Targeting of p300 to the interleukin-2 promoter via CREB-Rel cross-talk during mitogen and oncogenic molecular signaling in activated T-cells

Long-Range Transcriptional Control of the Il2 Gene by an Intergenic Enhancer

Interleukin-2 (IL-2) is a potent cytokine with roles in both immunity and tolerance. Genetic studies in humans and mice demonstrate a role for Il2 in autoimmune disease susceptibility, and for decades the proximal Il2 upstream regulatory region has served as a paradigm of tissue-specific, inducible gene regulation. In this study, we have identified a novel long-range enhancer of the Il2 gene located 83 kb upstream of the transcription start site. This element can potently enhance Il2 transcription in recombinant reporter assays in vitro, and the native region undergoes chromatin remodeling, transcribes a bidirectional enhancer RNA, and loops to physically interact with the Il2 gene in vivo in a CD28-dependent manner in CD4(+) T cells. This cis regulatory element is evolutionarily conserved and is situated near a human single-nucleotide polymorphism (SNP) associated with multiple autoimmune disorders. These results indicate that the regulatory architecture of the Il2 locus is more complex than previously appreciated and suggest a novel molecular basis for the genetic association of Il2 polymorphism with autoimmune disease.

Dynamic bookmarking of primary response genes by p300 and RNA polymerase II complexes

Profiling the dynamic interaction of p300 with proximal promoters of human T cells identified a class of genes that rapidly coassemble p300 and RNA polymerase II (pol II) following mitogen stimulation. Several of these p300 targets are immediate early genes, including FOS, implicating a prominent role for p300 in the control of primary genetic responses. The recruitment of p300 and pol II rapidly transitions to the assembly of several elongation factors, including the positive transcriptional elongation factor (P-TEFb), the bromodomain-containing protein (BRD4), and the elongin-like eleven nineteen lysine-rich leukemia protein (ELL). However, transcription at many of these rapidly induced genes is transient, wherein swift departure of P-TEFb, BRD4, and ELL coincides with termination of transcriptional elongation. Unexpectedly, both p300 and pol II remain accumulated or "bookmarked" at the proximal promoter long after transcription has terminated, demarking a clear mechanistic separation between the recruitment and elongation phases of transcription in vivo. The bookmarked pol II is depleted of both serine-2 and serine-5 phosphorylation of its C-terminal domain and remains proximally positioned at the promoter for hours. Surprisingly, these p300/pol II bookmarked genes can be readily reactivated, and elongation factors can be reassembled by subsequent addition of nonmitogenic agents that, alone, have minimal effects on transcription in the absence of prior preconditioning by mitogen stimulation. These findings suggest that p300 is likely to play an important role in biological processes in which transcriptional bookmarking or preconditioning influences cellular growth and development through the dynamic priming of genes for response to rechallenge by secondary stimuli.

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

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

Tcl1 functions as a transcriptional regulator and is directly involved in the pathogenesis of CLL

B cell chronic lymphocytic leukemia (B-CLL) is the most common human leukemia. Deregulation of the T cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. To examine the mechanisms by which Tcl1 protein exerts oncogenic activity in B cells, we investigated the effect of Tcl1 expression on NF-kappaB and activator protein 1 (AP-1) activity. We found that Tcl1 physically interacts with c-Jun, JunB, and c-Fos and inhibits AP-1 transcriptional activity. Additionally, Tcl1 activates NF-kappaB by physically interacting with p300/CREB binding protein. We then sequenced the TCL1 gene in 600 B-CLL samples and found 2 heterozygous mutations: T38I and R52H. Importantly, both mutants showed gain of function as AP-1 inhibitors. The results indicate that Tcl1 overexpression causes B-CLL by directly enhancing NF-kappaB activity and inhibiting AP-1.

