Recent advances in the understanding of interleukin-2 signal transduction

PTEN-inhibition by zinc ions augments interleukin-2-mediated Akt phosphorylation

Free zinc ions (Zn(2+)) participate in several signaling pathways. The aim of the present study was to investigate a potential involvement of Zn(2+) in the PI3K/Akt pathway of interleukin (IL)-2 signaling in T-cells. The IL-2 receptor triggers three major pathways, ERK1/2, JAK/STAT5, and PI3K/Akt. We have previously shown that an IL-2-mediated release of lysosomal Zn(2+) into the cytoplasm activates ERK1/2, but not STAT5. In the present study, Akt phosphorylation in response to IL-2 was abrogated by the Zn(2+) chelator N,N,N',N'-tetrakis-2(pyridyl-methyl)ethylenediamine, and was induced by treatment with Zn(2+) and the ionophore pyrithione. The latter were ineffective in cells that were treated with siRNA against the phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a phosphatase that degrades the lipid second messenger PI(3,4,5)P3, which is produced by PI3K and leads to activation of Akt. Inhibition of recombinant PTEN by Zn(2+)in vitro yielded an IC50 of 0.59 nM. Considering a resting free cytoplasmic Zn(2+) level of 0.2 nM in the T-cell line CTLL-2, this seems ideally suited for dynamic regulation by cellular Zn(2+). Oxidation with H2O2 and supplementation with Zn(2+) led to similar changes in the CD spectrum of PTEN. Moreover, Zn(2+) partially prevented the oxidation of cysteines 71 and 124. Hence, we hypothesize that zinc signals affect the IL-2-dependent PI3K/Akt pathway by inhibiting the negative regulator PTEN through binding with a sub-nanomolar affinity to cysteine residues that are essential for its catalytic activity.

Small-molecule inhibitors of IL-2/IL-2R: lessons learned and applied

The IL-2:IL-2R protein-protein interaction is of central importance to both healthy and diseased immune responses, and is one of the earliest examples of successful small-molecule inhibitor discovery against this target class. Drug-like inhibitors of IL-2 have been identified through a combination of fragment discovery, structure-based design, and medicinal chemistry; this discovery approach illustrates the importance of using a diverse range of complementary screening methods and analytical tools to achieve a comprehensive understanding of molecular recognition. The IL-2 story also provides insight into the dynamic nature of protein-protein interaction surfaces, their potential druggability, and the physical and chemical properties of effective small-molecule ligands. These lessons, from IL-2 and similar discovery programs, underscore an increasing awareness of the principles governing the development of drugs for protein-protein interactions.

Immunomodulatory cytokines as therapeutic agents for melanoma

Melanoma is the most aggressive form of skin cancer whose worldwide incidence is rising faster than any other cancer. Few treatment options are available to patients with metastatic disease, and standard chemotherapeutic agents are generally ineffective. Cytokines such as IFN-α or IL-2 can promote immune recognition of melanoma, occasionally inducing dramatic and durable clinical responses. Here, we discuss several immunomodulatory agents, the safety of which are being evaluated in clinical trials. Challenges include an incomplete understanding of signaling pathways, appropriate clinical dose and route, and systemic immunosuppression in advanced melanoma patients. We consider how targeted cytokine therapy will integrate into the clinical arena, as well as the low likelihood of success of single cytokine therapies. Evidence supports a synergy between cytokine immunotherapy and other therapeutic approaches in melanoma, and strengthening this area of research will improve our understanding of how to use cytokine therapy better.

The use of monoclonal antibodies for the treatment of graft-versus-host disease following allogeneic stem cell transplantation

INTRODUCTION

Graft-versus-host disease (GVHD) remains the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Steroids along with calcineurin inhibitors remain the standard initial therapy, however, less than half of the patients completely respond and there is no uniformly accepted therapy for patients with steroid-resistant GVHD.

AREAS COVERED

This paper reviews the current role and ongoing development of mAbs in the treatment of GVHD. Various mAbs to cell surface antigens on GVHD effector cells have been investigated for the treatment of acute GVHD: these include anti-TNF-α antibodies, IL-2 receptor antagonists, anti-CD3 and anti-CD52 mAbs, while anti-CD20 mAb has been extensively investigated in the setting of chronic GVHD. Overall, response rates have been reported to be greater than 60%, although it should be emphasized that the long-term survival still remains suboptimal, mainly due to the detrimental side effects of infectious complications, progressive GVHD and relapse of underlying malignancy.

EXPERT OPINION

Future challenges will include more appropriate definition of these agents in the therapeutic scenario of GVHD. Combinations of mAbs or mAb combined with newer immunosuppressive drugs might potentially achieve greater success, especially if used early in the disease process.

MicroRNA-26a-mediated regulation of interleukin-2 expression in transformed avian lymphocyte lines

Background

Micro(mi)RNAs are a class of small non-coding RNAs that play critical roles in the induction of various cancers, including lymphomas induced by oncogenic viruses. While some of the miRNAs are oncogenic, miRNAs such as miR-26a are consistently downregulated in a number of cancers, demonstrating their potential tumor suppressor functions. Global miRNA expression profiles of a number of virus-transformed avian lymphoma cell lines have shown downregulation of gga-miR-26a expression, irrespective of molecular mechanisms of transformation or the viral aetiology. The neoplastic transformation of lymphocytes by many viruses accompanies high levels of proliferative responses, mostly mediated through cytokines such as IL-2. Chicken IL-2 can modulate T-cell proliferation and cytotoxicity in vitro and in vivo and dysregulation of IL-2 expression is observed in diseases such as leukaemia.

Results

The expression levels of gga-miR-26a in chicken lymphoma cells transformed by 3 distinct avian oncogenic viruses, viz Marek's disease virus (MDV), avian leukosis virus (ALV) and Reticuloendotheliosis virus (REV) were consistently downregulated compared to the levels in the normal lymphocytes. This downregulation of miR-26a regardless of the viral etiology and molecular mechanisms of transformation was consistent with the tumor suppressor role of this miRNA. Notwithstanding this well-established role in cancer, we demonstrate the additional role of this miRNA in directly targeting chicken IL-2 through reporter and biochemical assays. The downregulation of miR-26a can relieve the suppressive effect of this miRNA on IL-2 expression.

Conclusions

We show that miR-26a is globally downregulated in a number of avian lymphoma cells irrespective of the mechanisms of transformation, reiterating the highly conserved tumor suppressor function of this miRNA. However, with the potential for directly targeting chicken IL-2, the downregulation of miR-26a in these tumor cells could relieve the inhibitory effect on IL-2 expression assisting in the proliferative features of the transformed lymphocyte lines.

IL-2 and IFN-gamma in the retina of diabetic rats

BACKGROUND

The pathophysiology of the early events leading to diabetic retinopathy is not fully understood. It has been suggested that Inflammatory processes are involved in the development of the disease; however, the concentrations of tissue retinal inflammatory mediators and their possible alteration in diabetic retinopathy have not been described. The aim of this work was to study T-helper cell cytokine and chemokine profiles, and tyrosine nitration in retinal tissue of diabetic rats.

METHODS

Cytokines (interleukin IL-1a, IL-1b, IL-2, IL-4, IL-6, IL-10, TNFa, GM-CSF, IFN-g), chemokines (MIP-1a, MIP-2, MIP-3a, MCP-1, GRO/KC, RANTES, Fractalkine), and tyrosine nitration were measured in retinal homogenate obtained from Long-Evans rats after 5 months of experimental diabetes.

RESULTS

The T-helper type 1 cytokines IL-2 and INF-gamma, in addition to NO production (measured as nitrotyrosine), were found to be significantly elevated in diabetic rat retina homogenates. None of the other cytokines and chemokines studied were affected by the diabetic condition.

