The AP-1 site at -150 bp, but not the NF-kappa B site, is likely to represent the major target of protein kinase C in the interleukin 2 promoter

Diacylglycerol kinase ζ limits IL-2-dependent control of PD-1 expression in tumor-infiltrating T lymphocytes

Background

The inhibitory functions triggered by the programmed cell death-1 (PD-1) receptor following binding to its ligand (PD-L1) protect healthy organs from cytotoxic T cells, and neutralize antitumor T cell attack. Antibody-based therapies to block PD-1/PD-L1 interaction have yielded notable results, but most patients eventually develop resistance. This failure is attributed to CD8⁺ T cells achieving hyporesponsive states from which recovery is hardly feasible. Dysfunctional T cell phenotypes are favored by a sustained imbalance in the diacylglycerol (DAG)- and Ca²⁺-regulated transcriptional programs. In mice, DAG kinase ζ (DGKζ) facilitates DAG consumption, limiting T cell activation and cytotoxic T cell responses. DGKζ deficiency facilitates tumor rejection in mice without apparent adverse autoimmune effects. Despite its therapeutic potential, little is known about DGKζ function in human T cells, and no known inhibitors target this isoform.

Methods

We used a human triple parameter reporter cell line to examine the consequences of DGKζ depletion on the transcriptional restriction imposed by PD-1 ligation. We studied the effect of DGKζ deficiency on PD-1 expression dynamics, as well as the impact of DGKζ absence on the in vivo growth of MC38 adenocarcinoma cells.

Results

We demonstrate that DGKζ depletion enhances DAG-regulated transcriptional programs, promoting interleukin-2 production and partially counteracting PD-1 inhibitory functions. DGKζ loss results in limited PD-1 expression and enhanced expansion of cytotoxic CD8⁺ T cell populations. This is observed even in immunosuppressive milieus, and correlates with the reduced ability of MC38 adenocarcinoma cells to form tumors in DGKζ-deficient mice.

Conclusions

Our results, which define a role for DGKζ in the control of PD-1 expression, confirm DGKζ potential as a therapeutic target as well as a biomarker of CD8⁺ T cell dysfunctional states.

A Review of Immunomodulatory Effects of Fluoroquinolones

Past researches indicate that some types of antibiotics, apart from their antimicrobial effects, have some other important effects which indirectly are exerted by modulating and regulating the immune system's mediators. Among the compounds with antimicrobial effects, fluoroquinolones (FQs) are known as synthetic antibiotics, which exhibit the property of decomposing of DNA and prevent bacterial growth by inactivating the enzymes involved in DNA twisting, including topoisomerase II (DNA gyrase) and IV. Interestingly, immune responses are indirectly modulated by FQs through suppressing pro-inflammatory cytokines, such as interleukin 1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-α), and super-inducing IL-2, which tend to increase both the growth and activity of T and B lymphocytes. In addition, they affect the development of immune responses by influencing of expression of other cytokines and mediators. This study aims to review past research on the immunomodulatory effects of FQs on the expression of cytokines, especially IL-2 and to discuss controversial investigations.

NFAT2 Regulates Generation of Innate-Like CD8+ T Lymphocytes and CD8+ T Lymphocytes Responses

Nuclear factor of activated T cells (NFAT) 2 null mutant mice die in utero of cardiac failure, precluding analysis of the role of NFAT2 in lymphocyte responses. Only the NFAT2^-/-/Rag-1^-/- chimeric mice model gave insight into the role of NFAT2 transcription factor in T lymphocyte development, activation, and differentiation. As reports are mainly focused on the role of NFAT2 in CD4⁺ T lymphocytes activation and differentiation, we decided to investigate NFAT2's impact on CD8⁺ T lymphocyte responses. We report that NFAT2 is phosphorylated and inactive in the cytoplasm of naive CD8⁺ T cells, and upon TCR stimulation, it is dephosphorylated and translocated into the nucleus. To study the role of NFAT2 in CD8⁺ T responses, we employed NFAT2^fl/flCD4-Cre mice with NFAT2 deletion specifically in T cells. Interestingly, the absence of NFAT2 in T cells resulted in increased percentage of non-conventional innate-like CD8⁺ T cells. These cells were CD122⁺, rapid producer of interferon gamma (IFN-γ) and had characteristics of conventional memory CD8⁺ T cells. We also observed an expansion of PLZF⁺ expressing CD3⁺ thymocyte population in the absence of NFAT2 and increased IL-4 production. Furthermore, we found that CD8⁺ T lymphocytes deficient in NFAT2 had reduced activation, proliferation, and IFN-γ and IL-2 production at suboptimal TCR strength. NFAT2 absence did not significantly influence differentiation of CD8⁺ T cells into cytotoxic effector cells but reduced their IFN-γ production. This work documents NFAT2 as a negative regulator of innate-like CD8⁺ T cells development. NFAT2 is required for complete CD8⁺ T cell responses at suboptimal TCR stimulation and regulates IFN-γ production by cytotoxic CD8⁺ T cells in vitro.

The Role of PKC-θ in CD4+ T Cells and HIV Infection: To the Nucleus and Back Again

Protein kinase C (PKC)-θ is the only member of the PKC family that has the ability to translocate to the immunological synapse between T cells and antigen-presenting cells upon T cell receptor and MHC-II recognition. PKC-θ interacts functionally and physically with other downstream effector molecules to mediate T cell activation, differentiation, and migration. It plays a critical role in the generation of Th2 and Th17 responses and is less important in Th1 and CTL responses. PKC-θ has been recently shown to play a role in the nucleus, where it mediates inducible gene expression in the development of memory CD4+ T cells. This novel PKC (nPKC) can up-regulate HIV-1 transcription and PKC-θ activators such as Prostratin have been used in early HIV-1 reservoir eradication studies. The exact manner of the activation of virus by these compounds and the role of PKC-θ, particularly its nuclear form and its association with NF-κB in both the cytoplasmic and nuclear compartments, needs further precise elucidation especially given the very important role of NF-κB in regulating transcription from the integrated retrovirus. Continued studies of this nPKC isoform will give further insight into the complexity of T cell signaling kinases.

Suppression of inflammatory gene expression in T cells by Porphyromonas gingivalis is mediated by targeting MAPK signaling

There is increasing awareness of the effects of Porphyromonas gingivalis on host immune responses. Degradation of cytokines and chemokines by cysteine proteinases has previously been reported. However, the precise mechanisms by which P. gingivalis is able to alter intracellular signaling, and thus proliferation and inflammation, have not been described. We have previously reported suppression of activator protein-1 (AP-1) and degradation of IL-2 by proteinases from P. gingivalis. In the present study, we have analyzed the effects of P. gingivalis on Jurkat T-cell signal transduction and subsequent IL-2 and CXCL8 expression. We found that CXCL8, but not IL-2, gene expression levels were significantly suppressed by viable P. gingivalis. Analysis of intracellular signaling revealed an inhibitory effect of P. gingivalis on c-Jun and c-Fos, but not NFκB (p50 and p65), NFAT or STAT5 expression. This inhibitory effect was not due to suppression of mitogen-activated protein kinase (MAPK) (p38, erk and JNK) gene expression, but was rather due to prevention of protein kinase C (PKC) and p38 phosphorylation, as demonstrated by western blot analysis. Furthermore, SOCS1 and SOCS3 expression levels decreased following treatment of Jurkat T cells with viable P. gingivalis. The results indicate that P. gingivalis is able to suppress inflammatory gene expression by targeting the activity of MAPK pathways in T cells, which was confirmed by using specific inhibitors of NF-κB, PKC, ERK, p38 and JNK.

