Cyclosporin A sensitivity of the NF-kappa B site of the IL2R alpha promoter in untransformed murine T cells

Roles of NF-κB in Cancer and Inflammatory Diseases and Their Therapeutic Approaches

Nuclear factor-κB (NF-κB) is a transcription factor that plays a crucial role in various biological processes, including immune response, inflammation, cell growth and survival, and development. NF-κB is critical for human health, and aberrant NF-κB activation contributes to development of various autoimmune, inflammatory and malignant disorders including rheumatoid arthritis, atherosclerosis, inflammatory bowel diseases, multiple sclerosis and malignant tumors. Thus, inhibiting NF-κB signaling has potential therapeutic applications in cancer and inflammatory diseases.

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

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

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

The JNk/NFkappaB pathway is required to activate murine lymphocytes induced by a sulfated polysaccharide from Ecklonia cava

BACKGROUND

The proven immunomodulatory and immune system activating properties of Ecklonia cava (E. cava) have been attributed to its plentiful polysaccharide content. Therefore, we investigated whether the sulfated polysaccharide (SP) of E. cava specifically activates the protein kinases (MAPKs) and nuclear factor-kappaB (NFkappaB) to incite immune responses.

METHODS

To assess immune responsiveness, lymphocytes were isolated from spleens of ICR mice and cultured with SP and its inhibitors. Assays included 3H-thymidine incorporation, flow cytometry, real time polymerase chain reaction (rtPCR), enzyme linked immunosorbent assay (ELISA), intracellular cytokine assay. Western blot, and electrophoretic mobility shift assay (EMSA).

RESULTS

SP dose-dependently increased the proliferation of lymphocytes without cytotoxicity. In particular, SP markedly enhanced the proliferation and differentiation of CD3+ mature T cells and CD45R/B220+ pan B cells. Additionally, SP increased the expression and/or production of IL-2, IgG(1a), and IgG(2b) compared to that in untreated cells. The subsequent application of JNK (SP600125), NFkappaB (PDTC), and serine protease (TPCK) inhibitors significantly inhibited the proliferation and IL-2 production of SP-treated lymphocytes as well as the phosphorylation of JNK and IkappaB, the activation of nuclear NFkappaB p65, and binding of NFkappaB p65 DNA. Moreover, co-application of both JNK and NFkappaB inhibitors completely blocked the proliferation of lymphocytes even in the presence of SP.

CONCLUSION

These results suggest that SP induced T and B cell responses via both JNK and NFkappaB pathways.

GENERAL SIGNIFICANCE

The effect of SP on splenic lymphocyte activation was assayed here for the first time and indicated the underlying functional mechanism.

Dephosphorylation of Bcl-10 by calcineurin is essential for canonical NF-κB activation in Th cells

Antigen-specific stimulation of T helper (Th) cells initiates signaling cascades that ultimately result in the activation of the transcription factors NF-κB, NFAT, and AP-1 which regulate, together with other factors, many T-cell functions such as cytokine production, proliferation, and differentiation. Ordered assembly and different phosphorylation events, along with subcellular translocation of the CARMA1/Bcl-10/MALT1 complex, determine NF-κB activation after T-cell receptor (TCR) triggering. We now provide evidence that inhibition of the Ser/Thr phosphatase calcineurin (CaN) prevents dephosphorylation of Bcl-10. CaN, in constant interaction with the Bcl-10/MALT1 complex, is able to dephosphorylate Bcl-10. The CaN inhibitor cyclosporine A (CsA) converts a transient phosphorylation of Bcl-10 Ser138 during the immediate early phase of T-cell activation into a persistent state. Thus, subsequent processes such as IKKβ phosphorylation, IκBα degradation, p65 nuclear translocation, and DNA binding are diminished. Consistently, CsA treatment does not affect the phosphorylation pattern of the upstream kinase PKCθ. Together, our findings demonstrate that CaN functions as a critical signaling molecule during Th cell activation, regulating Bcl-10 phosphorylation and thereby NF-κB activation.

Transcriptional control of rapid recall by memory CD4 T cells

Memory T cells are distinguished from naive T cells by their rapid production of effector cytokines, although mechanisms for this recall response remain undefined. In this study, we investigated transcriptional mechanisms for rapid IFN-γ production by Ag-specific memory CD4 T cells. In naive CD4 T cells, IFN-γ production only occurred after sustained Ag activation and was associated with high expression of the T-bet transcription factor required for Th1 differentiation and with T-bet binding to the IFN-γ promoter as assessed by chromatin immunoprecipitation analysis. By contrast, immediate IFN-γ production by Ag-stimulated memory CD4 T cells occurred in the absence of significant nuclear T-bet expression or T-bet engagement on the IFN-γ promoter. We identified rapid induction of NF-κB transcriptional activity and increased engagement of NF-κB on the IFN-γ promoter at rapid times after TCR stimulation of memory compared with naive CD4 T cells. Moreover, pharmacologic inhibition of NF-κB activity or peptide-mediated inhibition of NF-κB p50 translocation abrogated early memory T cell signaling and TCR-mediated effector function. Our results reveal a molecular mechanism for memory T cell recall through enhanced NF-κB p50 activation and promoter engagement, with important implications for memory T cell modulation in vaccines, autoimmunity, and transplantation.

