NFATc2 and NFATc3 transcription factors play a crucial role in suppression of CD4+ T lymphocytes by CD4+ CD25+ regulatory T cells

Genome-wide landscape of genetic diversity, runs of homozygosity, and runs of heterozygosity in five Alpine and Mediterranean goat breeds

BACKGROUND

Goat breeds in the Alpine area and Mediterranean basin exhibit a unique genetic heritage shaped by centuries of selection and adaptability to harsh environments. Understanding their adaptive traits can aid breeding programs target enhanced resilience and productivity, especially as we are facing important climate and agriculture challenges. To this aim the genomic architecture of 480 goats belonging to five breeds (i.e., Saanen [SAA], Camosciata delle Alpi [CAM], Murciano-Granadina [MUR], Maltese [MAL], Sarda [SAR]) reared in the Sardinia Island were genotyped and their genomic architecture evaluated to find molecular basis of adaptive traits. Inbreeding, runs of homozygosity (ROH) and runs of heterozygosity (ROHet) were identified. Finally, candidate genes in the ROH and ROHet regions were explored through a pathway analysis to assess their molecular role.

RESULTS

In total, we detected 10,341 ROH in the SAA genome, 11,063 ROH in the CAM genome, 12,250 ROH in the MUR genome, 8,939 ROH in the MAL genome, and 18,441 ROH in the SAR genome. Moreover, we identified 4,087 ROHet for SAA, 3,360 for CAM, 2,927 for MUR, 3,701 for MAL, and 3,576 for SAR, with SAR having the highest heterozygosity coefficient. Interestingly, when computing the inbreeding coefficient using homozygous segment (FROH), SAA showed the lowest value while MAL the highest one, suggesting the need to improve selecting strategies to preserve genetic diversity within the population. Among the most significant candidate genes, we identified several ones linked to different physiological functions, such as milk production (e.g., DGAT1, B4GALT1), immunity (GABARAP, GPS2) and adaptation to environment (e.g., GJA3, GJB2 and GJB6).

CONCLUSIONS

This study highlighted the genetic diversity within and among five goat breeds. The high levels of ROH identified in some breeds might indicate high levels of inbreeding and a lack in genetic variation, which might negatively impact the animal population. Conversely, high levels of ROHet might indicate regions of the genetic diversity, beneficial for breed health and resilience. Therefore, these findings could aid breeding programs in managing inbreeding and preserving genetic diversity.

Molecular networks in atopic mothers impact the risk of infant atopy

BACKGROUND

The prevalence of atopic diseases has increased with atopic dermatitis (AD) as the earliest manifestation. We assessed if molecular risk factors in atopic mothers influence their infants' susceptibility to an atopic disease.

METHODS

Pregnant women and their infants with (n = 174, high-risk) or without (n = 126, low-risk) parental atopy were enrolled in a prospective birth cohort. Global differentially methylated regions (DMRs) were determined in atopic (n = 92) and non-atopic (n = 82) mothers. Principal component analysis was used to predict atopy risk in children dependent on maternal atopy. Genome-wide transcriptomic analyses were performed in paired atopic (n = 20) and non-atopic (n = 15) mothers and cord blood. Integrative genomic analyses were conducted to define methylation-gene expression relationships.

RESULTS

Atopic dermatitis was more prevalent in high-risk compared to low-risk children by age 2. Differential methylation analyses identified 165 DMRs distinguishing atopic from non-atopic mothers. Inclusion of DMRs in addition to maternal atopy significantly increased the odds ratio to develop AD in children from 2.56 to 4.26. In atopic compared to non-atopic mothers, 139 differentially expressed genes (DEGs) were identified significantly enriched of genes within the interferon signaling pathway. Expression quantitative trait methylation analyses dependent on maternal atopy identified 29 DEGs controlled by 136 trans-acting methylation marks, some located near transcription factors. Differential expression for the same nine genes, including MX1 and IFI6 within the interferon pathway, was identified in atopic and non-atopic mothers and high-risk and low-risk children.

CONCLUSION

These data suggest that in utero epigenetic and transcriptomic mechanisms predominantly involving the interferon pathway may impact and predict the development of infant atopy.

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.

NFAT Factors Are Dispensable for the Development but Are Critical for the Maintenance of Foxp3+ Regulatory T Cells

The transcription factors of the nuclear factor of activated T cell (NFAT) family play a crucial role in multiple aspects of T cell function. It has recently been reported that NFATs play an important role in the suppressive function of CD4⁺CD25⁺Foxp3⁺ regulatory T (T_reg) cells. In this study, we have investigated the role of NFATs in the thymic development of T_reg cells in mice. We show that NFAT factors are dispensable for the development of Foxp3⁺ T_reg cells in the thymus but are critical for the maintenance of both the phenotype and survival of T_reg cells in the thymus as well as in peripheral lymphoid organs. Specifically, the homeostasis of CD4⁺CD25⁺Foxp3⁺ but not the CD4⁺CD25⁻Foxp3⁺ fraction is severely perturbed when NFAT signaling is blocked, leading to a strongly reduced T_reg population. We underscored this intriguing effect of NFAT on CD4⁺CD25⁺Foxp3⁺ T_reg cells to the disruption of survival signals provided by interleukin 2 (IL-2). Accordingly, blocking T_reg cell death by abolishing the activity of pro-apoptotic Bcl-2 family member Bim, compensated for the survival defects induced due to a lack of NFAT-IL-2-IL-2R signaling. Inhibition of NFAT activity led to a strong reduction in the number of Foxp3⁺ T_reg cells; however, it did not influence the level of Foxp3 expression on an individual cell basis. In addition, we show a differential effect of IL-2 and IL-7 signaling on Foxp3⁺ T_reg versus CD4⁺CD25⁻ T cell development, again underlining the dispensability of NFAT signaling in the development, but not in the maintenance of Foxp3⁺ T_reg cells.

