The immediate-early gene product Egr-1 regulates the human interleukin-2 receptor beta-chain promoter through noncanonical Egr and Sp1 binding sites

Early Growth Response-1: Friend or Foe in the Heart?

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Early growth response-1 (Egr-1) plays a critical regulatory role in a range of experimental models of cardiovascular diseases. Egr-1 is an immediate-early gene and is upregulated by various stimuli including shear stress, oxygen deprivation, oxidative stress and nutrient deprivation. However, recent research suggests a new, underexplored cardioprotective side of Egr-1. The main purpose of this review is to explore and summarise the dual nature of Egr-1 in cardiovascular pathobiology.

Immunomodulatory Effects of IL-2 and IL-15; Implications for Cancer Immunotherapy

The type I cytokine family members interleukin-2 (IL-2) and IL-15 play important roles in the homeostasis of innate and adaptive immunity. Although IL-2 and IL-15 receptor complexes activate similar signal transduction cascades, triggering of these receptors results in different functional activities in lymphocytes. While IL-2 expands regulatory T cells and CD4+ helper T cells, IL-15 supports the development of central memory T cells and NK cells. Recent data have provided evidence that IL-2 and IL-15 differ in their ability to activate T and NK cells to resist various forms of immune suppression. The diverse roles of these two cytokines have on immune cells lead to critical therapeutic implications for cancer treatment. In this review, we discuss the distinct roles of IL-2 and IL-15 in activating various functions in T and NK cells with a particular focus on the signals that participate in the resistance of tumor-derived immune suppressive factors. Furthermore, we summarize current clinical applications of IL-2 and IL-15 in metastatic malignancies, either as monotherapy or in combination with other agents, and highlight the future trends for research on these cytokine-based immunotherapies.

Molecular mechanisms of T-cell anergy

Anergy is a long-term stable state of T-lymphocyte unresponsiveness to antigenic stimulation associated with the blockade of IL-2 production and proliferation. Anergy is a pathway of peripheral tolerance formation. In this review, mechanisms underlying T-cell tolerization are considered in a classical in vitro model of clonal anergy, and these mechanisms are compared with different pathways of anergy induction in vivo. Special attention is given to regulatory T-lymphocytes because, on one hand, anergy is a specific feature of these cells, and on the other hand anergy is also a mechanism of their action on target cells - effector T-lymphocytes. The role of this phenomenon in the differentiation of regulatory T-cells and also in the development of activation-induced apoptosis in effector T-lymphocytes is discussed.

Altered calcium regulation in isolated cardiomyocytes from Egr-1 knock-out mice

Early growth response-1 one gene (Egr-1), one of the immediate early response genes, plays an important role in the adaptive response of the myocardium to hypertrophic stimuli. We aimed to investigate the effects of Egr-1 deletion on cardiac function. Egr-1 knock-out (Egr-1(-/-)) homozygous mice were employed to evaluate the electrophysiological and molecular properties of left ventricular cardiomyocytes (VCM) by using patch-clamp technique, intracellular calcium measurements, real-time PCR, and Western blot. Action potential was prolonged and diastolic potential was positive-shifted in VCMs isolated from Egr-1(-/-) mice, in comparison with those from their wild-type (WT) littermates. The calcium content of the sarcoplasmic reticulum was reduced and the decay time for steady-state calcium transient slowed down. Serca2, Ryr, L-type Ca(2+)-channel, and PLB mRNA expression were reduced in Egr-1(-/-) mice compared with the controls. Moreover, Serca2 protein was reduced, while the amount of Ncx1 protein was increased in Egr-1(-/-) hearts compared with those of the WT littermates. Furthermore, genes involved in heart development (GATA-4, TGF-β) and in Egr-1 regulation (Nab1, Nab2) were down regulated in Egr-1(-/-) mice. These results suggest that Egr-1 plays a pivotal role in regulating excitation-contraction coupling in cardiac myocytes.

Dietary obesity-induced Egr-1 in adipocytes facilitates energy storage via suppression of FOXC2

The molecular mechanism to regulate energy balance is not completely understood. Here we observed that Egr-1 expression in white adipose tissue (WAT) was highly correlated with dietary-induced obesity and insulin resistance both in mice and humans. Egr-1 null mice were protected from diet-induced obesity and obesity-associated pathologies such as fatty liver, insulin resistance, hyperlipidemia and hyperinsulinemia. This phenotype can be largely explained by the increase of energy expenditure in Egr-1 null mice. Characterization of these mice revealed that the expression of FOXC2 and its target genes were significantly elevated in white adipose tissues, leading to WAT energy expenditure instead of energy storage. Altogether, these studies suggest an important role for Egr-1, which, by repressing FOXC2 expression, promotes energy storage in WAT and favored the development of obesity under high energy intake.

Interleukin-2 at the crossroads of effector responses, tolerance, and immunotherapy

Interleukin-2 (IL-2) is a pleiotropic cytokine produced after antigen activation that plays pivotal roles in the immune response. Discovered as a T cell growth factor, IL-2 additionally promotes CD8(+) T cell and natural killer cell cytolytic activity and modulates T cell differentiation programs in response to antigen, promoting naïve CD4(+) T cell differentiation into T helper 1 (Th1) and T helper 2 (Th2) cells while inhibiting T helper 17 (Th17) and T follicular helper (Tfh) cell differentiation. Moreover, IL-2 is essential for the development and maintenance of T regulatory cells and for activation-induced cell death, thereby mediating tolerance and limiting inappropriate immune reactions. In this review, we focus on the molecular mechanisms and complex cellular actions of IL-2, its cooperative and opposing effects with other cytokines, and how both promoting and blocking the actions of IL-2 are being utilized in clinical medicine.

Egr-1 induces DARPP-32 expression in striatal medium spiny neurons via a conserved intragenic element

DARPP-32 (dopamine and adenosine 3', 5'-cyclic monophosphate cAMP-regulated phosphoprotein, 32 kDa) is a striatal-enriched protein that mediates signaling by dopamine and other first messengers in the medium spiny neurons. The transcriptional mechanisms that regulate striatal DARPP-32 expression remain enigmatic and are a subject of much interest in the efforts to induce a striatal phenotype in stem cells. We report the identification and characterization of a conserved region, also known as H10, in intron IV of the gene that codes for DARPP-32 (Ppp1r1b). This DNA sequence forms multiunit complexes with nuclear proteins from adult and embryonic striata of mice and rats. Purification of proteins from these complexes identified early growth response-1 (Egr-1). The interaction between Egr-1 and H10 was confirmed in vitro and in vivo by super-shift and chromatin immunoprecipitation assays, respectively. Importantly, brain-derived neurotrophic factor (BDNF), a known inducer of DARPP-32 and Egr-1 expression, enhanced Egr-1 binding to H10 in vitro. Moreover, overexpression of Egr-1 in primary striatal neurons induced the expression of DARPP-32, whereas a dominant-negative Egr-1 blocked DARPP-32 induction by BDNF. Together, this study identifies Egr-1 as a transcriptional activator of the Ppp1r1b gene and provides insight into the molecular mechanisms that regulate medium spiny neuron maturation.