CONCLUSIONS

Immunoregulatory cytokines belonging to the Th-1 group (IL-2 and IFN-gamma) were increased in the retina of experimental diabetic rats. Moreover, the nitrotyrosine formation (as an expression of increased NO production) was significantly elevated in the diabetic retina, supporting the concept of an inflammatory element in the development of diabetic retinopathy.

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.

CUX1 and E2F1 regulate coordinated expression of the mitotic complex genes Ect2, MgcRacGAP, and MKLP1 in S phase

Rho GTPases are critical for mitosis progression and completion of cytokinesis. During mitosis, the GDP/GTP cycle of Rho GTPases is regulated by the exchange factor Ect2 and the GTPase activating protein MgcRacGAP which associates with the kinesin MKLP1 in the centralspindlin complex. We report here that expression of Ect2, MgcRacGAP, and MKLP1 is tightly regulated during cell cycle progression. These three genes share similar cell cycle-related signatures within their promoter regions: (i) cell cycle gene homology region (CHR) sites located at -20 to +40 nucleotides of their transcription start sites that are required for repression in G(1), (ii) E2F binding elements, and (iii) tandem repeats of target sequences for the CUX1 transcription factor. CUX1 and E2F1 bind these three promoters upon S-phase entry, as demonstrated by chromatin immunoprecipitation, and regulate transcription of these genes, as established using promoter-luciferase reporter constructs and expression of activated or dominant negative transcription factors. Overexpression of either E2F1 or CUX1 increased the levels of the endogenous proteins whereas small interfering RNA knockdown of E2F1 or use of a dominant negative E2F1 reduced their expression levels. Thus, CUX1, E2F, and CHR elements provide the transcriptional controls that coordinate induction of Ect2, MgcRacGAP, and MKLP1 in S phase, leading to peak expression of these interacting proteins in G(2)/M, at the time they are required to regulate cytokinesis.

Activation of extracellular signaling regulated kinase in natural killer cells and monocytes following IL-2 stimulation in vitro and in patients undergoing IL-2 immunotherapy: analysis via dual parameter flow-cytometric assay

Interleukin-2 (IL-2) activates extracellular signal-regulated protein kinase (ERK) within immune cells. To examine the profile of phosphorylated ERK (p-ERK) in IL-2 stimulated immune cells of normal donors and patients receiving IL-2 therapy, we developed a dual parameter flow-cytometric assay. An analysis of PBMCs stimulated with IL-2 indicated that IL-2 exposure induced p-ERK in CD56bright NK cells and CD14+ monocytes, but not in CD3+ T cells or CD21+ B cells. CD3+ T cells that were induced to express functional high-affinity IL-2R did not exhibit enhanced p-ERK following IL-2 treatment. Measurement of p-ERK within PBMCs from cancer patients 1 h following their first dose of IL-2 revealed a complete absence of circulating NK cells, consistent with earlier observations. However, the total number of circulating CD14+ monocytes increased in these samples and 97% of these cells exhibited ERK activation. p-ERK was not observed in T cells post-IL-2 therapy. Analysis of PBMCs obtained 3 weeks post-IL-2 therapy revealed high-p-ERK levels in CD56bright NK cells in a subset of patients, while levels of p-ERK returned to baseline in monocytes. These studies reveal an effective method to detect ERK activation in immune cells and demonstrate that IL-2 activates ERK in a subset of NK cells and monocytes but not T cells.

Mechanisms in prostatitis/chronic pelvic pain syndrome

PURPOSE

We reviewed the current literature on mechanisms involved in the pathogenesis of prostatitis/chronic pelvic pain syndrome (CPPS).

MATERIALS AND METHODS

A literature review for the years 1966 to 2003 was performed using the MEDLINE database of the United States National Library of Medicine.

RESULTS

National Institutes of Health categories I and II prostatitis result from identifiable prostatic infections, whereas patients with category IV are asymptomatic. The majority of symptomatic cases are category III or chronic prostatitis (CP)/CPPS. The etiology of CP/CPPS is unknown. The traditional marker of inflammation, namely white blood cells in prostatic fluids, does not correlate with the predominant symptom of pelvic pain. An imbalance toward increased proinflammatory and decreased anti-inflammatory cytokines has been implicated and a few studies have shown some correlation of this with pelvic pain. The imbalance in some men may result from polymorphisms at the cytokine loci. An autoimmune process may be involved and experimental evidence indicates that this can be under hormonal influence. Recent findings include possible defects in the androgen receptor. The prostate may not even be the source of the symptoms. Pelvic pain also correlates with the neurotrophin nerve growth factor implicated in neurogenic inflammation and central sensitization. Finally, psychological stress may produce measurable biochemical changes and influence the other processes. The role of normal prostatic bacterial flora in inciting the inflammatory response has also been reconsidered.

CONCLUSIONS

The symptoms of CP/CPPS appear to result from an interplay between psychological factors and dysfunction in the immune, neurological and endocrine systems.

Disruption of the gamma c cytokine network in T cells during HIV infection

The common gamma chain (gammac)-sharing cytokines (IL's-2, 4, 7, 9, 15, and 21) play a vital role in the survival, proliferation, differentiation and function of T lymphocytes. As such, disruption of their signaling pathways would be expected to have severe consequences on the integrity of the immune system. Indeed, it appears that the signaling network of these cytokines is both disrupted and exploited by HIV at various stages of infection. IL-2 secretion and signaling downstream of its receptor are impaired in T cells from chronically-infected HIV+ patients. Elevated plasma IL-7 levels and decreased IL-7Ralpha expression in patient T cells results in significantly decreased responsiveness to this critical cytokine. Interestingly, IL-2 and IL-15 are also able to render CD4+ T cells permissive to HIV infection through their influence on the activity of the APOBEC3G deaminase enzyme. Herein, we describe the current state of knowledge on how the gammac cytokine network is affected during HIV infection, with a focus on how this impairs CD4+ and CD8+ T cell function while also benefiting the virus itself. We also address the use of cytokines as adjuncts to highly active antiretroviral therapy to bolster immune reconstitution in infected patients.

Identification of expression patterns of IL-2-responsive genes in the murine T cell line CTLL-2

Interleukin-2 (IL-2) influences T cell proliferation and differentiation through regulation of a number of genes. Many such genes are known, yet their expression profiles have remained elusive. Using Affymetrix mouse genome arrays and the mouse T cell line CTLL-2, we studied the transcriptional response to IL-2 stimulation. A total of 2813 genes (represented by 3838 probes) showed > or =2-fold changes in expression level at one or more time points (10 were analyzed) during the first 24 h poststimulation. Cluster analyses indicated that these 2813 genes showed nine different expression patterns. Of these genes, approximately 1400 were not previously known to be regulated by interleukin-2 (IL-2). In the control, 666 genes with > or =2-fold changes at the mRNA level were identified in cells without IL-2 stimulation; 222 of them were among the 2813 IL-2-responsive genes. Possibly, the expression of these genes was altered because of changes in cell density or cell growth rate. The newly identified IL-2-responsive genes play roles in a variety of biologic processes, including signal transduction, apoptosis, cell cycle regulation, and transcription. Our data will be useful for studying biochemical events in IL-2 signaling.