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.

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.

CD4 T cell-intrinsic role for the T helper 17 signature cytokine IL-17: Effector resistance to immune suppression

Untoward effector CD4+ T cell responses are kept in check by immune regulatory mechanisms mediated by CD4+ and CD8+ T cells. CD4+ T helper 17 (Th17) cells, characterized by IL-17 production, play important roles in the pathogenesis of autoimmune diseases (such as arthritis, multiple sclerosis, psoriasis, inflammatory bowel disease, among others) and in the host response to infection and cancer. Here, we demonstrate that human CD4+ T cells cells exposed to a Th17-differentiating milieu are significantly more resistant to immune suppression by CD8+ T cells compared to control Th0 cells. This resistance is mediated, in part, through the action of IL-17A, IL-17F, and IL-17AF heterodimer through their receptors (IL-17RA and IL-17RC) on CD4+ T cells themselves, but not through their action on CD8+ T cells or APC. We further show that IL-17 can directly act on non-Th17 effector CD4+ T cells to induce suppressive resistance, and this resistance can be reversed by blockade of IL-1β, IL-6, or STAT3. These studies reveal a role for IL-17 cytokines in mediating CD4-intrinsic immune resistance. The pathways induced in this process may serve as a critical target for future investigation and immunotherapeutic intervention.

Metalloimmunology: The metal ion-controlled immunity

Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation. Metal ions are also involved in the immune system from metal allergies to nutritional immunity. Within the past decade, much attention has been drawn to the roles of metal ions in the immune system, since increasing evidence has mounted to suggest that metals are critically implicated in regulating both the innate immune sensing of and the host defense against invading pathogens. The importance of ions in immunity is also evidenced by the identification of various immunodeficiencies in patients with mutations in ion channels and transporters. In addition, cancer immunotherapy has recently been conclusively demonstrated to be effective and important for future tumor treatment, although only a small percentage of cancer patients respond to immunotherapy because of inadequate immune activation. Importantly, metal ion-activated immunotherapy is becoming an effective and potential way in tumor therapy for better clinical application. Nevertheless, we are still in a primary stage of discovering the diverse immunological functions of ions and mechanistically understanding the roles of these ions in immune regulation. This review summarizes recent advances in the understanding of metal-controlled immunity. Particular emphasis is put on the mechanisms of innate immune stimulation and T cell activation by the essential metal ions like calcium (Ca²⁺), zinc (Zn²⁺), manganese (Mn²⁺), iron (Fe²⁺/Fe³⁺), and potassium (K⁺), followed by a few unessential metals, in order to draw a general diagram of metalloimmunology.

Tissue resident and follicular Treg cell differentiation is regulated by CRAC channels

T regulatory (Treg) cells maintain immunological tolerance and organ homeostasis. Activated Treg cells differentiate into effector Treg subsets that acquire tissue-specific functions. Ca²⁺ influx via Ca²⁺ release-activated Ca²⁺ (CRAC) channels formed by STIM and ORAI proteins is required for the thymic development of Treg cells, but its function in mature Treg cells remains unclear. Here we show that deletion of Stim1 and Stim2 genes in mature Treg cells abolishes Ca²⁺ signaling and prevents their differentiation into follicular Treg and tissue-resident Treg cells. Transcriptional profiling of STIM1/STIM2-deficient Treg cells reveals that Ca²⁺ signaling regulates transcription factors and signaling pathways that control the identity and effector differentiation of Treg cells. In the absence of STIM1/STIM2 in Treg cells, mice develop a broad spectrum of autoantibodies and fatal multiorgan inflammation. Our findings establish a critical role of CRAC channels in controlling lineage identity and effector functions of Treg cells.

Regulatory T (Treg) cells are important for maintaining immune homeostasis. Here the authors show that STIM1 and STIM2, which activate the Ca²⁺ channel ORAI1, are essential for the differentiation of peripheral Treg cells into tissue-resident and follicular Treg cells and their ability to limit autoimmunity in mice.

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.

Restoring self-tolerance in autoimmune diseases by enhancing regulatory T-cells

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

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.

The Transcription Factor NFATc1 Supports the Rejection of Heterotopic Heart Allografts

The immune suppressants cyclosporin A (CsA) and tacrolimus (FK506) are used worldwide in transplantation medicine to suppress graft rejection. Both CsA and FK506 inhibit the phosphatase calcineurin (CN) whose activity controls the immune receptor-mediated activation of lymphocytes. Downstream targets of CN in lymphocytes are the nuclear factors of activated T cells (NFATs). We show here that the activity of NFATc1, the most prominent NFAT factor in activated lymphocytes supports the acute rejection of heterotopic heart allografts. While ablation of NFATc1 in T cells prevented graft rejection, ectopic expression of inducible NFATc1/αA isoform led to rejection of heart allografts in recipient mice. Acceptance of transplanted hearts in mice bearing NFATc1-deficient T cells was accompanied by a reduction in number and cytotoxicity of graft infiltrating cells. In CD8⁺ T cells, NFATc1 controls numerous intracellular signaling pathways that lead to the metabolic switch to aerobic glycolysis and the expression of numerous lymphokines, chemokines, and their receptors, including Cxcr3 that supports the rejection of allogeneic heart transplants. These findings favors NFATc1 as a molecular target for the development of new strategies to control the cytotoxicity of T cells upon organ transplantation.

