Expression of PILOT, a putative transcription factor, requires two signals and is cyclosporin A sensitive in T cells

Egr3 induces a Th17 response by promoting the development of γδ T cells

The transcription factor Early Growth Response 3 (Egr3) has been shown to play an important role in negatively regulating T cell activation and promoting T cell anergy in Th1 cells. However, its role in regulating other T helper subsets has yet to be described. We sought to determine the role of Egr3 in a Th17 response using transgenic mice that overexpress Egr3 in T cells (Egr3 TG). Splenocytes from Egr3 TG mice demonstrated more robust generation of Th17 cells even under non-Th17 skewing conditions. We found that while Egr3 TG T cells were not intrinsically more likely to become Th17 cells, the environment encountered by these cells was more conducive to Th17 development. Further analysis revealed a considerable increase in the number of γδ T cells in both the peripheral lymphoid organs and mucosal tissues of Egr3 TG mice, a cell type which normally accounts for only a small fraction of peripheral lymphocytes. Consistent with this marked increase in peripheral γδ T cells, thymocytes from Egr3 TG mice also appear biased toward γδ T cell development. Coculture of these Egr3-induced γδ T cells with wildtype CD4+ T cells increases Th17 differentiation, and Egr3 TG mice are more susceptible to bleomycin-induced lung inflammation. Overall our findings strengthen the role for Egr3 in promoting γδ T cell development and show that Egr3-induced γδ T cells are both functional and capable of altering the adaptive immune response in a Th17-biased manner. Our data also demonstrates that the role played by Egr3 in T cell activation and differentiation is more complex than previously thought.

Egr2 induced during DC development acts as an intrinsic negative regulator of DC immunogenicity

Early growth response gene 2 (Egr2), which encodes a zinc finger transcription factor, is rapidly and transiently induced in various cell types independently of de novo protein synthesis. Although a role for Egr2 is well established in T-cell development, Egr2 expression and its biological function in dendritic cells (DCs) have not yet been described. Here, we demonstrate Egr2 expression during DC development, and its role in DC-mediated immune responses. Egr2 is expressed in the later stage of DC development from BM precursor cells. Even at steady state, Egr2 is highly expressed in mouse splenic DCs. Egr2-knockdown (Egr2-KD) DCs showed increased levels of major histocompatability complex (MHC) class I and II and co-stimulatory molecules, and enhanced antigen uptake and migratory capacities. Furthermore, Egr2-KD abolished SOCS1 expression and signal transducer and activator of transcription 5 (STAT5) activation during DC development, probably resulting in the enhancement of IL-12 expression and Th1 immunogenicity of a DC vaccine. DC-mediated cytotoxic T lymphocyte (CTL) activation and antitumor immunity were significantly enhanced by Egr2-KD, and impaired by Egr2 overexpression in antigen-pulsed DC vaccines. These data suggest that Egr2 acts as an intrinsic negative regulator of DC immunogenicity and can be an attractive molecular target for DC vaccine development.

Vascular endothelial growth factor activation of endothelial cells is mediated by early growth response-3

Endothelial cell activation and dysfunction underlie many vascular disorders, including atherosclerosis, tumor growth, and sepsis. Endothelial cell activation, in turn, is mediated primarily at the level of gene transcription. Here, we show that in response to several activation agonists, including vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha, and thrombin, endothelial cells demonstrate rapid and profound induction of the early growth response (Egr) genes egr-1 and egr-3. In VEGF-treated endothelial cells, induction of Egr-3 was far greater and more prolonged compared with Egr-1. VEGF-mediated stimulation of Egr-3 involved the inducible binding of NFATc, serum response factor, and CREB to their respective consensus motifs in the upstream promoter region of Egr-3. Knockdown of Egr-3 markedly impaired VEGF-mediated proliferation, migration, and tube formation of endothelial cells and blocked VEGF-induced monocyte adhesion. Egr-3 knockdown abrogated VEGF-mediated vascular outgrowth from ex vivo aortic rings and attenuated Matrigel plug vascularization and melanoma tumor growth in vivo. Together, these findings suggest that Egr-3 is a critical determinant of VEGF signaling in activated endothelial cells. Thus, Egr-3 represents a potential therapeutic target in VEGF-mediated vasculopathic diseases.

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.

