Contribution of both STAT and SRF/TCF to c-fos promoter activation by granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic growth factor that has been shown to support call proliferation in murine fibroblasts engineered to stably express both chains of the human GM-CSF receptor (NIH-GMR). Because the proto-oncogene c-fos is believed to provide a link between short-term signals elicited at the membrane and long-term cellular response, we chose to study the mechanism of GM-CSF-dependent cell regulation using c-fos promoter activity as a molecular marker in both NIH-GMR transfectants and in the CD34+ cell line TF-1. The importance of c-fos and related AP-1 activity in GM-CSF signalling was suggested by a tight correlation between GM-CSF-dependent activation of the c-fos promoter and cell proliferation and by the inhibitory effect of a trans-dominant c-fos mutant on cell growth. To evaluate the contribution of the serum response factor (SRF) associated with the ternary complex factor (TCF) and of STAT proteins to c-fos promoter activation in response to GM-CSF, the SRF binding site (SRE) and/or the STAT binding site (SIE) were inactivated. In serum-free medium, both SRE and SIE are essential to c-fos promoter activation by GM-CSF in NIH-GMR transfectants and in TF-1 cells. No response to GM-CSF was observed when both sites were mutated. The nature of the STAT family member was further investigated by Wester blots and DNA retardation assays using an SIE probe. Our data indicate that GM-CSF induced DNA binding of both STAT1 and STAT3 in NIH-GMR and mainly of STAT3 in TF-1 cells. STAT5 tyrosine phosphorylation was also observed in TF-1 cells. Finally, expression of a dominant negative MAPK mutant, ERK192A, resulted in a decrease of both SRE- and SIE-dependent activation of c-fos promoter by GM-CSF, suggesting that STAT1/3 are regulated not only by tyrosine kinases, but also partially by MAPK.

Hematopoiesis in mice lacking the entire granulocyte-macrophage colony-stimulating factor/interleukin-3/interleukin-5 functions

Interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 are major hematopoietic cytokines produced by activated T cells and exhibit similar biologic activities by signaling through a common receptor subunit (beta c). Mice lacking beta c show a pulmonary alveolar proteinosis-like disease and reduced numbers of peripheral eosinophils, which are explained by the lack of GM-CSF and IL-5 function, respectively. However, beta c-deficient hematopoietic cells do respond to IL-3 normally, probably through an additional beta subunit of the IL-3 receptor (beta IL3) that is present in the mouse. Thus, almost normal hematopoiesis in beta c-deficient mice may be caused by functional redundancy between IL-3 and GM-CSF. To clarify the role of the entire IL-3/GM-CSF/IL-5 system in hematopoiesis in vivo, we crossed the beta c mutant mice with mice deficient for IL-3 ligand to generate mice lacking the entire IL-3/GM-CSF/IL-5 functions. The double-mutant mice were apparently normal and fertile. The severity of the lung pathology in the beta c/IL-3 double-mutant mice showed normal hemodynamic parameters except for reduced numbers of eosinophils and the lack of eosinophilic response to parasites, which were also found in beta c mutant mice. The immune response of the beta c/IL-3 double-mutant mice to Listeria mono-cytogenes was normal, as was hematopoietic recovery after administration of the cytotoxic drug, 5-fluorouracil. Although it has been believed that IL-3/GM-CSF/IL-5 produced by activated T cells play a major role in expansion of hematopoietic cells in emergency, our results indicate that the entire function of IL-3/GM-CSF/IL-5 is dispensable for hematopoiesis in emergency as well as in the steady state. Thus, there must be an alternative mechanism to produce blood cells in both situations.

Granulocyte-macrophage colony-stimulating factor: presence in human follicular fluid, protein secretion and mRNA expression by ovarian cells

In recent years it has become evident that a leukocyte-cytokine network contributes to the paracrine regulation of ovarian function. The objectives of this study were to examine the presence of a potent lympho-haemopoietic cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), in tissues and fluids from human ovaries. In a prospective study, follicular fluid and plasma were collected from naturally cycling women and women undergoing hyperstimulation for in-vitro fertilization (IVF). Granulosa-lutein cells were collected at the time of oocyte recovery for IVF and corpora lutea were collected at the time of hysterectomy for non-ovarian reasons. Culture supernatants from ovarian cell and tissue cultures were harvested on completion of a 48 h incubation. Immunoactive GM-CSF was measured by enzyme-linked immunosorbent assay, and was found to be present at statistically significantly higher levels in follicular fluid (8.9 +/- 0.7 pg/ml) and plasma (11.3 +/- 0.8 pg/ml) of women undergoing hyperstimulation compared to follicular fluid (5.3 +/- 0.3 pg/ml) and plasma (7.1 +/- 0.5 pg/ml) from naturally cycling women. Immunoactive GM-CSF was also detected in culture supernatants of granulosa-lutein cells (47.6 pg/10(5) cells), early luteal phase corpora lutea (0.52 pg/microgram DNA) and mid-luteal phase corpora lutea (0.98 pg/microgram DNA). Furthermore, transcripts for GM-CSF, and both the alpha and beta subunits of the GM-CSF receptor, were detected by reverse transcription polymerase chain reaction (RT-PCR) in granulosa-lutein cell culture preparations and corpora lutea collected during the early, mid- and late luteal phase of the menstrual cycle. These results show that GM-CSF is expressed and secreted by cells within the human ovary, and, together with the finding of expression of mRNA for GM-CSF receptor, suggest a role for GM-CSF in the local regulation of ovarian events.

