Transcriptional and posttranscriptional modulation of myeloid colony-stimulating factor expression by tumor necrosis factor and other agents

Lethal eosinophilic crystalline pneumonia in mice expressing a stabilized Csf2 mRNA

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine that stimulates the proliferation and differentiation of granulocyte and macrophage precursors. The mouse gene-encoding GM-CSF, Csf2, is regulated at both transcriptional and post-transcriptional levels. An adenine-uridine-rich element (ARE) within the 3'-untranslated region of Csf2 mRNA was shown in cell transfection studies to confer instability on this transcript. To explore the physiological importance of this element in an intact animal, we generated mice with a knock-in deletion of the 75-nucleotide ARE. Mice heterozygous for this ARE deletion developed severe respiratory distress and death within about 12 weeks of age. There was dense infiltration of lung alveolar spaces by crystal-containing macrophages. Increased stability of Csf2 mRNA was confirmed in bone marrow-derived macrophages, and elevated GM-CSF levels were observed in serum and lung. These mice did not exhibit notable abnormalities in blood or bone marrow, and transplantation of bone marrow from mutant mice into lethally irradiated WT mice did not confer the pulmonary phenotype. Mice with a conditional deletion of the ARE restricted to lung type II alveolar cells exhibited an essentially identical lethal lung phenotype at the same ages as the mice with the whole-body deletion. In contrast, mice with the same conditional ARE deletion in myeloid cells, including macrophages, exhibited lesser degrees of macrophage infiltration into alveolar spaces much later in life, at approximately 9 months of age. Post-transcriptional Csf2 mRNA stability regulation in pulmonary alveolar epithelial cells appears to be essential for normal physiological GM-CSF secretion and pulmonary macrophage homeostasis.

Uncovering the Role of RNA-Binding Proteins in Gene Expression in the Immune System

Fighting external pathogens requires an ever-changing immune system that relies on tight regulation of gene expression. Transcriptional control is the first step to build efficient responses while preventing immunodeficiencies and autoimmunity. Post-transcriptional regulation of RNA editing, location, stability, and translation are the other key steps for final gene expression, and they are all controlled by RNA-binding proteins (RBPs). Nowadays we have a deep understanding of how transcription factors control the immune system but recent evidences suggest that post-transcriptional regulation by RBPs is equally important for both development and activation of immune responses. Here, we review current knowledge about how post-transcriptional control by RBPs shapes our immune system and discuss the perspective of RBPs being the key players of a hidden immune cell epitranscriptome.

Post-transcriptional regulatory networks in immunity

Post-transcriptional mechanisms that modulate global and/or transcript-specific mRNA stability and translation contribute to the rapid and flexible control of gene expression in immune effector cells. These mechanisms rely on RNA-binding proteins (RBPs) that direct regulatory complexes (e.g. exosomes, deadenylases, decapping complexes, RNA-induced silencing complexes) to the 3'-untranslated regions of specific immune transcripts. Here, we review the surprising variety of post-transcriptional control mechanisms that contribute to gene expression in the immune system and discuss how defects in these pathways can contribute to autoimmune disease.

IL-17A-producing neutrophil-regulatory Tn lymphocytes

The proinflammatory cytokine IL-17A, mainly produced by specialized T cells, plays an important homeostatic role in regulating neutrophil production and blood neutrophil counts. This review will assemble and discuss the evidence for this function of IL-17A-producing cells, which are collectively called neutrophil-regulatory T cells or Tn cells. IL-17A-producing lymphocytes are most abundant in the mesenteric lymph node, where they account for 0.15% of all lymphocytes. About 60% of the Tn cells are gammadelta T cells, about 25% NKTlike cells, and less than 15% are CD4 T cells. These latter cells are also known as T-17 or ThIL-17 cells, a subset of Tn cells that also plays an important role in autoimmune diseases. IL-17A produced by Tn cells regulates the production of G-CSF, which in turn promotes the proliferation of promyelocytes and maturation of neutrophils. This homeostatic mechanism plays an important role in normal physiology and in host defense against bacterial infections. This review is aimed at highlighting the important role of IL-17A-producing T cells at the interface between the adaptive and innate immune system.

p38 mitogen-activated protein kinase/Hog1p regulates translation of the AU-rich-element-bearing MFA2 transcript

