Inhibition of NF-AT-dependent transcription by NF-kappa B: implications for differential gene expression in T helper cell subsets

Light-inducible T cell engagers trigger, tune, and shape the activation of primary T cells

To mount appropriate responses, T cells integrate complex sequences of receptor stimuli perceived during transient interactions with antigen-presenting cells. Although it has been hypothesized that the dynamics of these interactions influence the outcome of T cell activation, methodological limitations have hindered its formal demonstration. Here, we have engineered the Light-inducible T cell engager (LiTE) system, a recombinant optogenetics-based molecular tool targeting the T cell receptor (TCR). The LiTE system constitutes a reversible molecular switch displaying exquisite reactivity. As proof of concept, we dissect how specific temporal patterns of TCR stimulation shape T cell activation. We established that CD4+ T cells respond to intermittent TCR stimulation more efficiently than their CD8+ T cells counterparts and provide evidence that distinct sequences of TCR stimulation encode different cytokine programs. Finally, we show that the LiTE system could be exploited to create light-activated bispecific T cell engagers and manipulate tumor cell killing. Overall, the LiTE system provides opportunities to understand how T cells integrate TCR stimulations and to trigger T cell cytotoxicity with high spatiotemporal control.

Arbitrary Ca2+ regulation for endothelial nitric oxide, NFAT and NF-κB activities by an optogenetic approach

Modern western dietary habits and low physical activity cause metabolic abnormalities and abnormally elevated levels of metabolites such as low-density lipoprotein, which can lead to immune cell activation, and inflammatory reactions, and atherosclerosis. Appropriate stimulation of vascular endothelial cells can confer protective responses against inflammatory reactions and atherosclerotic conditions. This study aims to determine whether a designed optogenetic approach is capable of affecting functional changes in vascular endothelial cells and to evaluate its potential for therapeutic regulation of vascular inflammatory responses in vitro. We employed a genetically engineered, blue light-activated Ca²⁺ channel switch molecule that utilizes an endogenous store-operated calcium entry system and induces intracellular Ca²⁺ influx through blue light irradiation and observed an increase in intracellular Ca²⁺ in vascular endothelial cells. Ca²⁺-dependent activation of the nuclear factor of activated T cells and nitric oxide production were also detected. Microarray analysis of Ca²⁺-induced changes in vascular endothelial cells explored several genes involved in cellular contractility and inflammatory responses. Indeed, there was an increase in the gene expression of molecules related to anti-inflammatory and vasorelaxant effects. Thus, a combination of human blue light-activated Ca²⁺ channel switch 2 (hBACCS2) and blue light possibly attenuates TNFα-induced inflammatory NF-κB activity. We propose that extrinsic cellular Ca²⁺ regulation could be a novel approach against vascular inflammation.

Trans-activation of eotaxin-1 by Brg1 contributes to liver regeneration

Infiltration of eosinophils is associated with and contributes to liver regeneration. Chemotaxis of eosinophils is orchestrated by the eotaxin family of chemoattractants. We report here that expression of eotaxin-1 (referred to as eotaxin hereafter), but not that of either eotaxin-2 or eotaxin-3, were elevated, as measured by quantitative PCR and ELISA, in the proliferating murine livers compared to the quiescent livers. Similarly, exposure of primary murine hepatocytes to hepatocyte growth factor (HGF) stimulated eotaxin expression. Liver specific deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated eosinophil infiltration and down-regulated eotaxin expression in mice. Brg1 deficiency also blocked HGF-induced eotaxin expression in cultured hepatocytes. Further analysis revealed that Brg1 could directly bind to the proximal eotaxin promoter to activate its transcription. Mechanistically, Brg1 interacted with nuclear factor kappa B (NF-κB)/RelA to activate eotaxin transcription. NF-κB knockdown or pharmaceutical inhibition disrupted Brg1 recruitment to the eotaxin promoter and blocked eotaxin induction in hepatocytes. Adenoviral mediated over-expression of eotaxin overcame Brg1 deficiency caused delay in liver regeneration in mice. On the contrary, eotaxin depletion with RNAi or neutralizing antibodies retarded liver regeneration in mice. More important, Brg1 expression was detected to be correlated with eotaxin expression and eosinophil infiltration in human liver specimens. In conclusion, our data unveil a novel role of Brg1 as a regulator of eosinophil trafficking by activating eotaxin transcription.

Type 2 Innate Lymphocytes Actuate Immunity Against Tumours and Limit Cancer Metastasis

Type 2 innate lymphoid cells (ILC2) potentiate immune responses, however, their role in mediating adaptive immunity in cancer has not been assessed. Here, we report that mice genetically lacking ILC2s have significantly increased tumour growth rates and conspicuously higher frequency of circulating tumour cells (CTCs) and resulting metastasis to distal organs. Our data support the model that IL-33 dependent tumour-infiltrating ILC2s are mobilized from the lungs and other tissues through chemoattraction to enter tumours, and subsequently mediate tumour immune-surveillance by cooperating with dendritic cells to promote adaptive cytolytic T cell responses. We conclude that ILC2s play a fundamental, yet hitherto undescribed role in enhancing anti-cancer immunity and controlling tumour metastasis.

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

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

Triterpenoids and Polysaccharide Fractions of Ganoderma tsugae Exert Different Effects on Antiallergic Activities

This study was to investigate antiallergic effects of triterpenoids (Gt-TRE) and polysaccharide (Gt-PS) extracts from Ganoderma tsugae, using mast cell line RBL-2H3, T cell line EL4, primary T cells, and transfected RAW264.7 macrophage cells. The results showed that histamine secreted from activated RBL-2H3 mast cells was significantly suppressed by Gt-TRE but not Gt-PS. Interleukin- (IL-) 4 secreted from activated EL4 cells was significantly suppressed by Gt-TRE but not Gt-PS. Further primary CD4⁺ T cells cultures also confirmed that Gt-TRE (5 ~ 50 µg/mL) significantly suppressed Th2 cytokines IL-4 and IL-5 secretions but had no effect on Th1 cytokines IL-2 and interferon (IFN)-γ. Gt-PS did not affect IL-4 and IL-5 secretions until higher doses (400, 500 µg/mL) and significantly suppressed IFNγ secretions but enhanced IL-2 at these high doses. The reporter gene assay indicated that Gt-TRE inhibited but Gt-PS enhanced the transcriptional activity of NF-κB in activated transfected RAW264.7 cells and transfected EL4 cells. IL-4 secreted by this transfected EL-4 cells was also significantly decreased by Gt-TRE but not by Gt-PS, suggesting that these two fractions may exert different effects on NF-κB related cytokines expression. These data suggested that triterpenoids fraction of Ganoderma tsugae might be the main constituents to alleviate allergic asthma.

Cytokine-induced cytokine production by conventional and innate lymphoid cells

Innate immune and differentiated T cells produce signature cytokines in response to cytokine stimulation. Optimal production requires stimulation by an NF-κB inducer, most commonly an interleukin (IL)-1 family member, and a STAT activator. Usually, there is linkage between the IL-1 family member, the activated STAT and the cytokines produced: IFNγ producers respond to the IL-1 family member, IL-18 and IL-12, a STAT4 activator; IL-13 producers respond to IL-33 (although for ILC2 cells this may be replaced by IL-25) and STAT5 activators; for cells producing IL-17A or IL-22, the combination is IL-1 and a STAT3 inducer. Cytokine-induced cytokine production may have broad significance in orchestrating innate responses to distinct infectious agents and in maintaining inflammatory responses after elimination of the inciting antigen.

