The granulocyte-macrophage colony-stimulating factor/interleukin 3 locus is regulated by an inducible cyclosporin A-sensitive enhancer

Calcineurin and hypertrophic heart disease: novel insights and remaining questions

In the past 2 years, an emerging body of research has focused on a novel transcriptional pathway involved in the cardiac hypertrophic response. Ever since its introduction, the significance of the calcineurin-NFAT module has been subject of controversy. The aim of this review is to provide both an update on the current status of knowledge and discuss the remaining issues regarding the involvement of calcineurin in hypertrophic heart disease. To this end, the molecular biology of calcineurin and its direct downstream transcriptional effector NFAT are discussed in the context of the genetic studies that established the existence of this signaling paradigm in the heart. The pharmacological mode-of-action and specificity of the calcineurin inhibitors cyclosporine A (CsA) and FK506 is discussed, as well as their inherent limitations to study the biology of calcineurin. A critical interpretation is given on studies aimed at analyzing the role of calcineurin in cardiac hypertrophy using systemic immunosuppression. To eliminate the controversy surrounding CsA/FK506 usage, recent studies employed genetic inhibitory strategies for calcineurin, which confirm the pivotal role for this signal transduction pathway in the ventricular hypertrophy response. Finally, unresolved issues concerning the role of calcineurin in cardiac pathobiology are discussed based upon the information available, including its controversial role in cardiomyocyte viability, the reciprocal relationship between myocyte Ca(2+) homeostasis and calcineurin activity and the relative importance of calcineurin in relation to other hypertrophic signaling cascades.

Regulation of cytokine gene transcription in the immune system

The controlled expression of cytokine genes is an essential component of an immune response. The specific types of cytokines as well as the time and place of their production is important in generating an appropriate immune response to an infectious agent. Aberrant expression is associated with pathological conditions of the immune system such as autoimmunity, atopy and chronic inflammation. Cytokine gene transcription is generally induced in a cell-specific manner. Over the last 15 years, a large amount of information has been generated describing the transcriptional controls that are exerted on cytokine genes. Recently, efforts have been directed at understanding how these genes are transcribed in a chromatin context. This review will discuss the mechanisms by which cytokine genes become available for transcription in a cell-restricted manner as well as the mechanisms by which these genes sense their environment and activate high level transcription in a transient manner. Particular attention will be paid to the role of chromatin in allowing transcription factor access to appropriate genes.

Suppression of granulocyte-macrophage colony-stimulating factor expression by glucocorticoids involves inhibition of enhancer function by the glucocorticoid receptor binding to composite NF-AT/activator protein-1 elements

Increased expression of a number of cytokines including GM-CSF is associated with chronic inflammatory conditions such as bronchial asthma. Glucocorticoid therapy results in suppression of cytokine levels by a mechanism(s) not yet fully understood. We have examined regulation of GM-CSF expression by the synthetic glucocorticoid dexamethasone in human T cells. Transient transfection assays with reporter constructs revealed that dexamethasone inhibited the function of the GM-CSF enhancer, but had no effect on regulation of GM-CSF expression occurring through the proximal promoter. Activation of the GM-CSF enhancer involves cooperative interaction between the transcription factors NF-AT and AP-1. We demonstrate here that glucocorticoid-mediated inhibition of enhancer function involves glucocorticoid receptor (GR) binding to the NF-AT/AP-1 sites. These elements, which do not constitute recognizable glucocorticoid response elements, support binding of the GR, primarily as a dimer. This binding correlates with the ability of dexamethasone to inhibit enhancer activity of the NF-AT/AP-1 elements, suggesting a competition between NF-AT/AP-1 proteins and GR.

Regulation of interferon-gamma gene expression by nuclear factor of activated T cells

Transcription factors of the nuclear factor of activated T cells (NFAT) family are thought to regulate the expression of a variety of inducible genes such as interleukin-2 (IL-2), IL-4, and tumor necrosis factor-alpha. However, it remains unresolved whether NFAT proteins play a role in regulating transcription of the interferon- gamma (IFN-gamma) gene. Here it is shown that the transcription factor NFAT1 (NFATc2) is a major regulator of IFN-gamma production in vivo. Compared with T cells expressing NFAT1, T cells lacking NFAT1 display a substantial IL-4-independent defect in expression of IFN-gamma mRNA and protein. Reduced IFN-gamma production by NFAT1(-/-)x IL-4(-/-) T cells is observed after primary in vitro stimulation of naive CD4+ T cells, is conserved through at least 2 rounds of T-helper cell differentiation, and occurs by a cell-intrinsic mechanism that does not depend on overexpression of the Th2-specific factors GATA-3 and c-Maf. Concomitantly, NFAT1(-/-)x IL-4(-/-) mice show increased susceptibility to infection with the intracellular parasite Leishmania major. Moreover, IFN-gamma production in a murine T-cell clone is sensitive to the selective peptide inhibitor of NFAT, VIVIT. These results suggest that IFN-gamma production by T cells is regulated by NFAT1, most likely at the level of gene transcription.

A NF-kappa B/Sp1 region is essential for chromatin remodeling and correct transcription of a human granulocyte-macrophage colony-stimulating factor transgene

The GM-CSF gene is expressed following activation of T cells. The proximal promoter and an upstream enhancer have previously been characterized using transfection and reporter assays in T cell lines in culture. A 10.5-kb transgene containing the entire human GM-CSF gene has also been shown to display inducible, position-independent, copy number-dependent transcription in mouse splenocytes. To determine the role of individual promoter elements in transgene function, mutations were introduced into the proximal promoter and activity assessed following the generation of transgenic mice. Of four mutations introduced into the transgene promoter, only one, in an NF-kappaB/Sp1 region, led to decreased induction of the transgene in splenocytes or bone marrow-derived macrophages. This mutation also affected the activity of reporter gene constructs stably transfected into T cell lines in culture, but not when transiently transfected into the same cell lines. The mutation alters the NF-kappaB family members that bind to the NF-kappaB site as well as reducing the binding of Sp1 to an adjacent element. A DNase I hypersensitive site that is normally generated at the promoter following T cell activation on the wild-type transgene does not appear in the mutant transgene. These results suggest that the NF-kappaB/Sp1 region plays a critical role in chromatin remodeling and transcription on the GM-CSF promoter in primary T cells.

Novel CD28-responsive enhancer activated by CREB/ATF and AP-1 families in the human interleukin-2 receptor alpha-chain locus

The interaction of interleukin-2 (IL-2) with its receptor (IL-2R) critically regulates the T-cell immune response, and the alpha chain CD25/IL-2Ralpha is required for the formation of the high-affinity receptor. Tissue-specific, inducible expression of the IL-2Ralpha gene is regulated by at least three positive regulatory regions (PRRI, PRRII, and PRRIII), but none responded to CD28 engagement in gene reporter assays although CD28 costimulation strongly amplifies IL-2Ralpha gene transcription. By DNase I hypersensitivity analysis, we have identified a novel TCR-CD3- and CD28-responsive enhancer (CD28rE) located 8.5 kb 5' of the IL-2Ralpha gene. PRRIV/CD28rE contains a functional CRE/TRE element required for CD28 signaling. The T-cell-specific, CD28-responsive expression of the IL-2Ralpha gene appears controlled through PRRIV/CD28rE by cooperation of CREB/ATF and AP-1 family transcription factors.