Anticancer and immunosuppressive properties of bacterial prodiginines

Bacterial prodiginines are a family of red-pigmented, tripyrrolic compounds that display numerous biological activities, including antibacterial, antifungal, antiprotozoal, antimalarial, immunosuppressive and anticancer properties. Recently, significant progress has been made in understanding the biosynthesis and regulation of bacterial prodiginines. An understanding of the biosynthesis of prodiginines will allow engineering of bacterial strains capable of synthesizing novel prodiginines through rational design and mutasynthesis experiments. Bacterial prodiginines and synthetic derivatives are effective proapoptotic agents with multiple cellular targets, and they are active against numerous cancer cell lines, including multidrug-resistant cells, with little or no toxicity towards normal cell lines. A synthetic derivative, GX15-070 (Obatoclax), developed through structure-activity relationship studies of the pyrrolic ring A of GX15, is in multiple Phase I and II clinical trials in both single and dual-agent studies to treat different types of cancer. Therefore, prodiginines have real therapeutic potential in the clinic.

The excitotoxic effect of NMDA on human lymphocyte immune function

N-Methyl-d-aspartate (NMDA)-activated glutamate receptors are expressed in lymphocytes, but their roles have not yet been defined. We show that incubation of human peripheral blood lymphocytes with NMDA resulted in increased intracellular calcium and reactive oxygen species (ROS) levels through effects on NMDA-activated glutamate receptors. In terms of ROS production, T cells were most affected, followed by NK cells, whereas B cell ROS levels were not increased. In unstimulated T and NK cells, interferon-gamma (IFN-gamma) production was unaffected by NMDA, whereas interleukin-2 stimulation of IFN-gamma production was significantly suppressed by NMDA. Simultaneous incubation of the cells with NMDA and IL-2 resulted in a dramatic increase in the amount of cells expressing the NR1 subunit of the NMDA-activated receptors. We conclude that NMDA-activated glutamate receptor activation, accompanied by the changes in intracellular calcium and ROS levels, may be involved in the modification of immune functions of human T and NK cells.

Signaling by small GTPases in the immune system

The Ras superfamily consists of over 50 low-molecular-weight proteins that cycle between an inactive guanosine diphosphate-bound state and an active guanosine triphosphate (GTP)-bound state. They are involved in a variety of signal transduction pathways that regulate cell growth, intracellular trafficking, cell migration, and apoptosis. Several methods have been devised to measure the activation state of Ras proteins, defined as the percent of Ras molecules in the active GTP-bound state. We have previously developed a quantitative biochemical method that can be applied to animal and human tissues and have used it to measure the activation state of Ras, Rap1, Rheb, and Rho proteins in cultured cells and in animal and human tumors. Ras, Rac, and Rho all play roles in regulating the functions of T and B lymphocytes and dendritic cells, and these proteins are clearly important in maintaining normal immune system function.

IL-2-induced IL-9 production by allergen-specific human helper T-cell clones

BACKGROUND

IL-9 is an important cytokine in allergic diseases such as asthma, atopic dermatitis, etc. T helper (Th) cells seem to be the main source of IL-9. Cellular and molecular mechanisms of IL-9 production by human Th cells have been poorly understood.

METHODS

Dermatophagoides farinae(Der f)-specific Th clones were established from peripheral blood lymphocytes of atopic asthmatics, and cytokine synthesis in response to various stimuli was determined by specific ELISAs.

RESULTS

IL-9 was produced by 14 of 27 human Th clones upon T cell receptor (TCR) stimulation, immobilized anti-CD3 antibody (Ab). IL-9 production was significantly enhanced by the addition of anti-CD28 Ab into the culture, indicating the role of costimulatory signal on IL-9 synthesis. Pharmacologically, IL-9 production was induced by ionomycin (IOM) alone, and enhanced by phorbol 12-myristate 13-acetate (PMA). rIL-2 induced IL-9 production by 8 out of 19 Th clones. IL-9 production by Th clones stimulated with immobilized anti-CD3 Ab was significantly suppressed by the addition of anti-IL-2 neutralizing Ab into the culture.

CONCLUSION

Approximately half of the Der f-specific Th clones derived from atopic asthmatics produced IL-9 upon TCR stimulation. Ca(2+) signal, CD28 signal, and IL-2 receptor signal seem to play important roles in IL-9 production by human Th cells. Moreover, synthesis of IL-9, a Th2 cytokine, is dependent on IL-2, a Th1 cytokine, which is produced by Th cells themselves.

IL-2-induced IL-13 production by allergen-specific human helper T cell clones

BACKGROUND

Interleukin (IL)-5 and IL-13 are important cytokines in allergic diseases such as asthma and atopic dermatitis. We have reported that the production of IL-5 and IL-13 by mite-responsive T helper cells (Th) is controlled under similar signal requirements, but precise mechanisms are not yet well characterized.

METHODS

Allergen-specific Th clones were established from peripheral blood lymphocytes of atopic asthmatics, and cytokine synthesis in response to various stimuli was determined by specific ELISAs. IL-13 gene expression was enumerated by quantitative real-time PCR.

RESULTS

IL-13 production was clearly induced by IL-2. IL-13 mRNA expression was also induced.

CONCLUSION

The IL-2 signal by itself causes IL-13 synthesis independent of T cell receptor stimulation.

Autoimmune regulator (AIRE) gene is expressed in human activated CD4+ T-cells and regulated by mitogen-activated protein kinase pathway

The autoimmune regulator (AIRE) gene is a gene responsible for autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy. Here we show that AIRE is expressed in human peripheral CD4-positive T-cells, and most highly in antigen-and interleukin 2-stimulated T (IL-2T) cells. Mitogen-activated protein kinases (MAPKs), including MAPK kinase (MEK) 1/2 and p38 MAPK, were phosphorylated in IL-2T cells and the expression of the AIRE gene was inhibited by a specific p38 MAPK inhibitor (SB203580), thereby indicating that AIRE gene expression is controlled by the MAPK pathway in IL-2T cells. These data suggested the possible significance of the AIRE gene in the peripheral immune system.

Interleukin-2: from T cell growth and homeostasis to immune reconstitution of HIV patients

Interleukin (IL)-2 was initially described as a major stimulant of T lymphocytes in vitro. Later, the characterization of IL-2 knockout animals showed that the ability to stimulate T cells could be replaced by other cytokines. In vivo, IL-2 plays a unique role in controlling lymphoproliferation. This is partly explained by its role in the generation and maintenance of T regulatory cells (Treg). In HIV-infected patients, the IL-2/IL-2 receptor (IL-2R) system is dysregulated. The fact that IL-2 is underproduced along with defective IL-2R signaling detected in patient lymphocytes, may explain the progressive impairment of the immune system that occurs during chronic infection with this virus. These defects are partly reversed by highly active antiretroviral therapy (HAART). However, in some patients IL-2R defects persist and the CD4 counts remain low despite good control of the viral load. These patients benefit from HAART given in conjunction with IL-2 therapy.

Regulation of Rho signaling pathways in interleukin-2-stimulated human T-lymphocytes

Rho GTPases are key regulators of many cellular functions, including cytoskeleton organization which is important for cell morphology and mobility, gene expression, cell cycle progression, and cytokinesis. In addition, it has recently been recognized that Rho GTPase activity is required for development of the immune system, as well as for the specialized functions of the peripheral cells that act in the immune response such as antigen presenting cells and lymphocytes. Stimulation of T lymphocytes with interleukin-2 (IL-2) induces clonal expansion of antigen-specific populations and provides a model to study cell cycle entry and cell cycle progression. We have performed gene expression analysis in a model of human T lymphocytes, which proliferate in response to IL-2. In addition to changes in genes relevant to cell cycling and to the antiapoptotic effects of IL-2, we have analyzed expression and variations of more than 300 genes involved in Rho GTPase signaling pathways. We report here that IL-2 regulates the expression of a number of proteins, which participate in the Rho GTPase pathways, including some of the GTPases themselves, GDP/GTP exchange factors, GTPase activating proteins, as well as GDIs and effectors. Our results suggest that regulation of expression of components of the Rho GTPase pathways may be an important mechanism in assembling specific signal transduction cascades that need to be active at certain times during the cell cycle. Some of our findings may also be relevant to the roles of Rho GTPases in T lymphocyte functions and proliferation.