Whole blood flow cytometric measurement of NFATc1 and IL-2 expression to analyze cyclosporine A-mediated effects in T cells

The calcineurin inhibitor Cyclosporine A (CsA) is one of the crucial immunosuppressive drugs given after organ transplantation. The small therapeutic window of CsA generates the dilemma that efficient and toxic drug doses differ only slightly. Moreover, these threshold concentrations differ considerably between individuals; therefore, functional assays are urgently needed. We explored whether the transcription factor NFATc1, a direct as well as indirect target of CsA, can be used as a potential biomarker to determine the individual immunosuppressive activity of CsA. First, in isolated human T cells we showed that flow cytometry is practicable to measure NFATc1, the most abundant NFATc isoform in activated T cells. Second, for whole blood we developed a flow cytometric assay to determine in parallel the inducible transcription factor NFATc1 and the cytokine IL-2 in stimulated T cells. We found that added CsA inhibits both the expression of NFATc1 and IL-2 in T cells of stimulated whole blood samples with IC(50) values of 200 and 150 nM, respectively. The intra- and inter-assay variability was low, and clinical practicability was good. Further experiments have to demonstrate whether the parallel cytometric measurement of NFATc1 and IL-2 in whole blood is a good predictor of individual CsA efficacy and toxicity in CsA-treated patients.

Regulation of human dendritic cells by a novel specific nuclear factor-kappaB inhibitor, dehydroxymethylepoxyquinomicin

Regulation of antigen-presenting cells (APC) is crucial in controlling allograft rejection. Dendritic cells (DC) are the most potent APC and must mature to present antigens to T-cell receptors. During DC maturation, nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor. We synthesized dehydroxymethylepoxyquinomicin (DHMEQ), which specifically inhibits the final step of nuclear translocation of activated NF-kappaB proteins and examined its immunoregulatory effects on human monocyte-derived DC (Mo-DC). Regulatory Mo-DC were generated by pretreatment with DHMEQ before LPS stimulation, which were termed dl-DC. DHMEQ pretreatment (5 microg/ml) completely inhibited nuclear translocation of activated NF-kappaB. DHMEQ significantly inhibited DC production of proinflammatory cytokines (IL-6, TNF-alpha, and IL-12 p70) in a dose-dependent manner. IL-12 was most potently inhibited. However, IL-10 production by dl-DC was only moderately affected by DHMEQ. Although CD40 and the expression of HLA-DR (HLA-DR) expression on dl-DC was downregulated, CD80 and CD86 expression was moderately upregulated. Induction of T helper 1 cell responses was efficiently impaired by dl-DC. This confirmed that DHMEQ-treated Mo-DC exhibited immunoregulatory effects. These findings suggest that DHMEQ has potential as an immunosuppressive drug for human immune cells.

Inhibiting NF-κB activation by small molecules as a therapeutic strategy

Because nuclear factor-κB (NF-κB) is a ubiquitously expressed proinflammatory transcription factor that regulates the expression of over 500 genes involved in cellular transformation, survival, proliferation, invasion, angiogenesis, metastasis, and inflammation, the NF-κB signaling pathway has become a potential target for pharmacological intervention. A wide variety of agents can activate NF-κB through canonical and noncanonical pathways. Canonical pathway involves various steps including the phosphorylation, ubiquitination, and degradation of the inhibitor of NF-κB (IκBα), which leads to the nuclear translocation of the p50-p65 subunits of NF-κB followed by p65 phosphorylation, acetylation and methylation, DNA binding, and gene transcription. Thus, agents that can inhibit protein kinases, protein phosphatases, proteasomes, ubiquitination, acetylation, methylation, and DNA binding steps have been identified as NF-κB inhibitors. Because of the critical role of NF-κB in cancer and various chronic diseases, numerous inhibitors of NF-κB have been identified. In this review, however, we describe only small molecules that suppress NF-κB activation, and the mechanism by which they block this pathway.

An emerging player in the adaptive immune response: microRNA-146a is a modulator of IL-2 expression and activation-induced cell death in T lymphocytes

Activation of the T cell-mediated immune response has been associated with changes in the expression of specific microRNAs (miRNAs). However, the role of miRNAs in the development of an effective immune response is just beginning to be explored. This study focuses on the functional role of miR-146a in T lymphocyte-mediated immune response and provides interesting clues on the transcriptional regulation of miR-146a during T-cell activation. We show that miR-146a is low in human naive T cells and is abundantly expressed in human memory T cells; consistently, miR-146a is induced in human primary T lymphocytes upon T-cell receptor (TCR) stimulation. Moreover, we identified NF-kB and c-ETS binding sites as required for the induction of miR-146a transcription upon TCR engagement. Our results demonstrate that several signaling pathways, other than inflammation, are influenced by miR-146a. In particular, we provide experimental evidence that miR-146a modulates activation-induced cell death (AICD), acting as an antiapoptotic factor, and that Fas-associated death domain (FADD) is a target of miR-146a. Furthermore, miR-146a enforced expression impairs both activator protein 1 (AP-1) activity and interleukin-2 (IL-2) production induced by TCR engagement, thus suggesting a role of this miRNA in the modulation of adaptive immunity.

The proline-rich N-terminal sequence of calcineurin Abeta determines substrate binding

Three different genes of catalytic subunit A of the Ca(2+)-dependent serine/threonine protein phosphatase calcineurin (CaN) are encoded in the human genome forming heterodimers with regulatory subunit B. Even though physiological roles of CaN have been investigated extensively, less is known about the specific functions of the different catalytic isoforms. In this study, all human CaN holoenzymes containing either the alpha, beta, or gamma isoform of the catalytic subunit (CaN alpha, beta, or gamma, respectively) were expressed for the first time. Comparative kinetic analysis of the dephosphorylation of five specific CaN substrates provided evidence that the distinct isoforms of the catalytic subunit confer substrate specificities to the holoenzymes. CaN alpha dephosphorylates the transcription factor Elk-1 with 7- and 2-fold higher catalytic efficiencies than the beta and gamma isoforms, respectively. CaN gamma exhibits the highest k(cat)/K(m) value for DARPP-32, whereas the catalytic efficiencies for the dephosphorylation of NFAT and RII peptide were 3- and 5-fold lower, respectively, when compared with the other isoforms. Elk-1 and NFAT reporter gene activity measurements revealed even more pronounced substrate preferences of CaNA isoforms. Moreover, kinetic analysis demonstrated that CaN beta exhibits for all tested protein substrates the lowest K(m) values. Enzymatic characterization of the CaN beta(P14G/P18G) variant as well as the N-terminal truncated form CaN beta(22-524) revealed that the proline-rich sequence of CaN beta is involved in substrate recognition. CaN beta(22-524) exhibits an at least 4-fold decreased substrate affinity and a 5-fold increased turnover number. Since this study demonstrates that all CaN isoforms display the same cytoplasmic subcellular distribution and are expressed in each tested cell line, differences in substrate specificities may determine specific physiological functions of the distinct isoforms.