GGPPS, a new EGR-1 target gene, reactivates ERK 1/2 signaling through increasing Ras prenylation

Cigarette smoke activates the extracellular signal-regulated kinase (ERK) 1/2 mitogen activated-protein kinase pathway, which, in turn, is responsible for early growth response gene-1 (EGR-1) activation. Here we provide evidence that EGR-1 activation can also reactivate ERK 1/2 mitogen activated-protein kinase through a positive feedback loop through its target gene (geranylgeranyl diphosphate synthase) GGPPS. For the first time, the GGPPS gene is identified as a target of EGR-1, as EGR-1 can directly bind to the predicted consensus-binding site in the GGPPS promoter and regulate its transcription. Long-term observations show that there are two ERK 1/2 phosphorylation peaks after cigarette smoke extract stimulation in human lung epithelial Beas-2B cells. The first peak (at 10 minutes) is responsible for EGR-1 accumulation, and the second (at 4 hours) is diminished after the disruption of EGR-1 transcriptional activity. EGR-1 overexpression enhances Ras prenylation and membrane association in a GGPPS-dependent manner, and it augments ERK 1/2 activation. Likewise, a great reduction of the second peak of ERK 1/2 phosphorylation is observed during long-term cigarette smoke extract stimulation in cells where GGPPS is disrupted. Thus, we have uncovered an intricate positive feedback loop in which ERK 1/2-activated EGR-1 promotes ERK 1/2 reactivation through promoting GGPPS transcription, which might affect cigarette smoke-related lung pathological processes.

The early growth response gene Egr2 (Alias Krox20) is a novel transcriptional target of transforming growth factor-β that is up-regulated in systemic sclerosis and mediates profibrotic responses

Although the early growth response-2 (Egr-2, alias Krox20) protein shows structural and functional similarities to Egr-1, these two related early-immediate transcription factors are nonredundant. Egr-2 plays essential roles in peripheral nerve myelination, adipogenesis, and immune tolerance; however, its regulation and role in tissue repair and fibrosis remain poorly understood. We show herein that transforming growth factor (TGF)-β induced a Smad3-dependent sustained stimulation of Egr2 gene expression in normal fibroblasts. Overexpression of Egr-2 was sufficient to stimulate collagen gene expression and myofibroblast differentiation, whereas these profibrotic TGF-β responses were attenuated in Egr-2-depleted fibroblasts. Genomewide transcriptional profiling revealed that multiple genes associated with tissue remodeling and wound healing were up-regulated by Egr-2, but the Egr-2-regulated gene expression profile overlapped only partially with the Egr-1-regulated gene profile. Levels of Egr-2 were elevated in lesional tissue from mice with bleomycin-induced scleroderma. Moreover, elevated Egr-2 was noted in biopsy specimens of skin and lung from patients with systemic sclerosis. These results provide the first evidence that Egr-2 is a functionally distinct transcription factor that is both necessary and sufficient for TGF-β-induced profibrotic responses and is aberrantly expressed in lesional tissue in systemic sclerosis and in a murine model of scleroderma. Together, these findings suggest that Egr-2 plays an important nonredundant role in the pathogenesis of fibrosis. Targeting Egr-2 might represent a novel therapeutic strategy to control fibrosis.

Cigarette smoke-induced pulmonary inflammatory responses are mediated by EGR-1/GGPPS/MAPK signaling

Early growth response 1 (EGR-1) contributes to the development of chronic obstructive pulmonary disease in the lungs of smokers by mediating pulmonary inflammatory responses, but the direct downstream genes of EGR-1 that regulate this process remain unknown. We show that a new EGR-1 target gene, geranylgeranyl diphosphate synthase (GGPPS), which controls protein prenylation, can regulate the proinflammatory function of EGR-1 by activating MAPK signaling. When C57BL/6 mice were exposed to cigarette smoke, EGR-1 and GGPPS levels increased in their lungs, and the inflammatory responses were augmented, whereas these effects could be reversed by the down-regulation of EGR-1 transcription activity. The accumulation of EGR-1 and GGPPS was induced by MAPK/ERK pathway activation when Beas-2B human bronchial epithelial cells were exposed to cigarette smoke extract (CSE). Further examination showed that EGR-1 in turn regulated Erk1/2 activity because inhibition of EGR-1 transcription activity decreased CSE-induced Erk1/2 phosphorylation. Furthermore, EGR-1-promoted Erk1/2 activation was dependent on GGPPS transcription. Knockdown of GGPPS expression with small-interfering RNA abolished the EGR-1-activated Erk1/2 activity. Both EGR-1 transcription inhibition and GGPPS expression knockdown decreased the inflammatory response induced by CSE in Beas-2B cells. Our results reveal a new EGR-1/GGPPS/MAPK signaling pathway that controls cigarette smoke-induced pulmonary inflammation, and this may shed light on our understanding of the mechanism of cigarette smoke-related pulmonary diseases such as chronic obstructive pulmonary disease.

Inferring time-varying network topologies from gene expression data

Most current methods for gene regulatory network identification lead to the inference of steady-state networks, that is, networks prevalent over all times, a hypothesis which has been challenged. There has been a need to infer and represent networks in a dynamic, that is, time-varying fashion, in order to account for different cellular states affecting the interactions amongst genes. In this work, we present an approach, regime-SSM, to understand gene regulatory networks within such a dynamic setting. The approach uses a clustering method based on these underlying dynamics, followed by system identification using a state-space model for each learnt cluster--to infer a network adjacency matrix. We finally indicate our results on the mouse embryonic kidney dataset as well as the T-cell activation-based expression dataset and demonstrate conformity with reported experimental evidence.

EGR-1 activation by EGF inhibits MMP-9 expression and lymphoma growth

Progression of hematologic malignancies is strongly dependent on bidirectional interactions between tumor cells and stromal cells. Expression of members of the matrix metalloproteinase (MMP) family by stromal cells is a central event during these interactions. However, although several studies have focused on the mechanisms responsible for induction of MMP in stromal cells, the signals that negatively regulate their secretion of in these cells remain largely unknown. Here, we provide evidence that MMP-9 production by stromal cells is suppressed through activation of early growth response protein 1 (EGR-1), thereby inhibiting the growth of thymic lymphoma. We found that EGR-1 expression is induced in stromal cells after contact with lymphoma cells via epidermal growth factor (EGF). Moreover, development of thymic lymphoma was inhibited when induced by lymphoma cells overexpressing EGF compared with control lymphoma cells. Using transgenic mice containing MMP-9 promoter-driven luciferase transgene in its genome, we further demonstrated that EGF/EGR-1 repressed transcriptional activation of the MMP-9 gene by stromal cells. De novo expression of EGR-1 alone by gene transfer or exposure to recombinant human EGF also inhibited MMP-9 expression. Taken together, these results indicate that EGR-1 could be a source of novel targets for therapeutic intervention in lymphoid tumors in which MMP-9 plays a critical role.

Snail associates with EGR-1 and SP-1 to upregulate transcriptional activation of p15INK4b

Snail is a multifunctional transcriptional factor that has been described as a repressor in many different contexts. It is also proposed as an activator in a few cases relevant to tumor progression and cell-cycle arrest. This study investigated the detailed mechanisms by which Snail upregulates gene expression of the CDK inhibitor p15(INK4b) in HepG2 induced by the tumor promoter tetradecanoyl phorbol acetate (TPA). Using deletion mapping, the TPA-responsive element on the p15(INK4b) promoter was located between 77 and 228 bp upstream of the transcriptional initiation site, within which the putative binding regions of early growth response gene 1 (EGR-1) and stimulatory protein 1 (SP-1) were found. Gene expression of EGR-1, Snail and SP-1 can be induced by TPA within 0.5-6 h. In addition, basal levels of SP-1, but not of the other two transcriptional factors, were observed. Blockade of TPA-induced gene expression of Snail, EGR-1 or SP-1 suppressed activation of the p15-pro228 reporter plasmid harboring the TPA-responsive element. More detailed deletion mapping and site-directed mutagenesis further concluded that the overlapping EGR-1/SP-1-binding site was required for TPA-induced p15-pro228 activation. In an EMSA, a DNA-protein complex was elevated by TPA, which can be blocked by antibodies against EGR-1, SP-1 or Snail at 6 h. Immunoprecipitation/western blotting demonstrated that TPA could trigger the association of EGR-1 with Snail or SP-1. Furthermore, a double chromatin immunoprecipitation assay verified that EGR-1 could form a complex with Snail or SP-1 on the TPA-responsive element after treatment with TPA for 2-6 h. Finally, we demonstrated a novel Snail-target region which could be bound by Snail and was also required for TPA-induced p15-pro228 activation. In conclusion, Snail associates with EGR-1 and SP-1 to mediate TPA-induced transcriptional upregulation of p15(INK4b) in HepG2.