AU-rich-element (ARE)-mediated mRNA regulation occurs in Saccharomyces cerevisiae in response to external and internal stimuli through the p38 mitogen-activated protein kinase (MAPK)/Hog1p pathway. We demonstrate that the ARE-bearing MFA2 3' untranslated region (UTR) controls translation efficiency in a p38 MAPK/Hog1p-dependent manner in response to carbon source growth conditions. The carbon source-regulated effect on MFA2 3'-UTR-controlled translation involves the role of conserved ARE binding proteins, the ELAV/TIA-1-like Pub1p, which can interact with the cap/eIF4G complex, and the translation/mRNA stability factor poly(A) binding protein (Pab1p). Pub1p binds the MFA2 3'-UTR in a p38 MAPK/Hog1p-regulated manner in response to carbon source growth conditions. Significantly, the p38 MAPK/Hog1p is also required to modulate Pab1p in response to carbon source. We find that Pab1p can bind the MFA2 3'-UTR in a regulated manner to control MFA2 3'-UTR reporter translation. Binding of full-length Pab1p to the MFA2 3'-UTR correlates with translation repression. Importantly, Pab1p binds the MFA2 3'-UTR only in a PUB1 strain, and correlating with this requirement, Pub1p controls translation repression of MFA2 in a carbon source/Hog1p-regulated manner. These results suggest that the p38 MAPK/Hog1p pathway regulates 3'-UTR-mediated translation by modulating recruitment of Pab1p and Pub1p, which can interact with the translation machinery.

Changes in chromatin accessibility across the GM-CSF promoter upon T cell activation are dependent on nuclear factor kappaB proteins

Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a key cytokine in myelopoiesis and aberrant expression is associated with chronic inflammatory disease and myeloid leukemias. This aberrant expression is often associated with constitutive nuclear factor (NF)-kappaB activation. To investigate the relationship between NF-kappaB and GM-CSF transcription in a chromatin context, we analyzed the chromatin structure of the GM-CSF gene in T cells and the role of NF-kappaB proteins in chromatin remodeling. We show here that chromatin remodeling occurs across a region of the GM-CSF gene between -174 and +24 upon T cell activation, suggesting that remodeling is limited to a single nucleosome encompassing the proximal promoter. Nuclear NF-kappaB levels appear to play a critical role in this process. In addition, using an immobilized template assay we found that the ATPase component of the SWI/SNF chromatin remodeling complex, brg1, is recruited to the GM-CSF proximal promoter in an NF-kappaB-dependent manner in vitro. These results suggest that chromatin remodeling across the GM-CSF promoter in T cells is a result of recruitment of SWI/SNF type remodeling complexes by NF-kappaB proteins binding to the CD28 response region of the promoter.

RNA destabilization by the granulocyte colony-stimulating factor stem-loop destabilizing element involves a single stem-loop that promotes deadenylation

Granulocyte colony-stimulating factor (G-CSF) mRNA contains two distinct types of cis-acting mRNA destabilizing elements in the 3'-untranslated region. In addition to several copies of the AU-rich element the G-CSF mRNA also contains a destabilizing region that includes several predicted stem-loop structures. We report here that the destabilizing activity resides in a single stem-loop structure within this region. A consensus sequence for the active structure has been derived by site-directed mutagenesis, revealing that a three-base loop of sequence YAU and unpaired bases either side of the stem contribute to the activity. The helical nature of the stem is essential and the stem must be less than 11 bp in length, but the destabilizing activity is relatively insensitive to the sequence within the helix. The stem-loop increases the rate of mRNA deadenylation, most likely by enhancing the processivity of the deadenylation reaction. A protein that binds the stem-loop, but not an inactive mutant form, has been detected in cytoplasmic lysates.

TNF-α-Induced Growth Suppression of CD34+ Myeloid Leukemic Cell Lines Signals Through TNF Receptor Type I and Is Associated with NF-κB Activation

Conflicting results have been reported regarding the effect of TNF-α on the growth of human primitive hemopoietic cells. In this study, we have examined the effect of TNF-α on the proliferation of several CD34+/CD38+ (KG-1, TF-1) and CD34+/CD38− (KG-1a, TF-1a) myeloid leukemic progenitor cell lines. Our data show that TNF-α markedly inhibits the growth of these cells in both liquid and soft agar cultures. Addition of GM-CSF or IL-3 does not prevent TNF-α-induced growth inhibition. Flow cytometry analyses of propidium iodide-stained cells demonstrated cell death of all four cell lines, as judged by the presence of cells with hypodiploid DNA content after exposure of cells to TNF-α for 4 days. Annexin V assays detected apoptosis in TF-1, but not in TF-1a, KG-1, and KG-1a cells in terms of translocation of phosphatidylserine shortly after TNF-α treatment. Neutralizing anti-TNF receptor type I (TNFR-I; p55) Ab almost completely reversed TNF-α-induced growth inhibition in both liquid and soft agar cultures, whereas anti-TNFR-II (p75) Ab had only a marginal effect. TNF-α rapidly induced marked activation of nuclear transcription factor NF-κB in all 4 cell lines. The majority of this effect was abolished by the type I receptor Ab, whereas the type II receptor neutralizing Ab had no effect. Our data also show that TNF-α is incapable of inducing activation of the mitogen-activated protein kinase pathway in these leukemic cell lines.

