Immunosuppressive drugs prevent a rapid dephosphorylation of transcription factor NFAT1 in stimulated immune cells

Mechanical lesion activates newly identified NFATc1 in primary astrocytes: implication of ATP and purinergic receptors

Ca2+-dependent calcineurin is upregulated in reactive astrocytes in neuroinflammatory models. Therefore, the fact that the nuclear factor of activated T cells (NFAT) is activated in response to calcineurin qualifies this family of transcription factors with immune functions as candidates to mediate astrogliosis. Brain trauma induces a neuroinflammatory state in which ATP is released from astrocytes, stimulating calcium signalling. Our goal here is to characterize NFATc1 and NFATc2 in mouse primary astrocyte cultures, also exploring the implication of NFAT in astrocyte activation by mechanical lesion. Quantitative reverse transcriptase-polymerase chain reaction, Western blot analysis and immunofluorescence microscopy identified NFATc1 in astrocytes, but not NFATc2. Moreover, NFATc1 was expressed in the cytosol of resting astrocytes, whereas activation of the Ca2+-calcineurin pathway by ionomycin translocated NFATc1 to the nucleus, which is a requirement for activation. The implication of astrocytic NFAT in brain trauma was analysed using an in vitro scratch lesion model. Mechanical lesion caused a rapid NFATc1 translocation that progressed throughout the culture as a gradient and was maintained for at least 4 h. We also demonstrate that ATP, released by lesion, is a potent inducer of NFATc1 translocation and activation. Moreover, the use of P2Y receptor modulators showed that such ATP action is mediated by stimulation of several G(q)-protein-coupled P2Y purinergic receptors, among which P2Y(1) and P2Y(6) are included. In conclusion, this work provides evidence that newly identified NFATc1 is translocated in astrocytes in response to lesion following a pathway that involves ATP release and activation of metabotropic purinergic receptors.

Wnt and calcium signaling: beta-catenin-independent pathways

Wnt signaling is a complex pathway in which beta-catenin is typically viewed as a central mediator. However, within the past 15 years, at least three Wnt-mediated pathways have been proposed that function independent of beta-catenin. One pathway involves activation of calcium/calmodulin-dependent kinase II (CamKII) and protein kinase C (PKC). Another includes recruitment of heterotrimeric GTP-binding proteins to activate phospholipase C (PLC) and phosphodiesterase (PDE). Lastly, a pathway similar to the planar cell polarity (PCP) pathway in Drosophila has been identified that activates the Jun-N-terminal kinase (JNK) and, perhaps, small GTP-binding proteins. Calcium has been implicated as an important second messenger in all of these pathways. This review will focus on the role of calcium in Wnt signaling and, as a consequence, provide a limited overview of beta-catenin-independent Wnt signaling.

PICOT attenuates cardiac hypertrophy by disrupting calcineurin-NFAT signaling

PICOT (protein kinase C-interacting cousin of thioredoxin) was previously shown to inhibit pressure overload-induced cardiac hypertrophy, concomitant with an increase in ventricular function and cardiomyocyte contractility. The combined analyses of glutathione S-transferase pull-down experiments and mass spectrometry enabled us to determine that PICOT directly interacts with muscle LIM protein (MLP) via its carboxyl-terminal half (PICOT-C). It was also shown that PICOT colocalizes with MLP in the Z-disc. MLP is known to play a role in anchoring calcineurin to the Z-disc in the sarcomere, which is critical for calcineurin-NFAT (nuclear factor of activated T cells) signaling. We, therefore, suggested that PICOT may affect calcineurin-NFAT signaling through its interaction with MLP. Consistent with this hypothesis, PICOT, or more specifically PICOT-C, abrogated phenylephrine-induced increases in calcineurin phosphatase activity, NFAT dephosphorylation/nuclear translocation, and NFAT-dependent transcriptional activation in neonatal cardiomyocytes. In addition, pressure overload-induced upregulation of NFAT target genes was significantly diminished in the hearts of PICOT-overexpressing transgenic mice. PICOT interfered with MLP-calcineurin interactions in a dose-dependent manner. Moreover, calcineurin was displaced from the Z-disc, concomitant with an abrogated interaction between calcineurin and MLP, in the hearts of PICOT transgenic mice. Replenishment of MLP restored the hypertrophic responses and the increase in calcineurin phosphatase activity that was inhibited by PICOT in phenylephrine-treated cardiomyocytes. Finally, PICOT-C inhibited cardiac hypertrophy to an extent that was comparable to that of full-length PICOT. Taken together, these data suggest that PICOT inhibits cardiac hypertrophy largely by negatively regulating calcineurin-NFAT signaling via disruption of the MLP-calcineurin interaction.

Expression of the transcription factor NFAT2 in human neutrophils: IgE-dependent, Ca2+- and calcineurin-mediated NFAT2 activation

NFAT (nuclear factors of activated T cells) proteins constitute a family of transcription factors involved in mediating signal transduction. The presence of NFAT isoforms has been described in all cell types of the immune system, with the exception of neutrophils. In the present work we report for the first time the expression in human neutrophils of NFAT2 mRNA and protein. We also report that specific antigens were able to promote NFAT2 protein translocation to the nucleus, an effect that was mimicked by the treatment of neutrophils with anti-immunoglobulin E (anti-IgE) or anti-Fcepsilon-receptor antibodies. Antigens, anti-IgE and anti-FcepsilonRs also increased Ca2+ release and the intracellular activity of calcineurin, which was able to interact physically with NFAT2, in parallel to eliciting an enhanced NFAT2 DNA-binding activity. In addition, specific chemical inhibitors of the NFAT pathway, such as cyclosporin A and VIVIT peptide, abolished antigen and anti-IgE-induced cyclooxygenase-2 (COX2) gene upregulation and prostaglandin (PGE(2)) release, suggesting that this process is through NFAT. Our results provide evidence that NFAT2 is constitutively expressed in human neutrophils, and after IgE-dependent activation operates as a transcription factor in the modulation of genes, such as COX2, during allergic inflammation.

Expression analysis of nuclear factor of activated T cells (NFAT) during myeloid differentiation of CD34+ cells: regulation of Fas ligand gene expression in megakaryocytes

OBJECTIVE

Nuclear factor of activated T cells (NFAT) transcription factors belong to a family of five proteins that are primarily known for their central role in the regulation of inducible gene expression in activated T cells. Little information exists on the expression or function of NFAT family members in hematopoietic cells, during myeloid differentiation or in myeloid cells.

MATERIALS AND METHODS

In the present study, we establish a comprehensive expression profile of all five NFAT family members in human CD34+ hematopoietic progenitor cells and during their ex vivo differentiation into neutrophil, eosinophil, erythroid, and megakaryocytic lineages. Based on the observed expression pattern, the role of NFAT in Fas ligand gene expression in megakaryocytes was investigated.

RESULTS

When CD34+ cells are induced to differentiate into neutrophil granulocytes, expression of all NFAT family members is rapidly suppressed. In contrast, regulation of NFAT expression during eosinophil, erythroid, and megakaryocytic differentiation follows a family member- and lineage-specific pattern. Most obviously, transcript and protein levels of NFATc4 are specifically upregulated about 10-fold during megakaryocytic differentiation, while they remain almost undetectable in neutrophil, eosinophil, and erythroid cells. As a first evidence for a functional role for NFAT in this cell type, NFAT was found to be strictly required for both the constitutive and inducible expression of the Fas ligand gene in megakaryocytes.

CONCLUSION

The expression pattern of NFAT and its family member- and lineage-specific regulation during myeloid differentiation will prompt further studies on the role of NFAT in myeloid cells, particularly in megakaryocytes.

NIM811, a nonimmunosuppressive cyclosporine analogue, suppresses collagen production and enhances collagenase activity in hepatic stellate cells

BACKGROUND/AIMS

A recent decrease in patient survival has been reported among hepatitis C virus (HCV)-infected liver transplant recipients and this may be attributable to progression of fibrosis. We reported previously that cyclosporine suppressed the proliferation of, and collagen production in, hepatic stellate cells (HSCs). Here, we investigated the effects of NIM811, a cyclosporine analogue, on cell growth, collagen production and collagenase activity in HSCs.