Reconsolidation or extinction: transcription factor switch in the determination of memory course after retrieval

In fear conditioning, aversive stimuli are readily associated with contextual features. A brief reexposure to the training context causes fear memory reconsolidation, whereas a prolonged reexposure induces memory extinction. The regulation of hippocampal gene expression plays a key role in contextual memory consolidation and reconsolidation. However, the mechanisms that determine whether memory will reconsolidate or extinguish are not known. Here, we demonstrate opposing roles for two evolutionarily related transcription factors in the mouse hippocampus. We found that nuclear factor-κB (NF-κB) is required for fear memory reconsolidation. Conversely, calcineurin phosphatase inhibited NF-κB and induced nuclear factor of activated T-cells (NFAT) nuclear translocation in the transition between reconsolidation and extinction. Accordingly, the hippocampal inhibition of both calcineurin and NFAT independently impaired memory extinction, whereas inhibition of NF-κB enhanced memory extinction. These findings represent the first insight into the molecular mechanisms that determine memory reprocessing after retrieval, supporting a transcriptional switch that directs memory toward reconsolidation or extinction. The precise molecular characterization of postretrieval processes has potential importance to the development of therapeutic strategies for fear memory disorders.

Short Promoters in Viral Vectors Drive Selective Expression in Mammalian Inhibitory Neurons, but do not Restrict Activity to Specific Inhibitory Cell-Types

Short cell-type specific promoter sequences are important for targeted gene therapy and studies of brain circuitry. We report on the ability of short promoter sequences to drive fluorescent protein expression in specific types of mammalian cortical inhibitory neurons using adeno-associated virus (AAV) and lentivirus (LV) vectors. We tested many gene regulatory sequences derived from fugu (Takifugu rubripes), mouse, human, and synthetic composite regulatory elements. All fugu compact promoters expressed in mouse cortex, with only the somatostatin (SST) and the neuropeptide Y (NPY) promoters largely restricting expression to GABAergic neurons. However these promoters did not control expression in inhibitory cells in a subtype specific manner. We also tested mammalian promoter sequences derived from genes putatively coexpressed or coregulated within three major inhibitory interneuron classes (PV, SST, VIP). In contrast to the fugu promoters, many of the mammalian sequences failed to express, and only the promoter from gene A930038C07Rik conferred restricted expression, although as in the case of the fugu sequences, this too was not inhibitory neuron subtype specific. Lastly and more promisingly, a synthetic sequence consisting of a composite regulatory element assembled with PAX6 E1.1 binding sites, NRSE and a minimal CMV promoter showed markedly restricted expression to a small subset of mostly inhibitory neurons, but whose commonalities are unknown.

IL-1 family members and STAT activators induce cytokine production by Th2, Th17, and Th1 cells

Expression of T1ST2, the IL-33R, by Th2 cells requires GATA3. Resting Th2 cells express little GATA3, which is increased by IL-33 and a STAT5 activator, in turn increasing T1ST2 from its low-level expression on resting Th2 cells. Th2 cells that have upregulated T1ST2 produce IL-13, but not IL-4, in response to IL-33 plus a STAT5 activator in an antigen-independent, NF-kappaB-dependent, cyclosporin A (CsA)-resistant manner. Similarly, Th17 cells produce IL-17A in response to IL-1beta and a STAT3 activator and Th1 cells produce IFNgamma in response to IL-18 and a STAT4 inducer. Thus, each effector Th cell produces cytokines without antigenic stimulation in response to an IL-1 family member and a specific STAT activator, implying an innate mechanism through which memory CD4 T cells are recruited by an induced cytokine environment.

SUMO conjugation contributes to immune deviation in nonobese diabetic mice by suppressing c-Maf transactivation of IL-4

It is not clear why the development of protective Th2 cells is poor in type 1 diabetes (T1D). c-Maf transactivates the IL-4 gene promoting Th2 cell development; therefore, abnormalities in c-Maf may contribute to reduced IL-4 production by CD4 cells from nonobese diabetic (NOD) mice. In this study we demonstrate that despite normal expression, c-Maf binds poorly to the IL-4 promoter (IL-4p) in NOD CD4 cells. Immunoblotting demonstrates that c-Maf can be modified at lysine 33 by SUMO-1 (small ubiquitin-like modifier 1). Sumoylation is facilitated by direct interaction with the E2-conjugating enzyme Ubc9 and increases following T cell stimulation. In transfected cells, sumoylation decreases c-Maf transactivation of IL-4p-driven luciferase reporter activity, reduces c-Maf binding to the IL-4p in chromatin immunoprecipitation assays, and enhances c-Maf localization into promyelocytic leukemia nuclear bodies. Sumoylation of c-Maf is increased in NOD CD4 cells as compared with CD4 cells from diabetes-resistant B10.D2 mice, suggesting that increased c-Maf sumoylation contributes to immune deviation in T1D by reducing c-Maf access to and transactivation of the IL-4 gene.

A dimer-specific function of the transcription factor NFATp

The transcription factor NFATp integrates multiple signal transduction pathways through coordinate binding with basic-region leucine zipper (bZIP) proteins and other transcription factors. The NFATp monomer, even in the absence of its activation domains, recruits bZIP proteins to canonical NFAT-bZIP composite DNA elements. By contrast, the NFATp dimer and its bZIP partner bind noncooperatively to the NFAT-bZIP element of the tumor necrosis factor (TNF) gene promoter. This observation raises the possibility that the function of the activation domains of NFATp is dimer-specific. Here, we determine the consensus DNA binding site of the NFATp dimer, describe monomer- and dimer-specific NFATp-DNA contact patterns, and demonstrate that NFATp dimerization and dimer-specific activation subdomains are required for transcriptional activation from the TNF NFAT-bZIP element. We also show that these NFATp subdomains interact with the coactivator CBP (CREB-binding protein), which is required for NFATp-dependent TNF gene transcription. Thus, the context-specific function of the activation domains of NFAT can be potentiated by DNA-directed dimerization.

Coincident activation of Th2 T cells with onset of the disease and differential expression of GRO-gamma in peripheral blood leukocytes in minimal change disease

BACKGROUND

Involvement of Th2 T cells/NFkappaB in minimal change disease (MCD) has been postulated. A promising but unconfirmed glomerular permeability factor (GPF) from MCD T cells has been described. We explored whether GPF was the consequence of Th2 cell activation.

METHODS

Peripheral blood leukocytes (PBL) from 16 MCD patients and 7 normal controls were analyzed and the results were statistically compared.

RESULTS

Flow cytometry demonstrated a significant expansion of CD4+ T cell population and dramatically increased CD69+ cells among CD4+ T cells in MCD, suggesting coincident activation of T cells with onset of the disease. RT-PCR on RNA from either freshly isolated PBL or post in vitroactivation showed high-level expression of the Th2 cytokine interleukin-4 in all MCD patients. Importantly, both antibody microarray assay on sera and RT-PCR on mRNA of PBL revealed expression of a CXC chemokine GRO-gamma (growth-related oncogene) in all MCD patients as compared with one of 7 controls.

