NFAT5 regulates T lymphocyte homeostasis and CD24-dependent T cell expansion under pathologic hypernatremia

Tissue Sodium Accumulation Induces Organ Inflammation and Injury in Chronic Kidney Disease

High salt intake is a primary cause of over-hydration in chronic kidney disease (CKD) patients. Inflammatory markers are predictors of CKD mortality; however, the pathogenesis of inflammation remains unclear. Sodium storage in tissues has recently emerged as an issue of concern. The binding of sodium to tissue glycosaminoglycans and its subsequent release regulates local tonicity. Many cell types express tonicity-responsive enhancer-binding protein (TonEBP), which is activated in a tonicity-dependent or tonicity-independent manner. Macrophage infiltration was observed in the heart, peritoneal wall, and para-aortic tissues in salt-loading subtotal nephrectomized mice, whereas macrophages were not prominent in tap water-loaded subtotal nephrectomized mice. TonEBP was increased in the heart and peritoneal wall, leading to the upregulation of inflammatory mediators associated with cardiac fibrosis and peritoneal membrane dysfunction, respectively. Reducing salt loading by a diuretic treatment or changing to tap water attenuated macrophage infiltration, TonEBP expression, and inflammatory marker expression. The role of TonEBP may be crucial during the cardiac fibrosis and peritoneal deterioration processes induced by sodium overload. Anti-interleukin-6 therapy improved cardiac inflammation and fibrosis and peritoneal membrane dysfunction. Further studies are necessary to establish a strategy to regulate organ dysfunction induced by TonEBP activation in CKD patients.

A Novel Single-Nucleotide Polymorphism in WNT4 Promoter Affects Its Transcription and Response to FSH in Chicken Follicles

The signaling pathway of the wingless-type mouse mammary tumor virus integration site (Wnt) plays an important role in ovarian and follicular development. In our previous study, WNT4 was shown to be involved in the selection and development of chicken follicles by upregulating the expression of follicle-stimulating hormone receptors (FSHR), stimulating the proliferation of follicular granulosa cells, and increasing the secretion of steroidal hormones. FSH also stimulates the expression of WNT4. To further explore the molecular mechanism by which FSH upregulates WNT4 and characterize the cis-elements regulating WNT4 transcription, in this study, we determined the critical regulatory regions affecting chicken WNT4 transcription. We then identified a single-nucleotide polymorphism (SNP) in this region, and finally analyzed the associations of the SNP with chicken production traits. The results showed that the 5′ regulatory region from −3354 to −2689 of WNT4 had the strongest activity and greatest response to FSH stimulation, and we identified one SNP site in this segment, −3015 (G > C), as affecting the binding of NFAT5 (nuclear factor of activated T cells 5) and respones to FSH stimulation. When G was replaced with C at this site, it eliminated the NFAT5 binding. The mRNA level of WNT4 in small yellow follicles of chickens with genotype GG was significantly higher than that of the other two genotypes. Moreover, this locus was found to be significantly associated with comb length in hens. Individuals with the genotype CC had longer combs. Collectively, these data suggested that SNP−3015 (G > C) is involved in the regulation of WNT4 gene expression by responding FSH and affecting the binding of NFAT5 and that it is associated with chicken comb length. The current results provide a reference for further revealing the response mechanism between WNT and FSH.

The modulatory effect of high salt on immune cells and related diseases

BACKGROUND

The adverse effect of excessive salt intake has been recognized in decades. Researchers have mainly focused on the association between salt intake and hypertension. However, studies in recent years have proposed the existence of extra-renal sodium storage and provided insight into the immunomodulatory function of sodium.

OBJECTIVES

In this review, we discuss the modulatory effects of high salt on various innate and adaptive immune cells and immune-regulated diseases.

METHODS

We identified papers through electronic searches of PubMed database from inception to March 2022.

RESULTS

An increasing body of evidence has demonstrated that high salt can modulate the differentiation, activation and function of multiple immune cells. Furthermore, a high-salt diet can increase tissue sodium concentrations and influence the immune responses in microenvironments, thereby affecting the development of immune-regulated diseases, including hypertension, multiple sclerosis, cancer and infections. These findings provide a novel mechanism for the pathology of certain diseases and indicate that salt might serve as a target or potential therapeutic agent in different disease contexts.

CONCLUSION

High salt has a profound impact on the differentiation, activation and function of multiple immune cells. Additionally, an HSD can modulate the development of various immune-regulated diseases.

NFAT5 Controls the Integrity of Epidermis

The skin protects the human body against dehydration and harmful challenges. Keratinocytes (KCs) are the most abundant epidermal cells, and it is anticipated that KC-mediated transport of Na⁺ ions creates a physiological barrier of high osmolality against the external environment. Here, we studied the role of NFAT5, a transcription factor whose activity is controlled by osmotic stress in KCs. Cultured KCs from adult mice were found to secrete more than 300 proteins, and upon NFAT5 ablation, the secretion of several matrix proteinases, including metalloproteinase-3 (Mmp3) and kallikrein-related peptidase 7 (Klk7), was markedly enhanced. An increase in Mmp3 and Klk7 RNA levels was also detected in transcriptomes of Nfat5^-/- KCs, along with increases of numerous members of the 'Epidermal Differentiation Complex' (EDC), such as small proline-rich (Sprr) and S100 proteins. NFAT5 and Mmp3 as well as NFAT5 and Klk7 are co-expressed in the basal KCs of fetal and adult epidermis but not in basal KCs of newborn (NB) mice. The poor NFAT5 expression in NB KCs is correlated with a strong increase in Mmp3 and Klk7 expression in KCs of NB mice. These data suggests that, along with the fragile epidermis of adult Nfat5^-/- mice, NFAT5 keeps in check the expression of matrix proteases in epidermis. The NFAT5-mediated control of matrix proteases in epidermis contributes to the manifold changes in skin development in embryos before and during birth, and to the integrity of epidermis in adults.

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.