Granulocyte-macrophage colony-stimulating factor receptor: stage-specific expression and function on late B cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors (GMR) are expressed on myeloid cells throughout their maturational sequence. During myelopoiesis, GM-CSF induces the proliferation of precursors and has multiple effects on more mature cells; such effects include induction of maturation and priming for subsequent stimulation. GMR is expressed on a range of other cell types including acute leukemic blasts of myeloid and lymphoid lineage, but has been little studied on more mature lymphoid cells. Using sensitive triple-layer immunophenotypic techniques, we show here that both the alpha and beta c chains of the GMR are expressed on hairy cells (HCs) and myelomatous plasma cells (PCs), but not on chronic lymphocytic leukemia (CLL) or prolymphocytic leukemia (PLL) lymphocytes. The receptor was demonstrable on normal PCs in tonsil, but not on either activated or resting tonsillar B cells or on circulating normal B lymphocytes. The expression of the receptor is therefore stage specific, rather than a feature of activation. Perhaps, surprisingly, in view of its effects on myeloid cells, GM-CSF did not stimulate the proliferation or differentiation of HCs and did not protect them from apoptosis. However, the cytokine had a profound effect on the interaction of the HC with its environment. Thus, the cytokine caused a major cytoskeletal reorganization resulting in the inhibition of motility and loss of adhesion to cellular and matrix ligands. These studies indicate the importance of GM-CSF outside myelopoiesis and demonstrate a previously unrecognized stage specific role for the cytokine in B-cell biology. Taken together with our previous report that M-CSF enhances B-cell motility, the present findings indicate that myeloid growth factors act in concert to facilitate the controlled migration of certain B cells into and within tissues.

A constitutively activated chimeric cytokine receptor confers factor-independent growth in hematopoietic cell lines

The high-affinity receptor for granulocyte-macrophage colony-stimulating factor (GMR) comprises at least 2 distinct subunits, alpha and beta common (beta c), whereas the normal erythropoietin receptor (nEpoR) comprises only one known subunit. An arginine to cysteine (R129C) mutation of the extracytoplasmic domain of the murine EpoR leads to Epo-independent growth in transduced cells (cEpoR). To investigate the proliferative functions of the cytoplasmic regions of each GMR subunit separately and the potential of the R129C EpoR mutation to induce factor-independent growth through heterologous receptor regions, we constructed four hybrid receptors: the extracellular region of either murine nEpoR or cEpoR linked to the transmembrane and cytoplasmic regions of either the human GMR alpha or beta c subunit (nE alpha, nE beta, cE alpha, and cE beta). We then expressed them in an interleukin-3-dependent murine cell line, Ba/F3. Expression of nE beta led to Epo-dependent growth, whereas expression of cE beta conferred factor-independent growth. Surprisingly, expression of cE alpha also resulted in factor-independent cell growth, whereas nE alpha did not respond to Epo. Furthermore, the functional hybrid receptors showed Epo-dependent (nE beta) or constitutive (cE alpha and cE beta) tyrosine phosphorylation of the cytoplasmic kinases JAK1 and JAK2. We reasoned that the proliferative signal of cE alpha was transduced either through the alpha tail itself or through an accessory protein such as the endogenous murine beta common subunit (mu beta c). To distinguish these possibilities, the chimeric receptor cE alpha was expressed in the interleukin-2-dependent murine cell line, CTLL-2, that does not express mu beta c. cE alpha did not induce cell growth in CTLL-2; however, when mu beta c was coexpressed with cE alpha in CTLL-2, factor-independent growth was reconstituted. In conclusion, the cytoplasmic domain of the GMR alpha subunit requires a beta chain for transduction of a proliferative signal. Furthermore, the R129C EpoR mutation can constitutively activate heterologous receptors to mediate factor-independent proliferation.

The pulmonary alveolar proteinosis in granulocyte macrophage colony-stimulating factor/interleukins 3/5 beta c receptor-deficient mice is reversed by bone marrow transplantation

Mice mutant for granulocyte macrophage colony-stimulating factor (GM-CSF) or the common receptor component (beta c) for GM-CSF, interleukin (IL)-3, and IL-5 exhibit a lung disorder similar to human pulmonary alveolar proteinosis, a rare disease with congenital, infantile, and adult forms. Bone marrow transplantation and hematopoietic reconstitution of beta c mutant mice with wild-type bone marrow reversed the established disease state in the lungs, defining this disease as hematopoietic in nature. It is likely that the disease involves alveolar macrophages, as donor myeloid cell engraftment into the lungs of mutant recipient mice correlated with reverting both the disease and an abnormal macrophage morphology seen in the lungs of affected animals. Recombination Activating Gene-2 mutant donor bone marrow, which lacks the potential to develop lymphocytes, reversed the pathology in the lungs to the same extent as whole bone marrow. These data establish that certain lung disorders, if of cell-autonomous hematopoietic origin, can be manipulated by bone marrow transplantation.

