IL-2R Subunits Research Articles

Blimp-1 is a negative regulator of IL-2 signaling in T cells

Abstract Interleukin-2 (IL-2) is a T cell growth factor with immunomodulatory effects and pleiotropic actions on T cells. IL-2 signaling occurs via the intermediate IL-2Rb and IL-2Rg and high-affinity IL-2Ra receptors, fine-tuning tolerance and effector functions. To investigate key regulators of the IL-2 signaling pathway, we performed genome-wide CRISPR-Cas9 screening in IL-2-dependent ED40515(+) cells, which were derived from a patient with HTLV-I associated Adult T Cell Leukemia. We found a significant dropout of sgRNAs for genes known to be important in IL-2 signaling, whereas sgRNAs targeting Prdm1 were highly enriched, with its being the top enriched hit in the screen. Prdm1 encodes Blimp-1, which is known to inhibit IL-2 production in T cells; however, its precise role in IL-2 signaling pathway remains elusive. Overexpression of Prdm1 resulted in lower expression of IL-2R subunits (CD25, CD122, CD132) and decreased IL-2-induced phosphorylation of STAT5, AKT, ERK in mouse CD4 +T cells. Correspondingly, conditional knockout (CKO) of Prdm1 in mouse CD4 +T cells and Tregs led to enhanced expression of IL-2R subunits, pSTAT5, pAKT and pERK. In an influenza infection mouse model, CD122 expression and pSTAT5 levels were higher in T follicular helper (T FH) cells from Prdm1 CKO mice as compared to WT T FHcells. Further, adoptive transfer of Prdm1 CKO Tregs into Rag1 −/−mice resulted in augmented IL-2 signaling and ameliorated inflammation in colitis. Concordantly, CRISPR/Cas9-mediated deletion of Prdm1 in human CD4 +T cells and Tregs resulted in increased expression of IL-2R subunits and IL-2-induced phosphorylation of STAT5, AKT and ERK. These results suggest that Blimp-1 is a negative regulator of IL-2 signaling in mouse and human T cells. Supported by intramural funding from NIH

IL-2 receptors preassemble and signal in the ER/Golgi causing resistance to antiproliferative anti–IL-2Rα therapies

Interleukin-2 (IL-2) and IL-15 play pivotal roles in T cell activation, apoptosis, and survival, and are implicated in leukemias and autoimmune diseases. Their heterotrimeric receptors share their β- and γc-chains, but have distinct α-chains. Anti-IL-2Rα (daclizumab) therapy targeting cell surface-expressed receptor subunits to inhibit T cell proliferation has only brought limited success in adult T cell leukemia/lymphoma (ATL) and in multiple sclerosis. We asked whether IL-2R subunits could already preassemble and signal efficiently in the endoplasmic reticulum (ER) and the Golgi. A combination of daclizumab and anti-IL-2 efficiently blocked IL-2-induced proliferation of IL-2-dependent wild-type (WT) ATL cells but not cells transfected with IL-2, suggesting that in IL-2-producing cells signaling may already take place before receptors reach the cell surface. In the Golgi fraction isolated from IL-2-producing ATL cells, we detected by Western blot phosphorylated Jak1, Jak3, and a phosphotyrosine signal attributed to the γc-chain, which occurred at much lower levels in the Golgi of WT ATL cells. We expressed EGFP- and mCherry-tagged receptor chains in HeLa cells to study their assembly along the secretory pathway. Confocal microscopy, Förster resonance energy transfer, and imaging fluorescence cross-correlation spectroscopy analysis revealed partial colocalization and molecular association of IL-2 (and IL-15) receptor chains in the ER/Golgi, which became more complete in the plasma membrane, further confirming our hypothesis. Our results define a paradigm of intracellular autocrine signaling and may explain resistance to antagonistic antibody therapies targeting receptors at the cell surface.

CD25 and Protein Phosphatase 2A Cooperate to Enhance IL-2R Signaling in Human Regulatory T Cells.

