were found significantly decreased after allergen exposure and in the absence of NFATc1 in T cells in experimental allergic asthma.

CONCLUSIONS AND CLINICAL RELEVANCE

Targeting NFATc1 in T lymphocytes ameliorated the allergic trait in the airways of NFATc1(fl/fl) xCD4Cre mice. NFATc1 emerges as a novel target for anti-allergy intervention.

Yin-Yang 1 and Yin-Yang 2 exert opposing effects on the promoter activity of interleukin 4

Interleukin (IL)-4 acts on T cells as a growth and activation factor, and promotes the differentiation of type 2 T helper cells. In T cells, expression of the gene encoding IL-4 is regulated by inducible or constitutive factors. Yin-Yang (YY)-1 is one of constitutive transcription factors binding to the IL-4 promoter. The recently identified YY2 protein is similar to YY1, with both sharing high levels of homology in their zinc finger motifs. However, the role of YY2 in T cells is unclear. YY1 and YY2 were constitutively expressed in EL4 T cells, and their expression was not dependent on stimulation. IL-4 promoter (-741/+56 fragment) activity was enhanced by YY1, but inhibited by YY2. The enhanced IL-4 promoter activity by YY1 was reduced by simultaneous expression of YY2. In addition, the DNA binding affinity of YY1 to the IL-4 promoter was adversely affected by YY2. Our results suggest that YY1 and YY2 exert opposing effects on the IL-4 promoter as they compete for the same DNA binding sites.

Consequences of chromsome18q deletions

Providing clinically relevant prognoses and treatment information for people with a chromsome18q deletion is particularly challenging because every unrelated person has a unique region of hemizygosity. The hemizygous region can involve almost any region of 18q including between 1 and 101 genes (30 Mb of DNA). Most individuals have terminal deletions, but in our cohort of over 350 individuals 23% have interstitial deletions. Because of this heterogeneity, we take a gene by gene approach to understanding the clinical consequences. There are 196 genes on 18q. We classified 133 of them as dosage insensitive, 15 (8%) as dosage sensitive leading to haploinsufficiency while another 10 (5%) have effects that are conditionally haploinsufficient and are dependent on another factor, genetic or environmental in order to cause an abnormal phenotype. Thirty-seven genes (19%) have insufficient information to classify their dosage effect. Phenotypes attributed to single genes include: congenital heart disease, minor bone morphology changes, central nervous system dysmyelination, expressive speech delay, vesicouretreral reflux, polyposis, Pitt-Hopkins syndrome, intellectual disability, executive function impairment, male infertility, aural atresia, and high frequency sensorineural hearing loss. Additionally, identified critical regions for other phenotypes include: adolescent idiopathic scoliosis and pectus excavatum, Virchow-Robin perivascular spaces, small corpus callosum, strabismus, atopic disorders, mood disorder, IgA deficiency, nystagmus, congenital heart disease, kidney malformation, vertical talus, CNS dysmyelination growth hormone deficiency and cleft palate. Together these findings make it increasingly feasible to compile an individualized syndrome description based on each person's individuated genotype. Future work will focus on understanding molecular mechanisms leading to treatment.

Transcription factors and target genes of pre-TCR signaling

Almost 30 years ago pioneering work by the laboratories of Harald von Boehmer and Susumo Tonegawa provided the first indications that developing thymocytes could assemble a functional TCRβ chain-containing receptor complex, the pre-TCR, before TCRα expression. The discovery and study of the pre-TCR complex revealed paradigms of signaling pathways in control of cell survival and proliferation, and culminated in the recognition of the multifunctional nature of this receptor. As a receptor integrated in a dynamic developmental process, the pre-TCR must be viewed not only in the light of the biological outcomes it promotes, but also in context with those molecular processes that drive its expression in thymocytes. This review article focuses on transcription factors and target genes activated by the pre-TCR to drive its different outcomes.