Regulation of granulocyte-macrophage colony-stimulating factor in human retinal pigment epithelial cells by IL-1beta and IFN-gamma

GM-CSF production by RPE cells, which form part of the blood-retina barrier, is upregulated by IL-1beta and this increase can be reversed by IFN-gamma. IL-1beta up-regulation is not dependent on PKC but the PKC activator PMA induces low levels of GM-CSF production and acts synergistically with IL-1beta to further increase GM-CSF. Although A23187 and ionomycin stimulated low levels of GM-CSF production, the IL-1beta pathway was cyclosporin A insensitive and did not interact with the calcium pathway. IL-1beta-stimulated GM-CSF mRNA expression and production was strongly dependent on NF-kappaB. IFN-gamma inhibition of the GM-CSF response to IL-1beta acted via NF-kappaB, reducing the translocation of NF-kappaB to the nuclei of RPE cells treated with IL-1beta and IFN-gamma. The results show that IFN-gamma down-regulation acts either directly on NF-kappaB or its activation or by blockade of a pathway upstream of NF-kappaB. However, any such blockade does not involve PKC or intracellular calcium.

A new regulatory region of the IL-2 locus that confers position-independent transgene expression

Although the promoter/enhancer of the IL-2 gene mediates inducible reporter gene expression in vitro, it cannot drive consistent expression in transgenic mice. The location and existence of any regulatory elements that could open the IL-2 locus in vivo have remained unknown, preventing analysis of IL-2 regulation in developmental contexts. In this study, we report the identification of such a regulatory region, marked by novel DNase-hypersensitive sites upstream of the murine IL-2 promoter in unstimulated and stimulated T cells. Inclusion of most of these sites in an 8.4-kb IL-2 promoter green fluorescent protein transgene gives locus control region-like activity. Expression is efficient, tissue specific, and position independent. This transgene is expressed not only in peripheral T cells, but also in immature thymocytes and thymocytes undergoing positive selection, in agreement with endogenous IL-2 expression. In contrast, a 2-kb promoter green fluorescent protein transgene, lacking the new hypersensitive sites, is expressed in only a few founder lines, and expression is dysregulated in CD8(+) cells. Thus, the 6.4 kb of additional upstream IL-2 sequence contains regulatory elements that provide integration site independence and differential regulation of transgene expression in CD8 vs CD4 cells.

The molecular basis of T helper 1 and T helper 2 cell differentiation

Cytokines such as interleukin 12 (IL-12) and IL-4 are dominant factors in driving the development of T helper 1 (Th1) and Th2 cells, respectively, through specific signalling pathways. In addition, it has been demonstrated more recently that T helper-cell-specific transcription factors exist that determine the commitment of Th1 and Th2 cells for the production of distinct profiles of cytokines. In addition to the expression of distinct cytokine genes and transcription factors, the molecular basis for commitment to a Th1 or Th2 phenotype can probably be explained by multiple mechanisms, including differential cytokine signalling, exclusive cytokine receptor expression, differential expression of transcription factors and/or differential chromatin remodelling of Th1- and Th2-specific genes.

Reconstitution of T cell-specific transcription directed by composite NFAT/Oct elements

The complex nature of most promoters and enhancers makes it difficult to identify key determinants of tissue-specific gene expression. Furthermore, most tissue-specific genes are regulated by transcription factors that have expression profiles more widespread than the genes they control. NFAT is an example of a widely expressed transcription factor that contributes to several distinct patterns of cytokine gene expression within the immune system and where its role in directing specificity remains undefined. To investigate distinct combinatorial mechanisms employed by NFAT to regulate tissue-specific transcription, we examined a composite NFAT/AP-1 element from the widely active GM-CSF enhancer and a composite NFAT/Oct element from the T cell-specific IL-3 enhancer. The NFAT/AP-1 element was active in the numerous cell types that express NFAT, but NFAT/Oct enhancer activity was T cell specific even though Oct-1 is ubiquitous. Conversion of the single Oct site in the IL-3 enhancer to an AP-1 enabled activation outside of the T cell lineage. By reconstituting the activities of both the IL-3 enhancer and its NFAT/Oct element in a variety of cell types, we demonstrated that their T cell-specific activation required the lymphoid cofactors NIP45 and OCA-B in addition to NFAT and Oct family proteins. Furthermore, the Oct family protein Brn-2, which cannot recruit OCA-B, repressed NFAT/Oct enhancer activity. Significantly, the two patterns of combinatorial regulation identified in this study mirror the cell-type specificities of the cytokine genes that they govern. We have thus established that simple composite transcription factor binding sites can indeed establish highly specific patterns of gene expression.

Generation of an improved luciferase reporter gene plasmid that employs a novel mechanism for high-copy replication

We have engineered the reporter gene plasmid pXPG by incorporating a novel high-copy origin of replication and a modified luciferase gene into a pXP1-derived vector that efficiently blocks read-through transcription in eukaryotic cells. pXPG contains the Luc+ luciferase gene derived from pGL3 that lacks a peroxisomal targeting sequence, thereby allowing accumulation of luciferase protein in the cytoplasm rather than subcellular organelles of transfected eukaryotic cells. pXPG has distinct advantages over pGL3, because it contains SV40 polyadenylation signals that appear to be more efficient at blocking read-through transcription than the synthetic polyadenylation signal present in pGL3. pXPG contains a novel mutation near the origin of replication that increases plasmid copy number in Escherichia coli. This mutation alters the -10 sequence in the RNA II promoter of the ColE1 origin of replication from TAATCT to TAATAT. As this sequence is a closer match to the consensus -10 element, we suggest that the mutation increases copy number by increasing the rate of transcription of the RNA II replication primer. This novel mechanism for increasing copy number may have more widespread applications than the commonly used pUC high-copy origin of replication mutation. Unlike pUC, which reverts to low copy number at 30 degrees C, the pXPG mutation supports a higher copy number at both 37 and 30 degrees C.

Gene expression elicited by NFAT in the presence or absence of cooperative recruitment of Fos and Jun

Cooperation between nuclear factor of activated T cells (NFAT) and AP-1 (Fos-Jun) proteins on composite NFAT-AP-1 DNA elements constitutes a powerful mechanism for signal integration of the calcium and protein kinase C/Ras pathways in the regulation of gene expression. Here we report that NFAT can induce expression of certain genes in T cells without the need for cooperative recruitment of Fos and Jun. Using NFAT1 mutant proteins that are unable to interact with Fos-Jun dimers but are unaffected in DNA binding or transcriptional activity, we show that expression of interleukin (IL)-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, IL-4, MIP1alpha and Fas ligand mRNAs is absolutely dependent on cooperation between NFAT and Fos-Jun; in contrast, NFAT induces tumor necrosis factor alpha (TNFalpha) mRNA and IL-13 promoter activity without any necessity to recruit Fos and Jun. Furthermore, we show that NFAT-Fos-Jun cooperation is also essential to elicit the NFAT-dependent program of activation-induced cell death. Our results support the hypothesis that even in a single cell type, NFAT activation can evoke two distinct biological programs of gene expression, dependent or independent of NFAT-AP-1 cooperation.