Butyrate in vitro immune-modulatory effects might be mediated through a proliferation-related induction of apoptosis

Survival and proliferation signals are two processes closely interrelated and finely controlled in most cell types, whose deregulation may lead to carcinogenesis. In the last decade, different studies have suggested that both cellular functions are also intimately associated with other cellular activities such as differentiation and cellular activation, especially in immune cells. The aim of this study was to evaluate the effects of the short-chain fatty acid (SCFA) butyrate on the proliferation and activation state of different cell types involved in inflammatory bowel disease. We focused on intestinal epithelial cells, macrophages and T-lymphocytes, using both primary non-transformed cultures and established cell lines. The results showed that low concentrations of butyrate inhibited the proliferation of all the immune cell types tested in this work, whereas it only induced apoptosis in activated T-lymphocytes, non-differentiated epithelial cells and macrophage cell lines, but not in differentiated epithelial cells or primary macrophages. Butyrate apoptosis induction was mediated by caspase-3/7 activation. This SCFA was only able to modify cell activation, measured as expression of inflammatory cytokines, in those cell types in which apoptosis was induced. In conclusion, our results suggest a cell type-specificity of the immune-modulatory effects of butyrate based on the proliferation/activation characteristic physiology of these processes in different cells types.

Early growth response transcription factors and the modulation of immune response: implications towards autoimmunity

Early Growth Response (EGR) zinc finger transcription factors are induced under diverse mitogenic signals on different cell types such as lymphocytes. Their genetic expression does not require de novo protein synthesis, which suggests its role as immediate response mediators between cell surface receptor signaling and gene expression regulation. EGR factors are involved in modulating the immune response, by means of the induction of differentiation of lymphocyte precursors, activation of T and B cells, as well as their involvement in central and peripheral tolerance. The maturation state, particularly for B cells, and signaling through the T or B cell receptors seems to be quite relevant for the induction of the expression of these transcription factors. EGR-1 functions as a positive regulatory factor for B and T cells mediated by transcriptional regulation of key cytokines and costimulatory molecules, and its interaction with NFAT. On the opposite, EGR-2 and 3 act as negative regulators involved in anergy induction and apoptosis. EGR-2 and 3 deficiency has been related to the development of lupus like disease in murine models. The deficiency of these transcription factors has been associated to deficient Cbl-b expression, a resistant to anergy phenotype, and expansion of effector and activated T cells.

Early growth response protein-1 (Egr-1) is preferentially expressed in T helper type 2 (Th2) cells and is involved in acute transcription of the Th2 cytokine interleukin-4

The early growth response gene product Egr-1 has been shown to have great impact on growth, proliferation, and differentiation in a wide variety of cells, including T cells. In this study, we show that Egr-1 is rapidly induced upon T cell stimulation and is expressed predominantly in T helper type 2 (Th2) compared with type 1 (Th1) cells. We further investigate the role of Egr-1 in regulation of the Th2 cytokine interleukin-4 (IL-4) expression. IL-4 is a key Th2 cytokine that regulates humoral immunity and also causes allergic inflammation. Regulation of IL-4 gene transcription in Th2 cells has been shown to be controlled by multiple T cell receptor (TCR)-induced transcription factors. However, only a few transcription factors were shown to be selectively induced in differentiated Th2 cells in response to TCR stimulation. Chromatin immunoprecipitation analysis demonstrates that Egr-1 binds to the IL-4 promoter in vivo upon T cell stimulation. Ectopic expression of Egr-1 enhances endogenous IL-4 mRNA expression and elevates IL-4 promoter activity. We also show that Egr-1, nuclear factor of activated T cell, and NF-kappaB cooperatively bind to an NFAT/NF-kappaB-overlapping IL-4 enhancer element and activate the IL-4 promoter synergistically. Furthermore, we show that antisense oligonucleotides that knock down Egr-1 expression attenuate IL-4 transcription. Our study provides the first evidence that Egr-1 protein is differentially expressed in Th1 and Th2 cells and is involved in the acute phase of the IL-4 transcription in response to TCR stimulation.

T-bet expression is regulated by EGR1-mediated signaling in activated T cells

T-bet is a Th1-specific transcription factor that is directly involved in three important pathways for Th1 cell differentiation, namely TCR signaling, and the IFN-gamma-STAT1 and IL-12-STAT4 pathways. A recent study also showed that T-bet plays a vital role in innate immunity. However, the molecular mechanism responsible for transcriptional activation of T-bet during T cell development is not yet known. Here, we characterize the essential human T-bet promoter elements and show that binding of EGR1 to this promoter induces T-bet transcription. Notably, overexpression of EGR1 transactivates and, synergistically in concert with TCR signaling, induces T-bet expression in activated T cells. In contrast, depletion of EGR1 significantly decreases T-bet induction. Finally, we report a positive correlation between EGR1 and T-bet expression during T helper cell differentiation. Collectively, these findings provide molecular insight into T-bet transcription and suggest that EGR1 is an upstream regulator of T-bet induction.

Posttranscriptional regulation of interleukin-10 expression by hsa-miR-106a

IL-10 is a key regulator of the immune system that critically determines health and disease. Its expression is finely tuned both at the transcriptional and posttranscriptional levels. Although the importance of posttranscriptional regulation of IL-10 has been previously shown, understanding the underlying mechanisms is still in its infancy. In this study, using a combination of bioinformatics and molecular approaches, we report that microRNA (hsa-miR-106a) regulates IL-10 expression. The hsa-miR-106a binding site in the 3' UTR of IL10 has been identified by site-directed mutagenesis studies. Also, the involvement of transcription factors, Sp1 and Egr1, in the regulation of hsa-miR-106a expression and concomitant decrease in the IL-10 expression, has also been demonstrated. In summary, our results showed that IL-10 expression may be regulated by miR-106a, which is in turn transcriptionally regulated by Egr1 and Sp1.

Late expression of granulysin by microbicidal CD4+ T cells requires PI3K- and STAT5-dependent expression of IL-2Rbeta that is defective in HIV-infected patients

Granulysin is a cytolytic effector molecule used by lymphocytes to kill tumor and microbial cells. Regulation of granulysin production is complex. A significant delay (5 days) following stimulation of CD4(+) T cells with IL-2 occurs before granulysin is produced. Unfortunately, the mechanisms responsible for this delay are unknown. We have recently demonstrated that granulysin-mediated killing of Cryptococcus neoformans by CD4(+) T cells is defective during HIV infection. This is because CD4(+) T cells from HIV-infected patients fail to produce granulysin in response to IL-2 activation. The present studies examined the mechanism of delayed production of granulysin and the mechanism of the defect in HIV patients. We demonstrate that IL-2 initially requires both STAT5 and PI3K activation to increase expression of IL-2Rbeta, produce granulysin, and kill C. neoformans. The increased expression of IL-2Rbeta precedes granulysin, and preventing the increased expression of IL-2Rbeta using small interfering RNA knockdown abrogates granulysin expression. Moreover, following the increased expression of IL-2Rbeta, blocking subsequent signaling by IL-2 using IL-2Rbeta-specific blocking Abs abrogates expression of granulysin. Finally, CD4(+) T cells from HIV-infected patients, who are defective in both STAT5 and PI3K signaling, fail to express IL-2Rbeta and fail to produce granulysin. These results suggest that IL-2 signals via PI3K and STAT5 to increase expression of IL-2Rbeta, which in turn is required for production of granulysin. These results provide a mechanism to explain the "late" production of granulysin during normal T cell responses, as well as for defective granulysin production by CD4(+) T cells in HIV-infected patients.