A broader role for AU-rich element-mediated mRNA turnover revealed by a new transcriptional pulse strategy

The widespread occurrence of AU-rich elements (AREs) in mRNAs encoding proteins with diversified functions and synthesized under a vast variety of physiological conditions suggests that AREs are involved in finely tuned and stringent control of gene expression. Thus it is important to investigate the regulation of ARE-mediated mRNA decay in a variety of mammalian cells in different physiological states. The tetracycline (Tet)-regulatory promoter system appears appropriate for these investigations. However, we found that efficient degradation of mRNAs bearing different AREs cannot be observed simply by blocking constitutive transcription from the Tet-regulated promoter with Tet, possibly due to saturation of the cellular decay machinery. In addition, deadenylation kinetics and their relationship to mRNA decay cannot be adequately measured under these conditions. To overcome these obstacles we have developed a new strategy that employs the Tet-regulated promoter system to achieve a transient burst of transcription that results in synthesis of a population of cytoplasmic mRNAs fairly homogeneous in size. Using this new system we show that ARE-destabilizing function, necessary for down-regulating mRNAs for cytokines, growth factors and transcription factors, is maintained in quiescent or growth-arrested cells as well as in saturation density-arrested NIH 3T3 cells. We also demonstrate that the ARE-mediated decay pathway is conserved between NIH 3T3 fibroblasts and K562 erythroblasts. These in vivo observations support a broader role for AREs in the control of cell growth and differentiation. In addition, we observed that there is a significant difference in deadenylation and decay rates for beta-globin mRNA expressed in these two cell lines. Deadenylation and decay of beta-globin mRNA in K562 cells is extraordinarily slow compared with NIH 3T3 cells, suggesting that the increased stability gained by beta-globin mRNA in K562 cells is mainly controlled at the deadenylation step. Our strategy for studying mammalian mRNA turnover now permits a more general application to different cell lines harboring the Tet-regulated system under various physiological conditions.

A cytokine mRNA-destabilizing element that is structurally and functionally distinct from A+U-rich elements

The control of mRNA stability is crucial to the regulation of cytokine expression. We describe here a novel, potent destabilizing element found in the 3' untranslated region of granulocyte colony-stimulating factor mRNA. This element, which appears to require at least one stem-loop structure, we term the stem-loop destabilizing element (SLDE). Functionally equivalent elements appear to also exist in the interleukin 2 and interleukin 6 mRNAs. The SLDE is functionally distinct from the A+U-rich elements, which are also present in these and other cytokine mRNAs, because it destabilizes a chimeric mRNA in a tumor cell line in which A+U-rich elements do not function. In addition, the effect of the SLDE is insensitive to calcium ionophore and is therefore regulated independently of A+U destabilizing elements. The existence of two distinct mRNA-destabilizing elements provides an additional mechanism for the differential regulation of cytokine expression.

AUUUA is not sufficient to promote poly(A) shortening and degradation of an mRNA: the functional sequence within AU-rich elements may be UUAUUUA(U/A)(U/A)

AU-rich elements (AREs) in the 3' untranslated regions of several cytokine and oncogene mRNAs have been shown to function as signals for rapid mRNA degradation, and it is assumed that the many other cytokine and oncogene mRNAs that contain AU-rich sequences in the 3' untranslated region are similarly targeted for rapid turnover. We have used a chimeric gene composed mostly of growth hormone sequences with expression driven by the c-fos promoter to investigate the minimal sequence required to act as a functional destabilizing element and to monitor the effect of these sequences on early steps in the degradation pathway. We find that neither AUUUA, UAUUUA, nor AUUUAU can function as a destabilizing element. However, the sequence UAUUUAU, when present in three copies, is sufficient to destabilize a chimeric mRNA. We propose that this sequence functions by virtue of being a sufficient portion of the larger sequence, UUAUUUA(U/A)(U/A), that we propose forms the optimal binding site for a destabilizing factor. The destabilizing effect depends on the number of copies of this proposed binding site and their degree of mismatch in the first two and last two positions, with mismatches in the AUUUA sequence not being tolerated. We found a strict correlation between the effect of an ARE on degradation rate and the effect on the rate of poly(A) shortening, consistent with deadenylation being the first and rate-limiting step in degradation, and the step stimulated by destabilizing AREs. Deadenylation was observed to occur in at least two phases, with an oligo(A) intermediate transiently accumulating, consistent with the suggestion that the degradation processes may be similar in yeast and mammalian cells. AREs that are especially U rich and contain no UUAUUUA(U/A)(U/A) motifs failed to influence the degradation rate or the deadenylation rate, either when downstream of suboptimal destabilizing AREs or when alone.