Brain-derived neurotrophic factor (BDNF)-induced synthesis of early growth response factor 3 (Egr3) controls the levels of type A GABA receptor alpha 4 subunits in hippocampal neurons

Altered function of gamma-aminobutyric acid type A receptors (GABA(A)Rs) in dentate granule cells of the hippocampus has been associated with temporal lobe epilepsy (TLE) in humans and in animal models of TLE. Such altered receptor function (including increased inhibition by zinc and lack of modulation by benzodiazepines) is related, in part, to changes in the mRNA levels of certain GABA(A)R subunits, including alpha4, and may play a role in epileptogenesis. The majority of GABA(A)Rs that contain alpha4 subunits are extra-synaptic due to lack of the gamma2 subunit and presence of delta. However, it has been hypothesized that seizure activity may result in expression of synaptic receptors with altered properties driven by an increased pool of alpha4 subunits. Results of our previous work suggests that signaling via protein kinase C (PKC) and early growth response factor 3 (Egr3) is the plasticity trigger for aberrant alpha4 subunit gene (GABRA4) expression after status epilepticus. We now report that brain derived neurotrophic factor (BDNF) is the endogenous signal that induces Egr3 expression via a PKC/MAPK-dependent pathway. Taken together with the fact that blockade of tyrosine kinase (Trk) neurotrophin receptors reduces basal GABRA4 promoter activity by 50%, our findings support a role for BDNF as the mediator of Egr3-induced GABRA4 regulation in developing neurons and epilepsy and, moreover, suggest that BDNF may alter inhibitory processing in the brain by regulating the balance between phasic and tonic inhibition.

Integration of G-protein coupled receptor signaling pathways for activation of a transcription factor (EGR-3)

We recently reported the use of a gene-trapping approach to isolate cell clones in which a reporter gene had integrated into genes modulated by T-cell activation. We have now tested a panel of clones from that report and identified the one that responds to a variety of G-protein coupled receptors (GPCR). The β-lactamase tagged EGR-3 Jurkat cell was used to dissect specific GPCR signaling in vivo. Three GPCRs were studied, including the chemokine receptor CXCR4 (Gi-coupled) that was endogenously expressed, the platelet activation factor (PAF) receptor (Gq-coupled), and β2 adrenergic receptor (Gs-coupled) that was both stably transfected. Agonists for each receptor activated transcription of the β-lactamase tagged EGR-3 gene. Induction of EGR-3 through CXCR4 was blocked by pertussis toxin and PD58059, a specific inhibitor of MEK (MAPK/ERK kinase). Neither of these inhibitors blocked isoproterenol or PAF-mediated activation of EGR-3. Conversely, β2- and PAF-mediated EGR-3 activation was blocked by the p38, specific inhibitor SB580. In addition, both β2- and PAF-mediated EGR-3 activation could be synergistically activated by CXCR4 activation. This combined result indicates that EGR-3 can be activated through distinct signal transduction pathways by different GPCRs and that signals can be integrated and amplified to efficiently tune the level of activation.

Developmental regulation of galactokinase in suckling mouse liver by the Egr-1 transcription factor

The numerous changes in metabolic pathways that accompany liver development entail associated changes in gene expression. Egr-1 is a zinc-finger transcription factor that regulates genes involved in cellular growth, differentiation, stress response, and apoptosis in many cell types. Egr-1 is induced in liver regeneration in rodents, but its role in normal hepatocyte function has not been characterized. We examined the developmental expression of Egr-1 in mouse liver and found that its expression increased during the suckling period. In screening the sequences of the genes involved in lactose assimilation, we found that the galactokinase gene Glk contains four potential Egr-1 binding sites in its proximal promoter. A minimal promoter of 155 nucleotides encompassing the four Egr-1 sites exhibited activity in hepatoma cell lines by transient transfection assays. Moreover, co-transfection of an Egr-1 expression plasmid increased promoter activity. Finally, mutations introduced into three of the four Egr-1 binding sites decreased activity, whereas mutation of the remaining site increased promoter activity. These data tie Egr-1 and galactokinase together in a developmentally regulated chain to prepare the neonate for suckling.

p300 regulates the synergy of steroidogenic factor-1 and early growth response-1 in activating luteinizing hormone-beta subunit gene

Tight regulation of luteinizing hormone-beta subunit (LHbeta) expression is critical for differentiation and maturation of mammalian sexual organs and reproductive function. Two transcription factors, steroidogenic factor-1 (SF-1) and early growth response-1 (Egr-1), play a central role in activating LHbeta promoter, and the synergy between these two factors is essential in mediating gonadotropin-releasing hormone stimulation of LHbeta promoter. Here we demonstrate that the transcriptional co-activator p300 regulates this synergy. Overexpression of p300 results in strong stimulation of LHbeta promoter but only in the presence of both SF-1 and Egr-1, and not in the presence of other Egr proteins. Mutation of the binding sites for either SF-1 or Egr-1 completely abolishes the synergy between these two factors, as well as the influence of p300. Importantly, LHbeta promoter is precipitated using p300 antibodies in a chromatin immunoprecipitation assay with LbetaT2 gonadotropes, and this effect is enhanced by gonadotropin-releasing hormone. The influence of p300 on LHbeta promoter is potentiated by steroid receptor co-activator, as well as by E1A proteins, and attenuated by Smad nuclear interacting protein 1. Taken together, these results suggest that p300 is recruited to LHbeta promoter where it coordinates the functional synergy between SF-1 and Egr-1.