Opposing regulation of T cell function by Egr-1/NAB2 and Egr-2/Egr-3

TCR-induced NF-AT activation leads to the up-regulation of multiple genes involved in T cell anergy. Since NF-AT is also involved in T cell activation, we have endeavored to dissect TCR-induced activating and inhibitory genetic programs. This approach revealed roles for the early growth response (Egr) family of transcription factors and the Egr coactivator/corepressor NGFI-A-binding protein (NAB)2 in regulating T cell function. TCR-induced Egr-1 and NAB2 enhance T cell function, while Egr-2 and Egr-3 inhibit T cell function. In this report, we demonstrate that Egr-2 and Egr-3 are induced by NF-AT in the absence of AP-1, while Egr-1 and NAB2 both require AP-1-mediated transcription. Our data suggest that Egr-3 is upstream of Egr-2, and that mechanistically Egr-2 and Egr-3 suppress Egr-1 and NAB2 expression. Functionally, T cells from Egr-2 and Egr-3 null mice are hyperresponsive while T cells from Egr-3 transgenic, overexpressing mice are hyporesponsive. Furthermore, an in vivo model of autoimmune pneumonitis reveals that T cells from Egr-3 null mice hasten death while Egr-3-overexpressing T cells cause less disease. Overall, our data suggest that just as the Egr/NAB network of genes control cell fate in other systems, TCR-induced Egr-1, 2, 3 and NAB2 control the fate of antigen recognition in T cells.

Angiotensin II induction of PDGF-C expression is mediated by AT1 receptor-dependent Egr-1 transactivation

Platelet-derived growth factors are a family of mitogens and chemoattractants comprising of four ligand genes (A-, B-, C-, D-chains) implicated in many physiologic and pathophysiologic processes, including atherosclerosis, fibrosis and tumorigenesis. Our understanding of the molecular mechanisms, which regulate PDGF-C transcription remains incomplete. Transient transfection analysis, conventional and quantitative real-time PCR revealed the induction of PDGF-C transcription and mRNA expression in smooth muscle cells (SMCs) exposed to the peptide hormone angiotensin (ATII), which induces Egr-1. Occupancy of a G + C-rich element in the proximal region of the PDGF-C promoter was unaffected by ATII. Instead we discovered, using both nuclear extracts and recombinant proteins with EMSA and ChIP analyses, the existence of a second Egr-1-binding element located 500 bp upstream. ATII induction of PDGF-C transcription is mediated by the angiotensin type 1 receptor (AT1R) and Egr-1 activation through this upstream element. DNAzyme ED5 targeting Egr-1 blocked ATII-inducible PDGF-C expression. Moreover, increased PDGF-C expression after exposure to ATII depends upon the differentiation state of the SMCs. This study demonstrates the existence of this novel ATII-AT1R-Egr-1-PDGF-C axis in SMCs of neonatal origin, but not in adult SMCs, where ATII induces Egr-1 but not PDGF-C.

Critical role for Rsk2 in T-lymphocyte activation

During T-cell activation, a number of cytokine-activated signaling cascades, including the Jak-STAT, phosphoinositol 3-kinase (PI 3-kinase), and mitogen-activated protein kinase (MAPK) pathways, play important roles in modulating the expression of target genes and mediating a cellular response. We now report that interleukin 2 (IL-2) and IL-15, but not IL-7, rapidly activate the p90 ribosomal S6 kinases, Rsk1 and Rsk2, in human T lymphocytes. Surprisingly, mouse spleen T cells transduced with either the wild-type or a dominant-negative (DN) Rsk2-expressing retrovirus could not be recovered, in contrast to the normal survival of T cells transduced with retroviruses expressing wild-type or DN mutants of Rsk1 or Rsk3. Examination of Rsk2 knockout (KO) mice revealed normal T-cell development, but these T cells had delayed cell-cycle progression and lower production of IL-2 in response to anti-CD3 and anti-CD28 stimulation in vitro. Moreover, Rsk2 KO mice had defective homeostatic T-cell expansion following sublethal irradiation in vivo, which is known to involve T-cell receptor (TCR), IL-2, and/or IL-15 signals, each of which we demonstrate can rapidly and potently activate Rsk2 in mouse T cells. These results indicate an essential nonredundant role of Rsk2 in T-cell activation.

Cascade of transcriptional induction and repression during IL-2 deprivation-induced apoptosis

Apoptosis of mature T lymphocytes is an essential process for maintaining immune system homeostasis. However, the details of the molecular signaling pathways leading to T cell apoptosis are poorly understood. We used cDNA microarrays containing 15,630 murine genes to study the gene expression profile in T lymphocytes at different time points of IL-2 withdrawal. Comparison of the gene expression profiles revealed that 2% of the genes were affected by cytokine starvation. Interestingly, the apoptotic program rather seems to activate gene expression in the early phase of cell death. On the contrary, transcription was strongly repressed in later stages of apoptosis. Self-organizing map clustering of the 270 differentially expressed transcripts revealed specific temporal expression patterns supporting the idea that IL-2 deprivation triggers a tightly regulated transcriptional program to induce cell death. To validate microarray results, changes in gene expression following IL-2 deprivation were confirmed for selected genes by Northern blot. In addition, the signaling pathways created can explain the molecular events leading to T cell apoptosis, even if the T cell line used in this study might not reflect individual T cell subpopulations expressing different level of IL-2 receptor or IL-2 dependence. Taken together, these results provide novel insights into the temporal regulation of gene expression during T lymphocyte death.

15-deoxy-Delta12,14-prostaglandin J2 negatively regulates rankl gene expression in activated T lymphocytes: role of NF-kappaB and early growth response transcription factors

Receptor activator of NF-kappaB ligand (RANKL) and its receptor RANK are cell surface proteins abundantly expressed in bone and lymphoid tissues, whose interaction triggers different signaling pathways leading to activation and differentiation of osteoclasts, pivotal actors of the normal bone remodeling cycle. Moreover, RANKL may act as an immunomodulator, representing an important dendritic cell survival factor produced by activated T cells. A large body of research has shown that not only does the RANKL/RANK system regulate the physiology of bone development but also plays an important pathological role in bone destruction mediated by inflammatory disorders or bone metastatic tumors. 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a cyclopentenone-type PG endowed with anti-inflammatory properties and produced by different cells, including those of the immune system. Although 15d-PGJ(2) has been studied as a natural ligand of the peroxisome proliferator-activated receptor-gamma nuclear receptor, relevant peroxisome proliferator-activated receptor-gamma-independent actions mediated by this prostanoid have been described. In this study, we describe the effect of 15d-PGJ(2) on the expression of the rankl gene in T lymphocytes. We show that 15d-PGJ(2) inhibits rankl mRNA expression, protein, and rankl promoter activity by mechanisms mediated by its chemically reactive cyclopentenone moiety. Our data also indicate that 15d-PGJ(2) represses rankl activation by interfering with the expression and/or activity of the transcription factors NF-kappaB, early growth response-2, and early growth response-3, whose altered balancing and transactivation may contribute for the repression of this gene. These results place rankl as a novel molecular target for the different immunoregulatory activities mediated by 15d-PGJ(2). The physiological and pharmacological implications of these observations are discussed.