Tumor Tolerance-Promoting Function of Regulatory T Cells Is Optimized by CD28, but Strictly Dependent on Calcineurin

Regulatory T cells (Treg) restrain immune responses against malignant tumors, but their global depletion in cancer patients will likely be limited by systemic autoimmune toxicity. Instead, approaches to "tune" their activities may allow for preferential targeting of tumor-reactive Treg. Although Ag recognition regulates Treg function, the roles of individual TCR-dependent signaling pathways in enabling Treg to promote tumor tolerance are not well characterized. In this study, we examined in mouse tumor models the role of calcineurin, a key mediator of TCR signaling, and the role of the costimulatory receptor CD28 in the differentiation of resting central Treg into effector Treg endowed with tumor tropism. We find that calcineurin, although largely dispensable for suppressive activity in vitro, is essential for upregulation of ICOS and CTLA-4 in Treg, as well as for expression of chemokine receptors driving their accumulation in tumors. In contrast, CD28 is not critical, but optimizes the formation of tumor-homing Treg and their fitness in tumor tissue. Accordingly, although deletion of either CnB or CD28 strongly impairs Treg-mediated tumor tolerance, lack of CnB has an even more pronounced impact than lack of CD28. Hence, our studies reveal distinct roles for what has classically been defined as signal 1 and signal 2 of conventional T cell activation in the context of Treg-mediated tumor tolerance.

NFAT control of immune function: New Frontiers for an Abiding Trooper

Nuclear factor of activated T cells (NFAT) was first described almost three decades ago as a Ca ²⁺/calcineurin-regulated transcription factor in T cells. Since then, a large body of research uncovered the regulation and physiological function of different NFAT homologues in the immune system and many other tissues. In this review, we will discuss novel roles of NFAT in T cells, focusing mainly on its function in humoral immune responses, immunological tolerance, and the regulation of immune metabolism.

NFAT1 Regulates Systemic Autoimmunity through the Modulation of a Dendritic Cell Property

The transcription factor NFAT1 plays a pivotal role in the homeostasis of T lymphocytes. However, its functional importance in non-CD4+ T cells, especially in systemic immune disorders, is largely unknown. In this study, we report that NFAT1 regulates dendritic cell (DC) tolerance and suppresses systemic autoimmunity using the experimental autoimmune myasthenia gravis (EAMG) as a model. Myasthenia gravis and EAMG are T cell-dependent, Ab-mediated autoimmune disorders in which the acetylcholine receptor is the major autoantigen. NFAT1-knockout mice showed higher susceptibility to EAMG development with enhanced Th1/Th17 cell responses. NFAT1 deficiency led to a phenotypic alteration of DCs that show hyperactivation of NF-κB-mediated signaling pathways and enhanced binding of NF-κB (p50) to the promoters of IL-6 and IL-12. As a result, NFAT1-knockout DCs produced much higher levels of proinflammatory cytokines such as IL-1β, IL-6, IL-12, and TNF-α, which preferentially induce Th1/Th17 cell differentiation. Our data suggest that NFAT1 may limit the hyperactivation of the NF-κB-mediated proinflammatory response in DCs and suppress autoimmunity by serving as a key regulator of DC tolerance.

Phosphoproteomics Reveals Regulatory T Cell-Mediated DEF6 Dephosphorylation That Affects Cytokine Expression in Human Conventional T Cells

Regulatory T cells (Tregs) control key events of immune tolerance, primarily by suppression of effector T cells. We previously revealed that Tregs rapidly suppress T cell receptor (TCR)-induced calcium store depletion in conventional CD4⁺CD25⁻ T cells (Tcons) independently of IP₃ levels, consequently inhibiting NFAT signaling and effector cytokine expression. Here, we study Treg suppression mechanisms through unbiased phosphoproteomics of primary human Tcons upon TCR stimulation and Treg-mediated suppression, respectively. Tregs induced a state of overall decreased phosphorylation as opposed to TCR stimulation. We discovered novel phosphosites (T595_S597) in the DEF6 (SLAT) protein that were phosphorylated upon TCR stimulation and conversely dephosphorylated upon coculture with Tregs. Mutation of these DEF6 phosphosites abrogated interaction of DEF6 with the IP₃ receptor and affected NFAT activation and cytokine transcription in primary Tcons. This novel mechanism and phosphoproteomics data resource may aid in modifying sensitivity of Tcons to Treg-mediated suppression in autoimmune disease or cancer.

IL-4/IL-13 Heteroreceptor Influences Th17 Cell Conversion and Sensitivity to Regulatory T Cell Suppression To Restrain Experimental Allergic Encephalomyelitis

IL-4 and IL-13 have been defined as anti-inflammatory cytokines that can counter myelin-reactive T cells and modulate experimental allergic encephalomyelitis. However, it is not known whether endogenous IL-4 and IL-13 contribute to the maintenance of peripheral tolerance and whether their function is coordinated with T regulatory cells (Tregs). In this study, we used mice in which the common cytokine receptor for IL-4 and IL-13, namely the IL-4Rα/IL-13Rα1 (13R) heteroreceptor (HR), is compromised and determined whether the lack of signaling by endogenous IL-4 and IL-13 through the HR influences the function of effector Th1 and Th17 cells in a Treg-dependent fashion. The findings indicate that mice-deficient for the HR (13R^-/-) are more susceptible to experimental allergic encephalomyelitis than mice sufficient for the HR (13R^+/+) and develop early onset and more severe disease. Moreover, Th17 cells from 13R^-/- mice had reduced ability to convert to Th1 cells and displayed reduced sensitivity to suppression by Tregs relative to Th17 effectors from 13R^+/+ mice. These observations suggest that IL-4 and IL-13 likely operate through the HR and influence Th17 cells to convert to Th1 cells and to acquire increased sensitivity to suppression, leading to control of immune-mediated CNS inflammation. These previously unrecognized findings shed light on the intricacies underlying the contribution of cytokines to peripheral tolerance and control of autoimmunity.