Low-dose IL-2 therapy is a direct approach to boost regulatory T cells (Tregs) and promote immune tolerance in autoimmune patients. However, the mechanisms responsible for selective response of Tregs to low-dose IL-2 is not fully understood. In this study we directly assessed the contribution of CD25 and protein phosphatase 2A (PP2A) in promoting IL-2R signaling in Tregs. IL-2-induced tyrosine phosphorylation of STAT5 (pSTAT5) was proportional to CD25 levels on human CD4+ T cells and YT human NK cell line, directly demonstrating that CD25 promotes IL-2R signaling. Overexpression of the PP2A catalytic subunit (PP2Ac) by lentiviral transduction in human Tregs increased the level of IL-2R subunits and promoted tyrosine phosphorylation of Jak3 and STAT5. Interestingly, increased expression of CD25 only partially accounted for this enhanced activation of pSTAT5, indicating that PP2A promotes IL-2R signaling through multiple mechanisms. Consistent with these findings, knockdown of PP2Ac in human Tregs and impaired PP2Ac activity in mouse Tregs significantly reduced IL-2-dependent STAT5 activation. In contrast, overexpression or knockdown of PP2Ac in human T effector cells did not affect IL-2-dependent pSTAT5 activation. Overexpression of PP2Ac in human Tregs also increased the expressions of proteins related to survival, activation, and immunosuppressive function, and upregulated several IL-2-regulated genes. Collectively, these findings suggest that CD25 and PP2A cooperatively enhance the responsiveness of Tregs to IL-2, which provide potential therapeutic targets for low-dose IL-2 therapy.

Protein phosphatase 2A promotes IL-2R signaling in human regulatory T cells

Abstract Low-dose IL-2 therapy is a direct approach to boost Tregs and promote immune tolerance in autoimmune patients. The selective response of Tregs to low-dose IL-2 has been suggested to be due to high level of CD25 and activity of the Ser/Thr phosphatase, PP2A. Here we directly assessed the contribution of these two parameters in promoting IL-2 signaling in human Tregs. IL-2-induced tyrosine phosphorylation of STAT5 (pSTAT5) was proportional to CD25 levels on human CD4+ T cells, directly demonstrating that high IL-2R levels promote the Treg response to low-dose IL-2. To evaluate the role of PP2A, expanded human Tregs were transduced with lentivirus to overexpress or knock down the PP2A catalytic subunit (PP2Ac). Overexpression of PP2Ac increased the level of all IL-2R subunits and promoted phosphorylation of Jak3 at Tyr980/981. Compared to control-transduced cells, PP2Ac-overexpressed Tregs were 3-fold more sensitive to IL-2 based on pSTAT5 activation. Increased expression of CD25 only partially accounted for this enhanced activation of pSTAT5. Consistent with these findings, knockdown of PP2Ac in Tregs significantly reduced the pSTAT5 responses to IL-2. Overexpression of PP2Ac in Tregs also increased the expressions of proteins related to growth, survival, activation, and immunosuppressive function, and included several IL-2-regulated genes. Collectively, these findings indicate that PP2A promotes IL-2R signaling through multiple mechanisms, one related to control of IL-2R expression and another that may directly regulate IL-2R signaling.

Abstract B296: NKTR-214: An immunotherapy with altered selectivity at the IL2 receptor; pharmacokinetics (PK) and pharmacodynamics (PD) in animal models.