CONCLUSIONS

Our results reveal an association between onset of MCD and activation of Th2 cells. The GRO family has been implicated in the function of endothelial cells, and its expression is under NFkappaB regulation. Thus, GRO-gamma is a promising candidate for Th2-associated GPF in MCD.

GATA3 up-regulation associated with surface expression of CD294/CRTH2: a unique feature of human Th cells

GATA-3 and T-box expressed in T cells (T-bet) play central roles in Th-cell development and function. Consistently, studies in mice document their selective expression in Th1 and Th2 cells, respectively. In contrast, it is not clear whether these genes are regulated in human Th cells. Here we show that T-bet expression is polarized to a comparable degree in human and mouse Th-cell cultures, while only mouse GATA3 is subject to substantial regulation. This did not reflect differential skewing efficiency in human versus mouse cultures, as these contained similar frequencies of IFN-gamma- and IL-4-producing cells. However, GATA-3 was expressed at significantly higher levels in human IL-4-producing cells enriched via capture with monoclonal antibodies (mAbs) against the PGD(2) receptor, CRTH2, the best selective Th2-cell surface marker to date. Along with increased IL-4 and GATA-3, CRTH2(+) Th cells isolated from Th2-skewed cultures or the circulating memory pool exhibited markedly decreased IFN-gamma and T-bet expression. Thus, the human GATA-3 gene is not regulated in response to polarizing signals that are sufficient to direct Th2-specific expression in mouse cells. This postulates the involvement of an additional level of complexity in the regulation of human GATA-3 expression and stresses the existence of nontrivial differences in the regulation of human versus mouse T-cell function.

Characterization of a novel PMA-inducible pathway of interleukin-13 gene expression in T cells

Although interleukin 13 (IL-13) is an important mediator of asthma and allergic diseases, the molecular mechanisms regulating IL-13 gene expression are not well understood. This study was designed to define the molecular mechanisms governing IL-13 gene expression in T cells. IL-13 expression was examined in human peripheral blood T cells and in the EL-4 T-cell line by enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction. An IL-13 promoter deletion analysis was performed using luciferase-based reporter plasmids transiently transfected into EL-4 cells by electroporation. DNA binding factors were investigated using electrophoretic mobility shift assays. In contrast to IL-4 expression, which required concomitant activation of calcium- and protein kinase C- (PKC-) dependent signalling pathways, PKC activation alone was sufficient for IL-13 protein secretion in mitogen-primed (but not resting) peripheral blood T cells, and for IL-13 mRNA expression and promoter activity in EL-4 T cells. Promoter deletion analysis localized a phorbol 12-myristate 13-acetate (PMA)-sensitive element to a proximal promoter region between -109 and -79 base pairs upstream from the IL-13 transcription start site. This promoter region supported the binding of both constitutive and PMA-inducible nuclear factors in gel shift assays.

Lysophosphatidic acid enhances interleukin-13 gene expression and promoter activity in T cells

Lysophosphatidic acid (LPA) is a membrane-derived lysophospholipid with wide-ranging effects on multiple lung cells including airway epithelial and smooth muscle cells. LPA can augment migration and cytokine synthesis in lymphocytes, but its potential effects on Th2 cytokines have not been well studied. We examined the effects of physiological concentrations of LPA on IL-13 gene expression in human T cells. The Jurkat T cell line and human peripheral blood CD4+ T cells were incubated with LPA alone or with 1) pharmacological agonists of different signaling pathways, or 2) antibodies directed against the T cell receptor complex and costimulatory molecules. Luciferase-based reporter constructs driven by different lengths of the human IL-13 promoter were transfected by electroporation in Jurkat cells treated with and without LPA. The effects of LPA on IL-13 mRNA stability were examined using actinomycin D to halt ongoing transcription. Expression of mRNA encoding LPA2 and LPP-1 increased with T cell activation. LPA augmented IL-13 secretion under conditions of submaximal T cell activation. This was observed using pharmacological agonists activating intracellular calcium-, PKC-, and cAMP-dependent signaling pathways, as well as antibodies directed against CD3 and CD28. LPA only slightly prolonged IL-13 mRNA half-life in submaximally stimulated Jurkat cells. In contrast, LPA significantly enhanced transcriptional activation of the IL-13 promoter via regulatory elements contained within proximal 312 bp. The effects of LPA on IL-13 promoter activation appeared to be distinct from those mediated by GATA-3. LPA can augment IL-13 gene expression in T cells, especially under conditions of submaximal activation.

Activation of Signaling Lymphocytic Activation Molecule Triggers a Signaling Cascade That Enhances Th1 Responses in Human Intracellular Infection

T cell production of IFN-gamma contributes to host defense against infection by intracellular pathogens, including mycobacteria. Lepromatous leprosy, the disseminated form of infection caused by Mycobacterium leprae, is characterized by loss of cellular response against the pathogen and diminished Th1 cytokine production. Relieving bacterial burden in Ag-unresponsive patients might be achieved through alternative receptors that stimulate IFN-gamma production. We have previously shown that ligation of signaling lymphocytic activation molecule (SLAM) enhances IFN-gamma in mycobacterial infection; therefore, we investigated molecular pathways leading from SLAM activation to IFN-gamma production in human leprosy. The expression of the SLAM-associated protein (an inhibitory factor for IFN-gamma induction) on M. leprae-stimulated cells from leprosy patients was inversely correlated to IFN-gamma production. However, SLAM ligation or exposure of cells from lepromatous patients to a proinflammatory microenvironment down-regulated SLAM-associated protein expression. Moreover, SLAM activation induced a sequence of signaling proteins, including activation of the NF-kappaB complex, phosphorylation of Stat1, and induction of T-bet expression, resulting in the promotion of IFN-gamma production, a pathway that remains quiescent in response to Ag in lepromatous patients. Therefore, our findings reveal a cascade of molecular events during signaling through SLAM in leprosy that cooperate to induce IFN-gamma production and strongly suggest that SLAM might be a focal point for therapeutic modulation of T cell cytokine responses in diseases characterized by dysfunctional Th2 responses.

Truncation of C-mip (Tc-mip), a new proximal signaling protein, induces c-maf Th2 transcription factor and cytoskeleton reorganization

Several arguments suggest that minimal change nephrotic syndrome (MCNS) results from yet unknown systemic disorder of T cell function. By screening a cDNA library from T cell relapse, we identified a new pleckstrin homology (PH) domain-containing protein encoded by a gene located on chromosome 16q24. Two alternative transcripts were identified. The first species (c-mip) was expressed in fetal liver, kidney, and peripheral blood mononuclear cells (PBMCs), but weakly detected in PBMCs from MCNS patients. The second form (Tc-mip, standing for truncated c-maf inducing protein), corresponds to subtracted transcript and lacks the NH2-terminal PH domain. The expression of Tc-mip was restricted to fetal liver, thymus, and MCNS PBMCs where it was specifically recruited in CD4+ T cells subset. Overexpression of Tc-mip in T cell Jurkat induced c-maf, transactivated the interleukin 4 gene and down-regulated the interferon gamma expression, characteristic of a Th2 commitment. Moreover, the overexpression of Tc-mip induced Src phosphorylation, T cell clustering, and a cellular redistribution of the cytoskeleton-associated L-plastin, by a PI3 kinase independent pathway. Tc-mip represents therefore the first identified protein, which links proximal signaling to c-maf induction.

