Identification of the soluble granulocyte-macrophage colony stimulating factor receptor protein in vivo

Identification and characterization of an alternative splice variant of Mpl with a high affinity for TPO and its activation of ERK1/2 signaling

The thrombopoietin receptor is a crucial element in thrombopoietin-initiated signaling pathways, which stimulates the differentiation of normal hematopoietic progenitor cells, the maturation of megakaryocytes, and the generation of platelets. In this study, we identified a novel activating variant of thrombopoietin receptor, termed Mpl-D, in human megakaryoblastic leukemia Dami cells and demonstrated that the binding affinity of the Mpl-D receptor for thrombopoietin is enhanced. Cell cycle analysis revealed that in the presence of thrombopoietin, most Mpl-D expressing NIH3T3 (NIH3T3/Mpl-D) cells were prevalent in G1 phase while the S and G2/M populations were less frequently observed. Unexpectedly, thrombopoietin induced strong and prolonged ERK1/2 signaling in NIH3T3/Mpl-D cells compared with its receptor wild-type expressing NIH3T3 (NIH3T3/Mpl-F) cells. Further analysis of the mRNA levels of cyclin D1/D2 in NIH3T3/Mpl-D cells demonstrated markedly down-regulated expression compared to NIH3T3/Mpl-F cells in the presence of thrombopoietin. Thus, the prolonged activation of ERK1/2 by Mpl-D might lead to G1 cell cycle arrest through a profound reduction of cyclin D1/D2 in order to support cell survival without proliferation. We also provided tertiary structural basis for the Mpl-D and thrombopoietin interaction, which might provide insights into how Mpl-D effectively increases binding to thrombopoietin and significantly contributes to its specific signaling pathway. These results suggest a new paradigm for the regulation of cytokine receptor expression and function through the alternative splicing variant of Mpl in Dami cells, which may play a role in the pathogenesis of megakaryoblastic leukemia.

Granulocyte macrophage colony-stimulating factor shows anti-apoptotic activity via the PI3K-NF-κB-HIF-1α-survivin pathway in mouse neural progenitor cells

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a hematopoietic cytokine that plays a crucial role in regulating the proliferation, differentiation, and survival of hematopoietic cells. Recent studies have shown that GM-CSF also has anti-apoptotic effects and regulates the expression of anti-apoptotic genes including Bcl-2 family proteins in neuronal cells in vitro and in vivo. However, the mechanism underlying the anti-apoptotic function of GM-CSF is not well understood. In the present work, we examined the role of phosphoinositide 3-kinase (PI3K)-AKT signal pathway in the anti-apoptotic activity of GM-CSF in mouse neural progenitor cells (NPCs). In terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, the anti-apoptotic effect of GM-CSF (apoptotic population of approximately 8.17 %) on staurosporine-induced apoptosis of NPCs (31.09 %) was significantly blocked by LY294002, an inhibitor of PI3K signal (24.04 %). We found that the PI3K-AKT signal pathway induced by GM-CSF treatment activated nuclear factor κB (NF-κB) and increased the expression of hypoxia-inducible factor 1α (HIF-1α) in normoxic conditions. Analyses using specific small interfering RNAs (siRNAs) showed that NF-κB was an upstream molecule of HIF-1α and activated its expression at the mRNA level. Further analyses using the siRNAs and chromatin immunoprecipitation (ChIP) showed that HIF-1α was responsible for the induced expression of survivin, a member of the inhibitor of apoptosis proteins (IAPs). Each of the specific siRNAs for NF-κB, HIF-1α, and survivin inhibited significantly the anti-apoptotic activity of GM-CSF on the staurosporine-induced apoptosis in NPCs in TUNEL assays. The results of this study showed the downstream signals and mechanism of PI3K/AKT-mediated anti-apoptotic activity of GM-CSF in NPCs, particularly revealing the role of the NF-κB-HIF-1α-survivin cascade.

