Evidence for a critical role for the cytoplasmic region of the interleukin 2 (IL-2) receptor gamma chain in IL-2, IL-4, and IL-7 signalling.

The high-affinity interleukin 2 receptor (IL-2R) consists of at least three distinct subunits: the IL-2R alpha chain (IL-2R alpha), beta chain (IL-2R beta), and gamma chain (IL-2R gamma). It has been shown that the cytoplasmic region of IL-2R beta, but not of IL-2R alpha, is essential for IL-2 signalling to the cell interior. In the present study, we examined the functional role of the IL-2R gamma cytoplasmic region in the IL-3-dependent mouse hematopoietic cell line BAF-B03, which expresses the endogenous IL-2R alpha and IL-2R gamma, or its subline F7, which additionally expresses human IL-2R beta cDNA. We show that overexpression of a mutant IL-2R gamma, lacking all but 7 amino acids of its cytoplasmic region, results in the selective inhibition of IL-2-induced c-fos gene activation and cellular proliferation in F7 cells. When two chimeric receptor molecules in which the cytoplasmic regions of IL-2R beta and IL-2R gamma had been swapped with each other (IL-2R beta/gamma and IL-2R gamma/beta) were coexpressed in BAF-B03, the cells responded to IL-2. These results indicate the critical importance of the IL-2-induced functional cooperation of the two cytoplasmic regions. Finally, we provide evidence that the IL-2R gamma cytoplasmic region is also critical for the IL-4 and IL-7-induced growth signal transduction in BAF-B03.     

Cell type-specific tyrosine phosphorylation of IL-2 receptor beta chain in response to IL-2.

Functional activities of the IL-2 receptor (IL-2R) beta chain exogenously expressed on lymphoid and non-lymphoid cells were examined in terms of phosphorylation of IL-2R beta and cell growth. Lymphoid MOLT-4 and its transfectants expressing IL-2R beta either alone or with IL-2R alpha chain were found to be rapidly phosphorylated predominantly at tyrosine residues of IL-2R beta and to be affected in their growth in an IL-2-dependent manner. In contrast, IL-2 induced neither phosphorylation of IL-2R beta nor cell growth in non-lymphoid transfectants derived from COS7, HeLa and L929, even though they acquired the IL-2 binding ability when coexpressed as IL-2R beta and IL-2R alpha. These results suggest that IL-2 induces activation of a tyrosine kinase possibly associated with IL-2R beta in a cell type-specific manner.     

Interleukin-2 (IL-2) induces erythroid differentiation and tyrosine phosphorylation in ELM-I-1 cells transfected with a human IL-2 receptor beta chain cDNA.

The molecular mechanism of erythroid differentiation has been still ill-defined. In this study, we introduced a human interleukin-2 receptor (IL-2R) beta chain cDNA into ELM-I-1 cells which differentiated into hemoglobin-positive cells in the presence of erythropoietin (Epo), and established the transformant which expressed IL-2R beta chain. In this transformant, we revealed that IL-2 induced erythroid differentiation and the same pattern of tyrosine phosphorylation as Epo. These data suggest that tyrosine phosphorylation is involved in signal transduction pathway of erythroid differentiation. It is also implicated that the Epo and IL-2 receptor system share a common signal transduction pathway.     

A tyrosine kinase physically associates with the beta-subunit of the human IL-2 receptor