Ikaros enforces the costimulatory requirement for IL2 gene expression and is required for anergy induction in CD4+ T lymphocytes

T cell activation results in dynamic remodeling of the chromatin at the IL2 promoter and induction of IL2 gene transcription. These processes are each dependent upon CD28 costimulation, but the molecular basis for this requirement is not clear. The IL2 promoter contains consensus-binding elements for Ikaros, a lymphocyte-specific zinc-finger DNA-binding protein that can regulate gene expression by recruiting chromatin-remodeling complexes. We find that native Ikaros in CD4(+) T cells exhibits sequence-specific binding to these elements in vitro, and interacts with the endogenous IL2 promoter in vivo, in a manner dependent upon its DNA-binding domain. This binding has important consequences on the regulation of the IL2 gene, because CD4(+) T cells with reduced Ikaros DNA-binding activity no longer require signals from the TCR or CD28 for histone acetylation at the endogenous IL2 promoter, and no longer require CD28 costimulation for expression of the IL2 gene. Furthermore, CD4(+) T cells with reduced Ikaros activity are resistant to clonal anergy induced by TCR ligation in the absence of either CD28 or IL-2R signals. These results establish Ikaros as a transcriptional repressor of the IL2 gene that functions through modulation of chromatin structure and has an obligate role in the induction of anergy.

CD4+ T cells from simian immunodeficiency virus disease-resistant sooty mangabeys produce more IL-2 than cells from disease-susceptible species: involvement of p300 and CREB at the proximal IL-2 promoter in IL-2 up-regulation

IL-2 is an important cytokine required for the physiological function of CD4(+) T cells. Immunological unresponsiveness-anergy- of CD4(+) T cells is characterized by the inability of these cells to synthesize IL-2. Both progressive HIV infection leading to AIDS in humans and SIV infection in rhesus macaques (RM) are associated with dysregulation of IL-2 synthesis. In certain nonhuman primate species, such as sooty mangabeys (SM), SIV infection does not lead to AIDS. We have shown that this is associated with the resistance of the CD4(+) T cells from SM to undergo anergy in vitro. In this study, we show that CD4(+) T cells from SM spontaneously synthesize 2- to 3-fold higher levels of IL-2 than corresponding cells from RM. Proximal IL-2 promoter constructs derived from SM show significantly higher activity than the RM-derived constructs in primary CD4(+) T cells, which is associated with an element at approximately nt -200. Activity of both constructs was up-regulated by p300 and down-regulated by CREB to a similar degree. Chromatin immunoprecipitation analysis showed significantly higher binding of p300 and lower binding of CREB to the SM promoter in vivo. Two single nucleotide substitutions present in the SM sequence around position -200 and -180 seem to increase the affinity of these sites for the binding of transcription factors, one of which was identified as Oct-1. These unique characteristics of the proximal IL-2 promoter in SM therefore can represent one of the mechanisms contributing to the resistance of these cells to undergo anergy.

The cyclin-dependent kinase inhibitor p27kip1 is required for transplantation tolerance induced by costimulatory blockade

The cyclin-dependent kinase (CDK) inhibitor p27kip1 is an important negative regulator of the cell cycle that sets a threshold for mitogenic signals in T lymphocytes, and is required for T cell anergy in vitro. To determine whether p27(kip1) is required for tolerance in vivo, we performed cardiac allograft transplantation under conditions of combined CD28/CD40L costimulatory blockade. Although this treatment induced long-term allograft survival in wild-type recipients, costimulatory blockade was no longer sufficient to induce tolerance in mice lacking p27kip1. Rejected allografts from p27kip1-/- mice contained more CD4+ T lymphocytes and exhibited more tissue damage than allografts from tolerant, wild-type mice. Infiltrating p27kip1-deficient T cells, but not wild-type T cells, exhibited nuclear expression of cyclins E and A, indicating uncontrolled T cell cycle progression in the graft. The failure of tolerance in p27kip1-/- mice was also accompanied by markedly increased numbers of allospecific, IFN-gamma-producing cells in the periphery, and occurred despite apparently normal regulatory T cell activity. These data demonstrate that the CDK inhibitor p27kip1 enforces the costimulatory requirement for the expansion and differentiation of alloimmune effector T lymphocytes in vivo, and point to CDKs as novel targets for immunosuppressive or tolerance-inducing therapies.

p300/Cyclic AMP-responsive element binding-binding protein mediates transcriptional coactivation by the CD28 T cell costimulatory receptor