METHODS

Rat HSCs and human HSC-derived TWNT-4 cells were cultured for the study. The expression of collagen, matrix metalloproteinase 1 (MMP-1) and tissue inhibitor of metalloproteinase-1 (TIMP-1) and collagenase activity was evaluated. Cell proliferation and apoptosis were measured. Phosphorylation of mitogen-activated protein kinases (MAPKs), Smad2 and Smad3 was evaluated. The expression of the tumour growth factor-beta (TGF-beta)-receptor and Smad7 genes was also evaluated.

RESULTS

NIM811, as well as cyclosporine, suppressed the transcription and synthesis of collagen and stimulated the production of MMP-1 with a concomitant enhancement of collagenase activity, although it did not change the expression of TIMP-1. NIM811 inhibited proliferation without induction of apoptosis. In the MAPKs and TGF-beta signalling pathways, NIM811 enhanced the phosphorylation of JNK and p38, but not extracellular signal-regulated kinases 1 and 2, and suppressed the phosphorylation of Smad2 and Smad3, accompanied by increased Smad7 transcription and decreased TGF-beta-receptor transcription.

CONCLUSION

These findings demonstrate that NIM811 not only suppresses collagen production and proliferation but also increases collagenase activity. These effects are accompanied by inhibition of TGF-beta signalling pathways.

Negative regulation of TCR signaling by NF-kappaB2/p100

The positive regulation of the NF-kappaB-signaling pathway in response to TCR stimulation has been well-studied. However, little is known about the negative regulation of this pathway in T cells. This negative regulation is crucial in controlling the duration of TCR signaling and preventing abnormal lymphocyte activation and proliferation. Therefore, understanding the negative regulation of TCR-mediated NF-kappaB signaling is essential in understanding the mechanisms involved in T cell function and homeostasis. TCR stimulation of human CD4+ T cells resulted in an increase in NF-kappaB2/p100 expression with no appreciable increase in p52, its cleavage product. Due to the presence of inhibitory ankyrin repeats in the unprocessed p100, this observation suggests that p100 may function as a negative regulator of the NF-kappaB pathway. Consistent with this hypothesis, ectopic expression of p100 inhibited TCR-mediated NF-kappaB activity and IL-2 production in Jurkat T cells. Conversely, knockdown of p100 expression enhanced NF-kappaB transcriptional activity and IL-2 production upon TCR activation. p100 inhibited the pathway by binding and sequestering Rel transcription factors in the cytoplasm without affecting the activity of the upstream IkappaB kinase. The kinetics and IkappaB kinase gamma/NF-kappaB essential modulator dependency of p100 induction suggest that NF-kappaB2/p100 acts as a late-acting negative-feedback signaling molecule in the TCR-mediated NF-kappaB pathway.

New insights into the pathophysiology of cyclosporine nephrotoxicity: a role of aldosterone

Cyclosporine A (CsA), a calcineurin inhibitor, has improved allograft survival in solid organ transplantation and has been increasingly applied in the management of autoimmune diseases. While marked progress has been made in patient and allograft survival rates, clinical use of CsA is often limited by its nephrotoxic effect, which can be presented as two distinct and well-characterized forms: acute and chronic nephrotoxicity. The acute form is characterized by renal vasoconstriction, induced by an imbalance of vasoactive substances release, which leads to renal dysfunction. This form is reversible. The chronic toxicity, in contrast, is characterized by the vasoconstriction plus the development of structural damage that includes arteriolopathy and tubulointerstitial fibrosis that are often not reversible. The exact mechanisms of these deleterious effects are not fully understood, but major advances have occurred over the last few years. Here we review the current literature regarding the pathogenesis and strategies that have been used to ameliorate renal injury in chronic CsA nephrotoxicity. Recent observations suggest that aldosterone plays a central role in the pathogenesis of CsA nephrotoxicity and that spironolactone could be a useful agent to prevent it. These studies and the use of mineralocorticoid receptor blockade are discussed.

Calcineurin inhibitors and rapamycin: cancer protection or promotion?

Since the introduction of cyclosporin A (CsA) in the early 1980s, the use of immunosuppressants has markedly increased. Already established drugs have proved effective in the treatment of a wide range of diseases outside transplantation medicine and new immunosuppressants have been developed for more specific indications such as psoriasis and atopic dermatitis. Patients in transplantation medicine as well as in dermatology have benefited significantly from systemic and topical application of both new and established drugs. But are these drugs without risks? Cancer-protecting effects have been reported for some of the available immunosuppressants. Conversely, other publications and the issue of a black box warning by the US Food and Drug Administration have increased concerns about cancer-promoting effects. Knowledge of the specific effects as well as adverse effects is paramount to ensure an application that is safe and beneficial for the patient. Here we review the mechanisms of action and therapeutic potential, and critically review recent literature with respect to possible carcinogenic side effects of systemic and topical CsA, tacrolimus, pimecrolimus and rapamycin.

Increased levels of NF-ATc2 differentially regulate CD154 and IL-2 genes in T cells from patients with systemic lupus erythematosus

T cells from patients with systemic lupus erythematosus (SLE) are characterized by heightened TCR-initiated free intracytoplasmic calcium responses. We demonstrate that activated T cells from SLE patients, but not from rheumatoid arthritis patients, displayed higher levels of the calcineurin-dependent transcription factor NF-ATc2 in the nucleus compared with control T cells. DNA NF-AT-binding activity was also increased, as was the amount of NF-ATc2 bound to the promoters of CD154 (CD40L) and IL-2 genes. Nevertheless, although high NF-ATc2 levels translated into higher CD154 transcription in SLE, IL-2 transcription was decreased. The absence of important transcriptional activators (AP-1, NF-kappaBeta) and the presence of transcriptional repressors (cAMP response element modulator) on the IL-2 promoter explain this dichotomous effect.

Calcineurin potentiates the activation of procaspase-3 by accelerating its proteolytic maturation

We have previously shown that procaspase-3 exists in a high molecular weight complex in neonatal rat brain. Here, we purify and identify the protein that interacts with procaspase-3 from rat neonatal cortex. We searched binding proteins to procaspase-3 from a cytosolic extract of neonatal rat brain using chromatogram, two-dimensional gel electrophoresis, and far Western immunoblot. Analysis by tandem mass spectrometry identified the protein as a regulatory subunit of calcineurin (calcineurin B). Overexpression of calcineurin B in HEK293 cells potentiated processing of caspase-3 and apoptosis triggered by tumor necrosis factor-alpha and cycloheximide treatment. In a cell-free system, overexpression of calcineurin B in HEK293 cells markedly increased processing of caspase-3 by cytochrome c. Immunodepletion of calcineurin B from cytosolic extracts from Jurkat cells decreased processing of caspase-3 by cytochrome c. Knockdown of calcineurin B by RNA interference resulted in reduced apoptosis in HEK293 cells but not in caspase-3-deficient MCF-7 cells. These results suggest that calcineurin B potentiates the activation of procaspase-3 by accelerating its proteolytic maturation.

Targeting calcineurin and associated pathways in cardiac hypertrophy and failure

Cardiac hypertrophy occurs in response to long-term increases in haemodynamic load related to a variety of physiological and pathological conditions. Cardiac hypertrophy developing in pathological conditions with increased load often progresses to a decompensated stage with cardiac contractile dysfunction, clinical signs of heart failure and premature death. Cardiac hypertrophy associated with adverse outcomes is said to be maladaptive. Conversely, there are settings where cardiac hypertrophy appears to be purely adaptive (e.g., hypertrophy in response to regular physical exercise). In these circumstances, hypertrophy is associated with preserved contractile performance and a favourable prognosis. Cardiac myocyte hypertrophy is controlled by growth factor receptors and mechanical stress sensors which activate a complex network of signalling pathways. These pathways promote a multitude of qualitative and quantitative changes in gene expression levels in cardiomyocytes. Reprogramming of gene expression, much more than cardiac (myocyte) hypertrophy per se, ultimately determines if cardiac hypertrophy will be adaptive or maladaptive. Pharmacological modification of gene expression in the hypertrophied heart may, therefore, be an attractive approach to prevent or even treat maladaptive hypertrophy and heart failure. Calcineurin is a serine-threonine phosphatase that is activated by sustained increases in [Ca2+]i in cardiomyocytes. Although it has been firmly established that calcineurin plays a critical role in the development of cardiac hypertrophy, the question of whether calcineurin activation serves an adaptive or maladaptive role is still unresolved. An answer to this question is crucial if calcineurin is to be developed as a drug target. The authors propose that calcineurin acts as a double-edged sword; excessive activation of calcineurin is maladaptive, its activation at endogenous levels and at specific subcellular microdomains, however, promotes adaptation. Calcineurin itself may, therefore, not be a convenient target for drug development. However, because maladaptive hypertrophy is ultimately a transcriptional disorder, definition of the transcriptional programme activated by distinct calcineurin activation levels may permit identification of novel, attractive drug targets.

