IL-2 and long-term T cell activation induce physical and functional interaction between STAT5 and ETS transcription factors in human T cells

ETS1 Function in Leukemia and Lymphoma

ETS proto-oncogene 1 (ETS1) is a transcription factor (TF) critically involved in lymphoid cell development and function. ETS1 expression is tightly regulated throughout differentiation and activation in T-cells, natural killer (NK) cells, and B-cells. It has also been described as an oncogene in a range of solid and hematologic cancer types. Among hematologic malignancies, its role has been best studied in T-cell acute lymphoblastic leukemia (T-ALL), adult T-cell leukemia/lymphoma (ATLL), and diffuse large B-cell lymphoma (DLBCL). Aberrant expression of ETS1 in these malignancies is driven primarily by chromosomal amplification and enhancer-driven transcriptional regulation, promoting the ETS1 transcriptional program. ETS1 also facilitates aberrantly expressed or activated transcriptional complexes to drive oncogenic pathways. Collectively, ETS1 functions to regulate cell growth, differentiation, signaling, response to stimuli, and viral interactions in these malignancies. A tumor suppressor role has also been indicated for ETS1 in select lymphoma types, emphasizing the importance of cellular context in ETS1 function. Research is ongoing to further characterize the clinical implications of ETS1 dysregulation in hematologic malignancies, to further resolve binding complexes and transcriptional targets, and to identify effective therapeutic targeting approaches.

Distinct use of super-enhancer elements controls cell type-specific CD25 transcription and function

The IL-2 receptor α chain (IL-2Rα/CD25) is constitutively expressed on double-negative (DN2/DN3 thymocytes and regulatory T cells (Tregs) but induced by IL-2 on T and natural killer (NK) cells, with Il2ra expression regulated by a STAT5-dependent super-enhancer. We investigated CD25 regulation and function using a series of mice with deletions spanning STAT5-binding elements. Deleting the upstream super-enhancer region mainly affected constitutive CD25 expression on DN2/DN3 thymocytes and Tregs, with these mice developing autoimmune alopecia, whereas deleting an intronic region decreased IL-2-induced CD25 on peripheral T and NK cells. Thus, distinct super-enhancer elements preferentially control constitutive versus inducible expression in a cell type-specific manner. The mediator-1 coactivator colocalized with specific STAT5-binding sites. Moreover, both upstream and intronic regions had extensive chromatin interactions, and deletion of either region altered the super-enhancer structure in mature T cells. These results demonstrate differential functions for distinct super-enhancer elements, thereby indicating previously unknown ways to manipulate CD25 expression in a cell type-specific fashion.

Batf stabilizes Th17 cell development via impaired Stat5 recruitment of Ets1-Runx1 complexes

Although the activator protein-1 (AP-1) factor Batf is required for Th17 cell development, its mechanisms of action to underpin the Th17 program are incompletely understood. Here, we find that Batf ensures Th17 cell identity in part by restricting alternative gene programs through its actions to restrain IL-2 expression and IL-2-induced Stat5 activation. This, in turn, limits Stat5-dependent recruitment of Ets1-Runx1 factors to Th1- and Treg-cell-specific gene loci. Thus, in addition to pioneering regulatory elements in Th17-specific loci, Batf acts indirectly to inhibit the assembly of a Stat5-Ets1-Runx1 complex that enhances the transcription of Th1- and Treg-cell-specific genes. These findings unveil an important role for Stat5-Ets1-Runx1 interactions in transcriptional networks that define alternate T cell fates and indicate that Batf plays an indispensable role in both inducing and maintaining the Th17 program through its actions to regulate the competing actions of Stat5-assembled enhanceosomes that promote Th1- and Treg-cell developmental programs.

Transcriptional Regulation of Natural Killer Cell Development and Functions

Natural killer (NK) cells are the major lymphocyte subset of the innate immune system. Their ability to mediate anti-tumor cytotoxicity and produce cytokines is well-established. However, the molecular mechanisms associated with the development of human or murine NK cells are not fully understood. Knowledge is being gained about the environmental cues, the receptors that sense the cues, signaling pathways, and the transcriptional programs responsible for the development of NK cells. Specifically, a complex network of transcription factors (TFs) following microenvironmental stimuli coordinate the development and maturation of NK cells. Multiple TFs are involved in the development of NK cells in a stage-specific manner. In this review, we summarize the recent advances in the understandings of TFs involved in the regulation of NK cell development, maturation, and effector function, in the aspects of their mechanisms, potential targets, and functions.