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.

HIV Tat binds Egr proteins and enhances Egr-dependent transactivation of the Fas ligand promoter

HIV Tat can enhance activation-induced up-regulation of Fas ligand (FasL), which may contribute to T cell apoptosis in human immune deficiency virus (HIV)-infected individuals. We have assessed functional and physical interactions between Tat and the Egr family of transcription factors (Egr-1, -2, and -3), the latter two of which are major participants in activation-induced FasL up-regulation. Here we report that whereas Tat itself has no effect on the FasL promoter, it binds to Egr-2 and -3 and synergizes with them to superinduce expression of a FasL promoter-driven reporter. A Tat molecule containing a single amino acid substitution that results in the loss of transactivation activity for the HIV long terminal repeat still binds Egr-3 but can no longer enhance Egr-mediated transactivation of the FasL promoter. Furthermore, the mutated Tat acts as a dominant negative inhibitor, blocking the superinduction of FasL caused by wild type Tat. Because Tat is present in virus-infected cells and in the serum of HIV-infected individuals, these results suggest that increased expression of FasL in these circumstances may result from the cooperative activities of activation-induced Egrs and Tat.

Differential expression of Fas ligand in Th1 and Th2 cells is regulated by early growth response gene and NF-AT family members

Inducible expression of Fas ligand (CD95 ligand) by activated T cells and the resulting apoptosis of CD95-bearing cells is a critical component of peripheral T cell homeostasis and cytotoxic effector mechanisms. Transcriptional control of the expression of Fas ligand has been attributed to a number of factors, including early growth response gene 2 (Egr2), Egr3, Sp1, and NF-AT, although a direct contribution of NF-AT is controversial. The present study confirms a role for Egr factors and indicates that NF-AT is essential for optimal expression of murine Fas ligand through a direct interaction with an NF-AT consensus element. The role of these factors was further defined by studying the differential expression of Fas ligand in Th1 and Th2 lines derived from DO11.10 TCR transgenic mice. EMSA analyses of a composite Egr/NF-AT site showed recruitment of Sp1 to this site in Th2 cells, but not in Th1 cells. Furthermore, gel-shift analyses demonstrated the binding of Egr1, 2, and 3 in Th2 cells and Egr1 and 2, but not Egr3 in Th1 cells at a known Egr site. Northern analysis corroborated the lack of Egr3 in Th1 cells. Differential usage of these transcription factors by Th1 and Th2 cells suggests a potential mechanism underlying the differential expression of Fas ligand by distinct T cell lineages.

Induction, binding specificity and function of human ICOS

Recently, we have identified the inducible co-stimulator (ICOS), an activation-dependent, T cell-specific cell surface molecule related to CD28 and CTLA-4. Detailed analysis of human ICOS presented here shows that it is a 55-60-kDa homodimer with differently N-glycosylated subunits of 27 and 29 kDa. ICOS requires both phorbol 12-myristate 13-acetate and ionomycin for full induction, and is sensitive to Cyclosporin A. ICOS is up-regulated early on all T cells, including the CD28- subset, and continues to be expressed into later phases of T cell activation. On stimulation of T cells by antigen-presenting cells, the CD28/B7, but not the CD40 ligand/CD40 pathway is critically involved in the induction of ICOS. ICOS does not bind to B7-1 or B7-2, and CD28 does not bind to ICOS ligand; thus the CD28 and ICOS pathways do not cross-interact on the cell surface. In vivo, ICOS is expressed in the medulla of the fetal and newborn thymus, in the T cell zones of tonsils and lymph nodes, and in the apical light zones of germinal centers (predominant expression). Functionally, ICOS co-induces a variety of cytokines including IL-4, IL-5, IL-6, IFN-gamma, TNF-alpha, GM-CSF, but not IL-2, and superinduces IL-10. Furthermore, ICOS co-stimulation prevents the apoptosis of pre-activated T cells. The human ICOS gene maps to chromosome 2q33 - 34.

