Transcriptional regulation of the interleukin-2 gene in normal human peripheral blood T cells. Convergence of costimulatory signals and differences from transformed T cells

Diagnostic and therapeutic potential of RNASET2 in Crohn's disease: Disease-risk polymorphism modulates allelic-imbalance in expression and circulating protein levels and recombinant-RNASET2 attenuates pro-inflammatory cytokine secretion

Ribonuclease T2 gene (RNASET2) variants are associated in genome wide association studies (GWAS) with risk for several autoimmune diseases, including Crohn's disease (CD). In T cells, a functional and biological relationship exists between TNFSF15-mediated enhancement of IFN-γ production, mucosal inflammation and RNASET2. Disease risk variants are associated with decreased mRNA expression and clinical characteristics of severe CD; however, functional classifications of variants and underlying molecular mechanisms contributing to pathogenesis remain largely unknown. In this study we demonstrate that allelic imbalance of RNASET2 disease risk variant rs2149092 is associated with transcriptional and post-transcriptional mechanisms regulating transcription factor binding, promoter-transactivation and allele-specific expression. RNASET2 mRNA expression decreases in response to multiple modes of T cell activation and recovers following elimination of activator. In CD patients with severe disease necessitating surgical intervention, preoperative circulating RNASET2 protein levels were decreased compared to non-IBD subjects and rebounded post-operatively following removal of the inflamed region, with levels associated with allelic carriage. Furthermore, overexpression or treatment with recombinant RNASET2 significantly reduced IFN-γ secretion. These findings reveal that RNASET2 cis- and trans-acting variation contributed regulatory complexity and determined expression and provide a basis for linking genetic variation with CD pathobiology. These data may ultimately identify RNASET2 as an effective therapeutic target in a subset of CD patients with severe disease.

CD58 Immunobiology at a Glance

The glycoprotein CD58, also known as lymphocyte-function antigen 3 (LFA-3), is a costimulatory receptor distributed on a broad range of human tissue cells. Its natural ligand CD2 is primarily expressed on the surface of T/NK cells. The CD2-CD58 interaction is an important component of the immunological synapse (IS) that induces activation and proliferation of T/NK cells and triggers a series of intracellular signaling in T/NK cells and target cells, respectively, in addition to promoting cell adhesion and recognition. Furthermore, a soluble form of CD58 (sCD58) is also present in cellular supernatant in vitro and in local tissues in vivo. The sCD58 is involved in T/NK cell-mediated immune responses as an immunosuppressive factor by affecting CD2-CD58 interaction. Altered accumulation of sCD58 may lead to immunosuppression of T/NK cells in the tumor microenvironment, allowing sCD58 as a novel immunotherapeutic target. Recently, the crucial roles of costimulatory molecule CD58 in immunomodulation seem to be reattracting the interests of investigators. In particular, the CD2-CD58 interaction is involved in the regulation of antiviral responses, inflammatory responses in autoimmune diseases, immune rejection of transplantation, and immune evasion of tumor cells. In this review, we provide a comprehensive summary of CD58 immunobiology.

Antigen Presentation by Vascular Cells

Antigen presentation by cells of the vessel wall may initiate rapid and localized memory immune responses in peripheral tissues. Peptide antigens displayed on major histocompatibility complex (MHC) molecules on the surface of endothelial cells (ECs) can be recognized by T cell receptors on circulating effector memory T cells (T_EM), triggering both transendothelial migration and activation. The array of co-stimulatory receptors, adhesion molecules, and cytokines expressed by ECs serves to modulate T cell activation responses. While the effects of these interactions vary among species, vascular beds, and vascular segments within the same tissue, they are capable of triggering allograft rejection without direct involvement of professional antigen-presenting cells and may play a similar role in host defense against infections and in autoimmunity. Once across the endothelium, extravasating T_EM then contact mural cells of the vessel wall, including pericytes or vascular smooth muscle cells, which may also present antigens and provide signals that further regulate T cell responses. Collectively, these interactions provide an unexplored opportunity in which targeting of vascular cells can be used to modulate immune responses. In organ transplantation, targeting ECs with siRNA to reduce expression of MHC molecules may additionally mitigate perioperative injuries by preformed alloantibodies, further reducing the risk of graft rejection. Similarly, genetic manipulation of vascular cells to minimize antigen-dependent responses can be used to increase perfusion of tissue engineered organs without triggering rejection.

Stomatin-like protein 2 of turbot Scopthalmus maximus: Gene cloning, expression profiling and immunoregulatory properties

Stomatin-like protein 2 (SLP-2) is a novel and unusual member of the stomatin gene superfamily. In this study, we obtained a full-length SLP-2 (SmSLP-2) cDNA from turbot (Scopthalmus maximus) spleen cDNA library. The cDNA sequence of SmSLP-2 contains a 5'-UTR of 107 bp, an ORF of 1050 bp, and a 3'-UTR of 959 bp. The ORF encodes a putative protein of 349 residues, which has a calculated molecular mass of 38.7 kDa. The SmSLP-2 protein possesses a prohibitin-homology (PHB) domain (residues 40 to 198) and shares 72.4-87.6% overall sequence identity with that of the teleost species. The highest expression of SmSLP-2 mRNA was found in the skin, followed by the head kidney, gut, spleen, liver, heart, gill and muscle. Moreover, both viral and bacterial pathogen infection resulted in the up-regulation of SmSLP-2 mRNA in the turbot head kidney and spleen in vivo. Subcellular localization analysis indicated that the SmSLP-2 proteins are mainly located in the peripheral membrane of ZF4 cells. This study also demonstrated that SmSLP-2 modulates IL-2 expression via active NFκB signaling pathway, and is possibly involved in host immune defense against bacterial and viral pathogens.

The impact of Nucleofection® on the activation state of primary human CD4 T cells

Gene transfer into primary human CD4 T lymphocytes is a critical tool in studying the mechanism of T cell-dependent immune responses and human immunodeficiency virus-1 (HIV-1) infection. Nucleofection® is an electroporation technique that allows efficient gene transfer into primary human CD4 T cells that are notoriously resistant to traditional electroporation. Despite its popularity in immunological research, careful characterization of its impact on the physiology of CD4 T cells has not been documented. Herein, using freshly-isolated primary human CD4 T cells, we examine the effects of Nucleofection® on CD4 T cell morphology, intracellular calcium levels, cell surface activation markers, and transcriptional activity. We find that immediately after Nucleofection®, CD4 T cells undergo dramatic morphological changes characterized by wrinkled and dilated plasma membranes before recovering 1h later. The intracellular calcium level also increases after Nucleofection®, peaking after 1h before recovering 8h post transfection. Moreover, Nucleofection® leads to increased expression of T cell activation markers, CD154 and CD69, for more than 24h, and enhances the activation effects of phytohemagglutinin (PHA) stimulation. In addition, transcriptional activity is increased in the first 24h after Nucleofection®, even in the absence of exogenous stimuli. Therefore, Nucleofection® significantly alters the activation state of primary human CD4 T cells. The effect of transferred gene products on CD4 T cell function by Nucleofection® should be assessed after sufficient resting time post transfection or analyzed in light of the activation caveats mentioned above.

Role of CREM in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease. Immune complex, autoantibodies and autoreactive lymphocytes are involved in manifestations of SLE. Recently, investigations have indicated that expression of the transcription factor cAMP responsive element modulator (CREM) is abnormal in T cells and might play an important role in the pathogenesis of SLE. CREM has much influence on the promoters, such as IL-2, c-fos, TCR ζ, and SYK. Moreover, activity of CREM itself has been demonstrated, particularly with an auto-regulatory feedback mechanism. Therefore, we will discuss the association of CREM and SLE based on current knowledge to unravel the mechanism of CREM performance.

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.

CD155 on Human Vascular Endothelial Cells Attenuates the Acquisition of Effector Functions in CD8 T Cells

Objective—

CD155 is a cell surface protein that has recently been described to exert immune regulatory functions. We have characterized the expression of CD155 on human vascular endothelial cells (ECs) and examined its role in the regulation of T-cell activation.