The evolving role of TonEBP as an immunometabolic stress protein

Tonicity-responsive enhancer-binding protein (TonEBP), which is also known as nuclear factor of activated T cells 5 (NFAT5), was discovered 20 years ago as a transcriptional regulator of the cellular response to hypertonic (hyperosmotic salinity) stress in the renal medulla. Numerous studies since then have revealed that TonEBP is a pleiotropic stress protein that is involved in a range of immunometabolic diseases. Some of the single-nucleotide polymorphisms (SNPs) in TONEBP introns are cis-expression quantitative trait loci that affect TONEBP transcription. These SNPs are associated with increased risk of type 2 diabetes mellitus, diabetic nephropathy, inflammation, high blood pressure and abnormal plasma osmolality, indicating that variation in TONEBP expression might contribute to these phenotypes. In addition, functional studies have shown that TonEBP is involved in the pathogenesis of rheumatoid arthritis, atherosclerosis, diabetic nephropathy, acute kidney injury, hyperlipidaemia and insulin resistance, autoimmune diseases (including type 1 diabetes mellitus and multiple sclerosis), salt-sensitive hypertension and hepatocellular carcinoma. These pathological activities of TonEBP are in contrast to the protective actions of TonEBP in response to hypertonicity, bacterial infection and DNA damage induced by genotoxins. An emerging theme is that TonEBP is a stress protein that mediates the cellular response to a range of pathological insults, including excess caloric intake, inflammation and oxidative stress.

Peritoneal dialysis induces alterations in the transcriptome of peritoneal cells before detectible peritoneal functional changes

Long-term peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. Inflammation may be the key moment, and, consequently, fibrosis may be the end result of chronic inflammatory reaction. The objective of the present study was to identify genes involved in peritoneal alterations during PD by comparing the transcriptome of peritoneal cells in patients with short- and long-term PD. Peritoneal effluent of the long dwell of patients with stable PD was centrifuged to obtain peritoneal cells. The gene expression profiles of peritoneal cells using microarray between patients with short- and long-term PD were compared. Based on microarray analysis, 31 genes for quantitative RT-PCR validation were chosen. A 4-h peritoneal equilibration test was performed on the day after the long dwell. Transport parameters and protein appearance rates were assessed. Genes involved in the immune system process, immune response, cell activation, and leukocyte and lymphocyte activation were found to be substantially upregulated in the long-term group. Quantitative RT-PCR validation showed higher expression of CD24, lymphocyte antigen 9 ( LY9), TNF factor receptor superfamily member 4 ( TNFRSF4), Ig associated-α ( CD79A), chemokine (C-C motif) receptor 7 ( CCR7), carcinoembryonic antigen-related cell adhesion molecule 1 ( CEACAM1), and IL-2 receptor-α ( IL2RA) in patients with long-term PD, with CD24 having the best discrimination ability between short- and long-term treatment. A relationship between CD24 expression and genes for collagen and matrix formation was shown. Activation of CD24 provoked by pseudohypoxia due to extremely high glucose concentrations in dialysis solutions might play the key role in the development of peritoneal membrane alterations.

Regulation of Inflammatory Functions of Macrophages and T Lymphocytes by NFAT5

The transcription factor NFAT5, also known as TonEBP, belongs to the family of Rel homology domain-containing factors, which comprises the NF-κB proteins and the calcineurin-dependent NFAT1 to NFAT4. NFAT5 shares several structural and functional features with other Rel-family factors, for instance it recognizes DNA elements with the same core sequence as those bound by NFAT1 to 4, and like NF-κB it responds to Toll-like receptors (TLR) and activates macrophage responses to microbial products. On the other hand, NFAT5 is quite unique among Rel-family factors as it can be activated by hyperosmotic stress caused by elevated concentrations of extracellular sodium ions. NFAT5 regulates specific genes but also others that are inducible by NF-κB and NFAT1 to 4. The ability of NFAT5 to do so in response to hypertonicity, microbial products, and inflammatory stimuli may extend the capabilities of immune cells to mount effective anti-pathogen responses in diverse microenvironment and signaling conditions. Recent studies identifying osmostress-dependent and -independent functions of NFAT5 have broadened our understanding of how NFAT5 may modulate immune function. In this review we focus on the role of NFAT5 in macrophages and T cells in different contexts, discussing findings from in vivo mouse models of NFAT5 deficiency and reviewing current knowledge on its mechanisms of regulation. Finally, we propose several questions for future research.

Role of NFAT5 in the Immune System and Pathogenesis of Autoimmune Diseases

The nuclear factor of activated T cells (NFAT5), also known as a tonicity-responsive enhancer-binding protein, was originally identified as a key transcription factor involved in maintaining cellular homeostasis against hypertonic and hyperosmotic environments. Although NFAT5 has been expressed and studied in various types of hyperosmolar tissues, evidence has emerged that NFAT5 plays a role in the development and activation of immune cells, especially T cells and macrophages. The immune-regulatory function of NFAT5 is achieved by inducing different target genes and different signaling pathways in both tonicity-dependent and -independent manners. Particularly in response to hyperosmotic stress, NFAT5 induces the generation of pathogenic T_H17 cells and pro-inflammatory macrophages, contributing to autoimmune and inflammatory diseases. Meanwhile, with tonicity-independent stimuli, including activation of the Toll-like receptors and inflammatory cytokines, NFAT5 also can be activated and promotes immune cell survival, proliferation, migration, and angiogenesis. Moreover, under isotonic conditions, NFAT5 has been implicated in the pathogenesis of a variety of inflammatory and autoimmune diseases including rheumatoid arthritis. This review describes the current knowledge of NFAT5, focusing on its immune-regulatory functions, and it highlights the importance of NFAT5 as a novel therapeutic target for chronic inflammatory diseases.

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.