Novel Egr/NF-AT composite sites mediate activation of the CD95 (APO-1/Fas) ligand promoter in response to T cell stimulation

Expression of the CD95 (APO-1/Fas) ligand (CD95L) in activated T cells is a major cause of activation-induced T cell apoptosis. The transcription factors NF-AT and Egr-3 (a member of the immediate-early transcription factors involved in cellular growth and differentiation) have been implicated in activation of the CD95L promoter upon T cell activation. On the basis of DNase I footprinting, electrophoretic mobility shift assay, antibody supershift analysis and transfection studies, we have identified two novel Egr-binding sites 5' upstream of the previously identified Egr site. Mutation analysis of each Egr site shows that all three sites are important for full CD95L promoter activity. Strikingly, all Egr sites, including the previously identified Egr site, are adjacent to or overlap with DNA sequences homologous to NF-AT binding sites and confer T cell activation-induced, cyclosporin A-sensitive transcriptional activity. Antibody supershift analysis revealed that NF-AT and Egr proteins are the components of inducible DNA-binding complexes formed on the two novel Egr sites. Cotransfection experiments showed that Egr-1, Egr-3 and NF-AT display a cooperative and synergistic activation of transcription mediated by these three Egr/NF-AT composite regulatory elements. These findings provide further insight into the mechanisms involved in the regulation of the CD95L expression in response to T cell activation.

The EGR family of transcription-regulatory factors: progress at the interface of molecular and systems neuroscience

The EGR family of transcription regulatory factors, which is implicated in orchestrating the changes in gene expression that underlie neuronal plasticity, has attracted the attention of both molecular and systems neuroscientists. In this article, the advances made in both these fields of research are reviewed. Recent systems-based studies underscore the remarkable sensitivity and specificity of the induction of the expression of genes encoding EGR-family members in naturally occurring plasticity paradigms. However, they also challenge conventional views of the role of this family in plasticity. Recent molecular studies have identified the gonadotropin subunit, luteinizing hormone beta, as an EGR1-regulated gene in vivo and uncovered an essential role for EGR3 in muscle-spindle development. In addition, the discovery of novel proteins that are capable of suppressing EGR-mediated transcription cast doubt over the prevalent assumption that changes in EGR mRNA or protein levels provide an accurate measure of EGR-driven transcriptional activity.

Regulation of Egr-1-dependent gene expression by the C-terminal activation domain

The present study analyzes the role of the C-terminal activation domain for Egr-1 transcriptional activity using N-terminal deletion mutants. Mutant N372 comprising the entire C-terminal activation domain and partly truncated DNA-binding and nuclear translocation domains functioned as the transdominant repressor of Egr-1-dependent gene transcription. Activity of the SV40 promoter, however, was not affected by the N372 mutant. Analysis of additional Egr-1 mutants revealed that the transdominant negative effect of N372 was dependent on truncation of the zinc finger motifs that mediate DNA binding. Reconstitution of the zinc fingers was sufficient to generate Egr-1 proteins with potent transcriptional activity. The inhibitory mutant N372 is efficiently translocated to the nucleus, but fails to bind DNA and does not displace DNA-bound wildtype Egr-1. These results provide evidence for an Egr-1-specific cofactor that interacts with the C-terminal activation domain and is essential for Egr-1 transcriptional activity.

Role of Egr-2 in up-regulation of Fas ligand in normal T cells and aberrant double-negative lpr and gld T cells

We previously identified a Fas ligand regulatory element (FLRE) in the Fas ligand (fasL) promoter that binds Egr family proteins and demonstrated that Egr-3 (PILOT) but not Egr-1 (NGFI-A, Krox-24, Tis-8, and Zif-268) induces transcription of fasL. The aberrant CD4(-)CD8(-) T cells from lpr/lpr and gld/gld mice, which have mutations in the genes encoding Fas and FasL, respectively, have an activated phenotype and constitutively express high levels of fasL mRNA, prompting us to ask what role if any the FLRE and Egr family proteins have in this aberrant expression of fasL. Unstimulated MRL-lpr/lpr and C3H-gld/gld CD4(-)CD8(-) T cells constitutively contained high levels of two proteins that bound to the FLRE. Supershift analysis revealed these proteins to be Egr-1 and Egr-2 (Krox-20); Egr-3 was not detected. Activation of normal lymph node cells resulted in increased expression of Egr-1, -2, and -3. As with egr-3, expression of egr-2 was blocked by cyclosporin A. Although overexpressed Egr-1 was ineffective, overexpressed Egr-2 was as potent as Egr-3 in inducing fasL promoter-dependent reporter constructs in T cell hybridomas and HeLa cells, and both up-regulated endogenous fasL mRNA in HeLa cells. FasL-dependent reporter constructs in MRL-lpr/lpr and C3H-gld/gld CD4(-)CD8(-) T cells were constitutively active, and this activity was largely prevented by mutation of the critical Egr family binding element. Thus, Egr-2, in addition to Egr-3, regulates FasL expression in activated normal T cells, and Egr-2 is likely to play a direct role in aberrant fasL up-regulation in lpr/lpr and gld/gld CD4(-)CD8(-) T cells.