Feedback inhibition of calcineurin and Ras by a dual inhibitory protein Carabin

Feedback regulation of adaptive immunity is a fundamental mechanism for controlling the overall output of different signal transduction pathways, including that mediated by the T-cell antigen receptor (TCR). Calcineurin and Ras are known to have essential functions during T-cell activation. However, how the calcineurin signalling pathway is terminated in the process is still largely unknown. Although several endogenous inhibitors of calcineurin have been reported, none fulfils the criteria of a feedback inhibitor, as their expression is not responsive to TCR signalling. Here we identify an endogenous inhibitor of calcineurin, named Carabin, which also inhibits the Ras signalling pathway through its intrinsic Ras GTPase-activating protein (GAP) activity. Expression of Carabin is upregulated on TCR signalling in a manner that is sensitive to inhibitors of calcineurin, indicating that Carabin constitutes part of a negative regulatory loop for the intracellular TCR signalling pathway. Knockdown of Carabin by short interfering RNA led to a significant enhancement of interleukin-2 production by antigen-specific T cells in vitro and in vivo. Thus, Carabin is a negative feedback inhibitor of the calcineurin signalling pathway that also mediates crosstalk between calcineurin and Ras.

Competition Effects Shape the Response Sensitivity and Kinetics of Phosphorylation Cycles in Cell Signaling

Phosphorylation cycles are a core component of cell signaling networks. The response sensitivity and kinetics of these cycles are controlled by thermodynamic, kinetic, and structural factors, including binding affinities, catalytic activities, and the phosphorylation order of multiple sites. Based on mathematical models, we interpret the role of these factors in terms of competition effects. For the regulation of a single phosphorylation site, two kinds of competition effects turn out to shape behavior: the competition between kinase and phosphatase to bind the substrate, and the competition between the distinct phosphorylation forms of the substrate for binding to either enzyme. Depending on the concentrations and mutual affinities of the enzymes and the target, the response function can be graded, ultrasensitive, or biphasic. In multiply phosphorylatable proteins, additional factors generating competition effects are present and more complex responses can be obtained. For example, the combination of a cooperative kinetics with the conditions for zero-order ultrasensitivity may yield a bistable response. We show that a repeated competition between kinase and phosphatase for binding the substrate and/or between the phosphorylation and dephosphorylation reactions at each phosphorylation site generally result in a threshold response. The phosphorylation time is also strongly affected by the kinetic design of the cycle. In particular, threshold responses are generally associated with very long phosphorylation times. We also argue here that a description in terms of elementary binding and reaction steps is required for an appropriate analysis of these cycles in cell signaling.

Distinct role of IL-3 promoter and enhancer region in murine mast cells

Crosslinking of Fcvarepsilon receptor on mast cells induces IL-3 gene expression with the concentration dependent of intracellular calcium, but its regulatory mechanism remains unclear. Here, we found that phorbol 12-myristate 13-acetate (PMA) alone did not induce IL-3 gene expression, but potentiated A23187-induced IL-3 gene expression. Interestingly, the A23187-induced IL-3 promoter activity was suppressed by PMA, but it was enhanced when IL-3 promoter contained enhancer region, a DH site. While IL-3 mRNA expression was increased by A23187 and PMA in a dose-dependent manner, the promoter activity appeared all or none in all doses of A23187 and PMA. IL-3 promoter region between -293 and -150bp was responsible for A23187-induced gene expression and PMA- or cyclosporin A (CsA)-mediated suppression. Taken together, IL-3 gene expression was primarily regulated at the transcriptional level, which was differentially controlled by a restricted promoter and enhancer region.

NFAT and NFkappaB activation in T lymphocytes: a model of differential activation of gene expression

Mathematical models for the regulation of the Ca(2+)-dependent transcription factors NFAT and NFkappaB that are involved in the activation of the immune and inflammatory responses in T lymphocytes have been developed. These pathways are important targets for drugs, which act as powerful immunosuppressants by suppressing activation of NFAT and NFkappaB in T cells. The models simulate activation and deactivation over physiological concentrations of Ca(2+), diacyl glycerol (DAG), and PKCtheta using single and periodic step increases. The model suggests the following: (1) the activation NFAT does not occur at low frequencies as NFAT requires calcineurin activated by Ca(2+) to remain dephosphorylated and in the nucleus; (2) NFkappaB is activated at lower Ca(2+) oscillation frequencies than NFAT as IkappaB is degraded in response to elevations in Ca(2+) allowing free NFkappaB to translocate into the nucleus; and (3) the degradation of IkappaB is essential for efficient translocation of NFkappaB to the nucleus. Through sensitivity analysis, the model also suggests that the largest controlling factor for NFAT activation is the dissociation/reassociation rate of the NFAT:calcineurin complex and the translocation rate of the complex into the nucleus and for NFkappaB is the degradation/resynthesis rate of IkappaB and the import rate of IkappaB into the nucleus.

Molecular cloning, characterization and expression analysis of grass carp (Ctenopharyngodon idellus) NF45 (ILF2) cDNA, a subunit of the nuclear factor of activated T-cells (NF-AT)

NF45 (ILF2) and NF90 (ILF3) regulate the IL-2 gene transcription via interaction with the antigen receptor response element. Much work on NF45 has been done in human and mammals while little in fish. In the present study, we have cloned and characterized the full-length cDNA of NF45 in grass carp (Ctenopharyngodon idellus). The grass carp NF45 cDNA of 1563bp contains a short 5'UTR of 24bp, a 3'UTR of 375bp and an open reading frame of 1164bp coding for a protein of 387 aa with a predicted molecular mass of 42.8kDa. The encoded protein shares 86.3-96.7% identities to other homologues. RT-PCR was optimized to estimate the expression level of NF45 in grass carp. The results showed that NF45 is constitutively expressed in most selected tissues, including head kidney, spleen, heart, brain, liver, and gill, although low levels were observed in spleen, liver and gill. The ubiquitous expression of NF45 is consistent with a postulated role in gene regulation at the level of transcription. Stimulating the fish with PHA significantly up-regulated the expression of NF45 in most tissues examined, which potentially indicated that NF45 was involved in the immune responses triggered by PHA.

Proteome modifications of the medicinal leech nervous system under bacterial challenge

Once considered as lacking intrinsic immune mechanisms, the CNS of vertebrates is now known to be capable of mounting its own innate immune response. Interestingly, while invertebrates have been very useful in the interpretation of general vertebrate innate immunity mechanisms, only scarce data are available on the immune response of nervous tissue within this group. This study provides new data on the innate immune response of medicinal leech Hirudo medicinalis CNS. We identified several spots in 2-D gels of leech CNS proteins that showed specific changes following bacterial challenge, thus demonstrating the ability of the leech nervous system to mount a response to an immune stress. Protein identifications were based on comparison of sequence data with publicly available databases and a recently established leech ESTs database. The broad nature of the identified proteins suggests a clear involvement of cytoskeletal rearrangements, endoplasmic reticulum stress, modulation of synaptic activity and calcium mobilization, all during the first 24 hours of this response. Moreover, several of these proteins are specifically expressed in glial cells, suggesting an important role for glial cells in the immune response of the leech nervous system, similar to what has been observed in vertebrates.