Efficacy of the interleukin-2 receptor antagonist basiliximab in steroid-refractory acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) occurs in up to 80% of patients who undergo allogeneic stem cell transplantation (SCT) and contributes significantly to transplant-related mortality (TRM). We conducted a prospective phase II trial to assess the efficacy and feasibility of treating steroid-refractory aGVHD with basiliximab, a chimaeric monoclonal antibody directed against the alpha chain of the interleukin-2 (IL-2) receptor. Basiliximab was administered intravenously at a dose of 20 mg on days 1 and 4. Twenty-three patients were enrolled between October 1999 and July 2004. We found a primary overall response rate of 82.5% with four patients (17.5%) showing a complete response and 15 patients (65%) a partial response. Six patients were again treated successfully with an IL-2 receptor antagonist because of recurrence of aGVHD. The rates of infections, chronic GVHD, malignancy recurrence and 1-year TRM following immunosuppression with basiliximab were comparable with those found with other treatment modalities for aGVHD. We conclude that basiliximab is efficient and feasible for steroid-refractory aGVHD and merits further evaluation.

IL-2 responsiveness of CD4 and CD8 lymphocytes: further investigations with human IL-2Rbeta transgenic mice

Responsiveness to IL-2 varies from one lympho-mononuclear subset to another. NK lymphocytes and monocytes spontaneously respond to IL-2 whereas it is generally accepted that T and B lymphocytes need to be activated to fully acquire this competence. To further investigate this phenomenon, we studied human IL-2Rbeta (hIL-2Rbeta) transgenic mice constitutively expressing heterospecific, intermediate-affinity IL-2R (hIL-2Rbeta/mouse IL-2Rgamma(c)). We noted that the B lymphocytes and monocytes from spleens of these hIL-2Rbeta transgenic animals failed to grow when cultured in IL-2-containing medium. Under the same experimental conditions, CD4 lymphocytes survived, again without growth, whereas CD8 lymphocytes and NK cells were able to proliferate and develop potent LAK cytotoxicity. The properties of these CD4 and CD8 lymphocytes were then compared after purification. Both subsets expressed functional IL-2R able to induce global protein phosphorylation and, more precisely, signal transducer and activation of transcription 5 and Erk phosphorylation. Therefore, the differential growth potential of these CD4 and CD8 lymphocytes cannot be explained by the lack of IL-2R-dependent early signaling events. When the entrance of purified CD4 and CD8 lymphocytes into the cell cycle was analyzed, we found that the CD4 lymphocytes were unable to enter the G1 phase in the absence of anti-CD3 stimulation. This correlates with the effect of IL-2 on cyclin-dependent kinase inhibitor p27(kip1). In CD4 lymphocytes, IL-2 does not affect p27(kip1) expression. But in CD8 lymphocytes, IL-2 down-modulates p27(kip1). These results indicate that, aside from IL-2R expression and function, IL-2 responsiveness is also controlled by lineage-specific mechanisms.

CD4+CD25+ regulatory T cells attenuate the phosphatidylinositol 3-kinase/Akt pathway in antigen-primed immature CD8+ CTLs during functional maturation

This study was designed to determine the role of CD25(+)CD4(+) regulatory T (Tr) cells in CTL maturation and effector functions using a murine CTL line and in vitro MLC. Tr cells inhibited CTL functional maturation, but had no effect on CTL effector functions. In CD4(+) responder T cell-depleted MLC supplemented with IL-2, Tr cells suppressed mature CTL generation only when added within the first 2 days of culture. Tr cells down-regulated levels of active Akt, but not STAT5 or ZAP70 in Ag-primed immature CTLs. Down-regulation of active Akt was accompanied by a reduction in CTL cell size and IL-2Ralpha expression. In Tr cell-depleted MLC, CTLs were generated that exhibited high levels of nonspecific cytotoxicity. Our in vitro findings suggest that Tr cells regulate functional CTL maturation to generate optimal Ag-specific immune responses through the control of the PI3K/Akt pathway.

Ligation of RARgamma inhibits proliferation of phytohaemagglutinin-stimulated T-cells via down-regulating JAK3 protein levels

The mechanisms whereby Vitamin A regulates the immune system are poorly understood. We have shown previously that retinoic acids, the Vitamin A derivatives, promote both apoptosis of neglected thymocytes and the activation-induced cell death of peripheral T-cells via ligating the nuclear retinoid receptor (RAR) gamma. In the present study, we found that human peripheral T-cells express RARalpha and gamma, but not RARbeta. Increasing concentrations of 9-cis RA inhibited phytohaemagglutinin (PHA)-induced proliferation of T-cells, an effect that could be mimicked only by addition of RARgamma agonists and could be inhibited by an RARgamma antagonist. Interleukin-2 (IL-2) produced is known to mediate PHA-induced proliferation of T lymphocytes. Ligation of RARgamma did not affect the PHA-induced high affinity IL-2 receptor expression, slightly reduced the PHA-induced IL-2 production, but interfered with the IL-2-mediated signal transduction resulting in inhibition of PHA-induced phosphorylation of retinoblastoma protein and of up-regulation of Bcl-2. Janus kinases JAK1 and JAK3 play a determinant role in IL-2-dependent signal transduction. Ligation of RARgamma did not affect the levels of JAK1, but prevented IL-2-induced expression of JAK3 resulting in inhibition of PHA-induced phosphorylation of Stat5 molecules. Our data suggest that the previously observed toxic effect of high concentrations of retinoids on the immune system might be mediated via formation of 9-cis RA, which via ligation of RARgamma not only induces cell death in immature thymocytes, but inhibits proliferation of T-cells as well.

FoxO3 mediates antagonistic effects of glucocorticoids and interleukin-2 on glucocorticoid-induced leucine zipper expression

We have analyzed the promoter of human gilz (glucocorticoid-induced leucine zipper), a dexamethasone-inducible gene that is involved in regulating apoptosis, and identified six glucocorticoid (GC)-responsive elements and three Forkhead responsive elements (FHREs). Promoter deletion analysis and point mutations showed that individual mutation of the GC-responsive elements does not affect GC-induced transcription and that FHRE-1 and FHRE-3 elements contribute to the effects of GCs. Furthermore, overexpression of the Forkhead transcription factor FoxO3 enhances GC-induced gilz mRNA expression. The functional significance of the interaction between FoxO3 and GC receptor was established in T lymphocytes. Indeed, we show that GCs failed to induce GILZ expression in the presence of IL-2, a cytokine known to antagonize GC effects in T cells. Using a constitutive active mutant of protein kinase B that inactivates FoxO3 or a FoxO3 mutant that cannot be inactivated by protein kinase B, we demonstrate that IL-2 inhibitory effects on GILZ expression are mediated through inhibition of FoxO3 transcriptional activity. Therefore, FoxO3 appears to be a key factor mediating GC and IL-2 antagonism for gilz regulation in T lymphocytes. This regulation of GILZ expression was placed in a meaningful context in evaluating the effects of GILZ on GC-induced apoptosis in T lymphocytes.