Utilization of an NF-ATp binding promoter element for EGR3 expression in T cells but not fibroblasts provides a molecular model for the lymphoid cell-specific effect of cyclosporin A

Cyclosporin A (CsA) mainly exerts its immunosuppressive action by selectively inhibiting Ca2+/calcineurin-dependent gene transcription in lymphoid cells. A model explaining the tissue-specific effect of this drug on gene expression has not been established to date, since none of the known intracellular targets of CsA (e.g., cyclophilins, calcineurin, and NF-AT) is lymphoid cell specific. To investigate this issue, we performed a detailed comparative analysis of the promoter regulating the two-signal-dependent (Ca2+ ionophore plus phorbol myristate acetate [PMA]), CsA-sensitive expression of EGR3 in T cells and the one-signal-dependent (PMA), CsA-insensitive expression of EGR3 in fibroblasts. As a result, we identified a 27-bp promoter element functionally interacting with transcription factors NF-ATp and NF-ATc that is crucial for the CsA-sensitive expression of the EGR3 gene in T cells. In contrast, the same element was without function in fibroblasts, and other, CsA-insensitive promoter regions were found to be responsible for EGR3 gene expression in these cells. The inactivity of the 27-bp element in fibroblasts was apparently due to insufficient expression levels of NF-ATp, since overexpression of NF-ATp, but not NF-ATc, restored the two-signal phenotype and CsA sensitivity of EGR3 promoter induction in these cells. The differential usage of an NF-AT binding site explains the selective effect of CsA on EGR3 gene expression in T cells versus fibroblasts and may represent one of the basic mechanisms underlying the tissue specificity of CsA.

A genome-wide functional assay of signal transduction in living mammalian cells

We describe a genome-wide functional assay for rapid isolation of cell clones and genetic elements responsive to specific stimuli. A promoterless beta-lactamase reporter gene was transfected into a human T-cell line to generate a living library of reporter-tagged clones. When loaded with a cell-permeable fluorogenic substrate, the cell library simultaneously reports the expression of a large number of endogenous genes. Flow cytometry was used to recover individual clones whose reporter-tagged genes were either induced or repressed following T-cell activation. Responsive clones were expanded and analyzed pharmacologically to identify patterns of regulation associated with specific genes. Although demonstrated using T cells, the genomic assay could be applied to map downstream transcriptional consequences for any propagating cell line in response to any stimulus of interest.

The early growth response protein (EGR-1) regulates interleukin-2 transcription by synergistic interaction with the nuclear factor of activated T cells

The early growth response-1 gene (EGR-1) is induced by a wide range of stimuli in diverse cell types; however, EGR-1-regulated genes display a highly restricted pattern of expression. Recently, an overlapping Sp1.EGR-1 binding site has been identified within the interleukin-2 (IL-2) gene promoter directly upstream of the binding site for the nuclear factor of activated T cells (NFAT). We used transfection assays to study how the abundantly and constitutively expressed Sp1 protein and the immediate early EGR-1 zinc finger protein regulate IL-2 gene expression. Here, we identify EGR-1 as an important activator of the IL-2 gene. In Jurkat T cells, EGR-1 but not Sp1 acts as a potent coactivator for IL-2 transcription, and in combination with NFATc, EGR-1 increases transcription of an IL-2 reporter construct 200-fold. Electrophoretic mobility shift assays reveal that recombinant EGR-1 and NFATc bind independently to their target sites within the IL-2 promoter, and the presence of both sites on the same DNA molecule is required for EGR-1.NFATc.DNA complex formation. The transcriptional synergy observed here for EGR-1 and NFATc explains how the abundant nuclear factor EGR-1 contributes to the expression of restrictively expressed genes.