On the Role IL-4/IL-13 Heteroreceptor Plays in Regulation of Type 1 Diabetes

Type 1 diabetes (T1D) manifests when the insulin-producing pancreatic β cells are destroyed as a consequence of an inflammatory process initiated by lymphocytes of the immune system. The NOD mouse develops T1D spontaneously and serves as an animal model for human T1D. The IL-4Rα/IL-13Rα1 heteroreceptor (HR) serves both IL-4 and IL-13 cytokines, which are believed to function as anti-inflammatory cytokines in T1D. However, whether the HR provides a responsive element to environmental (i.e., physiologic) IL-4/IL-13 in the regulation of peripheral tolerance and the development of T1D has yet to be defined. In this study, NOD mice deficient for the HR have been generated by means of IL-13Rα1 gene disruption and used to determine whether such deficiency affects the development of T1D. Surprisingly, the findings indicate that NOD mice lacking the HR (13R^-/-) display resistance to T1D as the rise in blood glucose level and islet inflammation were significantly delayed in these HR-deficient relative to HR-sufficient (13R^+/+) mice. In fact, the frequency and spleen-to-pancreas dynamics of both Th1 and Th17 cells were affected in 13R^-/- mice. This is likely due to an increase in the frequency of mTGFβ⁺Foxp3^int regulatory T cells and the persistence of CD206⁺ macrophages in the pancreas as both types of cells confer resistance to T1D upon transfer to 13R^+/+ mice. These findings reveal new insights as to the role environmental IL-4/IL-13 and the HR play in peripheral tolerance and the development of T1D.

MicroRNA-214 regulates immunity-related genes in bovine mammary epithelial cells by targeting NFATc3 and TRAF3

In human, microRNA-214 (miR-214) plays crucial roles in mechanisms of immunity. However, the potential importance of miR-214 in immune mechanisms in dairy cows has not been investigated. In this study, we assessed potential immunity-related functions of miR-214 in human 293A cells and in bovine mammary epithelial cells (BMECs). We found that NFATc3 and TRAF3 could be targeted by miR-214 in both 293A cells and BMECs. We also found that miR-214 indirectly inhibited the expression of MAP3K14, TBK1 and inflammatory cytokines IL-6 and IL-1β. Taken together, our data revealed miR-214 regulated immunity-related genes by targeting NFATc3 and TRAF3, which provides insight into the molecular basis of immunity.

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.

Protein kinase CK2 governs the molecular decision between encephalitogenic TH17 cell and Treg cell development

T helper 17 (TH17) cells represent a discrete TH cell subset instrumental in the immune response to extracellular bacteria and fungi. However, TH17 cells are considered to be detrimentally involved in autoimmune diseases like multiple sclerosis (MS). In contrast to TH17 cells, regulatory T (Treg) cells were shown to be pivotal in the maintenance of peripheral tolerance. Thus, the balance between Treg cells and TH17 cells determines the severity of a TH17 cell-driven disease and therefore is a promising target for treating autoimmune diseases. However, the molecular mechanisms controlling this balance are still unclear. Here, we report that pharmacological inhibition as well as genetic ablation of the protein kinase CK2 (CK2) ameliorates experimental autoimmune encephalomyelitis (EAE) severity and relapse incidence. Furthermore, CK2 inhibition or genetic ablation prevents TH17 cell development and promotes the generation of Treg cells. Molecularly, inhibition of CK2 leads to reduced STAT3 phosphorylation and strongly attenuated expression of the IL-23 receptor, IL-17, and GM-CSF. Thus, these results identify CK2 as a nodal point in TH17 cell development and suggest this kinase as a potential therapeutic target to treat TH17 cell-driven autoimmune responses.

Breaking Free of Control: How Conventional T Cells Overcome Regulatory T Cell Suppression

Conventional T (Tcon) cells are crucial in shaping the immune response, whether it is protection against a pathogen, a cytotoxic attack on tumor cells, or an unwanted response to self-antigens in the context of autoimmunity. In each of these immune settings, regulatory T cells (Tregs) can potentially exert control over the Tcon cell response, resulting in either suppression or activation of the Tcon cells. Under physiological conditions, Tcon cells are able to transiently overcome Treg-imposed restraints to mount a protective response against an infectious threat, achieving clonal expansion, differentiation, and effector function. However, evidence has accumulated in recent years to suggest that Tcon cell resistance to Treg-mediated suppression centrally contributes to the pathogenesis of autoimmune disease. Tipping the balance too far in the other direction, cancerous tumors utilize Tregs to establish an overly suppressive microenvironment, preventing antitumor Tcon cell responses. Given the wide-ranging clinical importance of the Tcon/Treg interaction, this review aims to provide a better understanding of what determines whether a Tcon cell is susceptible to Treg-mediated suppression and how perturbations to this finely tuned balance play a role in pathological conditions. Here, we focus in detail on the complex array of factors that confer Tcon cells with resistance to Treg suppression, which we have divided into two categories: (1) extracellular factor-mediated signaling and (2) intracellular signaling molecules. Further, we explore the therapeutic implications of manipulating the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway, which is proposed to be the convergence point of signaling pathways that mediate Tcon resistance to suppression. Finally, we address important unresolved questions on the timing and location of acquisition of resistance, and the stability of the “Treg-resistant” phenotype.

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.