Evidence for a physical association between the Shc-PTB domain and the beta c chain of the granulocyte-macrophage colony-stimulating factor receptor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates the growth and function of several myeloid cell types at different stages of maturation. The effects of GM-CSF are mediated through a high affinity receptor that is composed of two chains: a unique, ligand-specific alpha chain and a beta common chain (beta c) that is also a component of the receptors for interleukin 3 (IL-3) and IL-5. Beta c plays an essential role in the transduction of extra cellular signals to the nucleus through its recruitment of secondary messengers. Several downstream signaling events induced by GM-CSF stimulation have been described, including activation of tyrosine kinases and tyrosine phosphorylation of cellular proteins (including beta c) and activation of the Ras/mitogen-activated protein kinase and the JAK/STAT pathways. A region within the beta c cytoplasmic tail (amino acids 517-763) has been reported to be necessary for tyrosine phosphorylation of the adapter protein, Shc, and for the subsequent GM-CSF-induced activation of Ras. In this paper, we describe a physical association between the tyrosine phosphorylated GM-CSF receptor (GMR)-beta c chain and Shc in vivo. Using a series of cytoplasmic truncation mutants of beta c and various mutant Shc proteins, we demonstrate that the N-terminal phosphotyrosine-binding (PTB) domain of Shc binds to a short region of beta c (amino acids 549-656) that contains Tyr577. Addition of a specific phosphopeptide encoding amino acids surrounding this tyrosine inhibited the interaction between beta c and shc. Moreover, mutation of a key residue within the phosphotyrosine binding pocket of the Shc-PTB domain abrogated its association with beta c. These observations provide an explanation for the previously described requirement for Tyr577 of beta c for GM-CSF-induced tyrosine phosphorylation of Shc and have implications for Ras activation through the GM-CSF, IL-3, and IL-5 receptors.

Expression of two alternatively spliced forms of the 5' untranslated region of the GM-CSF receptor alpha chain mRNA

The granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) is composed of at least two chains (alpha and beta). The alpha chain binds GM-CSF specifically with low affinity, and the binding is converted to high affinity when the alpha chain is associated with the beta chain. To date, there are at least six isoforms described for the GM-CSFR alpha, all involving alternative splicing at the 3' end, which alters the coding region and hence the protein produced. To detect variants at the 5' end of the GM-CSFR alpha mRNA, RNAse protection and reverse transcriptase polymerase chain reaction (RT-PCR) assays were performed using a probe spanning nucleotides 102-392 and pairs of primers covering exons 1-4. in addition to the expected full-length transcript, two mRNAs were detected, one containing a deletion of 24 nucleotides by alternative splicing at the 3' end of exon 2 (exon 2b-deleted isoform) and another in which exon 2 was completely deleted (exon 2-deleted isoform). Together, the isoforms were more highly expressed form). Together, the isoforms were more highly expressed than the full-length sequence (TF-1 cells: full-length 36 +/- 2.8% vs. exon 2-deleted isoforms 64 +/- 5.5%). These isoforms were detected in primary hematopoietic cells, blasts from patients with acute myeloid leukemia (AML), and malignant cell lines and the relative mRNA expression for the isoforms, was always similar to that of TF-1 cells. As sequences in the 5'untranslated region can be involved in the modulation of translational efficiency, translation of constructs constructs corresponding to these exon 2 deleted isoforms was assessed using an in vitro reticulocyte lysate system. Deletion of exon 2 resulted in significantly lower in vitro translation of the receptor protein relative to the full-length sequence (53, 56, and 76% in three separate batches of reticulocytes), while deletion of exon 2b resulted in higher translation of the sequence (164, 128, and 305%; p = 0.01). These data suggest a mechanism by which expression of the GM-CSFR alpha protein may be regulated by alternatively spliced transcripts with different translational efficiencies.

The beta subunit of human granulocyte-macrophage colony-stimulating factor receptor forms a homodimer and is activated via association with the alpha subunit

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) receptor (hGMR) consists of alpha and beta subunits, and the precise stoichiometry of these subunits has remained to be determined. In this work, oligomerization of the beta subunit was studied using a chemical cross-linker. In Ba/F3, a mouse interleukin-3-dependent cell line expressing both subunits of hGMR (Ba/F3-alpha,beta), a protein with a molecular mass corresponding to that of a homodimer of the beta subunit (beta homodimer) was detected only when cells were treated with the cross-linker. Dimerization of the beta subunit was confirmed by coimmunoprecipitation of a tagged beta subunit with the wild type beta subunit COS7 cells. The beta homodimer had already formed in the absence of hGM-CSF, whereas stimulation with the ligand brought both alpha and beta subunits into a complex, the result being tyrosine phosphorylation of the beta homodimer. Tyrosine phosphorylation of the subunit was impaired by deletion of the cytoplasmic domain of the alpha subunit without interfering with the association of both subunits. These results indicate that the beta homodimer, which alone is insufficient for signaling, forms the functional hGMR with the alpha subunit in response to hGM-CSF.