Cyclosporin A-sensitive transcription factor Egr-3 regulates Fas ligand expression

Activation-induced transcriptional upregulation of the ligand for Fas (FasL) and the resulting apoptosis of Fas-bearing cells constitute essential steps in a host of normal and pathological processes. Here we describe an activation-inducible cis-acting regulatory element in the fasL promoter that is required for gene expression. Oligonucleotide competition and antibody supershift analyses identified two activation-induced DNA-binding species: Egr-1 (NGFI-A, krox-24, zif268, TIS-8), a transcription factor that has been implicated in growth, differentiation, and apoptosis; and Egr-3 (PILOT), a transcription factor of no previously known function. Activation-induced expression of Egr-3, like that of FasL, was inhibited by cyclosporin A, whereas expression of Egr-1 was unaffected. Transient expression of Egr-3 alone increased fasL promoter activity in a cyclosporin A-insensitive manner, whereas expression of Egr-1 had little effect. Moreover, endogenous fasL mRNA was induced in nonlymphoid cells by forced expression of Egr-3 in the absence of any other stimulus. These studies identify a critical Egr family-binding site in the fasL promoter and demonstrate that activation-induced Egr-3, but not Egr-1, directly upregulates fasL transcription in response to activating stimuli.

Coordinate expression and distinct DNA-binding characteristics of the four EGR-zinc finger proteins in Jurkat T lymphocytes

The Early Growth Response Genes (EGR-1 to AT133/EGR-4) encode a family of proteins that are composed of three homologous consecutive zinc fingers of the Cys2-His2 type and different flanking sequence. Upon growth stimulation of resting cells the four EGR-genes are simultaneously transcribed. We have analyzed the expression of the four EGR-proteins in Jurkat T cells and show by Western blot analysis that the four EGR-proteins are coordinately induced upon treatment with a combination of PHA and PMA. As the individual proteins are reported to bind to identical target sequences, we have analyzed the DNA-binding of the native proteins. Using nuclear extract in which we have demonstrated expression of all four EGR-proteins, only EGR-1, but no other member of this protein family is found to bind to the EGR-consensus site (GCG GGG GCG). In addition, DNA-binding of both native EGR-1 and of recombinant EGR-1 and AT133/EGR-4 proteins expressed in insect cells was analyzed. This comparison revealed distinct binding properties of recombinant EGR-1 and AT133/EGR-4 to oligonucleotides that include the EGR-consensus sites. The distinct binding affinities suggest that in vivo EGR-proteins bind to different target sequences and that each EGR-protein regulates distinct target genes. This is underlined by demonstrating that EGR-1 but not AT133/EGR-4 binds to a related G-rich promoter element with the sequence GGG GTG GGG. This G-rich sequence serves as an overlapping binding site for the two zinc finger proteins EGR-1 and Sp1. As similar overlapping binding sites for EGR-1 and Sp1 have been identified in several human and mouse gene promoters, we raise the question whether the Sp1 binding sites described in a large number of eukaryotic gene promoters also represent binding sites for EGR-1.

Effects of the immunosuppressive drugs CsA and FK506 on intracellular signalling and gene regulation

The isolation of Cyclosporin A (CsA) from cultures of the fungus Tolypocladium inflatum and its subsequent elucidation of immunosuppressive properties by Borel et al. (1) was of great clinical consequence. In the early 80s CsA was introduced in the field of organ transplantation resulting in extraordinary improvements of graft survival. CsA has become a first choice drug for patients with allograft organs. The discovery of FK506 by Kino et al. (2) as a novel immuno-suppressant and its introduction into clinics in 1989 (3) extended the available regimen for immunosuppressive therapy. Yet despite their advantages both CsA and FK506 display unwanted side effects and a possible preference of one drug over another remains controversial (4, 5). Although identification of the involvement of the transcription factor NF-AT was an important step forward (6), it has become clear that immunosuppressant action is more complex. CsA and FK506 selectively interact with certain cellular signal transduction pathways. This review briefly describes these effects on signal transduction. We further concentrate on the major known effect of these immunosuppressants, namely the inhibition of the PP2B phosphatase calcineurin. In addition we provide a compilation of effects of CsA and FK506 on gene expression at the level of transcription.

The human zinc finger protein EGR-4 acts as autoregulatory transcriptional repressor

The human EGR-4 (AT133) gene represents one member of a family of four related zinc finger proteins, that are simultaneously and coordinately induced in resting cells upon growth stimulation. In order to characterise the function of the EGR-4 zinc finger protein, we have expressed the protein in the eukaryotic baculovirus system. The recombinant EGR-4 protein has a molecular mass of 78 kDa, as demonstrated by SDS-PAGE and Western blotting. DNA binding studies revealed that the EGR-4 protein binds to the EGR consensus motif GCGTGGGCG, but not to the G-rich regulatory ZIP-element of the human IL-2 gene, that is a binding site for EGR-1. EGR-4 functions as transcriptional repressor. Overexpression of EGR-4 mediates repression of a minimal c-fos promoter through a threefold EGR consensus site. Furthermore the EGR-4 protein displays autoregulatory activities. This protein downregulates expression of its own gene promoter in a dose dependent manner. A G-rich region in the EGR-4 promoter, located at position -106 to -82, could be identified as binding site for the recombinant EGR-4 protein. A comparison of the two related zinc finger proteins EGR-4 and EGR-1 revealed for each protein distinct and specific DNA binding- and transcriptional regulatory activities.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