Transcriptome and ultrastructural changes in dystrophic Epidermolysis bullosa resemble skin aging

The aging process of skin has been investigated recently with respect to mitochondrial function and oxidative stress. We have here observed striking phenotypic and clinical similarity between skin aging and recessive dystrophic Epidermolysis bullosa (RDEB), which is caused by recessive mutations in the gene coding for collagen VII, COL7A1. Ultrastructural changes, defects in wound healing, and inflammation markers are in part shared with aged skin. We have here compared the skin transcriptomes of young adults suffering from RDEB with that of sex‐ and age‐matched healthy probands. In parallel we have compared the skin transcriptome of healthy young adults with that of elderly healthy donors. Quite surprisingly, there was a large overlap of the two gene lists that concerned a limited number of functional protein families. Most prominent among the proteins found are a number of proteins of the cornified envelope or proteins mechanistically involved in cornification and other skin proteins. Further, the overlap list contains a large number of genes with a known role in inflammation. We are documenting some of the most prominent ultrastructural and protein changes by immunofluorescence analysis of skin sections from patients, old individuals, and healthy controls.

Transcription factor NFAT1 controls allergic contact hypersensitivity through regulation of activation induced cell death program

Allergic contact hypersensitivity (CHS) is an inflammatory skin disease mediated by allergen specific T cells. In this study, we investigated the role of transcription factor NFAT1 in the pathogenesis of contact hypersensitivity. NFAT1 knock out (KO) mice spontaneously developed CHS-like skin inflammation in old age. Healthy young NFAT1 KO mice displayed enhanced susceptibility to hapten-induced CHS. Both CD4⁺ and CD8⁺ T cells from NFAT1 KO mice displayed hyper-activated properties and produced significantly enhanced levels of inflammatory T helper 1(Th1)/Th17 type cytokines. NFAT1 KO T cells were more resistant to activation induced cell death (AICD), and regulatory T cells derived from these mice showed a partial defect in their suppressor activity. NFAT1 KO T cells displayed a reduced expression of apoptosis associated BCL-2/BH3 family members. Ectopic expression of NFAT1 restored the AICD defect in NFAT1 KO T cells and increased AICD in normal T cells. Recipient Rag2^−/− mice transferred with NFAT1 KO T cells showed more severe CHS sensitivity due to a defect in activation induced hapten-reactive T cell apoptosis. Collectively, our results suggest the NFAT1 plays a pivotal role as a genetic switch in CD4⁺/CD8⁺ T cell tolerance by regulating AICD process in the T cell mediated skin inflammation.

The Molecular Control of Regulatory T Cell Induction

Regulatory T cells (Tregs) are characterized by the expression of the master transcription factor forkhead box P3 (Foxp3). Although Foxp3 expression is widely used as a marker of the Treg lineage, recent data show that the Treg fate is determined by a multifactorial signaling pathway, involving cytokines, nuclear factors, and epigenetic modifications. Foxp3 expression and the Treg phenotype can be acquired by T cells in the periphery, illustrating that the Treg fate is not necessarily conferred during thymic development. The two main Treg populations in vivo, thymic Tregs and peripheral Tregs, differ in the pathways followed for their maturation. This chapter discusses the molecular control of Treg induction, in the thymus as well as the periphery.

Pak2 Links TCR Signaling Strength to the Development of Regulatory T Cells and Maintains Peripheral Tolerance

Although significant effort has been devoted to understanding the thymic development of Foxp3(+) regulatory T cells (Tregs), the precise signaling pathways that govern their lineage commitment still remain enigmatic. Our findings show a novel role for the actin cytoskeletal remodeling protein, p21-activated kinase 2 (Pak2), in Treg development and homeostasis. The absence of Pak2 in T cells resulted in a marked reduction in both thymus- and peripherally derived Tregs, accompanied by the development of spontaneous colitis in Pak2-deficient mice. Additionally, Pak2 was required for the proper differentiation of in vitro-induced Tregs as well as maintenance of Tregs. Interestingly, Pak2 was necessary for generating the high-affinity TCR- and IL-2-mediated signals that are required by developing Tregs for their lineage commitment. These findings provide novel insight into how developing thymocytes translate lineage-specific high-affinity TCR signals to adopt the Treg fate, and they further posit Pak2 as an essential regulator for this process.

STIM1 controls T cell-mediated immune regulation and inflammation in chronic infection

Chronic infections induce a complex immune response that controls pathogen replication, but also causes pathology due to sustained inflammation. Ca2+ influx mediates T cell function and immunity to infection, and patients with inherited mutations in the gene encoding the Ca2+ channel ORAI1 or its activator stromal interaction molecule 1 (STIM1) are immunodeficient and prone to chronic infection by various pathogens, including Mycobacterium tuberculosis (Mtb). Here, we demonstrate that STIM1 is required for T cell-mediated immune regulation during chronic Mtb infection. Compared with WT animals, mice with T cell-specific Stim1 deletion died prematurely during the chronic phase of infection and had increased bacterial burdens and severe pulmonary inflammation, with increased myeloid and lymphoid cell infiltration. Although STIM1-deficient T cells exhibited markedly reduced IFN-γ production during the early phase of Mtb infection, bacterial growth was not immediately exacerbated. During the chronic phase, however, STIM1-deficient T cells displayed enhanced IFN-γ production in response to elevated levels of IL-12 and IL-18. The lack of STIM1 in T cells was associated with impaired activation-induced cell death upon repeated TCR engagement and pulmonary lymphocytosis and hyperinflammation in Mtb-infected mice. Chronically Mtb-infected, STIM1-deficient mice had reduced levels of inducible regulatory T cells (iTregs) due to a T cell-intrinsic requirement for STIM1 in iTreg differentiation and excessive production of IFN-γ and IL-12, which suppress iTreg differentiation and maintenance. Thus, STIM1 controls multiple aspects of T cell-mediated immune regulation to limit injurious inflammation during chronic infection.