Repression of IL-2 promoter activity by the novel basic leucine zipper p21SNFT protein

IL-2 is the major autocrine and paracrine growth factor produced by T cells upon T cell stimulation. The inducible expression of IL-2 is highly regulated by multiple transcription factors, particularly AP-1, which coordinately activate the promoter. Described here is the ability of the novel basic leucine zipper protein p21SNFT to repress AP-1 activity and IL-2 transcription. A detailed analysis of the repression by p21SNFT repression on the IL-2 promoter distal NF-AT/AP-1 site demonstrates that it can bind DNA with NF-AT and Jun, strongly suggesting that it represses NF-AT/AP-1 activity by competing with Fos proteins for Jun dimerization. The importance of this repression is that p21SNFT inhibits the trans-activation potential of protein complexes that contain Jun, thereby demonstrating an additional level of control for the highly regulated, ubiquitous AP-1 transcription factor and the IL-2 gene.

The duration of nuclear residence of NFAT determines the pattern of cytokine expression in human SCID T cells

The expression of cytokine genes and other inducible genes is crucially dependent on the pattern and duration of signal transduction events that activate transcription factor binding to DNA. Two infant patients with SCID and a severe defect in T cell activation displayed an aberrant regulation of the transcription factor NFAT. Whereas the expression levels of the NFAT family members NFAT1, -2, and -4 were normal in the patients' T cells, dephosphorylation and nuclear translocation of these NFAT proteins occurred very transiently and incompletely upon stimulation. Only after inhibition of nuclear export with leptomycin B were we able to demonstrate a modest degree of nuclear translocation in the patients' T cells. This transient activation of NFAT was not sufficient to induce the expression of several cytokines, including IL-2, IL-3, IL-4, and IFN-gamma, whereas mRNA levels for macrophage inflammatory protein-1alpha, GM-CSF, and IL-13 were only moderately reduced. By limiting the time of NFAT activation in normal control cells using the calcineurin inhibitor cyclosporin A, we were able to mimic the cytokine expression pattern in SCID T cells, suggesting that the expression of different cytokine genes is differentially regulated by the duration of NFAT residence in the nucleus.

Molecular regulation of granulocyte macrophage colony-stimulating factor in human lung epithelial cells by interleukin (IL)-1beta, IL-4, and IL-13 involves both transcriptional and post-transcriptional mechanisms

Interleukin (IL)-1beta stimulates the release of granulocyte macrophage colony-stimulating factor (GM-CSF) from lung epithelial cells. To investigate the molecular mechanisms underlying GM-CSF regulation, we studied GM-CSF production, messenger RNA (mRNA) expression levels, and GM-CSF promoter activity in A549 human alveolar carcinoma cells stimulated with IL-1beta. Coincubation with IL-4 or IL-13 dose-dependently inhibited IL-1beta-induced GM-CSF release. Time-course studies of intracellular and extracellular protein release and mRNA expression indicated tight coupling of protein and mRNA synthesis within 6 h after stimulation. IL-4 and IL-13 both inhibited expression of GM-CSF mRNA and protein by 2 h after stimulation. Stable transfection of A549 cells, with GM-CSF promoter/ enhancer constructs containing up to 3.3 kb upstream of the transcription start site, revealed maximal activation by IL-1beta and phorbol 12-myristate 13-acetate (PMA) with a reporter containing the proximal promoter (-627 to +35). This excludes sequences further upstream from a major regulatory role in GM-CSF promoter activation by IL-1beta or PMA in these cells. IL-4 and IL-13 downregulated promoter activation but had no effect on GM-CSF mRNA half-life. However, IL-1beta activation of all constructs was far less pronounced than in Jurkat T cells, suggesting a requirement for additional mechanisms, possibly post-transcriptional, to potentiate the observed transcriptional induction.

IL-4 regulation of IL-6 production involves Rac/Cdc42- and p38 MAPK-dependent pathways in keratinocytes

The stress-activated pathways leading to activation of p38 MAP kinase (p38 MAPK) and c-jun N-terminal kinases (JNK) have been shown to be activated by pro-inflammatory cytokines, physical and chemical stresses as well as a variety of hematopoietic growth factors. One exception is interleukin (IL)-4, which does not activate this pathway in hematopoietic cell. We report here that in A431, a keratinocytic cell line, IL-4 activates Rac and Cdc42 and their downstream effector p21-activated kinase (PAK). Rac and Cdc42 appear to regulate a protein kinase cascade initiated at the level of PAK and leading to activation of p38 MAPK, since IL-4 stimulates tyrosine phosphorylation of p38 MAPK and increases its catalytic activity. As A431 cells are able to produce IL-6 in response to IL-4 stimulation, we assessed the involvement of p38 MAPK in IL-6 gene expression. A pyrimidazole compound, SB203580, a specific inhibitor of p38 MAPK, inhibits production and gene expression of IL-6. SB203580 reduced significantly the stability of IL-6 mRNA. Here we provide evidence that p38 MAPK is activated in response to IL-4 and is involved in IL-6 synthesis by stabilizing IL-6 mRNA.

Educating T cells: early events in the differentiation and commitment of cytokine-producing CD4+ and CD8+ T cells

T lymphocytes acquire the ability to synthesize cytokines during their primary response to antigen, often giving rise to effector populations with a polarized type 1 or type 2 cytokine profile. However, polarization is not a simple choice between two differentiation pathways. This article reviews the evidence, particularly from single-cell and clonal studies, that polarization is the outcome of a series of stochastic events whose probabilities are determined in part by genetic background and in part by extracellular signals received during activation and clonal expansion. The data suggest that these extracellular signals independently and differentially regulate the probability of expression of each cytokine gene, for example by their effects on clonal expansion and chromatin remodeling, CpG demethylation and transcriptional activation of cytokine genes. Polarization is, therefore, achieved at the population level by altering frequencies of expression among cells with many different expression patterns, rather than by selective differentiation of a discrete subset. Type 1 and type 2 populations progressively lose responsiveness to counter-polarizing stimuli. While the molecular basis of this process is not yet known, the observed persistence of cells with flexible cytokine profiles in some polarized populations suggests that loss of flexibility may also be a probabilistic event.

The nuclear factor of activated T cells (NFAT) transcription factor NFATp (NFATc2) is a repressor of chondrogenesis

Nuclear factor of activated T cells (NFAT) transcription factors regulate gene expression in lymphocytes and control cardiac valve formation. Here, we report that NFATp regulates chondrogenesis in the adult animal. In mice lacking NFATp, resident cells in the extraarticular connective tissues spontaneously differentiate to cartilage. These cartilage cells progressively differentiate and the tissue undergoes endochondral ossification, recapitulating the development of endochondral bone. Proliferation of already existing articular cartilage cells also occurs in some older animals. At both sites, neoplastic changes in the cartilage cells occur. Consistent with these data, NFATp expression is regulated in mesenchymal stem cells induced to differentiate along a chondrogenic pathway. Lack of NFATp in articular cartilage cells results in increased expression of cartilage markers, whereas overexpression of NFATp in cartilage cell lines extinguishes the cartilage phenotype. Thus, NFATp is a repressor of cartilage cell growth and differentiation and also has the properties of a tumor suppressor.

Stat6-independent GATA-3 autoactivation directs IL-4-independent Th2 development and commitment

The initial source of IL-4-inducing Th2 development and the mechanism of stable Th2 commitment remain obscure. We found the reduced level of IL-4 production in Stat6-deficient T cells to be significantly higher than in Th1 controls. Using a novel cell surface affinity matrix technique, we found that IL-4-secreting Stat6-deficient T cells stably expressed GATA-3 and Th2 phenotype. Introducing GATA-3 into Stat6-deficient T cells completely restored Th2 development, inducing c-Maf, Th2-specific DNase I hypersensitive sites in the IL-4 locus, and Th2 cytokine expression. The fact that GATA-3 fully reconstitutes Th2 development in Stat6-deficient T cells indicates it is a master switch in Th2 development. Finally, GATA-3 exerts Stat6-independent autoactivation, creating a feedback pathway stabilizing Th2 commitment.