NFATc1 deficiency in T cells protects mice from experimental autoimmune encephalomyelitis

NFATc1 is a member of the nuclear factor of activated T cells (NFAT) family of transcription factors. NFAT is activated upon T-cell receptor activation followed by intracytoplasmatic calcium influx where calmodulin, a calcium sensor protein, activates the phosphatase calcineurin that dephosphorylates NFAT proteins and results in NFAT nuclear import. Here, we show the analysis of conditional NFATc1-deficient mice bearing a deletion of NFATc1 in CD4(+) and CD8(+) T cells. NFATc1-deficient CD4(+) T cells polarized under Th17 conditions express reduced levels of the Th17-associated transcription factor RORγT (where ROR is RAR-related orphan receptor) as well as the Th17-associated cytokines IL-17A, IL-17F, IL-21, and IL-10. In the murine model of experimental EAE, we found a strong reduction of the disease outcome in conditional NFATc1-deficient mice, as compared with control littermates. This was accompanied by a diminished inflammation in the brain and spinal cord and reduced IL-17A and IFN-γ expression by antigen-specific spleen, spinal cord, and brain cells. Altogether, these results reveal an important role of NFATc1 in inducing Th17-cell responses and IFN-γ, both being relevant for the EAE development.

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.

Role of IL-25 in Immunity

IL-25 a 2o KDa protein mostly known as IL-17E, encoded by chromosome 14, and containing 117 amino acids. Cytokine IL-17 family consists of 6 members; IL-17A to IL-17F, among which IL-25 has a unique structure and function. The receptor of IL-25 (IL-17BR) is highly expressed in the main Th2 cells. IL-25 regulates the internal safety of adaptive immune responses which leads to begin allergic diseases and plays a role in stimulation of pulmonary mucosal cells and fibroblasts. IL-25 can also have some effects on production of other cytokines. For instance, production of IL-25 in human and mice or injection of IL-25 to animals has resulted in production of high concentrations of Th2 cytokines, including IL-4, IL-5, and IL-13. Pilot studies have shown that mRNA of IL-25 has a high expression in Th2 cells. However, the mechanism through which IL-25 leads to Th2 immune response is still unknown. Reaction between IL-25 and IL-17BR leads to activation of transcription factors, such as NF-KB, STAT6, GATA3, NF-ATC1, JUNNB, MAPK, and JNK. IL-25 has been used against the kidney damage in mice. A large number of researchers in various countries, including the U.S. and Taiwan, have stated that IL-25 is a strong inflammatory cytokine protein which is involved in allergic inflammations.

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.

Regulation of NFATc1 in Osteoclast Differentiation

Osteoclasts are unique cells that degrade the bone matrix. These large multinucleated cells differentiate from the monocyte/macrophage lineage upon stimulation by two essential cytokines, macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL). Activation of transcription factors such as microphthalmia transcription factor (MITF), c-Fos, NF-κB, and nuclear factor-activated T cells c1 (NFATc1) is required for sufficient osteoclast differentiation. In particular, NFATc1 plays the role of a master transcription regulator of osteoclast differentiation. To date, several mechanisms, including transcription, methylation, ubiquitination, acetylation, and non-coding RNAs, have been shown to regulate expression and activation of NFATc1. In this review, we have summarized the various mechanisms that control NFATc1 regulation during osteoclast differentiation.

Pathophysiology of tobacco smoke exposure: recent insights from comparative and redox proteomics

First-hand and second-hand tobacco smoke are causally linked to a huge number of deaths and are responsible for a broad spectrum of pathologies such as cancer, cardiovascular, respiratory, and eye diseases as well as adverse effects on female reproductive function. Cigarette smoke is a complex mixture of thousands of different chemical species, which exert their negative effects on macromolecules and biochemical pathways, both directly and indirectly. Many compounds can act as oxidants, pro-inflammatory agents, carcinogens, or a combination of these. The redox behavior of cigarette smoke has many implications for smoke related diseases. Reactive oxygen and nitrogen species (both radicals and non-radicals), reactive carbonyl compounds, and other species may induce oxidative damage in almost all the biological macromolecules, compromising their structure and/or function. Different quantitative and redox proteomic approaches have been applied in vitro and in vivo to evaluate, respectively, changes in protein expression and specific oxidative protein modifications induced by exposure to cigarette smoke and are overviewed in this review. Many gel-based and gel-free proteomic techniques have already been used successfully to obtain clues about smoke effects on different proteins in cell cultures, animal models, and humans. The further implementation with other sensitive screening techniques could be useful to integrate the comprehension of cigarette smoke effects on human health. In particular, the redox proteomic approach may also help identify biomarkers of exposure to tobacco smoke useful for preventing these effects or potentially predictive of the onset and/or progression of smoking-induced diseases as well as potential targets for therapeutic strategies.