The class III histone deacetylase sirtuin 1 in immune suppression and its therapeutic potential in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic debilitating disease of the joints. Both the innate and adaptive immune responses participate in the development and progression of RA. While several therapeutic reagents, such as TNF-α agonists, have been successfully developed for the clinical use in the treatment of RA, more than half of the patients do not respond to anti-TNF therapy. Therefore, new therapeutic reagents are needed. Recent studies have shown that sirtuin 1 (Sirt1), a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, is a critical negative regulator of both the innate and adaptive immune response in mice, and its altered functions are likely to be involved in autoimmune diseases. Small molecules that modulate Sirt1 functions are potential therapeutic reagents for autoimmune inflammatory diseases. This review highlights the role of Sirt1 in immune regulation and RA.

Altered T-cell responses by the periodontal pathogen Porphyromonas gingivalis

Several studies support an association between the chronic inflammatory diseases periodontitis and atherosclerosis with a crucial role for the periodontal pathogen Porphyromonas gingivalis. However, the interplay between this pathogen and the adaptive immune system, including T-cells, is sparsely investigated. Here we used Jurkat T-cells to determine the effects of P. gingivalis on T-cell-mediated adaptive immune responses. We show that viable P. gingivalis targets IL-2 expression at the protein level. Initial cellular events, including ROS production and [Ca(2+)](i), were elevated in response to P. gingivalis, but AP-1 and NF-κB activity dropped below basal levels and T-cells were unable to sustain stable IL-2 accumulation. IL-2 was partially restored by Leupeptin, but not by Cathepsin B Inhibitor, indicating an involvement of Rgp proteinases in the suppression of IL-2 accumulation. This was further confirmed by purified Rgp that caused a dose-dependent decrease in IL-2 levels. These results provide new insights of how this periodontal pathogen evades the host adaptive immune system by inhibiting IL-2 accumulation and thus attenuating T-cell proliferation and cellular communication.

Stable IL-2 decision making by endogenous c-Fos amounts in peripheral memory T-helper cells

The cytokine IL-2 performs opposite functions supporting efficient immune responses and playing a key role in peripheral tolerance. Therefore, precise fine-tuning of IL-2 expression is crucial for adjusting the immune response. Combining transcription factor analysis at the single cell and the single nucleus level using flow cytometry with statistical analysis, we showed that physiological differences in the expression levels of c-Fos and NFATc2, but not of c-Jun and NF-κBp65, are limiting for the decision whether IL-2 is expressed in a strongly activated human memory T-helper (Th) cell. Variation in the expression of c-Fos leads to substantial diversity of IL-2 expression in ∼40% of the memory Th cells. The remaining cells exhibit an equally high c-Fos expression level, thereby ensuring robustness in IL-2 response within the population. These findings reveal how memory Th cells benefit from regulated variation in transcription factor expression to achieve a certain stability and variability of cytokine expression in a controlled manner.

Comparison of the efficacy of tacrolimus and cyclosporine A in a murine model of dinitrofluorobenzene-induced atopic dermatitis

Tacrolimus (FK506) and cyclosporine A (Cys A) are immunosuppressive drugs used in the treatment of inflammatory diseases and for preventing rejection of allogeneic transplants. Tacrolimus forms a complex with FK506 binding protein (FKBP), and Cys A forms a complex with cyclophilin. These tacrolimus-FKBP and Cys A-cyclophilin complexes interact with calcineurin (CaN), thereby suppressing activation of T cells. In contrast, steroidal anti-inflammatory drugs suppress the immune system mainly via inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB) and the activating protein-1 (AP-1) pathway. Previously, we reported that tacrolimus, but not dexamethasone, reduced scratching behavior in a murine model of atopic dermatitis. To elucidate the mechanism involved in the inhibition of scratching behavior, we used a mouse model of allergic dermatitis to compare the characteristics of tacrolimus and Cys A treatment. We found that Cys A suppressed scratching behavior induced by application of 2,4-dinitrofluorobenzene, as did tacrolimus. In addition, both drugs attenuated increases in vascular permeability and scratching behavior induced by passive cutaneous anaphylaxis. These results indicate that inhibition of the CaN pathway plays an important role in tacrolimus- and Cys A-induced inhibition of scratching behavior in mice. Furthermore, we observed that CaN inhibitors suppressed mast cell-dependent allergic reaction.

Differential cytokine regulation by NF-kappaB and AP-1 in Jurkat T-cells

Background

Activator protein (AP)-1 and nuclear factor (NF)-κB largely control T-cell activation, following binding of foreign antigens to the T-cell receptor leading to cytokine secretion. Elevated levels of pro-inflammatory cytokines and chemokines such as TNF, IL-6 and CXCL8 are associated with several human diseases including cystic fibrosis, pulmonary fibrosis and AIDS. The aim of this study was to investigate the role of the transcription factors, AP-1 and NF-κB, in IL-6 and CXCL8 regulation in Jurkat T-cells.

Results

Phorbol myristate acetate (PMA) exposure resulted in an up-regulation of AP-1 and down-regulation of NF-κB activity, however, exposure to heat killed (HK) Escherichia. coli MG1655 resulted in a dose-dependent increase in NF-κB activity without affecting AP-1. The cytokine profile revealed an up-regulation of the chemokine CXCL8 and the pro-inflammatory cytokines TNF, IL-2 and IL-6 following treatment with both PMA and HK E. coli, while the levels of the anti-inflammatory cytokine IL-10 were not affected by PMA but were significantly down-regulated by HK E. coli. AP-1 activation was significantly increased 2 h after PMA exposure and continued to increase thereafter. In contrast, NF-κB responded to PMA exposure by a rapid up-regulation followed by a subsequent down-regulation. Increased intracellular Ca²⁺ concentrations countered the down-regulation of NF-κB by PMA, while similar treatment with calcium ionophore resulted in a reduced NF-κB activity following induction with HK E. coli. In order to further study NF-κB activation, we considered two up-stream signalling proteins, PKC and Bcl10. Phosphorylated-PKC levels increased in response to PMA and HK E. coli, while Bcl10 levels significantly decreased following PMA treatment. Using an NF-κB activation inhibitor, we observed complete inhibition of IL-6 expression while CXCL8 levels only decreased by 40% at the highest concentration. Treatment of Jurkat T-cells with PMA in the presence of JNK-inhibitor suppressed both CXCL8 and IL-6 while PKC-inhibitor primarily decreased CXCL8 expression.

Conclusion

The present study shows that NF-κB regulated IL-6 but not CXCL8. This complex regulation of CXCL8 suggests that there is a need to further evaluate the signalling pathways in order to develop new treatment for diseases with elevated CXCL8 levels, such as AIDS and autoimmune diseases.

The transcription repressor, ZEB1, cooperates with CtBP2 and HDAC1 to suppress IL-2 gene activation in T cells

Activation of T cells leads to the induction of many cytokine genes that are required for appropriate immune responses, including IL-2, a key cytokine for T cell proliferation and homeostasis. The activating transcription factors such as nuclear factor of activated T cells, nuclear factor kappaB/Rel and activated protein-1 family members that regulate inducible IL-2 gene expression have been well documented. However, negative regulation of the IL-2 gene is less studied. Here we examine the role of zinc finger E-box-binding protein (ZEB) 1, a homeodomain/Zn finger transcription factor, as a repressor of IL-2 gene transcription. We show here that ZEB1 is expressed in non-stimulated and stimulated T cells and using chromatin immunoprecipitation assays we show that ZEB1 binds to the IL-2 promoter. Over-expression of ZEB1 can repress IL-2 promoter activity, as well as endogenous IL-2 mRNA production in EL-4 T cells, and this repression is dependent on the ZEB-binding site at -100. ZEB1 cooperates with the co-repressor C-terminal-binding protein (CtBP) 2 and with histone deacetylase 1 to repress the IL-2 promoter and this cooperation depends on the ZEB-binding site in the promoter as well as the Pro-X-Asp-Leu-Ser protein-protein interaction domain in CtBP2. Thus, ZEB1 may function to recruit a repressor complex to the IL-2 promoter.