Different chromatin and DNA sequence characteristics define glucocorticoid receptor binding sites that are blocked or not blocked by coregulator Hic-5

The glucocorticoid receptor (GR) regulates genes in many physiological pathways by binding to enhancer and silencer elements of target genes, where it recruits coregulator proteins that remodel chromatin and regulate the assembly of transcription complexes. The coregulator Hydrogen peroxide-inducible clone 5 (Hic-5) is necessary for glucocorticoid (GC) regulation of one group of GR target genes, is irrelevant for a second group, and inhibits GR binding to a third gene set, thereby blocking their regulation by GC. Gene-specific characteristics that distinguish GR binding regions (GBR) at Hic-5 blocked genes from GBR at other GC-regulated genes are unknown. Here we show genome-wide that blocked GBR generally require CHD9 and BRM for GR occupancy in contrast to GBR that are not blocked by Hic-5. Hic-5 blocked GBR are enriched near Hic-5 blocked GR target genes but not near GR target genes that are not blocked by Hic-5. Furthermore blocked GBR are in a closed conformation prior to Hic-5 depletion, and require Hic-5 depletion and glucocorticoid treatment to create an open conformation necessary for GR occupancy. A transcription factor binding motif characteristic of the ETS family was enriched near blocked GBR and blocked genes but not near non-blocked GBR or non-blocked GR target genes. Thus, we identify specific differences in chromatin conformation, chromatin remodeler requirements, and local DNA sequence motifs that contribute to gene-specific actions of transcription factors and coregulators. These findings shed light on mechanisms that contribute to binding site selection by transcription factors, which vary in a cell type-specific manner.

Whole-genome DNA methylation status associated with clinical PTSD measures of OIF/OEF veterans

Emerging knowledge suggests that post-traumatic stress disorder (PTSD) pathophysiology is linked to the patients' epigenetic changes, but comprehensive studies examining genome-wide methylation have not been performed. In this study, we examined genome-wide DNA methylation in peripheral whole blood in combat veterans with and without PTSD to ascertain differentially methylated probes. Discovery was initially made in a training sample comprising 48 male Operation Enduring Freedom (OEF)/Operation Iraqi Freedom (OIF) veterans with PTSD and 51 age/ethnicity/gender-matched combat-exposed PTSD-negative controls. Agilent whole-genome array detected ~5600 differentially methylated CpG islands (CpGI) annotated to ~2800 differently methylated genes (DMGs). The majority (84.5%) of these CpGIs were hypermethylated in the PTSD cases. Functional analysis was performed using the DMGs encoding the promoter-bound CpGIs to identify networks related to PTSD. The identified networks were further validated by an independent test set comprising 31 PTSD+/29 PTSD- veterans. Targeted bisulfite sequencing was also used to confirm the methylation status of 20 DMGs shown to be highly perturbed in the training set. To improve the statistical power and mitigate the assay bias and batch effects, a union set combining both training and test set was assayed using a different platform from Illumina. The pathways curated from this analysis confirmed 65% of the pool of pathways mined from training and test sets. The results highlight the importance of assay methodology and use of independent samples for discovery and validation of differentially methylated genes mined from whole blood. Nonetheless, the current study demonstrates that several important epigenetically altered networks may distinguish combat-exposed veterans with and without PTSD.

The dual role of LSD1 and HDAC3 in STAT5-dependent transcription is determined by protein interactions, binding affinities, motifs and genomic positions

STAT5 interacts with other factors to control transcription, and the mechanism of regulation is of interest as constitutive active STAT5 has been reported in malignancies. Here, LSD1 and HDAC3 were identified as novel STAT5a interacting partners in pro-B cells. Characterization of STAT5a, LSD1 and HDAC3 target genes by ChIP-seq and RNA-seq revealed gene subsets regulated by independent or combined action of the factors and LSD1/HDAC3 to play dual role in their activation or repression. Genes bound by STAT5a alone or in combination with weakly associated LSD1 or HDAC3 were enriched for the canonical STAT5a GAS motif, and such binding induced activation or repression. Strong STAT5 binding was seen more frequently in intergenic regions, which might function as distal enhancer elements. Groups of genes bound weaker by STAT5a and stronger by LSD1/HDAC3 showed an absence of the GAS motif, and were differentially regulated based on their genomic binding localization and binding affinities. These genes exhibited increased binding frequency in promoters, and in conjunction with the absence of GAS sites, the data indicate a requirement for stabilization by additional factors, which might recruit LSD1/HDAC3. Our study describes an interaction network of STAT5a/LSD1/HDAC3 and a dual function of LSD1/HDAC3 on STAT5-dependent transcription, defined by protein–protein interactions, genomic binding localization/affinity and motifs.

The role of the transcription factor Ets1 in carcinoma

Ets1 belongs to the large family of the ETS domain family of transcription factors and is involved in cancer progression. In most carcinomas, Ets1 expression is linked to poor survival. In breast cancer, Ets1 is primarily expressed in the triple-negative subtype, which is associated with unfavorable prognosis. Ets1 contributes to the acquisition of cancer cell invasiveness, to EMT (epithelial-to-mesenchymal transition), to the development of drug resistance and neo-angiogenesis. The aim of this review is to summarize the current knowledge on the functions of Ets1 in carcinoma progression and on the mechanisms that regulate Ets1 activity in cancer.