NFAT5 up-regulates expression of the kidney-specific ubiquitin ligase gene Rnf183 under hypertonic conditions in inner-medullary collecting duct cells

We previously reported that among the 37 RING finger protein (RNF) family members, RNF183 mRNA is specifically expressed in the kidney under normal conditions. However, the mechanism supporting its kidney-specific expression pattern remains unclear. In this study, we elucidated the mechanism of the transcriptional activation of murine Rnf183 in inner-medullary collecting duct cells. Experiments with anti-RNF183 antibody revealed that RNF183 is predominantly expressed in the renal medulla. Among the 37 RNF family members, Rnf183 mRNA expression was specifically increased in hypertonic conditions, a hallmark of the renal medulla. RNF183 up-regulation was consistent with the activation of nuclear factor of activated T cells 5 (NFAT5), a transcription factor essential for adaptation to hypertonic conditions. Accordingly, siRNA-mediated knockdown of NFAT5 down-regulated RNF183 expression. Furthermore, the -3,466 to -3,136-bp region upstream of the mouse Rnf183 promoter containing the NFAT5-binding motif is conserved among mammals. A luciferase-based reporter vector containing the NFAT5-binding site was activated in response to hypertonic stress, but was inhibited by a mutation at the NFAT5-binding site. ChIP assays revealed that the binding of NFAT5 to this DNA site is enhanced by hypertonic stress. Of note, siRNA-mediated RNF183 knockdown increased hypertonicity-induced caspase-3 activation and decreased viability of mIMCD-3 cells. These results indicate that (i) RNF183 is predominantly expressed in the normal renal medulla, (ii) NFAT5 stimulates transcriptional activation of Rnf183 by binding to its cognate binding motif in the Rnf183 promoter, and (iii) RNF183 protects renal medullary cells from hypertonicity-induced apoptosis.

NFAT5 Has a Job in the Brain

Nuclear factor of activated T cells 5 (NFAT5) has recently been classified as a new member of the Rel family. In addition, there are 5 more well-defined members (NF-κB and NFAT1-4) in the Rel family, which participate in regulating the expression of immune and inflammatory response-related genes. NFAT5 was initially identified in renal medullary cells where it regulated the expression of osmoprotective-related genes during the osmotic response. Many studies have demonstrated that NFAT5 is highly expressed in the nuclei of neurons in fetal and adult brains. Additionally, its expression is approximately 10-fold higher in fetal brains. With the development of detection technologies (laser scanning confocal microscopy, transgene technology, etc.), recent studies suggest that NFAT5 is also expressed in glial cells and plays a more diverse functional role. This article aims to summarize the current knowledge regarding the expression of NFAT5, its regulation of activation, and varied biological functions in the brain.

Macrophage-specific MHCII expression is regulated by a remote Ciita enhancer controlled by NFAT5

NFAT5 regulates macrophage MHCII expression by controlling the transcription of its coactivator Ciita through a remote enhancer. This mechanism differs from those previously found in DCs and B lymphocytes and distinguishes macrophages from these APC lineages.

MHCII in antigen-presenting cells (APCs) is a key regulator of adaptive immune responses. Expression of MHCII genes is controlled by the transcription coactivator CIITA, itself regulated through cell type–specific promoters. Here we show that the transcription factor NFAT5 is needed for expression of Ciita and MHCII in macrophages, but not in dendritic cells and other APCs. NFAT5-deficient macrophages showed defective activation of MHCII-dependent responses in CD4⁺ T lymphocytes and attenuated capacity to elicit graft rejection in vivo. Ultrasequencing analysis of NFAT5-immunoprecipitated chromatin uncovered an NFAT5-regulated region distally upstream of Ciita. This region was required for CIITA and hence MHCII expression, exhibited NFAT5-dependent characteristics of active enhancers such as H3K27 acetylation marks, and required NFAT5 to interact with Ciita myeloid promoter I. Our results uncover an NFAT5-regulated mechanism that maintains CIITA and MHCII expression in macrophages and thus modulates their T lymphocyte priming capacity.

Search for Upstream Cell Volume Sensors: The Role of Plasma Membrane and Cytoplasmic Hydrogel

The plasma membrane plays a prominent role in the regulation of cell volume by mediating selective transport of extra- and intracellular osmolytes. Recent studies show that upstream sensors of cell volume changes are mainly located within the cytoplasm that displays properties of a hydrogel and not in the plasma membrane. Cell volume changes occurring in anisosmotic medium as well as in isosmotic environment affect properties of cytoplasmic hydrogel that, in turn, trigger rapid regulatory volume increase and decrease (RVI and RVD). The downstream signaling pathways include reorganization of 2D cytoskeleton and altered composition of polyphosphoinositides located on the inner surface of the plasma membrane. In addition to its action on physico-chemical properties of cytoplasmic hydrogel, cell volume changes in anisosmotic conditions affect the ionic strength of the cytoplasm and the [Na⁺]_i/[K⁺]_i ratio. Elevated intracellular ionic strength evoked by long term exposure of cells to hypertonic environment resulted in the activation of TonEBP and augmented expression of genes controlling intracellular organic osmolyte levels. The role of Na⁺_i/K⁺_i -sensitive, Ca²⁺_i -mediated and Ca²⁺_i-independent mechanisms of excitation-transcription coupling in cell volume-adjustment remains unknown.

NFAT5-Regulated Macrophage Polarization Supports the Proinflammatory Function of Macrophages and T Lymphocytes

Macrophages are exquisite sensors of tissue homeostasis that can rapidly switch between pro- and anti-inflammatory or regulatory modes to respond to perturbations in their microenvironment. This functional plasticity involves a precise orchestration of gene expression patterns whose transcriptional regulators have not been fully characterized. We had previously identified the transcription factor NFAT5 as an activator of TLR-induced responses, and in this study we explore its contribution to macrophage functions in different polarization settings. We found that both in classically and alternatively polarized macrophages, NFAT5 enhanced functions associated with a proinflammatory profile such as bactericidal capacity and the ability to promote Th1 polarization over Th2 responses. In this regard, NFAT5 upregulated the Th1-stimulatory cytokine IL-12 in classically activated macrophages, whereas in alternatively polarized ones it enhanced the expression of the pro-Th1 mediators Fizz-1 and arginase 1, indicating that it could promote proinflammatory readiness by regulating independent genes in differently polarized macrophages. Finally, adoptive transfer assays in vivo revealed a reduced antitumor capacity in NFAT5-deficient macrophages against syngeneic Lewis lung carcinoma and ID8 ovarian carcinoma cells, a defect that in the ID8 model was associated with a reduced accumulation of effector CD8 T cells at the tumor site. Altogether, detailed analysis of the effect of NFAT5 in pro- and anti-inflammatory macrophages uncovered its ability to regulate distinct genes under both polarization modes and revealed its predominant role in promoting proinflammatory macrophage functions.