Autocrine IL-4 gene regulation at late phases of TCR activation in differentiated Th2 cells

IL-4 is a multifunctional cytokine whose secretion displays important immunomodulatory functions. Its expression is regulated at the level of transcription, and one of the main factors involved is NFAT. The IL-4-induced transcription factor Stat6 is required for the development of naive T cells into Th2 phenotype, capable of secreting IL-4. However, IL-4 production by differentiated Th2 cells is IL-4 independent; thus, it remains unclear whether Stat6 plays any role in the IL-4 expression by mature Th2 cells. We have analyzed in the Th2 clone D10.G4.1 the nuclear proteins able to bind the regulatory element P1 of the IL-4 promoter. Gel-shift assays show NFAT1 as the most abundant nuclear protein that binds to P1 after ionomycin plus PMA activation, whereas Stat6 accounts for the bulk of the P1 binding in the presence of exogenous IL-4. Reporter experiments agree with an inhibitory effect of Stat6 on the NFAT1-induced transcriptional activity directed by the P1 element. CD3 signaling leads to an early induction of NFAT1-P1 complexes correlating with a strong induction of the IL-4 gene. In later phases of CD3 activation, P1 is also bound by Stat6 and a fall in the IL-4 mRNA levels takes place. These two late events during CD3 activation were found to be sensible in experiments conducted with an anti-IL-4 Ab. These results suggest that IL-4 endogenously produced by Th2 cells under TCR triggering modulates its own expression through Stat6.

NF-kappaB family of transcription factors: central regulators of innate and adaptive immune functions

Transcription factors of the Rel/NF-kappaB family are activated in response to signals that lead to cell growth, differentiation, and apoptosis, and these proteins are critical elements involved in the regulation of immune responses. The conservation of this family of transcription factors in many phyla and their association with antimicrobial responses indicate their central role in the regulation of innate immunity. This is illustrated by the association of homologues of NF-kappaB, and their regulatory proteins, with resistance to infection in insects and plants (M. S. Dushay, B. Asling, and D. Hultmark, Proc. Natl. Acad. Sci. USA 93:10343-10347, 1996; D. Hultmark, Trends Genet. 9:178-183, 1993; J. Ryals et al., Plant Cell 9:425-439, 1997). The aim of this review is to provide a background on the biology of NF-kappaB and to highlight areas of the innate and adaptive immune response in which these transcription factors have a key regulatory function and to review what is currently known about their roles in resistance to infection, the host-pathogen interaction, and development of human disease.

Activation of nuclear factor-kappaB induced by diabetes and high glucose regulates a proapoptotic program in retinal pericytes

To reconstruct the events that may contribute to the accelerated death of retinal vascular cells in diabetes, we investigated in situ and in vitro the activation of nuclear factor-kappaB (NF-kappaB), which is triggered by cellular stress and controls several programs of gene expression. The retinal capillaries of diabetic eye donors showed an increased number of pericyte nuclei positive for NF-kappaB, when compared with nondiabetic donors, whereas endothelial cells were negative. Microvascular cell apoptosis and acellular capillaries were increased only in the diabetic donors with numerous NF-kappaB-positive pericytes. Likewise, high glucose in vitro activated NF-kappaB in retinal pericytes but not in endothelial cells, and increased apoptosis only in pericytes. Studies with NF-kappaB inhibitors suggested that in pericytes, basal NF-kappaB has prosurvival functions, whereas NF-kappaB activation induced by high glucose is proapoptotic. Pericytes exposed to high glucose showed increased expression of Bax and of tumor necrosis factor-alpha, which were prevented by the NF-kappaB inhibitors and mimicked by transfection with the p65 subunit of NF-kappaB, and failed to increase the levels of the NF-kappaB-dependent inhibitors of apoptosis. Colocalization of activated NF-kappaB and Bax overexpression was observed in the retinal pericytes of diabetic donors. A proapoptotic program triggered by NF-kappaB selectively in retinal pericytes in response to hyperglycemia is a possible mechanism for the early demise of pericytes in diabetic retinopathy.

Flux through the hexosamine pathway is a determinant of nuclear factor kappaB- dependent promoter activation

The hexosamine pathway may mediate some of the toxic effects of glucose. We hypothesized that flux through this pathway might regulate the activity of nuclear factor kappaB (NF-kappaB)-dependent genes in mesangial cells (MCs). In MCs, RT-PCR revealed that high glucose (30 mmol/l) and glucosamine (1 mmol/l) increased mRNA levels for vascular cell adhesion molecule 1 (VCAM-1) and increased the activity of an NF-kappaB enhancer by 1.5- and 2-fold, respectively. Overexpression of glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme for flux through the hexosamine pathway, led to a 2.2-fold increase in NF-kappaB enhancer activity; the combination of GFAT overexpression and high glucose increased activity 2.8-fold, and these increases were prevented by 40 micromol/l O-diazoacetyl-L-serine (azaserine) or 6-diazo-5-oxonorleucine. High glucose, glucosamine, and GFAT overexpression increased binding of MC nuclear proteins to NF-kappaB consensus sequences. Immunoblotting revealed that the p65 subunit of NF-kappaB was O-glycosylated in MC cultured in physiologic glucose and that significant enhancement occurred with high glucose and glucosamine. Both glucose and glucosamine dose-dependently increased human VCAM-1 promoter activity. In addition, GFAT overexpression activated the VCAM-1 promoter (2.25-fold), with further augmentation by high glucose and abrogation by inhibitors of GFAT, NF-kappaB, and O-glycosylation. Inactivation of the two NF-kappaB sites in the VCAM-1 promoter abolished its response to high glucose, glucosamine, and GFAT overexpression. These results suggest that increased flux through the hexosamine pathway leads to NF-kappaB-dependent promoter activation in MCs.

Selective expression of nuclear factor of activated T cells 2/c1 in human basophils: evidence for involvement in IgE-mediated IL-4 generation

BACKGROUND

The nuclear factor of activated T cells (NFAT) family of transcription factors plays a key role in rapidly inducing IL4 gene expression in effector T cells.

OBJECTIVE

Because human basophils secrete high levels of IL-4, we have examined whether specific NFAT species are expressed in these cells and whether Fc(epsilon)RI-mediated activation affects their subcellular localization and transcriptional function.

METHODS

Intracellular NFAT protein was identified by using 2-color flow cytometry; gene expression was done with RT-PCR. Subcellular localization of NFAT was assessed by means of Western blotting. Electrophoretic mobility shift assays assessed NFAT involvement in IL-4 transcription.