Modulation of NFAT-5, an outlying member of the NFAT family, in human keratinocytes and skin

BACKGROUND

Cyclosporin A (CsA) and tacrolimus block T cell activation by inhibiting the phosphatase calcineurin and preventing translocation from the cytoplasm to the nucleus of the transcription factor Nuclear Factor of Activated T cells (NFAT). NFAT compose a family of transcription factors that are turned on during T cell activation.

AIMS

To study the expression of NFAT-5 mRNA and protein in normal human keratinocytes and to investigate the cellular and subcellular pattern of expression of NFAT-5 in normal human skin and psoriasis, and analyze effects of different agonists and ultraviolet radiation on NFAT-5 in normal human skin.

METHODS

Tissue cultures, Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), Western analysis, immunostaining, confocal microscopy.

RESULTS

Sequencing of RT-PCR products confirmed the identity of the product that showed 100 % homology with the predicted NFAT-5 sequence. anti-NFAT-5 mainly detected a single band in cultured keratinocytes and dermal fibroblasts using Western analysis. Immunohistochemistry showed that epidermal keratinocytes and dermal fibroblasts in normal human and psoriatic skin express NFAT-5. NFAT-5 showed predominantly nuclear localization in epidermal keratinocytes and dermal fibroblasts within five normal adult skin biopsies. Our data also suggest that UV irradiation reduces NFAT-5 nuclear localization within the epidermis. Unlike NFAT 1-4, NFAT-5/TonEBP was localized to both nucleus and cytoplasm of cultured keratinocytes. Cyclosporin A induces nuclear membrane translocation of NFAT-5 in cultured keratinocytes and raffinose (a hypertonicity inducing agent) induces more nuclear localization of NFAT-5 compared to untreated cells. In addition, differentiation-promoting agonists that induce sustained rise in intracellular calcium did not result in changes in NFAT-5 localization in cultured keratinocytes.

CONCLUSION

These studies provide the first observation of expression of NFAT-5/TonEBP mRNA protein in cultured keratinocytes and dermal fibroblasts and possible functional regulation in cultured keratinocytes. CsA and raffinose effects on NFAT-5/TonEBP in cultured keratinocytes suggest diverse intracellular signaling pathways for NFAT-5/TonEBP in these cells, and that NFAT-5/TonEBP might function to translate different extracellular stimuli into appropriate functional responses.

The transcriptional repressor cAMP response element modulator alpha interacts with histone deacetylase 1 to repress promoter activity

Transcriptional repression is a fundamental mechanism of gene regulation. cAMP response element (CRE) modulator (CREM)alpha is an ubiquitously expressed transcription factor and a counterpart of the activator CREB. In T cells, CREM is responsible for the termination of the IL-2 expression by a chromatin-dependent mechanism. We demonstrate in this study that CREMalpha associates with histone deacetylase (HDAC)1 through its H domain, which is located between the kinase inducible and DNA binding domains. The CREMalpha-mediated recruitment of HDAC1 to the CRE sites of the IL-2 and c-Fos promoter causes histone deacetylation and inaccessibility to restriction enzymes and limited transcriptional activity. Importantly, the CRE sites of these promoters are crucial for the activity and binding of HDAC1. Therefore, CREMalpha exerts its repressor activity by a mechanism that involves recruitment of HDAC1, increased deacetylation of histones, and repression of promoter activity.

Control of interleukin-2 gene transcription: a paradigm for inducible, tissue-specific gene expression

Interleukin-2 (IL-2) is a key cytokine that controls immune cell function, in particular the adaptive arm of the immune system, through its ability to control the clonal expansion and homeostasis of peripheral T cells. IL-2 is produced almost exclusively by T cells in response to antigenic stimulation and thus provides an excellent example of a cell-specific inducible gene. The mechanisms that control IL-2 gene transcription have been studied in detail for the past 20 years and our current understanding of the nature of the inducible and tissue-specific controls will be discussed.

Vav1: an oncogene that regulates specific transcriptional activation of T cells

The nuclear factor of activated T cells (NFAT) proteins are a family of transcription factors whose activation is controlled by calcineurin, a Ca2+-dependent phosphatase. Once dephosphorylated, these proteins move to the nucleus where they interact with cofactors to form transcription factor complexes. Inhibition of NFAT proteins by immunosuppressants, such as cyclosporin A (CsA) and FK506, is used clinically to prevent transplant rejection. Although these drugs have revolutionized organ transplantation, their use is associated with severe side effects in other organs in which NFAT proteins are important. One of the signal transducers that controls NFAT activity is Vav1, which is exclusively expressed in the hematopoietic system. Vav1 contains numerous modular domains that enable its function as a guanine exchange factor (GEF) toward RhoGTPases as well as participate in protein-protein interactions. This review focuses on the mechanisms by which Vav1 regulates NFAT through GEF-dependent and -independent cascades, emphasizing the newly assigned role of Vav1 in the regulation of Ca2+ release. Because of its restriction to hematopoietic cell lineages and its importance in the regulation of NFAT, targeting Vav1 and, in particular, its association with other proteins may offer a highly selective means of modifying T-cell behavior, thus allowing the development of more specific immunosuppressive therapies.

Targeting combinatorial transcriptional complex assembly at specific modules within the interleukin-2 promoter by the immunosuppressant SB203580

The proximal promoter sequence of the interleukin-2 (IL-2) gene contains a series of composite sites or modules that controls much of its responsiveness to environmental stimuli. The integrated targeting of these modules is therefore a major mode of regulation. This report describes how multiple functional hierarchies, required for the recruitment of the p300 co-activator to the CD28RE/AP1 (TRE) module of the IL-2 promoter, are selectively disrupted in human T-cells by the immunosuppressive and anti-inflammatory actions of the p38 mitogen-activated protein kinase inhibitor (MAPK), SB203580. The molecular hierarchies targeted by SB203580 include the combinatorial interaction of NF-kappaB and CREB at the CD28RE/AP1 element coupled with the subsequent dynamic co-assembly and activation of p300. Several aspects of this targeting are linked to the ability of SB203580 to inhibit p38 MAPK-controlled pathways. Together, these results provide the molecular basis through which the combinatorial structure and context of the composite elements of the IL-2 promoter dictates mitogen responsiveness and drug susceptibility that are quantitatively and qualitatively distinct from the isolated action of single consensus sequences and/or transcriptional motifs.

The PKC gene module: molecular biosystematics to resolve its T cell functions

The distinct protein kinase C (PKC) multigene family (PKC gene module) is known to be the 'classic' intracellular receptor for mitogenic phorbol esters, and it is widely accepted in the scientific community that the 'PKC effect' is essential in activation, differentiation, adhesion and motility, as well as in cellular survival, of T cells. Nevertheless, the first concepts about PKC isotype heterogeneity of cellular localization and function emerged only recently, when the PKC-theta pathways were mapped to critical signaling networks that control T cell receptor (TCR)/CD3-dependent interleukin (IL)-2 production and proliferation in T lymphocytes. This review summarizes the current knowledge about T cell expressed PKC gene products, their known and/or suspected regulation and cellular effector pathways, as well as physiological functions in T lymphocytes (as determined by molecular cell biology and ongoing mouse genetic studies). Given PKCs integral role in T cell function but today's very fragmentary molecular understanding of directly PKC-mediated effector functions in transmembrane signaling, a 'molecular biosystematics' approach is suggested to resolve the isotype-selective functions of this PKC gene family. Such an approach has to be based not only on genomic/cytogenetic analysis to establish its genetic relationships but also on biochemical/cell biology and genetic studies to resolve its functional diversity and, ultimately, nonredundant roles in real T cell physiology.