Cutting Edge: TCR-induced NAB2 enhances T cell function by coactivating IL-2 transcription

TCR engagement leads to the up-regulation of genetic programs that can both activate and inhibit T cell function. The early growth receptor (Egr) proteins Egr-2 and Egr-3 have recently been identified as TCR-induced negative regulators of T cell function. NAB2 (NGFI-A-binding protein 2) is both a coactivator and a corepressor of Egr-mediated transcription and has been implicated in regulating Schwann cell myelination. In this report we demonstrate that NAB2 is induced by TCR engagement and that its expression is enhanced by the presence of costimulation. The overexpression of NAB2 enhanced IL-2 production while small interfering RNA to NAB2 markedly inhibited IL-2 expression. Mechanistically, we demonstrate that NAB2 enhances IL-2 transcription by acting as a coactivator for Egr-1. Indeed, chromatin immunoprecipitation analysis reveals that NAB2 is recruited to the Egr-1 binding site of the IL-2 promoter. Taken together, our findings identify NAB2 as a novel coactivator of T cell function.

Both integrated and differential regulation of components of the IL-2/IL-2 receptor system

Interleukin-2 was discovered in 1976 as a T-cell growth factor. It was the first type I cytokine cloned and the first for which a receptor component was cloned. Its importance includes its multiple actions, therapeutic potential, and lessons for receptor biology, with three components differentially combining to form high, intermediate, and low-affinity receptors. IL-2Ralpha and IL-2Rbeta, respectively, are markers for double-negative thymocytes and regulatory T-cells versus memory cells. gamma(c), which is shared by six cytokines, is mutated in patients with X-linked severe-combined immunodeficiency. We now cover an under-reviewed area-the regulation of genes encoding IL-2 and IL-2R components, with an effort to integrate/explain this knowledge.

Molecular mechanisms underlying FOXP3 induction in human T cells

FOXP3 is playing an essential role for T regulatory cells and is involved in the molecular mechanisms controlling immune tolerance. Although the biological relevance of this transcription factor is well documented, the pathways responsible for its induction are still unclear. The current study reveals structure and function of the human FOXP3 promoter, revealing essential molecular mechanisms of its induction. The FOXP3 promoter was defined by RACE, cloned, and functionally analyzed using reporter-gene constructs in primary human T cells. The analysis revealed the basal, T cell-specific promoter with a TATA and CAAT box 6000 bp upstream the translation start site. The basal promoter contains six NF-AT and AP-1 binding sites, which are positively regulating the trans activation of the FOXP3 promoter after triggering of the TCR. The chromatin region containing the FOXP3 promoter was bound by NF-ATc2 under these conditions. Furthermore, FOXP3 expression was observed following TCR engagement. Promoter activity, mRNA, and protein expression of T cells were suppressed by addition of cyclosporin A. Taken together, this study reveals the structure of the human FOXP3 promoter and provides new insights in mechanisms of addressing T regulatory cell-inducing signals useful for promoting immune tolerance. Furthermore, the study identifies essential, positive regulators of the FOXP3 gene and highlights cyclosporin A as an inhibitor of FOXP3 expression contrasting other immunosuppressants such as steroids or rapamycin.

Early growth response-1 is required for CD154 transcription

CD154 (CD40 ligand) expression on CD4 T cells is normally tightly controlled, but abnormal or dysregulated expression of CD154 has been well documented in autoimmune diseases, such as systemic lupus erythematosus. Beyond regulation by NFAT proteins, little is known about the transcriptional activation of the CD154 promoter. We identified a species-conserved purine-rich sequence located adjacent to the CD154 transcriptional promoter proximal NFAT site, which binds early growth response (Egr) transcription factors. Gel shift assays and chromatin immunoprecipitation assays reveal that Egr-1, Egr-3, and NFAT1 present in primary human CD4 T cells are capable of binding this combinatorial site in vitro and in vivo, respectively. Multimerization of this NFAT/Egr sequence in the context of a reporter gene demonstrates this sequence is transcriptionally active upon T cell activation in primary human CD4 T cells. Overexpression of Egr-1, but not Egr-3, is capable of augmenting transcription of this reporter gene as well as that of an intact CD154 promoter. Conversely, overexpression of small interfering RNA specific for Egr-1 in primary human CD4 T cells inhibits CD154 expression. Similarly, upon activation, CD154 message is notably decreased in splenic CD4 T cells from Egr-1-deficient mice compared with wild-type controls. Our data demonstrate that Egr-1 is required for CD154 transcription in primary CD4 T cells. This has implications for selective targeting of Egr family members to control abnormal expression of CD154 in autoimmune diseases such as systemic lupus erythematosus.

Interleukin-21 receptor gene induction in human T cells is mediated by T-cell receptor-induced Sp1 activity

Interleukin-21 (IL-21) plays important roles in regulating the immune response. IL-21 receptor (IL-21R) mRNA is expressed at a low level in human resting T cells but is rapidly induced by mitogenic stimulation. We now investigate the basis for IL21R gene regulation in T cells. We found that the -80 to -20 region critically regulates IL-21R promoter activity and corresponds to a major DNase I-hypersensitive site. Electrophoretic mobility shift assays, DNA affinity chromatography followed by mass spectrometry, and chromatin immunoprecipitation assays revealed that Sp1 binds to this region in vitro and in vivo. Moreover, mutation of the Sp1 motif markedly reduced IL-21R promoter activity, and Sp1 small interfering RNAs effectively diminished IL-21R expression in activated T cells. Interestingly, upon T-cell receptor (TCR) stimulation, T cells increased IL-21R expression and Sp1 protein levels while decreasing Sp1 phosphorylation. Moreover, phosphatase inhibitors that increased phosphorylation of Sp1 diminished IL-21R transcription. These data indicate that TCR-induced IL-21R expression is driven by TCR-mediated augmentation of Sp1 protein levels and may partly depend on the dephosphorylation of Sp1.

Early growth response proteins EGR-4 and EGR-3 interact with immune inflammatory mediators NF-κB p50 and p65

Here, we characterize the basis for the T-cell-specific activity of the human zinc-finger protein early growth response factor 4 (EGR-4). A yeast two-hybrid screen showed interaction of EGR-4 with NF-κB p50. Using recombinant proteins, stable physical complex formation was confirmed for EGR-4 and EGR-3 with p50 and with p65 using glutathione-S-transferase pull-down assays and surface-plasmon-resonance and peptide-spot analyses. In vivo interaction of EGR-4 and EGR-3 with NF-κB p65 was demonstrated by immunoprecipitation experiments and fluorescence-resonance-energy transfer (FRET) analysis showing interaction in the nucleus of transfected Jurkat T cells. In transfection assays, EGR-p50 complexes were transcriptionally inactive and EGR-p65 complexes strongly activated transcription of the promoters of the human genes encoding the cytokines interleukin 2, tissue necrosis factor α and ICAM-1. The EGR-p65 complexes increased reporter-gene activity about 100-fold and thus exceeded the transcriptional activities of the p65 homodimer and the p65/p50 heterodimers. The major interaction domain for p65 was localized within the third zinc finger of EGR-4 using deletion mutants for pull-down assays and peptide-spot assays. By computer modeling, this interaction domain was localized to an α-helical region and shown to have the central amino acids surface exposed and thus accessible for interaction. In summary, in T cells, the two zinc-finger proteins EGR-4 and EGR-3 interact with the specific nuclear mediator NF-κB and control transcription of genes encoding inflammatory cytokines.