Protein kinase CK2 enables regulatory T cells to suppress excessive TH2 responses in vivo

The quality of the adaptive immune response depends on the differentiation of distinct CD4(+) helper T cell subsets, and the magnitude of an immune response is controlled by CD4(+)Foxp3(+) regulatory T cells (Treg cells). However, how a tissue- and cell type-specific suppressor program of Treg cells is mechanistically orchestrated has remained largely unexplored. Through the use of Treg cell-specific gene targeting, we found that the suppression of allergic immune responses in the lungs mediated by T helper type 2 (TH2) cells was dependent on the activity of the protein kinase CK2. Genetic ablation of the β-subunit of CK2 specifically in Treg cells resulted in the proliferation of a hitherto-unexplored ILT3(+) Treg cell subpopulation that was unable to control the maturation of IRF4(+)PD-L2(+) dendritic cells required for the development of TH2 responses in vivo.

Selective NFAT targeting in T cells ameliorates GvHD while maintaining antitumor activity

Graft-versus-host disease (GvHD) is a life-threatening immunological complication after allogenic hematopoietic stem cell transplantation (allo-HCT). The intrinsic graft-versus-leukemia (GvL) effect, however, is the desirable curative benefit. Patients with acute GvHD are treated with cyclosporine A (CsA) or tacrolimus (FK506), which not only often causes severe adverse effects, but also interferes with the anticipated GvL. Both drugs inhibit calcineurin, thus at first suppressing activation of the nuclear factor of activated T cells (NFAT). Therefore, we explored the specific contribution of individual NFAT factors in donor T cells in animal models of GvHD and GvL. Ablation of NFAT1, NFAT2, or a combination of both resulted in ameliorated GvHD, due to reduced proliferation, target tissue homing, and impaired effector function of allogenic donor T cells. In contrast, the frequency of Foxp3(+) regulatory T (Treg) cells was increased and NFAT-deficient Tregs were fully protective in GvHD. CD8(+) T-cell recall response and, importantly, the beneficial antitumor activity were largely preserved in NFAT-deficient effector T cells. Thus, specific inhibition of NFAT opens an avenue for an advanced therapy of GvHD maintaining protective GvL.

Superiority of rapamycin over tacrolimus in preserving nonhuman primate Treg half-life and phenotype after adoptive transfer

Many critical issues remain concerning how best to deploy adoptive regulatory T cell (Treg) immunotherapy to the clinic. These include a determination of their pharmacokinetic characteristics, their optimal dose, their phenotypic stability and the best therapies with which to pair Tregs. By performing a CFSE-labeled autologous Treg pulse experiment, we determined that the accessible peripheral blood Treg pool in rhesus macaques is quite large (75 ± 11 × 10(6) Tregs/kg). Pharmacokinetic analysis revealed that Tregs have two phases of elimination: an α phase, with a T1/2 in the peripheral blood of 32.4 ± 11.3 h and a β phase with a T1/2 of 120.4 ± 19.7 h. In addition to their short initial half-life, Tregs underwent rapid phenotypic shifts after infusion, with significant loss of both CD25 and FoxP3 by day +6. While tacrolimus stabilized CD25 expression, it did not improve T1/2 , nor mitigate the loss of FoxP3. In contrast, rapamycin significantly stabilized both CD25 and FoxP3, and supported an increased half-life, with an α phase of 67.7 ± 6.9 h and a β phase of 252.1 ± 54.9 h. These results suggest that rapamycin may be a necessary addition to Treg immunotherapy, and that tacrolimus may be deleterious to Treg integrity posttransfer.

Integrating canonical and metabolic signalling programmes in the regulation of T cell responses

Over the past decade, our understanding of T cell activation, differentiation and function has markedly expanded, providing a greater appreciation of the signals and pathways that regulate these processes. It has become clear that evolutionarily conserved pathways that regulate stress responses, metabolism, autophagy and survival have crucial and specific roles in regulating T cell responses. Recent studies suggest that the metabolic pathways involving MYC, hypoxia-inducible factor 1α (HIF1α), AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) are activated upon antigen recognition and that they are required for directing the consequences of T cell receptor engagement. The purpose of this Review is to provide an integrated view of the role of these metabolic pathways and of canonical T cell signalling pathways in regulating the outcome of T cell responses.

Regulatory T cells suppress CD4+ T cells through NFAT-dependent transcriptional mechanisms

Regulatory T cells (Tregs) control autoreactive T cells by inhibiting activation-induced proliferation and cytokine expression. The molecular mechanisms responsible for the inactivation of effector T cells by Tregs remain yet to be fully characterized. We report that T-helper cells stimulated in the presence of Tregs quickly activate NFAT1 and have increased NFAT1-dependent expression of the transcription repressor Ikaros. NFAT1 deficiency or dominant-negative Ikaros compromises Treg-mediated inhibition of T-helper cells in vitro and in vivo. Thus, our results place NFAT-dependent mechanisms as general regulators of T-cell tolerance and show that Treg-mediated suppression of T-helper cells results from the activation of NFAT-regulated gene expression.