Abstract Background: Aldesleukin (IL2) has been successfully used to treat cancer, with the potential for durable responses. However, its efficacy is limited by concomitant enhancement of immunosuppression. An immunostimulatory therapeutic approach that lacks certain immunosuppressive side effects can be achieved by targeting the appropriate subunits of the heterotrimeric interleukin 2 receptor, IL2R. NKTR-214 is a releasable multi-PEGylated conjugate of IL2. Upon in vivo administration, active forms of less conjugated-IL2 are released, which exhibit altered IL2R subunit selectivity. These forms favor proliferation of tumor-killing immune cells (CD8T) over immunosuppressive T cells (Treg) in the tumor (Charych, JCO 2013, 31:15, Suppl. 1). Here we show that polymer conjugation also prolongs exposure and activates known immune pharmacodynamic markers in mice, rats, and monkeys. These combined attributes improve efficacy and tolerability of NKTR-214 compared to the clinically approved cytokine aldesleukin. Methods: NKTR-214 PK and PD were assessed after single IV bolus doses in mice bearing B16F10 melanoma (2 mg/kg), rats (1 mg/kg), and monkeys (0.1 mg/kg). Aldesleukin was assessed in mice bearing B16F10 melanoma after 3 mg/kg IP qdx5. For assessment of PK, serial plasma samples were assayed for IL2 by ELISA. For NKTR-214, conjugated-IL2 was chemically released prior to ELISA. Immune system activation was monitored in plasma by sequential measurement of sCD25, C-reactive protein (CRP), lymphocyte counts, IFNγ, and TNFα. Results: The half-life of NKTR-214 was 20 hr in mice, which is considerably longer than the 5 hr half-life for aldesleukin, contributing to a 600-fold greater dose-normalized exposure. Consistent with the sustained exposure, altered receptor selectivity and favorable immune cell response, a single 2 mg/kg dose of NKTR-214 maintained greater suppression of tumor growth compared to daily 3 mg/kg doses of aldesleukin. NKTR-214 half-life was similar in rats and monkeys. In addition, NKTR-214 triggered a robust activation of known systemic immune system markers. For example, after a single efficacious dose of NKTR-214 in mice (2 mg/kg), sCD25 increased 25-fold compared to 5-fold for 5 daily doses of aldesleukin. In monkeys, an equally robust activation of sCD25 was observed at a single dose of 0.1 mg/kg (MTD) of NKTR-214. The kinetic profiles of CRP and lymphocyte counts following NKTR-214 were similar to that of sCD25 in monkeys, while the inflammatory cytokines IFNγ and TNFα remained undetectable. Conclusions: A single dose of NKTR-214 results in sustained exposure, robust immune system activation, and favorable immune cell changes in the tumor microenvironment. Based on NKTR-214 PK and PD in animals, infrequent dosing is feasible in humans, allowing convenient combination with other immunotherapies. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B296. Citation Format: Ute Hoch, Paul Sims, Murali Addepalli, Yuan Song, Chunmei Ji, Peter Kirk, Theresa Sweeney, Deborah Charych, Seema Kantak. NKTR-214: An immunotherapy with altered selectivity at the IL2 receptor; pharmacokinetics (PK) and pharmacodynamics (PD) in animal models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B296.

Construction of unnatural heterodimeric receptors based on IL‐2 and IL‐6 receptor subunits

Cells have various receptors on their surface for responding to extracellular signals that involve intercellular communication. Although the mechanism of signal transduction by such wild-type receptors has been studied intensively, there has been minimal effort in investigating whether such receptors could signal when unnaturally coupled. In this study, we investigated whether unnatural receptor pairs comprising interleukin-2 (IL-2) and interleukin-6 (IL-6) receptor subunits could transduce a signal through forced dimerization. We replaced the extracellular domain of IL-2R and IL-6R signaling subunits (IL-2Rβ, IL-2Rγ, and gp130) with the FK506-binding protein (FKBP) or the FKBP12-rapamycin binding (FRB) domain, the protein pair known to be heterodimerized by rapamycin. When expressed in a hematopoietic cell line, unnatural heterodimers (IL-2Rβ-gp130 and IL-2Rγ-gp130 pairs) successfully transduced a signal. While the IL-2Rγ-gp130 pair maximally mimicked gp130 signaling, the IL-2Rβ-gp130 pair gave weaker gp130 signaling and no significant induction of IL-2Rβ signaling, indicating a high potential of the IL-2Rγ chain in terms of activating the coupled partners. This is the first report demonstrating that heterodimeric combinations of IL-2R and IL-6R subunits are functional for signaling. Further extension of this approach may attain a creative design of artificial receptor pairs that have distinct signaling properties when compared with natural receptors.

Human IL-2 Mutein with Higher Antitumor Efficacy Than Wild Type IL-2

IL-2 has been used for the treatment of melanoma and renal cell carcinoma, but this therapy has limited efficacy and severe toxicity. Currently, it is assumed that part of the limited efficacy is due to the IL-2-driven preferential expansion of regulatory T cells, which dampen the antitumor immunity. In this study, we characterize a human IL-2 mutant with higher antitumor efficacy and lower toxicity than wild type human IL-2 (wtIL-2). The mutant differs from wtIL-2 by four mutations at the interface with the α subunit of IL-2R. The IL-2 mutant induces in vitro proliferation of CD8(+)CD44(hi) and NK1.1 cells as efficiently as does wtIL-2, but it shows a reduced capacity to induce proliferation of CD4(+)Foxp3(+) regulatory T cells. The IL-2 mutant shows a higher antimetastatic effect than does wtIL-2 in several transplantable tumor models: the experimental metastasis model of MB16F0 melanoma and the experimental and spontaneous metastasis models for the mouse pulmonary carcinoma 3LL-D1222. Relevantly, the IL-2 mutant also exhibits lower lung and liver toxicity than does wtIL-2 when used at high doses in mice. In silico simulations, using a calibrated mathematical model, predict that the properties of IL-2 mutein are a consequence of the reduction, of at least two orders of magnitude, in its affinity for the α subunit of IL-2R (CD25). The human IL-2 mutant described in the present work could be a good candidate for improving cancer therapy based on IL-2.