Granulocyte macrophage-colony stimulating factor shows anti-apoptotic activity in neural progenitor cells via JAK/STAT5-Bcl-2 pathway

Recently, many studies have shown that granulocyte macrophage-colony stimulating factor (GM-CSF) has anti-apoptotic activity and regulates the expression of anti-apoptotic genes including Bcl-2 family proteins in neuronal cells in vitro and in vivo. This study investigated detailed mechanism of GM-CSF involved in its anti-apoptotic activity and regulation of Bcl-2 expression in neural progenitor cells (NPCs) as a model. NPCs were cultured from the brain of E13 ICR mouse. When NPCs were treated with staurosporine at 1 μM, apoptosis occurred in more than 30% of cells in TUNEL assay. However, apoptosis was significantly inhibited by pre-treatment with GM-CSF at 10 ng/ml. Under the same experimental condition, the expression of both Bcl-2 and Bcl-xl was clearly induced by GM-CSF regardless of staurosporine treatment in RT-PCR and Western blot analyses. GM-CSF was shown to induce the expression of Bcl-2 and Bcl-xl via Janus tyrosine kinase (JAK) but not via phosphatidylinositol 3-kinase (PI3K) or RAS-mitogen activated protein kinase kinase-1 (MEK-1) using specific signal pathway inhibitors. Further analyses showed that the expression of Bcl-2 and Bcl-xl was induced by GM-CSF via signal transducers and activators of transcription 5 (STAT5) and STAT3, respectively. In addition, JAK/STAT5-Bcl-2 pathway but not JAK/STAT3-Bcl-xl pathway was responsible for the anti-apoptotic activity of GM-CSF in NPCs in TUNEL assay. To our knowledge, this study is the first report that shows differential roles of Bcl-2 and Bcl-xl, and their regulation mechanism involved in the anti-apoptotic activity of GM-CSF in NPCs.

GM-CSF: a role in immune and inflammatory reactions in the intestine

Granulocyte macrophage colony-stimulating factor (GM-CSF) is a cytokine that promotes myeloid cell development and maturation, and dendritic cell differentiation and survival in vitro. Growing evidence supports the notion that GM-CSF has a major role in some inflammatory and autoimmune reactions and in the host's response to pulmonary infection, but few studies have addressed its functions and importance in the GI tract. Recent studies demonstrated that administration of GM-CSF can result in clinical improvement in patients with Crohn's disease. Mice deficient in GM-CSF (GM-CSF(-/-) ) developed more severe intestinal and systemic infection after an enteric infection, and more severe colitis in response to enteric exposure to dextran sodium sulfate. Both the severity of infection and colitis were largely prevented by GM-CSF administration. Such studies indicate that GM-CSF has an important role in the regulation of intestinal immune and inflammatory responses.

Granulocyte/macrophage–colony-stimulating factor autoantibodies and myeloid cell immune functions in healthy subjects

High levels of granulocyte/macrophage–colony-stimulating factor (GM-CSF) autoantibodies are thought to cause pulmonary alveolar proteinosis (PAP), a rare syndrome characterized by myeloid dysfunction resulting in pulmonary surfactant accumulation and respiratory failure. Paradoxically, GM-CSF autoantibodies have been reported to occur rarely in healthy people and routinely in pharmaceutical intravenous immunoglobulin (IVIG) purified from serum pooled from healthy subjects. These findings suggest that either GM-CSF autoantibodies are normally present in healthy people at low levels that are difficult to detect or that serum pooled for IVIG purification may include asymptomatic persons with high levels of GM-CSF autoantibodies. Using several experimental approaches, GM-CSF autoantibodies were detected in all healthy subjects evaluated (n = 72) at low levels sufficient to rheostatically regulate multiple myeloid functions. Serum GM-CSF was more abundant than previously reported, but more than 99% was bound and neutralized by GM-CSF autoantibody. The critical threshold of GM-CSF autoantibodies associated with the development of PAP was determined. Results demonstrate that free serum GM-CSF is tightly maintained at low levels, identify a novel potential mechanism of innate immune regulation, help define the therapeutic window for potential clinical use of GM-CSF autoantibodies to treat inflammatory and autoimmune diseases, and have implications for the pathogenesis of PAP.