Role of granulocyte-macrophage colony-stimulating factor in Philadelphia (Ph1)-positive acute lymphoblastic leukemia: studies on two newly established Ph1-positive acute lymphoblastic leukemia cell lines (Z-119 and Z-181)

Philadelphia chromosome (Ph1)-positive acute lymphoblastic leukemia (ALL) is a malignant disorder characterized by a poor prognosis. In recent years hematopoietic growth factors have been used to recruit myeloid leukemia blasts into the proliferative phase of the cell cycle and as supportive agents, both with cytotoxic regimens and in the setting of bone marrow transplantation. This approach prompted us to investigate whether myeloid growth factors have a role in Ph1 positive ALL. To do this, we utilized two newly established Ph1-positive cell lines, Z-119 and Z-181. Both lines have L2 morphology, ultrastructural characteristics of lymphoblasts and typical B-lineage surface markers identical to those observed in the two Ph1-positive ALL patients from whom they were derived. In addition, a single rearranged immunoglobulin heavy-chain gene (JH) band was found in both cell lines by Southern blot analysis, confirming B-cell clonality. Cytogenetic analysis of the two lines revealed t(9;22). Polymerase chain reaction (PCR) amplified cDNA from both Z-119 and Z-181 cells revealed an e1--a2 BCR-ABL junction, and p190BCR-ABL protein was detected in them by the immune complex kinase assay. Both cell lines produce interleukin (IL)-1 beta, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage CSF (GM-CSF), but neither IL-1 beta, G-CSF, their corresponding antibodies and inhibitory molecules, nor GM-CSF, affected the cell lines' growth. However, GM-CSF neutralizing antibodies inhibited Z-181 but not Z-119 colony formation in a dose-dependent fashion by up to 77% and addition of GM-SCF reversed this inhibitory effect. Receptor studies with radiolabeled GM-CSF demonstrated specific binding to Z-181 but not to Z-119 cells, and Scatchard analysis revealed that Z-181 cells express high-affinity GM-CSF receptors. Furthermore, PCR analysis showed that Z-181 but not Z-119 bears the transcript for the GM-CSF receptor. Finally, studies using PH1-positive ALL patients' marrow cells revealed similar data. In 3 of 8 samples we detected significant concentrations of GM-CSF (7.5-13 pg/2 x 10(7) cells) and in 2 of 3 cases GM-CSF significantly stimulated Ph1-positive ALL colony proliferation. These data suggest that Ph1-positive ALL cells may produce GM-CSF, express GM-CSF receptors and thus show a proliferative response to this cytokine.

Regulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors in a GM-CSF-dependent human myeloid leukemia cell line (AML-193) by interleukin-6

AML-193 is a cytokine-dependent human leukemia cell line established from the bone marrow of an M5-type acute monocytic leukemia (AML) patient. The effect of recombinant human interleukin-6 (rhIL-6) on the proliferation of AML-193 cells was investigated. Both granulocyte-macrophage colony-stimulating factor (rhGM-CSF) and rhIL-3 promoted the DNA synthesis and growth of AML-193 cells in vitro. rhIL-6 alone did not support the growth of AML-193 cells, yet pretreatment of AML-193 cells with rhIL-6 markedly enhanced their proliferative response to subsequent rhGM-CSF or rhIL-3 stimulation. The growth-promoting effect induced by rhIL-6 was attributable in part to the upregulation of GM-CSF receptors on AML-193 cells; treatment of AML-193 cells with rhIL-6 for 24 to 48 hours greatly increased their GM-CSF binding activity, which occurred in a dose-dependent manner. Both the growth-promoting and receptor-upregulating effects induced by rhIL-6 could be blocked by treating AML-193 cells with neutralizing anti-gp130 antibodies (GPX7). Treatment of AML-193 cells with anti-gp130 antibodies alone also led to a notable decline in GM-CSF binding activity, suggesting a possible role of gpl30 in regulating the expression of GM-CSF receptors. When AML-193 cells were starved in cytokine-free medium and then restimulated with rhGM-CSF, a rapid increase (5 minutes) in lyn kinase activity was observed. A similar upregulation of lyn kinase activity by rhIL-6 treatment also was noted in AML-193 cells, but only after a prolonged incubation of the cells with rhIL-6 (>24 hours). These findings show that the growth-promoting effects of rhIL-6 are mediated through the upregulation of GM-CSF receptors on AML-193 cells by mechanisms that appear to involve the activation of both gp130 and lyn kinase.