CD3-specific antibodies: a portal to the treatment of autoimmunity

Targeted immunotherapies hold great promise for the treatment and cure of autoimmune diseases. The efficacy of CD3-specific monoclonal antibody therapy in mice and humans stems from its ability to re-establish immune homeostasis in treated individuals. This occurs through modulation of the T-cell receptor (TCR)-CD3 complex (also termed antigenic modulation) and/or induction of apoptosis of activated autoreactive T cells, which leaves behind 'space' for homeostatic reconstitution that favours selective induction, survival and expansion of adaptive regulatory T cells, which establishes long-term tolerance. This Review summarizes the pre-clinical and clinical studies of CD3-specific monoclonal antibody therapy and highlights future opportunities to enhance the efficacy of this potent immunotherapeutic.

The influence of antioxidant supplementation on markers of inflammation and the relationship to oxidative stress after exercise

Interest in the relationship between inflammation and oxidative stress has increased dramatically in recent years, not only within the clinical setting but also in the fields of exercise biochemistry and immunology. Inflammation and oxidative stress share a common role in the etiology of a variety of chronic diseases. During exercise, inflammation and oxidative stress are linked via muscle metabolism and muscle damage. Because oxidative stress and inflammation have traditionally been associated with fatigue and impaired recovery from exercise, research has focused on nutritional strategies aimed at reducing these effects. In this review, we have evaluated the findings of studies involving antioxidant supplementation on alterations in markers of inflammation (e.g., cytokines, C-reactive protein and cortisol). This review focuses predominantly on the role of reactive oxygen and nitrogen species generated from muscle metabolism and muscle damage during exercise and on the modulatory effects of antioxidant supplements. Furthermore, we have analyzed the influence of factors such as the dose, timing, supplementation period and bioavailability of antioxidant nutrients.

NFAT signaling and the invention of vertebrates

The calcium/calcineurin-dependent NFATc family is thought to have arisen following the recombination of an ancient precursor with a Rel domain about 500 million years ago, producing a new group of signaling and transcription factors (the NFATc genes) found only in the genomes of vertebrates. Cell biological, genetic and biochemical evidence indicates that the circuitry of this pathway is well suited for intercalation with older pathways. We propose that this recombination enabled Ca(2+) signals to be redirected to a new transcriptional program, which provided part of the groundwork for vertebrate morphogenesis and organogenesis. This notion predicts that calcineurin-NFAT signaling would be essential for much of vertebrate development. We review recent evidence supporting this prediction and propose a systematic approach to explore aspects of vertebrate morphogenesis.

Introduction to NF-kappaB: players, pathways, perspectives

This article serves as an introduction to the collection of reviews on nuclear factor-kappaB (NF-kappaB). It provides an overview of the discovery and current status of NF-kappaB as a research topic. Described are the structures, activities and regulation of the proteins in the NF-kappaB family of transcription factors. NF-kappaB signaling is primarily regulated by inhibitor kappaB (IkappaB) proteins and the IkappaB kinase complex through two major pathways: the canonical and non-canonical NF-kappaB pathways. The organization and focus of articles included in the following reviews are described, as well as likely future areas of research interest on NF-kappaB.

Differential regulation of IL-6 and TNF-α via calcineurin in human skeletal muscle cells

Interleukin-6 increases in skeletal muscle during exercise, and evidence points to Ca2+ as an initiator of IL-6 production. However, the signalling pathway whereby this occurs is unknown. One candidate for Ca2+ -mediated IL-6 induction is calcineurin, an activator of NF-AT. Here we investigated whether skeletal myocytes produce IL-6 in a Ca2+/calcineurin-dependent manner, and whether TNF-alpha, an inducer of IL-6, is affected by these stimuli. Human skeletal muscle cell cultures were stimulated with ionomycin time-and dose-dependently to elevate intracellular Ca2+ levels, with or without addition of cyclosporin A (CSA); a calcineurin inhibitor. mRNA was extracted from myocytes and analysed for IL-6 and TNF-alpha gene expression. IL-6 mRNA increased time- and dose-dependently with ionomycin stimulation, an effect that was blunted by approximately 75% in the presence of CSA. In contrast, TNF-alpha gene expression was decreased by approximately 70% in response to ionomycin treatment, but increased in response to addition of CSA. These data demonstrate that IL-6 and TNF-alpha are regulated differentially in skeletal muscle cells in response to a Ca2+ stimulus. Blocking the calcineurin pathway resulted in inhibition of the IL-6 response to ionomycin, whereas TNF-alpha increased by addition of CSA, further indicating a differential regulation of IL-6 and TNF-alpha in human skeletal myocytes.