The human granulocyte-macrophage colony-stimulating factor gene is autonomously regulated in vivo by an inducible tissue-specific enhancer

The granulocyte-macrophage colony-stimulating factor (GM-CSF) gene is part of a cytokine gene cluster and is directly linked to a conserved upstream inducible enhancer. Here we examined the in vitro and in vivo functions of the human GM-CSF enhancer and found that it was required for the correctly regulated expression of the GM-CSF gene. An inducible DNase I-hypersensitive site appeared within the enhancer in cell types such as T cells, myeloid cells, and endothelial cells that express GM-CSF, but not in nonexpressing cells. In a panel of transfected cells the human GM-CSF enhancer was activated in a tissue-specific manner in parallel with the endogenous gene. The in vivo function of the enhancer was examined in a transgenic mouse model that also addressed the issue of whether the GM-CSF locus was correctly regulated in isolation from other segments of the cytokine gene cluster. After correction for copy number the mean level of human GM-CSF expression in splenocytes from 11 lines of transgenic mice containing a 10.5-kb human GM-CSF transgene was indistinguishable from mouse GM-CSF expression (99% +/- 56% SD). In contrast, a 9.8-kb transgene lacking just the enhancer had a significantly reduced (P = 0.004) and more variable level of activity (29% +/- 89% SD). From these studies we conclude that the GM-CSF enhancer is required for the correct copy number-dependent expression of the human GM-CSF gene and that the GM-CSF gene is regulated independently from DNA elements associated with the closely linked IL-3 gene or other members of the cytokine gene cluster.

Nuclear factor of activated T cells contributes to the function of the CD28 response region of the granulocyte macrophage-colony stimulating factor promoter

The granulocyte macrophage colony stimulating factor (GM-CSF) promoter contains a 10 bp element known as CK-1 or CD28RE that specifically responds to the co-stimulatory signal delivered to T cells via the CD28 surface receptor. This element is a variant NFkappaB site that does not function alone but requires an adjacent promoter region that includes a classical NFkappaB element, an Sp-1 site and a putative activator protein-1 (AP-1)-like binding site. The entire region is referred to as the CD28 response region (CD28RR). The GM-CSF CK-1 element has been shown to bind NFkappaB proteins, in particular c-Rel, whose binding and function is dependent on the architectural transcription factor HMGI(Y). It has been previously suggested that the nuclear factor of activated T cells (NFAT) family of proteins also plays a role in the activity of this region. We show here that recombinant NFATp but not AP-1 can bind to the GM-CSF CD28RR. NFATp present in activated Jurkat T cell extracts can also interact with the CD28RR. The binding of NFATp and Rel proteins requires the same core CK-1 sequences, and appears to be mutually exclusive. We investigated the functional significance of NFATp binding to CK-1 by overexpressing the protein in Jurkat T cells and found that NFATp cannot activate the CD28RR alone but can cooperate with signals generated by phorbol 12-myristate 13-acetate/calcium ionophore. The CD28RR is therefore a complex region that can bind and respond to a combination of transcription factors and signals.

Erythromycin inhibits transcriptional activation of NF-kappaB, but not NFAT, through calcineurin-independent signaling in T cells

The molecular mechanism of the anti-inflammatory effect of erythromycin (EM) was investigated at the level of transcriptional regulation of cytokine gene expression in T cells. EM (>10(-6) M) significantly inhibited interleukin-8 (IL-8) expression but not IL-2 expression from T cells induced with 20 ng of phorbol 12-myristate 13-acetate (PMA) per ml plus 2 microM calcium ionophore (P-I). In electrophoretic mobility shift assays EM at 10(-7) to 10(-5) M concentrations inhibited nuclear factor kappa B (NF-kappaB) DNA-binding activities induced by P-I. Reporter gene assays also showed that EM (10(-5) M) inhibited IL-8 NF-kappaB transcription by 37%. The inhibitory effects of EM on transcriptional activation of IL-2 and DNA-binding activity of nuclear factor of activated T cells (NFAT) were not seen in T cells. On the other hand, FK506, which is also a macrolide derivative, inhibited transcriptional activation of both NF-kappaB and NFAT more strongly than EM did. The mechanism of EM inhibition of transactivation of NF-kappaB was further investigated in transiently transfected T cells that express calcineurin A and B subunits. Expression of calcineurin did not render transactivation of NF-kappaB in T cells more resistant to EM, while the inhibitory effect of FK506 on transactivation of NF-kappaB was attenuated. These findings indicate that EM is capable of inhibiting expression of the IL-8 gene in T cells through transcriptional inhibition and that this inhibition is mediated through a non-calcineurin-dependent signaling event in T lymphocytes.

Role of nuclear factor of activated T cells (NFAT) in the expression of interleukin-5 and other cytokines involved in the regulation of hemopoetic cells

NFAT (nuclear factor of activated T cells) is a transcription factor that plays a role in the regulation of various cytokines, including those involved in the regulation of hemopoetic cells such as granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-4 (IL4), interleukin-3 (IL3), interleukin-13 (IL13) and interleukin-5 (IL5). In this report we provide a summary of the various locations in the promoters of each of these cytokines where NFAT has been shown or suggested to bind, and at which sites NFAT has been shown to be involved in transcriptional regulation. We also provide experimental data to show that the binding of NFAT to the nucleotides GAA at positions -113 to -111 of the human IL5 promoter is associated with functional activity in human T cells.

A two-hit mechanism for vitamin D3-mediated transcriptional repression of the granulocyte-macrophage colony-stimulating factor gene: vitamin D receptor competes for DNA binding with NFAT1 and stabilizes c-Jun

We previously described a control element in the granulocyte-macrophage colony-stimulating factor (GM-CSF) enhancer that is necessary and sufficient to mediate both transcriptional activation in response to T-cell stimuli and transcriptional repression by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] through the vitamin D3 receptor (VDR). This DNA element is a composite site that is recognized by both Fos-Jun and NFAT1; it is directly bound by VDR in the absence of a retinoid X receptor as an apparent monomer, and it is bound in a unique tertiary conformation. We describe here the mechanism by which VDR elicits its transcriptional inhibitory effect. Firstly, VDR outcompetes NFAT1 for binding to the composite site. Overexpression of NFAT1 in vivo by transient transfection is able to relieve the 1,25(OH)2D3-dependent repression. Secondly, VDR stabilizes the binding of a Jun-Fos heterodimer to the adjacent AP-1 portion of the element. This appears to occur through a direct interaction between VDR and c-Jun, as demonstrated in vitro by direct glutathione S-transferase coprecipitation assays. In vivo, overexpression of c-Jun, but not c-Fos, leads to a rescue of the 1, 25(OH)2D3-mediated repression. Transfected FLAG-VDR bound to the NFAT1-AP-1 DNA binding element can be selectively precipitated from nuclear extracts that are made from cells treated with activating agents in the presence of 1,25(OH)2D3. VDR is not detected in the complex in the absence of the ligand. Thus, VDR acts selectively on the two components required for activation of this promoter/enhancer: it competes with NFAT1 for binding to the composite site, positioning itself adjacent to Jun-Fos on the DNA. Co-occupancy apparently leads to an inhibitory effect on c-Jun's transactivation function. These two events mediated by VDR effectively block the NFAT1-AP-1 activation complex, resulting in an attenuation of activated GM-CSF transcription.