CD25 content variation with the responses of T helper cell to IL-2 induced proliferation

Objective To elucidate the expression diversity of IL-2R subunits in T helper(Th) cells under different activation condition and clarify its relationship with the response to IL-2 induced proliferation.Methods In vitro cultured Th1 cells were activated by plate bound anti-mouse CD3 McAb.In both activated and inactivated Th1 cells the expression of different IL-2R subunit was evaluated by real-time PCR and fluorescence staining,3H incorporation assay was adopt to measure the proliferation of the cells in response to IL-2 treatment,IL-2 affinity was determined via I125 labeled IL-2.IL-2Rα siRNA transfection was applied to knockdown CD25 expression in activated Th1 cells and its effect was confirmed by Western blot,IL-2 induced proliferation in IL-2Rα siRNA transfected Th1 cells were subsequently detected.CD4 cells were isolated from na(i)ve BALB/c mice and were also stimulated by plate bound anti-CD3 McAb.Cells were harvested at different days posterior to the stimulation,CD25 content and IL-2 induced proliferation were determined by flow cytometry and 3H incorporation assay respectively.Results In comparison with inactivated cells,only the expression of CD25but not other IL-2R subunits was significantly increased in activated Th1 cells.In accordance with elevated CD25,IL-2 affinity was also increased in activated Th1 cells,however,which resulted in decreased cell proliferation in response to IL-2 treatment.In activated Th1 cells,when CD25 expression was differently knockdown by different-dosed IL-2Rα siRNA transfection,the highest IL-2 response was observed in the cells with partially CD25 depression.Forin vitro activated na(i)ve CD4 cells the elevated CD25 expression gradually decreased and the highest proliferation response was detected at day 8 post stimulation upon IL-2 treatment.Conclusion Although CD25 is necessary for IL-2 induced proliferation,however,the excessively expressed CD25 lead to lower proliferation response.Not fully activated Thl or CD4 cells,but partially activated cells with lightly increased CD25 content possessed highest proliferation rate in response to IL-2 treatment. Key words: CD25; IL-2; T helper cells; Proliferation

Measurement and cellular sources of the soluble interleukin-2 receptor in primary central nervous system lymphoma

The aims of this study were to determine the diagnostic utility of the serum levels of the soluble interleukin 2 receptor (sIL-2R) as a tumor marker of primary central nervous system lymphoma (PCNSL) and to investigate the cellular source of sIL-2R using immunohistochemical staining. The serum sIL-2R levels of 37 samples from suspected PCNSL patients were measured. There were 13 patients with PCNSL and 24 patients with other diseases such as glioma, metastatic tumor, inflammation, or cerebrovascular disease. The serum sIL-2R levels of the PCNSL cases and other brain diseases were 629.5±586.0U/ml (mean±SD; range 189-2220U/ml) and 408.5±250.7U/ml (160-837U/ml), respectively. The serum sIL-2R levels of the two groups overlapped, and hence the difference between them was not significant. sIL-2R is the α subunit of IL-2R. It is also known as CD25, and is cleaved from its position in the cell membrane and released into the blood. CD25 expression was immunohistochemically detected in 7 of 11 PCNSL samples. Confocal laser microscopy revealed that CD25 signals were present in atypical cells and mononuclear cells. We concluded that both lymphoma cells and infiltrating T cells express CD25, which is one of the cellular sources of sIL-2R.