Soluble CD22 as a tumor marker for hairy cell leukemia

CD22 is an important immunotherapeutic target on B-cell malignancies, particularly hairy cell leukemia (HCL), but its soluble extracellular domain, sCD22, has not yet been reported in the blood. By immunoaffinity and enzyme-linked immunosorbent assay techniques using anti-CD22 monoclonal antibodies, we identified the 100-kDa extracellular domain of CD22 and an 80-kDa processed form in serum of patients with HCL. The median sCD22 level measured by enzyme-linked immunosorbent assay was 18 ng/mL for 93 patients with HCL. sCD22 levels varied from 2.1 to 163 ng/mL and were higher (P < .001) than 23 normal donors (median, 0.6 ng/mL). More than 95% of normal donors had sCD22 levels less than 1.9 ng/mL. sCD22 levels were proportional to concentrations of circulating HCL cells (P = .002), and HCL spleen size (P < .001). sCD22 levels normalized with complete but not partial response to treatment. sCD22 levels up to 300 ng/mL had less than a 2-fold effect on the cytotoxicity of the anti-CD22 recombinant immunotoxin BL22. sCD22 levels may be useful to follow in patients with HCL and may be more specific than sCD25 in patients with CD22(+)/CD25(-) disease. Trials are listed on www.cancer.gov as NCT00002765, NCT00021983, NCT00074048, NCT00085085, NCT00337311, and NCT00462189.

Differential regulation of c-Jun N-terminal kinase and NF-kappaB pathway by caffeic acid phenethyl ester in astroglial and monocytic cells

Caffeic acid phenethyl ester (CAPE), an active component of propolis extracts, has been known for its specific inhibition of nuclear factor kappaB (NF-kappaB) and subsequent anti-inflammatory activity. In this study, we report that (i) CAPE exerts its anti-inflammatory action (inhibition of tumor necrosis factor-induced expression of intercellular adhesion molecule-1 and CC chemokine ligand-2) via NF-kappaB inhibition by two distinct molecular mechanisms in a cell-specific manner: CAPE inhibited downstream pathways of inhibitor kappaB (IkappaB) degradation in monocytic cells, while activation of upstream IkappaB kinase was suppressed by CAPE pre-treatment in astroglial cells; and (ii) CAPE paradoxically activates the c-Jun N-terminal kinase (JNK) pathway, which might be responsible for its pro-apoptotic action and divergent regulation of proinflammatory mediators such as CXC chemokine ligand-8.

Discovery and characterization of a novel splice variant of the GM-CSF receptor α subunit

OBJECTIVE

To characterize a novel splice variant of the alpha subunit of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GMRalpha), which we discovered in human neutrophils.

METHODS

We used reverse transcriptase polymerase chain reaction to identify, characterize, and examine the expression of a novel splice variant of the GMRalpha transcript. At the protein level, surface plasmon resonance was used to measure the affinity of a recombinant soluble form of the novel GMRalpha protein for GM-CSF ligand. The full-length novel GMRalpha protein was expressed in a recombinant cell culture system, and its expression and localization were examined using Western blotting, I(125) GM-CSF binding assays, flow cytometry, and a soluble GMRalpha enzyme-linked immunosorbent assay.

RESULTS

The novel GMRalpha transcript identified herein contains a previously undescribed exon of the GMRalpha gene; this exon derives from an Alu DNA repeat element, and is alternatively spliced in the novel GMRalpha transcript. Inclusion of this 102 nucleotide exon results in translation of a protein product, which we have named Alu-GMRalpha. Alu-GMRalpha is identical to cell surface GMRalpha, but additionally contains a 34 amino-acid insert in the juxtamembrane region of the extracellular domain of GMRalpha. Functionally, the Alu-GMRalpha-specific epitope does not modify the ability of the protein to bind GM-CSF, but rather appears to be preferentially targeted by ectodomain proteases to mediate the release of a third soluble GM-CSF receptor into the extracellular space.

CONCLUSIONS

This study provides the first example of a cytokine receptor system in which soluble receptors are produced by three distinct mechanisms. Our results highlight the importance of soluble GMRalpha proteins in regulation of GM-CSF signaling.