The Ets-1 transcription factor is required for Stat1-mediated T-bet expression and IgG2a class switching in mouse B cells

In response to antigens and cytokines, mouse B cells undergo class-switch recombination (CSR) and differentiate into Ig-secreting cells. T-bet, a T-box transcription factor that is up-regulated in lymphocytes by IFN-γ or IL-27, was shown to regulate CSR to IgG2a after T cell-independent B-cell stimulations. However, the molecular mechanisms controlling this process remain unclear. In the present study, we show that inactivation of the Ets-1 transcription factor results in a severe decrease in IgG2a secretion in vivo and in vitro. No T-bet expression was observed in Ets-1-deficient (Ets-1(-/-)) B cells stimulated with IFN-γ and lipopolysaccharide, and forced expression of T-bet in these cells rescued IgG2a secretion. Furthermore, we identified a transcriptional enhancer in the T-bet locus with an activity in B cells that relies on ETS-binding sites. After IFN-γ stimulation of Ets-1(-/-) B cells, activated Stat1, which forms a complex with Ets-1 in wild-type cells, no longer binds to the T-bet enhancer or promotes histone modifications at this site. These results demonstrate that Ets-1 is critical for IgG2a CSR and acts as an essential cofactor for Stat1 in the regulation of T-bet expression in B cells.

The Ets-1 transcription factor controls the development and function of natural regulatory T cells

Regulatory T cells (T reg cells) constitute a population of CD4(+) T cells that limits immune responses. The transcription factor Foxp3 is important for determining the development and function of T reg cells; however, the molecular mechanisms that trigger and maintain its expression remain incompletely understood. In this study, we show that mice deficient for the Ets-1 transcription factor (Ets-1(-/-)) developed T cell-mediated splenomegaly and systemic autoimmunity that can be blocked by functional wild-type T reg cells. Spleens of Ets-1(-/-) mice contained mostly activated T cells, including Th2-polarized CD4(+) cells and had reduced percentages of T reg cells. Splenic and thymic Ets-1(-/-) T reg cells expressed low levels of Foxp3 and displayed the CD103 marker that characterizes antigen-experienced T reg cells. Thymic development of Ets-1(-/-) T reg cells appeared intrinsically altered as Foxp3-expressing cells differentiate poorly in mixed fetal liver reconstituted chimera and fetal thymic organ culture. Ets-1(-/-) T reg cells showed decreased in vitro suppression activity and did not protect Rag2(-/-) hosts from naive T cell-induced inflammatory bowel disease. Furthermore, in T reg cells, Ets-1 interacted with the Foxp3 intronic enhancer and was required for demethylation of this regulatory sequence. These data demonstrate that Ets-1 is required for the development of natural T reg cells and suggest a role for this transcription factor in the regulation of Foxp3 expression.

Functional cooperation between Stat-1 and ets-1 to optimize icam-1 gene transcription

Intercellular adhesion molecule-1 (ICAM-1) plays an important role in the immune system, enabling the interactions between effector cells and target cells. It is also known to be involved in tumor growth and metastasis. Its expression is transcriptionally regulated by several proinflammatory cytokines including IFN-gamma, which induces ICAM-1 transcription via the JAK-STAT signaling pathway in a Stat1-dependent fashion. The ICAM-1 promoter contains several cis-active regulatory elements including 2 Ets binding sites (EBSs) located at positions -158 and -138 relatively to the AUG, which were previously shown to play a role in the constitutive activity of the ICAM-1 promoter. In the present study, we have determined whether the EBSs are also involved in the regulation of ICAM-1 gene transcription by pro-inflammatory cytokines. Transient transfection assays were performed with reporter genes containing ICAM-1 promoter constructions cloned upstream from the firefly luciferase gene. Site-specific mutations of the EBS diminished the promoter activity stimulated by IFN-gamma, although the IFN-gamma responsive element (pIgammaRE), which binds Stat1, was intact. Stimulation of the transcriptional activity following IFN-gamma treatment was significantly reduced when both EBSs were inactivated. Co-immunoprecipitation experiments provided evidence of a physical interaction involving Ets1 and Stat1. In COS-1 and HEK 293 cells cotransfected with CFP-Stat1 and YFP-Ets fusion protein, fluorescence resonance energy transfer experiments confirmed the close proximity of these 2 proteins in living cells following treatment with IFN-gamma.

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.