Methods and Results—

CD155 was expressed on resting human vascular ECs and was upregulated in an interferon-γ (IFNγ)–dependent manner. When the function of CD155 in regulating T-cell activation was examined, antibody-mediated neutralization of CD155 did not affect CD8 T-cell proliferation in response to stimulation with ECs. However, neutralization of CD155 activity or small interfering RNA-mediated inhibition of CD155 expression in ECs increased expression of IFNγ and cytotoxic effector function in activated CD8 T cells.

Conclusion—

CD155 is an IFNγ-inducible immune regulatory protein on the surface of human ECs that attenuates the acquisition of effector functions in CD8 T cells.

Low levels of NF-κB/p65 mark anergic CD4+ T cells and correlate with disease severity in sarcoidosis

T lymphocytes from patients with sarcoidosis respond weakly when stimulated with mitogen or antigen. However, the mechanisms responsible for this anergy are not fully understood. Here, we investigated the protein levels of nuclear transcription factor NF-κB (p50, p65, and p105), IκBα (inhibitor of NF-κB), T-cell receptor (TCR) CD3ζ-chain, tyrosine kinase p56(LCK), and nuclear factor of activated T cells c2 (NF-ATc2) in peripheral blood CD4(+) T cells from patients with sarcoidosis. Baseline expression of p65 in these lymphocytes was reduced in 50% of patients. The reduced levels of p65 in sarcoid CD4(+) T cells concurred with decreased levels of p50, p105, CD3ζ, p56(LCK), IκBα, and NF-ATc2. Polyclonal stimulation of NF-κB-deficient sarcoid T cells resulted in reduced expression of CD69 and CD154, decreased proliferation, and cytokine (i.e., interleukin 2 [IL-2] and gamma interferon [IFN-γ]) production. The clinical significance of these findings is suggested by the association between low p65 levels and the development of more severe and active sarcoidosis. Although correlative, our results support a model in which multiple intrinsic signaling defects contribute to peripheral T-cell anergy and the persistence of chronic inflammation in sarcoidosis.

miR-200c affects the mRNA expression of E-cadherin by regulating the mRNA level of TCF8 during post-natal epididymal development in juvenile rats

The unique temporal expression pattern of miR-200c in epididymis during post-natal development in juvenile rats was revealed by our home-made miRNA microarray in this paper. It was found that miR-200c expressed in the lowest level at Day 7 and then increased to the highest at Day 36 followed by a dramatic decrease. The pattern was exactly inverse to that of mRNA expression of transcription factor 8 (TCF8) revealed by quantitative real-time polymerase chain reaction (qRT-PCR), providing an extra evidence that TCF8 is one degradation target of miR-200c even in epididymis. Moreover, the qRT-PCR study on expression of E-cadherin and interleukin-2 indicated that miR-200c does exert an obvious effect on the mRNA expression of E-cadherin by directly regulating the mRNA level of TCF8, although the effect on interleukin-2 is not obvious as on E-cadherin, which implicates that interleukin-2 may be also regulated by other factors besides TCF8 in rat epididymis.

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

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

Generation of NO by bystander human CD8 T cells augments allogeneic responses by inhibiting cytokine deprivation-induced cell death

Nitric oxide (NO), generated by inducible NO synthase (iNOS) in bystander human CD8 T cells, augments the accumulation of allogeneically activated human CD8 T cells in vitro and in vivo. Here, we report that iNOS-derived NO does not affect T-cell proliferation but rather inhibits cell death of activated human CD8 T cells after activation by allogeneic endothelial cells in culture. Exogenous NO did not affect activation-induced cell death of human CD8 T cells but specifically reduced death of activated T cells due to cytokine deprivation. NO-mediated inhibition of T-cell death did not involve cGMP signaling, and NO did not affect the expression of Bcl-2-related proteins known to regulate cytokine deprivation-induced cell death. However, NO inhibited the activity of caspases activated as a consequence of cytokine deprivation in activated T cells. This protective effect correlated with S-nitrosylation of caspases and was phenocopied by z-VAD.fmk and z-LEHD.fmk, pharmacological inhibitors of caspases. In summary, our findings indicate that NO augments the accumulation of activated human T cells principally by inhibiting cytokine deprivation-induced cell death through S-nitrosylation of caspases.

Production of specific mRNA transcripts, usage of an alternate promoter, and octamer-binding transcription factors influence the surface expression levels of the HIV coreceptor CCR5 on primary T cells

Surface levels of CCR5 on memory CD4(+) T cells influence HIV-1/AIDS susceptibility. Alternative promoter usage results in the generation of CCR5 mRNA isoforms that differ based on whether they contain or lack the untranslated exon 1. The impact of exon 1-containing transcripts on CCR5 surface expression is unknown. In this study, we show that the increased cell surface expression of CCR5 on primary T cells is associated with selective enrichment of exon 1-containing transcripts. The promoter that drives exon 1-containing transcripts is highly active in primary human T cells but not in transformed T cell lines. The transcription factors Oct-1 and -2 inhibit and enhance, respectively, the expression of exon 1-containing transcripts and CCR5 surface levels. However, polymorphisms at homologous octamer-binding sites in the CCR5 promoter of nonhuman primates abrogate the binding of these transcription factors. These results identify exon 1-containing transcripts, and the cis-trans factors that regulate the expression levels of these mRNA isoforms as key parameters that affect CCR5 surface expression levels, and by extension, susceptibility to HIV/AIDS among humans, and possibly, the observed interspecies differences in susceptibility to lentiviral infection.

Pertussis toxin utilizes proximal components of the T-cell receptor complex to initiate signal transduction events in T cells

Pertussis toxin (PTx) is an AB(5) toxin produced by the human pathogen Bordetella pertussis. Previous work demonstrates that the five binding (B) subunits of PTx can have profound effects on T lymphocytes independent of the enzymatic activity of the A subunit. Stimulation of T cells with holotoxin (PTx) or the B subunit alone (PTxB) rapidly induces signaling events resulting in inositol phosphate accumulation, Ca(2+) mobilization, interleukin-2 (IL-2) production, and mitogenic cell growth. Although previous reports suggest the presence of PTx signaling receptors expressed on T cells, to date, the receptor(s) and membrane proximal signaling events utilized by PTx remain unknown. Here we genetically and biochemically define the membrane proximal components utilized by PTx to initiate signal transduction in T cells. Using mutants of the Jurkat T-cell line deficient for key components of the T-cell receptor (TCR) pathway, we have compared stimulation with PTx to that of anti-CD3 monoclonal antibody (MAb), which directly interacts with and activates the TCR complex. Our genetic data in combination with biochemical analysis show that PTx (via the B subunit) activates TCR signaling similar to that of anti-CD3 MAb, including activation of key signaling intermediates such as Lck, ZAP-70, and phospholipase C-gamma1. Moreover, the data indicate that costimulatory activity, as provided by CD28 ligation, is required for PTx to fully stimulate downstream indicators of T-cell activation such as IL-2 gene expression. By illuminating the signaling pathways that PTx activates in T cells, we provide a mechanistic understanding for how these signals deregulate immune system functions during B. pertussis infection.

A self-inactivating retrovector incorporating the IL-2 promoter for activation-induced transgene expression in genetically engineered T-cells

Background

T-cell activation leads to signaling pathways that ultimately result in induction of gene transcription from the interleukin-2 (IL-2) promoter. We hypothesized that the IL-2 promoter or its synthetic derivatives can lead to T-cell specific, activation-induced transgene expression. Our objective was to develop a retroviral vector for stable and activation-induced transgene expression in T-lymphocytes.