Signal transduction pathways of GM-CSF in neural cell lines

GM-CSF is recently being suggested to play important role(s) in the nervous system. Present study was intended to understand signal transduction pathways of GM-CSF in human neuroblastoma (SK-N-(BE)2) and glioblastoma (A172) cell lines. The expression of GM-CSF receptors on the surface of these cells was confirmed by immunocytochemistry, Western blot analysis and RT-PCR. When treated for 10min, GM-CSF activated the signal transducer and activator of transcription 5 (STAT5) and extracellular signal regulated kinase (ERK) in both cell lines. However, Janus kinase 2 (JAK2) was activated only in A172 cells but not in SK-N-(BE)2 cells by GM-CSF. The GM-CSF-activated cellular signal pathways were specifically inhibited by the pretreatment of GM-CSF receptor alpha antibody, suggesting the specificity of the signal activation. The experiment using specific inhibitors (AG490) to the JAK/STAT pathway showed that JAK2/STAT5 cascade was well preserved and activated by GM-CSF in A172 cells, while STAT5 was activated by GM-CSF without JAK2 activation in SK-N-(EB)2 cells. The ERK pathway was activated by GM-CSF independently of JAK2 in both cell lines. Finally, GM-CSF showed cytoprotective effect on these cell lines by inhibiting cytotoxicity of saturosporine. The results revealed the signal transduction pathways activated by GM-CSF in neural cells and suggested that GM-CSF might affect the neural functions via these signal pathways.

Nervous system injury: focus on the inflammatory cytokine 'granulocyte-macrophage colony stimulating factor'

Any lesion in the nervous system, be it infectious, immunopathological, ischemic or traumatic, is followed by an inflammatory process that induces rapid activation of glial cells and additional recruitment of granulocytes, T-cells and monocytes/macrophages from the blood stream. Neuroinflammation is a double-sided sword. It can cause neuronal damage and participate in neuropathic pain, but it also has neuroprotective and neurotrophic effects at some stages. Cytokines are the main molecular actors of this 'network of inflammation'. Among them, granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pro-inflammatory hematopoietic cytokine widely used in haematological disorders to stimulate proliferation and differentiation of neutrophilic, eosinophilic and monocytic lineages. GM-CSF and its receptor are expressed in the brain and the cytokine can cross the blood-brain barrier. It is thus likely to affect various nervous system functions. This review will focus on the role of GM-CSF in nervous system disorders and their experimental models with particular emphasis on its possible beneficial effect on axonal regeneration after PNS and CNS injury.

Expression and regulation of NDRG2 (N-myc downstream regulated gene 2) during the differentiation of dendritic cells

We searched for genes with expressions specific to human monocyte-derived dendritic cells (DCs) using differential display reverse transcription-polymerase chain reaction, and found that N-myc downstream regulated gene 2 (NDRG2), a member of a new family of differentiation-related genes, was expressed in DCs. While DCs derived from CD34(+) progenitor cells also showed strong NDRG2 expression, the corresponding mRNA expression was absent in other cell lines including monocytes, B cells, and NK cells. The inhibition of DC differentiation by dexamethasone or vitamin D(3) treatment down-regulated the expression of the NDRG2 gene in DCs. In addition, gene expression was induced in a myelomonocytic leukemia cell line, which is capable of differentiating into DCs in cytokine-conditioned culture. The level of NDRG2 gene expression in DCs was significantly higher than that of other members of the NDRG gene family. Finally, in contrast to the stable NDRG2 expression in CD40-stimulated DCs, the induction of DC maturation by lipopolysaccharide (LPS) resulted in the down-regulation of NDRG2 gene expression. This down-regulation is likely to be due to a modification and subsequent destabilization of NDRG2 mRNA, because co-treating with actinomycin D and LPS significantly blocked this LPS effect. Taken together, our results indicate that NDRG2 is expressed during the differentiation of DCs, and that NDRG2 gene expression is differentially regulated by maturation-inducing stimuli.