Potential role of calcineurin for brain ischemia and traumatic injury

Calcineurin belongs to the family of Ca2+/calmodulin-dependent protein phosphatase, protein phosphatase 2B. Calcineurin is the only protein phosphatase which is regulated by a second messenger, Ca2+. Furthermore, calcineurin is highly localized in the central nervous system, especially in those neurons vulnerable to ischemic and traumatic insults. For these reasons, calcineurin is considered to play important roles in neuron-specific functions. Recently, on the basis of the finding that FK506 and cyclosporin A serve as calcineurin-specific inhibitors, this enzyme has become the subject of much study. It is clear that calcineurin is involved in many neuronal (or non-neuronal) functions such as neurotransmitter release, regulation of receptor functions, signal transduction systems, neurite outgrowth, gene expression and neuronal cell death. In this review, we describe the calcineurin functions, functions of the substrates, and the pathogenesis of traumatic and ischemic insults, and we discuss the potential role of calcineurin. There are many similarities in traumatic and ischemic pathogenesis of the brain in which the release of excessive glutamate is followed by an intracellular Ca2+ increase. However, the intracellular cascade which leads to neuronal cell death after the release of excess Ca2+ is unclear. Although calcineurin is thought to be a key toxic enzyme on the basis of studies using immunosuppressants (FK506 or cyclosporin A), many of the functions of the substrates for calcineurin protect against neuronal cell death. We concluded that calcineurin is a bi-directional enzyme for neuronal cell death, having protective and toxic actions, and the balance of the bi-directional effects may be important in ischemic and traumatic pathogenesis.

High-density lipoproteins differentially modulate cytokine-induced expression of E-selectin and cyclooxygenase-2

Atherogenesis is a multifactorial chronic inflammatory disease in which low plasma levels of HDLs are a strong predictor of the condition. Although the mechanism of protection by HDLs is not precisely known, HDLs have been shown to influence many of the events involved in the development of atherosclerosis. Previously we have shown that HDLs inhibited the cytokine-induced expression of adhesion molecules (E-selectin, VCAM-1, and ICAM-1) by endothelial cells (ECs). As the complete transcriptional regulation of all 3 genes requires the NF-kappaB family of transcription factors, we examined the effect of HDLs on activation of NF-kappaB. We also investigated the effect of HDLs on 2 other cytokine-induced genes, granulocyte-macrophage colony-stimulating factor (GM-CSF) and cyclooxygenase (Cox-2; prostaglandin H2 synthase, EC 0.1.14.99.1). E-selectin expression in response to tumor necrosis factor-alpha (TNFalpha) was, as expected, inhibited in ECs that had been preincubated with HDLs. However, the level of secretion of GM-CSF in the same cultures was no different from control. In a similar manner, although HDLs had no effect on steady-state mRNA levels of GM-CSF, the levels of E-selectin were significantly inhibited by HDLs. In transient cotransfection experiments we found that HDLs inhibited the cytokine-induced expression of a reporter gene driven by the E-selectin proximal promoter (-383 to 80) but had no effect on the expression of a reporter gene driven under the control of the proximal promoter of GM-CSF (-627 to 28). As would be predicted from this differential response, HDLs did not influence the nuclear translocation or DNA binding of NF-kappaB, or alter the kinetics of degradation and resynthesis of the inhibitory protein IkappaBalpha. We found that HDLs synergized with cytokine to enhance the expression of Cox-2 and induce the synthesis of its main EC product, prostacyclin (PGI2), a potent inhibitor of platelet and leukocyte functions. In conclusion, HDL induces an antiinflammatory phenotype in cytokine-induced ECs, synergizing with cytokine to induce elevation of Cox-2 in addition to inhibiting adhesion molecule expression. Our studies show that these differential effects are mediated in a manner that is likely to be independent of NF-kappaB per se.

Requirement for transcription factor NFAT in interleukin-2 expression

The nuclear factor of activated T cells (NFAT) transcription factor is implicated in expression of the cytokine interleukin-2 (IL-2). Binding sites for NFAT are located in the IL-2 promoter. Furthermore, pharmacological studies demonstrate that the drug cyclosporin A inhibits both NFAT activation and IL-2 expression. However, targeted disruption of the NFAT1 and NFAT2 genes in mice does not cause decreased IL-2 secretion. The role of NFAT in IL-2 gene expression is therefore unclear. Here we report the construction of a dominant-negative NFAT mutant (dnNFAT) that selectively inhibits NFAT-mediated gene expression. The inhibitory effect of dnNFAT is mediated by suppression of activation-induced nuclear translocation of NFAT. Expression of dnNFAT in cultured T cells caused inhibition of IL-2 promoter activity and decreased expression of IL-2 protein. Similarly, expression of dnNFAT in transgenic mice also caused decreased IL-2 gene expression. These data demonstrate that NFAT is a critical component of the signaling pathway that regulates IL-2 expression.

CTLA4 ligation attenuates AP-1, NFAT and NF-kappaB activity in activated T cells

CTLA4 is currently viewed as a late-appearing T cell surface receptor which is able to inhibit the proliferation of activated T cells. We sought to identify how CTLA4 ligation exerts these anti-proliferative effects by studying its influence on the activities of the relevant nuclear transcription factors AP-1, NFAT and NF-kappaB. We found that cross-linking CTLA4 on activated T cells completely blocks AP-1 and NFAT transcription factor activity before any effects on T cell proliferation can be observed, with NF-kappaB activity affected to a lesser degree. The suppression of AP-1 and NFAT transcriptional activity correlates with reduced levels of AP-1 and NFAT DNA binding as early as 10 h after T cell activation, prior to detectable up-regulation of CTLA4 on the T cell surface. Additionally, inhibitory effects on T cell proliferation only occurred when CTLA4 molecules were ligated in proximity to signaling TCR complexes, and inhibition of transcription factor DNA binding and activity was observed in the absence of CD28 stimulation. CTLA4 can thus act early during T cell activation to reduce the activity of several key nuclear transcription factors important for continued T cell proliferation and differentiation.

A novel role for the major histocompatibility complex class II transactivator CIITA in the repression of IL-4 production

Class II transactivator (CIITA) is known as a coactivator for MHC class II gene expression in antigen-presenting cells. Surprisingly, when CIITA-/- CD4 T cells were stimulated in the presence of IL-12, they produced not only IFNgamma but also high levels of IL-4. The IL-4 production is due to the accumulation of IL-4 gene transcripts in Th1 cells. This transcriptional control is observed in T cells differentiating to the Th1 but not Th2 lineage, consistent with induction of expression of the CIITA gene in T cells by IFNgamma. Thus, in addition to its role in transactivation of genes involved in antigen presentation, CIITA plays a critical role during the T cell differentiation by negatively regulating the IL-4 gene transcription.