Nfatc2 and Tob1 have non-overlapping function in T cell negative regulation and tumorigenesis

Nfatc2 and Tob1 are intrinsic negative regulators of T cell activation. Nfatc2-deficient and Tob1-deficient T cells show reduced thresholds of activation; however, whether these factors have independent or overlapping roles in negative regulation of T cell responses has not been previously examined. Here, we show that Nfatc2 knockout (KO) but not Tob1 KO mice have age-associated accumulation of persistently activated T cells in vivo and expansion of the CD44+ memory cell compartment and age-associated lymphocytic infiltrates in visceral organs, without significant changes in numbers of CD4+CD25+Foxp3+ regulatory T cells (Treg). In vitro, CD4+CD25- "conventional" T cells (Tconvs) from both KO strains showed greater proliferation than wild type (WT) Tconvs. However, while Tregs from Nfatc2 KO mice retained normal suppressive function, Tregs from Tob1 KOs had enhanced suppressive activity. Nfatc2 KO Tconvs expanded somewhat more rapidly than WT Tconvs under conditions of homeostatic proliferation, but their accelerated growth capacity was negated, at least acutely, in a lymphoreplete environment. Finally, Nfatc2 KO mice developed a previously uncharacterized increase in B-cell malignancies, which was not accelerated by the absence of Tob1. The data thus support the prevailing hypothesis that Nfatc2 and Tob1 are non-redundant regulators of lymphocyte homeostasis.

Transcriptional control of regulatory T cells

Regulatory T cells (Tregs) constitute unique T cell lineage that plays a key role for immunological tolerance. Tregs are characterized by the expression of the forkhead box transcription factor Foxp3, which acts as a lineage-specifying factor by determining the unique suppression profile of these immune cells. Here, we summarize the recent progress in understanding how Foxp3 expression itself is epigenetically and transcriptionally controlled, how the Treg-specific signature is achieved and how unique properties of Treg subsets are defined by other transcription factors. Finally, we will discuss recent studies focusing on the molecular targeting of Tregs to utilize the specific properties of this unique cell type in therapeutic settings.

Regulation of regulatory T cells: epigenetics and plasticity

Regulatory T (Treg) cells, as central mediators of immune suppression, play crucial roles in many aspects of immune system's physiology and pathophysiology. The transcription factor Foxp3 has been characterized as a master gene of Tregs. Yet Treg cells possess a distinct pattern of gene expression, including upregulation of immune-suppressive genes and silencing of inflammatory cytokine genes. Recent studies have revealed the molecular mechanisms that establish and maintain such gene regulation in Treg cells. This review discusses recent progress in our understanding of molecular features of Treg cells, with particular attention to Treg-cell lineage commitment and stability.

MiR-568 inhibits the activation and function of CD4⁺ T cells and Treg cells by targeting NFAT5

CD4(+) T cells play critical roles in orchestrating adaptive immune responses. Their activation and proliferation are critical steps that occur before they execute their biological functions. Despite the important role of this process, the underlying molecular events are not fully understood. MicroRNAs (miRNAs) have been shown to play important roles in lymphocyte development and function. However, the miRNAs that regulate T-cell differentiation, activation and proliferation are still largely unknown. In our previous study, using a miRNA array, we found that several miRNAs (including miR-202, 33b, 181c, 568 and 576) are differentially expressed between resting and activated CD4(+) T cells. In this study, we focused on the function of miR-568 during CD4(+) T-cell activation. We showed that the expression level of miR-568 decreased during the activation of T cells, including Jurkat cells and human peripheral blood CD4(+) T cells. When Jurkat or human peripheral blood CD4(+) T cells were transfected with miR-568 mimics, cell activation was significantly inhibited, as shown by the inhibited expression of activation markers such as CD25, CD69 and CD154; decreased IL-2 production; and inhibited cell proliferation. Using software predictions and confirmatory experiments, we demonstrated that nuclear factor of activated T cells 5 (NFAT5) is a target of miR-568. Treg cells are an important CD4(+) T-cell subpopulation, so we also evaluated the function of miR-568 in Treg-cell activation and differentiation. We showed that the miR-568 level decreased, while the NFAT5 protein level increased during CD4(+)CD25(+) Treg-cell activation, and the transfection of miR-568 mimics inhibited the NFAT5 expression, inhibited the production of both TGF-β and IL-10 and also inhibited the proliferation of Treg cells. Our further study showed that over-expression of miR-568 can inhibit Treg-cell differentiation and can inhibit the suppressive effect of these cells on effector cells. In addition, inhibition of NFAT5 by siRNA-mediated knockdown can inhibit the activation and differentiation of Treg cells. These findings reveal that miR-568 can inhibit the activation and function of both CD4(+) T cells and Treg cells by targeting NFAT5. Since miR-568 plays an important role in both CD4(+) T cells and Treg cells, these findings may provide leads for the development of novel treatments for human inflammatory and autoimmune diseases.

Molecular mechanisms of T-cell anergy

Anergy is a long-term stable state of T-lymphocyte unresponsiveness to antigenic stimulation associated with the blockade of IL-2 production and proliferation. Anergy is a pathway of peripheral tolerance formation. In this review, mechanisms underlying T-cell tolerization are considered in a classical in vitro model of clonal anergy, and these mechanisms are compared with different pathways of anergy induction in vivo. Special attention is given to regulatory T-lymphocytes because, on one hand, anergy is a specific feature of these cells, and on the other hand anergy is also a mechanism of their action on target cells - effector T-lymphocytes. The role of this phenomenon in the differentiation of regulatory T-cells and also in the development of activation-induced apoptosis in effector T-lymphocytes is discussed.

Thymic regulatory T cell development: role of signalling pathways and transcription factors

Regulatory T cells (Tregs) are a subset of CD4 T cells that are key mediators of immune tolerance. Most Tregs develop in the thymus. In this review we summarise recent findings on the role of diverse signalling pathways and downstream transcription factors in thymic Treg development.