Rational primer design greatly improves differential display-PCR (DD-PCR)

Since its conception in 1992, differential display PCR (DD-PCR) has attracted widespread interest. Theoretically an attractive cloning approach, it combines the comparative analysis of several samples with the sensitivity of PCR. Although a large number of studies embracing this technology have been initiated, few novel genes of interest have been identified, suggesting that the method has not realised its potential. The present report shows that by modifying primer design, sampling of differentially expressed genes can be greatly enhanced and relevant genes can be isolated. Using our modified conditions DD-PCR efficiently screens a wide range of gene expression levels, in which differences are represented on a linear scale.

Purification, structural analysis, and function of natural ATAC, a cytokine secreted by CD8(+) T cells

Recently, we identified a novel putative human cytokine expressed by activated CD8(+) T cells, which was designated ATAC (activation-induced, T cell-derived, and chemokine-related; the same molecule has been identified independently as lymphotactin and single cysteine motif-1). In this report, we provide evidence that ATAC is a secreted 93-amino acid protein that is generated from its precursor by proteolytic cleavage between Gly21 and Val22. An estimated 60% of ATAC (Val22-Gly114) is secreted as an unmodified protein with a molecular mass of 10,271.72 Da (apparent molecular mass of 12 kDa in SDS-polyacrylamide gel electrophoresis) and in which Cys32 and Cys69 are linked by a disulfide bridge. Unmodified ATAC is a cationic protein with a pI of 11.35 and is capable of binding to heparin. Some 40% of ATAC is O-glycosylated within 25 min of synthesis, giving rise to the appearance of a homogeneous 15-kDa (minor fraction) and a heterogeneous, terminally sialylated 17-19-kDa (major fraction) protein species in SDS-polyacrylamide gel electrophoresis. The secretion of all ATAC protein variants is completed within 30-40 min of synthesis. In terms of function, various ATAC protein forms were consistently ineffective in chemotaxis assays. In contrast, both purified natural ATAC and a chemically synthesized aglycosyl analog induced locomotion (chemokinesis) in purified CD4(+) and CD8(+) T cell populations at 400 ng/ml.

Induction of the early growth response (Egr) family of transcription factors during thymic selection

There is little known about the regulation of gene expression during TCR-mediated differentiation of immature CD4+8+ (double positive) thymocytes into mature T cells. Using the DPK CD4+8+ thymocyte precursor cell line, we demonstrate that the early growth response-1 gene (Erg-1), encoding a zinc finger transcription factor, is rapidly upregulated after TCR stimulation. We also report that Egr-1 is expressed by a subset of normal double positive thymocytes in the thymic cortex, as well by a majority of medullary single positive thymocytes. Expression of Egr-1 is dramatically reduced in the thymus of major histocompatibility complex knockout mice, but can be induced by anti-CD3 antibody stimulation of isolated thymocytes from these animals. These and other data suggest that high level expression of Egr-1 in the thymus is a consequence of selection. A similar pattern of expression is found for family members Egr-2 and Egr-3. Using the DPK cell line, we also demonstrate that expression of Egr-1, 2, and 3 is dependent upon ras activation, as is the initiation of differentiation to a single positive cell. In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1. The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

A regulatory element in the human interleukin 2 gene promoter is a binding site for the zinc finger proteins Sp1 and EGR-1

Activation of the interleukin 2 (IL-2) gene after antigen recognition is a critical event for T cell proliferation and effector function. Prior studies have identified several transcription factors that contribute to the activity of the IL-2 promoter in stimulated T lymphocytes. Here we describe a novel regulatory element within the IL-2 promoter located immediately upstream of the nuclear factor of activated T cell (NFAT) domain. This region (termed the zinc finger protein binding region (ZIP)) serves as binding site for two differently regulated zinc finger proteins: the constitutively expressed transcription factor Sp1 and the inducible early growth response protein EGR-1. In unstimulated cells which do not secrete IL-2, only Sp1 binds to this region, while in stimulated IL-2 secreting cells the inducible EGR-1 protein recognizes this element. In Jurkat T cells, the ZIP site serves as an activator for IL-2 gene expression, and a combination of ZIP and NFAT binding sites is required for maximal IL-2 promoter activity. These results suggest a critical role of the ZIP site for IL-2 promoter activity.