Oxidized low-density lipoprotein elicits an intracellular calcium rise and increases the binding activity of the transcription factor NFAT

Oxidized low-density lipoprotein (OxLDL) plays a key role in the generation and progression of atherosclerosis, which might be considered as an inflammatory disease. The transcription factor NFAT(Nuclear Factor of Activated T cells) plays an important role in the control of cytokine genes involved in the inflammatory response. The effect of copper-oxidized LDL (CuLDL) and monocyte-oxidized LDL (M-LDL) on the DNA-binding activity of NFAT was investigated in the T lymphocyte cell line Jurkat. Both OxLDL increased NFAT-binding activity in a dose-dependent manner within the range of 25-75 microg LDL protein/ml. This effect reached a maximum 1 h after the introduction of OxLDL in the medium. CuLDL and M-LDL both induce an intracellular calcium rise in a dose-dependent manner, with a maximum increase 15 min after the addition of OxLDL. The CuLDL-induced NFAT-binding activity was abolished in the presence of the calcium chelator EGTA or of the intracellular calcium trapping drug BAPTA, further indicating the involvement of calcium ions in the effect of OxLDL. In addition, cyclosporin A and FK 506, two inhibitors of calcineurin, a calcium-dependent phosphatase upstream of NFAT, also prevented the CuLDL-induced NFAT-binding activity, thus demonstrating the role of calcineurin. CuLDL and M-LDL also induced an increase in the intracellular level of reactive oxygen species (ROS), which reached a maximum 30 min after the addition of OxLDL. Finally, a pretreatment of cells with the antioxidant vitamin E blocked the CuLDL-induced increase in reactive oxygen species, in intracellular calcium rise and the CuLDL-induced NFAT-binding activity. The lipid extract of CuLDL, which includes the lipid peroxidation products, reproduced the effect of the CuLDL itself. These results suggest that the effect of OxLDL on NFAT is initiated by an oxidative stress, which then in turn activates the calcium-calcineurin signaling pathway of the transcription factor NFAT. This effect of OxLDL might be involved in the inflammatory process observed in atherosclerotic lesions.

Frontline: The p85alpha isoform of phosphoinositide 3-kinase is essential for a subset of B cell receptor-initiated signaling responses

Phosphoinositide 3-kinase (PI3K) is a ubiquitously expressed signaling enzyme that plays an integral role in development and activation of B cells. B cell receptor (BCR)-driven proliferation is completely blocked either in cells lacking the p85alpha regulatory isoform of PI3K or in wild-type cells treated with pharmacological PI3K inhibitors. However, the contribution of p85alpha to early signaling events has not been fully investigated. Here we show that B cells lacking p85alpha have signaling impairments that are both quantitatively and qualitatively different from those in cells treated with PI3K inhibitors. Loss of p85alpha results in partial reductions in Ca2+ mobilization and IkappaB phosphorylation, whereas ERK phosphorylation is not diminished. Moreover, although Akt phosphorylation is partially reduced, phosphorylation of several proteins downstream of Akt is preserved. These partial impairments suggest that there are other routes to PI3K activation in B cells apart from p85alpha-associated catalytic subunits. Notably, addition of phorbol ester restores BCR-mediated proliferation in p85alpha-deficient cells but not wild-type cells treated with PI3K inhibitors. These findings suggest that the primary BCR signaling defect in B cells lacking p85alpha is a failure to activate diacylglycerol-regulated signaling enzymes, most likely protein kinase C.

Calcineurin B1 Is Essential for Positive but Not Negative Selection during Thymocyte Development

During development, discrete cell fates often result from variation in the intensity of a particular signal. The mechanisms underlying these seemingly analog-to-digital switches are not understood. In developing T lymphocytes, low-intensity signals through the antigen receptor result in positive selection while more intense signals give rise to negative selection. By deleting the genetic locus encoding the regulatory B1 subunit of calcineurin specifically in thymocytes, we found an absolute requirement for calcineurin in positive selection. In contrast, calcineurin activity was dispensable in several models of negative selection. Unexpectedly, we found that removal of calcineurin activity from thymocytes results in inefficient ERK activation at the double-positive stage of thymocyte development, when selection occurs. These studies clarify the mechanism by which graded signals are converted to discrete outcomes in T cell development and further indicate that the developmental roles of calcineurin likely contribute to immunosuppression by calcineurin inhibitors.

Transfection of NFkappaB-decoy oligodeoxynucleotides using efficient ultrasound-mediated gene transfer into donor kidneys prolonged survival of rat renal allografts

Nuclear factor kappaB (NFkappaB) plays a pivotal role in the coordinated transactivation of a series of genes of cytokines and adhesion molecules that are highly involved in the onset of acute rejection in organ transplantation. We previously developed decoy cis-elements oligo deoxyribonucleic acid against NFkappaB (NFkappaB-decoy) that effectively inhibited the activation of major inflammatory mediators in vitro and in vivo. Accordingly, we hypothesized that transfection of NFkappaB-decoy into the donor kidney would prevent acute rejection and prolong graft survival, and thus provide effective therapy for renal acute rejection. To transfect NFkappaB-decoy, we employed a novel approach using ultrasound exposure with an echocardiographic contrast agent, Optison, and clearly demonstrated successful transfection of NFkappaB-decoy into renal tissue. The therapeutic effect of NFkappaB-decoy on renal allografts was then evaluated in a rat renal allograft model (Wistar-Lewis). In the control group, graft function significantly deteriorated with marked destruction of renal tissue, accompanied by increased production of major inflammatory mediators, and all animals died of renal failure by 9 days. In contrast, graft function (serum creatinine on day 2, NFkappaB-treated: 0.97+/-0.16 versus control: 1.84+/-0.23 mg/dl, P<0.01) and histological structure were well preserved with significantly decreased expression of NFkappaB-regulated cytokines and adhesion molecules, including IL-1, iNOS, MCP-1, TNF-alpha, and ICAM-1, in allografts transfected with NFkappaB-decoy. As a result, animal survival was significantly prolonged in this group as compared to controls (14.2+/-5.2 versus 7.1+/-1.2 days, P<0.01). Thus, we established a novel ultrasound-Optison-mediated gene transfection approach and demonstrated the significant prolongation of graft survival by the successful transfection of NFkappaB-decoy into the donor kidney in a rat renal allograft model.