Vav-induced activation of the human IFN-gamma gene promoter is mediated by upregulation of AP-1 activity

The role of Vav in the transcriptional regulation of the human interferon-gamma (IFN-gamma) promoter was investigated. Overexpression of Vav in Jurkat-TAg cells enhanced T cell receptor (TCR)-induced activation of a luciferase (Luc) reporter gene construct driven by cis-regulatory element of the IFN-gamma gene (-346 to +7). Electrophoresis mobility shift and Luc reporter assays demonstrated that the DNA-binding and transcriptional activity of the proximal AP-1-dependent NFAT site (positions -172 to -138), the AP-1/Ying-Yang 1 (YY1)-binding site (-209 to -184), and a consensus AP-1-binding site were upregulated by Vav. Vav enhanced TCR-induced activation of c-Jun N-terminal kinase (JNK) and its upstream regulator, Rho family GTPases. Finally, coexpression of a dominant-negative Rac1 mutant suppressed Vav-mediated upregulation of the transcriptional and DNA-binding activity of the proximal NFAT/AP-1 site and the AP-1/YY1 site, as well as the complete IFN-gamma promoter activity. Vav activates the IFN-gamma promoter via upregulation of AP-1-binding through a Rac1/JNK pathway.

Protein kinase C-theta participates in the activation of cyclic AMP-responsive element-binding protein and its subsequent binding to the -180 site of the IL-2 promoter in normal human T lymphocytes

IL-2 gene expression is regulated by the cooperative binding of discrete transcription factors to the IL-2 promoter/enhancer and is predominantly controlled at the transcriptional level. In this study, we show that in normal T cells, the -180 site (-164/-189) of the IL-2 promoter/enhancer is a p-cAMP-responsive element-binding protein (p-CREB) binding site. Following activation of the T cells through various membrane-initiated and membrane-independent pathways, protein kinase C (PKC)-theta phosphorylates CREB, which subsequently binds to the -180 site and associates with the transcriptional coactivator p300. Rottlerin, a specific PKC-theta inhibitor, diminished p-CREB protein levels when normal T cells were treated with it. Rottlerin also prevented the formation of p-CREB/p300 complexes and the DNA-CREB protein binding. Cotransfection of fresh normal T cells with luciferase reporter construct driven by two tandem -180 sites and a PKC-theta construct caused a significant increase in the transcription of the reporter gene, indicating that this site is functional and regulated by PKC-theta. Cotransfection of T cells with a luciferase construct driven by the -575/+57 region of the IL-2 promoter/enhancer and a PKC-theta construct caused a similar increase in the reporter gene transcription, which was significantly limited when two bases within the -180 site were mutated. These findings show that CREB plays a major role in the transcriptional regulation of IL-2 and that a major pathway for the activation of CREB and its subsequent binding to the IL-2 promoter/enhancer in normal T cells is mediated by PKC-theta.

Identification and characterization of a novel nuclear factor of activated T-cells-1 isoform expressed in mouse brain

The nuclear factor of activated T-cells (NFAT) family transcription factors play a key role in the control of cytokine gene expression in T-cells. Although initially identified in T-cells, recent data have unveiled unanticipated roles for NFATs in the development, proliferation, and differentiation of other tissues. Here we report the identification, cDNA cloning, and functional characterization of a new isoform of NFAT1 highly expressed in mouse brain. This isoform, which we named NFAT1-D, is identical to NFAT1 throughout the N-terminal regulatory domain and the portion of the Rel domain which includes the minimal region required for specific binding to DNA and interaction with AP-1. The homology stops sharply upstream of the 3'-boundary of the Rel homology domain and is followed by a short unique C-terminal region. NFAT1-D was expressed at high levels in all brain districts and was found as a constitutively active transcription complex. Transfection of a NFAT/luciferase reporter in the neuronal cell line PC12, which also expresses NFAT1-D, showed that these cells expressed a constitutive NFAT activity that was enhanced after nerve growth factor-induced differentiation but was resistant to the immunosuppressant cyclosporin A. NFAT1-D was, however, inducibly activated in a cyclosporin A-sensitive manner when expressed in T-cells, suggesting that the activity of NFAT proteins might be controlled by their specific cellular context.

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.

PKC-theta is required for TCR-induced NF-kappaB activation in mature but not immature T lymphocytes

Productive interaction of a T lymphocyte with an antigen-presenting cell results in the clustering of the T-cell antigen receptor (TCR) and the recruitment of a large signalling complex to the site of cell-cell contact. Subsequent signal transduction resulting in cytokine gene expression requires the activation of one or more of the multiple isoenzymes of serine/threonine-specific protein kinase C (PKC). Among the several PKC isoenzymes expressed in T cells, PKC-theta is unique in being rapidly recruited to the site of TCR clustering. Here we show that PKC-theta is essential for TCR-mediated T-cell activation, but is dispensable during TCR-dependent thymocyte development. TCR-initiated NF-kappaB activation was absent from PKC-theta(-/-) mature T lymphocytes, but was intact in thymocytes. Activation of NF-kappaB by tumour-necrosis factor alpha and interleukin-1 was unaffected in the mutant mice. Although studies in T-cell lines had suggested that PKC-theta regulates activation of the JNK signalling pathway, induction of JNK was normal in T cells from mutant mice. These results indicate that PKC-theta functions in a unique pathway that links the TCR signalling complex to the activation of NF-kappaB in mature T lymphocytes.

Methamphetamine-induced increase in striatal NF-kappaB DNA-binding activity is attenuated in superoxide dismutase transgenic mice

Methamphetamine injection (x4 with 2-h interval) caused dose-dependent activation of striatal NF-kappaB activity. Striatal NF-kappaB binding increased significantly at 1-3 h after the last injection of methamphetamine (10 mg/kg, i.p. x4). This induction of striatal NF-kappaB activity was significantly attenuated in Cu, Zn-superoxide dismutase transgenic mice in a gene dosage-dependent fashion. The present results suggest that reactive oxygen species generated by methamphetamine injections can activate striatal NF-kappaB DNA-binding during this drug-induced toxic process.

Ciprofloxacin induces an immunomodulatory stress response in human T lymphocytes

Exposure of cells to adverse environmental conditions invokes a genetically programmed series of events resulting in the induction of specific genes. The fluoroquinolone antibiotic ciprofloxacin has recently been reported to upregulate interleukin-2 (IL-2) gene induction. In the present investigation, the effect of ciprofloxacin at supratherapeutic concentrations on immediate-early (<2 h) gene expression in primary human peripheral blood lymphocytes was studied with Northern blots. In addition, transcriptional activity of IL-2 and metallothionein enhancer and promoter regions and transcription factors AP-1, NF-kappaB, and NF-AT were analyzed by chloramphenicol acetyltransferase (CAT) and electrophoretic mobility shift assays, respectively. The concentration of c-fos, c-jun, c-myc, junB, and fra-1 mRNAs was increased in activated peripheral blood lymphocytes incubated with ciprofloxacin compared to that in untreated controls. Ciprofloxacin increased CAT activity in stimulated lymphocytes transfected with plasmids containing either the IL-2 or metallothionein enhancer. Furthermore, among the transcription factors tested, AP-1 activity was increased in stimulated purified T helper lymphocytes incubated with ciprofloxacin compared to drug-free controls. Taken together, ciprofloxacin increased the levels of immediate-early transcripts, enhanced IL-2 and metallothionein promoter induction, and upregulated AP-1 concentrations in primary lymphocytes, reflecting a program commonly observed in mammalian stress responses.

Atypical signaling defects prevent IL-2 gene expression in lpr/lpr CD4-CD8- cells

T cells with CD4-CD8- (double negative, DN) phenotype in MRL-lpr/lpr mouse serve as a model to establish the correlation between the extremely low IL-2 gene expression and the specific signaling inactivation. The extent of nonresponsiveness in lpr DN cells was distinctive in several unusual defects. First, the poor IL-2 production in lpr DN cells could not be restored by supplement of signals known to augment IL-2 response in normal T cells. Second, the activations of both mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK) were attenuated in lpr DN cells upon direct activation by TPA/A23187. Third, IL-2 mRNA was degraded much faster in lpr DN cells than that in normal T cells. Fourth, of the four major transcriptional elements on IL-2 promoter, only AP-1 and nuclear factor of activated T cells (NFAT)-binding activities were suppressed in lpr DN T cells. Altogether, these results suggest that an extremely low level of IL-2 production in lpr DN T cells was due to both the increased instability of mRNA and the reduced activation of IL-2 gene promoter, the latter defect could be attributed to the inactivation of AP-1 and NF-AT as well as the poor activation of the upstream MAP kinase and JNK.