Nonsteroid immune modulators and bone disease

Glucocorticoids have been the main agents for preventing organ rejection,but unfortunately they possess serious side effects. Newer immunosuppressive agents have therefore been introduced to overcome these effects and have had a dramatic impact on reducing the incidence of organ rejection, enhancing donor organ acceptance, and hence patient survival posttransplantation. However, calcineurin inhibitors (CIs), such as cyclosporine and tacrolimus, also have serious effects causing rapid and severe bone loss in animal models and humans. The mechanism accounting for this action is unclear at present, but the role of T lymphocyte action via RANKL seems to be of essence in triggering bone loss. The mechanism is complex and in vitro studies often produce results that are opposite to those seen in vivo. In addition to acute, rapid, and severe bone loss (ARSBL), the clinical picture shows an extremely high incidence of fractures at all sites, and depends upon the organ transplanted, preexisting bone disease, interval before transplantation, and the dose and duration of multiple immunosuppressive drugs. Other immune-modifying drugs, such as azathioprine, mycophenolate mofetil, and sirolimus, which are used in conjunction with glucocorticoids and CIs have not been shown to promote bone loss experimentally or clinically. With the exception of glucocorticoids, all of the agents discussed here demand further investigation with regard to their effects on bone health in the clinical setting.

Human tonsillar tissue block cultures differ from autologous tonsillar cell suspension cultures in lymphocyte subset activation and cytokine gene expression

Lymphoid tissues cultured either as tissue blocks or as cell suspensions are used to study the behaviour of immune cells within their habitat. The preservation of tissue structures in tissue blocks, which is considered to be a major advantage, has been poorly defined. We characterised the morphological evolution of tissue cultures from human palatine tonsils and compared their lymphocyte subsets and the constitutive cytokine gene expression to those in autologous tonsillar single-cell suspension cultures over time, and after adding cyclosporin A (CsA) to mimic the situation in individuals treated with immunosuppressive drugs. Density and morphology of follicles were conserved up to 4 days, during which tissue cultures exhibited similar cell viability as suspension cultures, but a significantly less frequent increase of CD95 expression in T cells, smaller variation of the proportion of CD4(+) cells and better CD21(+)/CD23(-) B-cell survival. Treatment with cyclosporin A at higher concentrations resulted in superior histologic preservation of lymphoid tissue structures and seemed to further prevent the expression of CD95 by CD3(+) cells and the activation in tissue culture of CD21(+) cells. Constitutive gene expression levels of the stromal cytokines interleukin (IL)-1beta and interleukin-6 in tissue culture were significantly higher than those in suspension cultures. These results suggest that tonsillar tissue cultures preserve their structure only for a limited time, during which they more closely reflect processes in vivo, including a state of iatrogenic immunosuppression, than do their cell suspension counterparts.

Abnormal intracellular distribution of NFAT1 in T lymphocytes from patients with systemic lupus erythematosus and characteristic clinical features

Systemic lupus erythematosus (SLE) presents various clinical features; however, underlying mechanisms remain unclear. In the immunity of SLE, impaired T cell receptor (TCR) signaling and altered cytokine production are in the center of pathogenesis, although, little is known about NFAT (nuclear factor of activated T cells) in lupus T lymphocytes. TCR stimulation activates NFAT1 through Ca2+/calcineurin (Cn) pathway, facilitating nuclear translocation of NFAT1 from cytosol. Therefore, we investigated relationship of disease activity/features and intracellular NFAT1 localization in T lymphocytes from active lupus patients by fractionation. Results showed no significant relationship between disease activity and NFAT1 distribution. However, interestingly, we observed skewed NFAT1 distribution in pellet in patients with active lupus nephritis or pleuritis. In vitro cyclosporin A treatment suggested autonomously activated Ca2+/Cn pathway in lupus T lymphocytes. Considering these results, NFAT1 might be presenting the clinical heterogeneity in SLE.

Thrombin-induced autoinhibitory factor, Down syndrome critical region-1, attenuates NFAT-dependent vascular cell adhesion molecule-1 expression and inflammation in the endothelium

Activation and dysfunction of the endothelium underlie many vascular disorders including atherosclerosis, tumor growth, and inflammation. We recently reported that thrombin and vascular endothelial growth factor, but not tumor necrosis factor-alpha, results in dramatic up-regulation of Down syndrome critical region (DSCR)-1 gene in endothelial cells, a negative feedback regulator of calcineurin-NFAT signaling. Constitutive expression of DSCR-1 in activated endothelial cells markedly impaired NFAT nuclear localization, proliferation, tube formation, and tumor growth. The goal of the present study was to elucidate the relative roles of NFAT/DSCR-1 and NF-kappaB/I-kappaB in mediating thrombin-responsive gene expression in endothelial cells. DNA microarrays of thrombin-treated human umbilical vein endothelial cells overexpressing DSCR-1 or constitutive active IkappaBalpha revealed genes that were dependent on NFAT and/or NF-kappaB activity. Vascular cell adhesion molecule-1 was inhibited both by DSCR-1 and I-kappaB at the level of mRNA, protein, promoter activity, and function (monocyte adhesion). Using a combination of transient transfections, electrophoretic mobility shift assays, and chromatin immunoprecipitation, thrombin was shown to induce time-dependent coordinate binding of RelA and NFATc to a tandem NF-kappaB element in the upstream promoter region of vascular cell adhesion molecule-1. Together, these findings suggest that thrombin-mediated activation of endothelial cells involves an interplay between NFAT and NF-kappaB signaling pathways and their negative feedback inhibitors, DSCR-1 and I-kappaB, respectively. As natural brakes in the inflammatory process, DSCR-1 and I-kappaB may lend themselves to therapeutic manipulation in vasculopathic disease states.

Evaluation of the anti-hepatitis C virus effects of cyclophilin inhibitors, cyclosporin A, and NIM811

Hepatitis C virus (HCV) is a major causative agent of hepatocellular carcinoma. We recently discovered that the immunosuppressant cyclosporin A (CsA) and its analogue lacking immunosuppressive function, NIM811, strongly suppress the replication of HCV in cell culture. Inhibition of a cellular replication cofactor, cyclophilin (CyP) B, is critical for its anti-HCV effects. Here, we explored the potential use of CyP inhibitors for HCV treatment by analyzing the HCV replicon system. Treatment with CsA and NIM811 for 7 days reduced HCV RNA levels by 2-3 logs, and treatment for 3 weeks reduced HCV RNA to undetectable levels. NIM811 exerted higher anti-HCV activity than CsA at lower concentrations. Both CyP inhibitors rapidly reduced HCV RNA levels even further in combination with IFNalpha without modifying the IFNalpha signal transduction pathway. In conclusion, CyP inhibitors may provide a novel strategy for anti-HCV treatment.

NFAT induces breast cancer cell invasion by promoting the induction of cyclooxygenase-2

The NFAT (nuclear factor of activated T cells) family of transcription factors plays a fundamental role in the transcriptional regulation of the immune response. However, NFATs are ubiquitously expressed, and recent evidence points to their important functions in human epithelial cells and carcinomas. Specifically, NFAT has been shown to be active in human breast and colon carcinoma cells and to promote their invasion through Matrigel. The mechanisms by which NFAT promotes invasion have not been defined. To identify NFAT target genes that induce carcinoma invasion, we have established stable breast cancer cell lines that inducibly express transcriptionally active NFAT. Gene expression profiling by cDNA microarray of cells induced to express NFAT revealed up-regulation of cyclooxygenase-2 (COX-2). Increased NFAT expression and activity induced COX-2 expression as well as prostaglandin E2 synthesis. This induction was more prominent when NFAT was activated by phorbol 12-myristate 13-acetate and calcium ionophore ionomycin and was blocked by the NFAT antagonist cyclosporin A. Breast cancer cells with elevated COX-2 expression showed increased invasion through Matrigel, and this was reduced in cells treated with COX-2 inhibitors. Conversely, loss of NFAT1 protein expression using small interfering RNA led to a reduction in COX-2 transcription and reduced invasion. Similarly, Matrigel invasion was reduced in cells in which COX-2 expression was reduced using specific siRNA. These findings demonstrate that NFAT promotes breast cancer cell invasion through the induction of COX-2 and the synthesis of prostaglandins.

