Characterization of the cytoplasmic domain of interleukin-13 receptor-alpha

Interleukin (IL)-13 and IL-4 are pleiotropic immunoregulatory cytokines that share many overlapping biological properties reflecting the fact that both can utilize a receptor complex composed of the IL-4 receptor-alpha (IL-4Ralpha) chain and the IL-13Ralpha chain. The cytoplasmic domain of the IL-13Ralpha is 60 amino acids long and is essential for IL-13-dependent growth. It contains a Pro-rich domain in the membrane-proximal region and two Tyr residues. Here we show that a truncated IL-13Ralpha, lacking the 38 carboxyl-terminal residues but retaining the Pro-rich region, can support IL-13-dependent proliferation, although with reduced efficiency. A Y402F mutant of the cytoplasmic domain of IL-13Ralpha supported normal IL-13-induced growth. However, tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3), which we show is induced by IL-13 and IL-4 in cells that express the IL-13Ralpha, was significantly reduced. The cytoplasmic domain of IL-13Ralpha was constitutively associated with STAT3, Tyk2, and Janus kinase 1 (JAK1). IL-13-induced tyrosine phosphorylation of IL-13Ralpha in vivo could not be detected using anti-Tyr(P) antibodies. A glutathione S-transferase fusion protein of the cytoplasmic domain of IL-13Ralpha was phosphorylated on tyrosine in vitro by JAK1, JAK3, and Tyk2, although the tyrosine phosphorylation events mediated by Tyk2 and JAK3 were not detectable using anti-phosphotyrosine antibodies. These data, together with the demonstration that IL-13Ralpha associates constitutively with Tyk2 and that Tyr-402 is involved in IL-13-induced phosphorylation of STAT3, suggest that the latter is mediated by Tyk2. Tyrosine phosphorylation of STAT3, which was not necessary for IL-13-induced proliferation, may account for some of the effects of IL-4 and IL-13 on the function of their targets.

An interleukin (IL)-13 receptor lacking the cytoplasmic domain fails to transduce IL-13-induced signals and inhibits responses to IL-4

Interleukin (IL)-13 is a pleiotropic immunoregulatory cytokine that shares many, although not all, of the biological activities of IL-4. The overlapping biological properties of IL-4 and IL-13 appear to be due to the existence of shared components of the receptors, and we and others showed that the IL-4 receptor-alpha is involved in signal transduction paths activated by both. We show here that expression of the IL-13 receptor-alpha in two factor-dependent cell lines, the premyeloid FD5 and the T lymphoid CT4.S, conferred the ability to grow continuously in response to IL-13; to respond to IL-13 with tyrosine phosphorylation of JAK1, Tyk2, IL-4Ralpha, IRS-2, and STAT6; and to respond to IL-4 with tyrosine phosphorylation of Tyk2 in addition to those induced in parental cell lines. Expression of a truncated IL-13 receptor-alpha that lacked the cytoplasmic domain demonstrated that this domain was essential for IL-13-dependent growth and phosphorylation of the above substrates. Expression of this truncated IL-13 receptor also resulted in an inhibition of biochemical and biological responses to IL-4 that was exacerbated by the presence of IL-13. These dominant inhibitory effects indicate that the extracellular domain of the truncated IL-13 receptor competes with gammac for complexes of IL-4 and the IL-4 receptor-alpha, or, when itself bound to IL-13, competes with IL-4 for the IL-4 receptor-alpha.

Differential regulation of p72syk expression in naive and proliferating CD4-CD8+ T cells

A well-known consequence of TCR stimulation in proliferating T cells is cell death by apoptosis. We have previously shown that the extent of tyrosine phosphorylation of TCR zeta, CD3 gamma, and CD3 epsilon subunits in proliferating CD4-CD8+ T cells after TCR stimulation was decreased when compared to similarly stimulated naive T cells expressing the same TCR. Furthermore, these differences correlated with a decrease in the specific kinase activity of p56lck and p59fyn, with a corresponding increase in the specific kinase activity of p50rsk, a negative regulator of src-family tyrosine kinases. In this study we determined whether kinases that bind tyrosine phosphorylated TCR zeta chain were differentially regulated in naive and proliferating cells. Chemically synthesized cytoplasmic domains of the TCR zeta chain were fully phosphorylated in vitro with p56lck and used to precipitate TCR zeta binding proteins in naive and proliferating cells. Using this method we found that both ZAP-70 and p72syk bound tyrosine phosphorylated TCR zeta very efficiently. More interestingly, p72syk was found to be expressed only in naive but not proliferating cells. Kinetic studies indicate that more than 48 hr of activation was required for ceasation of p72syk expression. We also showed that the inability to detect p72syk expression in proliferating cells was not due to its translocation to cytoskeletal compartments in proliferating cells. We propose that the differential regulation of ZAP-70 and p72syk in naive and proliferating cells may contribute to the uncoupling of the TCR signaling pathway from downstream signaling events leading to distinct functional outcomes in these two cell types after TCR stimulation.