RESULTS

Basophils constitutively expressed high levels of NFAT2. In contrast, NFAT1 (NFATp), which is found in most leukocytes, was not seen in basophils. Low-level staining for NFAT4 was detected but was variably expressed among donor cells. Likewise, NFAT2 mRNA was constitutively expressed in basophils, and message for NFAT4 was seen in 3 of 5 preparations, whereas that for NFAT1 was found in only 1 of 5 preparations. NFAT2 protein accumulated in the nuclei of basophils activated for 1 hour with anti-IgE, and this was inhibited with the addition of FK506. A protein-DNA complex was formed with nuclear lysates from basophils and an IL-4 promoter NFAT consensus probe, with greater binding intensities detected in lysates of activated cells. An antibody to NFAT2 reduced the formation of the complex, whereas no effects were seen with antibodies to NFAT1, NFAT4, or unrelated transcription factors.

CONCLUSIONS

The selective and specific expression of NFAT2 in basophils is unique among leukocytes. This transcription factor also appears to play a critical role in the Fc(epsilon)RI-mediated production of IL-4 in these cells.

Histone deacetylation inhibits IL4 gene expression in T cells

BACKGROUND

Dysregulated expression of IL-4 has been linked with allergic diseases. IL-4 expression is controlled at the level of gene transcription by the coordinated action of multiple factors that bind regulatory promoter elements. In addition, alterations in chromatin structure are thought to play a role in regulating the expression of cytokines in the T(H)2 gene cluster, although the biochemical basis for these alterations in human T cells is not well understood.

OBJECTIVE

We sought to define the role of histone acetylation in the regulation of IL4 gene expression in human T cells.

METHODS

IL-4 protein production was measured by means of ELISA. IL-4 promoter activity was measured with luciferase-based reporter constructs transiently transfected into Jurkat T cells. The acetylation status of histones associated with the IL4 gene was analyzed with chromatin immunoprecipitation assays.

RESULTS

IL-4 production from activated peripheral blood T cells was enhanced by the histone deacetylase inhibitor trichostatin A. Overexpression of the type 1 histone deacetylases 1, 2, and 3 inhibited transcription driven by the IL-4 promoter in Jurkat T cells, whereas cotransfection of the histone acetyltransferase CREB-binding protein potentiated IL-4 promoter activity. Using chromatin immunoprecipitation assays, we show that nucleosomes in the proximal IL-4 promoter are acetylated on T-cell activation.

CONCLUSION

Our results demonstrate that the acetylation state of histones associated with the IL-4 promoter is a key regulator of IL4 gene expression.

ERM transactivation is up-regulated by the repression of DNA binding after the PKA phosphorylation of a consensus site at the edge of the ETS domain

The final step of the transduction pathway is the activation of gene transcription, which is driven by kinase cascades leading to changes in the activity of many transcription factors. Among these latter, PEA3/E1AF, ER81/ETV1, and ERM, members of the well conserved PEA3 group from the Ets family are involved in these processes. We show here that protein kinase A (PKA) increases the transcriptional activity of human ERM and human ETV1, through a Ser residue situated at the edge of the ETS DNA-binding domain. PKA phosphorylation does not directly affect the ERM transactivation domains but does affect DNA binding activity. Unphosphorylated wild-type ERM bound DNA avidly, whereas after PKA phosphorylation it did so very weakly. Interestingly, S367A mutation significantly reduced the ERM-mediated transcription in the presence of the kinase, and the DNA binding of this mutant, although similar to that of unphosphorylated wild-type protein, was insensitive to PKA treatment. Mutations, which may mimic a phosphorylated serine, converted ERM from an efficient DNA-binding protein to a poor DNA binding one, with inefficiency of PKA phosphorylation. The present data clearly demonstrate a close correlation between the capacity of PKA to increase the transactivation of ERM and the drastic down-regulation of the binding of the ETS domain to the targeted DNA. What we thus demonstrate here is a relatively rare transcription activation mechanism through a decrease in DNA binding, probably by the shift of a non-active form of an Ets protein to a PKA-phosphorylated active one, which should be in a conformation permitting a transactivation domain to be active.

Yin-Yang 1 activates interleukin-4 gene expression in T cells

Interleukin-4 (IL-4) is a multifunctional cytokine that plays an important role in immune and inflammatory responses. Expression of the IL-4 gene is tightly controlled at the level of gene transcription by both positive and negative regulatory elements in the IL-4 promoter. Several constitutive nuclear factors have been identified that can interact with IL-4 promoter elements in DNA binding assays. Here we report that the zinc-finger protein YY-1 (Yin-Yang 1) can bind to multiple elements within the human IL-4 promoter. Cotransfection of Jurkat T cells with different IL-4 promoter/reporter constructs together with expression vectors encoding antisense, wild-type, or zinc finger-deleted mutant YY-1 suggested that YY-1 enhanced IL-4 promoter activity in a DNA-binding domain-dependent manner. Site-directed mutagenesis revealed that a proximal YY-1-binding site, termed Y0 ((-59)TCATTTT(-53)), was essential for YY-1-driven IL-4 promoter activity. In addition, cotransfected YY-1 enhanced both IL-4 promoter activity and endogenous IL-4 gene expression in nontransformed peripheral blood T cells. Thus, YY-1 positively regulates IL-4 gene expression in lymphocytes.

Inhibition of NFATx activation by an oligopeptide: disrupting the interaction of NFATx with calcineurin

Calcium-dependent phosphatase calcineurin (CN) regulates the activation and nuclear translocation of NFAT. We identify here a novel CN-binding motif in one member of the NFAT family, NFATx, and a peptide based on this motif, Pep3. Pep3 binds CN and competes with wild-type NFATx for CN interaction. Amino acid mutations within Pep3 show that multiple amino acid residues are required for the effective functions of Pep3. Ectopic expression of Pep3 in a Th clone via a retrovirus-mediated gene transfer could selectively block the nuclear translocation of endogenous NFATx, whereas it had little effect on the nuclear translocation of another member of the NFAT family, NFATp. Furthermore, in transfection experiments, Pep3 also blocked the nuclear translocation of transfected NFATx, but not NFATp, in the B cell line M12, demonstrating specific inhibition of Pep3 for NFATx. Importantly, several cytokines produced by the T cell clone were severely repressed by ectopic Pep3, and indeed, the production of these cytokines was enhanced by the expression of wild-type NFATx. Our results show selective inhibition of NFATx activation and cytokine expression by Pep3 and suggest a new approach for studying the biology of each NFAT family member. This approach may provide an opportunity for pharmacological targeting of Ca(2+)-dependent signaling events.