Hyperosmotic stress stimulates autophagy via polycystin-2

Various intracellular mechanisms are activated in response to stress, leading to adaptation or death. Autophagy, an intracellular process that promotes lysosomal degradation of proteins, is an adaptive response to several types of stress. Osmotic stress occurs under both physiological and pathological conditions, provoking mechanical stress and activating various osmoadaptive mechanisms. Polycystin-2 (PC2), a membrane protein of the polycystin family, is a mechanical sensor capable of activating the cell signaling pathways required for cell adaptation and survival. Here we show that hyperosmotic stress provoked by treatment with hyperosmolar concentrations of sorbitol or mannitol induces autophagy in HeLa and HCT116 cell lines. In addition, we show that mTOR and AMPK, two stress sensor proteins involved modulating autophagy, are downregulated and upregulated, respectively, when cells are subjected to hyperosmotic stress. Finally, our findings show that PC2 is required to promote hyperosmotic stress-induced autophagy. Downregulation of PC2 prevents inhibition of hyperosmotic stress-induced mTOR pathway activation. In conclusion, our data provide new insight into the role of PC2 as a mechanosensor that modulates autophagy under hyperosmotic stress conditions.

Inflammatory role of high salt level in tumor microenvironment (Review)

Chronic inflammation is known to play a critical role in cancer development and progression. High salt is known to mediate several chronic inflammatory diseases including hypertension, myocardial infarction, neurological ischemic attack, autoimmune diseases and cancers. High salt level is shown to induce angiogenesis and immune-dysfunction, both of which play a direct role in cancer proliferation. Furthermore, salt has been suggested to enhance Warburg-like metabolic phenotype in cancer cells and at the same time also induce pro-tumor MΦ2-macrophage phenotype. Recent studies have identified several molecular targets such as tonicity specific transcript factor NFAT5/TonEBP, sodium ion channel γENaC, and vascular endothelial growth factor, VEGF, which are upregulated under high salt external environment. These molecular targets offer futuristic therapeutic application in precision medicine. In this review, we discuss the current understanding of the salt mediated metabolic and immune dysfunctions playing a potential role in cancerous changes.

CD24 aggravates acute liver injury in autoimmune hepatitis by promoting IFN-γ production by CD4+ T cells

The T-cell-mediated immune response is implicated in many clinical hepatic injuries, such as autoimmune hepatitis and acute virus hepatitis. CD24 is widely expressed by different immune cells and plays an important role in the pathogenesis of many autoimmune diseases. However, the role of CD24 in T-cell-mediated liver injury has not been elucidated until now. Here we showed that CD24 deficiency protects mice from concanavalin A (ConA)-induced fulminant liver injury by reducing serum interferon-γ (IFN-γ) levels. CD24 expression by hepatic T cells was markedly increased following ConA challenge. Moreover, decreased IFN-γ production by hepatic CD4⁺ T cells in CD24-deficient mice was detected, which was correlated with downregulated phosphorylation of STAT1 in hepatic tissue. In vitro experiments also supported the conclusion that CD24 deficiency impaired IFN-γ production by CD4⁺ T cells following ConA, CD3/CD28 and phorbol myristate acetate/ionomycin stimulation. Our study suggests that CD24 deficiency confers hepatoprotection by decreasing CD4⁺ T-cell-dependent IFN-γ production in vivo, which suggests that CD24 might be a potential target molecule for reducing clinical hepatitis.

miR-20b Inhibits T Cell Proliferation and Activation via NFAT Signaling Pathway in Thymoma-Associated Myasthenia Gravis

Purpose. We examined the role of miR-20b in development of thymoma-associated myasthenia gravis, especially in T cell proliferation and activation. Materials and Methods. Using qRT-PCR, we assessed expression levels of miR-20b and its target genes in cultured cells and patient samples and examined the proliferation of cultured cells, using MTT cell proliferation assays and flow cytometry based cell cycle analysis. Activation of T cells was determined by both flow cytometry and qRT-PCR of activation-specific marker genes. Results. Expression of miR-20b was downregulated in samples of thymoma tissues and serum from patients with thymoma-associated myasthenia gravis. In addition, T cell proliferation and activation were inhibited by ectopic overexpression of miR-20b, which led to increased T cell proliferation and activation. NFAT5 and CAMTA1 were identified as targets of miR-20b. Expression levels of NFAT5 and CAMTA1 were inhibited by miR-20b expression in cultured cells, and the expression levels of miR-20b and NFAT5/CAMTA1 were inversely correlated in patients with thymoma-associated myasthenia gravis. Conclusion. miR-20b acts as a tumor suppressor in the development of thymoma and thymoma-associated myasthenia gravis. The tumor suppressive function of miR-20b in thymoma could be due to its inhibition of NFAT signaling by repression of NFAT5 and CAMTA1 expression.

Context-dependent regulation of Th17-associated genes and IFNγ expression by the transcription factor NFAT5

Stress-activated transcription factors influence T-cell function in different physiopathologic contexts. NFAT5, a relative of nuclear factor κB and the calcineurin-activated NFATc transcription factors, protects mammalian cells from hyperosmotic stress caused by the elevation of extracellular sodium levels. In T cells exposed to hypernatremia, NFAT5 not only induces osmoprotective gene products but also cytokines and immune receptors, which raises the question of whether this factor could regulate other T-cell functions in osmostress-independent contexts. Here we have used mice with a conditional deletion of Nfat5 in mature T lymphocytes to explore osmostress-dependent and -independent functions of this factor. In vitro experiments with CD4 T cells stimulated in hyperosmotic medium showed that NFAT5 enhanced the expression of IL-2 and the Th17-associated gene products RORγt and IL-23R. By contrast, NFAT5-deficient CD4 T cells activated in vivo by anti-CD3 antibody exhibited a different activation profile and were skewed towards enhanced interferon γ (IFNγ) and IL-17 expression and attenuated Treg responses. Using a model of experimental colitis, we observed that mice lacking NFAT5 in T cells exhibited exacerbated intestinal colitis and enhanced expression of IFNγ in draining lymph nodes and colon. These results show that NFAT5 can modulate different T-cell responses depending on stress conditions and stimulatory context.