Calcineurin dephosphorylates the C-terminal region of filamin in an important regulatory site: A possible mechanism for filamin mobilization and cell signaling

Filamin is a phosphoprotein that organizes actin filaments into networks. We report that a purified C-terminal recombinant region of filamin is a suitable substrate for calcineurin in vitro. Furthermore, 1 microM cyclosporin A (CsA), a specific calcineurin inhibitor, reduced the dephosphorylation of the recombinant fragment in 293FT cells. Mutagenesis analysis showed that a dephosphorylation step occurred in Ser 2152, which was previously shown to provide resistance to calpain cleavage when endogenous PKA is activated. In contrast, phosphorylation of Ser 2152 was recently reported to be necessary for membrane dynamic changes. In this regard, we found that CsA protects filamin in platelets from calpain degradation. Results could be combined with available information in a single model, assuming that some of the peptide fragments released by calcineurin-regulated calpain action could mediate actions in downstream pathways, which may help to resolve the controversies reported on the role of filamin phosphorylation in actin dynamics.

Kinetic models of phosphorylation cycles: A systematic approach using the rapid-equilibrium approximation for protein–protein interactions

Activation-inactivation cycles of signalling proteins and transcription factors catalysed by kinases and phosphatases are a core component of cellular signal transduction. We present a systematic kinetic analysis of a phosphorylation cycle that starts from the description of elementary protein-protein interaction and catalytic steps. A rapid-equilibrium approximation for protein interactions is used to reduce the set of parameters. The resulting description consists of a kinetic equation for the phosphorylation of the target and a set of conservation conditions for kinase and phosphatase. Generally no explicit rate laws exist for the two enzymes; linear or Michaelis-Menten rate equations can be obtained in special cases. Key parameters that determine the stimulus-response curve and the response time of the cycle are the concentrations of kinase and phosphatase relative to the target protein and the affinities of the two enzymes for the different phosphorylation states of the target. Characterizing the response curve by the global response coefficient, we obtain a phase diagram that shows the existence of three kinds of behaviours: graded, ultrasensitive, and a previously undescribed biphasic response. Two kinds of competition effect turn out to shape the behaviour: (1) the degree of product inhibition of each enzyme, and (2) the competition between kinase and phosphatase to bind the target protein, as determined by their relative target affinities. The approach outlined here may be useful also for analysing more complex systems, including multiple phosphorylation and kinase cascades.

Activation of the Ca(2+)/calcineurin/NFAT2 pathway controls smooth muscle cell differentiation

Cellular mechanisms controlling smooth muscle cells (SMCs) phenotypic modulation are largely unknown. Intracellular Ca2+ movements are essential to ensure SMC functions; one of the roles of Ca2+ is to regulate calcineurin, which in turn induces nuclear localization of the nuclear factor of activated T-cell (NFAT). In order to investigate, during phenotypic differentiation of SMCs, the effect of calcineurin inhibition on NFAT2 nuclear translocation, we used a culture model of SMC differentiation in serum-free conditions. We show that the treatment of cultured SMC with the calcineurin inhibitor cyclosporine A induced their dedifferentiation while preventing their differentiation. These findings suggest that nuclear translocation of NFAT2 is dependent of calcineurin activity during the in vitro SMC differentiation kinetic and that the nuclear presence of NFAT2 is critical in the acquisition and maintenance of SMC differentiation.

The molecular regulation of exercised-induced muscle fibre hypertrophy in the common carp: Expression of MyoD, PCNA and components of the calcineurin-signalling pathway

Growth was investigated over 16 d in juvenile common carp (Cyprinus carpio L.) held in either static water (tank rested, TR16) or exercised in a flume at 2.5-3.2 body lengths s-1 for 18 h a day (exercised, E16). Relative to the start of the experiment (TR0), the TR16 group showed a 31% increase in body mass (specific growth rate, 1.57% d-1), whereas there was no net change in the E16 group. There was, however, a significant exercise-induced hypertrophy of slow muscle fibres with average fibre cross-sectional area (FCSA) increasing by 35% in the E16 group, compared with 11% in the TR16 group. In contrast, FCSA of fast muscle fibres increased by 34% in the TR16 group compared to just 18% in the E16 group. The relative concentrations and subcellular localisation of proteins hypothesised to play a role in the regulation of muscle growth were measured. MyoD concentration was similar in the TR0, TR16 and E16 groups in both slow and fast muscle. However, there was a small (5%-10%) but statistically significant increase in nuclear localisation of MyoD in those groups showing a significant increase in FCSA over the time course of the experiment. PCNA concentration was 31% and 12% higher in the TR16 than in either the TR0 or E16 groups for slow and fast muscle, respectively. Exercise resulted in a approximately 10% increase in nuclear factor of T-cells (NFAT2) concentration in slow muscle but no change in NFAT2 localisation. Calcineurin B concentration was similar in tank rested and exercised groups. The results do not support a major role for the calcineurin-signalling pathway in the regulation of muscle hypertrophy in the common carp.

IFN-γ Production by CD8+ T Cells Depends on NFAT1 Transcription Factor and Regulates Th Differentiation

CD8+ T lymphocytes are excellent sources of IFN-gamma; however, the molecular mechanisms that dictate IFN-gamma expression upon TCR stimulation in these cells are not completely understood. In this study, we evaluated the involvement of NFAT1 in the regulation of IFN-gamma gene expression in murine CD8+ T cells and its relevance during Th differentiation. We show that CD8+, but not CD4+, T cells, represent the very first source of IFN-gamma upon primary T cell activation, and also that the IFN-gamma produced by naive CD8+ T cells may enhance CD4+ Th1 differentiation in vitro. TCR stimulation rapidly induced IFN-gamma expression in CD8+ T lymphocytes in a cyclosporin A-sensitive manner. Evaluation of CD8+ T cells showed that calcium influx alone was sufficient to activate NFAT1 protein, transactivate IFN-gamma gene promoter, and induce IFN-gamma production. In fact, NFAT1-deficient mice demonstrated highly impaired IFN-gamma production by naive CD8+ T lymphocytes, which were totally rescued after retroviral transduction with NFAT1-encoding vectors. Moreover, NFAT1-dependent IFN-gamma production by the CD8+ T cell compartment was crucial to control a Th2-related response in vivo, such as allergic inflammation. Consistently, CD8alpha- as well as IFN-gamma-deficient mice did not mount a Th1 immune response and also developed in vivo allergic inflammation. Our results clearly indicate that IFN-gamma production by CD8+ T cells is dependent of NFAT1 transcription factor and may be an essential regulator of Th immune responses in vivo.

Localisation of high acid phosphotyrosine phosphatase activity in afferent arterioles and glomeruli of human kidney

Endothelial cells contain a variety of specific protein tyrosine phosphatases and an acid phosphatase differing from other known phosphatases. The highest activity of this acid phosphatase with artificial or unspecific substrates is present in the afferent arterioles and glomeruli of human kidney, and the activity is inhibited by nephrotoxic fluoride concentrations, suggesting that it plays a role in circulatory regulation. Here the activity was characterised with physiological substrates. An incubation mixture containing phosphotyrosine or phosphoserine was stable at pH 5 when phosphate-precipitating lead was chelated with tartrate. The activities were studied in frozen sections. Only phosphotyrosine was hydrolysed by some cells. High activity of tartrate-resistant phosphotyrosine phosphatase was present in lymphocytes, endothelial cells of afferent arterioles, and glomerular mesangial cells of kidney, decidual cells, and alveolar macrophages. In lymphocytes the activity was fluoride-resistant and vanadate-sensitive, in other cells fluoride- and vanadate-sensitive. In decidual cells and alveolar macrophages, the activity is due to specific osteoclastic/macrophagic tartrate-resistant acid phosphatase, in lymphocytes to specific protein tyrosine phosphatases, and in endothelial and mesangial cells to a protein tyrosine phosphatase-like acid phosphatase. The results suggest that in endothelial cells of the afferent arterioles, mesangial cells, and lymphocytes the cellular activities are regulated by high constitutive phosphotyrosine phosphatase activity and this may be related to the exceptional cyclosporin A sensitivity of these cells.