Granulocyte macrophage colony stimulating factor (GM-CSF) activity is regulated by a GM-CSF binding molecule in Wallerian degeneration following injury to peripheral nerve axons

The hematopoietic factor and inflammatory cytokine GM-CSF is involved in PNS and CNS injury and disease, and in macrophage and microglia function regulation. We presently document that injury to PNS axons induces in vivo production of GM-CSF-inhibitor and GM-CSF-augmenter activities. GM-CSF-inhibitor activity was detected in extract and conditioned medium (CM) of injured PNS but not in extract of intact PNS, and was removed from CM by GM-CSF affinity chromatography, suggesting it is carried by a secreted GM-CSF binding molecule. CM further displayed GM-CSF-augmenter activity along with GM-CSF-inhibitor activity but at contrasting concentrations; augmentation at lowest and inhibition at highest. GM-CSF activity is thus regulated during Wallerian degeneration (WD); augmenter activity characterizes the onset and inhibitor activity the later stages of WD.

Neutrophil apoptosis pathways and their modifications in inflammation

Neutrophils are constantly produced in large numbers in the bone marrow, and the same numbers of cells need to die within a defined time period in order to keep cellular homeostasis under physiologic conditions. Changing the rate of apoptosis rapidly changes cell numbers in such systems. For instance, in many bacterial and autoimmune inflammatory diseases, delayed apoptosis is one important mechanism for neutrophil accumulation. Excessive production of granulocyte/macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF), two important neutrophil survival factors, is often observed in such inflammatory responses. Cytokine withdrawal, as it occurs in the resolution phase of inflammation, leads to the induction of apoptosis. Moreover, neutrophil apoptosis can be accelerated both in the presence and in the absence of survival factors by activation of distinct members of the tumor necrosis factor/nerve growth factor receptor family. This review focuses on recently published work regarding signaling pathways that regulate neutrophil apoptosis.

Clinical manifestations associated with the aberrant expression of the soluble granulocyte-macrophage colony-stimulating factor receptor in patients presenting with haematological malignancies

The receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) can exist as both transmembrane (tmGMRalpha) and soluble (solGMRalpha) isoforms, and the latter, is a normal constituent of human plasma. We investigated if aberrant solGMRalpha expression occurs in haematopoietic malignancies and whether or not solGMRalpha expression levels correlated with clinical presentation. Compared with the normal population, patients with acute lymphoblastic leukaemia (ALL) had low levels of solGMRalpha whereas clonal disorders of the myeloid lineage demonstrated higher levels of solGMRalpha. Patients with acute myelogenous leukaemia (AML) and high levels of solGMRalpha presented with a distinct clinical picture. These patients were older, predominantly belonged to the M4 and M5 French-American-British (FAB) subtypes, and they had higher white blood cell counts at presentation including myeloid precursors and myeloblasts. They often presented with either unexplained lung infiltrates or hypoxia and lower rates of microbiologically defined infections. Elevated solGMRalpha levels were not associated with decreased relapse-free and overall survival in the AML population. On multivariate analysis, the correlation between elevated solGMRalpha levels and age, M4 and M5 FAB subtypes and decreased numbers of infections persisted. Our study is the first to describe that distinct clinical presentations are associated with aberrant solGMRalpha levels in haematological malignancies.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and inflammatory stimuli up-regulate secretion of the soluble GM-CSF receptor in human monocytes: evidence for ectodomain shedding of the cell surface GM-CSF receptor alpha subunit