Mechanisms of Superior Anti-Tumor Cytotoxic Response of Interleukin 15-Induced Lymphokine-Activated Killer Cells

Interleukin (IL) 15 is one of the main cytokines controlling cytotoxic lymphocyte survival and growth. Despite its receptor and functional similarity to IL-2, IL-15 affects a wider target cell population and utilizes different mechanisms in cell activation. The role of IL-15 in lymphokine-activated killer (LAK) cell generation in vitro and potential mechanisms of cytotoxicity compared with equivalent low concentration of IL-2 with or without mitogens (phytohemoglutinin (PHA) and anti-CD3 antibody) have been investigated in this study. IL-15 treatment resulted in moderate cell proliferation over 7 days, whereas IL-2 treatment was associated with decreased cell numbers. Unlike IL-2 in combination with mitogens, IL-15 caused increases in both cytotoxic T lymphocytes (CTL) and CD56 LAK cells, particularly cytokine-induced killer and cytolytic natural killer T-cell (CNK-T) subpopulations, which are known to be highly effective in cytotoxicity. IL-15 also increased overall perforin and tumor necrosis factor-alpha expression and more prominently in CTLs. Consequently, IL-15 resulted in superior cytotoxicity against two different NK-sensitive (human K-562 and murine YAC-1) and LAK-sensitive (human Daudi and Raji) cell lines compared with other cytokine combinations. There was also no contribution of mitogens to IL-2-induced cytotoxicity. In conclusion, IL-15 at the concentration of 10 ng/mL used in this study causes moderate proliferation and superior cytotoxicity of LAK cells in vitro that was associated with induction of a specific LAK cell subpopulation profile and related cellular killing mechanisms. These results are encouraging for potential use of IL-15 as part of immunotherapy.

Interleukin-2-induced survival of natural killer (NK) cells involving phosphatidylinositol-3 kinase-dependent reduction of ceramide through acid sphingomyelinase, sphingomyelin synthase, and glucosylceramide synthase

Interleukin 2 (IL-2) rescued human natural killer (NK) KHYG-1 cells from apoptosis along with a reduction of ceramide. Conversely, an increase of ceramide inhibited IL-2-rescued survival. IL-2 deprivation-induced activation of acid sphingomyelinase (SMase) and inhibition of glucosylceramide synthase (GCS) and sphingomyelin synthase (SMS) were normalized by IL-2 supplementation. A phosphatidyl inositol-3 (PI-3) kinase inhibitor, LY294002, inhibited IL-2-rescued survival, but a mitogen-activated protein kinase inhibitor, PD98059, and an inhibitor of Janus tyrosine kinase/signal transducer and activator of transcription pathway, AG490, did not. LY294002 inhibited IL-2-induced reduction of ceramide through activation of acid SMase and inhibition of GCS and SMS, suggesting the positive involvement of PI-3 kinase in ceramide reduction through enzymatic regulation. Indeed, a constitutively active PI-3 kinase enhanced growth rate and ceramide reduction through inhibition of acid SMase and activation of GCS and SMS. Further, LY294002 inhibited IL-2-induced changes of transcriptional level as well as mRNA and protein levels in acid SMase and GCS but did not affect the stability of the mRNAs. These results suggest that PI-3 kinase-dependent reduction of ceramide through regulation of acid SMase, GCS, and SMS plays a role in IL-2-rescued survival of NK cells. (Blood. 2004;104:3285-3293)

Phosphorylation of Grb2-Associated Binder 2 on Serine 623 by ERK MAPK Regulates Its Association with the Phosphatase SHP-2 and Decreases STAT5 Activation

IL-2 stimulation of T lymphocytes induces the tyrosine phosphorylation and adaptor function of the insulin receptor substrate/Grb2-associated binder (Gab) family member, Gab2. In addition, Gab2 undergoes a marked decrease in its mobility in SDS-PAGE, characteristic of migration shifts induced by serine/threonine phosphorylations in many proteins. This migration shift was strongly diminished by treating cells with the MEK inhibitor U0126, indicating a possible role for ERK in Gab2 phosphorylation. Indeed, ERK phosphorylated Gab2 on a consensus phosphorylation site at serine 623, a residue located between tyrosine 614 and tyrosine 643 that are responsible for Gab2/Src homology 2 domain-containing tyrosine phosphatase (SHP)-2 interaction. We report that pretreatment of Kit 225 cells with U0126 increased Gab2/SHP-2 association and tyrosine phosphorylation of SHP-2 in response to IL-2, suggesting that ERK phosphorylation of serine 623 regulates the interaction between Gab2 and SHP-2, and consequently the activity of SHP-2. This hypothesis was confirmed by biochemical analysis of cells expressing Gab2 WT, Gab2 serine 623A or Gab2 tyrosine 614F, a mutant that cannot interact with SHP-2 in response to IL-2. Activation of the ERK pathway was indeed blocked by Gab2 tyrosine 614F and slightly increased by Gab2 serine 623A. In contrast, STAT5 activation was strongly enhanced by Gab2 tyrosine 614F, slightly reduced by Gab2 WT and strongly inhibited by Gab2 serine 623A. Analysis of the rate of proliferation of cells expressing these mutants of Gab2 demonstrated that tyrosine 614F mutation enhanced proliferation whereas serine 623A diminished it. These results demonstrate that ERK-mediated phosphorylation of Gab2 serine 623 is involved in fine tuning the proliferative response of T lymphocytes to IL-2.

Mechanisms in prostatitis/chronic pelvic pain syndrome

PURPOSE

We reviewed the current literature on mechanisms involved in the pathogenesis of prostatitis/chronic pelvic pain syndrome (CPPS).

MATERIALS AND METHODS

A literature review for the years 1966 to 2003 was performed using the MEDLINE database of the United States National Library of Medicine.

RESULTS

National Institutes of Health categories I and II prostatitis result from identifiable prostatic infections, whereas patients with category IV are asymptomatic. The majority of symptomatic cases are category III or chronic prostatitis (CP)/CPPS. The etiology of CP/CPPS is unknown. The traditional marker of inflammation, namely white blood cells in prostatic fluids, does not correlate with the predominant symptom of pelvic pain. An imbalance toward increased proinflammatory and decreased anti-inflammatory cytokines has been implicated and a few studies have shown some correlation of this with pelvic pain. The imbalance in some men may result from polymorphisms at the cytokine loci. An autoimmune process may be involved and experimental evidence indicates that this can be under hormonal influence. Recent findings include possible defects in the androgen receptor. The prostate may not even be the source of the symptoms. Pelvic pain also correlates with the neurotrophin nerve growth factor implicated in neurogenic inflammation and central sensitization. Finally, psychological stress may produce measurable biochemical changes and influence the other processes. The role of normal prostatic bacterial flora in inciting the inflammatory response has also been reconsidered.

CONCLUSIONS

The symptoms of CP/CPPS appear to result from an interplay between psychological factors and dysfunction in the immune, neurological and endocrine systems.

Interaction of the tyrosine phosphatase SHP-2 with Gab2 regulates Rho-dependent activation of the c-fos serum response element by interleukin-2

Gab2 (Grb2-associated binder-2), a member of the IRS (insulin receptor substrate)/Gab family of adapter proteins, undergoes tyrosine phosphorylation in response to cytokine or growth factor stimulation and serves as a docking platform for many signal transduction effectors, including the tyrosine phosphatase SHP-2 [SH2 (Src homology 2)-domain-containing tyrosine phosphatase]. Here, we report that, following IL-2 (interleukin-2) stimulation of human T lymphocytes, SHP-2 binds tyrosine residues 614 and 643 of human Gab2 through its N- and C-terminal SH2 domains respectively. However, the sole mutation of Tyr-614 into phenylalanine is sufficient to prevent Gab2 from recruiting SHP-2. Expression of the Gab2 Tyr-614-->Phe (Y614F) mutant, defective in SHP-2 association, prevents ERK (extracellular-signal-regulated kinase) activation and expression of a luciferase reporter plasmid driven by the c-fos SRE (serum response element), indicating that interaction of SHP-2 with Gab2 is required for ERK activation in response to IL-2. Further investigation of IL-2-dependent induction of SRE showed that expression of a constitutively active mutant of the RhoA GTPase synergizes with IL-2 for SRE-driven transcription, whereas a dominant-negative mutant reduces the IL-2 response. Thus, in response to IL-2, full induction of the SRE requires ERK-dependent as well as Rho-dependent signals that target the Ets-box and the CArG-box respectively. We also report that the synergy between Gab2/SHP-2 and RhoA for IL-2-dependent CArG-box-driven transcription depends upon MEK (mitogen-activated protein kinase/ERK kinase) activation, and is likely to involve regulation of the serum response factor co-activator MAL. Our studies thus provide new insights into the role of Gab2 and SHP-2 in IL-2 signal transduction.