Results

First, we compared the transcriptional potency of the full-length IL-2 promoter with that of a synthetic promoter composed of 3 repeats of the Nuclear Factor of Activated T-Cells (NFAT) element following activation of transfected Jurkat T-cells expressing the large SV40 T antigen (Jurkat TAg). Although the NFAT3 promoter resulted in a stronger induction of luciferase reporter expression post stimulation, the basal levels of the IL-2 promoter-driven reporter expression were much lower indicating that the IL-2 promoter can serve as a more stringent activation-dependent promoter in T-cells. Based on this data, we generated a self-inactivating retroviral vector with the full-length human IL-2 promoter, namely SINIL-2pr that incorporated the enhanced green fluorescent protein (EGFP) fused to herpes simplex virus thymidine kinase as a reporter/suicide "bifunctional" gene. Subsequently, Vesicular Stomatitis Virus-G Protein pseudotyped retroparticles were generated for SINIL-2pr and used to transduce the Jurkat T-cell line and the ZAP-70-deficient P116 cell line. Flow cytometry analysis showed that EGFP expression was markedly enhanced post co-stimulation of the gene-modified cells with 1 μM ionomycin and 10 ng/ml phorbol 12-myristate 13-acetate (PMA). This activation-induced expression was abrogated when the cells were pretreated with 300 nM cyclosporin A.

Conclusion

These results demonstrate that the SINIL-2pr retrovector leads to activation-inducible transgene expression in Jurkat T-cell lines. We propose that this design can be potentially exploited in several cellular immunotherapy applications.

A specific CpG site demethylation in the human interleukin 2 gene promoter is an epigenetic memory

DNA demethylation plays a critical role in transcriptional regulation in differentiated somatic cells. However, there is no experimental evidence that CpG methylation in a small region of a genome restricts gene expression. Here, we show that the anti-CD3repsilon/CD28 antibody stimulation of human CD4+ T cells induces IL2 expression following epigenetic changes, including active demethylation of a specific CpG site, recruitment of Oct-1, and changes in histone modifications. When the stimulatory signal is withdrawn, Oct-1 remains on the enhancer region as a stable marker of the stimulation, causing the second induction to be faster and stronger. Our observations indicate that Oct-1-binding followed by CpG demethylation are key events in the epigenetic regulation of IL2 expression and may act as a memory of the regulatory event.

Immunomodulatory Drugs (IMiDs) Increase the Production of IL-2 from Stimulated T Cells by Increasing PKC-θ Activation and Enhancing the DNA-Binding Activity of AP-1 but Not NF-κB, OCT-1, or NF-AT

Immunomodulatory drugs (IMiDs) are orally available small molecules that potently inhibit tumor necrosis factor-alpha (TNF-alpha) production by lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (HuPBMCs) but enhance secretion of such cytokines as interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) by stimulated T cells. The mechanism of cytokine regulation by IMiDs has not yet been determined. In the present study, we investigated the effects of one of the IMiDs, CC-4047 (Actimid, Celgene, Warren, NJ), on synthesis of IL-2 protein and mRNA and on the activity and expression of transcription factors. Treatment with CC-4047 enhances the secretion of IL-2 protein and the expression of IL-2 mRNA in a dose-dependent and time-dependent manner. In T cells stimulated with phorbol myristate acetate (PMA)/ionomycin, CC-4047 enhanced the DNA-binding activity of activated protein-1 (AP-1) but not NF-kappaB, Octomer-1 (OCT-1), or NFAT by 2-fold and 4-fold after an incubation time of 1 and 3 h, respectively. Luciferase reporter assays in Jurkat cells showed similar effects on transcription factor activity. Using in vitro kinase activity assays, we also showed that CC-4047 enhances the activity of protein kinase C-theta (PKC-theta) in stimulated T cells. The secreted IL-2 from HuPBMCs was shown to activate natural killer (NK) cells to lyse their target cell line K562. Taken together, our results demonstrate that the IMiDs exert their effects at least in part by activating PKC-theta and acting on AP-1 DNA-binding activity in T cells, resulting in augmented IL-2 synthesis and activation of IL- 2-dependent downstream effectors, such as NK cells.

A new sensitive and quantitative HTLV-I-mediated cell fusion assay in T cells

Similar to several other viruses, human T cell leukemia virus type I (HTLV-I) induces the formation of multinucleated giant cells (also known as syncytium) when amplified in tissue culture. These syncytia result from the fusion of infected cells with uninfected cells. Due to the intrinsic difficulty of infecting cells with cell-free HTLV-I virions, syncytium formation has become an important tool in the study of HTLV-I infection and transmission. Since most HTLV-I-based cell fusion assays rely on the use of non-T cells, the aim of this study was to optimize a new HTLV-I-induced cell fusion assay in which HTLV-I-infected T cell lines are co-cultured with T cells that have been transfected with an HTLV-I long terminal repeat (LTR) luciferase reporter construct. We demonstrate that co-culture of various HTLV-I-infected T cells with different transfected T cell lines resulted in induction of luciferase activity. Cell-to-cell contact and expression of the viral gp46 envelope protein was crucial for this induction while other cell surface proteins (including HSC70) did not have a significant effect. This quantitative assay was shown to be very sensitive. In this assay, the cell fusion-mediated activation of NF-kappaB and the HTLV-I LTR occurred through previously described Tax-dependent signaling pathways. This assay also showed that cell fusion could activate Tax-inducible cellular promoters. These results thus demonstrate that this new quantitative HTLV-I-dependent cell fusion assay is versatile, highly sensitive, and can provide an important tool to investigate cellular promoter activation and intrinsic signaling cascades that modulate cellular gene expression.

Cellular FLIP (long form) regulates CD8+ T cell activation through caspase-8-dependent NF-kappa B activation

Cellular FLIP long form (c-FLIP(L)) was originally identified as an inhibitor of Fas (CD95/Apo-1). Subsequently, additional functions of c-FLIP(L) were identified through its association with receptor-interacting protein (RIP)1 and TNFR-associated factor 2 to activate NF-kappaB, as well as by its association with and activation of caspase-8. T cells from c-FLIP(L)-transgenic (Tg) mice manifest hyperproliferation upon activation, although it was not clear which of the various functions of c-FLIP(L) was involved. We have further explored the effect of c-FLIP(L) on CD8(+) effector T cell function and its mechanism of action. c-FLIP(L)-Tg CD8(+) T cells have increased proliferation and IL-2 responsiveness to cognate Ags as well as to low-affinity Ag variants, due to increased CD25 expression. They also have a T cytotoxic 2 cytokine phenotype. c-FLIP(L)-Tg CD8(+) T cells manifest greater caspase activity and NF-kappaB activity upon activation. Both augmented proliferation and CD25 expression are blocked by caspase inhibition. c-FLIP(L) itself is a substrate of the caspase activity in effector T cells, being cleaved to a p43(FLIP) form. p43(FLIP) more efficiently recruits RIP1 than full-length c-FLIP(L) to activate NF-kappaB. c-FLIP(L) and RIP1 also coimmunoprecipitate with active caspase-8 in effector CD8(+) T cells. Thus, one mechanism by which c-FLIP(L) influences effector T cell function is through its activation of caspase-8, which in turn cleaves c-FLIP(L) to allow RIP1 recruitment and NF-kappaB activation. This provides a partial explanation of why caspase activity is required to initiate proliferation of resting T cells.

Endothelial cell co-stimulation through OX40 augments and prolongs T cell cytokine synthesis by stabilization of cytokine mRNA

Human endothelial cells (ECs) constitutively express OX40L and co-stimulate memory CD4(+) T cell proliferation that is dependent upon OX40-OX40L interaction. In vivo, OX40 prolongs T cell survival; however, an unanswered question is whether it can also prolong synthesis of proliferation-sustaining cytokines such as IL-2. Here we show that EC co-stimulation results in the secretion of T cell IL-2, IL-3 and IFN-gamma and that in the absence of OX40 signals synthesis largely ceases by 12-18 h, but is prolonged up to 60 h in the presence of OX40 signaling. Blocking OX40-mediated cytokine expression at later times suppresses T cell proliferation and this can be overcome by addition of exogenous IL-2. We find that OX40 signaling has discrete effects on T cell activation as it does not affect expression of IL-10, CD25, CD69 or soluble IL-2R. Also, OX40 does not appear to alter IL-2 transcription, but rather acts to stabilize a subset of cytokine mRNAs, increasing their half-lives by 3-6-fold. We further show that OX40L induces activation of p38 mitogen-activated protein kinase (MAPK) and phosphotidyl-inositol-3-kinase (PI3K) in T cells, and using specific inhibitors, we find that increased mRNA half-life is dependent upon both these pathways but is independent of c-jun-N-terminal kinase (JNK). Thus, EC co-stimulation through OX40 leads to prolonged T cell cytokine synthesis and enhanced proliferation.