Th17/Treg Imbalance Induced by Dietary Salt Variation Indicates Inflammation of Target Organs in Humans

The functions of T helper 17 (Th17) and regulatory T (Treg) cells are tightly orchestrated through independent differentiation pathways that are involved in the secretion of pro- and anti-inflammatory cytokines induced by high-salt dietary. However, the role of imbalanced Th17/Treg ratio implicated in inflammation and target organ damage remains elusive. Here, by flow cytometry analysis, we demonstrated that switching to a high-salt diet resulted in decreased Th17 cells and reciprocally increased Treg cells, leading to a decreased Th17/Treg ratio. Meanwhile, Th17-related pathway was down-regulated after one day of high salt loading, with the increase in high salt loading as shown by microarray and RT-PCR. Subsequently, blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) observed hypoxia in the renal medulla (increased R2^* signal) during high-salt loading, which was regressed to its baseline level in a step-down fashion during low-salt feeding. The flow-mediated vasodilatation (FMD) of the branchial artery was significantly higher on the first day of high salt loading. Collectively, these observations indicate that a short-term increase in dietary salt intake could induce reciprocal switches in Th17/Treg ratio and related cytokines, which might be the underlying cellular mechanism of high-salt dietary induced end organ inflammation and potential atherosclerotic risk.

NFAT5/STAT3 interaction mediates synergism of high salt with IL-17 towards induction of VEGF-A expression in breast cancer cells

Chronic inflammation has been considered an important player in cancer proliferation and progression. High salt (sodium chloride) levels have been considered a potent inducer of chronic inflammation. In the present study, the synergistic role of high salt with interleukin (IL)-17 towards induction of the inflammatory and angiogenic stress factor vascular endothelial growth factor (VEGF)-A was investigated. Stimulation of MCF-7 breast cancer cells with high salt (0.2 M NaCl) and sub-minimal IL-17 (1 ng/ml) enhanced the expression of VEGF-A (2.9 and 2.6-fold, respectively, P<0.05) compared with untreated cells. Furthermore, co-treatment with both high salt and sub-minimal IL-17 led to a 5.9-fold increase in VEGF-A expression (P<0.01), thus suggesting a synergistic role of these factors. VEGF-A promoter analysis and specific small interfering RNA knock-down of transcription factors revealed that high salt induced VEGF-A expression through nuclear factor of activated T-cells (NFAT)5, while IL-17 induced VEGF-A expression via signal transducer and activator of transcription (STAT)3 signaling mechanisms. Treatment of normal human aortic endothelial cells with the supernatant of activated MCF-7 cells enhanced cell migration and induced expression of migration-specific factors, including vascular cell adhesion protein, β1 integrin and cluster of differentiation 31. These data suggest that high salt levels synergize with pro-inflammatory IL-17 to potentially induce cancer progression and metastasis through VEGF-A expression. Therefore, low-salt diet, anti-NFAT5 and anti-STAT3 therapies may provide novel avenues for enhanced efficiency of the current cancer therapy.

Inflammatory signals induce the expression of tonicity-responsive enhancer binding protein (TonEBP) in microglia

Tonicity-responsive enhancer (TonE) binding protein (TonEBP) is known as an osmosensitive transcription factor that regulates cellular homeostasis during states of hypo- and hypertonic stress. In addition to its role in osmoadaptation, growing lines of evidence suggest that TonEBP might have tonicity-independent functions. In particular, a number of studies suggest that inflammatory stimuli induce the expression and activation of TonEBP in peripheral immune cells. However, whether TonEBP is expressed in microglia, resident immune cells of the central nervous system, is unknown. Here we show that inflammatory signals induce the expression of TonEBP in microglia both in vitro and in vitro. In cultured primary microglia, treatment with lipopolysaccharide (LPS), interferon-γ, and interleukin 4 increased the expression of TonEBP. Moreover, we found that stereotaxic injection of LPS into the substantia nigra region of rat brain increased TonEBP expression in OX-42-positive cells. Furthermore, expression of TonEBP was induced in OX-42-positive cells in a rat model of transient middle cerebral artery occlusion. Together these results show that the expression of TonEBP is regulated by inflammatory signals in mammalian brain, suggesting that TonEBP might play a part during neuroinflammation.

Repression of CD24 surface protein expression by oncogenic Ras is relieved by inhibition of Raf but not MEK or PI3K

CD24 is a dynamically regulated cell surface protein. High expression of CD24 leads to progression of lung, prostrate, colon, and pancreatic cancers, among others. In contrast, low expression of CD24 leads to cell proliferation and metastasis of breast cancer stem cells (BCSCs). Activating mutations in Ras are found in 30% of all human cancers. Oncogenic Ras constitutively stimulates the Raf, PI3K, and Ral GDS signaling pathways, leading to cellular transformation. Previous studies have shown that expression of oncogenic Ras in breast cancer cells generates CD24⁻ cells from CD24⁺ cells. However, the molecular mechanisms involved in the generation of CD24⁻ cells were not determined. Here, we demonstrate that oncogenic Ras (RasV12) expression suppresses CD24 mRNA, protein, and promoter levels when expressed in NIH/3T3 cells. Furthermore, activation of only the Raf pathway was sufficient to downregulate CD24 mRNA and protein expression to levels similar to those seen in with RasV12 expression. In contrast, activation of the PI3K pathway downregulated mRNA expression with a partial effect on protein expression whereas activation of the RalGDS pathway only partially affected protein expression. Surprisingly, inhibition of MEK with U0126 only partially restored CD24 mRNA expression but not surface protein expression. In contrast, inhibition of Raf with sorafenib did not restore CD24 mRNA expression but significantly increased the proportion of RasV12 cells expressing CD24. Therefore, the Raf pathway is the major repressor of CD24 mRNA and protein expression, with PI3K also able to substantially inhibit CD24 expression. Moreover, these data indicate that the levels of CD24 mRNA and surface protein are independently regulated. Although inhibition of Raf by sorafenib only partially restored CD24 expression, sorafenib should still be considered as a potential therapeutic strategy to alter CD24 expression in CD24⁻ cells, such as BCSCs.