Regulation of nuclear factor of activated T cells by phosphotyrosyl-specific phosphatase activity: a positive effect on HIV-1 long terminal repeat-driven transcription and a possible implication of SHP-1

Although protein tyrosine phosphatase (PTP) inhibitors used in combination with other stimuli can induce interleukin 2 (IL-2) production in T cells, a direct implication of nuclear factor of activated T cells (NFAT) has not yet been demonstrated. This study reports that exposure of leukemic T cells and human peripheral blood mononuclear cells to bis-peroxovanadium (bpV) PTP inhibitors markedly induce activation and nuclear translocation of NFAT. NFAT activation by bpV was inhibited by the immunosuppressive drugs FK506 and cyclosporin A, as well as by a specific peptide inhibitor of NFAT activation. Mobility shift assays showed specific induction of the NFAT1 member by bpV molecules. The bpV-mediated NFAT activation was observed to be important for the up-regulation of the human immunodeficiency virus 1 (HIV-1) long terminal repeat (LTR) and the IL-2 promoter; NFAT1 was demonstrated to be particularly important in bpV-dependent positive action on HIV-1 LTR transcription. The active participation of p56(lck), ZAP-70, p21(ras), and calcium in the bpV-mediated signaling cascade leading to NFAT activation was confirmed, using deficient cell lines and dominant-negative mutants. Finally, overexpression of wild-type SHP-1 resulted in a greatly diminished activation of NFAT by bpV, suggesting an involvement of SHP-1 in the regulation of NFAT activation. These data were confirmed by constitutive NFAT translocation observed in Jurkat cells stably expressing a dominant-negative version of SHP-1. The study proposes that PTP activity attenuates constitutive kinase activities that otherwise would lead to constant NFAT activation and that this activation is participating in HIV-1 LTR stimulation by PTP inhibition.

Regulation of nuclear factor of activated T-cell family transcription factors during T-cell development in the thymus

BACKGROUND

T lymphocytes undergo a series of developmental events in the thymus, and signaling through the T-cell antigen receptor is crucial in this differential program. The nuclear factor of activated T cells (NFATs) may be involved in transcriptional induction of cytokine genes and other immunoregulatory genes in T cells.

OBJECTIVES

We have examined the distribution of 3 NFAT family members (NFAT1, NFATc, and NFATx) in human fetal thymocytes, by using semiquantitative RT-PCR and electrophoretic mobility shift assay.

RESULTS

The messenger RNA of NFATx was expressed in all T-lymphocyte subsets tested, and expression was highest in CD4(+)CD8(+) thymocytes. Conversely, mRNA of NFAT1 was preferentially expressed in mature CD4(+) single-positive cells. NFATc mRNA was present at low levels in all subsets but was strongly induced by treatment with phorbol ester plus calcium ionophore. Using electrophoretic mobility shift assay, we observed stimulation-dependent NFAT-DNA binding in CD4(+)CD8(+) thymocytes, which was largely dependent on NFATx protein. This DNA-binding activity was inhibited by cyclosporin A, which indicated that NFATx nuclear translocation in CD4(+)CD8(+) thymocytes was regulated by calcineurin phosphatase. In contrast, NFAT1 and NFATc (and to some extent NFATx) were responsible for NFAT DNA binding in the CD4(+) cells.

CONCLUSIONS

Expression of NFAT family members is differentially regulated during T-cell development, and NFATx may be involved in T-cell antigen receptor/calcineurin-dependent signaling in CD4(+)CD8(+) thymocytes.

NFAT1 enhances HIV-1 gene expression in primary human CD4 T cells

Cyclosporin A (CsA) is a potent inhibitor of the NFAT family of transcription factors that enhance T cell activation. The observation that human immunodeficiency virus type 1 (HIV-1)-positive transplant recipients have a reduced HIV-1 viral burden during treatment with CsA suggested that NFAT may play a direct role in enhancing transcription of the HIV-1 viral genome. Two sets of NFAT binding sites were identified in the HIV-1 long terminal repeat (LTR) promoter by in vitro footprinting with full-length recombinant NFAT protein, and gel shift analysis of nuclear protein from polyclonally activated primary CD4 T cells revealed specific binding of NFAT1 to the NFkappaB binding sites of the HIV-1 LTR. Activation of primary CD4 T cells transiently transfected with a HIV-1 LTR luciferase reporter plasmid, lacking the NFAT binding sites in the upstream putative negative regulatory element but maintaining the NFkappaB/NFAT sites, demonstrated increased HIV-1 gene expression when cotransfected with a NFAT1 expression vector. Moreover, CsA, FK506, and a dominant-negative NFAT1 protein independently inhibited HIV-1 LTR promoter activity in CD4 T cells stimulated with phorbol ester and calcium ionophore. In primary human CD4 T cells, CsA also inhibited promoter activity directed by multimers of binding sites for NFAT, while having no effect on NFkappaB multimer-driven promoter activity. Increasing NFAT1 levels in CD4 T cells transiently transfected with a HIV-1 provirus also increased p24 protein expression. Thus, NFAT may be a target for prevention of HIV-1 LTR-directed gene expression in human CD4 T cells.