Transcriptional control of regulatory T cell development and function

•

An intermediate amount of T cell stimulation induces Foxp3 transcription.

•

Treg cell lineage factor Foxp3 cooperates with its partners to promote Treg cell function.

•

Cell signaling-regulated Foxo1 is indispensable for Treg cell function.

Regulatory T (Treg) cells differentiate from thymocytes or peripheral T cells in response to host and environmental cues, culminating in induction of the transcription factor forkhead box P3 (Foxp3) and the Treg cell-specific epigenome. An intermediate amount of antigen stimulation is required to induce Foxp3 expression by engaging T cell receptor (TCR)-activated [e.g., nuclear factor (NF)-κB] and TCR-inhibited (e.g., Foxo) transcription factors. Furthermore, Treg cell differentiation is associated with attenuated Akt signaling, resulting in enhanced nuclear retention of Foxo1, which is indispensable for Treg cell function. These findings reveal that Treg cell lineage commitment is not only controlled by genetic and epigenetic imprinting, but also modulated by transcriptional programs responding to extracellular signals.

Nuclear factor of activated T cells - a transcription factor family as critical regulator in lung and colon cancer

Nuclear factor of activated T cells (NFAT) was first identified as a transcription factor which is activated upon T cell stimulation. Subsequent studies uncovered that a whole family of individual NFAT proteins exists with pleiotropic functions not only in immune but also in nonimmune cells. However, dysregulation of NFAT thereby favors malignant growth and cancer. Summarizing the recent advances in understanding how individual NFAT factors regulate the immune system, this review gives new insights into the critical role of NFAT in cancer development with special focus on inflammation-associated colorectal cancer.

Dependence on nuclear factor of activated T-cells (NFAT) levels discriminates conventional T cells from Foxp3+ regulatory T cells

Several lines of evidence suggest nuclear factor of activated T-cells (NFAT) to control regulatory T cells: thymus-derived naturally occurring regulatory T cells (nTreg) depend on calcium signals, the Foxp3 gene harbors several NFAT binding sites, and the Foxp3 (Fork head box P3) protein interacts with NFAT. Therefore, we investigated the impact of NFAT on Foxp3 expression. Indeed, the generation of peripherally induced Treg (iTreg) by TGF-β was highly dependent on NFAT expression because the ability of CD4(+) T cells to differentiate into iTreg diminished markedly with the number of NFAT family members missing. It can be concluded that the expression of Foxp3 in TGF-β-induced iTreg depends on the threshold value of NFAT rather than on an individual member present. This is specific for iTreg development, because frequency of nTreg remained unaltered in mice lacking NFAT1, NFAT2, or NFAT4 alone or in combination. Different from expectation, however, the function of both nTreg and iTreg was independent on robust NFAT levels, reflected by less nuclear NFAT in nTreg and iTreg. Accordingly, absence of one or two NFAT members did not alter suppressor activity in vitro or during colitis and transplantation in vivo. This scenario emphasizes an inhibition of high NFAT activity as treatment for autoimmune diseases and in transplantation, selectively targeting the proinflammatory conventional T cells, while keeping Treg functional.

Cyclic AMP underpins suppression by regulatory T cells

Elevated levels of intracellular cyclic adenosine monophosphate (cAMP) in naturally occurring T regulatory (nTreg) cells play a key role in nTreg-cell-mediated suppression. Upon contact with nTreg cells, cAMP is transferred from nTreg cells into activated target CD4(+) T cells and/or antigen-presenting cells (APCs) via gap junctions to suppress CD4(+) T-cell function. cAMP facilitates the expression and nuclear function of a potent transcriptional inhibitor, inducible cAMP early repressor (ICER), resulting in ICER-mediated suppression of interleukin-2 (IL-2). Furthermore, ICER inhibits transcription of nuclear factor of activated T cell c1/α (NFATc1/α) and forms inhibitory complexes with preexisting NFATc1/c2, thereby inhibiting NFAT-driven transcription, including that of IL-2. In addition to its suppressive effects mediated via ICER, cAMP can also modulate the levels of surface-expressed cytotoxic T lymphocyte antigen-4 (CTLA-4) and its cognate B7 ligands on conventional CD4(+) T cells and/or APCs, fine-tuning suppression. These cAMP-driven nTreg-cell suppression mechanisms are the focus of this review.

NFAT1 supports tumor-induced anergy of CD4(+) T cells

Cancer cells express antigens that elicit T cell-mediated responses, but these responses are limited during malignant progression by the development of immunosuppressive mechanisms in the tumor microenvironment that drive immune escape. T-cell hyporesponsiveness can be caused by clonal anergy or adaptive tolerance, but the pathophysiological roles of these processes in specific tumor contexts has yet to be understood. In CD4+ T cells, clonal anergy occurs when the T-cell receptor is activated in the absence of a costimulatory signal. Here we report that the key T-cell transcription factor NFAT mediates expression of anergy-associated genes in the context of cancer. Specifically, in a murine model of melanoma, we found that cancer cells induced anergy in antigen-specific CD4+ T-cell populations, resulting in defective production of several key effector cytokines. NFAT1 deficiency blunted the induction of anergy in tumor antigen-specific CD4+ T cells, enhancing antitumor responses. These investigations identified tumor-induced T-cell hyporesponsiveness as a form of clonal anergy, and they supported an important role for CD4+ T-cell anergy in driving immune escape. By illustrating the dependence of tumor-induced CD4+ T-cell anergy on NFAT1, our findings open the possibility of targeting this transcription factor to improve the efficacy of cancer immunotherapy or immunochemotherapy.

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.