Dynamic upregulation of CD24 in pre-adipocytes promotes adipogenesis

The development of mature adipocytes from pre-adipocytes is a highly regulated process. CD24 is a glycophosphatidylinositol-linked cell surface receptor that has been identified as a critical cell surface marker for identifying pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Here, we examined the role and regulation of CD24 during adipogenesis in vitro. We found that CD24 mRNA and protein expression is upregulated early during adipogenesis in the 3T3-L1 pre-adipocytes and in murine primary pre-adipocytes isolated from subcutaneous and visceral WAT, followed by downregulation in mature adipocytes. CD24 mRNA expression was found to be dependent on increased transcription due to increased promoter activity in response to activation of a pre-existing transcriptional regulator. Furthermore, either intracellular cAMP or dexamethasone were sufficient to increase expression in pre-adipocytes, while both additively increased CD24 expression. Preventing the increase in CD24 expression, by siRNA-mediated knock-down, resulted in fewer mature lipid-laden adipocytes and decreased expression of mature adipogenic genes. Therefore, conditions experienced during adipogenesis in vitro are sufficient to increase CD24 expression, which is necessary for differentiation. Overall, we conclude that the dynamic upregulation of CD24 actively promotes adipogenesis in vitro.

Immunodeficiency and autoimmune enterocolopathy linked to NFAT5 haploinsufficiency

The link between autoimmune diseases and primary immunodeficiency syndromes has been increasingly appreciated. Immunologic evaluation of a young man with autoimmune enterocolopathy and unexplained infections revealed evidence of immunodeficiency, including IgG subclass deficiency, impaired Ag-induced lymphocyte proliferation, reduced cytokine production by CD8(+) T lymphocytes, and decreased numbers of NK cells. Genetic evaluation identified haploinsufficiency of NFAT5, a transcription factor regulating immune cell function and cellular adaptation to hyperosmotic stress, as a possible cause of this syndrome. Inhibition or deletion of NFAT5 in normal human and murine cells recapitulated several of the immune deficits identified in the patient. These results provide evidence of a primary immunodeficiency disorder associated with organ-specific autoimmunity linked to NFAT5 deficiency.

NFAT as cancer target: mission possible?

The NFAT signaling pathway regulates various aspects of cellular functions; NFAT acts as a calcium sensor, integrating calcium signaling with other pathways involved in development and growth, immune response, and inflammatory response. The NFAT family of transcription factors regulates diverse cellular functions such as cell survival, proliferation, migration, invasion, and angiogenesis. The NFAT isoforms are constitutively activated and overexpressed in several cancer types wherein they transactivate downstream targets that play important roles in cancer development and progression. Though the NFAT family has been conclusively proved to be pivotal in cancer progression, the different isoforms play distinct roles in different cellular contexts. In this review, our discussion is focused on the mechanisms that drive the activation of various NFAT isoforms in cancer. Additionally, we analyze the potential of NFAT as a valid target for cancer prevention and therapy.

Nuclear factor of activated T-cells 5 increases intestinal goblet cell differentiation through an mTOR/Notch signaling pathway

This study demonstrates a role for nuclear factor of activated T-cell 5 (NFAT5) in the regulation of mTOR signaling in intestinal cells, which suggests that NFAT5 participates in the regulation of intestinal homeostasis via suppression of the mTORC1/Notch signaling pathway.

The intestinal mucosa undergoes a continual process of proliferation, differentiation, and apoptosis that is regulated by multiple signaling pathways. Previously, we have shown that the nuclear factor of activated T-cells 5 (NFAT5) is involved in the regulation of intestinal enterocyte differentiation. Here we show that treatment with sodium chloride (NaCl), which activates NFAT5 signaling, increased mTORC1 repressor regulated in development and DNA damage response 1 (REDD1) protein expression and inhibited mTOR signaling; these alterations were attenuated by knockdown of NFAT5. Knockdown of NFAT5 activated mammalian target of rapamycin (mTOR) signaling and significantly inhibited REDD1 mRNA expression and protein expression. Consistently, overexpression of NFAT5 increased REDD1 expression. In addition, knockdown of REDD1 activated mTOR and Notch signaling, whereas treatment with mTOR inhibitor rapamycin repressed Notch signaling and increased the expression of the goblet cell differentiation marker mucin 2 (MUC2). Moreover, knockdown of NFAT5 activated Notch signaling and decreased MUC2 expression, while overexpression of NFAT5 inhibited Notch signaling and increased MUC2 expression. Our results demonstrate a role for NFAT5 in the regulation of mTOR signaling in intestinal cells. Importantly, these data suggest that NFAT5 participates in the regulation of intestinal homeostasis via the suppression of mTORC1/Notch signaling pathway.

Leishmania infantum-chagasi activates SHP-1 and reduces NFAT5/TonEBP activity in the mouse kidney inner medulla

Visceral leishmaniasis patients have been reported to have a urine concentration defect. Concentration of urine by the renal inner medulla is essentially dependent on a transcription factor, NFAT5/TonEBP, because it activates expression of osmoprotective genes betaine/glycine transporter 1 (BGT1) and sodium/myo-inositol transporter (SMIT), and water channel aquaporin-2, all of which are imperative for concentrating urine. Leishmania parasites evade macrophage immune defenses by activating protein tyrosine phosphatases, among which SHP-1 is critical. We previously demonstrated that SHP-1 inhibits tonicity-dependent activation of NFAT5/TonEBP in HEK293 cells through screening a genome-wide small interfering (si) RNA library against phosphatases (Zhou X, Gallazzini M, Burg MB, Ferraris JD. Proc Natl Acad Sci USA 107: 7072-7077, 2010). We sought to examine whether Leishmania can activate SHP-1 and inhibit NFAT5/TonEBP activity in the renal inner medulla in a murine model of visceral leishmaniasis by injection of female BALB/c mice with a single intravenous dose of 5 × 10(5) L. chagasi metacyclic promastigotes. We found that SHP-1 is expressed in the kidney inner medulla. L. chagasi activates SHP-1 with an increase in stimulatory phosphorylation of SHP-1-Y536 in the region. L. chagasi reduces expression of NFAT5/TonEBP mRNA and protein as well as expression of its targeted genes: BGT1, SMIT, and aquaporin-2. The culture supernatant from L. chagasi metacyclic promastigotes increases SHP-1 protein abundance and potently inhibits NFAT5 transcriptional activity in mIMCD3 cells. However, L. chagasi in our animal model has no significant effect on urinary concentration. We conclude that L. chagasi, most likely through its secreted virulence factors, activates SHP-1 and reduces NFAT5/TonEBP gene expression, which leads to reduced NFAT5/TonEBP transcriptional activity in the kidney inner medulla.