Transcriptional regulation of the mouse interleukin-2 receptor beta chain gene by Ets and Egr-1

To clarify the mechanisms and factors involved in the regulation of mouse IL-2Rbeta gene expression, we isolated the 5'-flanking region of IL-2Rbeta gene and investigated the promoter activity. Here we elucidated the positive regulatory regions, the most potent of which are located between -50 to -30bp and -164 to -135bp. These regions contain a potentially functional Ets and Egr-1-binding sites whose mutations abrogate promoter activity. Data from electrophoretic mobility shift assay indicate that Ets and Egr-1, but not Sp1, bind to the positive regulatory regions, -50 to -30bp and -164 to -135bp, respectively. Furthermore, recruitment of Ets and Egr-1 at endogenous IL-2Rbeta promoter segments in an IL-2-dependent F7 cells was verified by the chromatin immunoprecipitation assay. This study for the first time delineates the molecular mechanisms underlying regulation of mouse IL-2Rbeta gene transcription by Ets family proteins, partially with Egr-1, and thereby further elucidates the molecular basis of lymphocyte activation and differentiation.

Egr-2 and Egr-3 are negative regulators of T cell activation

T cell receptor engagement in the absence of proper accessory signals leads to T cell anergy. E3 ligases are involved in maintaining the anergic state. However, the specific molecules responsible for the induction of anergy have yet to be elucidated. Using microarray analysis we have identified here early growth response gene 2 (Egr-2) and Egr-3 as key negative regulators of T cell activation. Overexpression of Egr2 and Egr3 was associated with an increase in the E3 ubiquitin ligase Cbl-b and inhibition of T cell activation. Conversely, T cells from Egr3(-/-) mice had lower expression of Cbl-b and were resistant to in vivo peptide-induced tolerance. These data support the idea that Egr-2 and Egr-3 are involved in promoting a T cell receptor-induced negative regulatory genetic program.

VDUP1 Is Required for the Development of Natural Killer Cells

Vitamin D3 upregulated protein 1 (VDUP1) is a stress-response gene that is upregulated by 1,25(OH)2D3 in tumor cells. The in vivo roles of VDUP1 were investigated by producing mice lacking VDUP1 (VDUP1-/- mice). VDUP1-/- mice showed minimal changes in the development of T and B cells, but there was a profound reduction in the numbers of natural killer (NK) cells. As well, these mice showed decreased NK activity. In the VDUP1-/- mice, the expression of CD122 was reduced, demonstrating that VDUP1 is required for CD122 expression and NK maturation. In addition, severe lymphoid hyperplasia in the small intestine was observed in VDUP1-/- mice. Taken together, these results suggest that VDUP1 is a critical factor for the development and function of NK cells in vivo.

Co-operative interactions between NFAT (nuclear factor of activated T cells) c1 and the zinc finger transcription factors Sp1/Sp3 and Egr-1 regulate MT1-MMP (membrane type 1 matrix metalloproteinase) transcription by glomerular mesangial cells

The transition of normally quiescent glomerular MCs (mesangial cells) to a highly proliferative phenotype with characteristics of myofibroblasts is a process commonly observed in inflammatory diseases affecting the renal glomerulus, the ultimate result of which is glomerulosclerosis. Generation of proteolytically active MMP (matrix metalloproteinase)-2 by the membrane-associated membrane type 1 (MT1)-MMP is responsible for the transition of mesangial cells to the myofibroblast phenotype [Turck, Pollock, Lee, Marti and Lovett (1996) J. Biol. Chem. 271, 15074-15083]. In the present study, we show that the expression of MT1-MMP within the context of MCs is mediated by three discrete cis -acting elements: a proximal non-canonical Sp1 site that preferentially binds Sp1; an overlapping Sp1/Egr-1-binding site that preferentially binds Egr-1; and a more distal binding site for the NFAT (nuclear factor of activated T cells) that binds the NFAT c1 isoform present in MC nuclear extracts. Transfection with an NFAT c1 expression plasmid, or activation of calcineurin with a calcium ionophore, yielded major increases in NFAT c1 nuclear DNA-binding activity, MT1-MMP transcription and protein synthesis, which were additive with the lower levels of transactivation provided by the proximal Sp1 and the overlapping Sp1/Egr-1 sites. Specific binding of NFAT c1 to the MT1-MMP promoter was confirmed by chromatin immunoprecipitation studies, while MT1-MMP expression was suppressed by treatment with the calcineurin inhibitor, cyclosporin A. These studies are the first demonstration that a specific NFAT isoform enhances transcription of an MMP (MT1-MMP) that plays a major role in the proteolytic events that are a dominant feature of acute glomerular inflammation. Suppression of MT1-MMP by commonly used calcineurin inhibitors may play a role in the development of renal fibrosis following renal transplantation.

CD8 T cell responses to lymphocytic choriomeningitis virus in early growth response gene 1-deficient mice

Previous in vitro work has implicated a role for transcriptional factor early growth response gene 1 (EGR1) in regulating immune responses. However, the in vivo role of EGR1 in orchestrating T cell responses has not been studied. To investigate the importance of EGR1 in T cell immunity, we compared Ag-specific CD8 T cell responses between wild type (+/+) and EGR1-deficient (EGR1-/-) mice following an acute infection with lymphocytic choriomeningitis virus (LCMV). These studies revealed that the expansion of LCMV-specific CD8 T cells was substantially reduced in EGR1-/- mice, as compared with +/+ mice. The reduced numbers of LCMV-specific CD8 T cells in EGR1-/- mice were not due to an intrinsic T cell defect per se because purified EGR1-deficient T cells exhibited normal proliferative response to anti-CD3 stimulation in vitro, and underwent normal activation and expansion in response to LCMV upon adoptive transfer into T cell-deficient mice. Furthermore, adoptive transfer of CD8 T cells bearing a transgenic TCR into EGR1-/- mice showed that EGR1 deficiency in non-CD8 T cells impaired CD8 T cell expansion in vivo following an LCMV infection. Further investigations on accessory cells showed that bone marrow-derived dendritic cells from EGR1-/- mice did not exhibit detectable impairment to prime Ag-specific CD8 T cell responses in vivo. However, in LCMV-infected mice, EGR1 deficiency selectively impaired the maturation of CD8alpha(+ve) plasmacytoid dendritic cells. Taken together, our findings suggest that EGR1 might promote expansion of CD8 T cells during an acute viral infection by modulating the cues in the lymphoid microenvironment.

Mouse Huntington's disease homolog mRNA levels: variation and allele effects

Huntington's disease homolog (Hdh) mRNA levels in mice with different Hdh alleles were measured. Brain Hdh mRNA levels varied up to threefold in genetically identical wild-type mice, indicating nongenetic factors influence Hdh expression. Striatal Hdh mRNA levels from an allele with a repeat expanded to 150 CAGs were diminished compared with wild-type and showed variation that might contribute to phenotypic variability in the Hdh(CAG)150 knock-in mouse model. To determine whether Hdh mRNA levels are tightly regulated, we assessed these levels in mice heterozygous for a deletion of the Hdh promoter. The loss of one allele reduced Hdh mRNA levels in most tissues, suggesting mechanisms to maintain Hdh mRNA levels are not in effect and should not impede therapies designed to destroy mutant huntingtin mRNA. Finally, we found a correlation between tissue mRNA levels and the susceptibility of the Hdh locus to Cre-mediated deletion. The two tissues with the highest levels of Hdh mRNA, testes and brain, were the only tissues susceptible to Cre-mediated recombination between loxP sites at Hdh locus. In contrast, the same Cre-expressing line caused recombination in every tissue for loxP sites at another genomic location. The pattern of Cre susceptibility at Hdh suggests a correlation between chromatin accessibility and high levels of Hdh expression in testes and brain.