Cell surface expression of the high affinity IL-2R regulates, in part, the proliferative response occurring in Ag- or mitogen-activated T cells. The functional high affinity IL-2R is composed of at least two distinct ligand-binding components, IL-2R alpha (Tac, p55) and IL-2R beta (p70/75). The IL-2R beta polypeptide appears to be essential for growth signal transduction, whereas the IL-2R alpha protein participates in the regulation of receptor affinity. We have prepared and characterized two mAb, DU-1 and DU-2, that specifically react with IL-2R beta. In vitro kinase assays performed with DU-2 immunoprecipitates, but not anti-IL-2R alpha or control antibody immunoprecipitates, have revealed co-precipitation of a tyrosine kinase enzymatic activity that mediates phosphorylation of IL-2R beta. Because both IL-2R alpha and IL-2R beta lack tyrosine kinase enzymatic domains, these findings strongly suggest that noncovalent association of a tyrosine kinase with the high affinity IL-2R complex. Deletion mutants of the intracellular region of IL-2R beta, lacking either a previously described "critical domain" between amino acids 267 and 322 or the carboxyl-terminal 198 residues (IL-2R beta 88), lacked the ability to co-precipitate this tyrosine kinase activity, as measured by phosphorylation of IL-2R beta in vitro. Both of these mutants also failed to transduce growth-promoting signals in response to IL-2 in vivo. Analysis of the IL-2R beta 88 mutant receptor suggested that a second protein kinase mediating phosphorylation on serine and threonine residues physically interacts with the carboxyl terminus of IL-2R beta. This kinase may be necessary but, alone, appears to be insufficient to support a full IL-2-induced proliferative response. These studies highlight the physical association of protein kinases with the cytoplasmic domain of IL-2R beta and their likely role in IL-2-induced growth signaling mediated through the multimeric high affinity IL-2R complex.     

Expression of murine IL-2 receptor beta-chain on thymic and splenic lymphocyte subpopulations as revealed by the IL-2-induced proliferative response in human IL-2 receptor alpha-chain transgenic mice

Lymphocytes from the human (h) IL-2R alpha chain transgenic mice (TGM) constitutively express high affinity binding sites for hIL-2, consisting of transgenic h-IL-2R alpha and endogenous murine IL-2R beta, and therefore easily proliferate in vitro in response to hIL-2. Our study was undertaken to clarify the hIL-2-responsive lymphocyte subsets in the TGM, which should most likely reflect the normal distribution of m IL-2R beta expression. In both thymus and spleen, the majority of expanded cells by hIL-2 was CD3+CD4-CD8+ TCR alpha beta+ cells. The proliferation of CD4+ cells was not observed at all from either organ despite the expression of transgenic hIL-2R alpha. Potent cellular proliferation was also observed from the thymocytes that had been depleted of CD8+ cells, the expanded cells consisting of CD3- (15-40%) and CD3+ populations (60-85%). Among CD3+ cells, approximately the half portion expressed TCR alpha beta, whereas the other half was suggested to express TCR gamma delta. A variable portion (5-20%) of the CD3+ cells expressed CD8 (Lyt-2) in the absence of Lyt-3, and the CD3+CD8+ cells were confined preferentially to the TCR alpha beta- (TCR gamma delta+) population. In the culture of splenocytes depleted of CD8+ cells, however, the proliferated cells were mostly CD3-CD4-CD8-TCR-Mac1-, whereas a minor portion (10-30%) was CD3+CD4-CD8-TCR alpha beta- (TCR gamma delta+. Analysis of TCR genes at both DNA and mRNA levels confirmed the phenotypical observations. These results strongly suggested that IL-2R beta was constitutively and selectively expressed on the primary murine thymocytes and splenic T and NK cells, except for CD4+ cells in both organs.     

IL-12 receptor beta 2 (IL-12R beta 2)-deficient mice are defective in IL-12-mediated signaling despite the presence of high affinity IL-12 binding sites

Two subunits of the IL-12 receptor (IL-12R), IL-12R beta 1 and IL-12R beta 2, have been identified and cloned. Previous studies demonstrated that the IL-12R beta 1 subunit was required for mouse T and NK cells to respond to IL-12 in vivo. To investigate the role of IL-12R beta 2 in IL-12 signaling, we have generated IL-12R beta 2-deficient (IL-12R beta 2(-/-)) mice by targeted mutation in embryonic stem (ES) cells. Although Con A-activated splenocytes from IL-12R beta 2(-/-) mice still bind IL-12 with both high and low affinity, no IL-12-induced biological functions can be detected. Con A-activated splenocytes of IL-12R beta 2(-/-) mice failed to produce IFN-gamma or proliferate in response to IL-12 stimulation. NK lytic activity of IL-12R beta 2(-/-) splenocytes was not induced when incubated with IL-12. IL-12R beta 2(-/-) splenocytes were deficient in IFN-gamma secretion when stimulated with either Con A or anti-CD3 mAb in vitro. Furthermore, IL-12R beta 2(-/-) mice were deficient in vivo in their ability to produce IFN-gamma following endotoxin administration and to generate a type 1 cytokine response. IL-12-mediated signal transduction was also defective as measured by phosphorylation of STAT4. These results demonstrate that although mouse IL-12R beta 1 is the subunit primarily responsible for binding IL-12, IL-12R beta 2 plays an essential role in mediating the biological functions of IL-12 in mice.     