Activation of HTLV-I gene transcription by protein tyrosine phosphatase inhibitors

Human T-cell leukemia virus type I (HTLV-I) transcription generally depends on the ability of the viral Tax protein to bind the CREB transcription factor and form an active complex by recruiting CBP/p300 coactivators to the long terminal repeat (LTR). Studies have demonstrated that T-cell activating agents that stimulate CREB are potent inducers of HTLV-I transcription. Herein, we demonstrate that bpV[pic], a protein tyrosine phosphatase (PTP) inhibitor activates the HTLV-I LTR in the presence and absence of Tax expression. Optimal activation occurred at 8 h and was synergistic with forskolin or PGE(2). Infected cell lines and cells transfected with HTLV-I proviral DNA were equally responsive to the synergistic effect of bpV and forskolin on HTLV-I gene expression. Activation of the LTR by bpV[pic] was T-cell receptor-independent, but required ZAP70, calcineurin activity and functional calcium entry. Inhibition of the SHP-1 PTP was suggested to be important. Transfection experiments with a CREB dominant-negative mutant and with isolated TRE1- or CREB-responsive reporter constructs and treatment with the MDL-12,330A adenylate cyclase inhibitor all supported the involvement of a CREB/ATF family member in this bpV-dependent activation of the HTLV-I LTR, although CREB itself did not seem to be involved. Analysis of HTLV-I reporter constructs containing mutated CREB-binding sites also implied the involvement of another element in this activation. These results demonstrate for the first time a powerful effect of PTP inhibitors on HTLV-I LTR activity and suggest participation of both CREB-dependent and -independent pathways in this activation.

Transcriptional regulation of interleukin 2 in SLE T cells

Interleukin-2 (IL-2) is a central cytokine required for the activation of T, B, and NK cells. It propagates the immune response and terminates it by promoting the activation induced cell death of T cells. IL-2 production is altered in T cells of patients with systemic lupus erythematosus (SLE). The consequence of reduced IL-2 production in SLE is decreased immune response to infectious agents. Decreased IL-2 production by SLE T cells is the result of transcriptional repression of the IL-2 gene. This article will review the defective transcription regulation of IL-2 in SLE T cells, which is the result of decreased expression of the enhancers NF-kappa B and AP1 and the increased expression of the transcriptional repressor CREM.

T lymphocyte-endothelial cell interactions

Human vascular endothelial cells (EC) basally display class I and II MHC-peptide complexes on their surface and come in regular contact with circulating T cells. We propose that EC present microbial antigens to memory T cells as a mechanism of immune surveillance. Activated T cells, in turn, provide both soluble and contact-dependent signals to modulate normal EC functions, including formation and remodeling of blood vessels, regulation of blood flow, regulation of blood fluidity, maintenance of permselectivity, recruitment of inflammatory leukocytes, and antigen presentation leading to activation of T cells. T cell interactions with vascular EC are thus bidirectional and link the immune and circulatory systems.

Preferential activation of an IL-2 regulatory sequence transgene in TCR gamma delta and NKT cells: subset-specific differences in IL-2 regulation

A transgene with 8.4-kb of regulatory sequence from the murine IL-2 gene drives consistent expression of a green fluorescent protein (GFP) reporter gene in all cell types that normally express IL-2. However, quantitative analysis of this expression shows that different T cell subsets within the same mouse show divergent abilities to express the transgene as compared with endogenous IL-2 genes. TCR gamma delta cells, as well as alpha beta TCR-NKT cells, exhibit higher in vivo transgene expression levels than TCR alpha beta cells. This deviates from patterns of normal IL-2 expression and from expression of an IL-2-GFP knock-in. Peripheral TCR gamma delta cells accumulate GFP RNA faster than endogenous IL-2 RNA upon stimulation, whereas TCR alpha beta cells express more IL-2 than GFP RNA. In TCR gamma delta cells, IL-2-producing cells are a subset of the GFP-expressing cells, whereas in TCR alpha beta cells, endogenous IL-2 is more likely to be expressed without GFP. These results are seen in multiple independent transgenic lines and thus reflect functional properties of the transgene sequences, rather than copy number or integration site effects. The high ratio of GFP: endogenous IL-2 gene expression in transgenic TCR gamma delta cells may be explained by subset-specific IL-2 gene regulatory elements mapping outside of the 8.4-kb transgene regulatory sequence, as well as accelerated kinetics of endogenous IL-2 RNA degradation in TCR gamma delta cells. The high levels and percentages of transgene expression in thymic and splenic TCR gamma delta and NKT cells, as well as skin TCR gamma delta-dendritic epidermal T cells, indicate that the IL-2-GFP-transgenic mice may provide valuable tracers for detecting developmental and activation events in these lineages.

The adapter molecule Sin regulates T-cell-receptor-mediated signal transduction by modulating signaling substrate availability

Engagement of the T-cell receptor (TCR) results in the activation of a multitude of signaling events that regulate the function of T lymphocytes. These signaling events are in turn modulated by adapter molecules, which control the final functional output through the formation of multiprotein complexes. In this report, we identified the adapter molecule Sin as a new regulator of T-cell activation. We found that the expression of Sin in transgenic T lymphocytes and Jurkat T cells inhibited interleukin-2 expression and T-cell proliferation. This inhibitory effect was specific and was due to defective phospholipase C-gamma (PLC-gamma) phosphorylation and activation. In contrast to other adapters that become phosphorylated upon TCR stimulation, Sin was constitutively phosphorylated in resting cells by the Src kinase Fyn and bound to signaling intermediates, including PLC-gamma. In stimulated cells, Sin was transiently dephosphorylated, which coincided with transient dissociation of Fyn and PLC-gamma. Downregulation of Sin expression using Sin-specific short interfering RNA oligonucleotides inhibited transcriptional activation in response to TCR stimulation. Our results suggest that endogenous Sin influences T-lymphocyte signaling by sequestering signaling substrates and regulating their availability and/or activity in resting cells, while Sin is required for targeting these intermediates to the TCR for fast signal transmission during stimulation.

Overexpression of octamer transcription factors 1 or 2 alone has no effect on HIV-1 transcription in primary human CD4 T cells

We explored the binding of octamer (Oct) transcription factors to the HIV-1 long terminal repeat (LTR) by gel shift assays and showed none of the previously identified four potential Oct binding sites bound Oct-1 or Oct-2. Overexpression of Oct-1 or Oct-2 had no effect on HIV-1 LTR activity in transiently transfected primary human CD4 T cells. Next, primary human CD4 T cells were co-transfected with a green fluorescent protein (GFP)-expression vector and an Oct-1 or Oct-2 expression plasmid. The transfected cells were stimulated for 2 days and then infected with the NL4-3 strain of HIV-1. After 3 days of infection, there were no differences in HIV-1 p24 supernatant levels. Apoptosis of infected or bystander cells overexpressing Oct-1 or Oct-2 compared to control was also unaffected. Our studies demonstrate that Oct-1 and Oct-2 fail to bind to the HIV-1 LTR and have no effect on HIV-1 transcription in primary human CD4 T cells.

Regulation of the human leukemia inhibitory factor gene by ETS transcription factors

OBJECTIVES

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine mainly produced by activated T lymphocytes. We previously demonstrated that human Jurkat T lymphoma cells represent a valid model of LIF gene expression. This study was designed to identify regions critical for LIF promoter activation in Jurkat cells.

METHODS

Luciferase constructs under the control of different portions of the human LIF promoter were transfected into Jurkat cells, and promoter activity was determined by luminometry. Similar experiments were performed with constructs bearing mutations in the putative ETS binding regions in the LIF promoter. RT-PCR, Western blot and gelshift experiments were performed to study expression and DNA binding of ETS factors in lymphoid cells.