Bifurcated converging pathways for high Ca2+- and TGFbeta-induced inhibition of growth of normal human keratinocytes

Growth suppression of normal human keratinocytes by high Ca2+ or TGFbeta was shown to be mediated by p21WAF1/CIP1 and Sp1 [Pardali, K., et al. (2000) J. Biol. Chem. 275, 29244-29256; Santini, M. P., Talora, C., Seki, T., Bolgan, L. & Dotto, G. P. (2001) Proc. Nat. Acad. Sci. USA 98, 9575-9580; Al-Daraji, W. I., Grant, K. R., Ryan, K., Saxton, A., & Reynolds, N. J. (2002) J. Invest. Dermatol. 118, 779-788]. We previously demonstrated that S100C/A11 is a key mediator for growth inhibition of normal human epidermal keratinocytes (NHK) triggered by high Ca2+ or TGFbeta [Sakaguchi, M., et al. (2003) J. Cell Biol. 163, 825-835; Sakaguchi, M., et al. (2004) 164, 979-984]. On exposure of NHK cells to either agent, S100C/A11 is transferred to nuclei, where it induces p21WAF1/CIP1 through activation of Sp1/Sp3. In the present study, we found that high Ca2+ activated NFAT1 through calcineurin-dependent dephosphorylation. In growing NHK cells, Krueppel-like factor (KLF)16, a member of the Sp/KLF family, bound to the p21WAF1/CIP1 promoter and, thereby, inhibited the transcription of p21(WAF1/CIP1). Sp1 complexed with NFAT1 in high Ca2+-treated cells or with Smad3 in TGFbeta1-treated cells, but not Sp1 alone, replaced KLF16 from the p21WAF1/CIP1 promoter and transcriptionally activated the p21WAF1/CIP1 gene. Thus, high Ca2+ and TGFbeta1 have a common S100C/A11-mediated pathway in addition to a unique pathway (NFAT1-mediated pathway for high Ca2+ and Smad-mediated pathway for TGFbeta1) for exhibiting a growth inhibitory effect on NHK cells, and both pathways were shown to be indispensable for growth inhibition.

Identification of a peptide fragment of DSCR1 that competitively inhibits calcineurin activity in vitro and in vivo

Calcineurin phosphatase activity regulates the nuclear localization of the nuclear factor of activated T cells (NFAT) family of transcription factors during immune challenge. Calcineurin inhibitors, such as the cyclosporin A-cyclophilin A and FK506-FKBP12 complexes, regulate this enzymatic activity noncompetitively by binding at a site distinct from the enzyme active site. A family of endogenous protein inhibitors of calcineurin was recently identified and shown to block calcineurin-mediated NFAT nuclear localization and transcriptional activation. One such inhibitor, Down Syndrome Critical Region 1 (DSCR1), functions in T cell activation, cardiac hypertrophy, and angiogenesis. We have identified a small region of DSCR1 that is a potent inhibitor of calcineurin activity in vitro and in vivo.

Transcription inhibitors in inflammation

Advances in molecular medicine have revealed a key role for altered gene expression in the aetiology of many inflammatory diseases, including asthma, rheumatoid arthritis, inflammatory bowel disease and sepsis. Until recently, however, modulation of gene transcription has not been the subject of directed pharmaceutical research efforts. Notwithstanding, it is clear that the efficacy of several well-established anti-inflammatory therapeutics is mediated through their ability to modulate gene transcription. Understanding the mechanisms of action of these therapeutics and defining new gene regulatory pathways has stimulated a new wave of anti-inflammatory drug discovery. This update aims to cover our current understanding of transcription inhibitors in inflammation, including the mechanism of action of established therapeutics and the properties of new chemical entities recently described in the literature.

The role of myostatin and the calcineurin-signalling pathway in regulating muscle mass in response to exercise training in the rainbow troutOncorhynchus mykissWalbaum

Rainbow trout Oncorhynchus mykiss Walbaum were exercised at 0.8 and 1.6 body lengths s-1 for 18 h a day over a 30 day period. Exercise resulted in a 24-30% increase in the average cross-sectional area of fast muscle fibres relative to tank-rested controls. The concentrations of growth factors and transcription factors hypothesised to play a role in regulating exercise-induced muscle fibre hypertrophy were measured. Exercise training resulted in a minor increase in calcineurin localisation in the nucleus. However, nuclear factor of T-cells 2 (NFAT2) nuclear localisation did not follow a pattern that was consistent with NFAT2-mediated transcriptional activity and changes in calcineurin signaling. The active peptide of myostatin, a negative regulator of muscle growth in mammals, was downregulated in exercise groups relative to tank-rested controls, but only by 6-7%. It was concluded that myostatin and calcineurin signaling do not play a major role in regulating exercise-induced muscle hypertrophy in trout.

Reepithelialized orthotopic tracheal allografts expand memory cytotoxic T lymphocytes but show no evidence of chronic rejection

BACKGROUND

Acute rejection of mouse tracheal allografts is characterized by infiltration of the lamina propria with CD4+/CD8+ T cells that leads to the destruction of the epithelium and luminal obliteration. The donor epithelium is progressively replaced by recipient-derived epithelium. Once allograft reepithelialization has occurred, immunosuppression can be withdrawn without inciting acute rejection. We hypothesize that reepithelialization will also prevent chronic rejection of the trachea after withdrawal of immunosuppression.

METHODS

BALB/c tracheal grafts were transplanted orthotopically into allogeneic C57BL/6 recipients. Allografted mice were nonimmunosuppressed for 10 or 100 days or immunosuppressed with cyclosporine A continuously for 50 days and then withdrawn from immunosuppression for an additional 50 days. In addition, grafts from this group were then heterotopically retransplanted into isogenic C57BL/6 or allogeneic BALB/c recipients to assess their immunogenicity.

RESULTS

Cyclosporine A-treated mice showed no signs of chronic rejection or priming of cellular immunity as measured by proliferation and cytokine secretion in a mixed leukocyte reaction. However, there was a notable expansion of memory CD8+ T cells specific for donor major histocompatibility complex. When these tracheal allografts were retransplanted heterotopically into C57BL/6 or BALB/c, they demonstrated reduced responses toward BALB/c and primed responses toward C57BL/6, respectively. These results suggest that the grafts express a chimeric phenotype consisting of both BALB/c and C57BL/6 antigens.

CONCLUSION

These observations suggest that long-term withdrawal of immunosuppression does not lead to chronic tracheal rejection even in the presence of alloantigen specific cytotoxic T-lymphocyte responses and that the reepithelialized grafts may contain donor elements that impact the generation of immunity.

Regulation of the human atrial myosin light chain 1 promoter by Ca2+‐calmodulin‐dependent signaling pathways

We investigated expression regulation of the human atrial myosin light chain 1 (hALC-1) gene using a cardiomyocyte H9c2 cell line stably transfected with a construct consisting of the human ALC-1 promoter cloned in front of the luciferase gene (H9c2T1). H9c2T1 cells were stimulated with vasopressin, which is known to induce cardiomyocyte hypertrophy and to activate a panel of signaling pathways. Those pathways involved in hALC-1 promoter activity regulation were dissected by using pharmacological inhibitor substances. Stimulation with vasopressin was associated with nuclear NFAT translocation and significantly increased human ALC-1 promoter activity. Inhibition of calcineurin by cyclosporin A blocked the effects of vasopressin on ALC-1 promoter activity to approximately 50%. This suggests that the Ca2+-calmodulin-calcineurin-NFAT pathway is involved in human ALC-1 promoter activation. However, inhibition of multifunctional Ca2+-calmodulin-dependent protein kinases (CaMK) by KN-93 decreased human ALC-1 promoter activity to almost basal levels. CaMK regulation of ALC-1 promoter activity effect could well be mediated by CaMKIV, which accumulated in the nucleus upon vasopressin stimulation. Inhibition of protein kinase C (PKC) isoforms by bisindolylmaleimide had no significant influence on human ALC-1 promoter activity. Thus, our results demonstrate a dominant role of Ca2+-calmodulin-dependent signaling pathways in the regulation of human ALC-1 expression.