Cyclosporin A protects against angiotensin II-induced end-organ damage in double transgenic rats harboring human renin and angiotensinogen genes

Leukocyte infiltration and adhesion molecule activation play a central role in the pathogenesis of angiotensin II (Ang II)-induced end-organ damage in double transgenic rats (dTGR) harboring human renin and angiotensinogen genes. We tested the hypothesis that the immunosuppressive agent cyclosporine (CsA) protects against the Ang II-induced myocardial and renal damage in dTGR. Furthermore, we investigated the influence of CsA on interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) expression and the DNA binding activity of transcription factor necrosis factor-kappaB (NF-kappaB). The 4-week-old rats were divided into 4 groups: (1) control dTGR (n=20), (2) dTGR plus CsA (5 mg/kg SC for 3 weeks, n=15), (3) normotensive Sprague-Dawley (SD) rats (n=10), and (4) SD rats plus CsA (n=8). In dTGR, CsA completely prevented cardiovascular death (0 of 15 versus 9 of 20), decreased 24-hour albuminuria by 90% and systolic blood pressure by 35 mm Hg, and protected against the development of cardiac hypertrophy. Whole blood CsA concentrations 24 hours after the last drug treatment were 850+/-15 ng/mL. Semiquantitative ED-1 and Ki-67 (a nuclear cell proliferation-associated antigen) scoring showed that CsA prevented perivascular monocyte/macrophage infiltration and prevented cell proliferation in the kidneys and hearts of dTGR, respectively. The beneficial effects of CsA were, at least in part, mediated by the suppression of IL-6 and iNOS expression. Electrophoretic mobility shift assay revealed that CsA regulated inflammatory response in part through the NF-kappaB transcriptional pathway. In contrast to dTGR, CsA increased blood pressure in normotensive SD rats by 10 mm Hg and had no effect on cardiac mass or 24-hour urinary albumin excretion. Perivascular monocyte/macrophage infiltration, IL-6, and iNOS expression or cell proliferation were not affected by CsA in SD rats. Our findings indicate that CsA protects against Ang II-induced end-organ damage and underscore the central role of vascular inflammatory response in the pathogenesis of myocardial and renal damage in dTGR. The beneficial effects of CsA in the kidney and heart are mediated, at least in part, by suppression of IL-6 and iNOS expression via NF-kappaB transcriptional pathway.

Diverse agents act at multiple levels to inhibit the Rel/NF-kappaB signal transduction pathway

Rel/NF-kappaB transcription factors regulate several important physiological processes, including developmental processes, inflammation and immune responses, cell growth, cancer, apoptosis, and the expression of certain viral genes. Therefore, they have also been sought-after molecular targets for pharmacological intervention. As details of the Rel/NF-kappaB signal transduction pathway are revealed, it is clear that modulators of this pathway can act at several levels. Inhibitors of the Rel/NF-kappaB pathway include a variety of natural and designed molecules, including anti-oxidants, proteasome inhibitors, peptides, small molecules, and dominant-negative or constitutively active polypeptides in the pathway. Several of these molecules act as general inhibitors of Rel/NF-kappaB induction, whereas others inhibit specific pathways of induction. Inhibitors of Rel/NF-kappaB are likely to gain stature as treatments for certain cancers and neurodegenerative and inflammatory diseases.

Nuclear factor kappa B: important transcription factor and therapeutic target

Nuclear factor kappa B (NF-kappa B) is an ubiquitous rapid response transcription factor in cells involved in immune and inflammatory reactions, and exerts its effect by expressing cytokines, chemokines, cell adhesion molecules, growth factors, and immunoreceptors. In this manner, NF-kappa B contributes to immunologically mediated diseases such as allograft rejection, rheumatoid arthritis, and bronchial asthma. The prototypic inducible form of NF-kappa B is a heterodimer composed of NF-kB1 and RelA, which both belong to the NF-kappa B/Rel family of proteins. Inactive NF-kappa B is present in the cytoplasm complexed with an inhibitory protein, I kappa B. NF-kappa B is activated by a number of incoming signals from the cell surface. Released from I kappa B inhibition, NF-kappa B translocates into the nucleus and binds to the kappa B motif of the target gene. The NF-kappa B activation process can be inhibited by pharmacologic agents at each activation step. Glucocorticoids inhibit NF-kappa B by directly associating with NF-kappa B or by upregulating I kappa B expression. Cyclosporine and tacrolimus prevent NF-kappa B activation by inhibiting the action of calcineurin, a phosphatase that indirectly induces I kappa B degradation. Deoxyspergualin inhibits NF-kappa B by blocking its nuclear translocation. Aspirin and salicylates inhibit upstream events inducing I kappa B phosphorylation. Tepoxalin and antioxidants inhibit NF-kappa B activation by influencing the redox state of the cell. Further research is required to develop more specific inhibitors to treat diseases mediated by NF-kappa B.

Myocardial nuclear factor-kappaB activity and nitric oxide production in rejecting cardiac allografts

BACKGROUND

Nuclear factor-kappaB (NF-kappaB) is a rapid response transcription factor for genes whose products are critical for inflammation and immunity. In a rat model of heterotopic cardiac transplantation, we studied NF-kappaB DNA binding activity and nitric oxide (.NO) production in untreated allografts and whether inhibition of NF-kappaB suppresses .NO production and prolongs graft survival.

METHODS

In allograft recipients and isograft controls, NF-kappaB was assayed by electrophoretic mobility shift assay, daily from transplant until rejection. Myocardial .NO was directly detected in explanted allografts by electron spin resonance spectroscopy on day 6 after transplant. The potent inhibitor of NF-kappaB, pyrrolidine dithiocarbamate (PDTC; 250 mg/kg s.c.) was administered daily from transplant until day of rejection. The extent of graft lymphocytic infiltrate was assessed by routine hematoxylin and eosin staining. Immunohistochemical staining of NF-kappaB was per formed to identify the cell type responsible for NF-kappaB activity.