CsA-sensitive purine-box transcriptional regulator in bronchial epithelial cells contains NF45, NF90, and Ku

Human bronchial epithelial (HBE) cells express interleukin (IL)-2 [Y. Aoki, D. Qiu, A. Uyei, and P. N. Kao. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L276-L286, 1997]. 16HBE-transformed cells contain constitutive and inducible nuclear DNA-binding activity for the purine-box/nuclear factor (NF) of activated T cell (NFAT) target DNA sequence in the human IL-2 enhancer. Transcriptional activation through the purine-box DNA sequence requires stimulation with phorbol 12-myristate 13-acetate + ionomycin, and this activation is inhibited by cyclosporin A. Immunohistochemical staining of 16HBE cells demonstrates nuclear expression of the purine-box DNA-binding proteins NF45 and NF90 and no expression of NFATp or NFATc. NF90 and NF45 associate with the DNA-dependent protein kinase catalytic subunit and the DNA-targeting subunits Ku80 and Ku70 (N. S. Ting, P. N. Kao, D. W. Chan, L. G. Lintott, and S. P. Lees-Miller. J. Biol. Chem. 273: 2136-2145, 1998). Antibodies to Ku potently inhibit the purine-box DNA-binding complex. The purine-box transcriptional regulator in 16HBE cells likely comprises NF45, NF90, Ku80, Ku70, and the DNA-dependent protein kinase catalytic subunit.

Modulation of chromatin structure regulates cytokine gene expression during T cell differentiation

Differentiating cells undergo programmed alterations in their patterns of gene expression, which are often regulated by structural changes in chromatin. Here we demonstrate that T cell differentiation results in long-range changes in the chromatin structure of effector cytokine genes, which persist in resting Th1 and Th2 cells in the absence of further stimulation. Differentiation of naive T helper cells into mature Th2 cells is associated with chromatin remodeling of the IL-4 and IL-13 genes, whereas differentiation into Th1 cells evokes remodeling of the IFNgamma but not IL-4 or IL-13 genes. IL-4 locus remodeling is accompanied by demethylation and requires both antigen stimulation and STAT6 activation. We propose that chromatin remodeling of cytokine gene loci is functionally associated with productive T cell differentiation and may explain the coordinate regulation of Th2 cytokine genes.

Characterisation of inducible DNase I hypersensitive sites flanking the human interleukin-5 gene

Interleukin-5 (IL-5) production is necessary for eosinophilia associated with allergic conditions and parasitic infection. IL-5 mRNA is transiently expressed by activated T-lymphocytes. In this report, we have analysed DNA regulatory regions associated with inducible IL-5 expression in the human HSB-2 T-cell line. Only low levels of transcriptional activity were induced in cells transfected with up to 1.2 kb of DNA upstream of the IL-5 gene. DNase I hypersensitivity analysis was employed to identify additional regulatory sequences located outside this region. Two hypersensitivity sites (HS) were identified, one 2.5 kb 5' and the other 1.6 kb 3' from the gene, that were induced on activation of HSB-2 cells by stimuli that induced IL-5 expression. The 5' site, but not the 3' site, was found in primary human T-cells. The presence of the 5' HS did not always coincide with IL-5 expression. Inclusion of the region encompassing the 5' HS in promoter studies mediated a moderate increase in transcriptional activity, suggesting that enhancer elements essential for induction of maximal IL-5 transcription reside at a greater distance from the IL-5 gene.

Familial eosinophilia maps to the cytokine gene cluster on human chromosomal region 5q31-q33

Familial eosinophilia (FE) is an autosomal dominant disorder characterized by peripheral hypereosinophilia of unidentifiable cause with or without other organ involvement. To localize the gene for FE, we performed a genomewide search in a large U.S. kindred, using 312 different polymorphic markers. Seventeen affected subjects, 28 unaffected bloodline relatives, and 8 spouses were genotyped. The initial linkage results from the genome scan provided evidence for linkage on chromosome 5q31-q33. Additional genotyping of genetic markers located in this specific region demonstrated significant evidence that the FE locus is situated between the chromosome 5q markers D5S642 and D5S816 (multipoint LOD score of 6.49). Notably, this region contains the cytokine gene cluster, which includes three genes-namely, those for interleukin (IL)-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF)-whose products play important roles in the development and proliferation of eosinophils. These three cytokine genes were screened for potential disease-specific mutations by resequencing of a subgroup of individuals from the present kindred. No functional sequence polymorphisms were found within the promoter, the exons, or the introns of any of these genes or within the IL-3/GM-CSF enhancer, suggesting that the primary defect in FE is not caused by a mutation in any one of these genes but, rather, is caused by another gene in the area.

The transcription factor NFAT4 is involved in the generation and survival of T cells

Nuclear factor of activated T cells (NFAT) is a family of four related transcription factors implicated in cytokine and early response gene expression in activated lymphocytes. Here we report that NFAT4, in contrast to NFATp and NFATc, is preferentially expressed in DP thymocytes. Mice lacking NFAT4 have impaired development of CD4 and CD8 SP thymocytes and peripheral T cells as well as hyperactivation of peripheral T cells. The thymic defect is characterized by increased apoptosis of DP thymocytes. The increased apoptosis and hyperactivation may reflect heightened sensitivity to TcR-mediated signaling. Further, mice lacking NFAT4 have impaired production of Bcl-2 mRNA and protein. NFAT4 thus plays an important role in the successful generation and survival of T cells.

Long-range transcriptional regulation of cytokine gene expression

Most studies on the control of cytokine gene expression have involved the functional analysis of proximal promoters. Recent work has identified distal elements that mediate long-range cytokine gene regulation and has implicated chromatin reorganization in regulation of cytokine gene loci. These studies have begun to elucidate the basis for cell-specificity and high-level expression of cytokine genes.

Signal transduction during NK cell activation: balancing opposing forces

Significant progress has been made in our understanding of the basic signaling mechanisms regulating NK cell activation. Advances have been fueled in part by the molecular characterization of specific activating receptors (e.g., the Fc gamma RIII multi-subunit complex) and inhibitory receptors (e.g., novel MHC-recognizing inhibitory receptors). However, certain aspects of these analyses are complicated by the heterogeneous nature of the receptor-ligand interactions utilized during the development of a cytotoxic response. Future advances will depend in part on the further molecular characterization of the involved receptors and second messengers and on the development of experimental models for genetically manipulating the signaling elements. It will remain important to understand both activating and inhibitory signaling pathways as the emerging theme is that the balance of these two opposing forces determines the functional outcome of an NK cells interaction with its target.

Inhibitors of calcineurin block expression of cyclins A and E induced by fibroblast growth factor in Swiss 3T3 fibroblasts

In Swiss 3T3 fibroblasts, growth factor-stimulated progression from G1 to S phase involves activation of the Ca2+/calmodulin-dependent serine/threonine-specific protein phosphatase 2B (calcineurin). Here we report that both cobalt and the calcium chelator EGTA, inhibitors of calcium uptake, as well as cyclosporin A and FK-506, specific inhibitors of calcineurin function, abolished fibroblast growth factor (FGF)-induced expression of cyclins A and E, but not cyclin D1. At 0.1 microM concentration cyclosporin A completely blocked FGF-induced expression of cyclins E and A and it inhibited FGF-stimulated DNA synthesis by 40%; full inhibition of DNA synthesis required 10 microM cyclosporin A. PD 98059, an inhibitor of mitogen-activated protein (MAP) kinase kinase, and hemicholinium-3, an inhibitor of FGF-induced MAP kinase activity, did not inhibit the stimulatory effect of FGF on the expression of cyclin E. On the other hand, the inhibitory effect of 0.1 microM cyclosporin A on FGF-stimulated DNA synthesis was additive with that of hemicholinium-3, suggesting that the two inhibitors acted by different mechanisms. The inhibitors of calcineurin and calcium uptake also completely blocked the stimulatory effects of lysophosphatidic acid on the expression of cyclins E and A, but not cyclin D1. The results suggest that FGF- or lysophosphatidic acid-induced transcription of cyclin A and cyclin E genes is mediated by calcineurin involving a MAP kinase-independent mechanism and that increased expression of cyclins A and E is required for the maximal stimulatory effects of these mitogens on DNA synthesis.