During Ag stimulation of T cells, the recognition of B7 molecules by the CD28 costimulatory receptor increases the level of c-Fos, a component of the AP-1 transactivator known to bind the 5' Il2 gene enhancer. In this study, we show that the costimulation of Fos transcription by CD28 is associated with increased binding of p300/CREB-binding protein (CBP) molecules at the Fos promoter, and is blocked by an adenoviral E1A molecular antagonist of p300/CBP. Furthermore, transcriptional activation by a C-terminal domain of CBP is strengthened when CD28 molecules are actively signaling. This increased amount and activity of p300/CBP molecules at the Fos gene correlated with higher histone H4 acetylation and RNA polymerase II association with the promoter. These data suggest a global mechanism whereby CD28 signaling influences the rate and intensity of new gene expression during Ag recognition via direct control over the coactivator function of p300/CBP.

BCL11B participates in the activation of IL2 gene expression in CD4+ T lymphocytes

BCL11A and BCL11B are transcriptional regulators important for lymphopoiesis and previously associated with hematopoietic malignancies. Ablation of the mouse Bcl11b locus results in failure to generate double-positive thymocytes, implicating a critical role of Bcl11b in T-cell development. However, BCL11B is also expressed in CD4+ T lymphocytes, both in resting and activated states. Here we show both in transformed and primary CD4+ T cells that BCL11B participates in the control of the interleukin-2 (IL2) gene expression following activation through T-cell receptor (TCR). BCL11B augments expression from the IL2 promoter through direct binding to the US1 site. In addition, BCL11B associates with the p300 coactivator in CD4+ T cells activated through TCR, which may account for its transcriptional activation function. These results provide the first evidence that BCL11B, originally described as a transcriptional repressor, activates transcription of a target gene in the context of T-cell activation.

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

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

Protein phosphatase 2A is a negative regulator of IL-2 production in patients with systemic lupus erythematosus

Decreased IL-2 production in systemic lupus erythematosus (SLE) represents a central component of the disease immunopathology. We report that the message, protein, and enzymatic activity of the catalytic subunit of protein phosphatase 2A (PP2Ac), but not PP1, are increased in patients with SLE regardless of disease activity and treatment and in a disease-specific manner. Treatment of SLE T cells with PP2Ac-siRNA decreased the protein levels and activity of PP2Ac in a specific manner and increased the levels of phosphorylated cAMP response element-binding protein and its binding to the IL2 and c-fos promoters, as well as increased activator protein 1 activity, causing normalization of IL-2 production. Our data document increased activity of PP2A as a novel SLE disease-specific abnormality and define a distinct mechanism whereby it represses IL-2 production. We propose the use of PP2Ac-siRNA as a novel tool to correct T cell IL-2 production in SLE patients.

Pharmacologic profiling of transcriptional targets deciphers promoter logic

The blueprint for cellular diversity and response to environmental change is encoded in the cis-acting regulatory sequences of most genes. Deciphering this 'cis-regulatory code' requires multivariate data sets that examine how these regions coordinate transcription in response to diverse environmental stimuli and therapeutic treatments. We describe a transcriptional approach that profiles the activation of multiple transcriptional targets against combinatorial arrays of therapeutic and signal transducing agents. Application of this approach demonstrates how cis-element composition and promoter context combine to influence transcription downstream of mitogen-induced signaling networks. Computational dissection of these transcriptional profiles in activated T cells uncovers a novel regulatory synergy between IGF-1 and CD28 costimulation that modulates NF-kappaB and AP1 pathways through signaling cascades sensitive to cyclosporin A and wortmannin. This approach provides a broader view of the hierarchical signal integration governing gene expression and will facilitate a practical design of combinatorial therapeutic strategies for exploiting critical control points in transcriptional regulation.