Adenosine acts through A2 receptors to inhibit IL-2-induced tyrosine phosphorylation of STAT5 in T lymphocytes: role of cyclic adenosine 3',5'-monophosphate and phosphatases

Adenosine is a purine nucleoside with immunosuppressive activity that acts through cell surface receptors (A(1), A(2a), A(2b), A(3)) on responsive cells such as T lymphocytes. IL-2 is a major T cell growth and survival factor that is responsible for inducing Jak1, Jak3, and STAT5 phosphorylation, as well as causing STAT5 to translocate to the nucleus and bind regulatory elements in the genome. In this study, we show that adenosine suppressed IL-2-dependent proliferation of CTLL-2 T cells by inhibiting STAT5a/b tyrosine phosphorylation that is associated with IL-2R signaling without affecting IL-2-induced phosphorylation of Jak1 or Jak3. The inhibitory effect of adenosine on IL-2-induced STAT5a/b tyrosine phosphorylation was reversed by the protein tyrosine phosphatase inhibitors sodium orthovanadate and bpV(phen). Adenosine dramatically increased Src homology region 2 domain-containing phosphatase-2 (SHP-2) tyrosine phosphorylation and its association with STAT5 in IL-2-stimulated CTLL-2 T cells, implicating SHP-2 in adenosine-induced STAT5a/b dephosphorylation. The inhibitory effect of adenosine on IL-2-induced STAT5a/b tyrosine phosphorylation was reproduced by A(2) receptor agonists and was blocked by selective A(2a) and A(2b) receptor antagonists, indicating that adenosine was mediating its effect through A(2) receptors. Inhibition of STAT5a/b phosphorylation was reproduced with cell-permeable 8-bromo-cAMP or forskolin-induced activation of adenylyl cyclase, and blocked by the cAMP/protein kinase A inhibitor Rp-cAMP. Forskolin and 8-bromo-cAMP also induced SHP-2 tyrosine phosphorylation. Collectively, these findings suggest that adenosine acts through A(2) receptors and associated cAMP/protein kinase A-dependent signaling pathways to activate SHP-2 and cause STAT5 dephosphorylation that results in reduced IL-2R signaling in T cells.

GILZ, a new target for the transcription factor FoxO3, protects T lymphocytes from interleukin-2 withdrawal-induced apoptosis

Interleukin-2 (IL-2) withdrawal is a physiologic process inducing cell death in activated T lymphocytes. Glucocorticoid-induced leucine zipper (GILZ) has recently been identified as a protein modulating T-cell receptor activation by repressing various signaling pathways. We report here that IL-2 deprivation leads to expression of GILZ in T lymphocytes. We then characterized the human gilz promoter and showed that FoxO3 (Forkhead box class O3) binding to the Forkhead responsive elements identified in the promoter is necessary for induction of gilz expression upon IL-2 withdrawal. To assess the functional consequences of this induction, we used 2 strategies, GILZ overexpression and GILZ silencing in murine IL-2-dependent CTLL-2 cells. GILZ overexpression protects CTLL-2 cells from IL-2 withdrawal-induced apoptosis, whereas cell death is accelerated in cells unable to express GILZ. Concomitantly, the expression of Bim is inhibited in GILZ-overexpressing cells and enhanced when GILZ expression is impaired. Furthermore, GILZ inhibits FoxO3 transcriptional activity that leads to inhibition of Bim expression but also to down-regulation of GILZ itself. Therefore, GILZ is a transiently expressed protein induced upon IL-2 withdrawal that protects T cells from the onset of apoptosis.

Rat strain differences in the ectopic osteogenic potential of recombinant human BMP adenoviruses

Different animal strains have different genetic backgrounds that influence their physiological function and pathological process. The differences in genetic background may affect the efficiency of adenoviral infection and target gene expression and further cause different gene therapy results when target genes are delivered with adenoviral vectors. In this study, ectopic bone was not seen in ADCMVBMP4 injection sites, but was formed in ADCMVBMP9 injection sites in all rat strains. The mean volumes of bone induced with ADCMVBMP9 were 0.87 +/- 0.2 cm3 in Wistar, 0.26 +/- 0.1 cm3 in Long-Evans, 0.34 +/- 0.2 cm3 in Sprague-Dawley, 0.44 +/- 0.1 cm3 in ACI, 0.66 +/- 0.2 cm3 in PVG, and 0.58 +/- 0.1 cm3 in Fischer 344 rats. This indicates that ADCMVBMP9 has different bone formation potentials in different immunocompetent rat strains (P = 0.02). The basic levels of CD4+ and CD8+ T cells in blood before viral infection and titers of adenoviral neutralizing antibodies 30 days post-viral infection were significantly different among rat strains (P < 0.01). The efficiencies of target gene expression delivered with adenovirus were also significantly different in primary muscle cell cultures from different rat strains (P < 0.01). The different osteogenic potentials of ADCMVBMP9 among rat strains may be, in part, due to the differences in immune factors and target gene expression efficiency in muscle tissue.

Transcriptional program of apoptosis induction following interleukin 2 deprivation: identification of RC3, a calcium/calmodulin binding protein, as a novel proapoptotic factor

Apoptosis of mature T lymphocytes preserves immune system homeostasis by counteracting transient increases in T-cell number. This process is regulated, at least in part, by the cytokine interleukin 2 (IL-2): T cells deprived of IL-2 undergo apoptosis. The mechanism of apoptosis induction by IL-2 deprivation remains to be determined but is known to require RNA synthesis, implying the existence of transcriptionally activated genes whose products induce cell death. To identify such genes, we have performed expression profiling in IL-2-dependent T cells following cytokine deprivation. Our results reveal an intricate transcriptional program entailing the induction of known proapoptotic factors and the simultaneous repression of known antiapoptotic factors. Surprisingly, one gene whose transcription substantially increased was RC3 (also called neurogranin), which encodes a calmodulin binding protein thought to be a neural-specific factor involved in learning and memory. We show that ectopic expression of RC3 in IL-2-dependent T cells increases the intracellular Ca(2+) concentration and induces apoptosis even in the presence of cytokine. Buffering the Ca(2+) increase with the cytoplasmic Ca(2+) chelator BAPTA-AM [1,2-bis(2-aminophenoxy)ethane-N,N,N1,N-tetraacetic acid] blocks RC3-induced apoptosis, indicating that the rise in intracellular Ca(2+) is required for apoptotic death. RC3 mutants unable to bind calmodulin fail to increase intracellular Ca(2+) levels and to induce apoptosis. Based upon these results, we propose that IL-2 deprivation raises the level of RC3 and other apoptotic factors, which induce apoptosis by increasing the intracellular Ca(2+) concentration.