The beta subunit common to the GM-CSF, IL-3 and IL-5 receptors is highly polymorphic but pathogenic point mutations in patients with acute myeloid leukaemia (AML) are rare

The intracytoplasmic tail of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) beta c chain is essential for the activation of ligand-mediated signal transduction pathways in myeloid cells. Alterations in this region could deregulate normal signalling processes. We have therefore used RT-PCR-SSCP analysis of the receptor tail to look for point mutations in RNA from 35 patients with acute myeloid leukaemia (AML) and 10 haematologically normal controls. Patterns differing from those of the haemopoietic cell line TF-1 were detected in 25/35 (71%) AML patients and 8/10 (80%) normal controls. A total of six base substitutions were identified by sequencing. Three were conservative for the amino acid involved, three led to amino acid differences, valine652-->methionine, glycine647-->valine and proline603-->threonine. One alteration was found only in a normal control, the other five were all found in both AML patients and normal controls suggesting that they were DNA polymorphisms. Two substitutions were particularly common with allele frequencies of 0.23 (G1972-->A, unchanged proline648) and 0.13 (C1306-->T, unchanged serine426). These results indicate that the GM-CSFR beta c chain is highly polymorphic but point mutations of the intracytoplasmic tail do not appear to contribute frequently to the pathogenesis of AML.

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.

Expression of GM-CSF and a functional GM-CSF receptor in the human colon carcinoma cell line SW403

Only little is known about the expression of a functional granulocyte-macrophage colony-stimulating factor receptor (GMR) and its ligands in human colon carcinoma cell lines. To obtain more information on this subject, we investigated the human colon carcinoma cell line SW403, and we were able to demonstrate the constitutive synthesis of a 85-kDa GMR in SW403 cells. After stimulation with 10% fetal calf serum, GM-CSF transcripts were expressed as well. The incubation of SW403 cells with GM-CSF resulted in an intensive down-regulation of the activity of the interferon-gamma-receptor gene, which could be reconstituted by simultaneous addition of an anti-GM-CSF antibody. GM-CSF induced an activation of tyrosine-phosphorylated protein kinases with molecular weights in the range of 30 to 210 kDa, but it had no effect on the DNA synthesis of SW403 cells.

Gene structures of the alpha subunits of human IL-3 and granulocyte-macrophage colony-stimulating factor receptors: comparison with the cytokine receptor superfamily

Recently, many genes encoding the members of the cytokine receptor superfamily (CRSF), which have common structural features, have been characterized. Analyses on the structures of the genes encoding the alpha subunits of human IL-3 (hIL-3R alpha) and granulocyte-macrophage colony-stimulating factor receptors (hGMR alpha) revealed that they have the structural features common to all members of the CRSF (i.e., conservation of the intron phase pattern as "1-2-1-0-1" rule in the fibronectin type III domains located in extracellular segments of type I cytokine receptor subunits. This finding led us to propose a possible model for gene evolution for the CRSF. We pointed out that the CRSF genes derived from a putative common ancestral gene. In addition to these common features, we found an additional intron that is unique to the IL-3R alpha and the GMR alpha genes. This additional intron suggests that the IL-3R alpha and the GMR alpha genes evolved closely in the evolution process of the CRSF genes. This evidence and results of recent studies on the evolution of mammalian X chromosome make it tempting to speculate that a putative common ancestral gene of the subfamily including IL-3R alpha, GMR alpha, and IL-5R alpha emerged in an autosome at least before the divergence of marsupials and eutherian mammals, early in the 200 million-year history of mammals.

Roles of the cytoplasmic domains of the alpha and beta subunits of human granulocyte-macrophage colony-stimulating factor receptor

The high-affinity and functional granulocyte-macrophage colony-stimulating factor receptor (GMR) is composed of two distinct subunits, alpha and beta; and the cytoplasmic domain of the beta subunit is essential to transduce growth-promoting signals. In contrast to the beta subunit, the role of the alpha subunit is not well characterized. We examined the requirement of the cytoplasmic domain of the alpha subunit and its functional region by deletion analyses. We demonstrated that the cytoplasmic domain of the alpha subunit, especially 29 amino acids residues near the transmembrane domain, was absolutely required for various signaling events including activation of immediate early genes, induction of tyrosine phosphorylation of cellular proteins, and cell growth. We further analyzed the role of the cytoplasmic domain of each subunit by constructing chimeric subunits, designated alpha/beta and beta/alpha, by exchanging cytoplasmic domains of the alpha and beta subunits of human (h) GMR. Reconstituted high-affinity chimeric hGMRs, hGMR(alpha/beta,beta/alpha) and hGMR(alpha/beta,beta), transduced signals at levels similar to the wild type hGMR(alpha,beta) in Ba/F3 cells and in NIH3T3 cells. These observations indicate that the original configuration between the extracellular and the cytoplasmic domains of the hGMR(alpha,beta) subunits is not required and that hGMR(alpha/beta,beta) transduced signals through the cytoplasmic domain of the beta subunit in an oligomeric form, without involvement of the cytoplasmic domain of the alpha subunit. Therefore human granulocyte-macrophage colony-stimulating factor signals are mainly transduced through the beta subunit, and the cytoplasmic domain of the alpha subunit is likely to activate the beta subunit in the normal hGMR.