Granulocyte-macrophage colony-stimulating factor gene transcription is directly repressed by the vitamin D3 receptor. Implications for allosteric influences on nuclear receptor structure and function by a DNA element

The primary function of activated T lymphocytes is to produce various cytokines necessary to elicit an immune response; these cytokines include interleukin-2 (IL-2), interleukin-4, and granulocyte-macrophage colony-stimulating factor (GMCSF). Steroid hormones and vitamin A and D3 metabolites act to repress the expression of cytokines. 1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) down-modulates activated IL-2 expression at the level transcription, through direct antagonism of the transactivating complex NFAT-1/AP-1 by the vitamin D3 receptor (VDR). We report here that GMCSF transcription in Jurkat T cells is also directly repressed by 1, 25-(OH)2D3 and VDR. Among four NFAT/AP-1 elements in the GMCSF enhancer, we have focused on one such element that when multimerized, is sufficient in mediating both activation by NFAT-1 and AP-1 and repression in response to 1,25-(OH)2D3. Although this element does not contain any recognizable vitamin D response elements (VDREs), high affinity DNA binding by recombinant VDR is observed. In contrast to VDR interactions with positive VDREs, this binding is independent of VDR's heterodimeric partner, the retinoid X receptor. Moreover, VDR appears to bind the GMCSF element as an apparent monomer in vitro. Protease digestion patterns of bound VDR, and receptor mutations affecting DNA binding and dimerization, demonstrate that the receptor binds to the negative site in a distinct conformation relative to a positive VDRE, suggesting that the DNA element itself acts as an allosteric effector of VDR function. This altered conformation may account for VDR's action as a repressing rather than activating factor at this locus.

Fluid shear stress increases the production of granulocyte-macrophage colony-stimulating factor by endothelial cells via mRNA stabilization

To investigate whether the production of colony-stimulating factors (CSFs) by vascular endothelial cells is regulated by hemodynamic force, we exposed cultured human umbilical vein endothelial cells (HUVECs) to controlled levels of shear stress in a flow-loading apparatus and examined changes in the production of CSFs at both the protein and mRNA level. Exposure of HUVECs to a shear stress of 15 and 25 dyne/cm2 markedly increased the release of granulocyte-macrophage CSF (GM-CSF) detected by ELISA to 5.0 and 9.5 times, respectively, the amount released by the static controls at 24 hours, but it had no significant influence on the release of granulocyte CSF or macrophage CSF. The results of reverse transcriptase-polymerase chain reaction demonstrated that GM-CSF mRNA began to increase as early as 2 hours after initiation of 15 dyne/cm2 shear stress and continued to increase with time, reaching a peak of about four times the control levels at 24 hours. This increase in GM-CSF mRNA levels in response to shear stress depended on protein synthesis, because it was blocked by cycloheximide. Neither nuclear run-on assay or luciferase assay using a reporter gene containing GM-CSF gene promoter showed any significant change in transcription of the GM-CSF gene even after 24-hour exposure to a shear stress of 15 dyne/cm2. Actinomycin D chase experiments using a competitive polymerase chain reaction showed that shear stress extended the half-life of GM-CSF mRNA from approximately 23 to 42 minutes in HUVECs. These findings suggest that fluid shear stress increases the production of GM-CSF in HUVECs via mRNA stabilization.

Role of transcriptional repressor ICER in cyclic AMP-mediated attenuation of cytokine gene expression in human thymocytes

Proliferating human medullary thymocytes can exhibit characteristic T helper cell type 1 cytokine responses exemplified by the immediate early expression of interleukin-2, interferon-gamma, tumor necrosis factor-alpha, and lymphotoxin-beta. Here we report that cAMP-mediated attenuation of the transcription of T helper-1-specific cytokine genes in human medullary thymocytes correlates with the induction of the cAMP-mediated transcriptional repressor ICER (inducible cAMP early repressor). We show that ICER binds specifically to several NFAT/AP-1 (nuclear factor of activated T cells/activating protein-1) composite DNA sites essential for the activation of the interleukin (IL)-2 promoter as well as to a homologous DNA motif present in the proximal segment of the interferon-gamma promoter. In the presence of the minimal NFAT DNA-binding domain, which is sufficient for both DNA binding and AP-1 complex formation, ICER and NFAT form NFAT/ICER ternary complexes on several NFAT/AP-1 DNA composite sites previously identified as essential for the expression of the immunoregulatory cytokines such as IL-2, IL-4, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-alpha. In extracts prepared from human medullary thymocytes treated with forskolin and ionomycin, these composite sites bind endogenously expressed ICER either singly or in complexes. Moreover, in Jurkat cells, ectopically expressed ICER represses transcription from NFAT-mediated, phorbol ester/ionophore-activated IL-2, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-alpha promoters. We present evidence that ICER interactions with NFAT/AP-1 composite DNA sites correlate with its ability to repress transcription. These findings provide further insight into the mechanisms involved in cAMP-mediated transcriptional attenuation of cytokine expression.

Distinct NFAT Family Proteins Are Involved in the Nuclear NFAT-DNA Binding Complexes from Human Thymocyte Subsets

The nuclear factor of activated T cells (NFAT) is involved in the transcriptional induction of cytokine and other immunoregulatory genes during an immune response. Among four distinct NFAT family members identified to date, mRNAs of NFAT1, NFATc, and NFATx are expressed in the thymus. Here, we report the distribution of these three NFAT family members in human fetal thymocyte subsets and in peripheral mature T cells. We show that NFATx mRNA was expressed in all T lymphocyte subsets tested and was highest in CD4+CD8+ double positive (DP) thymocytes. Conversely, NFAT1 mRNA was preferentially expressed in the mature CD4+ single positive (SP) populations. NFATc mRNA was present at low levels in all subsets but strongly induced upon treatment with phorbol ester and calcium ionophore. Interestingly, we detected NFAT-DNA binding complexes in DP thymocytes, albeit at lower levels than in CD4 SP cells. Corresponding to the mRNA expression, we observed that NFATx was responsible for the NFAT-DNA binding in DP thymocytes. Moreover, this DNA binding was inhibited by cyclosporin A, indicating that NFATx nuclear translocation was regulated by the calcineurin phosphatase in DP thymocytes. For the CD4 SP populations, NFAT1 and NFATc, and to some extent NFATx, were responsible for the NFAT-DNA binding complexes. These results indicate that NFAT family members are differentially regulated during the development of T cells, and that NFATx may play a distinct role in calcineurin-dependent signaling in DP thymocytes.