Signals from CD28 induce stable epigenetic modification of the IL-2 promoter

CD28 costimulation controls multiple aspects of T cell function, including the expression of proinflammatory cytokine genes. One of these genes encodes IL-2, a growth factor that influences T cell proliferation, survival, and differentiation. Antigenic signaling in the absence of CD28 costimulation leads to anergy, a mechanism of tolerance that renders CD4+ T cells unable to produce IL-2. The molecular mechanisms by which CD28 costimulatory signals induce gene expression are not fully understood. In eukaryotic cells, the expression of many genes is influenced by their physical structure at the level of DNA methylation and local chromatin remodeling. To address whether these epigenetic mechanisms are operative during CD28-dependent gene expression in CD4+ T cells, we compared cytosine methylation and chromatin structure at the IL-2 locus in fully activated CD4+ effector T cells and CD4+ T cells rendered anergic by TCR ligation in the absence of CD28 costimulation. Costimulation through CD28 led to marked, stable histone acetylation and loss of cytosine methylation at the IL-2 promoter/enhancer. This was accompanied by extensive remodeling of the chromatin in this region to a structure highly accessible to DNA binding proteins. Conversely, TCR activation in the absence of CD28 costimulation was not sufficient to promote histone acetylation or cytosine demethylation, and the IL-2 promoter/enhancer in anergic cells remained completely inaccessible. These data suggest that CD28 may function through epigenetic mechanisms to promote CD4+ T cell responses.

Role of accessory proteins of HTLV-1 in viral replication, T cell activation, and cellular gene expression

Human T-cell lymphotropic virus type 1 (HTLV-1), causes adult T cell leukemia/lymphoma (ATLL), and initiates a variety of immune mediated disorders. The viral genome encodes common structural and enzymatic proteins characteristic of all retroviruses and utilizes alternative splicing and alternate codon usage to make several regulatory and accessory proteins encoded in the pX region (pX ORF I to IV). Recent studies indicate that the accessory proteins p12I, p27I, p13II, and p30II, encoded by pX ORF I and II, contribute to viral replication and the ability of the virus to maintain typical in vivo expression levels. Proviral clones that are mutated in either pX ORF I or II, while fully competent in cell culture, are severely limited in their replicative capacity in a rabbit model. These HTLV-1 accessory proteins are critical for establishment of viral infectivity, enhance T-lymphocyte activation and potentially alter gene transcription and mitochondrial function. HTLV-1 pX ORF I expression is critical to the viral infectivity in resting primary lymphocytes suggesting a role for the calcineurin-binding protein p12I in lymphocyte activation. The endoplasmic reticulum and cis-Golgi localizing p12I activates NFAT, a key T cell transcription factor, through calcium-mediated signaling pathways and may lower the threshold of lymphocyte activation via the JAK/STAT pathway. In contrast p30II localizes to the nucleus and represses viral promoter activity, but may regulate cellular gene expression through p300/CBP or related co-activators of transcription. The mitochondrial localizing p13II induces morphologic changes in the organelle and may influence energy metabolism infected cells. Future studies of the molecular details HTLV-1 "accessory" proteins interactions will provide important new directions for investigations of HTLV-1 and related viruses associated with lymphoproliferative diseases. Thus, the accessory proteins of HTLV-1, once thought to be dispensable for viral replication, have proven to be directly involved in viral spread in vivo and represent potential targets for therapeutic intervention against HTLV-1 infection and disease.

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

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

Effect of sesquiterpene lactones on the expression of the activation marker CD69 and of IL-2 in T-lymphocytes in whole blood

We used flow cytometry to investigate the inhibitory effect of sesquiterpene lactones (SLs) on T-cell activation measured by the expression of its early marker CD69, and on interleukin (IL)-2, a mediator of activation, in whole blood. SLs are biologically active compounds found especially in plants from the Asteraceae family. Overnight treatment of blood with these substances led to the inhibition of CD69 and IL-2 expression. Interestingly, bifunctional SLs showed a weaker activity than monofunctional substances, which is in contradiction with the data obtained so far, using other biological test systems. Additionally, SLs did not completely inhibit CD69 or IL-2 expression. We also determined their toxicity and observed only a low effect. Up to now, studies on cytotoxicity have only been performed using cultured cell lines. From these results it may be supposed that these natural compounds preferentially show toxic effects towards transformed cell lines. Altogether, the results demonstrated that SLs effectively inhibit the activation of the T-lymphocyte response in whole blood and proved the utility of a whole blood system in studying their biological effects.