Modified DT–IL2 fusion toxin targeting uniquely IL2Rα expressing leukemia cell lines – Construction and characterization

Immunotoxins are fusion proteins of modified toxin conjugated to tumor cell selective ligand. Denileukin diftitox approved by FDA for treatment of CTCL is diphtheria toxin (DT)/IL2 fusion protein targeted to high affinity IL2R. Here, we have attempted to target the more uniquely expressed low affinity IL2R (IL2Rα). We designed four immunotoxins, SPRSV1 was designed to code for a single protein of DT (390) and IL2 (133) without any extra amino acids at the junction. SPRSV2 was designed to selectively target low affinity IL2R, it codes for DT (390) and IL2 (69). We also constructed SPRSV3 encoding for only DT (390) without any ligand, as negative control and SPRSV4 was designed similar to commercial equivalent denileukin diftitox, it codes for DT (387) and IL2 (133) with His at the junction. The cytotoxic activities of these immunotoxins were tested in various cell lines, cell lines lacking IL2R expression and healthy MNC were used as controls. The activities of SPRSV1 and SPRSV2 were comparable to that of SPRSV4. SPRSV2 exhibited potent cytotoxicity effectively targeted to α subunit of IL2R on various leukemia cell lines. Our studies also showed a negative correlation between CD25 expression and percentage cell viability after treatment with immunotoxins.

Regulatory T cells in Graves’ disease

Graves' disease (GD) involves auto-immunity against thyroid cell antigens, but the reasons for induction of auto-immunity are uncertain. We wished to determine whether there was a deficiency of regulatory T cells in patients with active GD. Venous blood samples were obtained from patients with GD before and after treatment, and controls, and peripheral blood mononuclear cells were prepared. Regulatory T cells were enumerated by Fluorescent Activated Cell sorting (FACS) in nineteen patients with untreated GD, 9 patients 6-8 weeks post RAI therapy, and 30 control subjects. Twenty-one patients with active GD prior to control of hyperthyroidism, 23 euthyroid controls without known autoimmune thyroid disease, and 10 patients who were euthyroid 6-12 months after RAI treatment were studied for expression of genes found in regulatory T cells by real-time Polymerase Chain reaction (PCR). Percent distribution of CD4+, CD4+CD25+ and CD4+ CD25+(int-hi) CD127+(lo) regulatory T cells was similar in active GD patients and control subjects. The number of CD25+ and CD4+ CD25+(int-hi) CD127+(lo) cells was similar in GD patients and control subjects, but was lower in recently treated patients. Messenger RNA was prepared from PBMC, and reverse transcribed. Copy DNA abundance was evaluated by Real Time PCR using appropriate primers, for GAPDH (glyceraldehyde phosphate dehydrogenase) as a control housekeeping gene, and 5 genes related to function of regulatory T cells. Message RNA for Gadd45 alpha, Gadd45beta (growth arrest and damage inducible proteins), GITR (glucocorticoid inducible TNF receptor) and CD25 (IL-2R subunit) was more abundant in patients with active GD than in normal controls, and FoxP3 mRNA level was equal to that in controls. Message RNA levels in patients treated and euthyroid for 6 months were also greater than or equal to values in controls. This study provides evidence that there is no deficit in T regulatory cells during active GD, or during the months post therapy.

Retraction: Endogenous IL-15 Sustains Recruitment of IL-2Rβ and Common γ and IL-2-Mediated Chemokine Production in Normal and Inflamed Human Gingival Fibroblasts

We recently reported that anti-IL-15 neutralizing mAb has been shown to inhibit production of MCP-1 in response to IL-2 from normal human gingival fibroblasts (HGF), the major constituent of gingival tissue. In the present study, we examined the expression of IL-2R and IL-15R subunits in HGF from normal and inflamed regions and the role of endogenous IL-15 in IL-2-mediated signaling. Normal HGF expressed IL-2Rβ and common γ-chain (γ c ) but not IL-2Rα or IL-15Rα, whereas inflamed HGF expressed IL-2Rα, IL-15Rα, IL-2Rβ, and γ c , as assessed by RT-PCR and flow cytometry. Exogenous IL-2 and IL-15 induced production of MCP-1 but not IL-8 in normal HGF, and induced the production of both chemokines in inflamed HGF. Both HGF constitutively transcribed the 48 aa-IL-15 isoform, and the isoform was not actively secreted but rather existed as a membrane-bound form. Pretreatment with anti-IL-15 neutralizing mAb for 24 h completely inhibited the production of MCP-1 induced by IL-2 and IL-15 and IL-2-induced phosphorylation of Jak 1 and 3 in HGF. The pretreatment and RNA interference targeted to IL-15 mRNA resulted in total inhibition of the IL-2Rβ and γ c expression at mRNA and protein levels. Furthermore, excess amounts of IL-2 restored the inhibitory effect of anti-IL-15, inhibition of NF-κB abrogated the expression of IL-2Rβ and γ c , and IL-2-induced-nuclear translocation of NF-κB was completely inhibited by the RNA interference in HGF. These results suggest that endogenous membrane-bound IL-15 sustains recruitment of IL-2Rβ and γ c through activation of NF-κB in HGF.