RESULTS

With the exception of the shortest construct not including the putative ETS binding sites, all wildtype LIF promoter constructs were strongly inducible by phorbol ester/ionomycin. In contrast, the mutant constructs were significantly less inducible. Cotransfection of the wild-type constructs with ETS expression vectors resulted in significant enhancement of promoter activity. ets-1 and ets-2 mRNA and protein were shown to be expressed in Jurkat cells. Gelshift experiments revealed that proteins present in nuclear extracts from Jurkat cells specifically bind to both artificial ETS consensus sites and ETS binding sites present in the LIF promoter.

CONCLUSIONS

We conclude that binding of ETS transcription factors to the ETS binding sites in the human LIF promoter is critical for its inducibility in response to T cell activators. ETS transcription factors thus play an important functional role within the endocrine-immune network.

Gene transfection and expression in resting and activated murine CD4 T cell subsets

It has been difficult to assess the role of specific genes in activation and differentiation of peripheral T cell subsets such as naive, effector and memory T cells due to the impairments in T cell development and immune pathologies often observed in genetically manipulated mouse models, and the lack of reliable methods for introducing genes into primary mouse T cells. In this study, we demonstrate transient transfection of genes into resting and activated mouse CD4 T cell subsets using "Nucleofection", a modified electroporation technique. Using this approach, cDNA encoding green fluorescent protein (GFP) is efficiently taken up and expressed by purified polyclonal and antigen-specific mouse naive, effector and memory CD4 T cells isolated from BALB/c or TCR-transgenic mice. The resultant transfected resting T cells are fully amenable to TCR-mediated activation. We also demonstrate that expression of endogenous gene can be turned on in resting T cells by transfection of a transcriptional transactivator. Our results demonstrate for the first time, the expression of exogenously transfected genes and the modulation of endogenous gene expression in primary mouse T cell subsets. This technology will enable a variety of mechanistic questions on T cell activation, function and signaling to be addressed in T cells that differ in activation history and functional capacities.

What it takes to become an effector T cell: the process, the cells involved, and the mechanisms

When activated, CD4(+) T cells differentiate into two major sub-populations differing in their profiles of secreted cytokines. Type One, or TH1, cells secrete IL-2, IFNgamma, and TNFbeta and mediate a cellular immune response. Type Two, or TH2, cells secrete IL-4, IL-5, IL-6, IL-10, and IL-13 and potentiate a humoral response. The nature of any specific immune response depends on the interaction of antigen-presenting cells and T cells. The role of antigen-presenting cells is to respond to the nature of the immune challenge and signal differentiation of CD4(+) T cells. A number of factors are involved in the effector phenotype of T cells-nature and affinity of antigen, co-receptors signals, and cytokine environment. T-cell differentiation is a complex process comprising four defined developmental stages: activation of particular cytokine genes, commitment of the cells, silencing of the opposing cytokine genes, and stabilization of the phenotype. In each of these stages, the cells respond to the products of many signaling cascades from many membrane-bound receptors. The stages in development are mediated by different molecular mechanisms, involving control of gene expression and chromatin remodeling. This review centers on the factors, cellular interactions, and molecular mechanisms involved in the maturation of naïve CD4(+) T lymphocytes into fully effector cells.

Interaction with monocytes enhances IL-5 gene transcription in peripheral T cells of asthmatic patients

BACKGROUND

The regulatory mechanisms of IL-5 gene transcription in human peripheral T cells are unclear because the transfection efficiency of plasmid constructs into nontransformed T cells is very low.

METHODS

Concanavalin A (ConA)-stimulated blastocytes derived from peripheral blood lymphocytes of asthmatic subjects were transiently transfected with the human IL-5 gene promoter/enhancer-luciferase gene construct, pIL-5 (-511)Luc, and cultured with THP-1 cells (human monocytoid cells) and anti-CD3 monoclonal antibody (mAb). IL-5 level in the culture medium was determined by an enzyme-linked immunosorbent assay. Transcriptional activity of the IL-5 gene was measured by luciferase reporter analysis.

RESULTS

ConA-blast lymphocytes of asthmatic patients produced a significant amount of IL-5 upon combined stimulation with anti-CD3 mAb and THP-1 cells, but not with anti-CD3 mAb alone. Costimulation with anti-CD28 mAb also enhanced the anti-CD3 mAb- induced IL-5 production. Accordingly, luciferase activity induced by anti-CD3 mAb stimulation in pIL-5(-511)Luc-transfected ConA-blast lymphocytes was increased 1.9- and 3.4-fold by the addition of anti-CD28 mAb and THP-1 cells, respectively. Serial 5' deletion analysis of the reporter gene demonstrated that the cis-regulatory element located at -119 to -80 is critical for anti-CD3 mAb-induced IL-5 gene transcription.

CONCLUSIONS

Our present findings provide a useful model reflecting IL-5 gene transcription in human peripheral T cells in vivo, and clearly demonstrate that an interaction with monocytes enhances IL-5 gene transcription.

Enhancement of cytokine production and AP-1 transcriptional activity in T cells by thalidomide-related immunomodulatory drugs

CC-4047 (Actimid) and CC-5013 (Revimid) belong to a class of thalidomide analogs collectively known as the immunomodulatory drugs (IMiDs), which are currently being assessed in the treatment of patients with multiple myeloma and other cancers. IMiDs potently enhance T cell and natural killer cell responses and inhibit tumor necrosis factor-alpha, interleukin (IL)-1 beta, and IL-12 production from LPS-stimulated peripheral blood mononuclear cells. However, the molecular mechanism of action for these compounds is unknown. Herein, we report on the ability of the IMiDs to up-regulate production of IL-2 from activated human CD4+ and CD8+ peripheral blood T cells, production of IL-2 and IFN-gamma from T helper (Th)1-type cells, and production of IL-5 and IL-10 from Th2-type cells. Elevation of IL-2 production from Jurkat T cells was observed as early as 6 h poststimulation and correlated with an increase in IL-2 promoter activity that was dependent upon the proximal but not the distal AP-1 binding site. The IMiDs enhanced AP-1-driven transcriptional activity 2- to 4-fold after 6 h of T cell stimulation, and their relative potencies for AP-1 activation correlated with their potencies for increased IL-2 production in Jurkat T cells and in CD4+ or CD8+ human peripheral blood T cells. The most potent of these IMiDs, CC-4047, had no effect on nuclear factor of activated T cells transcriptional activity, calcium signaling, or phosphorylation of extracellular signal-regulated kinase 1/2, c-Jun NH2-terminal kinase 1/2, p38 mitogen-activated protein kinase, or c-Jun/Jun D in Jurkat T cells. These data suggest that IMiDs increase T cell cytokine production by potentiating AP-1 transcriptional activity.

The cyclic adenosine 5'-monophosphate response element modulator suppresses IL-2 production in stimulated T cells by a chromatin-dependent mechanism

The production of IL-2 is tightly controlled by several transcription factors that bind to the IL-2 promoter. The cAMP response element modulator (CREM) is known to form complexes with CREB and bind to the -180 site of the IL-2 promoter in anergic and in systemic lupus erythematosus T cells. In this study we show that CREM is transcriptionally induced in T cells following stimulation through CD3 and CD28, binds to the IL-2 promoter in vivo, and suppresses IL-2 production. Transfection of an antisense CREM plasmid into T cells blocked the expression and binding of CREM to the IL-2 promoter and the decrease of IL-2 production, which follows the early increase after T cell stimulation with CD3 and CD28. In addition, as assessed by chromatin immunoprecipitation experiments, antisense CREM prevented the binding of protein 300 and cAMP response element binding protein and promoted the acetylation of histones. Antisense CREM also enhanced the accessibility of the IL-2 promoter to endonucleases and prevented the condensation of chromatin in vivo. Our data suggest that upon T cell activation, CREM gradually replaces phosphorylated CREB at the -180 site of the IL-2 promoter. CREM, in turn, binds protein 300 and cAMP response element binding protein, but CREM is unable to activate its histone acetyltransferase activity, which results in condensation of chromatin and down-regulation of IL-2 production.