New perspectives on PKCtheta, a member of the novel subfamily of protein kinase C

Members of the protein kinase C (PKC) family of serine/threonine protein kinases have been implicated in numerous cellular responses in a large variety of cell types. Expression patterns of individual members and differences in their cofactor requirements and potential substrate specificity suggest that each isoenzyme may be involved in specific regulatory processes. The PKCtheta isoenzyme exhibits a relatively restricted expression pattern with high protein levels found predominantly in hematopoietic cells and skeletal muscle. PKCtheta was found to be expressed in T, but not B lymphocytes, and to colocalize with the T-cell antigen receptor (TCR) at the site of contact between the antigen-responding T cell and the antigen-presenting cell (APC). Colocalization of PKCtheta with the TCR was selective for this isoenzyme and occurred only upon antigen-mediated responses leading to T-cell activation and proliferation. PKCtheta was found to be involved in the regulation of transcriptional activation of early-activation genes, predominantly AP-1, and its cellular distribution and activation were found to be regulated by the 14-3-3 protein. Other findings indicated that PKCtheta can associate with the HIV negative factor (Nef) protein, suggesting that altered regulation of PKCtheta by Nef may contribute to the T-cell impairments that are characteristic of infection by HIV. PKCtheta is expressed at relatively high levels in skeletal muscle, where it is suggested to play a role in signal transduction in both the developing and mature neuromuscular junction. In addition, PKCtheta appears to be involved in the insulin-mediated response of intact skeletal muscle, as well as in experimentally induced insulin resistance of skeletal muscle. Further studies suggest that PKCtheta is expressed in endothelial cells and is involved in multiple processes essential for angiogenesis and wound healing, including the regulation of cell cycle progression, formation and maintenance of actin cytoskeleton, and formation of capillary tubes. Here, we review recent progress in the study of PKCtheta and discuss its potential role in various cellular responses.

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.

Coordinate transactivation of the interleukin-2 CD28 response element by c-Rel and ATF-1/CREB2

The interleukin-2 CD28 response element (CD28RE) acts as a composite enhancer, in conjunction with a 3'-12-O-tetradecanoylphorbol-13-acetate response element (TRE)-like element, to confer CD28 receptor-dependent inducibility to the interleukin-2 promoter in T-cells. When inserted as a single copy upstream of a basal promoter, this composite enhancer, termed the CD28RE-TRE, is both highly active and CD28-inducible in transactivation assays. A multicomponent nuclear protein complex that binds the CD28RE-TRE was isolated by DNA affinity chromatography from nuclear extracts of mitogen- and CD28 receptor-costimulated human T-cells. Immunological and biochemical analyses of this complex reveal the presence of c-Rel, ATF-1, and CREB2 as major DNA-binding components. Coexpression of c-Rel in combination with ATF-1, CREB2, or ATF-1/CREB2 leads to synergistic transactivation of a CD28RE-TRE reporter plasmid in quiescent Jurkat T-cells. Furthermore, CD28-dependent transactivation of the CD28RE-TRE is specifically inhibited by cAMP response element-binding protein (CREB) dominant-negative expression vectors. Moreover, mutant promoter constructs in which the internal 5'-CD28RE and 3'-TRE-like sequences have been topologically positioned 180 degrees out of phase with one another show loss of mitogen- and CD28-dependent inducibility. Finally, the addition of the CREB-binding transcriptional coactivator p300 leads to a dramatic CREB-dependent increase in both mitogen- and CD28-mediated transactivation of the CD28RE-TRE. These findings demonstrate that full physiological responsiveness to CD28 receptor stimulation in T-cells is dependent on topologically linked sequences within the CD28RE-TRE composite enhancer and provide strong support of a direct role for the CREB family of transcription factors and p300/CREB-binding protein coactivator proteins in cytokine gene induction during T-cell activation.

Signaling pathway triggered by a short immunomodulating peptide on human monocytes

A short synthetic peptide (Pa) containing a structural motif ("2-6-11" motif) present in a number of human extracellular matrix proteins was found to stimulate the production of cytokines IL-1alpha, IL-1beta, IL-6, and TNFalpha by human peripheral blood mononuclear cells. We have now investigated the signal transduction pathway involved in the elicitation of these immunomodulating properties on isolated human monocytes. Our results show that active peptide Pa provoked phosphoinositide hydrolysis, intracellular calcium elevation, and cAMP accumulation. Herbimycin A, an inhibitor of protein tyrosine kinases (PTK), markedly reduced these effects of peptide Pa. We have also found that this peptide stimulated CREB, NF-kappaB, and AP-1 DNA-binding activity. With the help of inhibitors of PTK (herbimycin A), phospholipase C (neomycin sulfate), protein kinase C (bis-indolyl maleimide), protein kinase A (H89), and the calmodulin antagonist W-7, as well as cholera toxin, an agent that increases intracellular cAMP, we showed that cytokine (IL-1alpha, IL-1-beta, IL-6, and TNFalpha) production could be modified by the signal transduction pathway triggered by peptide Pa on monocytes.

Overexpression of mitogen-activated protein kinase kinase kinase reversed cAMP inhibition of NF-kappaB in T cells

cAMP inhibits T cell activation by acting as an antagonist for selective kinases and transcriptional factors. We have recently demonstrated that cAMP inhibited c-Jun N-terminal kinase (JNK) but left the mitogen-activated protein (MAP) kinase cascade almost unaffected in T lymphocytes. In accordance with recent reports, we also observed a selective suppression of nuclear factor NF-kappaB activation by cAMP. The possible link between the JNK cascade and NF-kappaB activation was demonstrated by the fact that the active form of MAP kinase kinase kinase (deltaMEKK), a constitutive activator of JNK, induced NF-kappaB but not AP-1, Oct, and NF-AT in T cells. In contrast, the induction of MAP kinase kinase (MEK)-MAP kinase did not stimulate NF-kappaB activity. The specific activation of NF-kappaB by a single MEKK-JNK cascade was thus unusual, given that the activation of other transcriptional elements in T cells requires at least two signal pathways. This was further confirmed by the fact that cAMP inhibition of NF-kappaB activation was reversed by overexpression of deltaMEKK.

Calcium-dependent immediate-early gene induction in lymphocytes is negatively regulated by p21Ha-ras

The induction of immediate-early (IE) response genes, such as egr-1, c-fos, and c-jun, occurs rapidly after the activation of T lymphocytes. The process of activation involves calcium mobilization, activation of protein kinase C (PKC), and phosphorylation of tyrosine kinases. p21(ras), a guanine nucleotide binding factor, mediates T-cell signal transduction through PKC-dependent and PKC-independent pathways. The involvement of p21(ras) in the regulation of calcium-dependent signals has been suggested through analysis of its role in the activation of NF-AT. We have investigated the inductions of the IE genes in response to calcium signals in Jurkat cells (in the presence of activated p21(ras)) and their correlated consequences. The expression of activated p21(ras) negatively regulated the induction of IE genes by calcium ionophore. This inhibition of calcium-activated IE gene induction was reversed by treatment with cyclosporin A, suggesting the involvement of calcineurin in this regulation. A later result of inhibition of this activation pathway by p21(ras) was down-regulation of the activity of the transcription factor AP-1 and subsequent coordinate reductions in IL-2 gene expression and protein production. These results suggest that p2l(ras) is an essential mediator in generating not only positive but also negative modulatory mechanisms controlling the competence of T cells in response to inductive stimulations.