Uncoupling of promitogenic and antiapoptotic functions of IL-2 by Smad-dependent TGF-beta signaling

TGF-beta opposes proliferative signaling by IL-2 through mechanisms that remain incompletely defined. In a well-characterized CD8(+) T cell model using wild-type and mutated IL-2 receptors, we examined the effects of TGF-beta on distinct IL-2 signaling events in CD8(+) T cells. IL-2 induces c-myc, cyclin D2, and cyclin E in a redundant manner through the Shc and STAT5 pathways. TGF-beta inhibited the ability of either the Shc or STAT5 pathway to induce these genes, as well as T cell proliferation. The inhibitory effects of TGF-beta were reversed by expression of a dominant-negative form of Smad3. TGF-beta did not impair proximal signaling by Shc or STAT5, and induction of some downstream genes, including cytokine-inducible Src homology-2-containing protein (CIS), bcl-x(L), and bcl-2, was spared. Experiments with c-fos, cyclin D2, and CIS reporter genes revealed that promoter-proximal regulatory elements dictate the sensitivity of IL-2 target genes to inhibition by TGF-beta. By leaving the Shc and STAT5 pathways functional while inhibiting their target genes selectively, TGF-beta was found to uncouple the proliferative and antiapoptotic functions of IL-2. Thus, TGF-beta is not a simple antagonist of IL-2, but rather serves to qualitatively modify the IL-2 signal to create a unique pattern of gene expression that neither cytokine can induce independently.

Human immunodeficiency virus-1 envelope glycoproteins and anti-CD4 antibodies inhibit interleukin-2-induced Jak/STAT signalling in human CD4 T lymphocytes

Human immunodeficiency virus (HIV) infection leads to a profound T cell dysfunction well before the clinical onset of acquired immunodeficiency syndrome (AIDS). We have been accumulating evidence that one of the mechanisms responsible for this T cell deficiency may be the dysregulation of signal transduction via the interleukin (IL)-2/IL-2 receptor (R) complex. In CD4 T cells, we have observed previously that viral envelope (env) glycoproteins induce IL-2 unresponsiveness and the down-regulation of the three chains making up the IL-2R (alpha, beta, gamma) in vitro. We have now established further that this disruption of the IL-2/IL-2R system manifests itself in defective signal propagation via the Janus kinase (Jak)/signal transducer and activator of transcription (STAT) pathway in response to IL-2. The treatment of CD4 T cells with HIV env or surface ligation of CD4 with anti-CD4 monoclonal antibodies inhibited the IL-2-induced activation of Jak-1 and Jak-3, as well as their targets, STAT5a and STAT5b. This Jak/STAT deficiency may contribute to the crippling of CD4 T cell responses to a cytokine central to the immune response by HIV.

Interleukin-2 receptors and interleukin-2-mediated signaling in myelin: activation of diacylglycerol kinase and phosphatidylinositol 3-kinase

Myelin was previously shown to possess neurotransmitter and cytokine receptors that trigger well-defined signaling mechanisms within the multilamellar structure. The present study reveals the presence of an interleukin-2 (IL-2) receptor in isolated mouse CNS myelin that responds to recombinant mouse IL-2 by activating diacylglycerol kinase (DAGK) and phosphoinositide 3-kinase (PI3K); additional evidence suggests participation by protein tyrosine kinase. Activation of myelin DAGK by IL-2 occurred in brain stem tissue mince and was blocked by chelerythrin chloride, indicating an essential role for myelin-localized protein kinase C. Two inhibitors of PI3K, wortmannin and LY294002, blocked endogenous PI3K as well as that enhanced by IL-2. Activation of PI3K by IL-2 was also blocked by tyrphostin A25, a selective inhibitor of PTK, suggesting activation of the latter by IL-2 is upstream to PI3K activation. This reaction resulted in tyrosine phosphorylation of a protein tentatively identified as the p85 subunit of PI3K. Developmental changes were noted in that receptor density and signaling activity were robust during the period of rapid myelination and declined rapidly thereafter.

A role for STAT5 in the pathogenesis of IL-2-induced glucocorticoid resistance

Glucocorticoids (GC) are highly effective in the control of diseases associated with T cell activation. However, a subset of individuals is GC insensitive. Previous studies have demonstrated that IL-2 can induce steroid resistance in mouse T cells. However, the mechanism for this phenomenon is unknown. In the current study we found that the murine cell line (HT-2) is steroid resistant when incubated with IL-2, but steroid sensitive when grown in IL-4. Furthermore, when HT-2 cells are treated with IL-2, the glucocorticoid receptor (GCR) does not translocate to the cell nucleus after dexamethasone treatment. In contrast, the GCR in IL-4-stimulated HT-2 cells does translocate into the cell nucleus after dexamethasone treatment. IL-2-induced steroid insensitivity in HT-2 cells appears to be a signaling event as the effects of IL-2 on nuclear translocation of the GCR occurred within 30 min even in the presence of cycloheximide. Indeed, preincubation of HT-2 cells with a Janus-associated kinase 3 inhibitor restored nuclear translocation of the GCR even in the presence of IL-2. Immunoprecipitation experiments revealed that phosphorylated STAT5 and GCR formed immune complexes. This association may lead to retardation of GCR nuclear translocation because IL-2 was not able to induce steroid insensitivity in splenocytes from STAT5 knockout mice. This study demonstrates a novel role for STAT5 in IL-2-induced steroid insensitivity.

Retinoic acid stimulates the cell cycle machinery in normal T cells: involvement of retinoic acid receptor-mediated IL-2 secretion

The mechanisms whereby vitamin A stimulates the immune system are poorly understood. In the current study, we attempted to elucidate the potential mechanisms of action of all-trans retinoic acid (atRA) on proliferation of human T lymphocytes. We found that physiological levels of atRA potently augmented T cell proliferation when added in combination with common T cell-stimulating agents. This was reflected in a time- and concentration-dependent stimulation of the cell cycle machinery. The presence of atRA led to elevated levels of cyclin D3, -E, and -A, decreased levels of p27(Kip1), increased activity of cyclin-dependent kinase 2, and enhanced phosphorylation of the retinoblastoma protein (pRB). The atRA-mediated changes in the cell cycle machinery were late events, appearing after 20 h of stimulation, indicating that the effects of atRA were indirect. atRA did not alter the expression of the high-affinity IL-2R. However, the level of IL-2 secreted by T cells was strongly enhanced by atRA. rIL-2 was able to substitute for the effects of atRA on the cell cycle machinery and on DNA synthesis, and blocking the IL-2R markedly inhibited atRA-induced cell proliferation and pRB phosphorylation. A retinoic acid receptor (RAR)-selective agonist and 9-cis-RA had the same potency as atRA on T cell proliferation and IL-2 secretion, whereas a retinoid X receptor-selective agonist had only marginal effects. Furthermore, a RAR-selective antagonist completely suppressed T cell proliferation and pRB phosphorylation induced by atRA. Taken together, these results suggest that atRA stimulates the cell cycle machinery and proliferation of normal human T cells by increasing IL-2 secretion through mechanisms involving RARs.

Multiple cytokines sharing the common receptor gamma chain can induce CD154/CD40 ligand expression by human CD4+ T lymphocytes via a cyclosporin A-resistant pathway

Expression of CD154/CD40 ligand (CD154/CD40L), an important molecular component of CD4+ T-cell help, can be triggered by T-cell receptor (TCR) stimulation. Dephosphorylation of the transcriptional element Nuclear Factor of Activated T cells-1 (NFAT1) is a critical activation step in the TCR-initiated signal transduction cascade which promotes CD154/CD40L expression. Cyclosporin A (CsA), which interferes with NFAT1 activation, has been shown to be an effective inhibitor of TCR-triggered CD154/CD40L expression by resting T cells. We now report that recombinant interleukin-2 (rIL-2) is also capable of inducing CD154/CD40L on CD4+ T lymphoblasts via a pathway triggered independently of the CD3/TCR receptor complex. Recombinant IL-2-mediated CD154/CD40L expression, in contrast to that triggered by CD3/TCR stimulation, is only partially inhibited by CsA. The capacity of rIL-2 to induce CD154/CD40L expression by T lymphoblasts also extends to a restricted number of cytokines sharing the cytokine receptor common gamma chain, including IL-15, and, to a lesser extent, IL-7, but not IL-4. A similar CsA-resistant CD154/CD40L induction pathway can be triggered in primary T cells by the combination of anti-CD3 stimulation and recombinant lymphokines. In contrast to T lymphoblasts, the CsA-resistant CD154/CD40L induction in primary lymphocytes can be efficiently triggered by multiple cytokines which bind the common gamma chain receptor family. The data outline a novel pathway of CD154/CD40L induction which is, at least in part, independent of NFAT1 and resistant to CsA. A more complete understanding of the mechanisms governing CD154/CD40L expression may facilitate the rational design of specifically targeted immunotherapeutic agents.