Transgenic mice demonstrate novel promoter regions for tissue-specific expression of the urokinase receptor gene

The urokinase-type plasminogen activator receptor (u-PAR) contributes to cell migration and proteolysis in normal and cancerous tissues. Currently, there are no reports on the regulatory regions directing tissue-specific expression. Consequently, we undertook a study to identify novel promoter regions required for expression of this gene in transgenic mice bearing a LacZ reporter regulated by varying amounts (0.4, 1.5, and 8.5 kb) of upstream sequence. The 0.4-kb u-PAR upstream sequence directed weak and strong LacZ expression in the placenta and epididymis, respectively, both of which are tissues that express endogenous u-PAR. Conversely, transgene expression in the apical cells of the colon positive for endogenous u-PAR protein required 1.5 kb of upstream sequence for optimal expression. Furthermore, chromatin accessibility assays coupled with real-time polymerase chain reaction suggested a putative regulatory region spanning -1295/-1192 driving u-PAR expression in colonic cells. Interestingly, placental transgene expression was augmented with the 8.5-kb upstream fragment compared with the shorter 1.5-kb fragment indicating contributing element(s) between -1.5 and -8.5 kb. Thus, while 0.4 kb of upstream sequence directs u-PAR expression in the epididymis, sequences located between -0.4 and -1.5 kb and between -1.5 and -8.5 kb are required for optimal tissue-specific expression in the colon and the placenta, respectively.

Impaired hematopoiesis in mice lacking the transcription factor Sp3

As the zinc-finger transcription factor specificity protein 3 (Sp3) has been implicated in the regulation of many hematopoietic-specific genes, we analyzed the role of Sp3 in hematopoiesis. At embryonic day 18.5 (E18.5), Sp3-/- mice exhibit a partial arrest of T-cell development in the thymus and B-cell numbers are reduced in liver and spleen. However, pre-B-cell proliferation and differentiation into immunoglobulin M-positive (IgM+) B cells in vitro are not affected. At E14.5 and E16.5, Sp3-/- mice exhibit a significant delay in the appearance of definitive erythrocytes in the blood, paralleled by a defect in the progression of differentiation of definitive erythroid cells in vitro. Perinatal death of the null mutants precludes the analysis of adult hematopoiesis in Sp3-/- mice. We therefore investigated the ability of E12.5 Sp3-/- liver cells to contribute to the hematopoietic compartment in an in vivo transplantation assay. Sp3-/- cells were able to repopulate the B- and T-lymphoid compartment, albeit with reduced efficiency. In contrast, Sp3-/- cells showed no significant engraftment in the erythroid and myeloid lineages. Thus, the absence of Sp3 results in cell-autonomous hematopoietic defects, affecting in particular the erythroid and myeloid cell lineages.

Transcriptional control of the RECK metastasis/angiogenesis suppressor gene

The RECK gene is widely expressed in normal human tissues but is downregulated in tumor cell lines and oncogenically transformed fibroblasts. RECK encodes a membrane-anchored glycoprotein that suppresses tumor invasion and angiogenesis by regulating matrix-metalloproteinases (MMP-2, MMP-9 and MT1-MMP). Understanding of the transcriptional regulation of tumor/metastasis suppressor genes constitutes a potent approach to the molecular basis of malignant transformation. In order to uncover the mechanisms of control of RECK gene expression, the RECK promoter has been cloned and characterized. One of the elements responsible for the Ras-mediated downregulation of mouse RECK gene is the Sp1 site, to which Sp1 and Sp3 factors bind. Other regulatory events, such as DNA methylation of the RECK promoter and histone acetylation/deacetylation have been studied to understand the underlying mechanisms of RECK expression. Understanding of the mechanisms which control RECK gene transcription may lead to the development of new strategies for cancer prevention and treatment.

Early growth response proteins (EGR) and nuclear factors of activated T cells (NFAT) form heterodimers and regulate proinflammatory cytokine gene expression

Activation of transcription factors by receptor mediated signaling is an essential step for T lymphocyte effector function. Following antigenic stimulation of T cells the two central cytokines IL-2 and TNFalpha are co-expressed and co-regulated. Two important transcription factors, i.e., early growth response (EGR) protein EGR-1 and nuclear factors of activated T cells (NFAT) protein NFATc, regulate transcription of the human IL-2 cytokine and the same combination of EGR and NFAT proteins seems relevant for coordinated cytokine expression. Here we demonstrate that the zinc finger protein EGR-1 and two members of the NFAT protein family bind simultaneously to adjacent elements position -168 to -150 within the TNFalpha promoter. Both promoter sites are important for TNFalpha gene transcription as shown by transfection assays having the IL-2 and TNFalpha promoters linked to a luciferase reporter. The use of promoter deletion constructs with the zinc finger protein (ZIP), the NFAT binding element or a combination of both deleted show a functional cooperation of these elements and of their binding factors. These experiments demonstrate that EGR-1 as well as EGR-4 functionally cooperate with NFAT proteins and induce expression of both cytokine genes. Using tagged NFATc and NFATp in glutathione S-transferase pull down assays showed interaction and physical complex formation of each NFAT protein with recombinant, as well as native, EGR-1 and EGR-4 proteins. Thus EGR-NFAT interaction and complex formation seems essential for human cytokine expression as adjacent ZIP and NFAT elements are conserved in the IL-2 and TNFalpha gene promoters. Binding of regulatory EGR and NFAT factors to these sites and the functional interaction and formation of stable heterodimeric complexes indicate an important role of these factors for gene transcription.

Arginine butyrate increases the cytotoxicity of DAB(389)IL-2 in leukemia and lymphoma cells by upregulation of IL-2Rbeta gene

DAB(389)IL-2 (ONTAK) is a fusion protein consisting of the ADP-ribosyltransferase and membrane translocating domains of native diphtheria toxin and the full-length sequence for interleukin-2 (IL-2) gene. In vitro data demonstrates that DAB(389)IL-2 is cytotoxic to cells expressing the high affinity IL-2 receptor (IL-2R). In Phases I and II clinical trials of patients whose tumor cells express a component of the IL-2R, the response rates were 18% for B-cell non-Hodgkin lymphoma (NHL) and 30% for cutaneous T-cell lymphoma (CTCL). In this study, we examined the effects of arginine butyrate on IL-2R expression and susceptibility of leukemia cells to intoxication by DAB(389)IL-2. We demonstrate that the p75 subunit of the IL-2R (IL-2Rbeta) is upregulated in the presence of low concentrations of arginine butyrate (0.06mM) which had no direct growth inhibitory effect on the cells. To explore mechanisms of this upregulation, we examined the effect of 0.06mM arginine butyrate on relevant transcriptional elements and on histone deacetylase and found activation of cAMP response element (CRE) but not NFAT or NFKB, as well as inhibition of histone deacetylase (HDAC). Our results suggest that the effects of physiologically achievable concentrations of butyrate on IL-2R expression could be exploited to enhance the susceptibility of intermediate and low-affinity IL-2R expressing leukemia cells to DAB(389)IL-2.