RESULTS

A time-dependent increase in myocardial NF-kappaB activity was seen in untreated allografts as compared with isografts as determined by PhosphorImage analysis. Peak NF-kappaB activity occurred in allografts on day 4 with a ninefold increase as compared with isografts (24.0+/-3.7% vs. 2.7+/-0.5; P<0.05). On posttransplant day 6, electron spin resonance spectroscopy analysis of allografts demonstrated .NO identified by a triplet nitrogen signal centered at g=2.012 with hyperfine splitting of 17.5 Gauss, which is consistent with nitrosoheme formation and low-field signals at g=2.08 and g=2.03 consistent with nitrosomyoglobin. These signals were not seen in native hearts of allograft recipients. With PDTC administration, a threefold decrease in NF-kappaB activity within the transplanted heart was observed on posttransplant day 5 as compared with untreated allografts (9.7+/-1.6% vs. 23.5+/-2.5%; P<0.01). PDTC prolonged graft survival as compared with untreated allografts (11.7+/-0.3 vs. 6.6+/-0.2 days; P<0.05) and reduced the intensity of the nitrosoheme and nitrosomyoglobin signals. Allograft mononuclear cell infiltrate correlated with peak NF-kappaB activity with peak infiltrate on posttransplant day 4. PDTC treatment had no effect on the extent of infiltrate. Immunohistochemical staining localized NF-kappaB to the infiltrating mononuclear cells on posttransplant day 5.

CONCLUSION

These data support a role for NF-kappaB in allograft rejection.

Mechanism responsible for T-cell antigen receptor- and CD28- or interleukin 1 (IL-1) receptor-initiated regulation of IL-2 gene expression by NF-kappaB

Initiation of the T-helper lymphocyte activation program is regulated through the T-cell receptor (TCR) and costimulatory receptors. Analysis of TCR and either anti-CD28- or interleukin 1 (IL-1)-mediated activation of the IL-2 promoter shows that costimulatory signals augment promoter activity through NF-kappaB sites. This study comparatively evaluates the mechanisms whereby signals initiated from the TCR and these two costimulatory receptors converge to synergistically increase NF-kappaB transcriptional activity. IL-1 alone stimulates an acute but transient NF-kappaB nuclear localization and a suboptimal NF-kappaB transcriptional response. In contrast, anti-CD3-anti-CD28 or anti-CD3-IL-1 synergistically stimulate prolonged NF-kappaB nuclear localization and NF-kappaB-mediated transcription. Both TCR- and costimulatory receptor-initiated synergistic NF-kappaB responses result from prolonging high rates of cytosolic IkappaB degradation during the second phase of the biphasic NF-kappaB nuclear localization. However, in contrast to previous reports, prolonged nuclear localization of NF-kappaB complexes is not necessarily associated with long-term depletion of IkappaBbeta. In response to either costimulus, c-Rel selectively translocated to the nucleus as a result of induced c-Rel expression and the continued production of c-Rel-IkappaBalpha complexes, which turn over rapidly due to the high rate of IkappaBalpha degradation in the cytosol during the second phase of the response. In contrast, IkappaBbeta is nearly completely degraded during the acute response to either IL-1 or anti-CD3-IL-1 while anti-CD3-anti-CD28 stimulates only a partial reduction (35 to 40%) in cytosolic IkappaBbeta. Cyclosporine (CsA), which inhibits stimulus-induced NF-kappaB transcriptional activity, selectively inhibits the stimulus-induced c-Rel nuclear localization and the rapid formation and degradation of c-Rel-IkappaBalpha complexes in the cytosol. CsA also inhibits both the prolonged, high rate of IkappaBalpha degradation and the lower level of IkappaBbeta turnover during the second phase of the activation response. Together, these results suggest a mechanism by which signals from the T-cell antigen receptor and either CD28 or IL-1 synergistically regulate IL-2 gene transcription by modulating NF-kappaB nuclear translocation.

p53 transactivation of the HIV-1 long terminal repeat is blocked by PD 144795, a calcineurin-inhibitor with anti-HIV properties

Previous reports have indicated that benzothiophenes exhibit broad anti-inflammatory properties and inhibit human immunodeficiency virus-type 1 (HIV-1) replication. We show that the immunosuppressant cyclosporin A (CsA) and benzothiophene-2-carboxamide, 5-methoxy-3-(1-methyl ethoxy)-1-oxide (PD 144795) block the induction of p53 and NF-kappaB binding to the HIV-1 long terminal repeat (LTR) by the T cell receptor activator phytohemagglutinin. CsA and PD 144795 also inhibit the induction by phytohemagglutinin of the transcription mediated by an HIV-1 LTR fragment containing the p53 and NF-kappaB sites. These effects of PD 144795 on HIV-1 transcription correlate with its ability to inhibit the phosphatase activity of calcineurin and are similar to those previously described for CsA. Moreover, a constitutive active form of calcineurin is able to induce expression from the HIV-1 LTR in a p53- and NF-kappaB-dependent manner and PD 144795 is able to block this induction. These results demonstrate that the DNA binding of p53 to the HIV-1 LTR can be modulated by calcineurin and provide a framework to understand the anti-HIV properties of benzothiophene derivatives.

Effects of the immunosuppressive drugs CsA and FK506 on intracellular signalling and gene regulation

The isolation of Cyclosporin A (CsA) from cultures of the fungus Tolypocladium inflatum and its subsequent elucidation of immunosuppressive properties by Borel et al. (1) was of great clinical consequence. In the early 80s CsA was introduced in the field of organ transplantation resulting in extraordinary improvements of graft survival. CsA has become a first choice drug for patients with allograft organs. The discovery of FK506 by Kino et al. (2) as a novel immuno-suppressant and its introduction into clinics in 1989 (3) extended the available regimen for immunosuppressive therapy. Yet despite their advantages both CsA and FK506 display unwanted side effects and a possible preference of one drug over another remains controversial (4, 5). Although identification of the involvement of the transcription factor NF-AT was an important step forward (6), it has become clear that immunosuppressant action is more complex. CsA and FK506 selectively interact with certain cellular signal transduction pathways. This review briefly describes these effects on signal transduction. We further concentrate on the major known effect of these immunosuppressants, namely the inhibition of the PP2B phosphatase calcineurin. In addition we provide a compilation of effects of CsA and FK506 on gene expression at the level of transcription.