Increase in the specific activity of p50csk in proliferating T cells correlates with decreased specific activity of p56lck and p59fyn and reduced phosphorylation of CD3 subunits

Depending on their prior antigen recognition history, mature T cells respond with different functional outcomes to T cell receptor (TCR) stimulation. These functional outcomes include proliferation, anergy and cell death. The biochemical basis underlying differential responses by mature T cells at different stages of their developmental pathway to TCR stimulation remains to be determined. We have previously shown that proliferating but not naive T cells were susceptible to apoptosis after TCR stimulation and that the tyrosine phosphorylation of TCR zeta, CD3 gamma, and CD3 epsilon in proliferating T cells was decreased after TCR stimulation. In this study. We determined whether differences in phosphorylation between naive and proliferating T cells were due to altered regulation of p56lck (Lck) or p59fyn (Fyn) by their positive or negative regulators, CD45 or p5Ocsk (Csk), respectively. We found that Lck was expressed at the same level and had the same phosphotyrosine content in naive and proliferating T cells. However, its autophosphorylation activity was lower in proliferating cells, corresponding to a 2-fold decrease in its specific kinase activity. Similarly, the specific kinase activity of Fyn was also decreased by about 2-fold in proliferating T cells. In contrast, although Csk was expressed at the same level in both cell types its specific kinase activity was increased by 6-fold in proliferating T cells. The tyrosine phosphatase CD45, a positive regulator of src-family kinases, was overexpressed by 3- to 6-fold in proliferating cells. However, the specific activity of CD45 in naive and proliferating T cells was the same. Therefore, although the protein expression level of CD45 was increased in proliferating T cells it only partially compensated for the hyperactivity of Csk resulting in a 2-fold reduction in the specific activity of Lck and Fyn in proliferating T cells.

Differential activation of phospholipase C-gamma 1 and mitogen-activated protein kinase in naive and antigen-primed CD4 T cells by the peptide/MHC ligand

In this study, we determined the functional and biochemical differences in naive and primed CD4 T cells that expressed a TCR specific for the pigeon cytochrome c (pcc) peptide presented by I-Ek MHC class II molecules. Naive CD4 T cells expressing the transgenic TCR were isolated from the peripheral lymphoid organs of transgenic mice and stimulated with pcc peptide and IL-2 for 10 to 14 days. After this culture period, the Ag-primed cells were quiescent, as judged by the lack of expression of the early activation marker CD69, low expression of CD25 (IL-2R), and failure to incorporate thymidine. The primed cells required 10-fold less peptide than naive cells to achieve the same degree of proliferation and for the induction of CD69. Primed cells also mobilized calcium more efficiently with regard to Ag dose and magnitude of the response. The biochemical signal-transduction events in naive and primed T cells were compared by stimulating them with different concentrations of pcc peptide presented by adherent Ek-transfected fibroblasts. It was found that tyrosine phosphorylation and activation of mitogen-activated protein kinase (MAPK) in primed cells required 10-fold less Ag and occurred more rapidly and intensively. Interestingly, peptide stimulation induced tyrosine phosphorylation of phospholipase C (PLC)-gamma 1 exclusively in primed cells. RasGAP was also more efficiently tyrosine phosphorylated in primed cells. By contrast, Shc was tyrosine phosphorylated to the same extent in naive and primed cells. PI3Kp85 was not tyrosine-phosphorylated in naive and primed cells either before or after peptide stimulation. We propose that the higher sensitivity of the primed cells to Ag stimulation is most likely dependent, at last in part, on the more efficient activation of PLC-gamma 1, MAPK, and calcium-dependent pathways.