Pontin is required for pre-TCR signaling at the β-selection checkpoint in T cell development

Pontin is a chromatin remodeling factor that possesses both ATPase and DNA helicase activities. Based on high expression in lymphoid tissues, we examined whether Pontin has a T cell-specific function. We generated Pontin(f/f);Lck-Cre mice, in which Pontin can be conditionally deleted in T cells and then explored T cell-specific function of Pontin in vivo. Here, we show that specific abrogation of Pontin expression in T cells almost completely blocked development of αβ T cells at the β-selection checkpoint by inducing cell apoptosis indicating that Pontin is essential for early T cell development. Pontin-deficient thymocytes show a comparable expression level of T cell receptor (TCR)β chain, but have enhanced activation of p53 and Notch signaling compared to wild-type thymocytes. Intriguingly, the developmental block of αβ T cells can be partially rescued by loss of p53. Together, our data demonstrate a novel role of Pontin as a crucial regulator in pre-TCR signaling during T cell development.

Follicular regulatory T cells control humoral autoimmunity via NFAT2-regulated CXCR5 expression

T cell–specific NFAT2 deletion results in reduced CXCR5⁺ follicular regulatory T cells, leading to uncontrolled germinal center responses and humoral autoimmunity.

Maturation of high-affinity B lymphocytes is precisely controlled during the germinal center reaction. This is dependent on CD4⁺CXCR5⁺ follicular helper T cells (T_FH) and inhibited by CD4⁺CXCR5⁺Foxp3⁺ follicular regulatory T cells (T_FR). Because NFAT2 was found to be highly expressed and activated in follicular T cells, we addressed its function herein. Unexpectedly, ablation of NFAT2 in T cells caused an augmented GC reaction upon immunization. Consistently, however, T_FR cells were clearly reduced in the follicular T cell population due to impaired homing to B cell follicles. This was T_FR-intrinsic because only in these cells NFAT2 was essential to up-regulate CXCR5. The physiological relevance for humoral (auto-)immunity was corroborated by exacerbated lupuslike disease in the presence of NFAT2-deficient T_FR cells.

Role of Ca/CaN/NFAT signaling in IL-4 expression by splenic lymphocytes exposed to phthalate (2-ethylhexyl) ester in spleen lymphocytes

The aims of present study were to investigate the effect of phthalate (2-ethylhexyl) ester (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) on Th1/Th2 balance signaling for interleukin 4 (IL-4) expression in splenic lymphocytes, and contribution of MEHP to any hypothesized changes in vitro. Primary splenic lymphocytes were exposed to DEHP/MEHP. ELISA and Western blotting were used to detect proteins. Confocal-microscopy was used to examine nuclear translocation. Nuclear factor of activated T cells (NFAT) DNA binding activity was examined by electrophoretic mobility-shift assay. DEHP significantly increased IL-4 and interferon gamma (IFN-γ) level, and reduced Th1/Th2 ratio (reflected by IFN-γ/IL-4) with 5 μg/L Concanavalin A (ConA) treatment. While MEHP reduced Th1/Th2 ratio (represented by IFN-γ/IL-6). IL-4 mRNA was significantly increased by DEHP but not by MEHP after PMA and Ion treatment. DEHP significantly inhibited NFATp protein in cytosol and nucleus. DEHP augmented nuclear translocation of NFATc in transfected EL4 cells and NFAT DNA-binding activity. DEHP-mediated enhancement of calcium-dependent phosphatase calcineurin (CaN) protein, and NFAT and IL-4 expression were abrogated by calcium antagonist verapamil and CaN inhibitor tarcolimus. Ca(2+)/calmodulin antagonist chlorpromazine significantly suppressed IL-4 and CaN production with no NFAT mRNA change. Our study suggests that DEHP and MEHP impact Th1/Th2 balance by modulating different cytokines. DEHP-affected IL-4 expression through Ca/CaN/NFAT signaling pathway, but no effect was discovered for MEHP.

'All things considered': transcriptional regulation of T helper type 2 cell differentiation from precursor to effector activation

T helper type 2 (Th2) cells are critical to host defence against helminth infection and the pathogenesis of allergic diseases. The differentiation of Th2 cells from naive CD4 T cells is controlled by intricate transcriptional mechanisms. At the precursor stage of naive CD4 T cells, transcriptional mechanisms maintain the potential and in the meantime prevent spontaneous differentiation to Th2 fate. In addition, intrachromosomal interactions important for co-ordinated expression of Th2 cytokines pre-exist in naive CD4 T cells. Upon T-cell receptor (TCR) engagement, naive CD4 T cells are induced by polarizing signals of the interleukin-4/Stat6 and Jagged/Notch pathways to up-regulate the expression of GATA-3. Once up-regulated, GATA-3 drives Th2 and suppresses Th1 differentiation in a cell autonomous fashion. In this stage of differentiation, the Th2 cytokine locus, as well as the interferon-γ locus, undergoes chromatin remodelling and epigenetic modifications that contribute to the somatic memory of Th2 cytokine gene expression pattern. Once differentiated, Th2 effector cells promptly produce Th2 cytokines upon TCR stimulation, which is regulated by concerted actions of GATA-3, TCR signalling, enhancers and the Th2 locus control region. This review provides a detailed account of the transcriptional regulatory events at these different stages of Th2 differentiation.