Sfmbt2 10th intron-hosted miR-466(a/e)-3p are important epigenetic regulators of Nfat5 signaling, osmoregulation and urine concentration in mice

Sfmbt2-hosted miR-466a-3p and its close relatives are often among the most significantly up-regulated or down-regulated miRNAs in responses to numerous deleterious environmental stimuli. The exact roles of these miRNAs in cellular stress responses, however, are not clear. Here we showed that many Sfmbt2-hosted miRNAs were highly hypertonic stress responsive in vitro and in vivo. In renal medulla, water deprivation induced alterations in the expression of miR-466(a/b/c/e/p)-3p in a pattern similar to that of miR-200b-3p, a known regulator of osmoresponsive transcription factor Nfat5. Remarkably, exposure of mIMCD3 cells to an arginine vasopressin analog time-dependently down-regulated the expression of miR-466(a/b/c/e/p)-3p and miR-200b-3p, which provides a novel regulatory mechanism for these osmoresponsive miRNAs. In cultured mIMCD3 cells we further demonstrated that miR-466a-3p and miR-466g were capable of targeting Nfat5 by interacting with its 3'UTR. In transgenic mice overexpressing miR-466a-3p, significant down-regulation of Nfat5 and many other osmoregulation-related genes was observed in both the renal cortex and medulla. Moreover, sustained transgenic over-expression of miR-466a-3p was found to be associated with polydipsia, polyuria and disturbed ion homeostasis and kidney morphology. Since the mature sequence of miR-466a-3p is completely equivalent to that of miR-466e-3p and that the seed sequence of miR-466a-3p is completely equivalent to that of miR-297(a/b/c)-3p, miR-466d-3p, miR-467g and miR-669d-3p, and that miR-466a-3p differs from miR-466(b/c/p)-3p only in a 5' nucleotide, we propose that miR-466a-3p and many of its close relatives are important epigenetic regulators of renal Nfat5 signaling, osmoregulation and urine concentration in mice.

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.

NFAT5 represses canonical Wnt signaling via inhibition of β-catenin acetylation and participates in regulating intestinal cell differentiation

The intestinal mucosa undergoes a continual process of proliferation, differentiation, and apoptosis, which is regulated by multiple signaling pathways. The Wnt/β-catenin pathway has a critical role in this process. Previously, we have shown that the calcineurin-dependent nuclear factor of activated T cell (NFAT) is involved in the regulation of intestinal cell differentiation, as noted by the alteration of brush-border enzyme intestinal alkaline phosphatase (IAP) activity. Here, we show that calcineurin-independent NFAT5 interacts with β-catenin to repress Wnt signaling. We found that overexpression of NFAT5 inhibits, whereas knockdown of NFAT5 increases, TOPflash reporter activity and the expression of Wnt/β-catenin target genes, suggesting that NFAT5 inhibits Wnt signaling. In addition, we demonstrated that NFAT5 directly interacts with the C-terminal transactivation domain (TAD) of β-catenin, inhibits CBP interaction with β-catenin, and inhibits CBP-mediated β-catenin acetylation. Moreover, NFAT5 is expressed in the mucosa of human intestine, with the most pronounced staining in the most differentiated region near the epithelial surface. Knockdown of NFAT5 attenuated sodium butyrate (NaBT)-mediated induction of IAP and sucrase activities; overexpression of NFAT5 induced IAP promoter activity. In summary, we provide evidence showing that NFAT5 is a regulator of Wnt signaling. Importantly, our results suggest that NFAT5 regulation of intestinal cell differentiation may be through inhibition of Wnt/β-catenin signaling.

NFAT5 in cellular adaptation to hypertonic stress - regulations and functional significance

The Nuclear Factor of Activated T Cells-5 (NFAT5), also known as OREBP or TonEBP, is a member of the nuclear factors of the activated T cells family of transcription factors. It is also the only known tonicity-regulated transcription factor in mammals. NFAT5 was initially known for its role in the hypertonic kidney inner medulla for orchestrating a genetic program to restore the cellular homeostasis. Emerging evidence, however, suggests that NFAT5 might play a more diverse functional role, including a pivotal role in blood pressure regulation and the development of autoimmune diseases. Despite the growing significance of NFAT5 in physiology and diseases, our understanding of how its activity is regulated remains very limited. Furthermore, how changes in tonicities are converted into functional outputs via NFAT5 remains elusive. Therefore, this review aims to summarize our current knowledge on the functional roles of NFAT5 in osmotic stress adaptation and the signaling pathways that regulate its activity.

NFAT5 expression in bone marrow-derived cells enhances atherosclerosis and drives macrophage migration

OBJECTIVE

We have previously shown that the transcription factor, nuclear factor of activated T-cells 5 (NFAT5), regulates vascular smooth muscle cell phenotypic modulation, but the role of NFAT5 in atherosclerosis is unknown. Our main objective was to determine if NFAT5 expression in bone marrow (BM)-derived cells altered atherosclerotic development and macrophage function.

METHODS AND RESULTS

NFAT5(+/-)ApoE(-/-) mice were generated for in vivo atherosclerosis studies. Following high fat diet feeding, en face analysis of the thoracic aorta established that genome-wide NFAT5 haploinsufficiency reduced atherosclerotic lesion formation by 73%. BM transplant studies revealed that transplantation of NFAT5(+/-)ApoE(-/-) marrow into NFAT5(+/+)ApoE(-/-) mice resulted in a similar 86% reduction in lesion formation. In vitro functional analysis of BM-derived macrophages demonstrated that NFAT5 is required for macrophage migration, which is a key event in the propagation of atherosclerosis.

CONCLUSION

We have identified NFAT5 in BM-derived cells as a positive regulator of atherosclerotic lesion formation and macrophage function in the vasculature.