AUUUA is not sufficient to promote poly(A) shortening and degradation of an mRNA: the functional sequence within AU-rich elements may be UUAUUUA(U/A)(U/A)

AU-rich elements (AREs) in the 3' untranslated regions of several cytokine and oncogene mRNAs have been shown to function as signals for rapid mRNA degradation, and it is assumed that the many other cytokine and oncogene mRNAs that contain AU-rich sequences in the 3' untranslated region are similarly targeted for rapid turnover. We have used a chimeric gene composed mostly of growth hormone sequences with expression driven by the c-fos promoter to investigate the minimal sequence required to act as a functional destabilizing element and to monitor the effect of these sequences on early steps in the degradation pathway. We find that neither AUUUA, UAUUUA, nor AUUUAU can function as a destabilizing element. However, the sequence UAUUUAU, when present in three copies, is sufficient to destabilize a chimeric mRNA. We propose that this sequence functions by virtue of being a sufficient portion of the larger sequence, UUAUUUA(U/A)(U/A), that we propose forms the optimal binding site for a destabilizing factor. The destabilizing effect depends on the number of copies of this proposed binding site and their degree of mismatch in the first two and last two positions, with mismatches in the AUUUA sequence not being tolerated. We found a strict correlation between the effect of an ARE on degradation rate and the effect on the rate of poly(A) shortening, consistent with deadenylation being the first and rate-limiting step in degradation, and the step stimulated by destabilizing AREs. Deadenylation was observed to occur in at least two phases, with an oligo(A) intermediate transiently accumulating, consistent with the suggestion that the degradation processes may be similar in yeast and mammalian cells. AREs that are especially U rich and contain no UUAUUUA(U/A)(U/A) motifs failed to influence the degradation rate or the deadenylation rate, either when downstream of suboptimal destabilizing AREs or when alone.

Potentiation by granulocyte macrophage colony-stimulating factor of lipopolysaccharide toxicity in mice

GM-CSF is known to prime leukocytes for inflammatory stimuli in vitro. The objective of this study was to investigate the role of GM-CSF in vivo in a systemic inflammatory reaction syndrome. The results demonstrate a potentiation of LPS toxicity by GM-CSF in a mortality model as well as in a septic liver failure model in mice. Pretreatment of animals with 50 micrograms/kg GM-CSF induced lethality within 24 h in mice challenged with a subtoxic dose of LPS while controls survived > 72 h. A monoclonal anti-GM-CSF antibody significantly protected against a lethal LPS dose. Serum GM-CSF was inducible by LPS and peaked at 2 h. GM-CSF pretreatment dramatically potentiated systemic TNF release and hepatotoxicity induced by a subtoxic dose of LPS in galactosamine-sensitized mice. Potentiation of LPS hepatotoxicity was possible until 30 min after LPS challenge. Polyclonal anti-GM-CSF IgG protected against septic liver failure in this model and attenuated serum TNF concentrations. In vitro an ex vivo experiments revealed that after GM-CSF pretreatment LPS-induced IL-1 release from bone marrow or spleen cells was also enhanced. These findings suggest that GM-CSF represents an endogenous enhancer of LPS-induced organ injury, possibly by potentiating the release of proinflammatory cytokines such as TNF and IL-1.