2-Arachidonoyl-glycerol suppresses interferon-γ production in phorbol ester/ionomycin-activated mouse splenocytes independent of CB1 or CB2

2-Arachidonoyl-glycerol (2-AG), an endogenous ligand for cannabinoid receptor types 1 and 2 (CB1 and CB2), has previously been demonstrated to modulate immune functions including suppression of interleukin-2 expression and nuclear factor of activated T cells (NFAT) activity. The objective of the present studies was to investigate the effect of 2-AG on interferon-gamma (IFN-gamma) expression and associated upstream signaling events. Pretreatment of splenocytes with 2-AG markedly suppressed phorbol 12-myristate 13-acetate plus calcium ionophore (PMA/Io)-induced IFN-gamma secretion. In addition, 2-AG suppressed IFN-gamma steady-state mRNA expression in a concentration-dependent manner. To unequivocally determine the putative involvement of CB1 and CB2, splenocytes derived from CB1(-/-)/CB2(-/-) knockout mice were used. No difference in the magnitude of IFN-gamma suppression by 2-AG in wild-type versus CB1/CB2 null mice was observed. Time-of-addition studies revealed that 2-AG treatment up to 12 h post-cellular activation resulted in suppression of IFN-gamma, which was consistent with a time course conducted with cyclosporin A, an inhibitor of NFAT activity. Coincidentally, 2-AG perturbed the nuclear translocation of NFAT protein and blocked thapsigargin-induced elevation in intracellular calcium, suggesting that altered calcium regulation might partly explain the suppression of NFAT nuclear translocation and subsequent IFN-gamma production. Indeed, Io partially attenuated the 2-AG-induced suppression of PMA/Io-stimulated IFN-gamma production. Taken together, these data demonstrate that 2-AG suppresses IFN-gamma expression in murine splenocytes in a CB receptor-independent manner and that the mechanism partially involves suppression of intracellular calcium signaling and perturbation of NFAT nuclear translocation.

The mode of topical immunomodulators in the immunological network of atopic dermatitis

For a long time, therapeutic strategies of atopic dermatitis (AD) have been dominated by the application of local or systemic steroids or other immunosuppressive agents, which have been limited by their potential for unwanted local or systemic side effects. Recently, the use of a new generation of topical nonsteroidal, immunomodulatory drugs has revolutionized the therapeutic options of this often recalcitrant allergic-inflammatory skin disease. Research work has focused on the identification of the exact mode of action and the immune specificities of the so-called 'topical immunomodulators' (TIMs) such as tacrolimus and pimecrolimus in AD. In addition to the previous findings about the mode of action of TIMs on T cells, other target cells of TIMs such as keratinocytes, mast cells, eosinophils and dendritic cells have been identified recently as potential therapeutic targets. In this overview, we provide a research update about the anti-inflammatory and anti-allergic properties of TIMs on effector cells of AD that may be involved in the complex pathophysiology of AD.

Effect of phosphodiesterase 4 inhibitors on NFAT-dependent cyclooxygenase-2 expression in human T lymphocytes

Transcriptional induction of cyclooxygenase-2 (COX-2) occurs early after T cell receptor triggering and has functional implications in inflammation. Here, we show that phosphodiesterase (PDE)-4 inhibitors block COX-2 induction and prostaglandin synthesis in activated T cells. COX-2 inhibition by PDE4 inhibitors occurs mainly at the transcriptional level. Two response elements for the nuclear factor of activated T cells (NFAT) in the COX-2 promoter were required for inhibition by these drugs. PDE4 inhibitors did not affect NFAT nuclear translocation upon T cell activation; rather they prevented NFAT binding to DNA and induction of the transactivation function of GAL4-NFAT. These effects seem to be cAMP/PKA independent as they were not mimicked by the permeable analog dBcAMP or by forskolin, neither can be reverted by the PKA inhibitors H89 or KT-5720. These results may explain some of the anti-inflammatory properties of PDE4 inhibitors through the blockade of NFAT-mediated transactivation of pro-inflammatory genes such as COX-2.

The therapeutic potential of targeting drugs at transcription factors

The pivotal role of gene transcription in a plethora of biological processes indicates that transcription represents a suitable target for potential therapeutic intervention. Ultimately, the pathophysiology of numerous human disease processes must be understood in terms of changes in gene expression within relevant body cell types. There is mounting evidence that genetic variation in transcription factors and/or their binding-site sequences, as well as environmentally induced malfunctioning of these proteins, contribute to common multifactorial disorders including cancer, diabetes, ischaemic heart disease and neural disorders. Even in 'non-inheritable' infectious diseases, alterations of host-cell transcriptional regulation play an important role in pathogenesis. The enormous progress in understanding the mechanisms of transcriptional control offers hope for the development of a new generation of drugs. Such compounds could be specifically designed to modulate either the synthesis of transcription factors, the regulation of their activity by small-molecule bioligands or phosphorylation events, their interactions with activator/repressor proteins or their binding to DNA. Given the remarkable specificity of this approach, it is anticipated that these agents will provide superior tools for the prevention and treatment of a diverse panel of clinical disorders in the not too distant future.

Increased activity of the calcineurin-nuclear factor of activated T cells pathway in squirrel monkey B-Lymphoblasts identified by PowerBlot

New World primate-derived cell lines were instrumental in identifying the primary factors causing glucocorticoid resistance in these primate species. Their use is expanding because it has been recognized that some of these cell lines exhibit differential sensitivity to retroviral infection. To enhance their utility as cell models, we have further characterized one of these cell lines, squirrel monkey-derived B-lymphoblast (SML) cells, using PowerBlot. PowerBlot is a high-throughput, proteomic screen designed to identify differentially expressed proteins. We compared proteins expressed in SML cells and in a human B-lymphoblast (HL) cell line. We found that, relative to HL cells, SML cells overexpress the calcineurin-activated transcription factor nuclear factor of activated T cells 1 (NFAT-1), which exists in a cyclosporine A (CsA)-sensitive dephosphorylated, constitutively active state. We show that there is increased binding of NFAT-1 to deoxyribonucleic acid and greater activity of an NFAT-sensitive human interleukin-2 (IL-2) promoter-luciferase reporter gene in SML compared with activity in HL cells. The increased NFAT activity does not likely result from calcium-dependent activation of calcineurin because cytosolic calcium levels were not different in SML and HL cells. Rather, SML cells express a truncated form of the catalytic subunit of calcineurin that we propose is responsible for the increased activity of the NFAT pathway. Thus, these novel findings first uncovered by a proteomic screen will enhance the value of these New World primate cell lines as "experiments of nature" to gain insight into mechanisms of NFAT activation.

Tacrolimus suppresses glucose-induced insulin release from pancreatic islets by reducing glucokinase activity

Tacrolimus is widely used for immunosuppressant therapy, including various organ transplantations. One of its main side effects is hyperglycemia due to reduced insulin secretion, but the mechanism remains unknown. We have investigated the metabolic effects of tacrolimus on insulin secretion at a concentration that does not influence insulin content. Twenty-four-hour exposure to 3 nM tacrolimus reduced high glucose (16.7 mM)-induced insulin secretion (control 2.14 +/- 0.08 vs. tacrolimus 1.75 +/- 0.02 ng.islet(-1).30 min(-1), P < 0.01) without affecting insulin content. In dynamic experiments, insulin secretion and NAD(P)H fluorescence during a 20-min period after 10 min of high-glucose exposure were reduced in tacrolimus-treated islets. ATP content and glucose utilization of tacrolimus-treated islets in the presence of 16.7 mM glucose were less than in control (ATP content: control 9.69 +/- 0.99 vs. tacrolimus 6.52 +/- 0.40 pmol/islet, P < 0.01; glucose utilization: control 103.8 +/- 6.9 vs. tacrolimus 74.4 +/- 5.1 pmol.islet(-1).90 min(-1), P < 0.01). However, insulin release from tacrolimus-treated islets was similar to that from control islets in the presence of 16.7 mM alpha-ketoisocaproate, a mitochondrial fuel. Glucokinase activity, which determines glycolytic velocity, was reduced by tacrolimus treatment (control 65.3 +/- 3.4 vs. tacrolimus 49.9 +/- 2.8 pmol.islet(-1).60 min(-1), P < 0.01), whereas hexokinase activity was not affected. These results indicate that glucose-stimulated insulin release is decreased by chronic exposure to tacrolimus due to reduced ATP production and glycolysis derived from reduced glucokinase activity.