The transcription factor NF-ATc1 regulates lymphocyte proliferation and Th2 cytokine production

NF-ATc1 is a member of a family of genes that encodes the cytoplasmic component of the nuclear factor of activated T cells (NF-AT). In activated T cells, nuclear NF-AT binds to the promoter regions of multiple cytokine genes and induces their transcription. The role of NF-ATc1 was investigated in recombination activating gene-1 (RAG-1)-deficient blastocyst complementation assays using homozygous NF-ATc1-/- mutant ES cell lines. NF-ATc1-/-/RAG-1-/- chimeric mice showed reduced numbers of thymocytes and impaired proliferation of peripheral lymphocytes, but normal production of IL-2. Induction in vitro of Th2 responses, as demonstrated by a decrease in IL-4 and IL-6 production, was impaired in mutant T cells. These data indicate that NF-ATc1 plays roles in the development of T lymphocytes and in the differentiation of the Th2 response.

Inefficient termination of antigen responses in NF-ATp-deficient mice

In order to elucidate the role of NF-ATp, one of the most prominent members of family of NF-AT transcription factors in peripheral T lymphocytes, in T cell activation and differentiation we created NF-ATp-deficient mice by gene targeting. Such NF-ATp-/- mice are born and appear to develop a normal immune system. Apart from clear-cut defects in the synthesis of mRNAs for Th2-type lymphokines, such as IL-4, IL-5, IL-10 and IL-13, in primary and secondary stimulations of spleen cells in vitro, of a distinct impaired deletion of V beta 11+/CD4+ T lymphocytes from these mice was detected after superantigen injection. Moreover, NF-ATp-/- mice older than 6 weeks show an 2-5 fold increase in number of lymphocytes. This is correlated with an increased expression of activation markers CD44 and CD69 and decreased expression of CD62.

c-Rel and p65 subunits bind to an upstream NF-kappaB site in human granulocyte macrophage-colony stimulating factor promoter involved in phorbol ester response in 5637 cells

To further clarify the complex transcriptional regulation of the human GM-CSF gene, which was extensively investigated in activated T cells, we have studied the role of an upstream NF-kappaB like site in the 5637 non-lymphoid cell line, which derives from a bladder carcinoma and constitutively produces GM-CSF. This sequence, named the A element, has an active role on GM-CSF transcription and is responsive to the tumor promoter PMA in transient transfection experiments. We describe here a heterodimeric binding complex of NF-kappaB subunits (c-Rel and p65) which is identical to the one obtained using the HIV-LTR-kappaB site as recognition sequence and different from the one (c-Rel and p50) observed with nuclear extracts from Mo T-lymphoid HTLV-II infected cells.

Molecular cloning and functional characterization of murine cDNA encoding transcription factor NFATc

Transcription factors of the NFAT (nuclear factor of activated T cells) family play important roles in immune and inflammatory responses by regulating the expression of genes encoding cytokines and immunoregulatory proteins. Here we describe cloning and characterization of full-length cDNA encoding murine (m) NFATc which predicts that the protein has all the conserved structural motifs of NFAT family members, including the rel homology domain, the NFAT homology domain and the nuclear translocation signals. mNFATc complexed with AP-1 bound specifically to the murine IL-2 NFAT recognition sequence and activated transcription from the co-transfected IL-2 promoter in COS-7 cells. Northern blot analysis showed that the cDNA probe hybridized with a 4.5 kb transcript which is highly inducible in murine T cells. By Northern and in situ hybridization, mNFATc transcript was detected from the early stage of development. In the mouse embryo, mNFATc transcript was strongly expressed in thymus, lung and submandibular gland and weakly in skeletal muscle and heart suggesting that mNFATc may have a role both in embryogenesis and in mature T cells.

Blockade of T-cell activation by dithiocarbamates involves novel mechanisms of inhibition of nuclear factor of activated T cells

Dithiocarbamates (DTCs) have recently been reported as powerful inhibitors of NF-kappaB activation in a number of cell types. Given the role of this transcription factor in the regulation of gene expression in the inflammatory response, NF-kappaB inhibitors have been suggested as potential therapeutic drugs for inflammatory diseases. We show here that DTCs inhibited both interleukin 2 (IL-2) synthesis and membrane expression of antigens which are induced during T-cell activation. This inhibition, which occurred with a parallel activation of c-Jun transactivating functions and expression, was reflected by transfection experiments at the IL-2 promoter level, and involved not only the inhibition of NF-kappaB-driven reporter activation but also that of nuclear factor of activated T cells (NFAT). Accordingly, electrophoretic mobility shift assays (EMSAs) indicated that pyrrolidine DTC (PDTC) prevented NF-kappaB, and NFAT DNA-binding activity in T cells stimulated with either phorbol myristate acetate plus ionophore or antibodies against the CD3-T-cell receptor complex and simultaneously activated the binding of AP-1. Furthermore, PDTC differentially targeted both NFATp and NFATc family members, inhibiting the transactivation functions of NFATp and mRNA induction of NFATc. Strikingly, Western blotting and immunocytochemical experiments indicated that PDTC promoted a transient and rapid shuttling of NFATp and NFATc, leading to their accelerated export from the nucleus of activated T cells. We propose that the activation of an NFAT kinase by PDTC could be responsible for the rapid shuttling of the NFAT, therefore transiently converting the sustained transactivation of this transcription factor that occurs during lymphocyte activation, and show that c-Jun NH2-terminal kinase (JNK) can act by directly phosphorylating NFATp. In addition, the combined inhibitory effects on NFAT and NF-KB support a potential use of DTCs as immunosuppressants.

The cytokine network in juvenile chronic arthritis

This article is an overview of the cytokine network in patients with different types of juvenile chronic arthritis. The concept of the production of TH1-cell or TH2-cell differentiation as a result of cytokine production and the concept of the balance between proinflammatory and anti-inflammatory cytokines are explored. The balance of proinflammatory and anti-inflammatory cytokines could be altered as a result differences in the expression levels of a number of key cytokines and could be the critical events leading to chronic inflammation. Identifying molecular targets for intervention therapy to change the balance of the cytokine network is proposed.

Cyclosporin A and FK506 reduce interleukin-5 mRNA abundance by inhibiting gene transcription

The cytokine interleukin-5 (IL-5) selectively induces the proliferation, differentiation, and activation of mature eosinophils. The immunosuppressive agents cyclosporin A (CsA) and FK506 ameliorate the influx of eosinophils seen in allergic conditions such as asthma. We investigated the mechanisms controlling IL-5 messenger RNA (mRNA) expression in human T-lymphocytes in the presence of CsA or FK506. Fresh human peripheral blood mononuclear cells (PBMC); 7-day cultured PBMC, which represent a population of activated T-lymphocytes derived from PBMC; and the T-cell line HSB-2 were used. A novel polymerase chain reaction (PCR)-based nuclear run-on assay was employed to investigate the rate of IL-5 gene transcription. IL-5 mRNA degradation was measured by quantitative reverse transcriptase (RT)-PCR. CsA and FK506 strongly inhibited cellular IL-5 mRNA expression in response to phytohemagglutinin (PHA), or to phorbol myristate acetate (PMA), and/or calcium ionophore. Marked inhibition was observed in PBMC, 7-day cultured PBMC, and HSB-2 cells. Nuclear run-on assays done with either 7-day cultured PBMC or HSB-2 cells demonstrated striking inhibition of IL-5 gene transcription by both CsA and FK506 at levels reflecting the degree of reduction of total cellular IL-5 mRNA abundance. Neither CsA or FK506 had any detectable effect on the stability of IL-5 mRNA. Thus, the inhibitory effect of CsA and FK506 on cellular IL-5 mRNA expression can be explained by inhibition of the rate of IL-5 gene transcription.