The common gamma chain (gamma c) is a required signaling component of the IL-21 receptor and supports IL-21-induced cell proliferation via JAK3

The common cytokine receptor gamma chain (gamma c), an essential component of the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15, is critical for the development and function of lymphocytes. Recently, a novel lymphokine (IL-21) and its receptor (IL-21R alpha) were described which profoundly affect the growth and activation state of B, T, and NK cells in concert with other lymphokines or stimuli [Parrish-Novak, J., et al. (2000) Nature 408, 57-63]. In this report, we show that gamma c is also a required signaling component of the IL-21 receptor (IL-21R) using the gamma c-deficient X-linked severe combined immunodeficiency (XSCID) lymphoblastoid cell line JT, and JT cells reconstituted with gamma c (JT/gamma c). Moreover, we demonstrate a functional requirement for both gamma c and the gamma c-associated Janus family tyrosine kinase 3 (JAK3) in IL-21-induced proliferation of pro-B-lymphoid cells engineered to express human IL-21R alpha (BaF3/IL-21R alpha). Retroviral-mediated transduction of wild-type gamma c into XSCID JT cells restored function to the IL-21R, as shown by IL-21-induced tyrosine phosphorylation of JAK1 and JAK3, and downstream activation of STAT5, in JT/gamma c cells as well as BaF3/IL-21R alpha and primary splenic B cells. In contrast, IL-21 failed to activate the JAK-STAT pathway in nonreconstituted JT cells. Monoclonal antibodies specific for the gamma c chain effectively inhibited IL-21-induced growth of BaF3/IL-21R alpha cells, supporting a functional role for this molecule in the IL-21R complex. In addition, the specific JAK3 tyrosine kinase inhibitor WHI-P131 significantly reduced IL-21-induced proliferation of BaF3/IL-21R alpha cells. Taken together, these results definitively demonstrate that IL-21-mediated signaling requires the gamma c chain, and indicate that JAK3 is an essential transducer of gamma c-dependent survival and/or mitogenic signals induced by this cytokine.     

Interleukin-2 (IL-2) receptor-betagamma signalling is activated by c-Kit in the absence of IL-2, or by exogenous IL-2 via JAK3/STAT5 in human papillomavirus-associated cervical cancer

Activation of the interleukin-2 receptor (IL-2R) induces signalling cascades promoting T cell proliferation. However, signal transduction pathways triggered in IL-2R-expressing solid tumours are unknown. This report shows that human papillomavirus (HPV)-associated cervical cancer cells express an IL-2R composed of beta and gamma chains (IL-2Rbetagamma), and that IL-2-mediated activation increases the phosphorylation of JAK3 and STAT5, stimulating cell proliferation. Interestingly, endogenous IL-2 is not produced by these cells, suggesting the activation of IL-2Rbetagamma by an alternative mechanism. Accordingly, we found that Stem Cell Factor (SCF)-activated c-Kit induces phosphorylation of the IL-2Rbeta chain in the absence of IL-2. Moreover, inhibition of IL-2Rbeta phosphorylation by blocking c-Kit tyrosine kinase activity abolishes both, IL-2 and SCF-mediated proliferation. Thus, these results demonstrate that IL-2 triggers a JAK3/STAT5 cascade in HPV-associated cervical cancer cells expressing IL-2Rbetagamma, and that this receptor can be alternatively activated by SCF-activated c-Kit in the absence of IL-2.     