Characterization of a cell-type-restricted negative regulatory activity of the human granulocyte-macrophage colony-stimulating factor gene

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates the proliferation and maturation of normal myeloid progenitor cells and can also stimulate the growth of acute myelogenous leukemia (AML) blasts. GM-CSF is not normally produced by resting cells but is expressed by a variety of activated cells including T lymphocytes, macrophages, and certain cytokine-stimulated fibroblasts and endothelial cells. Production of GM-CSF by cultured AML cells has been demonstrated, and GM-CSF expression by normal myeloid progenitors has been postulated to play a role in myelopoiesis. We have investigated the regulation of expression of GM-CSF in AML cell lines, and our results demonstrate the presence of a strong constitutive promoter element contained within 53 bp upstream of the cap site. We have also identified a negative regulatory element located immediately upstream of the positive regulatory element (within 69 bp of the cap site) that is active in AML cell lines but not T cells or K562 CML cells. Competition transfection and mobility shift studies demonstrate that this activity correlates with binding of a 45-kDa protein.

Characterization of a cell-type-restricted negative regulatory activity of the human granulocyte-macrophage colony-stimulating factor gene

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates the proliferation and maturation of normal myeloid progenitor cells and can also stimulate the growth of acute myelogenous leukemia (AML) blasts. GM-CSF is not normally produced by resting cells but is expressed by a variety of activated cells including T lymphocytes, macrophages, and certain cytokine-stimulated fibroblasts and endothelial cells. Production of GM-CSF by cultured AML cells has been demonstrated, and GM-CSF expression by normal myeloid progenitors has been postulated to play a role in myelopoiesis. We have investigated the regulation of expression of GM-CSF in AML cell lines, and our results demonstrate the presence of a strong constitutive promoter element contained within 53 bp upstream of the cap site. We have also identified a negative regulatory element located immediately upstream of the positive regulatory element (within 69 bp of the cap site) that is active in AML cell lines but not T cells or K562 CML cells. Competition transfection and mobility shift studies demonstrate that this activity correlates with binding of a 45-kDa protein.

Production of granulocyte/macrophage-colony-stimulating factor by human natural killer cells. Modulation by the p75 subunit of the interleukin 2 receptor and by the CD2 receptor

Resting natural killer (NK) cells express the p75 chain of the IL-2 receptor (IL-2R beta) and most NK cells express the CD2 (erythrocyte rosette) receptor. The cell adhesion molecule, LFA-3, is a natural co-ligand for CD2. Tac antigen (IL-2R alpha), a p55 IL-2R subunit, can be expressed after NK activation and may play a role in IL-2-induced NK proliferation. Little is known of the molecular mechanisms underlying cytokine production in NK cells. We investigated the roles of IL-2R alpha, IL-2R beta, and CD2/LFA-3 in the molecular regulation of NK cell granulocyte/macrophage-colony-stimulating factor (GM-CSF) production. Enriched populations of peripheral blood NK cells were separated into CD16-positive and CD16-negative fractions by flow cytometry; positively selected cells were greater than 97% positive for CD16 (the FcIII receptor for IgG which is present on almost all NK cells), less than 1% positive for the T cell antigen CD3, and did not demonstrate rearrangement of the T cell receptor beta chain gene by Southern blot. NK cell supernatants were harvested after 3-4 d of incubation with 0-100 U/ml IL-2, or after incubation with anti-CD2 (T11(3] MAb and sheep red blood cells (SRBC are a homologue for LFA-3). Parallel cell aliquots were harvested at 3-16 h for transcriptional run-on assays, S1 nuclease assays, and actinomycin D mRNA t1/2 determinations. IL-2-activated NK supernatants contained large amounts of GM-CSF (178 +/- 35 pg/ml) by ELISA as did supernatants from CD2-activated NK cells (T11(3) MAb + SRBC: 212 +/- 42) vs. less than 20 pg/ml for NK cells incubated alone or with either SRBC or T11(3) MAb alone. Sepharose-linked anti-CD3 MAb did not induce GM-CSF release from NK cells. By S1 analysis, both IL-2 and CD2 stimulation markedly augmented GM-CSF mRNA expression but with very different latencies of onset. IL-2R beta MAb inhibited greater than 85% of GM-CSF release from IL-2-activated NK cells and markedly suppressed IL-2-induced GM-CSF mRNA expression, whereas IL-2R alpha MAb even at 2,000-fold molar excess of IL-2 had little effect (less than 10%) on either GM-CSF release or mRNA expression. Run-on assays showed that GM-CSF is constitutively transcribed in NK cells and that IL-2 and CD2-activated cells had a three- to fourfold increased rate of GM-CSF transcription compared to nonstimulated cells. The t1/2 of GM-CSF mRNA in IL-2-activated NK cells was identical to that of unstimulated NK cells (15 min), whereas GM-CSF mRNA t1/2 in CD2-activated NK cells was increased 2.5-fold. We conclude that GM-CSF production in NK cells is regulated by both the IL-2Rbeta and the CD2 receptor but not by IL-2Ralpha, that both transcriptional and posttranscriptional signals act together to modulate the level of GM-CSF mRNA in NK cells, and that the molecular mechanisms underlying NK cell GM-CSF production are dependent in part on differential surface receptor activation.