The role of hyperosmotic stress in inflammation and disease

Hyperosmotic stress is an often overlooked process that potentially contributes to a number of human diseases. Whereas renal hyperosmolarity is a well-studied phenomenon, recent research provides evidence that many non-renal tissues routinely experience hyperosmotic stress that may contribute significantly to disease initiation and progression. Moreover, a growing body of evidence implicates hyperosmotic stress as a potent inflammatory stimulus by triggering proinflammatory cytokine release and inflammation. Under physiological conditions, the urine concentrating mechanism within the inner medullary region of the mammalian kidney exposes cells to high extracellular osmolarity. As such, renal cells have developed many adaptive strategies to compensate for increased osmolarity. Hyperosmotic stress is linked to many maladies, including acute and chronic, as well as local and systemic, inflammatory disorders. Hyperosmolarity triggers cell shrinkage, oxidative stress, protein carbonylation, mitochondrial depolarization, DNA damage, and cell cycle arrest, thus rendering cells susceptible to apoptosis. However, many adaptive mechanisms exist to counter the deleterious effects of hyperosmotic stress, including cytoskeletal rearrangement and up-regulation of antioxidant enzymes, transporters, and heat shock proteins. Osmolyte synthesis is also up-regulated and many of these compounds have been shown to reduce inflammation. The cytoprotective mechanisms and associated regulatory pathways that accompany the renal response to hyperosmolarity are found in many non-renal tissues, suggesting cells are commonly confronted with hyperosmotic conditions. Osmoadaptation allows cells to survive and function under potentially cytotoxic conditions. This review covers the pathological consequences of hyperosmotic stress in relation to disease and emphasizes the importance of considering hyperosmolarity in inflammation and disease progression.

The Role of PEC Progenitors in ADPKD Progression

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease is a pathology mainly characterized by the progressive development and enlargement of cysts in each kidneys. Such as many adult epithelial tissue, renal tubule replaces damaged or death cells through the presence of stem/progenitor cells CD133(+)CD24(+) Obviously, in ADPKD the repair of damages is insufficient to block the disease, but renal stem cells could have a role in the pathology. In this study we investigate the localization and the involvement of cells CD133(+)CD24(+) in ADPKD progression.

METHODS AND RESULTS

Two normal kidneys and two ADPKD kidneys were examined. CD133 and CD24 expression was investigated by confocal microscopy and immunoblotting. Renal tissue and cells were analyzed. CD133 and CD24 have the same localization in ADPKD tissues and in normal kidneys: a subset of epithelial cells (PEC) of Bowman' s capsule and luminal side of tubules. It is interesting that CD133(+) CD24(+) cells are statistically more represented in ADPKD tubules (p＜ 0.001) and in healthy glomeruli (p= 0.0016). Cysts express CD133 and CD24.

CONCLUSIONS

Renal epithelial progenitors demonstrate to be involved in ADPKD pathogenesis but their role will have to be clarified and possibly managed to obtain improvement, or at least stabilization, of disease.

Gene expression induced by Toll-like receptors in macrophages requires the transcription factor NFAT5

NFAT5 regulates the induction of TLR-stimulated genes with constitutive binding to the Tnf promoter regardless of TLR ligation and recruitment to Nos2 and Il6 dependent on TLR activation and IKKb.

Toll-like receptors (TLRs) engage networks of transcriptional regulators to induce genes essential for antimicrobial immunity. We report that NFAT5, previously characterized as an osmostress responsive factor, regulates the expression of multiple TLR-induced genes in macrophages independently of osmotic stress. NFAT5 was essential for the induction of the key antimicrobial gene Nos2 (inducible nitric oxide synthase [iNOS]) in response to low and high doses of TLR agonists but is required for Tnf and Il6 mainly under mild stimulatory conditions, indicating that NFAT5 could regulate specific gene patterns depending on pathogen burden intensity. NFAT5 exhibited two modes of association with target genes, as it was constitutively bound to Tnf and other genes regardless of TLR stimulation, whereas its recruitment to Nos2 or Il6 required TLR activation. Further analysis revealed that TLR-induced recruitment of NFAT5 to Nos2 was dependent on inhibitor of κB kinase (IKK) β activity and de novo protein synthesis, and was sensitive to histone deacetylases. In vivo, NFAT5 was necessary for effective immunity against Leishmania major, a parasite whose clearance requires TLRs and iNOS expression in macrophages. These findings identify NFAT5 as a novel regulator of mammalian anti-pathogen responses.

Transcriptional regulation of gene expression during osmotic stress responses by the mammalian target of rapamycin

Although stress can suppress growth and proliferation, cells can induce adaptive responses that allow them to maintain these functions under stress. While numerous studies have focused on the inhibitory effects of stress on cell growth, less is known on how growth-promoting pathways influence stress responses. We have approached this question by analyzing the effect of mammalian target of rapamycin (mTOR), a central growth controller, on the osmotic stress response. Our results showed that mammalian cells exposed to moderate hypertonicity maintained active mTOR, which was required to sustain their cell size and proliferative capacity. Moreover, mTOR regulated the induction of diverse osmostress response genes, including targets of the tonicity-responsive transcription factor NFAT5 as well as NFAT5-independent genes. Genes sensitive to mTOR-included regulators of stress responses, growth and proliferation. Among them, we identified REDD1 and REDD2, which had been previously characterized as mTOR inhibitors in other stress contexts. We observed that mTOR facilitated transcription-permissive conditions for several osmoresponsive genes by enhancing histone H4 acetylation and the recruitment of RNA polymerase II. Altogether, these results reveal a previously unappreciated role of mTOR in regulating transcriptional mechanisms that control gene expression during cellular stress responses.

Tonicity-independent regulation of the osmosensitive transcription factor TonEBP (NFAT5)

Tonicity-responsive enhancer binding protein (TonEBP/nuclear factor of activated T-cells 5 [NFAT5]) is a Rel homology transcription factor classically known for its osmosensitive role in regulating cellular homeostasis during states of hypo- and hypertonic stress. A recently growing body of research indicates that TonEBP is not solely regulated by tonicity, but that it can be stimulated by various tonicity-independent mechanisms in both hypertonic and isotonic tissues. Physiological and pathophysiological stimuli such as cytokines, growth factors, receptor and integrin activation, contractile agonists, ions, and reactive oxygen species have been implicated in the positive regulation of TonEBP expression and activity in diverse cell types. These new data demonstrate that tonicity-independent stimulation of TonEBP is critical for tissue-specific functions like enhanced cell survival, migration, proliferation, vascular remodeling, carcinoma invasion, and angiogenesis. Continuing research will provide a better understanding as to how these and other alternative TonEBP stimuli regulate gene expression in both health and disease.