Ets-1 is a negative regulator of Th17 differentiation

IL-17 is a proinflammatory cytokine that plays a role in the clearance of extracellular bacteria and contributes to the pathology of many autoimmune and allergic conditions. IL-17 is produced mainly by a newly characterized subset of T helper (Th) cells termed Th17. Although the role of Th17 cells in the pathology of autoimmune diseases is well established, the transcription factors regulating the differentiation of Th17 cells remain poorly characterized. We report that Ets-1–deficient Th cells differentiated more efficiently to Th17 cells than wild-type cells. This was attributed to both low IL-2 production and increased resistance to the inhibitory effect of IL-2 on Th17 differentiation. The resistance to IL-2 suppression was caused by a defect downstream of STAT5 phosphorylation, but was not caused by a difference in the level of RORγt. Furthermore, Ets-1–deficient mice contained an abnormally high level of IL-17 transcripts in their lungs and exhibited increased mucus production by airway epithelial cells in an IL-17–dependent manner. Based on these observations, we report that Ets-1 is a negative regulator of Th17 differentiation.

Characterization of an enhancer region of the galanin gene that directs expression to the dorsal root ganglion and confers responsiveness to axotomy

Galanin expression markedly increases in the dorsal root ganglion (DRG) after sciatic nerve axotomy and modulates pain behavior and regeneration of sensory neurons. Here, we describe transgenic mice expressing constructs with varying amounts of sequence upstream of the murine galanin gene marked by LacZ. The 20 kb region upstream of the galanin gene recapitulates the endogenous expression pattern of galanin in the embryonic and adult intact DRG and after axotomy. In contrast, 1.9 kb failed to drive LacZ expression in the intact DRG or after axotomy. However, the addition of an additional 2.7 kb of 5' flanking DNA (4.6 kb construct) restored the expression in the embryonic DRG and in the adult after axotomy. Sequence analysis of this 2.7 kb region revealed unique 18 and 23 bp regions containing overlapping putative Ets-, Stat-, and Smad-binding sites, and adjacent putative Stat- and Smad-binding sites, respectively. Deletion of the 18 and 23 bp regions from the 4.6 kb construct abolished the upregulation of LacZ expression in the DRG after axotomy but did not affect expression in the embryonic or intact adult DRG. Also, a bioinformatic analysis of the upstream regions of a number of other axotomy-responsive genes demonstrated that the close proximity of putative Ets-, Stat-, and Smad-binding sites appears to be a common motif in injury-induced upregulation in gene expression.

PTHrP P3 promoter activity in breast cancer cell lines: role of Ets1 and CBP (CREB binding protein)

Parathyroid hormone-related protein (PTHrP) is produced by many tumors including breast cancer. We have reported that Ets1 factor activates P3 PTHrP promoter in our model of tumorigenic breast cancer cell and not in pre- or non-tumorigenic cell lines, thus contributing to an increased PTHrP production. In this study, gel retardation assays revealed that Etsl and its promoter binding site (EBS) specifically formed complexes whose abundance correlates with Ets1 levels in the three cell lines. Coexpression of Etsl and CBP induced a synergistic activation of the P3 promoter only in the tumorigenic cell line. This synergism required the integrity of the EBS and was abrogated by E1A. All breast cancer cell lines showed high basal concentrations of phosphorylated CREB. Moreover a CRE-like sequence was also required for Ets1/CBP synergy and, finally, CREB expression was found to enhance the PTHrP P3 promoter activity. Thus a multipartite complex of transcription factors and coactivators seems to regulate PTHrP transcription and contribute to the alterations that promote tumorigenic behavior in breast epithelial cells.

A role for mitogen-activated protein kinase and Ets-1 in the induction of interleukin-10 transcription by human immunodeficiency virus-1 Tat

The human immunodeficiency virus (HIV) Tat protein has multiple regulatory roles, including trans-activation of the HIV genome and regulation of immune signalling processes, including kinase activation and cytokine expression. We recently demonstrated that HIV-1 Tat induces the expression of interleukin (IL)-10 via p38 mitogen-activated protein kinase (MAPK) activation. We further delineated that the Tat-responsive element of the IL-10 promoter was located within 625 to 595 bp upstream from the transcription start site. Using electrophoretic mobility shift assays, the transcription factors Ets-1 and Sp-1 were shown to bind to the IL-10 promoter to activate transcription of the gene. Furthermore, sequential deletional mutations of the Ets-1- and Sp-1-binding sites in the -625/-595 region reduced the DNA binding and transcription activity of the IL-10 promoter. Our results also showed that both the Tat-induced and Ets-1-regulated IL-10 promoter-driven luciferase activity can be abrogated by inhibitors of the p38 MAPK activity. In conclusion, the coordinated activities of p38 MAPK and the transcription factors, Ets-1 and Sp-1, may play an important role in the HIV-1 Tat-induced IL-10 transcription.