Differential activation of phospholipase C-gamma 1 and mitogen-activated protein kinase in naive and antigen-primed CD4 T cells by the peptide/MHC ligand

In this study, we determined the functional and biochemical differences in naive and primed CD4 T cells that expressed a TCR specific for the pigeon cytochrome c (pcc) peptide presented by I-Ek MHC class II molecules. Naive CD4 T cells expressing the transgenic TCR were isolated from the peripheral lymphoid organs of transgenic mice and stimulated with pcc peptide and IL-2 for 10 to 14 days. After this culture period, the Ag-primed cells were quiescent, as judged by the lack of expression of the early activation marker CD69, low expression of CD25 (IL-2R), and failure to incorporate thymidine. The primed cells required 10-fold less peptide than naive cells to achieve the same degree of proliferation and for the induction of CD69. Primed cells also mobilized calcium more efficiently with regard to Ag dose and magnitude of the response. The biochemical signal-transduction events in naive and primed T cells were compared by stimulating them with different concentrations of pcc peptide presented by adherent Ek-transfected fibroblasts. It was found that tyrosine phosphorylation and activation of mitogen-activated protein kinase (MAPK) in primed cells required 10-fold less Ag and occurred more rapidly and intensively. Interestingly, peptide stimulation induced tyrosine phosphorylation of phospholipase C (PLC)-gamma 1 exclusively in primed cells. RasGAP was also more efficiently tyrosine phosphorylated in primed cells. By contrast, Shc was tyrosine phosphorylated to the same extent in naive and primed cells. PI3Kp85 was not tyrosine-phosphorylated in naive and primed cells either before or after peptide stimulation. We propose that the higher sensitivity of the primed cells to Ag stimulation is most likely dependent, at last in part, on the more efficient activation of PLC-gamma 1, MAPK, and calcium-dependent pathways.

Characterisation of the receptor for the macrophage colony-stimulating factor in monocytes/macrophages of patients congenitally infected with Trypanosoma cruzi

Trypanosoma cruzi, the aetiological agent of Chagas' disease, is able to parasitise almost any type of cell in the mammalian host. Only the macrophage, however, is potentially microbicidal for the parasite. The effectiveness of macrophages in killing T. cruzi appears to be related to the degree of activation of the cell. The macrophage colony-stimulating factor (MCSF) is a glycoprotein that promotes proliferation, differentiation and activation of macrophages. It acts through a cell-surface receptor that encodes a tyrosine kinase in its cytoplasmic domain. The MCSF receptor (MCSFR) autophosphorylates upon induction with the ligand. A three to seven-fold lower degree of phosphorylation of ligand-stimulated MCSFR in monocytes/macrophages of patients with chronic Chagas' disease compared with those of healthy donors has been previously demonstrated. Only 5-10% of the population infected with T. cruzi develop chronic Chagas' disease. Furthermore, members of this group have a functional defect of the MCSFR. I therefore decided to investigate the state of the MCSFR in patients congenitally infected with T. cruzi in whom the acute phase of the disease had subsided and who had subsequently become seronegative for Chagas' disease after treatment with Nifurtimox. I found a heterogeneous pattern of ligand-stimulated phosphorylation of MCSFR ranging from a nil to a six-fold difference within the population. Healthy children born to mothers with Chagas' disease showed a fully phosphorylated receptor protein after stimulation with MCSFR. The state of the MCSFR may correlate with the potential to develop Chagas' disease.

Activation-induced cell death in proliferating T cells is associated with altered tyrosine phosphorylation of TCR/CD3 subunits

The first signaling event that occurs after stimulation of the TCR is an increase in the tyrosine phosphorylation of a number of proteins including the TCR-zeta chain and CD3 subunits. It is known that proliferating T cells respond differently to TCR stimulation when compared with naive T cells. Stimulation of the TCR on proliferating T cells has been shown to result in cell death by apoptosis, a process referred to as activation-induced cell death (AICD). In this study we have determined the pattern of tyrosine phosphorylation of TCR-zeta and the CD3 subunits of naive and proliferating CD4- CD8+ T cells that express a transgenic TCR that is specific for the male Ag presented by Db class I molecules after TCR stimulation. AICD in proliferating T cells was mediated by stimulation with anti-TCR/CD3, but not anti-Thy-1, anti-CD8, or anti-Db mAbs. When compared with naive T cells, tyrosine phosphorylation of TCR-zeta was dramatically decreased in proliferating cells. Furthermore, whereas CD3 delta, CD3 epsilon, and CD3 gamma of naive T cells were phosphorylated in a 1:2:1 ratio after TCR stimulation, these subunits in proliferating T cells were tyrosine phosphorylated in a 1:1:0 ratio after TCR stimulation. Altered phosphorylation of these subunits was not caused by the lack of synthesis or amount of these proteins in proliferating cells. This is the first study implicating altered tyrosine phosphorylation of TCR/CD3 subunits in AICD.