NFAT5 induction by the pre-T-cell receptor serves as a selective survival signal in T-lymphocyte development

The Rel-like transcription factors nuclear factor kappa B (NF-κB) and the calcineurin-dependent nuclear factor of activated T cells (NFATc) control specific points of thymocyte maturation. Thymocytes also express a distinct member of the Rel family, the calcineurin-independent, osmostress response regulator NFAT5. Here we show that IKKβ regulates the expression of NFAT5 in thymocytes, which in turn contributes to the survival of T-cell receptor αβ thymocytes and the transition from the β-selection checkpoint to the double-positive stage in an osmostress-independent manner. NFAT5-deficient thymocytes had normal expression and proximal signaling of the pre-T-cell receptor but exhibited a partial defect in β-chain allelic exclusion and increased apoptosis. Further analysis showed that NFAT5 regulated the expression of the prosurvival factors A1 and Bcl2 and attenuated the proapoptotic p53/Noxa axis. These findings position NFAT5 as a target of the IKKβ/NF-κB pathway in thymocytes and as a downstream effector of the prosurvival role of the pre-T-cell receptor.

Inhibition of Th2 cytokine production in T cells by monascin via PPAR-γ activation

Yellow pigment monascin (MS) is a secondary metabolite isolated from Monascus -fermented products and has numerous physiological activities. However, the potential use of MS for immunomodulation remains unclear. We showed that MS and the synthetic peroxisome proliferator-activated receptor (PPAR)-γ ligand rosiglitazone (RG) significantly inhibited the production of Th2 cytokines, including IL-4, IL-5, and IL-13, in PMA/ionomycin-activated mouse EL-4 T cells. Moreover, we showed that this was due to cellular PPAR-γ translocation. These results indicate that MS and RG promote PPAR-γ-DNA interactions and suggest that the regulatory effects of MS and RG on Th2 cytokine production could be abolished with PPAR-γ antagonist treatment. MS and RG also suppressed Th2 transcription factor translocation (e.g., GATA-3 and nuclear factor of activated T cells) by preventing the phosphorylation of protein kinase C and signal transducer and activator of transcription 6.

Early signaling events that underlie fate decisions of naive CD4(+) T cells toward distinct T-helper cell subsets

CD4(+) T-helper (Th) cells are a major cell population that play an important role in governing acquired immune responses to a variety of foreign antigens as well as inducing some types of autoimmune diseases. There are at least four distinct Th cell subsets (Th1, Th2, Th17, and inducible T-regulatory cells), each of which has specialized functions to control immune responses. Each of these cell types emerge from naive CD4(+) T cells after encounter with foreign antigens presented by dendritic cells (DCs). Each Th cell subset expresses a unique set of transcription factors and produces hallmark cytokines. Both T-cell receptor (TCR)-mediated stimulation and the cytokine environment created by activated CD4(+) T cells themselves, by 'partner' DCs, and/or other cell types during the course of differentiation, play an important role in the fate decisions toward distinct Th subsets. Here, we review how TCR-mediated signals in collaboration with the cytokine environment influence the fate decisions of naive CD4(+) T cells toward distinct Th subsets at the early stages of activation. We also discuss the roles of TCR-proximal signaling intermediates and of the Notch pathway in regulating the differentiation to distinct Th phenotypes.

Nfatc1 directs the endocardial progenitor cells to make heart valve primordium

Heart valves arise from the cardiac endocardial cushions located at the atrioventricular canal (AVC) and cardiac outflow tract (OFT) during development. A subpopulation of cushion endocardial cells undergoes endocardial to mesenchymal transformation (EMT) and generates the cushion mesenchyme, which is then remodeled into the interstitial tissue of the mature valves. The cushion endocardial cells that do not undertake EMT proliferate to elongate valve leaflets. During EMT and the post-EMT valve remodeling, endocardial cells at the cushions highly express nuclear factor in activated T cell, cytoplasmic 1 (Nfatc1), a transcription factor required for valve formation in mice. In this review, we present the current knowledge of Nfatc1 roles in the ontogeny of heart valves with a focus on the fate decision of the endocardial cells in the processes of EMT and valve remodeling.