Cyclosporin A interferes with the inducible degradation of NF-kappa B inhibitors, but not with the processing of p105/NF-kappa B1 in T cells

The transcription factor NF-kappa B controls the induction of numerous cytokine promoters during the activation of T lymphocytes. Inhibition of T cell activation by the immunosuppressants cyclosporin A (CsA) and FK506 exerts a suppressive effect on the induction of these NF-kappa B-controlled cytokine promoters. We show for human Jurkat T leukemia cells, as well as human and mouse primary T lymphocytes, that this inhibitory effect is accompanied by an impaired nuclear translocation of the Rel proteins c-Rel, RelA/p65 and NF-kappa B1/p50, whereas the nuclear appearance of RelB remains unaffected. CsA does not interfere with the synthesis of Rel proteins, but prevents the inducible degradation of cytosolic NF-kappa B inhibitors I kappa B alpha and I kappa B beta upon T cell activation. CsA neither inhibits the processing of the NF-kappa B1 precursor p105 to p50, nor does it "stabilize" the C-terminal portion of p105, I kappa B gamma, which is degraded during p105 processing to mature p50. These results indicate that CsA interferes with a specific event in the signal-induced degradation of I kappa B alpha and I kappa B beta, but does not affect the processing of NF-kappa B1/p105 to p50.

Transcription factors of the NFAT family: regulation and function

As targets for the immunosuppressive drugs cyclosporin A and FK506, transcription factors of the NFAT (nuclear factor of activated T cells) family have been the focus of much attention. NFAT proteins, which are expressed in most immune-system cells, play a pivotal role in the transcription of cytokine genes and other genes critical for the immune response. The activity of NFAT proteins is tightly regulated by the calcium/calmodulin-dependent phosphatase calcineurin, a primary target for inhibition by cyclosporin A and FK506. Calcineurin controls the translocation of NFAT proteins from the cytoplasm to the nucleus of activated cells by interacting with an N-terminal regulatory domain conserved in the NFAT family. The DNA-binding domains of NFAT proteins resemble those of Rel-family proteins, and Rel and NFAT proteins show some overlap in their ability to bind to certain regulatory elements in cytokine genes. NFAT is also notable for its ability to bind cooperatively with transcription factors of the AP-1 (Fos/Jun) family to composite NFAT:AP-1 sites, found in the regulatory regions of many genes that are inducibly transcribed by immune-system cells. This review discusses recent data on the diversity of the NFAT family of transcription factors, the regulation of NFAT proteins within cells, and the cooperation of NFAT proteins with other transcription factors to regulate the expression of inducible genes.

Biological and biochemical inhibitors of the NF-kappa B/Rel proteins and cytokine synthesis

The NF-kappa B/Rel family of transcription factors participates in the activation of a diverse range of genes involved in inflammation, immune response, lymphoid differentiation, growth control and development. The present review provides a brief overview of NF-kappa B/Rel activation and a detailed analysis of important biological and biochemical inhibitors of the NF-kappa B/Rel pathway. Given the pleiotropic role of NF-kappa B in controlling cytokines and other immunoregulatory genes, the inhibition of NF-kappa B activation by steroid hormones, antioxidants, protease inhibitors and other compounds may provide a pharmacological basis for interfering with pathological inflammatory conditions, cancer and AIDS.

Transcription of the murine interleukin 5 gene is regulated by multiple promoter elements

Cis-acting regions in the 5'-flank of the mouse interleukin 5 (IL-5) gene involved in the specific and inducible regulation of IL-5 transcription in an untransformed mouse T cell clone, D10.G4.1, have been identified. Transient transfection assays with a series of deletion IL-5 promoter reporter constructs indicate that multiple regulatory elements in the 5'-flanking region of the IL-5 promoter play a role in regulating IL-5 transcription in Th2 cells. Negatively acting elements, NRE I and NRE II, map to the regions between positions -431 and -392 and positions -300 and -261. A positive regulatory element has been mapped to the region between positions -224 and -81. The activity of these elements is dependent on activation of the cells. A 40-bp sequence within this region, termed the IL-5 PRE, has been shown to bind at least two specific nuclear protein complexes from unstimulated and stimulated D10.G4.1 cells. An additional protein complex specific for this site has been identified in nuclear fractions from cells stimulated in the presence of the protein synthesis inhibitor, cycloheximide. Proteins that bind to these elements are likely to be important inducible and specific factors essential for control of IL-5 transcription in response to T cell receptor-mediated signaling events.

FK506 inhibits antigen receptor-mediated induction of c-rel in B and T lymphoid cells

Stimulation of B and T cells via the antigen receptor, by phorbol ester or by phorbol ester and ionomycin, leads to nuclear translocation of the inducible transcription factor NF-kappa B, comprising the p50 and p65 rel-related polypeptides. In this report we show that c-rel is a component of the antigen receptor-induced kappa B binding proteins in both B and T cells. Whereas NF-kappa B can be induced by phorbol ester alone, optimal induction of c-rel requires stimulation by both phorbol ester and ionomycin, the dual signal that is necessary for proliferation of untransformed lymphocytes. Furthermore, c-rel induction is blocked by the immunosuppressive drug FK506 that is known to inhibit B and T cell activation. c-rel-dependent transactivation of the interleukin-2 receptor alpha chain (IL-2R alpha) promoter is augmented by coexpression of calcineurin, suggesting the involvement of a calcineurin-dependent intracellular pathway. Our results identify c-rel as a target of immunosuppressive agents and illustrate the similarity of activation pathways in both B and T cells.