Destabilization of Raf-1 by geldanamycin leads to disruption of the Raf-1-MEK-mitogen-activated protein kinase signalling pathway

The serine/threonine kinase Raf-1 functions downstream of Rats in a signal transduction cascade which transmits mitogenic stimuli from the plasma membrane to the nucleus. Raf-1 integrates signals coming from extracellular factors and, in turn, activates its substrate, MEK kinase. MEK activates mitogen-activated protein kinase (MAPK), which phosphorylates other kinases as well as transcription factors. Raf-1 exists in a complex with HSP90 and other proteins. The benzoquinone ansamycin geldanamycin (GA) binds to HSP90 and disrupts the Raf-1-HSP90 multimolecular complex, leading to destabilization of Raf-1. In this study, we examined whether Raf-1 destabilization is sufficient to block the Raf-1-MEK-MAPK signalling pathway and whether GA specifically inactivates the Raf-1 component of this pathway. Using the model system of NIH 3T3 cells stimulated with phorbol 12-myristate 13-acetate (PMA), we show that GA does not affect the ability of protein kinase C alpha to be activated by phorbol esters, but it does block activation of MEK and MAPK. Further, GA does not decrease the activity of constitutively active MEK in transiently transfected cells. Finally, disruption of the Raf-1-MEK-MAPK signalling pathway by GA prevents both the PMA-induced proliferative response and PMA-induced activation of a MAPK-sensitive nuclear transcription factor. Thus, we demonstrate that interaction between HSP90 and Raf-1 is a sine qua non for Raf stability and function as a signal transducer and that the effects observed cannot be attributed to a general impairment of protein kinase function.

Protein kinase C-theta isoenzyme selective stimulation of the transcription factor complex AP-1 in T lymphocytes

T-lymphocyte stimulation requires activation of several protein kinases, including the major phorbol ester receptor protein kinase C (PKC), ultimately leading to induction of lymphokines, such as interleukin-2 (IL-2). The revelant PKC isoforms which are involved in the activation cascades of nuclear transcription factors involved in IL-2 production have not yet been clearly defined. We have examined the potential role of two representative PKC isoforms in the induction of the IL-2 gene, i.e., PKC-alpha and PKC-theta, the latter being expressed predominantly in hematopoietic cell lines, particularly T cells. Similar to that of PKC-alpha, PKC-theta overexpression in murine EL4 thymoma cells caused a significant increase in phorbol 12-myristate 13-acetate (PMA)-induced transcriptional activation of full-length IL-2-chloramphenicol acetyltransferase (CAT) and NF-AT-CAT but not of NF-IL2A-CAT or NF-kappaB promoter-CAT reporter gene constructs. Importantly, the critical AP-1 enhancer element was differentially modulated by these two distinct PKC isoenzymes, since only PKC-theta but not PKC-alpha overexpression resulted in an approximately 2.8-fold increase in AP-1-collagenase promoter CAT expression in comparison with the vector control. Deletion of the AP-1 enhancer site in the collagenase promoter rendered it unresponsive to PKC-theta. Expression of a constitutively active mutant PKC-theta A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-theta K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-RasS17N completely inhibited the PKC-O A148E-induced signal, PKC-O. Expression of a constitutively active mutant PKC-O A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-O K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-enRasS17N completely inhibited in the PKC-O A148E-induced signal, identifying PKC-theta as a specific constituent upstream of or parallel to Ras in the signaling cascade leading to AP transcriptional activation.

Phosphorylation of Bcl-2 protein and association with p21Ras in Ras-induced apoptosis

p21Ras mediates mitogenic responses and also renders cells susceptible to apoptosis after inhibition of protein kinase C (PKC) activity. Ras-induced apoptosis can be blocked by the proto-oncogene bcl-2, but the biochemical or functional nature of Bcl-2 regulation of Ras-induced apoptosis is not understood. We demonstrate that Bcl-2 and p21Ras molecules can be co-immunoprecipitated in Jurkat cells. The level of this association is enhanced when an apoptotic stimulus (inhibition of PKC activity) is delivered. Bcl-2/p21Ras association is coincident with new phosphorylation of the Bcl-2 protein. Inhibition of this phosphorylation prevents protection from apoptosis by Bcl-2, providing a functional correlation to the phosphorylation event. The Bcl-2/p21Ras association cannot be competed by exogenous glutathione S-transferase-Ras fusion protein, suggesting that the endogenous complex may be formed before cell lysis. These results provide a possible mechanism of regulation of Ras-induced apoptosis by Bcl-2.

Activation and expression of the nuclear factors of activated T cells, NFATp and NFATc, in human natural killer cells: regulation upon CD16 ligand binding

The putative factors that couple the signal transduction from surface receptors to the activation of cytokine synthesis in natural killer (NK) cells have not been elucidated. We report here that the nuclear factor of activated T cells (NFATp), a cyclosporin A (CsA)-sensitive factor that regulates the transcription of several cytokines, mediates CD16-induced activation of cytokine genes in human NK cells. CD16 (Fc gamma RIIIA)-induced expression of cytokine mRNA in NK cells occurs via a CsA-sensitive and Ca(2+)-dependent mechanism. Stimulation of NK cells with CD16 ligands induces NFAT-like DNA binding activity in the nuclear extracts from these cells, as detected in electrophoretic mobility shift assays. This occurs with fast kinetics after stimulation, via a CsA-sensitive and Ca(2+)-dependent mechanism that does not require de novo protein synthesis. NK cell NFAT is present in the cytosol of nonstimulated cells, migrates to the nucleus upon stimulation, and can associate with AP-1. Two distinct molecules, NFATp and NFATc, have been reported to mediate NFAT activity. The results of supershift assays using NFATp- and NFATc- specific antibodies indicate that NK cell activation early after CD16 ligand binding involves primarily, if not exclusively, NFATp, and Western blot analysis shows that this has the same electrophoretic mobility (approximately 120 kD) as that of T lymphocytes. NK cells do not express NFATc constitutively, but NFATc mRNA accumulation is induced in these cells within 2 h of stimulation with CD16 ligands. However, supershift assays using the available mAb recognizing the T cell NFATc revealed no detectable NFATc protein in nuclear and cytoplasmic extracts from CD16- or phorbol ester-stimulated cells at any time tested, up to 4 h. These results provide the first direct evidence that both CsA-sensitive transcription factors, NFATp and NFATc, are expressed in human NK cells, and that their activation and/or expression can be regulated in primary cells by a single stimulus, that, in the case of CD16 in NK cells, results in early activation of NFATp and subsequently induced expression of NFATc mRNA.

RelA is a potent transcriptional activator of the CD28 response element within the interleukin 2 promoter

T-cell activation requires two different signals. The T-cell receptor's recognition of a specific antigen on antigen-presenting cells provides one, and the second signal comes from costimulatory molecules such as CD28. In contrast, T cells that are stimulated with antigen in the absence of the CD28 costimulatory signal can become anergic (nonresponsive). The CD28 response element (CD28RE) has been identified as the DNA element mediating interleukin 2 (IL-2) gene activation by CD28 costimulation. Our previous work demonstrates that the Rel/NF-kappa B family proteins c-Rel, RelA (p65), and NFKB1 (p50) are involved in the complex that binds to the CD28RE. We also showed that c-Rel, but not NFKB1 (p50), can bind to the CD28RE and activate CD28RE-driven transcription in cotransfection assays. However, the role of RelA (p65) in CD28 signaling has not yet been addressed. We provide evidence that RelA (p65) itself bound directly to the CD28RE of the IL-2 promoter and other lymphokine promoters. In addition, RelA (p65) was a potent transcriptional activator of the CD28RE in vivo. We show that a RelA (p65)-c-Rel heterodimer bound to the CD28RE and synergistically activated the CD28RE enhancer activity. We also demonstrate that activated Raf-1 kinase synergized with RelA (p65) in activating the CD28RE enhancer activity. Interestingly, a soluble anti-CD28 monoclonal antibody alone, in the absence of other stimuli, also synergized with RelA (p65) in activating the CD28RE. Furthermore, we show that RelA (p65) activated expression of the wild-type IL-2 promoter but not the CD28RE-mutated IL-2 promoter. A combination of RelA (p65) and NFKB1 (p50) also activated the IL-2 promoter through the CD28RE site. These results demonstrate the functional regulation of the CD28RE, within the IL-2 promoter, by Rel/NF-kappa B transcription factors.