Transcriptional regulation of the IL-5 gene in peripheral T cells of asthmatic patients

Mechanisms that underlie the regulation of IL-5 gene expression in human peripheral T cells remain incompletely defined because of the low efficiency of transfection of plasmid constructs into non-transformed T cells. To elucidate the cellular and molecular mechanisms of IL-5 production, concanavalin A (ConA)-stimulated blastocytes derived from peripheral blood lymphocytes of asthmatic patients were employed in this study. Transcriptional activity of the synthetic human IL-5 promoter in ConA-stimulated blastocytes correlated with the production of IL-5. Deletion analysis of the reporter gene showed that the cis-regulatory element located at - 119 to - 80 is critical for inducible IL-5 promoter activity. Electrophoretic mobility shift assay revealed that an oligonucleotide probe corresponding to the element (- 119 to - 90) gave two specific bands. The slower migrating band was absolutely dependent on stimulation and was composed of a co-operative complex of the transcription factors, nuclear factor of activated T cells (NFAT) and activating protein-1 (AP-1). The faster migrating band was also inducible and was identified as AP-1-less NFAT. Mutation of either the NFAT or AP-1 element abrogated the slower migrating band and at the same time abolished transcriptional activity of the human IL-5 promoter/enhancer gene. Cyclosporin A equivalently suppressed DNA-binding activity of the composite NFAT/AP-1 site, promoter activity and protein production of IL-5. In conclusion, these data suggests that the composite NFAT/AP-1 binding element (- 115 to - 100) plays a crucial role in IL-5 synthesis by peripheral T cells of asthmatic patients.

Glucocorticoid-induced leucine zipper inhibits the Raf-extracellular signal-regulated kinase pathway by binding to Raf-1

Glucocorticoid-induced leucine zipper (GILZ) is a leucine zipper protein, whose expression is augmented by dexamethasone (DEX) treatment and downregulated by T-cell receptor (TCR) triggering. Stable expression of GILZ in T cells mimics some of the effects of glucocorticoid hormones (GCH) in GCH-mediated immunosuppressive and anti-inflammatory activity. In fact, GILZ overexpression inhibits TCR-activated NF-kappaB nuclear translocation, interleukin-2 production, FasL upregulation, and the consequent activation-induced apoptosis. We have investigated the molecular mechanism underlying GILZ-mediated regulation of T-cell activation by analyzing the effects of GILZ on the activity of mitogen-activated protein kinase (MAPK) family members, including Raf, MAPK/extracellular signal-regulated kinase (ERK) 1/2 (MEK-1/2), ERK-1/2, and c-Jun NH(2)-terminal protein kinase (JNK). Our results indicate that GILZ inhibited Raf-1 phosphorylation, which resulted in the suppression of both MEK/ERK-1/2 phosphorylation and AP-1-dependent transcription. We demonstrate that GILZ interacts in vitro and in vivo with endogenous Raf-1 and that Raf-1 coimmunoprecipitated with GILZ in murine thymocytes treated with DEX. Mapping of the binding domains and experiments with GILZ mutants showed that GILZ binds the region of Raf interacting with Ras through the NH(2)-terminal region. These data suggest that GILZ contributes, through protein-to-protein interaction with Raf-1 and the consequent inhibition of Raf-MEK-ERK activation, to regulating the MAPK pathway and to providing a further mechanism underlying GCH immunosuppression.

Correlation of transcriptional repression by p21(SNFT) with changes in DNA.NF-AT complex interactions

p21(SNFT) (21-kDa small nuclear factor isolated from T cells) is a novel human protein of the basic leucine zipper family. The overexpression of p21(SNFT) leads to the significant and specific repression of transcription from the interleukin-2 promoter as well as from several essential activator protein 1 (AP-1)-driven composite promoter elements. One example is the distal nuclear factor of activated T cells (NF-AT)/AP-1 element where the AP-1 (Fos/Jun) basic leucine zipper heterodimer interacts with members of the NF-AT family. p21(SNFT) has been shown to replace Fos in dimerization with Jun on a consensus AP-1 binding site (12-O-tetradecanolyphorbol-13-acetate response element (TRE)) and to interact with Jun and NF-AT at the distal NF-AT/AP-1 enhancer element. A detailed biochemical analysis presented here compares interactions involving p21(SNFT) with those involving Fos. The results demonstrate that a p21(SNFT)/Jun dimer binds a TRE similarly to AP-1 and like AP-1 binds cooperatively with NF-AT at the NF-AT/AP-1 composite element. However, Fos interacts significantly more efficiently than p21(SNFT) with Jun and NF-AT, and the replacement of Fos by p21(SNFT) in the trimolecular complex drastically alters protein-DNA contacts. The data suggest that p21(SNFT) may repress transcriptional activity by inducing a unique conformation in the transcription factor complex.

Regulation of leukocyte-endothelial interactions by glucocorticoids

Glucocorticoids (GCs) are steroid molecules endowed with powerful anti-inflammatory and immunosuppressive properties. Traditionally, the anti-inflammatory action of GC has been largely ascribed to the synthesis of lipocortin-1 (now know as annexin I), while the immunosuppressive effect has been linked to the inhibition of several immune functions and the synthesis of important cytokines and chemokines. In addition to these modes of action, there is a mounting body of evidence suggesting that GCs can also inhibit cell adhesion events, which also play a crucial role in the inflammatory/ immune response. The mechanisms by which GCs modulate cell adhesion are complex and multifactorial. It is now clear that GCs can directly regulate cell adhesion molecule (CAM) gene transactivation through the classical glucocorticoid receptor (GR) pathways. These involve interference with activation/ transcription factors such as AP-1 and NF-kappaB, as well as binding of the GC-GR complex to specific DNA sequences, called glucocorticoid response element "GRE," with ensuing CAM gene inhibition. In addition to these "genomic" mechanisms, there is increasing recognition of alternative modalities of action of GC that are independent from modulating gene expression and for this reason defined as "non-genomic." These are characterized by a rapid response (seconds/minutes) and insensitivity to inhibitors of gene transcription and protein synthesis. The non-genomic effects could be due to direct physicochemical interactions with cell membrane constituents including ion channels and membrane associated proteins. This would lead to inhibition of intracellular signaling pathways involved in CAM activation and cytoskeleton reorganization essential for cell adhesion and locomotion.

Stimulation through intercellular adhesion molecule-1 provides a second signal for T cell activation

Regulation of T cell activation requires two signals. First, appropriately presented Ag in the context of MHC interacts with the T cell Ag receptor-CD3 complex. The best-studied second signal is CD28, which resides on the T cell and responds to its counter receptor, B7. A second signal also can be delivered through LFA-1 residing on the T cell, responding to its counter receptor ICAM-1 residing on a different cell. Characterization of a second signal is tied to its ability to costimulate (along with stimulation through the TCR) proliferation, IL-2 secretion, and coactivation of phosphatidylinositol 3-kinase. We examined whether ICAM-1, residing on the T cell surface, could deliver a second signal into that T cell. Costimulation through CD3 plus ICAM-1 caused increased T cell proliferation, increased expression of the activation marker CD69, increased transcription through the IL-2 regulatory region, and increased secretion of selected Th1 but not Th2 cytokines. Costimulation through CD3 plus ICAM-1 caused synergistic activation of phosphatidylinositol 3-kinase. Finally, the combination of anti-CD3 plus anti-ICAM-1 (but not anti-CD3 alone) caused prolonged proliferation of naive T cells in a manner similar to costimulation through LFA-1 or CD28. Thus, we demonstrate for the first time that ICAM-1 resident on a T cell can deliver a costimulatory signal into that T cell.