Alveolar and lactogenic differentiation

The mouse mammary gland is a complex tissue that proliferates and differentiates under the control of systemic hormones during puberty, pregnancy and lactation. Once a highly branched milk duct system has been established, during mid/late pregnancy, alveoli, little saccular outpouchings, sprout all over the ductal system and differentiate to become the sites of milk secretion. Here, we review the emerging network of the signaling pathways that connects hormonal stimuli with locally produced signaling molecules and the components of intracellular pathways that regulate alveologenesis and lactation. The powerful tools of mouse genetics have been instrumental in uncovering many of the signaling components involved in controlling alveolar and lactogenic differentiation.

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.

Erm/thyroid transcription factor 1 interactions modulate surfactant protein C transcription

Expression of surfactant protein C (SP-C), which is restricted to alveolar type II epithelial cells of the adult lung, is critically dependent on thyroid transcription factor 1 (TTF-1). In the present study we have demonstrated that Erm, a member of the Ets family of transcription factors, is expressed in the distal lung epithelium during development and is also restricted to alveolar type II cells in the adult. Erm was up-regulated by fibroblast growth factors (FGFs) in culture, and blocking FGF signaling inhibited Erm expression both in vivo and in vitro. The SP-C minimal promoter was found to contain two potential Ets binding sites, and electrophoretic mobility shift assays showed that two 20-bp wild-type oligonucleotides containing the 5'-GGA(A/T)-3' Ets consensus binding motif were shifted by nuclear extracts from MLE15 cells. Co-transfection assays showed that Erm by itself had little effect on SP-C promoter activity but that Erm significantly enhanced TTF-1-mediated SP-C transcription. Mutation of one of the Ets binding sites reduced SP-C transcription to background levels, whereas mutation of the other site resulted in increased SP-C transcription. Protein-protein interactions between Erm and TTF-1 were demonstrated by mammalian two-hybrid assays and by co-immunoprecipitation assays. Mapping studies showed that the Ets domain of Erm and the combined N terminus and homeodomain of TTF-1 were critical for this interaction. Treatment of primary cultures of adult alveolar type II cells with siRNA targeting Erm diminished expression of both Erm and SP-C but had no effect on beta-actin or GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Taken together, these results demonstrate that Erm is involved in SP-C regulation, which results from an interaction with TTF-1.

Convergence of protein kinase C and JAK-STAT signaling on transcription factor GATA-4

Angiotensin II (AII), a potent vasoactive hormone, acts on numerous organs via G-protein-coupled receptors and elicits cell-specific responses. At the level of the heart, AII stimulation alters gene transcription and leads to cardiomyocyte hypertrophy. Numerous intracellular signaling pathways are activated in this process; however, which of these directly link receptor activation to transcriptional regulation remains undefined. We used the atrial natriuretic factor (ANF) gene (NPPA) as a marker to elucidate the signaling cascades involved in AII transcriptional responses. We show that ANF transcription is activated directly by the AII type 1 receptor and precedes the development of myocyte hypertrophy. This response maps to STAT and GATA binding sites, and the two elements transcriptionally cooperate to mediate signaling through the JAK-STAT and protein kinase C (PKC)-GATA-4 pathways. PKC phosphorylation enhances GATA-4 DNA binding activity, and STAT-1 functionally and physically interacts with GATA-4 to synergistically activate AII and other growth factor-inducible promoters. Moreover, GATA factors are able to recruit STAT proteins to target promoters via GATA binding sites, which are sufficient to support synergy. Thus, STAT proteins can act as growth factor-inducible coactivators of tissue-specific transcription factors. Interactions between STAT and GATA proteins may provide a general paradigm for understanding cell specificity of cytokine and growth factor signaling.

Ets-1, a functional cofactor of T-bet, is essential for Th1 inflammatory responses

To mount an effective type 1 immune response, type 1 T helper (Th1) cells must produce inflammatory cytokines and simultaneously suppress the expression of antiinflammatory cytokines. How these two processes are coordinately regulated at the molecular level is still unclear. In this paper, we show that the proto-oncogene E26 transformation-specific-1 (Ets-1) is necessary for T-bet to promote interferon-gamma production and that Ets-1 is essential for mounting effective Th1 inflammatory responses in vivo. In addition, Ets-1-deficient Th1 cells also produce a very high level of interleukin 10. Thus, Ets-1 plays a crucial and unique role in the reciprocal regulation of inflammatory and antiinflammatory Th responses.