Differential induction of the NF-AT complex during restimulation and the induction of T-cell anergy

Stimulation of human CD4+ T-cell clones through the T-cell receptor (TcR) by high doses of specific peptide results in the induction of a long-lived state of nonresponsiveness that has been called anergy. During the induction of anergy, T cells are phenotypically similar to cells responding to an immunogenic stimulus. The amount of TcR at the cell surface is downmodulated, whereas the CD2 and CD25 receptors are increased. When restimulated, however, anergic T cells fail to up-regulate transcription of the IL-2 gene and in consequence do not produce IL-2. In this study, we have compared the ability of various transcription factors to bind to their appropriate site on DNA. Factors were isolated from the nuclei of T cells that were in the induction phase of anergy or were undergoing activation. The pattern of binding activity in restimulated T cells is consistent with the pattern that has previously been shown to regulate T-cell-specific expression of the IL-2 and the beta chain of the TcR genes. The measured binding to a TCF-1 site is the same in the nuclei of resting, activated, and anergized cells. The inducible factors NK-kappa B, beta E2, CD28RC, and AP-1 are not expressed in resting cells and are twofold lower in anergized as compared with activated cells. In contrast, anergic T cells express approximately eightfold lower amounts of NF-AT, a member of the class of inducible factors that regulates IL-2 gene transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of transcription factors in human T lymphocytes by aspirin-like drugs

Aspirin-like drugs (ALD) induce calcium mobilization, an essential component of T cell activation, but do not induce the biosynthesis of IL-2. To understand the extent to which ALD may mimic mitogenic stimulation, we studied cytoplasmic and nuclear signaling steps in ALD-treated T cells. We found that ALD induce a transient activation of protein kinase (PKC) but have no effect (in comparison to anti-CD3 antibodies) on protein tyrosine phosphorylation nor on PCL gamma 1 tyrosine phosphorylation. ALD-induced calcium mobilization and PKC activation are independent of tyrosine protein kinase activity as shown by the lack of effect of herbimycin, a tyrosine-protein kinase-specific inhibitor. Although we detected no IL-2 mRNA in ALD-treated cells, the nuclei of these cells contain proteins capable of binding to three regulatory sequences in the IL-2 promoter region: NFAT, NF kappa B, and AP-1. These binding activities are expressed only in activated T cells. The expression of AP-1 depended on calcium mobilization and PKC activation. These data suggest that ALD cause transient but significant changes in T cell transmembrane signaling, although some events induced by stimulation with anti-CD3 antibodies are not induced by ALD. The signal is transmitted to the nucleus and induces DNA-binding activity by several transcription factors. However, the ALD stimulus is not capable of causing complete T cell activation.

Functional role of the cis-acting elements in human monocyte chemotactic protein-1 gene in the regulation of its expression by phorbol ester in human glioblastoma cells

The monocyte chemotactic protein-1 (MCP-1) is a 76 amino acid protein that specifically attracts monocytes. The expression of MCP-1 gene can be induced by lipopolysaccharides (LPS), phorbol esters (TPA) and several cytokines. However, how they regulate MCP-1 gene expression is not known. We tested whether the two putative TPA-responsive elements (TREs) and one kappa B enhancer-like region found in the MCP-1 promoter region, are involved in this regulation of MCP-1 gene expression. The 5' untranslated region of MCP-1 gene was linked to chloramphenicol acetyl transferase (CAT) reporter gene and transfected into human glioblastoma cells in which endogenous MCP gene expression was found to be stimulated by TPA and tumor necrosis factor-alpha (TNF-alpha). The 128 bp 5'-flanking region containing one TRE was adequate for basal promoter activity but the presence of both TREs in the MCP-1 promoter region were needed to give TPA responsive enhancement (2.5 fold) of expression of the marker gene. Mutations in either of the TRE's could abolish the TPA induction of CAT expression. Replacement of the kappa B enhancer-like element with a TRE-like sequence caused a 10-fold enhancement of CAT expression by TPA treatment. Random mutation of kappa B enhancer-like element did not affect CAT expression or its TPA induction. None of the MCP promoter constructs showed significant increase in CAT expression by treatment with tumor necrosis factor-alpha (TNF-alpha). This result suggested that the TNF regulation of MCP-1 gene involves other parts of the gene besides the proximal 5' flanking region.

Altered gene transcription after burn injury results in depressed T-lymphocyte activation

OBJECTIVE

Patients with major burns and an animal model of burn injury were studied to determine the mechanism of depressed interleukin-2 (IL-2) production after thermal injury and to determine the effect of such injury on IL-2 receptor (IL-2R) expression and function.

SUMMARY BACKGROUND DATA

Major burn injury is known to diminish resistance to infection by altering cytokine production and prostanoic secretion and by inhibiting T-lymphocyte activation. T-cell activation requires production of regulatory cytokines, principally IL-2, and expression of the appropriate cytokine receptors. Depressed IL-2 production after major burn injury is undisputed, although the molecular mechanisms remain undefined; the effect of burn injury on IL-2R expression and function currently is controversial.

METHODS

The authors studied serial samples of peripheral blood mononuclear cells (PBMC) from 11 patients with 25% to 95% surface area burns and 7 age-matched volunteer control subjects. Peripheral blood mononuclear cells were stimulated by the T-cell mitogen phytohemagglutinin (PHA), and IL-2 production and mRNA expression by Northern blot were determined. Expression and function of IL-2R were determined by monoclonal antibodies to the p55 and p75 chains of the IL-2R, binding of fluorescein-labeled IL-2, and response to exogenous recombinant IL-2. We also studied a mouse model of 20% burn injury known to mimic the immune abnormalities seen in humans with burns. Splenocytes from mice with burns (20-22 per group) were studied for IL-2 production and IL-2 mRNA expression after stimulation with the T-cell mitogen concanavalin A (ConA) and compared with sham burn control subjects. Kinetics of mRNA expression after ConA stimulation also were determined and a nuclear run-on assay performed to determine IL-2 gene transcription. The mRNA expression was determined for the proto-oncogenes c-jun and c-fos, whose protein products join to form transcription factor AP1, which is necessary for activation of the IL-2 promoter. Splenocytes from mice with burns after ConA stimulation also were studied for expression and function of the IL-2R.

RESULTS

Peripheral blood mononuclear cells from burn patients compared with healthy control subjects showed diminished (p < 0.05) IL-2 production and mRNA expression 4 to 10 days after burn injury. Burn PBMC demonstrated normal expression of IL-2R, p55, and p75 chains 0 to 7, 8 to 20, and 21 to 37 days after burn injury, normal IL-2R binding of fluorescein-labeled IL-2, and a normal proliferative response to PHA in the presence of exogenous recombinant IL-2. Splenocytes from mice 7 days after burn injury showed diminished production (p < 0.05) of IL-2 and IL-2 mRNA expression after ConA stimulation as compared with sham burn control subjects. Kinetics of mRNA expression after ConA stimulation were the same for burn and control mice, indicating that reduced IL-2 mRNA expression was not caused by altered mRNA degradation. A nuclear run-on assay confirmed decreased IL-2 gene transcription in burn splenocytes. Burn splenocytes showed normal expression of mRNA for c-jun but diminished expression of mRNA for c-fos. Finally, splenocytes from mice with burns after ConA stimulation showed normal expression and function of the IL-2R 7, 10, 14, and 21 days after burn injury.

CONCLUSIONS

These human and animal studies indicate that major burn injury depresses T-cell activation at the level of IL-2 gene transcription at least in part by inhibiting c-fos expression, whereas IL-2R expression and function remain normal and T-cell proliferation can be restored to normal levels by exogenous IL-2.