Neutrophils activated by granulocyte-macrophage colony-stimulating factor express receptors for interleukin-3 which mediate class II expression

Freshly isolated peripheral blood neutrophils, unlike monocytes and eosinophils, do not bind interleukin-3 (IL-3) or respond to IL-3). We show that neutrophils cultured for 24 hours in granulocyte-macrophage colony-stimulating factor (GM-CSF) express mRNA for the IL-3 receptor (R) alpha subunit, as shown by RNase protection assays, and IL-3R alpha chain protein, as shown by cytometric analysis using two different specific monoclonal antibodies. This effect was selective for GM-CSF, because granulocyte colony-stimulating factor, tumor necrosis factor-alpha, interferon-gamma, and IL-1 failed to induce the IL-3 receptor. Saturation binding curves with 125I-IL-3 and Scatchard transformation showed the presence of about 100 high-affinity and 4,000 low-affinity receptors. Because neutrophils have been shown to express human leukocyte antigen (HLA)-DR in response to GM-CSF, we examined the possibility that IL-3 could augment HLA-DR expression on GM-CSF-treated cells. We found that neutrophils incubated with 30 ng/mL IL-3 as well as 0.1 ng/mL GM-CSF expressed a mean of 2.1-fold higher levels of HLA-DR than with GM-CSF alone (P < .005), confirming the signaling competence of the newly expressed IL-3R. This increase was seen even at maximal concentrations of GM-CSF and IL-3 can have an additive effect on mature human cells. The augmentation of HLA-DR by IL-3 was specific because it could be inhibited by a blocking anti-IL-3R antibody. Expression of class II molecules by neutrophils under these conditions may have significance for antigen presentation. These results provide further evidence for the role of GM-CSF as an amplification factor in inflammation by inducing neutrophil responsiveness to IL-3 produced by T cells or mast cells.

Hematopoietic and lung abnormalities in mice with a null mutation of the common beta subunit of the receptors for granulocyte-macrophage colony-stimulating factor and interleukins 3 and 5

Gene targeting was used to create mice with a null mutation of the gene encoding the common beta subunit (beta C) of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3; multi-CSF), and interleukin 5 (IL-5) receptor complexes (beta C-/- mice). High-affinity binding of GM-CSF was abolished in beta C-/- bone marrow cells, while cells from heterozygous animals (beta C+/- mice) showed an intermediate number of high-affinity receptors. Binding of IL-3 was unaffected, confirming that the IL-3-specific beta chain remained intact. Eosinophil numbers in peripheral blood and bone marrow of beta C-/- animals were reduced, while other hematological parameters were normal. In clonal cultures of beta C-/- bone marrow cells, even high concentrations of GM-CSF and IL-5 failed to stimulate colony formation, but the cells exhibited normal quantitative responsiveness to stimulation by IL-3 and other growth factors. beta C-/- mice exhibited normal development and survived to young adult life, although they developed pulmonary peribronchovascular lymphoid infiltrates and areas resembling alveolar proteinosis. There was no detectable difference in the systemic clearance and distribution of GM-CSF between beta C-/- and wild-type littermates. The data establish that beta C is normally limiting for high-affinity binding of GM-CSF and demonstrate that systemic clearance of GM-CSF is not mediated via such high-affinity receptor complexes.

PU.1 (Spi-1) and C/EBP alpha regulate expression of the granulocyte-macrophage colony-stimulating factor receptor alpha gene

Growth factor receptors play an important role in hematopoiesis. In order to further understand the mechanisms directing the expression of these key regulators of hematopoiesis, we initiated a study investigating the transcription factors activating the expression of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor alpha gene. Here, we demonstrate that the human GM-CSF receptor alpha promoter directs reporter gene activity in a tissue-specific fashion in myelomonocytic cells, which correlates with its expression pattern as analyzed by reverse transcription PCR. The GM-CSF receptor alpha promoter contains an important functional site between positions -53 and -41 as identified by deletion analysis of reporter constructs. We show that the myeloid and B cell transcription factor PU.1 binds specifically to this site. Furthermore, we demonstrate that a CCAAT site located upstream of the PU.1 site between positions -70 and -54 is involved in positive-negative regulation of the GM-CSF receptor alpha promoter activity. C/EBP alpha is the major CCAAT/enhancer-binding protein (C/EBP) form binding to this site in nuclear extracts of U937 cells. Point mutations of either the PU.1 site or the C/EBP site that abolish the binding of the respective factors result in a significant decrease of GM-CSF receptor alpha promoter activity in myelomonocytic cells only. Furthermore, we demonstrate that in myeloid and B cell extracts, PU.1 forms a novel, specific, more slowly migrating complex (PU-SF) when binding the GM-CSF receptor alpha promoter PU.1 site. This is the first demonstration of a specific interaction with PU.1 on a myeloid PU.1 binding site. The novel complex is distinct from that described previously as binding to B cell enhancer sites and can be formed by addition of PU.1 to extracts from certain nonmyeloid cell types which do not express PU.1, including T cells and epithelial cells, but not from erythroid cells. Furthermore, we demonstrate that the PU-SF complex binds to PU.1 sites found on a number of myeloid promoters, and its formation requires an intact PU.1 site adjacent to a single-stranded region. Expression of PU.1 in nonmyeloid cells can activate the GM-CSF receptor alpha promoter. Deletion of the amino-terminal region of PU.1 results in a failure to form the PU-SF complex and in a concomitant loss of transactivation, suggesting that formation of the PU-SF complex is of functional importance for the activity of the GM-CSF receptor alpha promoter. Finally, we demonstrate that C/EBP alpha can also active the GM-CSF receptor alpha promoter in nonmyeloid cells. These results suggest that PU.1 and C/EBP alpha direct the cell-type-specific expression of GM-CSF receptor alpha, further establish the role of PU.1 as a key regulator of hematopoiesis, and point to C/EBP alpha as an additional important factor in this process.