Combinatorial regulation of the murine RAG-2 promoter by Sp1 and distinct lymphocyte-specific transcription factors

The recombination activation genes, RAG-1 and RAG-2, encode the critical components of the recombinase complex responsible for the generation of functional antigen receptor genes. In order to gain an insight into the transcription factors and cis-acting elements that regulate the lymphocyte-specific expression of RAG-2, the promoter-region of this gene was isolated and characterized. This analysis demonstrated that a relatively small promoter fragment could confer lymphocyte-restricted expression to a reporter construct. Our work and that of others subsequently revealed that RAG-2 promoter expression is positively regulated by BSAP (PAX-5) and c-Myb transcription factors in B- and T-lineage cells, respectively. Although BSAP and c-Myb were deemed necessary for lymphocyte-specific expression, our analysis also uncovered a G-rich region at the 5'-end of the core promoter that was essential for full activity in lymphocyte cell lines. Site-directed mutagenesis revealed that a GA-box within the G-rich region was required for full promoter activity and subsequent DNA binding assays demonstrated that this element was specifically recognized by Sp1. Apart from showing that Sp1 interacts within the RAG-2 promoter, we also demonstrate that the Sp1-binding site is necessary for the high-level activation of this promoter.

Induction of the interleukin-2/15 receptor beta-chain by the EWS-WT1 translocation product

EWS-WT1 is a chimeric transcription factor resulting from fusion of the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of the Wilms tumor suppressor WT1. This translocation underlies desmoplastic small round cell tumor (DSRCT), which is noted for the abundance of reactive stroma surrounding islets of tumor cells, suggestive of paracrine signals contributing to tumor cell proliferation. Hybridization to high-density oligonucleotide microarrays can be used to identify targets of EWS-WT1. Expression of EWS-WT1 from a tetracycline-regulated promoter leads to the induction of growth-associated genes, of which the most remarkable is the beta-chain of the interleukin-2/15 receptor (IL-2/15Rbeta). Potent transcriptional activation by the chimeric protein maps to two bindings sites within the IL-2/15Rbeta promoter. Analysis of primary DSRCT tumor specimens demonstrates high levels of IL-2/15Rbeta within the tumor cells, along with expression of IL-2 and IL-15 by the abundant hyperplastic endothelial cells within the reactive stroma. Activation of this cytokine signaling pathway is consistent with the nuclear localization of its downstream effectors, phosphorylated STAT3 and STAT5. These observations suggest that the transcriptional induction of a cytokine receptor by a tumor-associated translocation product enables a proliferative response of epithelial cancer cells to ligands secreted by the surrounding stroma.

The gene for interleukin-21 receptor is the partner of BCL6 in t(3;16)(q27;p11), which is recurrently observed in diffuse large B-cell lymphoma

BCL6 translocation affecting the chromosomal band 3q27 can involve a number of non-immunoglobulin (non-IG) gene loci as partners. We report here that the gene for interleukin-21 receptor (IL-21R) is the partner of BCL6 in t(3;16)(q27;p11) translocation. The two breakpoints on 16p11 of a lymphoma cell line YM and case no. 1012 with diffuse large B-cell lymphoma, both of which carried t(3;16), were localized within the 27-kb intron 1 of IL-21R. As a result of t(3;16), the promoter region of IL-21R was substituted for the regulatory sequences of BCL6 in the same transcriptional orientation. Reverse transcriptase-mediated polymerase chain reaction revealed chimeric mRNA consisting of two non-coding exons 1a/1b of IL-21R and coding exons of BCL6 in both lymphoma cells. Fluorescence in situ chromosomal hybridization of YM metaphase cells revealed fusion signals that contained both the BCL6 and IL-21R sequences on the der(3)t(3;16) chromosome. IL-21R was actively transcribed in YM cells, while BCL6 that was under the control of the IL-21R promoter was only moderately expressed at the mRNA and protein level. We constructed expression plasmid of BCL6 that followed the promoter sequences of IL-21R. COS-7 cells transiently transfected with the plasmid expressed high level Bcl-6 protein and displayed nuclear staining with a characteristic punctate pattern by immunofluorescence, indicating that expression of BCL6 can be enhanced by t(3;16). This study added to the list of non-IG partners of BCL6 translocations a new class of gene, i.e. cytokine receptor gene, the expression of which is closely associated with lymphoid cells.

Paroxysmal nocturnal hemoglobinuria: Differential gene expression of EGR-1 and TAXREB107

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal defect of hematopoietic stem cells characterized by deficiency in GPI-anchored surface proteins. It is not yet known how GPI-deficient stem cells are able to expand within the bone marrow and contribute considerably to the hematopoiesis. In PNH, as well as in AA and MDS, genetic instability and increased mutation frequency have been detected. Therefore, a second event is very likely, such as additional mutations, leading to clonal expansion of GPI-deficient bone marrow stem cell in PNH.

METHODS

In order to elucidate the molecular basis of clonal expansion in PNH, we identified several genes differentially expressed in normal and GPI-deficient cells of PNH patients by combination of RNA fingerprinting and cDNA array hybridization.

RESULTS

Expression of two of these genes, EGR-1 and TAXREB107, has been further investigated. EGR-1 is upregulated in granulocytes of all PNH patients analyzed so far. In contrast, significant upregulation of TAXREB107 is present only in some of our PNH patients. Further analysis confirmed their overexpression in PNH and excluded a possible secondary event character of observed overexpression. Moreover, similar levels of expression in cases of other clonal diseases, such as MPS and MDS, has been identified.

CONCLUSION

Our data suggest that additional genetic alterations apart from PIG-A mutations could be present in PNH granulocytes. In addition, these genetic changes might contribute to clonal expansion of GPI-deficient cells in PNH.

Defective expression of the interleukin-2/interleukin-15 receptor beta subunit leads to a natural killer cell-deficient form of severe combined immunodeficiency

Development of T and natural killer (NK) cells is critically dependent on cytokine signaling, and defects in cytokine receptor complex subunits have been shown to result in severe combined immunodeficiency (SCID) syndromes in humans and in murine models. An infant boy had typical clinical features of SCID and was found to lack NK cells in his peripheral circulation. Molecular analysis did not reveal abnormalities in his gammac or JAK-3 genes, and he was investigated for defects in the interleukin-15 (IL-15) receptor complex because functional IL-15 signaling is essential for NK cell development. Expression of the IL-2R/IL-15Rbeta chain was significantly reduced in the patient's peripheral blood mononuclear cells (PBMCs) by immunoblot, flow cytometry, and Northern blot analysis. Furthermore, IL-2 stimulation of PBMCs showed only minimal tyrosine phosphorylation of JAK-3. These data demonstrate that defects in IL-2R/1L-15Rbeta expression can lead to a unique NK-deficient SCID immunophenotype. (Blood. 2001;98:877-879)

Transcriptional regulation of CD28 expression by CD28GR, a novel promoter element located in exon 1 of the CD28 gene

CD28 provides an essential costimulatory signal required for Ag-mediated T cell activation via the TCR. Although accumulating evidence exists for the signaling properties of CD28, less is known regarding the regulation of CD28 expression. In this study, we have identified a novel promoter element of CD28, CD28GR (GGGGAGGAGGGG), which is located between +181 and +192 in exon 1 of the CD28 gene. Mutations within the 12-bp CD28GR sequence abolished its transcriptional activity. CD28GR contains a Sp1/EGR-1 binding site, which was found to act as the predominant functional element for regulating CD28 gene expression in Jurkat cells. Exon 1/CD28GR-driven transcription in Jurkat cells was augmented by cotransfection with Sp1 or EGR-1 expression plasmid. Similar augmentation was also shown with pharmacologic activation. This study is the first to identify a regulatory element that is critical for conferring constitutive and activation-induced transcriptional activation of the CD28 gene. Furthermore, our results proposed potential involvement of Sp1 in regulating CD28 expression. The linkage between Sp1 and the expression of CD28 has important implications in how viral infections, such as HIV, can induce immunosuppression.