STAT6 and Ets-1 Form a Stable Complex That Modulates Socs-1 Expression by Interleukin-4 in Keratinocytes

Supressor of cytokine signaling (SOCS)-1 is selectively and rapidly induced by appropriate agonists and modulates cytokine responses by interfering with the Janus kinase/signal transducer and activator of transcription (Jak/STAT) pathway. On the basis of the observation that interleukin (IL)-4 up-regulates Socs-1 in the keratinocyte HaCaT cell line, we investigated which sequences of the 5'-Socs-1 gene are responsive to IL-4. We therefore have cloned the 5'-flanking region of this gene, and by promoter analysis we identified a functional IL-4-responsive element located at nucleotide (-684/-570) upstream from the transcription initiation site, whose presence and integrity are necessary to ensure IL-4 responsiveness. This element contains three STAT6 and one Ets consensus binding sequences of which specific mutations abolished IL-4 responsiveness either partially or totally. We also report that Ets-1 physically interacted with STAT6. Exogenous expression of Ets-1 in conjunction with STAT6 activation strongly inhibited expression of a Socs-1 promoter-luciferase reporter. Collectively, our data demonstrated the involvement of STAT6 and Ets, via a composite DNA element, in the IL-4 regulation of Socs-1 gene expression in keratinocytes.

Human CD94 gene expression: dual promoters differing in responsiveness to IL-2 or IL-15

CD94 is a C-type lectin required for the dimerization of the CD94/NKG2 family of receptors, which are expressed on NK cells and T cell subsets. Little is known about CD94 gene expression and the elements that regulate CD94 transcription. In this study, we report that CD94 gene expression is regulated by distal and proximal promoters that transcribe unique initial exons specific to each promoter. This results in two species of transcripts; the previously described CD94 mRNA and a novel CD94C mRNA. All NK cells and CD94(+), CD8(+) alphabeta T cells transcribe CD94 mRNA. Stimulation of NK and CD8(+) alphabeta T cells with IL-2 or IL-15 induced the transcription of CD94C mRNA. The distal and proximal promoters both contain elements with IFN-gamma-activated and Ets binding sites, known as GAS/EBS. Additionally, an unknown element, termed site A, was identified in the proximal promoter. EMSA analyses showed that constitutive factors could bind to oligonucleotide probes containing each element. After treatment of primary NK cells with IL-2 or IL-15, separate inducible complexes could be detected with oligonucleotide probes containing either the proximal or distal GAS/EBS elements. These elements are highly conserved between mice and humans, which suggests that both species regulate CD94 gene expression via mechanisms that predate their evolutionary divergence.

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CD28-dependent HIV-1 transcription is associated with Vav, Rac, and NF-kappa B activation

Activation of HIV-1-infected T cells through the T cell receptor and costimulatory molecule CD28 induces proviral transcription; however, the mechanism behind this enhanced virus expression is unknown. Jurkat T cells and primary CD4+ T cells expressing a CD8 alpha/CD28 chimeric receptor containing a mutation at tyrosine 200 in the cytoplasmic tail were unable to fully induce HIV-1 proviral transcription in response to CD8 alpha/28 receptor cross-linking in comparison to CD28 costimulation. The loss of transactivation seen with the mutant chimeric receptor correlated with a decrease in Vav tyrosine phosphorylation. CD28-dependent activation of HIV-1 transcription also required the GTPase activity of Rac1, which was not activated during costimulation with the mutated receptor. Furthermore, the mutated receptor was unable to induce NF-kappa B DNA binding or transactivation, as demonstrated by electromobility shift assays and HIV-1 long terminal repeat and NF-kappa B-dependent reporter constructs. These studies show that signaling events initiated by tyrosine 200 of CD28 are required for efficient expression of HIV-1 transcription in activated T cells.

The biology of the Ets1 proto-oncogene

The Ets1 proto-oncoprotein is a member of the Ets family of transcription factors that share a unique DNA binding domain, the Ets domain. The DNA binding activity of Ets1 is controlled by kinases and transcription factors. Some transcription factors, such as AML-1, regulate Ets1 by targeting its autoinhibitory module. Others, such as Pax-5, alter Ets1 DNA binding properties. Ets1 harbors two phosphorylation sites, threonine-38 and an array of serines within the exon VII domain. Phosphorylation of threonine-38 by ERK1/2 activates Ets1, whereas phosphorylation of the exon VII domain by CaMKII or MLCK inhibits Ets1 DNA binding activity. Ets1 is expressed by numerous cell types. In haemotopoietic cells, it contributes to the regulation of cellular differentiation. In a variety of other cells, including endothelial cells, vascular smooth muscle cells and epithelial cancer cells, Ets1 promotes invasive behavior. Regulation of MMP1, MMP3, MMP9 and uPA as well as of VEGF and VEGF receptor gene expression has been ascribed to Ets1. In tumors, Ets1 expression is indicative of poorer prognosis.