Direct transfer of p65 into T lymphocytes from systemic lupus erythematosus patients leads to increased levels of interleukin-2 promoter activity

The recent identification of a number of molecular defects in T cells from patients with systemic lupus erythematosus (SLE) has raised expectations for gene replacement therapy as an option in the treatment of these diseases. In this report, we have adapted an electroporation-based technique to transfer successfully DNA to peripheral blood T cells from normal individuals and patients with systemic lupus erythematosus and rheumatoid arthritis. Transfection efficiency, judged by the percentage of live cells expressing green fluorescence after transfection with a pGFP (green fluorescence protein), reached 32 +/- 3% in normal, 13 +/- 3% in SLE, and 17 +/- 13% in RA T cells. The transfection efficiency was slightly higher in CD8+ than in CD4+ cells, and the cells maintained acceptable (75%) viability up to the fourth post-transfection day. SLE T cells have been shown to display low levels of the p65 subunit of the NF-kappaB transcription factor and decreased production of IL-2. Since NF-kappaB contributes to the transcriptional regulation of the IL-2 promoter, the effect of the forced replenishment of p65 on IL-2 transcription was tested. The low level of interleukin-2 promoter activity in SLE T cells increased to normal levels following transfection with cDNA encoding the NF-kappaB p65 subunit. Taken together, these results demonstrate the feasibility of transfection of T cells from SLE patients by electroporation and the reversal of decreased interleukin-2 promoter activity in SLE T cells, and are an early step toward gene therapy as a method of treatment for these individuals.

Reduced expression of nuclear cyclic adenosine 5'-monophosphate response element-binding proteins and IFN-gamma promoter function in disease due to an intracellular pathogen

Mycobacterium tuberculosis-induced IFN-gamma protein and mRNA expression have been shown to be reduced in tuberculosis patients, compared with healthy tuberculin reactors. To determine whether this decrease was associated with reduced activity of the IFN-gamma promoter, we first studied binding of nuclear proteins to the radiolabeled proximal IFN-gamma promoter (-71 to -40 bp), using EMSAs with nuclear extracts of freshly isolated peripheral blood T cells. Nuclear extracts of T cells from most tuberculosis patients showed markedly reduced expression of proteins that bind to the proximal IFN-gamma promoter, compared with findings in nuclear extracts of T cells from healthy tuberculin reactors. These DNA-binding complexes contained CREB proteins, based on competitive EMSAs, supershift assays, and Western blotting with an anti-CREB Ab. Transient transfection of PBLs with a luciferase reporter construct under the control of the IFN-gamma promoter revealed reduced IFN-gamma promoter activity in tuberculosis patients. Transient transfection of Jurkat cells with a dominant-negative CREB repressor plasmid reduced IFN-gamma promoter activity. These data suggest that reduced expression of CREB nuclear proteins in tuberculosis patients results in decreased IFN-gamma promoter activity and reduced IFN-gamma production.

Regulation of IL-13 synthesis in human lymphocytes: implications for asthma therapy

1. IL-13 is an important mediator in inflammatory diseases such as asthma. IL-13 is mainly produced by T cells. However, signalling pathways leading to induction of this cytokine are not well-characterized. We analysed the regulation of IL-13 in human peripheral blood mononuclear cells and CD4(+) T cells. 2. Cyclosporine (CsA) and FK-506 inhibited IL-13 synthesis, when cells were stimulated by TPA/ionomycin. However, stimulation by alpha-CD3/alpha-CD28 led to an enhanced IL-13 synthesis. 3. NF-kappa B inhibitor N-tosyl-L-lysine chloromethylketone (TLCK) inhibited IL-13 synthesis more effectively after TPA/ionomycin stimulation. After alpha-CD3/alpha-CD28 stimulation, only 300 microM TLCK inhibited IL-13 synthesis. Dexamethasone inhibited IL-13 equally effective after alpha-CD3/alpha-CD28 and TPA/ionomycin stimulation. 4. p38 MAPK inhibitor SB203580 inhibited IL-13 synthesis only partially. MEK inhibitor U0126 inhibited TPA/ionomycin induced IL-13 synthesis very effectively, whereas alpha-CD3/alpha-CD28 stimulated IL-13 induction was resistant to this drug. 5. These results were confirmed in purified CD4(+) T cells. In difference to PBMCs alpha-CD3/alpha-CD28 stimulated IL-13 synthesis was effectively inhibited by CsA, FK-506 and U0126. 6. Therefore U0126 was tested in an animal model of allergic asthma. We could demonstrate for the first time that inhibition of the MEK - ERK cascade is a therapeutic option for asthma. Intraperitoneal administration of 10 mg kg(-1) U0126 reduced lung eosinophilia in ovalbumin-challenged Brown Norway rats by 44%. 7. These results demonstrate that different signalling pathways are involved in regulating IL-13 synthesis in primary human T cells. Characterizing highly potent inhibitors of IL-13 synthesis can be exploited to identify new drugs to treat immunological diseases such as asthma.

Phosphorylation and O-linked glycosylation of Elf-1 leads to its translocation to the nucleus and binding to the promoter of the TCR zeta-chain

Elf-1, a member of the E 26-specific transcription factor family with a predicted molecular mass of 68 kDa, is involved in the transcriptional regulation of several hematopoietic cell genes. We demonstrate that Elf-1 exists primarily as a 98-kDa form in the nucleus and as an 80-kDa form in the cytoplasm. Phosphorylation and O-linked glycosylation contribute to the increased posttranslational molecular mass of Elf-1. The 98-kDa Elf-1 is released from the cytoplasm tethering retinoblastoma protein and moves to the nucleus, where it binds to the promoter of the TCR zeta-chain gene. Finally, the cytoplasmic 98-kDa form enters the proteasome pathway and undergoes degradation. In conclusion, different forms of Elf-1 are the products of posttranslational modifications that determine its subcellular localization, activity, and metabolic degradation.

A T cell-specific enhancer of the human CD40 ligand gene

We observed that the human CD40 ligand (CD40L) gene 5'-flanking region conferred weak promoter activity in activated CD4 T cells, suggesting that additional regions are required for optimal CD40L gene transcription. We therefore examined a 3'-flanking segment of the CD40L gene, which contained a putative NF-kappaB/Rel cis-element, for its ability to enhance CD40L promoter function. This segment augmented CD40L promoter activity in an orientation-independent manner in CD4 T-lineage cells but not in human B cell or monocyte cell lines. Mapping of CD4 T-lineage cell nuclei identified a DNase I-hypersensitive site in the flanking region near the NF-kappaB/Rel sequence, suggesting a transcriptional regulatory role. This was further supported by truncation analysis and site-directed mutagenesis, which indicated that the CD40L 3'-flanking NF-kappaB/Rel cis-element was critical for enhancer function. Electrophoretic mobility shift assays showed that the cis-element preferentially bound the p50 form of the NF-kappaB1 gene contained in human T cell nuclear protein extracts. This binding also appeared to occur in vivo in CD4 T cells based on chromatin immunoprecipitation assays using NF-kappaB p50-specific antiserum. Together, these results suggest that the CD40L gene 3'-flanking region acts as a T cell-specific classical transcriptional enhancer by a NF-kappaB p50-dependent mechanism.

Interleukin (IL)-4 indirectly suppresses IL-2 production by human T lymphocytes via peroxisome proliferator-activated receptor gamma activated by macrophage-derived 12/15-lipoxygenase ligands

The respective development of either T helper type 1 (Th1) or Th2 cells is believed to be mediated by the effects of cytokines acting directly on Th precursors (Thp). We have generated evidence for an indirect monocyte-dependent immunoregulatory pathway. Recently, interleukin (IL) 4 has been shown to produce "new" potential peroxisome proliferator-activated receptor gamma (PPARgamma) ligands by inducing macrophage 12/15-lipoxygenase (12/15-LO). We have shown previously that the activated PPARgamma is a profound inhibitor of IL-2 transcription in human T lymphocytes. It is hypothetically possible that IL-4 might indirectly affect IL-2 production by Thp cells via macrophage-derived PPARgamma ligands. Using human monocytes and T lymphocytes from same donors, we have found that monocyte 12/15-LO products mediate the indirect inhibitory effect of IL-4 on anti-CD3- or phytohemagglutinin/phorbol 12-myristate 13-acetate-stimulated IL-2 production by T lymphocytes. We further analyzed which major 12/15-LO metabolites contributed to the above inhibition. 13-Hydroxyoctadecadienoic acid (13-HODE), a 12/15-LO product, markedly blocked IL-2 production by human blood T lymphocytes, but not Jurkat T cells. Moreover, the IL-4-conditioned macrophage medium contained a sufficient amount of 13-HODE and anti-13-HODE antibody indeed neutralized the inhibitory effects of the IL-4-conditional medium on T-cell IL-2 production. Using human T lymphocytes and the PPARgamma-transfected Jurkat T cells, we demonstrated the specific inhibition by 13-HODE of the transcription factors NFAT (nuclear factor of activated T cells) and nuclear factor kappaB, the IL-2 promoter reporter, and IL-2 production. However, 15-hydroxytetraenoic acid had little inhibitory effect. The potency of such inhibitory effects correlates well with the capability of the above metabolic lipids to activate PPARgamma. These data provide a mechanism whereby IL-4 may indirectly affect Thp function via PPARgamma activated by macrophage products of the 12/15-LO pathway.