Impaired STAT Phosphorylation in T Cells from Melanoma Patients in Response to IL-2: Association with Clinical Stage

To assess the extent of signal transducer and activator of transcription (STAT) activation in response to interleukin 2 (IL-2) in melanoma patients' T cells, along with clinical stage of tumor progression. T lymphocytes from peripheral blood of healthy donors and of American Joint Committee on Cancer stage I to IV melanoma patients, as well as from metastatic lymph nodes of patients, were evaluated for responsiveness to IL-2. CFSE assays and single-cell phospho-STAT-specific flow cytometry screening were used. Results. T cells from advanced melanoma patients, in comparison with healthy donors, showed reduced proliferation to IL-2 and IL-15, but not to anti-CD3 monoclonal antibody. Impaired response occurred in CCR7(+) and CCR7(-) T-cell subsets, but not in CD3(-) CD8(+) natural killer (NK) cells, and was not explained by induction of apoptosis, increased cytokine consumption, or altered IL-2R subunit expression in patients' T lymphocytes. By phospho-specific flow cytometry, defective STAT1 and STAT5 activation in response to IL-2 was found mainly in T lymphocytes from peripheral blood and/or tumor site of American Joint Committee on Cancer stage III and IV patients, compared with stage I and II patients and to donors, and in melanoma antigen-specific T cells isolated from metastatic lymph nodes. At tumor site, impaired STAT activation in T cells did not correlate with frequency of CD4(+) CD25(+) Foxp3(+) T cells. Serum from advanced melanoma patients inhibited IL-2-dependent STAT activation in donors' T cells and a neutralizing monoclonal antibody to transforming growth factor beta1 counteracted such inhibition. These results provide evidence for development of impaired STAT signaling in response to IL-2, along with clinical evolution of the disease, in melanoma patients' T cells.

P110γ and p110δ Phosphoinositide 3-Kinase Signaling Pathways Synergize to Control Development and Functions of Murine NK Cells

Phosphoinositide 3-kinases (PI-3Ks) are key enzymes for cell development, activation, and survival. Here we showed that PI-3K class IB and class IA catalytic subunits, p110gamma and p110delta, played a crucial role in the development and functions of murine NK cells. p110gamma deficiency and impairment of G protein-coupled receptor (GPRC) signaling prevented full NK cell maturation. Concomitant loss of p110gamma and p110delta exacerbated this defect, resulting in a very small population of NK cells with a highly immature phenotype in the bone marrow and periphery. Moreover, combined p110gamma and p110delta signals were required for cytotoxicity and activation of the kinase ERK during NK cell-target cell interaction. p110gamma played a major role in receptor-induced interferon-gamma (IFN-gamma) production through a pathway that involved the kinase ERK and 5-Lipoxigenase, which most likely generates lipid mediators activating GPRCs. Conversely, PI3Ks negatively regulated interleukin-12 (IL-12) and IL-18-induced IFN-gamma by modulating p38 kinase activation. Our data shed light on the multiple intersecting pathways through which PI3Ks control NK cell-mediated innate responses.