Molecular biology of the Ets family of transcription factors

The Ets family of transcription factors characterized by an evolutionarily-conserved DNA-binding domain regulates expression of a variety of viral and cellular genes by binding to a purine-rich GGAA/T core sequence in cooperation with other transcriptional factors and co-factors. Most Ets family proteins are nuclear targets for activation of Ras-MAP kinase signaling pathway and some of them affect proliferation of cells by regulating the immediate early response genes and other growth-related genes. Some of them also regulate apoptosis-related genes. Several Ets family proteins are preferentially expressed in specific cell lineages and are involved in their development and differentiation by increasing the enhancer or promoter activities of the genes encoding growth factor receptors and integrin families specific for the cell lineages. Many Ets family proteins also modulate gene expression through protein-protein interactions with other cellular partners. Deregulated expression or formation of chimeric fusion proteins of Ets family due to proviral insertion or chromosome translocation is associated with leukemias and specific types of solid tumors. Several Ets family proteins also participate in malignancy of tumor cells including invasion and metastasis by activating the transcription of several protease genes and angiogenesis-related genes.

Role of Ets-1 in transcriptional regulation of transferrin receptor and erythroid differentiation

High expression of transferrin receptor (TfR) on the membrane of erythroid cells accounts for the high level of iron required to sustain heme synthesis. Several studies indicate that during erythroid differentiation TfR expression is highly dependent on transcriptional regulation. In this study we characterized the minimal region able to confer transcriptional regulation during erythroid differentiation in Friend leukemia cells (FLC). This region of 120 bp, upstream the transcription start site, contains an overlapping consensus recognition sequence for AP1/CREB/ATF transcription factors and for proteins of the Ets family and a GC rich region. Here, we report that both the Ets and the Ap1/CRE like sites are essential for promoter activity during erythroid differentiation. We showed that Ets-1 binds to the EBS-TfR and its binding activity decreases in FLC induced to differentiate and during normal erythroid differentiation. Consistent with this, FLC constitutively expressing Ets-1 show a decrease in TfR gene expression, globin mRNA and hemoglobin synthesis. We conclude that Ets-1 binding activity is modulated during erythroid maturation and that a deregulated expression of this transcription factor interferes with terminal erythroid differentiation.

Recruitment of phosphatidylinositol 3-kinase to CD28 inhibits HIV transcription by a Tat-dependent mechanism

Activation through the TCR and the costimulatory molecule CD28 influences the susceptibility of T cells to HIV-1 infection and regulates proviral gene expression. Signaling events initiated by CD28 that directly impact HIV-1 transcription have not been fully characterized. T cell lines expressing CD8alpha/28 chimeric receptors containing a mutation in tyrosine 173 to phenylalanine, which inhibits the recruitment of phosphatidylinositol 3-kinase (PI3K) to CD28, expressed higher levels of HIV-1 following T cell activation. Whereas constitutively active PI3K decreased provirus transcription, inhibiting endogenous PI3K with specific inhibitors or by overexpressing PTEN phosphatase enhanced HIV-1 expression. PI3K-dependent inhibition required the viral Tat protein and a trans activation response region element. Tat pull-down and coimmunoprecipitation experiments indicate that PI3K affects the formation of the Tat-associated kinase trans-activating complex. These studies demonstrate that PI3K negatively impacts HIV-1 transcription and that Tat activity is sensitive to T cell signaling events.

Sp1 transcriptional activity is up-regulated by phosphatase 2A in dividing T lymphocytes

We have followed Sp1 expression in primary human T lymphocytes induced, via CD2 plus CD28 costimulation, to sustained proliferation and subsequent return to quiescence. Binding of Sp1 to wheat germ agglutinin lectin was not modified following activation, indicating that the overall glycosylation of the protein was unchanged. Sp1 underwent, instead, a major dephosphorylation that correlated with cyclin A expression and, thus, with cell cycle progression. A similar change was observed in T cells that re-entered cell cycle following secondary interleukin-2 stimulation, as well as in serum-induced proliferating NIH/3T3 fibroblasts. Phosphatase 2A (PP2A) appears involved because 1) treatment of dividing cells with okadaic acid or cantharidin inhibited Sp1 dephosphorylation and 2) PP2A dephosphorylated Sp1 in vitro and strongly interacted with Sp1 in vivo. Sp1 dephosphorylation is likely to increase its transcriptional activity because PP2A overexpression potentiated Sp1 site-driven chloramphenicol acetyltransferase expression in dividing Kit225 T cells and okadaic acid reversed this effect. This increase might be mediated by a stronger affinity of dephosphorylated Sp1 for DNA, as illustrated by the reduced DNA occupancy by hyperphosphorylated Sp factors from cantharidin- or nocodazole-treated cells. Finally, Sp1 dephosphorylation appears to occur throughout cell cycle except for mitosis, a likely common feature to all cycling cells.

The role of mass spectrometry in proteome studies

Mass spectrometry (MS) is an important tool in modern protein chemistry. In proteome analyses the expression of hundreds or thousands of proteins can be monitored at the same time. First, complex protein mixtures are separated by two-dimensional gel electrophoresis (2-DE) and then individual proteins are identified by using MS followed by database searches. Recent developments in this field have made it possible to do automated, high-throughput protein identification that is needed in proteome analyses. MS can also be used to characterize post-translational modifications in proteins and to study protein complexes. This review will introduce the current MS methods used in proteome studies, and discuss their advantages and disadvantages. New instrumental MS developments are also presented that are useful in these analyses.