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

We have investigated the characteristics of IL2R alpha gene induction in untransformed murine T cells. Induction of IL2R alpha mRNA by TCR/CD3 ligands in a murine T cell clone and in short-term splenic T cell cultures was inhibited by protein synthesis inhibitors and by CsA. This result was contrary to previous observations in JURKAT T leukemia cells and human peripheral blood T cells, suggesting a difference in the mechanisms of IL2R alpha gene induction in these different cell types. The CsA sensitivity of IL2R alpha mRNA induction represented a direct effect on the TCR/CD3 response, and was not due to CsA-sensitive release of the lymphokines IL2 or tumour necrosis factor alpha (TNF alpha) and consequent lymphokine-mediated induction of IL2R alpha mRNA. The NF-kappa B site of the IL2R alpha promoter was essential for gene induction through the TCR/CD3 complex, and the induction of reporter plasmids containing multimers of this site was significantly inhibited by CsA. Northern blotting analysis indicated that while the p65 subunit of NF-kappa B was constitutively expressed and not appreciably induced upon T cell activation, mRNA for the p105 precursor of p50 NF-kappa B was induced in response to TCR/CD3 stimulation and this induction was sensitive to CsA. Electrophoretic mobility shift assays and antiserum against the p50 subunit of NF-kappa B indicated that p50 was a component of the inducible nuclear complex that bound to the IL2R alpha kappa B site. Appearance of the kB-binding proteins was insensitive to CsA at early times after activation (approximately 15 min), but was partially sensitive to CsA at later times. Based on these results, we propose that the NF-kappa B site of the IL2R alpha promoter mediates at least part of the CsA sensitivity of IL2R alpha gene induction in untransformed T cells, possibly because de novo synthesis of p105 NF-kappa B is required for sustained IL2R alpha expression.

Generation of normal T and B lymphocytes by c-jun deficient embryonic stem cells

To determine the potential roles of c-jun in lymphocyte development, we generated somatic chimeric mice by injecting homozygous c-jun mutant embryonic stem (ES) cells into blastocysts from recombination activating gene-2 (RAG-2)-deficient mice. Chimeric mice had poor restoration of thymocytes, but contained substantial numbers of mature T and B lymphocytes in the periphery. Stimulation of c-jun-/- B cells resulted in normal levels of proliferation and immunoglobulin secretion. Likewise, stimulation of c-jun-/- T cells resulted in essentially normal levels of IL-2R alpha expression, IL-2 secretion, and proliferation. We further showed that the relatively normal activation responses of the c-jun-/- T cells probably results from the fact that other members of the Jun family contribute to the bulk of the activator protein-1 (AP-1) complexes in normal T cells and, as a result, AP-1 complexes are found at relatively normal levels in c-jun-/- T cells.

Co-stimulation with anti-CD28 (Kolt-2) enhances DNA synthesis by defective T cells in common variable immunodeficiency

In normal T cells, an anti-CD28 MoAb (Kolt-2) will synergize with the mitogenic stimuli phytohaemagglutinin (PHA), anti-CD3 (OKT3) or a combination of anti-CD2 antibodies (OKT11 and GT2) in the induction of DNA synthesis. A subgroup of patients with common variable immunodeficiency (CVID) show a defect in DNA synthesis by T cells stimulated in vitro with the above mitogens. We have now investigated whether anti-CD28 will correct the defect. This strategy partially restored DNA synthesis, providing evidence that the CD28 co-stimulatory pathway in CVID T cells is normal. Ligation of CD28 acts through co-stimulating IL-2 secretion. The natural ligand (B7) for CD28 on antigen-presenting cells from CVID patients is expressed normally. We conclude that the defect in CVID T cells lies in pathways that lead to transcription of the IL-2 gene other than that induced by ligation of CD28 with Kolt-2.

Trypanosoma cruzi infection suppresses nuclear factors that bind to specific sites on the interleukin-2 enhancer

Interleukin-2 (IL-2) gene expression, a critical early event during T lymphocyte activation, is severely suppressed in mice infected with the protozoan parasite Trypanosoma cruzi, the causative agent of human Chagas' disease. Our previous observation that reduction of IL-2 mRNA in T cells from T. cruzi-infected mice is not due to an increased degradation of the mRNA suggests a repression of the IL-2 gene at the transcriptional level. In this study, we have measured the level of nuclear factors that bind to specific sites on the IL-2 enhancer. Splenocytes and splenic T cells from acutely infected mice show a marked decrease in the level of AP-1, and a modest decrease in the level of NF-kappa B and nuclear factor of activated T cells (NF-AT). DNA-binding activity of Oct-1 was least affected in T cells from infected mice. Although the basal level of AP-1 activity is comparable in cells from uninfected and infected mice, mitogen-induced AP-1 activation is absent in the cells from T. cruzi-infected mice. Sodium deoxycholate treatment slightly enhances NF-kappa B-binding activity in splenocyte nuclear and whole-cell extracts from infected mice, suggesting that a blockage of the activation of NF-kappa B is only partially responsible for the decrease in the level of NF-kappa B in T cells from T. cruzi-infected mice. These data identify the molecular basis of IL-2 gene regulation in T. cruzi infection and suggest that T cells are anergized as a result of the infection.

Multiple closely-linked NFAT/octamer and HMG I(Y) binding sites are part of the interleukin-4 promoter

We show here that the immediate upstream region (from position -12 to -270) of the murine interleukin 4 (Il-4) gene harbors a strong cell-type specific transcriptional enhancer. In T lymphoma cells, the activity of the Il-4 promoter/enhancer is stimulated by phorbol esters, Ca++ ionophores and agonists of protein kinase A and inhibited by low doses of the immunosuppressant cyclosporin A. The Il-4 promoter/enhancer is transcriptionally inactive in B lymphoma cells and HeLa cells. DNase I footprint protection experiments revealed six sites of the Il-4 promoter/enhancer to be bound by nuclear proteins from lymphoid and myeloid cells. Among them are four purine boxes which have been described to be important sequence motifs of the Il-2 promoter. They contain the motif GGAAA and are recognized by the inducible and cyclosporin A-sensitive transcription factor NFAT-1. Three of the Il-4 NFAT-1 sites are closely linked to weak binding sites of Octamer factors. Several purine boxes and an AT-rich protein-binding site of the Il-4 promoter are also recognized by the high mobility group protein HMG I(Y). Whereas the binding of NFAT-1 and Octamer factors enhance the activity of the Il-4 promoter, the binding of HMG I(Y) suppresses its activity and, therefore, appears to be involved in the suppression of Il-4 transcription in resting T lymphocytes.

Transcriptional regulation of interleukin-2 gene expression by CD69-generated signals

The 5' flanking region of the human interleukin (IL)-2 gene was investigated for enhancer activity in response to CD69-generated signals, using a chloramphenicol acetyltransferase (CAT)-driven transient expression system in Jurkat cells. The region extending from -317 to +47 relative to the initiation site of IL-2 gene transcription was shown to contain sequences able to respond to CD69 cross-linking, by enhancing by about 100% a phorbol 12-myristate 13-acetate (PMA)-plus-ionomycin stimulation of CAT activity. A similar increase in CAT activity produced by PMA-plus-anti-CD3 mAb was induced by CD69 cross-linking, while a 200% increase over that obtained by PMA-plus-anti-CD28 mAb stimulation was seen. Analysis of enhancer deletion mutants revealed that proximal AP-1, OCT-1/octamer-associated protein and nuclear factor of activated T cells (NFAT) binding regions were all necessary to allow CD69-mediated enhancement of CAT activity. By gel mobility shift analysis, cyclosporin A-sensitive NFAT-binding induction and enhancement of AP-1 binding activity could be detected in nuclear extracts of both Jurkat and peripheral blood T cells after simultaneous CD69 and protein kinase C stimulation. Finally, CD69-mediated signals could increase NFAT and AP-1 binding activity following PMA and ionomycin stimulation in peripheral blood T cells. Collectively, these data suggest that CD69-generated signals participate in the control of the IL-2 gene expression at the transcriptional level, likely acting through NFAT and AP-1 transcription factor complexes.