Differential effects of the antioxidant alpha-lipoic acid on the proliferation of mitogen-stimulated peripheral blood lymphocytes and leukaemic T cells

The effects of the antioxidant alpha-lipoic acid (LA) on the proliferation of mitogen-stimulated human peripheral blood lymphocytes (HPBL) were investigated in comparison to its effects on the proliferation of two leukaemic T cell lines, Jurkat and CCRF-CEM. At low mM concentrations, LA inhibited in a dose-dependent manner DNA synthesis of HPBL stimulated with either phorbol myristate acetate (PMA) in combination with ionomycin (IoM), or phytohaemagglutinin (PHA). At similar concentrations, LA inhibited the proliferation of Jurkat and CCRF-CEM cells. However, LA was preferentially cytotoxic to the leukaemic cell lines. The selective toxicity of LA to Jurkat cells was shown by electron microscopy (EM) to be due to the induction of apoptosis. Furthermore, LA had different effects on the secretion of interleukin-2 (IL-2) and steady-state levels of IL-2 mRNA in mitogen-stimulated HPBL depending on the mitogens used. LA dramatically increased the induction of IL-2 mRNA and IL-2 protein secretion in PMA/IoM-stimulated HPBL, whereas it inhibited these in HPBL stimulated with PHA. The differential effects of LA on normal and leukaemic T lymphocytes may indicate a new route towards development of therapeutic agents.

PIASy, a nuclear matrix-associated SUMO E3 ligase, represses LEF1 activity by sequestration into nuclear bodies

The Wnt-responsive transcription factor LEF1 can activate transcription in association with beta-catenin and repress transcription in association with Groucho. In search of additional regulatory mechanisms of LEF1 function, we identified the protein inhibitor of activated STAT, PIASy, as a novel interaction partner of LEF1. Coexpression of PIASy with LEF1 results in potent repression of LEF1 activity and in covalent modification of LEF1 with SUMO. PIASy markedly stimulates the sumoylation of LEF1 and multiple other proteins in vivo and functions as a SUMO E3 ligase for LEF1 in a reconstituted system in vitro. Moreover, PIASy binds to nuclear matrix-associated DNA sequences and targets LEF1 to nuclear bodies, suggesting that PIASy-mediated subnuclear sequestration accounts for the repression of LEF1 activity.

Molecular mechanisms of IL-2 gene regulation following costimulation through LFA-1

The integrin LFA-1 serves as an accessory molecule in T cell activation. In addition to its well-known role as an adhesion molecule, LFA-1 can contribute to T cell activation and up-regulation of IL-2 gene expression. However, the specific mechanisms by which LFA-1 influences T cell activation have not been elucidated. Therefore, we examined the impact of LFA-1:ICAM-1 interactions on transcriptional and posttranscriptional IL-2 gene regulation, using a costimulation-negative cell line transfected with MHC class II alone, or in combination with ICAM-1 or B7-1. IL-2 transcription was assessed utilizing transgenic mice expressing an IL-2 promoter luciferase reporter construct crossed to DO11.10 TCR-transgenic mice, and IL-2 mRNA stability was evaluated by real-time RT-PCR. Comparison of naive and previously activated T cells demonstrates a dramatic increase in IL-2-luciferase transcription in activated T cells that can, in part, be attributed to downstream signaling events. Costimulation through LFA-1 enhances transcription of the transgenic reporter construct across a wide Ag dose range, but does not affect IL-2 mRNA stability. In contrast, CD28 costimulation is clearly mediated through up-regulation of IL-2 transcription and through enhancement of mRNA stability. These results indicate that the primary pathway whereby engagement of LFA-1 through its ligand ICAM-1 up-regulates IL-2 gene expression is through enhanced IL-2 transcription, in the absence of any effect on IL-2 mRNA stabilization.

Endothelial cell costimulation of T cell activation through CD58-CD2 interactions involves lipid raft aggregation

Human endothelial cells (EC) costimulate CD4(+) memory T cell activation through CD58-CD2 interactions. In this study we tested the hypothesis that EC activate distinct costimulatory pathways in T cells that target specific transcription factors. AP-1, composed of fos and jun proteins, is a critical effector of TCR signaling and binds several sites in the IL-2 promoter. EC augment c-fos promoter activity in T cells; however, deletion analysis reveals no transcription factor binding sites in the promoter uniquely responsive to EC costimulation. Overexpression of AP-1 proteins in T cells augments the activity of an AP-1-luciferase reporter gene equally in the absence or the presence of EC costimulation. Interestingly, EC stimulate a similar 2- to 3-fold up-regulation of AP-1, NF-AT, NF-kappaB, and NF-IL-2-luciferase reporters. CD2 mAbs completely block EC effects on all of these pathways, as well as costimulation of IL-2 secretion. We conclude that EC costimulation through CD2 does not trigger a single distinct costimulatory pathway in T cells, but rather, it amplifies several pathways downstream of the TCR. Indeed, we find that early EC costimulation acts "upstream" of the TCR by promoting lipid raft aggregation, thus amplifying TCR signaling. Soluble CD2 mAbs block EC-induced raft aggregation, whereas cross-linking CD2 promotes aggregation. These data are consistent with the critical role of CD2 in organizing the T cell-APC contact zone.

The analysis of costimulatory receptor signaling cascades in normal T lymphocytes using in vitro gene transfer and reporter gene analysis

Ligation of the antigen receptor and costimulatory receptors on the surface of T lymphocytes initiates intracellular signals that regulate cell-cycle progression and cell differentiation. To effectively manipulate the activation of T cells for immunotherapeutic applications, it will be important to understand how these signaling pathways are integrated to control specific gene transcription events. Here we describe a novel transient transfection procedure that efficiently introduces DNA into non-dividing normal human and murine T lymphocytes while maintaining high cell viability. Using this technique, reporter genes can be introduced to characterize intracellular signaling pathways that regulate specific gene transcription events in normal T-lymphocyte populations. We show that the CD28 receptor can be differentially coupled to downstream signaling pathways in different T-lymphocyte populations. In addition, we demonstrate that a gene encoding a tagged constitutively active mitogen-activated kinase kinase-1 protein can be transfected and rapidly expressed to regulate the expression of Bcl-2 in normal thymocytes.

17-beta-estradiol suppresses IL-2 and IL-2 receptor

Interleukin-2 (IL-2) plays an important role in adaptive immune responses. These responses differ between females and males and may be due to the sex steroid estrogen. In this investigation we show that estrogen suppresses IL-2 production from activated peripheral blood T cells and CD4+ T cell lines at the transcriptional level. Suppression of IL-2 occurred at short term, high 17-beta-estradiol concentrations as well as longer term lower 17-beta-estradiol concentrations. In CD4+ Jurkat T cells, suppression of IL-2 was associated with decreased nuclear binding of two important IL-2 promoter transcription factors: NFkappaB and AP-1. The decreased nuclear binding of NFkappaB occurred in the setting of estrogen-induced increases in IkappaBalpha protein levels, an important inhibitor of NFkappaB nuclear translocation. 17-beta-Estradiol was also shown to inhibit IL-2 receptor (IL-2R) expression in activated peripheral blood T cells. Estrogen-induced suppression of IL-2 and its receptor may have many ramifications for our understanding of immune and autoimmune sexual dichotomies, immune responses during pregnancy, and potential therapeutic intervention with hormone agonists and antagonists.