Interleukins 2 and 15 Regulate Ets1 Expression via ERK1/2 and MNK1 in Human Natural Killer Cells

Interleukins (IL)-2 and IL-15 regulate natural killer (NK) cell proliferation, survival, and cytolytic activity. Ets1 is a transcription factor expressed early in NK cell differentiation. Because IL-2Rbeta, IL-2Rgamma, IL-15, and Ets1 knock-out mice similarly lack NK cells, we explored a molecular connection between IL-2R signaling and Ets1. Here we report the post-transcriptional regulation of Ets1 by IL-2R signaling in human NK cells. IL-2 and IL-15 stimulation leads to increased Ets1 protein levels with no significant change in mRNA levels. Pulse and pulse-chase experiments show that IL-2 stimulation results in both a marked increase in the nascent translation of Ets1 and an increased protein half-life. Pharmacological inhibition of MEK specifically blocks IL-2- and IL-15-induced translation, whereas p38, phosphatidylinositol 3-kinase, and mTOR inhibitors had no effect on Ets1 levels. Fli1, an Ets family member, exhibited a different mechanism of regulation, illustrating the specificity of IL-2R beta and gamma subunit signaling on the regulation of Ets1 expression. Expression of a dominant negative form of MNK1, a regulator of the translation initiation factor eIF4E, blocks the expression of Ets1 as do the dominant negative forms of the common IL-2R beta and gamma chains. Expression of Ets1 is regulated similarly in normal peripheral human NK cells. Taken together, our findings provide a direct link between IL-2R subunit signaling and Ets1 expression and helps to explain the interdependence of the IL-2R subunits and Ets1 for NK cell development and function.

Endogenous IL-15 sustains recruitment of IL-2Rbeta and common gamma and IL-2-mediated chemokine production in normal and inflamed human gingival fibroblasts.

We recently reported that anti-IL-15 neutralizing mAb has been shown to inhibit production of MCP-1 in response to IL-2 from normal human gingival fibroblasts (HGF), the major constituent of gingival tissue. In the present study, we examined the expression of IL-2R and IL-15R subunits in HGF from normal and inflamed regions and the role of endogenous IL-15 in IL-2-mediated signaling. Normal HGF expressed IL-2Rbeta and common gamma-chain (gammac) but not IL-2Ralpha or IL-15Ralpha, whereas inflamed HGF expressed IL-2Ralpha, IL-15Ralpha, IL-2Rbeta, and gammac, as assessed by RT-PCR and flow cytometry. Exogenous IL-2 and IL-15 induced production of MCP-1 but not IL-8 in normal HGF, and induced the production of both chemokines in inflamed HGF. Both HGF constitutively transcribed the 48 aa-IL-15 isoform, and the isoform was not actively secreted but rather existed as a membrane-bound form. Pretreatment with anti-IL-15 neutralizing mAb for 24 h completely inhibited the production of MCP-1 induced by IL-2 and IL-15 and IL-2-induced phosphorylation of Jak 1 and 3 in HGF. The pretreatment and RNA interference targeted to IL-15 mRNA resulted in total inhibition of the IL-2Rbeta and gammac expression at mRNA and protein levels. Furthermore, excess amounts of IL-2 restored the inhibitory effect of anti-IL-15, inhibition of NF-kappaB abrogated the expression of IL-2Rbeta and gammac, and IL-2-induced-nuclear translocation of NF-kappaB was completely inhibited by the RNA interference in HGF. These results suggest that endogenous membrane-bound IL-15 sustains recruitment of IL-2Rbeta and gammac through activation of NF-kappaB in HGF.

GPI-microdomains (membrane rafts) and signaling of the multi-chain interleukin-2 receptor in human lymphoma/leukemia T cell lines.

Subunits (alpha, beta and gamma) of the interleukin-2 receptor complex (IL-2R) are involved in both proliferative and activation-induced cell death (AICD) signaling of T cells. In addition, the signaling beta and gamma chains are shared by other cytokines (e.g. IL-7, IL-9, IL-15). However, the molecular mechanisms responsible for recruiting/sorting the alpha chains to the signaling chains at the cell surface are not clear. Here we show, in four cell lines of human adult T cell lymphoma/leukemia origin, that the three IL-2R subunits are compartmented together with HLA glycoproteins and CD48 molecules in the plasma membrane, by means of fluorescence resonance energy transfer (FRET), confocal microscopy and immuno-biochemical techniques. In addition to the beta and gamma(c) chains constitutively expressed in detergent-resistant membrane fractions (DRMs) of T cells, IL-2Ralpha (CD25) was also found in DRMs, independently of its ligand-occupation. Association of CD25 with rafts was also confirmed by its colocalization with GM-1 ganglioside. Depletion of membrane cholesterol using methyl-beta-cyclodextrin substantially reduced co-clustering of CD25 with CD48 and HLA-DR, as well as the IL-2 stimulated tyrosine-phosphorylation of STATs (signal transducer and activator of transcription). These data indicate a GPI-microdomain (raft)-assisted recruitment of CD25 to the vicinity of the signaling beta and gamma(c) chains. Rafts may promote rapid formation of a high affinity IL-2R complex, even at low levels of IL-2 stimulus, and may also form a platform for the regulation of IL-2 induced signals by GPI-proteins (e.g. CD48). Based on these data, the integrity of these GPI-microdomains seems critical in signal transduction through the IL-2R complex.