IL-2 regulation of tyrosine kinase activity is mediated through the p70-75 beta-subunit of the IL-2 receptor

The stimulation of activated human T lymphocytes with IL-2 results in increased tyrosine kinase activity. IL-2 treatment of Tac+ T cells stimulates the rapid phosphorylation of multiple protein substrates at M of 116, 100, 92, 70 to 75, 60, 56, 55, 33, and 32 kDa. Phosphorylation on tyrosine residues was detected by immunoaffinity purification of protein substrates with Sepharose linked antiphosphotyrosine mAb, 1G2. Although phorbol ester stimulated serine phosphorylation of the IL-2R alpha (p55) subunit recognized by alpha TAC mAb, IL-2 did not stimulate any detectable phosphorylation of IL-2R alpha or associated coimmune precipitated proteins. In fact, the tyrosine phosphorylated proteins did not coprecipitate with alpha Tac antibody and similar phosphoproteins were stimulated by IL-2 in IL-2R alpha- human large granular lymphocytes which express only the 70 to 75 kDa IL-2R beta subunit of the high affinity IL-2R. Anti-Tac mAb could inhibit IL-2-stimulated tyrosine phosphorylation in activated T cells, which express both IL-2R subunits that together form the high affinity receptor complex, but not in large granular lymphocytes expressing only the IL-2R beta subunit. The data suggest that IL-2 stimulation of tyrosine kinase activities requires only the IL-2R beta subunit.     

A membrane-proximal region of the interleukin-2 receptor gamma c chain sufficient for Jak kinase activation and induction of proliferation in T cells.

The interleukin-2 (IL-2) receptor (IL-2R) consists of three distinct subunits (alpha, beta, and gamma c) and regulates proliferation of T lymphocytes. Intracellular signalling results from ligand-mediated heterodimerization of the cytoplasmic domains of the beta and gamma c chains. To identify the residues of gamma c critical to this process, mutations were introduced into the cytoplasmic domain, and the effects on signalling were analyzed in the IL-2-dependent T-cell line CTLL2 and T-helper clone D10, using chimeric IL-2R chains that bind and are activated by granulocyte-macrophage colony-stimulating factor. Whereas previous studies of fibroblasts and transformed T cells have suggested that signalling by gamma c requires both membrane-proximal and C-terminal subdomains, our results for IL-2-dependent T cells demonstrate that the membrane-proximal 52 amino acids are sufficient to mediate a normal proliferative response, including induction of the proto-oncogenes c-myc and c-fos. Although gamma c is phosphorylated on tyrosine upon receptor activation and could potentially interact with downstream molecules containing SH2 domains, cytoplasmic tyrosine residues were dispensable for mitogenic signalling. However, deletion of a membrane-proximal region conserved among other cytokine receptors (cytoplasmic residues 5 to 37) or an adjacent region unique to gamma c (residues 40 to 52) abrogated functional interaction of the receptor chain with the tyrosine kinase Jak3. This correlated with a loss of all signalling events analyzed, including phosphorylation of the IL-2R beta-associated kinase Jak1, expression of c-myc and c-fos, and induction of the proliferative response. Thus, it appears in T cells that Jak3 is a critical mediator of mitogenic signaling by the gamma c chain.     

The role of the common cytokine receptor gamma-chain in regulating IL-2-dependent, activation-induced CD8+ T cell death.

IL-2-dependent, activation-induced T cell death (AICD) plays an important role in peripheral tolerance. Using CD8+ TCR-transgenic lymphocytes (2C), we investigated the mechanisms by which IL-2 prepares CD8+ T cells for AICD. We found that both Fas and TNFR death pathways mediate the AICD of 2C cells. Neutralizing IL-2, IL-2R alpha, or IL-2R beta inhibited AICD. In contrast, blocking the common cytokine receptor gamma-chain (gamma c) prevented Bcl-2 induction and augmented AICD. IL-2 up-regulated Fas ligand (FasL) and down-regulated gamma c expression on activated 2C cells in vitro and in vivo. Adult IL-2 gene-knockout mice displayed exaggerated gamma c expression on their CD8+, but not on their CD4+, T cells. IL-4, IL-7, and IL-15, which do not promote AICD, did not influence FasL or gamma c expression. These data provide evidence that IL-2 prepares CD8+ T lymphocytes for AICD by at least two mechanisms: 1) by up-regulating a pro-apoptotic molecule, FasL, and 2) by down-regulating a survival molecule, gamma c.     