Alveolar macrophages and T cells from sarcoid, but not normal lung, are permissive to adenovirus infection and allow analysis of NF-kappa b-dependent signaling pathways

Adenovirus (Adv)-mediated gene transfer requires efficient infection of target cells. The objective of this study was to establish whether alveolar macrophages (AM) and T cells (AT) from sarcoid patients were permissive to infection with Adv vectors and if this property could be used to investigate cytokine gene regulation. Sarcoid and normal bronchoalveolar lavage (BAL) specimens infected with Adv vectors expressing either beta-galactosidase or a green fluorescent protein were analyzed for transgene expression by fluorescence-activated cell sorter (FACS) and direct immunofluorescence, respectively. Expression of surface antigens previously associated with Adv infection, the coxsackie/adenovirus receptor (CAR), alpha v beta 3, and alpha v beta 5 integrins, was also assessed using FACS analysis. Sarcoid AM and AT were found to efficiently express Adv transgenes, unlike AM from normal volunteers, peripheral blood monocytes, and peripheral blood T cells. Cells permissive to Adv infection expressed the CAR and alpha v beta 5 integrin (also alpha v beta 3 integrin for AM). The data indicate that the upregulation of Adv receptors and the ability to infect sarcoid AM and AT are related to the inflammatory environment within the lung. Having demonstrated efficient Adv-mediated transgene delivery to sarcoid AM and AT, a construct encoding porcine I kappa B alpha was then used to investigate the requirement for nuclear factor (NF)-kappa B in the regulation of cytokine gene expression in pulmonary sarcoidosis. Overexpression of I kappa B alpha in sarcoid BAL specimens indicated that tumor necrosis factor-alpha and interleukin (IL)-6 production by AM and interferon (IFN)-gamma production by AT is NF-kappa B dependent, whereas IL-4 production by AT is NF-kappa B independent. This is the first occasion that the requirement for NF-kappa B in IFN-gamma gene expression within primary human T cells has been demonstrated. The results of this study have implications for the future investigation of molecular pathways in inflammatory lung disease.

Selective inhibition of interleukin-4 gene expression in human T cells by aspirin

Previous studies indicated that aspirin (acetylsalicylic acid [ASA]) can have profound immunomodulatory effects by regulating cytokine gene expression in several types of cells. This study is the first in which concentrations of ASA in the therapeutic range were found to significantly reduce interleukin (IL)-4 secretion and RNA expression in freshly isolated and mitogen-primed human CD4+ T cells. In contrast, ASA did not affect IL-13, interferon-gamma, and IL-2 expression. ASA inhibited IL-4, but not IL-2, promoter-driven chloramphenicol acetyltransferase expression in transiently transfected Jurkat T cells. The structurally unrelated nonsteroidal anti-inflammatory drugs indomethacin and flurbiprofen did not affect cytokine gene expression in T cells, whereas the weak cyclo-oxygenase inhibitor salicylic acid was at least as effective as ASA in inhibiting IL-4 expression and promoter activity. The inhibitory effect of ASA on IL-4 transcription was not mediated by decreased nuclear expression of the known salicylate target nuclear factor (NF)-kappaB and was accompanied by reduced binding of an inducible factor to an IL-4 promoter region upstream of, but not overlapping, the NF of activated T cells- and NF-kappaB-binding P1 element. It is concluded that anti-inflammatory salicylates, by means of a previously unrecognized mechanism of action, can influence the nature of adaptive immune responses by selectively inhibiting the expression of IL-4, a critical effector of these responses, in CD4+ T cells.

Identification and characterization of a critical CP2-binding element in the human interleukin-4 promoter

Expression of cytokine genes in T cells is thought to result from a complex network of antigen- and mitogen-activated transcriptional regulators. CP2, a factor homologous to Drosophila Elf-1 and previously found to be a critical regulator of several viral and cellular genes in response to developmental signals, is rapidly activated in T helper (Th) cells in response to mitogenic stimulation. Here we show that overexpression of CP2 enhances interleukin (IL)-4 promoter-driven chloramphenicol acetyltransferase expression, while repressing IL-2 promoter activity, in transiently transfected Jurkat cells. A CP2-protected element, partially overlapping the nuclear factor of activated T cell-binding P2 sequence, was required for IL-4 promoter activation in CP2-overexpressing Jurkat cells. This CP2-response element is the site of a cooperative interaction between CP2 and an inducible heteromeric co-factor(s). Mutation of conserved nucleotide contacts within the CP2-response element prevented CP2 binding and significantly reduced constitutive and induced IL-4 promoter activity. Expression of a CP2 mutant lacking the Elf-1-homology region of the DNA-binding domain inhibited IL-4 promoter activity in a dominant negative fashion in transiently transfected Jurkat cells. Moreover, overexpressed CP2 markedly enhanced, while its dominant negative mutant consistently suppressed, expression of the endogenous IL-4 gene in the murine Th2 cell line D10. Taken together, these findings point to CP2 as a critical IL-4 transactivator in Th cells.

A D-amino acid peptide inhibitor of NF-kappa B nuclear localization is efficacious in models of inflammatory disease

The transcription factor NF-kappa B regulates many genes involved in proinflammatory and immune responses. The transport of NF-kappa B into the nucleus is essential for its biologic activity. We describe a novel, potent, and selective NF-kappa B inhibitor composed of a cell-permeable peptide carrying two nuclear localization sequences (NLS). This peptide blocks NF-kappa B nuclear localization, resulting in inhibition of cell surface protein expression, cytokine production, and T cell proliferation. The peptide is efficacious in vivo in a mouse septic shock model as well as a mouse model of inflammatory bowel disease, demonstrating that NF-kappa B nuclear import plays a role in these acute inflammatory disease models.

Characterization of P5, a novel NFAT/AP-1 site in the human IL-4 promoter

Interleukin 4 (IL-4) gene expression is controlled at the level of transcription by the complex interactions of multiple factors that bind to a proximal promoter region. Nuclear factor of activated T cells (NFAT) can bind up to five purine-rich sequences in the IL-4 promoter termed the P elements (P0-P4). In this paper, we characterize a novel P element in the upstream region of the human IL-4 promoter that we term P5. P5 shares a core NFAT motif ((-353)GGAAA(-357)) and additional sequence similarity with the other P elements and supported strong interactions between the NFATp DNA-binding domain (DBD) and the AP-1 proteins cFos and cJun in DNA-binding assays. Inducibility of the IL-4 promoter was significantly impaired in a reporter construct in which the P5 element was mutated in the context of the full-length promoter. We conclude that P5 represents a novel IL-4 promoter P element that contributes to IL-4 promoter inducibility.

Characterization of a novel negative regulatory element in the human interleukin 4 promoter

Interleukin 4 (IL-4) is a multifunctional cytokine that plays an important role in hematopoiesis, tumor cell growth, and cellular immune responses. Expression of the IL-4 gene is tightly controlled at the level of gene transcription, and many positive regulatory cis-elements have been identified in the proximal IL-4 promoter region. Relatively little is known about factors that downregulate IL-4 transcription. We performed a detailed deletional analysis of the proximal human IL-4 promoter and studied reporter gene activity in transiently transfected Jurkat T lymphoblasts. In this report, we characterize a novel negative regulatory element (termed P2 NRE) that is adjacent to a binding site for nuclear factor of activated T cells. Mutation of P2 NRE significantly enhanced the activity of a 175 base pair IL-4 promoter construct in transiently transfected Jurkat T lymphoblasts. Using nuclear extracts from Jurkat cells, we identify a candidate factor (termed Rep-1) that binds uniquely to the P2 NRE in DNA-binding assays. Rep-1 is not related to other factors previously shown to interact with the IL-4 promoter, and by UV cross-linking and SDS-PAGE analysis, we found that it migrates with a molecular mass of approximately 150 kDa. Characterizing the molecular mechanisms responsible for downregulating the IL-4 promoter should enhance our understanding of IL-4-gene dysregulation in disease states.