Activation-induced cell death in proliferating T cells is associated with altered tyrosine phosphorylation of TCR/CD3 subunits

The first signaling event that occurs after stimulation of the TCR is an increase in the tyrosine phosphorylation of a number of proteins including the TCR-zeta chain and CD3 subunits. It is known that proliferating T cells respond differently to TCR stimulation when compared with naive T cells. Stimulation of the TCR on proliferating T cells has been shown to result in cell death by apoptosis, a process referred to as activation-induced cell death (AICD). In this study we have determined the pattern of tyrosine phosphorylation of TCR-zeta and the CD3 subunits of naive and proliferating CD4- CD8+ T cells that express a transgenic TCR that is specific for the male Ag presented by Db class I molecules after TCR stimulation. AICD in proliferating T cells was mediated by stimulation with anti-TCR/CD3, but not anti-Thy-1, anti-CD8, or anti-Db mAbs. When compared with naive T cells, tyrosine phosphorylation of TCR-zeta was dramatically decreased in proliferating cells. Furthermore, whereas CD3 delta, CD3 epsilon, and CD3 gamma of naive T cells were phosphorylated in a 1:2:1 ratio after TCR stimulation, these subunits in proliferating T cells were tyrosine phosphorylated in a 1:1:0 ratio after TCR stimulation. Altered phosphorylation of these subunits was not caused by the lack of synthesis or amount of these proteins in proliferating cells. This is the first study implicating altered tyrosine phosphorylation of TCR/CD3 subunits in AICD.

Conversion of human interferon-beta from a secreted to a phosphatidylinositol anchored protein by fusion of a 17 amino acid sequence to its carboxyl terminus

A number of cell-surface proteins are anchored in plasma membranes by a glycosylated phosphatidylinositol (PI) moiety that is covalently attached to the carboxyl-terminal amino acid of the mature protein. We have previously reported the construction of a cDNA clone of a truncated Platelet-derived growth factor (PDGF) receptor that consists of the extracellular domain without the transmembrane and cytoplasmic domains. In the construction of the vector, a sequence of 51 base pairs (bp) from the 3'-untranslated region of the receptor cDNA was linked in frame with the external domain coding sequence. The truncated receptor protein with the peptide VTSGHCHEERVDRHDGE fused to its carboxyl terminus was covalently attached to the membrane by a PI linkage and it was released by phosphatidylinositol specific-phospholipase C (PI-PLC). When the 51 bp sequence was deleted, the external domain receptor protein was secreted into the media. To determine whether the PI linkage of the protein was due to the 17 amino acids added, the peptide was fused to the carboxyl terminus of the secreted protein human Interferon-beta (hu-IFN-beta). Chinese hamster ovary (CHO) cells transfected with the hu-IFN-beta cDNA secreted the protein to the conditioned media, whereas CHO cells transfected with the carboxyl terminus modified-hu-IFN-beta cDNA did not secrete detectable levels of protein. CHO cells expressing the carboxyl terminus modified-hu-IFN-beta were treated with PI-PLC, the media and cell lysates were analyzed by SDS-PAGE after immunoprecipitation with antibodies against hy-IFN-beta. The modified protein is anchored to the plasma membrane by a PI linkage and it is specifically released by PI-PLC, whereas a control preparation of CHO cells expressing wild type hu-IFN-beta does not show the same pattern. The 17 amino acid peptide fused to the carboxyl terminus of IFN-beta directs attachment of a PI anchor and targets the fusion protein to the plasma membrane.

Phosphatidylinositol linkage of a truncated form of the platelet-derived growth factor receptor

The platelet-derived growth factor (PDGF) receptor is usually anchored to the plasma membrane through a membrane-spanning hydrophobic amino acid sequence that splits the molecule into two approximately equal pieces, an amino-terminal external domain that contains the binding site for PDGF and a carboxyl-terminal cytoplasmic domain that includes the tyrosine kinase coding sequences. Here we report the expression of a truncated PDGF receptor that consists of the extracellular domain without the transmembrane and cytoplasmic domains. Unexpectedly, this form of the receptor that lacks a hydrophobic membrane-anchoring sequence was bound to the membrane and was not secreted into the culture media. Conventional methods to dissociate noncovalent protein-protein interactions failed to release the protein from the membrane. When the transmembrane and cytoplasmic sequences were artificially deleted from the PDGF receptor, the truncated extracellular domain was anchored to the membrane through phospholipids and could be released by phospholipase C treatment. This truncated form of the receptor bound PDGF with an affinity 5-20-fold lower than the full-length receptor.