Preferential proliferation of T cell receptor V gamma 3-positive cells in IL-2-stimulated fetal thymocytes

Thymocyte cell suspensions, prepared from mice at different ages, were cultured in vitro with human rIL-2. This stimulation resulted in a cell population that contained almost 50% TCR-gamma delta-positive cells if thymocytes were taken from fetal day 17 until just after birth. Analysis of the variable (V gamma) region used by the TCR-gamma delta cells revealed that 90% of them expressed TCR-V gamma 3, and less than 5% expressed TCR-V gamma 2. Cells positive for TCR-alpha beta were barely detectable. If fetal day 18 organ cultured thymus lobes, instead of a cell suspension, were stimulated with IL-2, no rise in the number of TCR-V gamma 3+ or TCR-delta+ cells was observed, whereas a partial outgrowth of TCR-alpha beta+ cells occurred. From day 1 after birth, the number of TCR-gamma delta cells recovered from an IL-2-stimulated thymocyte cell suspension dropped to reach a plateau of 15% of the total cell number, whereas TCR-V gamma 3+ cells became undetectable in older animals. TCR-alpha beta+ cells, on the other hand, quickly rose in cell number after birth. Kinetic analysis showed that the preferential outgrowth of TCR-V gamma 3+ cells in IL-2-stimulated fetal day 18 thymocyte cell suspensions was present from the onset of the culture; a significant proliferation of CD4 or CD8 single positive TCR-alpha beta cells was never observed. This lack of proliferation of TCR-alpha beta cells was not due to inhibition by the activated TCR-V gamma 3+ cells. Throughout the IL-2 culture, one-fourth of the TCR-V gamma 3+ thymocytes was positive for CD8. Analysis of the DNA content and the IL-2 receptor (IL-2R) p55 expression showed that during the first days of culture the TCR-V gamma 3+ cells had a much higher proliferation rate than the TCR-V gamma 3- cells, although TCR-V gamma 3+ IL2R p55+ cells could not be detected. From day 3 to 4 of culture, the proliferation rate of TCR-V gamma 3+ cells equaled that of the rest of the cells and less than 20% of the TCR-V gamma 3+ cells expressed the IL-2R p55. The biologic significance of our findings is discussed.     

Hematopoietic cell phosphatase associates with the interleukin-3 (IL-3) receptor beta chain and down-regulates IL-3-induced tyrosine phosphorylation and mitogenesis.

Hematopoietic cell phosphatase (HCP) is a tyrosine phosphatase with two Src homology 2 (SH2) domains that is predominantly expressed in hematopoietic cells, including cells whose growth is regulated by interleukin-3 (IL-3). The potential effects of HCP on IL-3-induced protein tyrosine phosphorylation and growth regulation were examined to assess the role of HCP in hematopoiesis. Our studies demonstrate that, following ligand binding, HCP specifically associates with the beta chain of the IL-3 receptor through the amino-terminal SH2 domain of HCP, both in vivo and in vitro, and can dephosphorylate the receptor chain in vitro. The effects of increasing or decreasing HCP levels in IL-3-dependent cells were assessed with dexamethasone-inducible constructs containing an HCP cDNA in sense and antisense orientations. Increased HCP levels were found to reduce the levels of IL-3-induced tyrosine phosphorylation of the receptor and to dramatically suppress cell growth. Conversely, decreasing the levels of HCP increased IL-3-induced tyrosine phosphorylation of the receptor and marginally increased growth rate. These results support a role for HCP in the regulation of hematopoietic cell growth and begin to provide a mechanistic explanation for the dramatic effects that the genetic loss of HCP, which occurs in motheaten (me) and viable motheaten (mev) mice, has on hematopoiesis.     

Identification and cloning of a novel IL-15 binding protein that is structurally related to the alpha chain of the IL-2 receptor.

Interleukin-15 (IL-15) is a novel cytokine of the four-helix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor beta and gamma (IL-2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-15R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R alpha mRNA suggests that IL-15 may have biological activities distinct from IL-2.     