Expression and selective cellular localization of granulocyte-macrophage colony-stimulating factor (GM-CSF) and GM-CSF alpha and beta receptor messenger ribonucleic acid and protein in human ovarian tissue

Reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical observations revealed that human ovarian tissue expressed granulocyte-macrophage colony-stimulating factor (GM-CSF) as well as GM-CSF alpha and beta receptor (R) mRNA and protein. The RT-PCR products revealed the predicted 286-, 546-, and 380-bp fragments for GM-CSF, GM-CSF alpha R, and GM-CSF beta R, respectively, which were further verified by restriction enzyme digestion analysis. In situ hybridization revealed that the theca interna of the large follicles and luteal cells are the exclusive site of GM-CSF mRNA expression. Furthermore, immunohistochemical studies using specific monoclonal antibodies indicated that the theca interna of the large follicles are the exclusive site of GM-CSF protein, whereas theca externa and to a lesser extent the granulosa cells are the major sites of GM-CSF alpha R and beta R proteins. Atretic follicles and follicular cysts showed very low or no detectable levels of GM-CSF and GM-CSF alpha R and beta R. In the luteal tissue, both the small and large luteal cells of early luteal (Days 14-19) and midluteal (Days 20-25) phase expressed GM-CSF mRNA and protein as well as GM-CSF alpha R and beta R proteins, and their immunostaining intensity was similar to that seen with theca cells. Luteal cells from late luteal phase (Days 26-28), corpus albicans, and ectopic pregnancy expressed a low level of GM-CSF, GM-CSF alpha R, and GM-CSF beta R mRNA and protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a viability domain in the granulocyte/macrophage colony-stimulating factor receptor beta-chain involving tyrosine-750

The granulocyte/macrophage colony-stimulating factor (GM-CSF) receptor (GMR) is a heterodimeric receptor expressed by myeloid lineage cells. In this study we have investigated domains of the GMR beta-chain (GMR beta) involved in maintaining cellular viability. Using a series of nested GMR beta deletion mutants, we demonstrate that there are at least two domains of GMR beta that contribute to viability signals. Deletion of amino acid residues 626-763 causes a viability defect that can be rescued with fetal calf serum (FCS). Deletion of residues 518-626, in contrast, causes a further decrement in viability that can be only partially compensated by the addition of FCS. GMR beta truncated proximal to amino acid 517 will not support long-term growth under any conditions. Site-directed mutagenesis of tyrosine-750 (Y750), which is contained within the distal viability domain, to phenylalanine eliminates all demonstrable tyrosine phosphorylation of GMR beta. Cell lines transfected with mutant GMR beta (Y750-->F) have a viability disadvantage when compared to cell lines containing wild-type GMR that is partially rescued by the addition of FCS. We studied signal transduction in mutant cell lines in an effort to identify pathways that might participate in the viability signal. Although tyrosine phosphorylation of JAK2, SHPTP2, and Vav is intact in Y750-->F mutant cell lines, Shc tyrosine phosphorylation is reduced. This suggests a potential role for Y750 and potentially Shc in a GM-CSF-induced signaling pathway that helps maintain cellular viability.

Activating point mutations in the common beta subunit of the human GM-CSF, IL-3 and IL-5 receptors suggest the involvement of beta subunit dimerization and cell type-specific molecules in signalling

We have combined retroviral expression cloning with random mutagenesis to identify two activating point mutations in the common signal-transducing subunit (h beta c) of the receptors for human granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3 and IL-5 by virtue of their ability to confer factor independence on the haemopoietic cell line, FDC-P1. One mutation (V449E) is located within the transmembrane domain and, by analogy with a similar mutation in the neu oncogene, may act by inducing dimerization of h beta c. The other mutation (I374N) lies in the extracellular, membrane-proximal portion of h beta c. Neither of these mutants, nor a previously described mutant of h beta c (FI delta, which has a small duplication in the extracellular region), was capable of inducing factor independence in CTLL-2 cells, while only V449E could induce factor independence in BAF-B03 cells. These results imply that the extracellular and transmembrane mutations act by different mechanisms. Furthermore, they imply that the mutants, and hence also wild-type h beta c, interact with cell type-specific signalling molecules. Models are presented which illustrate how these mutations may act and predict some of the characteristics of the putative receptor-associated signalling molecules.