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.

NFAT1 C-terminal domains are necessary but not sufficient for inducing cell death

The proteins belonging to the nuclear factor of activated T cells (NFAT) family of transcription factors are expressed in several cell types and regulate genes involved in differentiation, cell cycle and apoptosis. NFAT proteins share two conserved domains, the NFAT-homology region (NHR) and a DNA-binding domain (DBD). The N- and C-termini display two transactivation domains (TAD-N and TAD-C) that have low sequence similarity. Due to the high sequence conservation in the NHR and DBD, NFAT members have some overlapping roles in gene regulation. However, several studies have shown distinct roles for NFAT proteins in the regulation of cell death. The TAD-C shows low sequence similarity among NFAT family members, but its contribution to specific NFAT1-induced phenotypes is poorly understood. Here, we described at least two regions of NFAT1 TAD-C that confer pro-apoptotic activity to NFAT1. These regions extend from amino acids 699 to 734 and 819 to 850 of NFAT1. We also showed that the NFAT1 TAD-C is unable to induce apoptosis by itself and requires a functional DBD. Furthermore, we showed that when fused to NFAT1 TAD-C, NFAT2, which is associated with cell transformation, induces apoptosis in fibroblasts. Together, these results suggest that the NFAT1 TAD-C includes NFAT death domains that confer to different NFAT members the ability to induce apoptosis.

Host factor transcriptional regulation contributes to preferential expression of HIV type 1 in IL-4-producing CD4 T cells

HIV type 1 (HIV-1) replicates preferentially in IL-4-producing CD4 T cells for unclear reasons. We show increased HIV-1 expression is irrespective of viral tropism for chemokine receptors as previously suggested, but rather transcription of the HIV-1 long terminal repeat (LTR) is increased in IL-4-producing CD4 T cells. Increased expression of HIV-1 message is also confirmed in IL-4-producing CD4 T cells from HIV-1-infected individuals ex vivo. In exploring a transcriptional mechanism, we identify a novel c-maf (required for IL-4 expression) transcription factor binding site just upstream of the dual NF-κB/NFAT binding sites in the proximal HIV-1 LTR. We demonstrate that c-maf binds this site in vivo and synergistically augments HIV-1 transcription in cooperation with NFAT2 and NF-κB p65, but not NFAT1 or NF-κB p50. Conversely, small interfering RNA inhibition of c-maf reduces HIV-1 transcription in IL-4-producing T cells. Thus, c-maf increases HIV-1 expression in IL-4-producing CD4 T cells by binding the proximal HIV-1 LTR and augmenting HIV-1 transcription in partnership with NFAT2 and NF-κB p65 specifically. This has important implications for selective targeting of transcription factors during HIV-1 infection because, over the course of HIV-1 progression/AIDS, IL-4-producing T cells frequently predominate and substantially contribute to disease pathology.

NFATc1/αA: The other Face of NFAT Factors in Lymphocytes

In effector T and B cells immune receptor signals induce within minutes a rise of intracellular Ca++, the activation of the phosphatase calcineurin and the translocation of NFAT transcription factors from cytosol to nucleus. In addition to this first wave of NFAT activation, in a second step the occurrence of NFATc1/αA, a short isoform of NFATc1, is strongly induced. Upon primary stimulation of lymphocytes the induction of NFATc1/αA takes place during the G1 phase of cell cycle. Due to an auto-regulatory feedback circuit high levels of NFATc1/αA are kept constant during persistent immune receptor stimulation. Contrary to NFATc2 and further NFATc proteins which dampen lymphocyte proliferation, induce anergy and enhance activation induced cell death (AICD), NFATc1/αA supports antigen-mediated proliferation and protects lymphocytes against rapid AICD. Whereas high concentrations of NFATc1/αA can also lead to apoptosis, in collaboration with NF-κB-inducing co-stimulatory signals they support the survival of mature lymphocytes in late phases after their activation. However, if dysregulated, NFATc1/αA appears to contribute to lymphoma genesis and - as we assume - to further disorders of the lymphoid system. While the molecular details of NFATc1/αA action and its contribution to lymphoid disorders have to be investigated, NFATc1/αA differs in its generation and function markedly from all the other NFAT proteins which are expressed in lymphoid cells. Therefore, it represents a prime target for causal therapies of immune disorders in future.