A critical cytoplasmic domain of the interleukin-5 (IL-5) receptor alpha chain and its function in IL-5-mediated growth signal transduction.

Interleukin-5 (IL-5) regulates the production and function of B cells, eosinophils, and basophils. The IL-5 receptor (IL-5R) consists of two distinct membrane proteins, alpha and beta. The alpha chain (IL-5R alpha) is specific to IL-5. The beta chain is the common beta chain (beta c) of receptors for IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF). The cytoplasmic domains of both alpha and beta chains are essential for signal transduction. In this study, we generated cDNAs of IL-5R alpha having various mutations in their cytoplasmic domains and examined the function of these mutants by expressing them in IL-3-dependent FDC-P1 cells. The membrane-proximal proline-rich sequence of the cytoplasmic domain of IL-5R alpha, which is conserved among the alpha chains of IL-5R, IL-3R, and GM-CSF receptor (GM-CSFR), was found to be essential for the IL-5-induced proliferative response, expression of nuclear proto-oncogenes such as c-jun, c-fos, and c-myc, and tyrosine phosphorylation of cellular proteins including JAK2 protein-tyrosine kinase. In addition, analysis using chimeric receptors which consist of the extracellular domain of IL-5R alpha and the cytoplasmic domain of beta c suggested that dimerization of the cytoplasmic domain of beta c may be an important step in activating the IL-5R complex and transducing intracellular growth signals.     

A novel monoclonal antibody against murine IL-2 receptor beta-chain. Characterization of receptor expression in normal lymphoid cells and EL-4 cells

A mAb specific for the murine IL-2R beta-chain (IL-2R beta) was produced by immunizing a rat with a rat transfectant cell line expressing a large number of cDNA-encoded murine IL-2R beta. The mAb, designated TM-beta 1, is specifically reactive with the murine IL-2R beta cDNA-transfectant but not with the recipient cell, and immunoprecipitates murine IL-2R beta of Mr 75 to 85 kDa. TM-beta 1 mAb completely abolished the high affinity IL-2 binding by inhibiting the ligand binding to IL-2R beta. Murine IL-2R beta was found to be constitutively expressed on a subpopulation of CD8+ T cells and almost all NK1.1+ NK cells in the spleen, whereas TM-beta 1 mAb inhibited the proliferation of spleen cells induced by 1 nM of IL-2. Interestingly, EL-4 cells that express murine IL-2R beta as detected by TM-beta 1 mAb can bind neither human nor murine IL-2 under the intermediate affinity conditions, although cDNA-directed human IL-2R beta expressed in the same EL-4 cells has been previously shown to manifest the intermediate affinity IL-2 binding. These results may imply that functional expression of IL-2R beta is differentially regulated between humans and mice. Finally, our neutralizing anti-IL-2R beta mAb TM-beta 1 will be useful not only for various in vitro studies but also for in vivo studies to directly investigate the possible involvement of the IL-2/IL-2R pathway in the generation and differentiation of T lymphocytes and NK cells.     

Activation of the interleukin 2 receptor: a possible role for tyrosine phosphatases

Engagement of interleukin-2 (IL-2) mediates the heterodimeridation of the common beta chain (beta(c)) and common gamma chain (gamma(c)) of the IL-2 receptor (IL-2R). This is sufficient and necessary for receptor activation and signal transduction. It is generally held that the IL-2R is activated by the trans-activity of the protein tyrosine kinases (PTKs) Jak1 and Jak3 associated with beta(c) and gamma(c) respectively. Transduction of proliferative signals requires Jak3 activity. A Jak3 independent signalling pathway involving p56(lck), generating anti-apoptotic signals, can be observed and requires the PROX domain of gamma(c). p56(lck) can be activated by dephosphorylation of an inhibitory carboxyl terminal phosphorylated tyrosine residue (Y505). We propose that this is mediated by a PROX domain associated protein tyrosine phosphatase (PTP). Activation of p56(lck) alone is insufficient for transduction of proliferative signals and thus works in concert with Jak3 mediated receptor activation. This indicates that both gamma(c) domains are vital for signal transduction.