Cloning of ATAC, an activation-induced, chemokine-related molecule exclusively expressed in CD8+ T lymphocytes

A cDNA clone, designated ATAC, was isolated from a collection of human T cell activation genes. Analysis of tissue distribution determined that ATAC mRNA of approximately 0.9 kb is exclusively expressed in activated CD8+ T cells. Induction of the ATAC gene requires stimulation by both phorbol 12-myristate 13-acetate and Ca2+ ionophore A23187 ("two-signal gene") and is fully abrogated by the immunosuppressive agent cyclosporin A. Upon stimulation, ATAC mRNA is detectable within 30 min, maximal expression is seen after 4 h. The polypeptide encoded by the open reading frame of ATAC mRNA is 114 amino acids long with a calculated M(r) of 12.52 kDa. The structural features predict the cleavage and secretion of a mature ATAC protein of approximately 10 kDa from the 12.52-kDa precursor. ATAC is highly similar to a very recently identified murine molecule designated lymphotactin both at the cDNA (73.8% identity) and the protein (61.4% identity) levels, and related to members of the C-C and C-X-C chemokine families. Two variants of the ATAC protein were expressed and tested for chemotaxis and Ca2+ release on a variety of target cells. The ATAC gene was located to chromosome 1q23.

Egr3/Pilot, a zinc finger transcription factor, is rapidly regulated by activity in brain neurons and colocalizes with Egr1/zif268

Programs of gene activation may underlie long-term adaptive cellular responses to extracellular ligands. We have used a differential cDNA cloning strategy to identify genes that are strongly induced by excitatory stimuli in the adult rat hippocampus. Here, we report the rat cDNA sequence of a zinc-finger transcription factor, Egr3/Pilot, and characterize its regulated mRNA expression in brain. Egr3 mRNA is rapidly and transiently induced in neurons of the hippocampus and cortex by electroconvulsive seizure. mRNA levels peak 2 hr after the seizure and remain elevated for as long as 8 hr. Egr3 mRNA is also rapidly induced in granule cells of the dentate gyrus by synaptic NMDA receptor activation elicited by patterned stimulation of the perforant pathway and by drugs that alter dopamine neurotransmission in the striatum. Basal levels of Egr3 mRNA in the cortex appear to be driven by natural synaptic activity because monocular deprivation rapidly decreases Egr3 mRNA in the deafferented visual cortex. Aspects of the protein structure, sequence-specific DNA binding, transcriptional activity, and regulation of Egr3 are highly similar to another zinc-finger transcription factor, Egr1/zif268. Moreover, we demonstrate colocalization of Egr3 and zif268 mRNAs in neurons of normal and stimulated cortex. Our studies suggest that interactions between these coregulated transcription factors may be important in defining long-term, neuroplastic responses.

Defective expression of CD40 ligand on T cells causes "X-linked immunodeficiency with hyper-IgM (HIGM1)"

X-linked immunodeficiency with hyper-IgM (HIGM1) is a rare disorder, characterized by recurrent infections associated with very low or absent IgG and IgA, and normal to increased IgM serum levels. The disease has been earlier mapped to the q26-27 region of the X-chromosome. We have identified a novel molecule expressed on the surface of activated T cells, which was designated TRAP (Tumor necrosis factor Related Activation Protein), and could demonstrate that TRAP is a ligand for the CD40 receptor expressed on B cells. Our mapping of the TRAP gene to the Xq26.3-27.1 region suggested a causal relationship to HIGM1. Further work revealed that various mutations of the TRAP/CD40 ligand (CD40L) gene may lead to a defective expression of the TRAP/CD40L molecule on the T-cell surface in HIGM1 patients. A combination of structural and functional analyses finally demonstrated that the failure of TRAP/CD40L on T cells to interact with CD40 on B cells is responsible for the inefficient T-cell help for B cells observed in HIGM1. The observations made in HIGM1 allowed us to conclude that TRAP/CD40L is not required for IgM synthesis. In contrast, functional expression of TRAP is a prerequisite for effective immunoglobulin isotype switching and subsequent production of IgG, IgA and IgE by B cells in vivo. The interaction of TRAP/CD40L with CD40 thus provides a very critical link between the cellular and the humoral part of the immune system. The knowledge of TRAP/CD40L cDNA sequence, the availability of various reagents for the testing of expression and function of TRAP/CD40L, and our recent elucidation of the exon-intron structure of the TRAP/CD40L gene now provide all necessary tools for early diagnosis of affected patients and the detection of female carriers of HIGM1. The available information will also provide a basis for future attempts at gene therapy in this disease.