Novel CD28-responsive enhancer activated by CREB/ATF and AP-1 families in the human interleukin-2 receptor alpha-chain locus

The interaction of interleukin-2 (IL-2) with its receptor (IL-2R) critically regulates the T-cell immune response, and the alpha chain CD25/IL-2Ralpha is required for the formation of the high-affinity receptor. Tissue-specific, inducible expression of the IL-2Ralpha gene is regulated by at least three positive regulatory regions (PRRI, PRRII, and PRRIII), but none responded to CD28 engagement in gene reporter assays although CD28 costimulation strongly amplifies IL-2Ralpha gene transcription. By DNase I hypersensitivity analysis, we have identified a novel TCR-CD3- and CD28-responsive enhancer (CD28rE) located 8.5 kb 5' of the IL-2Ralpha gene. PRRIV/CD28rE contains a functional CRE/TRE element required for CD28 signaling. The T-cell-specific, CD28-responsive expression of the IL-2Ralpha gene appears controlled through PRRIV/CD28rE by cooperation of CREB/ATF and AP-1 family transcription factors.

The Ets-transcription factor family in embryonic development: lessons from the amphibian and bird

This chapter reviews the expression and role of Ets-genes during embryogenesis of amphibians and birds. In addition to overlapping expression domains, some of them exhibit cell type-specific expression. Many of them are expressed in migratory cells: neural crest, endothelial, and pronephric duct cells for instance. They are also transcribed in embryonic areas affected by epithelio-mesenchymal transitions. Both processes involve modifications of cellular adhesion. Ets-family genes appear to coordinate changes in the expression of adhesion molecules and degradation of the extracellular matrix upon regulation of matrix metalloproteinases and their specific inhibitors. These functions are essential for physiological processes like tissue remodelling during embryogenesis or wound healing. Unfortunately they also play a harmful role in metastasis. Recent studies in the nervous system showed that Ets-genes contribute to the establishment of a cellular identity. This identity could rely on definite cell-surface determinants, among which cadherins could play an important role. In addition to cell-type specific expression, other factors contribute to the specificity of function of Ets-genes. These genes have a broad specificity of recognition of target sequences in gene promoters, insufficient for accurate control of gene expression. A fine tuning could arise from combinatorial interactions with other Ets- or accessory proteins.

Regulation of Ets function by protein - protein interactions

Ets proteins are a family of transcription factors that share an 85 amino acid conserved DNA binding domain, the ETS domain. Over 25 mammalian Ets family members control important biological processes, including cellular proliferation, differentiation, lymphocyte development and activation, transformation and apoptosis by recognizing the GGA core motif in the promoter or enhancer of their target genes. Protein - protein interactions regulates DNA binding, subcellular localization, target gene selection and transcriptional activity of Ets proteins. Combinatorial control is a characteristic property of Ets family members, involving interaction between Ets and other key transcriptional factors such as AP-1, NFkappaB and Pax family members. Specific domains of Ets proteins interact with many protein motifs such as bHLH, bZipper and Paired domain. Such interactions coordinate cellular processes in response to diverse signals including cytokines, growth factors, antigen and cellular stresses.

Signal transduction and the Ets family of transcription factors

Cellular responses to environmental stimuli are controlled by a series of signaling cascades that transduce extracellular signals from ligand-activated cell surface receptors to the nucleus. Although most pathways were initially thought to be linear, it has become apparent that there is a dynamic interplay between signaling pathways that result in the complex pattern of cell-type specific responses required for proliferation, differentiation and survival. One group of nuclear effectors of these signaling pathways are the Ets family of transcription factors, directing cytoplasmic signals to the control of gene expression. This family is defined by a highly conserved DNA binding domain that binds the core consensus sequence GGAA/T. Signaling pathways such as the MAP kinases, Erk1 and 2, p38 and JNK, the PI3 kinases and Ca2+-specific signals activated by growth factors or cellular stresses, converge on the Ets family of factors, controlling their activity, protein partnerships and specification of downstream target genes. Interestingly, Ets family members can act as both upstream and downstream effectors of signaling pathways. As downstream effectors their activities are directly controlled by specific phosphorylations, resulting in their ability to activate or repress specific target genes. As upstream effectors they are responsible for the spacial and temporal expression or numerous growth factor receptors. This review provides a brief survey of what is known to date about how this family of transcription factors is regulated by cellular signaling with a special focus on Ras responsive elements (RREs), the MAP kinases (Erks, p38 and JNK) and Ca2+-specific pathways and includes a description of the multiple roles of Ets family members in the lymphoid system. Finally, we will discuss other potential mechanisms and pathways involved in the regulation of this important family of transcription factors.