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

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

Interleukin-2 receptor-gamma -dependent endocytosis depends on biotin in Jurkat cells

Biotin has been credited with having beneficial effects on immune function despite observations that biotin supplementation causes decreased secretion of interleukin-2. Here this paradox was addressed by determining whether receptor-dependent internalization of interleukin-2 by immune cells depends on biotin. Theoretically, this would be consistent with both decreased net secretion of interleukin-2 by biotin-supplemented cells (causing increased endocytosis) and beneficial effects of biotin on immune function (causing increased receptor signaling). Jurkat cells were cultured in biotin-defined media (25, 250, or 10,000 pM). Secretion of interleukin-2 correlated negatively with biotin supply, but transcriptional activity of the interleukin-2 gene correlated positively with biotin supply, suggesting that decreased secretion of interleukin-2 by biotin-supplemented cells was not caused by decreased gene expression. Expression of the interleukin-2 receptor-gamma gene was greater at 10,000 pM than 25 pM biotin, mediating increased endocytosis of interleukin-2 in biotin-supplemented medium. Inhibition of endocytosis by genistein and overexpression of interleukin-2 receptor-gamma abolished the effect of biotin. These findings suggest that endocytosis of interleukin-2 depends on biotin.

Novel cell-specific and dominant negative anti-apoptotic roles of p73 in transformed leukemia cells

Although extensive homology exists between related genes p53 and p73, recent data suggest that the family members have divergent roles. We demonstrate that the differential regulatory roles of p53 family member p73 are highly cell-context and promoter-specific. Full-length p73 expressed in the transformed leukemia cell line Jurkat behaves as a specific dominant negative transcriptional repressor of the cell cycle inhibitor gene p21 and blocks p53-mediated apoptosis. These findings provide evidence for a new mechanism in oncogenesis through which the functional properties of p73 can be altered in an inheritable and cell-specific fashion independent of transcriptional coding.

Cross-regulation of T cell growth factor expression by p53 and the Tax oncogene

In this study, we demonstrate that p53 directly inhibits expression of the T cell growth factor (IL-2) in activated T cells. This repression is independent of the intrinsic transcriptional activity of p53 and is mediated by the Tax-responsive CD28RE-3'-12-O-tetradecanoylphorbol-13-acetate response element (AP1) element of the IL-2 promoter. Coexpression of the Tax oncogene causes full reversal of this repression through coordinate targeting of p300, CREB, and the NF-kappaB pathways. Paradoxically, IL-2 repression by p53 is not reversed by mdm2. Instead, mdm2 represses the IL-2 promoter by a mechanism that is synergistic with p53 and resistant to Tax reversal. The p300 structure-function studies show that these effects are linked to competitive associations among p53, Tax, and mdm2 with multiple domains of p300. The functional outcome of these antagonistic associations is revealed further by the observation that Tax and p53 induce apoptosis in activated T cells through separate and mutually exclusive pathways. Interestingly, both pathways are abrogated by mdm2. These results provide evidence that a dynamic interplay, between Tax and specific elements of the p53 network, mediates growth factor expression and programmed cell death in activated T cells.

Protein kinase C and AKT/protein kinase B in CD4+ T-lymphocytes: new partners in TCR/CD28 signal integration

T-cell biological responses appear to involve the complex interaction of T-cell surface receptors, intracellular signaling molecules and the cytoskeleton. Both the serine/threonine protein kinase families protein kinase C (PKC) and protein kinase B or RAC-PK (AKT/PKB) have been implicated in signal transmission leading to activation, differentiation as well as cellular survival of T-lymphocytes. The PKC gene family consists of nine diverse isotypes (PKC alpha, beta, gamma, delta, epsilon, xi, eta, theta; and iota), the AKT/PKB gene family includes three kinases (AKT1/PKB alpha, AKT2/PKB beta, AKT3/PKB gamma). Here, we attempt to summarize the regulation as well as downstream signaling pathways of PKC and AKT/PKB isotypes, that may act additive in TCR/CD28 induced proliferation and survival of peripheral CD4+ T-lymphocytes.