Interleukin-3 treatment of rhesus monkeys leads to increased production of histamine-releasing cells that express interleukin-3 receptors at high levels

To understand the hematopoietic and nonhematopoietic responses to interleukin-3 (IL-3), expression of cell-surface IL-3 receptors (IL-3R) was examined on bone marrow (BM) cells and peripheral blood (PB) cells of rhesus monkeys during the course of in vivo IL-3 treatment. Whereas IL-3R expression is low in untreated monkeys, IL-3 administration led to a gradual increase in both low- and high-affinity binding sites for IL-3. This increase reflected the total number of cells expressing IL-3Rs, as detected by flow cytometry using biotinylated IL-3. Most of these IL-3R+ cells in both BM and PB could be characterized as basophilic granulocytes that contained high levels of histamine. In contrast to the effect on these differentiated cells, IL-3 administration did not significantly alter the low level IL-3R expression on immature, CD34+ cells. Further flow cytometric analysis using biotinylated growth factors showed that the IL-3R+ basophils also expressed receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF), but not for IL-6 or Kit ligand. These findings indicated that the IL-3R+ cells included neither monocytes, which express GM-CSFRs and IL-6Rs abundantly, nor mast cells, which express c-kit. By combining flow cytometric and Scatchard data, it was calculated that the basophils contain as many as 1 to 2 x 10(3) high-affinity IL-3Rs and 15 to 30 x 10(3) low-affinity sites. The finding that in vivo IL-3 treatment leads to the production of large numbers of cells that express high levels of IL-3R and are capable of producing histamine provides an explanation for the often severe allergic reactions that occur during prolonged IL-3 administration. It also indicates that IL-3, in addition to its direct effects on hematopoietic cells, may also stimulate hematopoiesis through the release of secondary mediators such as histamine by IL-3-responsive mature cells.

Characterization of cis-regulatory elements of the c-myc promoter responding to human GM-CSF or mouse interleukin 3 in mouse proB cell line BA/F3 cells expressing the human GM-CSF receptor

Interleukin 3 (IL-3) or granulocyte macrophage colony-stimulating factor (GM-CSF) activates c-fos, c-jun, and c-myc genes and proliferation in both hematopoietic and nonhematopoietic cells. Using a series of deletion mutants of the beta subunit of human GM-CSF receptor (hGMR) and inhibitors of tyrosine kinase, two distinct signaling pathways, one for activation of c-fos and c-jun genes, and the other for cell proliferation and activation of c-myc gene have been elucidated. In contrast to wealth of information on the pathway leading to activation of c-fos/c-jun genes, knowledge of the latter is scanty. To clarify the mechanisms of activation of c-myc gene by cytokines, we established a transient transfection assay in mouse proB cell line BA/F3 cells expressing hGMR. Analyses of hGMR beta subunit mutants revealed two cytoplasmic regions involved in activation of the c-myc promoter, one is essential and the other is dispensable but enhances the activity. These regions are located at the membrane proximal and the distal regions covering amino acid positions 455-544 and 544-589, respectively. Characterization of cis-acting regulatory elements of the c-myc gene showed that the region containing the P2 promoter initiation site is sufficient to mediate the response to mIL-3 or hGM-CSF. Electrophoretic mobility shift assay using an oligonucleotide corresponding to the distal putative E2F binding site revealed that p107/E2F complex, the negative regulator of E2F, decreased, and free E2F increased after mIL-3 stimulation. These results support the thesis that mIL-3 or hGM-CSF regulates the c-myc promoter by altering composition of the E2F complexes at E2F binding site.

A human GM-CSF receptor expressed in transgenic mice stimulates proliferation and differentiation of hemopoietic progenitors to all lineages in response to human GM-CSF

Granulocyte-macrophage colony-stimulating factor (GM-CSF) mainly stimulates proliferation and maturation of myeloid progenitor cells. Although the signal transduction pathways triggered by GM-CSF receptor (GMR) have been extensively characterized, the roles of GMR signals in differentiation have remained to be elucidated. To examine the relationship between receptor expression and differentiation of hemopoietic cells, we used transgenic mice (Tg-mice) that constitutively express human (h) GMR at almost all stages of hemopoietic cell development. Proliferation and differentiation of hemopoietic progenitors in bone marrow cells from these Tg-mice were analyzed by methylcellulose colony formation assay. High affinity GMR interacts with GM-CSF in a species-specific manner, therefore one can analyze the effects of hGMR signals on differentiation of mouse hemopoietic progenitors using hGM-CSF. Although mouse (m) GM-CSF yielded only GM colonies, hGM-CSF supported various types of colonies including GM, eosinophil, mast cell, erythrocyte, megakaryocyte, blast cell, and mixed hemopoietic colonies. Thus, the effects of hGM-CSF on colony formation more closely resembled mIL-3 than those of mGM-CSF. In addition, hGM-CSF generated a much larger number of blast cell colonies and mixed cell colonies than did mIL-3. hGM-CSF also generated erythrocyte colonies in the absence of erythropoietin. Therefore, GM-CSF apparently has the capacity to promote growth of cells of almost all hemopoietic cell lineages, if functional hGMR is present.