Altered T cell signalling in ageing

T cell responses are altered in the aged in a manner usually interpreted as detrimental to host defences against infectious agents and possibly also against cancer. T cell dysregulation may be caused by any or a combination of stem cell deficits, compromised T cell differentiation, inefficient antigen processing and presentation by antigen presenting cells, suboptimal processing of the antigenic signal by T cells or inability of the T cell to respond appropriately thereafter. This review will focus on altered T cell signalling in ageing, encompassing not only alterations in signal transduction by the antigen-specific T cell receptor, but changes in the balance of positive and negative T cell costimulation and the resultant modified cytokine environment, the response to which is itself altered in ageing.

Cyclodextrin modulation of T lymphocyte signal transduction with aging

There is an alteration of the immune response in aging that leads to the increased incidence of infections, cancers and autoimmune disorders. The aim of the present study was to investigate whether there exists changes in signal transduction under the IL-2 receptor stimulation and the role of plasma membrane cholesterol in the activation of T cells with aging. We report age-related changes in the JAK-STAT signalling pathway that results in decreased tyrosine phosphorylation of STAT5. We present evidence for the importance of cholesterol content in regulating signalling pathways in T cells and in modulating their proliferation by using the plasma membrane cholesterol-depleting agent methyl-beta-cyclodexrin (MBCD). MBCD treatment (0.5 mM) induced a significant decrease in the cholesterol content of T cells of elderly subjects whereas it was increased in T cells of young subjects. MBCD induced changes in the phosphorylation of p56(lck), especially in T cells of elderly subjects. The proliferation of MBCD-treated T cells decreased in lymphocytes of young subjects but did not change in T cells of elderly subjects. These results suggest a role for plasma membrane cholesterol in the regulation of the TcR signalling pathways with differential effects related to aging. However, the data suggest that modulation of the plasma membrane cholesterol content alone may not be enough to restore signal transduction changes with aging.

Interleukin-2 inhibits glucocorticoid receptor transcriptional activity through a mechanism involving STAT5 (signal transducer and activator of transcription 5) but not AP-1

Cytokines and glucocorticoids (GCs) signaling pathways interfere with each other in the regulation of apoptosis and gene expression in the immune system. Interleukin-2 (IL-2), through the Janus kinase/signal transducers and activators of transcription (Jak/STAT) and mitogen-activated protein kinase (MAPK) pathways, activates STAT5 and activated protein-1 (AP-1) transcription factors, respectively, which are known to repress glucocorticoid receptor (GR) activity, at least in part, through protein-protein interactions. In this work, we have analyzed the mechanisms whereby IL-2 down-regulates the GC-induced transactivation of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in murine CTLL-2 T lymphocytes. Mutagenesis studies revealed that the MMTV-LTR STAT5 binding site (-923/-914) was not required for IL-2-mediated inhibition but identified both glucocorticoid response elements (GREs) and the -104/+1 region as critical elements for this negative response. The DNA binding activities of transcription factors required for GC-mediated activation of the MMTV-LTR promoter and that bind to the -104/+1 region (nuclear factor-1, Oct-1) were not affected by IL-2 treatment. Overexpression of wild-type STAT5B enhanced the effect of IL-2 on MMTV-LTR activity, and a dominant negative form of STAT5B (Y699F) abolished the IL-2-mediated MMTV-LTR inhibition, whereas AP-1 activation had no effect in this system. Direct interaction between liganded GR and STAT5 was observed in CTLL-2 cells in a STAT5 phosphorylation-independent manner. Overexpression of nuclear coactivators CBP (CREB-binding protein) or SRC-1a (steroid receptor coactivator 1a) did not blunt IL-2 inhibitory effects. We suggest that the STAT5-repressive activity on the GC-dependent transcription may involve direct interaction of STAT5 with GR, is dependent on the promoter context and STAT5 activation level, and occurs independently of coactivators levels in T cells.

CD45 tyrosine phosphatase controls common gamma-chain cytokine-mediated STAT and extracellular signal-related kinase phosphorylation in activated human lymphoblasts: inhibition of proliferation without induction of apoptosis

The objective of this study was to test whether CD45 signals can influence signaling processes in activated human lymphoblasts. To this end, we generated lymphoblasts which proliferate in response to common gamma-chain cytokines, but readily undergo apoptosis after cytokine withdrawal. In experiments with the CD45R0 mAb UCHL-1, but not control CD45 mAbs, we found significant inhibition of proliferation. Interestingly, the pan-CD45 mAb GAP8.3, which is most effective in inhibition of OKT-3-mediated proliferation in quiescent lymphocytes, was ineffective in lymphoblasts. Addition of CD3 mAb OKT-3 had no influence on IL-2-mediated proliferation (with or without UCHL-1). In contrast, after addition of OKT-3 to IL-4- and IL-7-stimulated proliferation assays, UCHL-1 signals could not significantly alter cellular proliferation. We did not find induction of apoptosis following CD45R0 signaling. In Western blots using mAbs detecting phosphorylated STAT-3, STAT-5, STAT-6, or extracellular signal-related kinase 1/2, we found that CD45R0 signaling could effectively diminish phosphorylation of these intracellular signaling components. Using RT-PCR, we found that CD45R0 signaling inhibited IL-2 mRNA production without major influence on IL-13, IL-5, or IFN-gamma mRNA levels. Costimulation with OKT-3 and IL-2 optimally induced secretion of IFN-gamma, TNF-alpha, and IL-5, which was not decreased by CD45 signals. In conclusion, we illustrate that CD45R0 signals control early cytokine receptor-associated signaling processes and mRNA and DNA synthesis in activated human lymphoblasts. Furthermore, we show the existence of CD45 epitopes (GAP8.3), which are active and critical for signaling in quiescent lymphocytes, but are nonfunctional in activated human lymphoblasts.

A yeast two-hybrid study of human p97/Gab2 interactions with its SH2 domain-containing binding partners

p97/Gab2 is a recently characterized member of a large family of scaffold proteins that play essential roles in signal transduction. Gab2 becomes tyrosine-phosphorylated in response to a variety of growth factors and forms multimolecular complexes with SH2 domain-containing signaling molecules such as the p85-regulatory subunit of the phosphoinositide-3-kinase (p85-PI3K), the tyrosine phosphatase SHP-2 and the adapter protein CrkL. To characterize the interactions between Gab2 and its SH2-containing binding partners, we designed a modified yeast two-hybrid system in which the Lyn tyrosine kinase is expressed in a regulated manner in yeast. Using this assay, we demonstrated that p97/Gab2 specifically interacts with the SH2 domains of PI3K, SHP-2 and CrkL. Interaction with p85-PI3K is mediated by tyrosine residues Y452, Y476 and Y584 of Gab2, while interaction with SHP-2 depends exclusively on tyrosine Y614. CrkL interaction is mediated by its SH2 domain recognizing Y266 and Y293, despite the latter being in a non-consensus (YTFK) environment.