NF-kappa B/Rel participation in the lymphokine-dependent proliferation of T lymphoid cells.

Proliferative responses of lymphoid cells to IL-2 and IL-4 depend on activation of the cells, but the mechanism(s) by which activation enhances cellular competence to respond to cytokines is not fully understood. The NF-kappaB/Rel family represents one signal transduction pathway induced during such activation. We show in this study that inhibition of NF-kappaB through the expression of an IkappaBalpha (inhibitory protein that dissociates from NF-kappaB) mutant refractory to signal-induced degradation (IkappaBalpha(DeltaN)) interfered with the acquisition of competence to proliferate in response to IL-4 as well as IL-2. Thymocytes and T cells from IkappaBalpha(DeltaN) transgenic mice expressed normal levels of IL-2R subunits. However, transgenic cells exhibited a dramatic defect in Stat5A activation treatment with IL-2, and a similar defect was observed for IL-4-induced Stat5. In contrast, T lymphoid cells with inhibition of NF-kappaB showed normal insulin receptor substrate-2 phosphorylation and only a modest decrease in Stat6 activation and insulin receptor substrate-1 phosphorylation after IL-4 stimulation. These results indicate that the NF-kappaB/Rel/IkappaBalpha system can regulate cytokine receptor capacitation through effects on the induction of downstream signaling by the Stat transcription factor family.

The generation of human dendritic and NK cells from hemopoietic progenitors induced by interleukin-15.

Interleukin-15 (IL-15) is a pleiotropic cytokine that induces the generation and differentiation of lymphoid cells and shares many biological activities with IL-2. We have shown here the development of dendritic cells (DC) from human CD34+ hemopoietic precursor cells cultured for 2-4 weeks with IL-15 alone. DC generated with IL-15 have typical morphological, immunocytochemical, phenotypic, and functional characteristics of mature DC. Dual flow cytometry analysis performed weekly demonstrated increasing co-expression of CD1a or CD83 with HLA-DR, CD80, CD86, IL-2R alpha, beta, and gamma. Two populations of cells were distinguished among CD34+ progeny. Small and medium-size cells were mainly natural killer (NK) cells (72.6-85.2% CD56+) and low numbers of DC (9.1-21.3% CD1a+). Large cells were mostly DC (75.4-95.4% CD1a+). Isolated CD34+ cells did not express IL-2R subunits but after 2-3 days in culture with IL-15, they were found to express IL-2Rgamma. Induced expression of IL-2Rgamma on CD34+ cells may explain the primary mechanism of IL-15-regulated differentiation of hemopoietic precursor cells. Thus, our data suggest that IL-15 stimulates CD34+ cells to differentiate into NK and DC and may represent a new growth and survival factor for lymphoid DC.

A nucleoside analogue, 7-thia-8-oxoguanosine stimulates proliferation of thymocytes in vitro

7-thia-8-oxoguanosine (immunosine) is a nucleoside analogue with immunoenhancing activity. In this work, its effects on proliferation of thymocytes in vitro were studied. It was found that immunosine stimulated proliferation of thymocytes both of mice and rats. The stimulatory effect depended on antigen presenting cells (APC), since thymocytes depleted of accessory cells did not proliferate to immunosine. In addition, pretreatment of APC with immunosine for 24 h significantly increased proliferation of thymocytes. Immunosine stimulated interleukin 2 (IL-2) production and the expression of activation markers (CD25 and CD71). The upregulation of CD25 (α subunit of IL-2R) was detected both on thymocytes and thymic dendritic cells. Proliferation of thymocytes in the presence of immunosine was predominantly mediated by IL-2 since blocking IL-2Rα by specific monoclonal antibodies inhibited cell proliferation by 65–85%.