Cyclosporine A and its non-immunosuppressive derivative NIM811 induce apoptosis of malignant melanoma cells inin vitro andin vivo studies

Advanced melanoma is a highly malignant tumor with an increasing incidence that has a poor prognosis due to resistance to common therapeutic strategies. We have demonstrated previously that cyclosporine A (CsA) induces apoptosis of rat glioma cells, reactive astrocytes, and fibroblasts. In our present study, we investigated effects of CsA and its nonimmunosuppressive derivative NIM811 on survival of human and murine melanoma cells. We demonstrated that CsA and NIM811 affect survival of human and murine melanoma cells and induce morphological changes, alterations in nuclear morphology and an internucleosomal DNA fragmentation, consistent with an apoptotic type of death. Western blot analysis showed an activation of caspases 9, 7, 3 and PARP cleavage detectable at 24 hr after exposure of human melanoma cells to the drugs. CsA and NIM811 induced a significant increase in subG1 population of murine B16F10 melanoma cells indicative of apoptotic DNA fragmentation. Studies in murine model of melanoma showed that NIM811, but not CsA, retards tumor progression and significantly decreases tumor volume after intratumoral application. Our findings indicate that CsA and its derivatives may be new candidates for the treatment of melanoma patients.

The viral protein A238L inhibits cyclooxygenase-2 expression through a nuclear factor of activated T cell-dependent transactivation pathway

Cyclooxygenase-2 is transiently induced upon cell activation or viral infections, resulting in inflammation and modulation of the immune response. Here we report that A238L, an African swine fever virus protein, efficiently inhibits cyclooxygenase-2 gene expression in Jurkat T cells and in virus-infected Vero cells. Transfection of Jurkat cells stably expressing A238L with cyclooxygenase-2 promoter-luciferase constructs containing 5'-terminal deletions or mutations in distal or proximal nuclear factor of activated T cell (NFAT) response elements revealed that these sequences are involved in the inhibition induced by A238L. Overexpression of a constitutively active version of the calcium-dependent phosphatase calcineurin or NFAT reversed the inhibition mediated by A238L on cyclooxygenase-2 promoter activation, whereas overexpression of p65 NFkappaB had no effect. A238L does not modify the nuclear localization of NFAT after phorbol 12-myristate 13-acetate/calcium ionophore stimulation. Moreover, we show that the mechanism by which the viral protein down-regulates cyclooxygenase-2 activity does not involve inhibition of the binding between NFAT and its specific DNA sequences into the cyclooxygenase-2 promoter. Strikingly, A238L dramatically inhibited the transactivation mediated by a GAL4-NFAT fusion protein containing the N-terminal transactivation domain of NFAT1. Taken together, these data indicate that A238L down-regulates cyclooxygenase-2 transcription through the NFAT response elements, being NFAT-dependent transactivation implicated in this down-regulation.

Expression and regulation of NFAT (nuclear factors of activated T cells) in human CD34+cells: down-regulation upon myeloid differentiation

The calcineurin-dependent, cyclosporin A (CsA)-sensitive transcription factor nuclear factor of activated T cells (NFAT) represents a group of proteins, which is well-characterized as a central regulatory element of cytokine expression in activated T cells. In contrast, little is known about the expression or function of NFAT family members in myeloid cells; moreover, it is unclear whether they are expressed by hematopoietic stem/progenitor cells. Here, we show that NFATc2 (NFAT1) is expressed at high levels in CD34+ cells and megakaryocytes but not in cells committed to the neutrophilic, monocytic, or erythroid lineages. Cytokine-induced in vitro differentiation of CD34+ cells into neutrophil granulocytes results in the rapid suppression of NFATc2 RNA and protein. NFATc2 dephosphorylation/rephosphorylation as well as nuclear/cytoplasmic translocation in CD34+ cells follow the same calcineurin-dependent pattern as in T lymphocytes, suggesting that NFATc2 activation in these cells is equally sensitive to inhibition with CsA. Finally, in vitro proliferation, but not differentiation, of CD34+ cells cultured in the presence of fms-like tyrosine kinase 3 ligand (FLT3L), stem cell factor, granulocyte macrophage-colony stimulating factor (GM-CSF), interleukin-3, and G-CSF is profoundly inhibited by treatment with CsA in a dose-dependent manner. These results suggest a novel and unexpected role for members of the NFAT transcription factor family in the hematopoietic system.

Evidence for Cyclin D3 as a Novel Target of Rapamycin in Human T Lymphocytes

The immunosuppressant rapamycin has been shown to inhibit G(1)/S transition of the cell cycle. This inhibition is thought to be mediated by maintenance of the threshold levels of cyclin-dependent kinase (CDK) inhibitor p27(Kip1) (p27) and inhibition of p70 s6 kinase (p70(s6k)). However, recent evidence suggests that cells still remain sensitive to rapamycin in the absence of functional p27 or p70(s6k). Here, we show that rapamycin represses cyclin D3 levels in activated human T lymphocytes with no inhibitory effects on cyclin D2. Furthermore, rapamycin elicits similar cyclin D3 modulatory effects in B lymphocytes. The overall effect of rapamycin on cyclin D3 leads to impaired formation of active complexes with Cdk4 or Cdk6 and subsequent inhibition of cyclin D3/CDK kinase activity. Decrease in cyclin D3 protein levels is due to translational repression and not due to attenuated transcription of the cyclin D3 gene. Importantly, stable overexpression of cyclin D3 (2-2.5 fold) in Jurkat T cell transfectants renders them resistant to lower doses (1-10 ng/ml) of rapamycin. These results point to a critical role of cyclin D3 in rapamycin-mediated immunosuppressive effects in T cells and cell cycle regulation in lymphocytes in general.

Cyclosporin A differentially inhibits multiple steps in VEGF induced angiogenesis in human microvascular endothelial cells through altered intracellular signaling

The immunosuppressive agent cyclosporin A (CsA), a calcineurin inhibitor which blocks T cell activation has provided the pharmacologic foundation for organ transplantation. CsA exerts additional effects on non-immune cell populations and may adversely effect microvascular endothelial cells, contributing to chronic rejection, a long-term clinical complication and significant cause of mortality in solid-organ transplants, including patients with small bowel allografts. Growth of new blood vessels, or angiogenesis, is a critical homeostatic mechanism in organs and tissues, and regulates vascular populations in response to physiologic requirements. We hypothesized that CsA would inhibit the angiogenic capacity of human gut microvessels. Primary cultures of human intestinal microvascular endothelial cells (HIMEC) were used to evaluate CsA's effect on four in vitro measures of angiogenesis, including endothelial stress fiber assembly, migration, proliferation and tube formation, in response to the endothelial growth factor VEGF. We characterized the effect of CsA on intracellular signaling mechanisms following VEGF stimulation. CsA affected all VEGF induced angiogenic events assessed in HIMEC. CsA differentially inhibited signaling pathways which mediated distinct steps of the angiogenic process. CsA blocked VEGF induced nuclear translocation of the transcription factor NFAT, activation of p44/42 MAPK, and partially inhibited JNK and p38 MAPK. CsA differentially affected signaling cascades in a dose dependent fashion and completely blocked expression of COX-2, which was integrally linked to HIMEC angiogenesis. These data suggest that CsA inhibits the ability of microvascular endothelial cells to undergo angiogenesis, impairing vascular homeostatic mechanisms and contributing to the vasculopathy associated with chronic rejection.