Soluble GM-CSF receptor alpha subunit (sGMRalpha) is a soluble isoform of the GMRalpha that is believed to arise exclusively through alternative splicing of the GMRalpha gene product. The sGMRalpha mRNA is expressed in a variety of tissues, but it is not clear which cells are capable of secreting the protein. We show here that normal human monocytes, but not lymphocytes, constitutively secrete sGMRalpha. Stimulation of monocytes with GM-CSF, LPS, PMA, or A23187 rapidly up-regulates the secretion of sGMRalpha in a dose-dependent manner, demonstrating that secretion is also regulated. To determine whether sGMRalpha arose exclusively through alternative splicing of the GMRalpha gene product, or whether it could also be generated through ectodomain shedding of GMRalpha, we engineered a murine pro-B cell line (Ba/F3) to express exclusively the cDNA for cell surface GMRalpha (Ba/F3.GMRalpha). The Ba/F3.GMRalpha cell line, but not the parental Ba/F3 cell line, constitutively shed a sGMRalpha-like protein that bound specifically to GM-CSF, was equivalent in size to recombinant alternatively spliced sGMRalpha (60 kDa), and was recognized specifically by a mAb raised against the ectodomain of GMRalpha. Furthermore, a broad-spectrum metalloprotease inhibitor (BB94) reduced constitutive and PMA-, A23187-, and LPS-induced secretion of sGMRalpha by monocytes, suggesting that shedding of GMRalpha by monocytes may be mediated in part through the activity of metalloproteases. Taken together, these observations demonstrate that sGMRalpha is constitutively secreted by monocytes, that GM-CSF and inflammatory mediators up-regulate sGMRalpha secretion, and that sGMRalpha arises not only through alternative splicing but also through ectodomain shedding of cell surface GMRalpha.

Tyrosine kinases and gastric cancer

Carcinoma of the stomach is one of the most prevalent cancer types in the world today. Two major forms of gastric cancer are distinguished according to their morphological and clinicopathological classifications (well differentiated/intestinal type and poorly differentiated/diffuse type), characteristics that could also be attributed to the altered expression of different types of oncogenes or tumor suppressor genes. Significant differences exist for gastric cancer incidence comparing people of different ethnic origins, implicating various genetic and epigenetic factors for gastric oncogenesis. There are only a limited number of molecular markers available for gastric cancer detection and prognostic evaluation, among which are tyrosine kinases. There is convincing evidence that tyrosine kinases are involved in oncogenesis and disease progression for many human cancers. Amplifications of certain tyrosine kinases (c-met, k-sam and erbB2/neu) have been associated with human gastric cancer progression. Alternatively spliced transcripts and enhanced protein-expression levels for some of these tyrosine kinases are correlated with clinical outcomes for gastric cancer patients. With advent of high throughput techniques, it is now possible to detect nearly all expressed tyrosine kinases in a single screen. This increases the chance to identify additional tyrosine kinases as predictive markers for gastric cancers. In this article, we will first review the literature data concerning certain tyrosine kinases implicated in gastric carcinogenesis and then summarize more recent work which provide comprehensive tyrosine kinase profiles for gastric cancer specimens and cell lines. Two new gastric cancer molecular markers (tie-1 and mkk4) have been identified through the use of these profiles and demonstrated effective as clinical prognostic indicators.

Monoclonal antibodies against the human interleukin-11 receptor alpha-chain (IL-11Ralpha) and their use in studies of human mononuclear cells

A panel of 14 hybridoma cell lines secreting monoclonal antibodies against the human interleukin-11 receptor alpha chain (hIL-11Ralpha) was obtained using two different approaches. Two antibodies were raised against peptides of the N- and C-terminal sequences, respectively, of the extracellular part of the hIL-11Ralpha. Another group of 12 antibodies was generated against a hybrid protein consisting of the extracellular part of the hIL-11Ralpha fused to mature full-length human IL-2. All these antibodies recognized native hIL-11Ralpha and most also recognized the denatured receptor on immunoblots after SDS-PAGE. Four different epitopes were identified on the extracellular part of the hIL-11Ralpha. One epitope, defined by the E27 antibody, is located at the N-terminus and the other three epitopes are clustered in the membrane-proximal, C-terminal region. The antibodies defining epitopes I and II recognized membrane-bound hIL-11Ralpha expressed in gp130/hIL-11Ralpha-co-transfected Ba/F3 cells. The E27 antibody cross-reacted with murine IL-11Ralpha, in agreement with the fact that the N-terminal region is highly conserved between species. The other 13 antibodies all recognized a region between amino acids 319 and 363, which is the membrane-proximal part of the hIL-11Ralpha. This region, which is less conserved between mouse and human, is shown here to be an immunodominant region. Anti-IL-11Ralpha monoclonal antibodies, which have not been described previously enabled us to explore the expression and tissue distribution of IL-11Ralpha on human peripheral blood mononuclear cells and cell lines. The antibodies provide powerful tools for the study of the regulation and function of the receptor.