The structure of the nuclear factor-kappaB protein-DNA complex varies with DNA-binding site sequence

Transcriptional regulation of many immune responsive genes is under the control of the transcription factor NF-kappaB. This factor is found in cells as a dimer which can contain any two members of the Rel family of proteins (p50, p65, p52, c-Rel, and RelB). The different dimers show distinct preferences for DNA-binding site sequences. To understand the relationship between the DNA binding properties of the dimer forms and transcriptional activation, the physical properties of the complexes of p50 and p65 with DNA have been analyzed. Comparison of apparent DNA binding affinity showed differences in selectivity of DNA-binding site sequence. The ionic strength dependence of apparent binding affinity has shown that the number of ionic interactions in the protein-DNA complex depends on the DNA-binding site sequence and the dimer form, which are consistent with changes in the structure of the protein-DNA complex. Using a fluorescent technique to measure DNA structure changes, protein binding does not appear to alter the structure of the DNA-binding site within the limits of detection. These results are consistent with a change in protein structure that may result in activation differences due to alternative interactions with other transcription proteins.

Dependence of mast cell IgE-mediated cytokine production on nuclear factor-kappaB activity

BACKGROUND

The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated in the regulation of a number of inflammatory cytokines and has been the proposed target for anti-inflammatory therapeutics.

OBJECTIVE

Our purpose was to explore the role of NF-kappaB in the regulation of allergic inflammation.

METHODS

To determine whether NF-kappaB is activated during IgE-mediated reactions and what types of mediators it regulates, a mutant form of IkappaB was used to block the ability of NF-kappaB to translocate to the nucleus and promote the transcription of selected genes.

RESULTS

Mouse bone marrow-derived mast cells stimulated by IgE receptor cross-linking exhibited an activation of NF-kappaB as assessed by electrophoretic mobility shift assays. Transfected mast cells expressing the mutant IkappaB showed very little NF-kappaB activation. Both control and transfected cells released beta-hexosaminidase after specific antigen challenge, and this release could be potentiated by exogenous adenosine. Transfected mast cells that failed to develop NF-kappaB activation did not produce IL-6 messenger RNA or protein after IgE-mediated stimulation, but these cells retained the ability to produce transcripts for IL-4 and IL-5 in spite of the suppression of NF-kappaB activity.

CONCLUSIONS

It appears that NF-kappaB is activated during IgE-mediated allergic inflammation and that this activity is necessary for the production of IL-6, but not IL-4 or IL-5. When considering the use of agents that target NF-kappaB to reduce inflammatory processes, it is important to know precisely which cytokines are under its control.

Glucocorticoids inhibit calcium- and calcineurin-dependent activation of the human IL-4 promoter

The mechanism by which glucocorticoids (GC) inhibit IL-4 gene expression is currently unknown. In T lymphocytes, IL-4 gene expression is regulated at the level of transcription by increases in intracellular calcium concentration and by the calcium-activated phosphatase calcineurin. In this paper we report that dexamethasone (Dex) inhibits calcium ionophore-induced activation of the human IL-4 promoter in transiently transfected Jurkat T cells. Inhibition of the promoter by Dex is dependent on expression of the GC receptor (GR), because it does not occur in GR-deficient cells. Dex also represses activation of the promoter induced by cotransfecting cells with a constitutively active mutant of calcineurin. Using a series of deletion constructs, we show that the proximal 95 bp of the IL-4 promoter contain a Dex-sensitive regulatory element. This region contains the P1 sequence, a proximal binding site for NF-AT. A calcium-induced but Dex-inhibited nuclear complex containing NF-AT binds to the P1 element in EMSA. Using immunoprecipitation under nondenaturing conditions, we found that the GRalpha isoform coprecipitates with NF-ATc in nuclear extracts of calcium ionophore- and Dex-treated cells. Taken together, our results show that GC inhibit IL-4 gene expression by interfering with NF-AT-dependent transactivation of the proximal human IL-4 promoter.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

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.

In Vivo Inhibition of NF-κB in T-Lineage Cells Leads to a Dramatic Decrease in Cell Proliferation and Cytokine Production and to Increased Cell Apoptosis in Response to Mitogenic Stimuli, But Not to Abnormal Thymopoiesis

To understand the role of NF-κB complexes in T cell development and activation, we have generated transgenic mice in which RelA and c-Rel complexes were selectively inhibited in the T-lineage cells by specific expression of a trans-dominant form of IκBα. Transgene expression did not affect the thymic development, but led to lowered numbers of splenic T cells and to a dramatic decrease in the ex vivo proliferative response of splenic T lymphocytes. Analysis of IL-2 and IL-2Rα expression demonstrated that the perturbation of the proliferation response was not attributable to an abnormal expression of these genes. In contrast, expression of IL-4, IL-10, and IFN-γ was strongly inhibited in the transgenic T cells. The proliferative deficiency of the transgenic T cells was associated with an increased apoptosis. These results point out the involvement of NF-κB/Rel family proteins in growth signaling pathways by either regulating proteins involved in the IL-2 signaling or by functionally interfering with the cell cycle progression.

Costimulation Reverses the Defect in IL-2 But Not Effector Cytokine Production by T Cells with Impaired IκBα Degradation

Although the transcriptional basis for states of unresponsiveness in primary T cells is unclear, tolerant B lymphocytes exhibit inhibition of both c-Jun N-terminal kinase induction and IκBα (inhibitor of NF-κBα) degradation, leading to lower levels of both nuclear AP-1 and NF-κB. Expression of an IκBα mutant resistant to signal-induced degradation in transgenic T cells caused markedly deficient effector cytokine (IL-4, IFN-γ) production after primary TCR stimulation despite a detectable level of nuclear NF-κB. A TCR response element from the IFN-γ promoter, despite lacking detectable NF-κB/Rel sites, was also unresponsive to TCR ligation. Nuclear induction of AP-1 proteins in response to T cell activation was diminished in transgenic T cells. Costimulation induced by anti-CD28 mAb increased IL-2 production, but failed to reverse the defects in effector cytokine production. Taken together, these data indicate that impaired NF-κB/Rel signaling in T cells interferes with the signal transduction pathways required for efficient induction of effector cytokine production.

Recognition of NFATp/AP-1 composite elements within genes induced upon the activation of immune cells

Composite elements are regulatory modules of promoters or enhancers that consist of binding sites of two different but synergizing transcription factors. A well-studied example is nuclear factors of activated T-cell (NFAT) sites which are composite elements of a NFATp/c and an activating protein 1 (AP-1) binding site. We have developed a computational approach to identify potential NFAT target genes which (a) comprises an improved method to scan for individual NFAT composite elements; (b) considers positional effects relative to transcription start sites; and (c) involves cluster analysis of potential NFAT composite elements. All three steps progressively helpX?ed to discriminate T-cell-specific promoter sequences against other functional regions (coding and intronic sequences) of the same genes, against promoters of muscle-specific genes or against random sequences. Using this approach, we identified potential NFAT composite elements in promoters of cytokine genes and their receptors as well as in promoters of genes for AP-1 family members, Ca2+-binding proteins and some other components of the regulatory network operating in activated T-cells and other immune cells. The method developed can be adapted to characterize and identify other composite elements as well. The program for recognition NFAT composite elements is available through the World Wide Web (http://compel.bionet.nsc.ru/FunSite/CompelScan. html and http://transfac.gbf.de/dbsearch/funsitep/s _comp.html).

Reciprocal modulatory interaction between human immunodeficiency virus type 1 Tat and transcription factor NFAT1

Human immunodeficiency virus type 1 (HIV-1) gene expression is regulated by interactions between both viral and host factors. These interactions are also responsible for changes in the expression of many host cell genes, including cytokines and other immune regulators, which may account for the state of immunological dysregulation that characterizes HIV-1 infection. We have investigated the role of a host cell protein, the transcription factor NFAT1, in HIV-1 pathogenesis. We show that NFAT1 interacts with Tat and that this interaction, which involves the major transactivation domain of NFAT1 and the amino-terminal region of Tat, results in a reciprocal modulatory interplay between the proteins: whereas Tat enhances NFAT1-driven transcription in Jurkat T cells, NFAT1 represses Tat-mediated transactivation of the HIV-1 long terminal repeat (LTR). Moreover, NFAT1 binds to the kappaB sites on the viral LTR and negatively regulates NF-kappaB-mediated activation of HIV-1 transcription, by competing with NF-kappaB1 for its binding sites on the HIV-1 LTR. Tat-mediated enhancement of NFAT1 transactivation may explain the upregulation of interleukin 2 and other cytokines that occurs during HIV-1 infection. We discuss the potentially opposing roles of NFAT1 and another family member, NFAT2, in regulating gene transcription of HIV-1 and endogenous cytokine genes.

Apoptosis-resistant T cells have a deficiency in NF-kappaB-mediated induction of Fas ligand transcription

Apoptosis induced through the TCR in CD4+ T cells is mostly mediated by the inducible expression of Fas ligand (FasL) as a primary event leading to the commitment to death. To gain a better understanding of the transcriptional events that regulate this expression, we took advantage of our previously described mutant Jurkat cells. These cells are deficient in FasL expression and apoptosis induced upon TCR triggering, although their cytokine (IL-2 and IFN-gamma) production is normal. Here we show that both a FasL- and a consensus NF-kappaB-reporter construct are inefficiently induced in these cells compared to wild-type cells. In addition, we demonstrate that the inducible transcriptional activity of the FasL reporter is abolished by specific inhibitors of NF-kappaB activation. Thus, we could trace the deficit of the mutant cells to an inefficient NF-kappaB activation, evidencing a relevant role for NF-kappaB in the regulation of FasL expression in activated T cells. Furthermore, our results suggest that the induction of FasL versus cytokine gene expression is differentially sensitive to NF-kappaB deprivation.

Stat6 Inhibits Human Interleukin-4 Promoter Activity in T Cells

The differentiation of naive T-helper (Th) cells into cytokine-secreting effector Th cells requires exposure to multiple signals, including exogenous cytokines. Interleukin-4 (IL-4) plays a major role in this process by promoting the differentiation of IL-4–secreting Th2 cells. In Th2 cells, IL-4 gene expression is tightly controlled at the level of transcription by the coordinated binding of multiple transcription factors to regulatory elements in the proximal promoter region. Nuclear factor of activated T cell (NFAT) family members play a critical role in regulating IL-4 transcription and interact with up to five sequences (termed P0 through P4) in the IL-4 promoter. The molecular mechanisms by which IL-4 induces expression of the IL-4 gene are not known, although the IL-4–activated transcription factor signal transducer and activator of transcription 6 (Stat6) is required for this effect. We report here that Stat6 interacts with three binding sites in the human IL-4 promoter by electrophoretic mobility shift assays. These sites overlap the P1, P2, and P4 NFAT elements. To investigate the role of Stat6 in regulating IL-4 transcription, we used Stat6-deficient Jurkat T cells with different intact IL-4 promoter constructs in cotransfection assays. We show that, whereas a multimerized response element from the germline IgE promoter was highly induced by IL-4 in Stat6-expressing Jurkat cells, the intact human IL-4 promoter was repressed under similar conditions. We conclude that the function of Stat6 is highly dependent on promoter context and that this factor promotes IL-4 gene expression in an indirect manner.

Stat6 Inhibits Human Interleukin-4 Promoter Activity in T Cells

The differentiation of naive T-helper (Th) cells into cytokine-secreting effector Th cells requires exposure to multiple signals, including exogenous cytokines. Interleukin-4 (IL-4) plays a major role in this process by promoting the differentiation of IL-4–secreting Th2 cells. In Th2 cells, IL-4 gene expression is tightly controlled at the level of transcription by the coordinated binding of multiple transcription factors to regulatory elements in the proximal promoter region. Nuclear factor of activated T cell (NFAT) family members play a critical role in regulating IL-4 transcription and interact with up to five sequences (termed P0 through P4) in the IL-4 promoter. The molecular mechanisms by which IL-4 induces expression of the IL-4 gene are not known, although the IL-4–activated transcription factor signal transducer and activator of transcription 6 (Stat6) is required for this effect. We report here that Stat6 interacts with three binding sites in the human IL-4 promoter by electrophoretic mobility shift assays. These sites overlap the P1, P2, and P4 NFAT elements. To investigate the role of Stat6 in regulating IL-4 transcription, we used Stat6-deficient Jurkat T cells with different intact IL-4 promoter constructs in cotransfection assays. We show that, whereas a multimerized response element from the germline IgE promoter was highly induced by IL-4 in Stat6-expressing Jurkat cells, the intact human IL-4 promoter was repressed under similar conditions. We conclude that the function of Stat6 is highly dependent on promoter context and that this factor promotes IL-4 gene expression in an indirect manner.

Involvement of Jun and Rel proteins in up-regulation of interleukin-4 gene activity by the T cell accessory molecule CD28

CD28 serves as a costimulatory cell surface molecule in T cell activation. CD28 signaling may also play a role in balancing the inflammatory/humoral (Th1/Th2) responses during an immune reaction. CD28 costimulation has been shown to promote the production of Th2 cytokines including interleukin (IL)-4, a key cytokine essential for Th2 differentiation and for the pathogenesis of allergic inflammation. In this study, we show that IL-4 mRNA and activity of the IL-4 promoter can be activated by the CD28 signal alone and are further augmented by CD28 costimulation of alpha-CD3- or mitogen-activated Jurkat T cells. Two important IL-4 enhancer elements, positive regulatory element (PRE)-I and P1, are found to respond to CD28 stimulation-induced transactivation. In contrast to the Th1 IL-2 CD28RE, activity of the IL-4 PRE-I and P1 can be induced by the CD28 signal alone. In correlation with CD28-induced transcriptional activation, AP-1 (c-Jun, JunD) and NF-kappaB/Rel (c-Rel, RelA) family members are found to bind to the two regulatory elements PRE-I and P1 upon CD28 stimulation. The data provide the first mapping of the CD28-responsive site in a Th2 cytokine gene, the IL-4 gene. They also show that the CD28 signal can directly activate a gene (e.g. IL-4) at the transcriptional level.

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.