Assessment of DNA 'fingerprinting' as a method for validating the identity of cancer cell lines maintained in long-term culture

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Expression of ras oncogenes in cultured human cells alters the transcriptional and posttranscriptional regulation of cytokine genes

Autonomous production of cytokines such as the hematopoietic colony-stimulating factors (CSFs), IL-1, or IL-6 has been demonstrated in numerous human and murine neoplasms, and may be involved in the pathogenesis of several paraneoplastic syndromes such as leukocytosis, fever, and hypercalcemia. Because of the high frequency with which mutations in ras protooncogenes have been detected in human tumors, as well as evidence linking ras gene products to activation of certain cellular functions, we investigated whether ras mutations might influence the regulation of cytokine genes. Normal human fibroblasts transfected with a mutant val12 H-ras oncogene expressed increased levels of mRNA transcripts encoding granulocyte-CSF (G-CSF), granulocyte-macrophage-CSF (GM-CSF), and IL-1 beta compared with controls. Human mesothelioma cells transfected with a mutant asp12 N-ras oncogene exhibited similar alterations in cytokine gene expression. Estimates of transcriptional activity by nuclear run-on analysis revealed a selective increase in transcription only for the IL-1 gene. Analysis of mRNA half-life demonstrated a marked increase in the stability of numerous cytokine transcripts, including G-CSF, GM-CSF, IL-1, and IL-6. The addition of anti-IL-1 neutralizing antibody to cultures of cells expressing ras mutants did not block the expression of any of the cytokines examined, suggesting that the baseline expression of GM-CSF, G-CSF, and IL-6 was not a secondary event due to the increased transcription of IL-1. These results indicate that mutations in ras genes may alter expression of several cytokine genes through both transcriptional and posttranscriptional mechanisms.

A novel tumor necrosis factor-responsive transcription factor which recognizes a regulatory element in hemopoietic growth factor genes

A conserved DNA sequence element, termed cytokine 1 (CK-1), is found in the promoter regions of many hemopoietic growth factor (HGF) genes. Mutational analyses and modification interference experiments show that this sequence specifically binds a nuclear transcription factor, NF-GMa, which is a protein with a molecular mass of 43 kilodaltons. It interacts with different affinities with the CK-1-like sequence from a number of HGF genes, including granulocyte macrophage colony-stimulating factor (GM-CSF), granulocyte (G)-CSF, interleukin 3 (IL-3), and IL-5. We show here that the level of NF-GMa binding is induced in embryonic fibroblasts by tumor necrosis factor-alpha (TNF-alpha) treatment and that the CK-1 sequence from the G-CSF gene is a TNF-alpha-responsive enhancer in these cells. The NF-GMa protein is distinct from another TNF-alpha-responsive transcription factor, NF-kappa B, by several criteria. Firstly, several NF-kappa B-binding sites, although having sequence similarity with the CK-1 sequence, cannot compete efficiently for NF-GMa binding to CK-1. Secondly, the CK-1 sequence from both G-CSF and GM-CSF does not respond to phorbol ester treatment as would an NF-kappa B-binding element. These results demonstrate that NF-GMa is a novel transcription factor inducible by TNF-alpha and binds to a common element in HGF gene promoters.

A novel tumor necrosis factor-responsive transcription factor which recognizes a regulatory element in hemopoietic growth factor genes

A conserved DNA sequence element, termed cytokine 1 (CK-1), is found in the promoter regions of many hemopoietic growth factor (HGF) genes. Mutational analyses and modification interference experiments show that this sequence specifically binds a nuclear transcription factor, NF-GMa, which is a protein with a molecular mass of 43 kilodaltons. It interacts with different affinities with the CK-1-like sequence from a number of HGF genes, including granulocyte macrophage colony-stimulating factor (GM-CSF), granulocyte (G)-CSF, interleukin 3 (IL-3), and IL-5. We show here that the level of NF-GMa binding is induced in embryonic fibroblasts by tumor necrosis factor-alpha (TNF-alpha) treatment and that the CK-1 sequence from the G-CSF gene is a TNF-alpha-responsive enhancer in these cells. The NF-GMa protein is distinct from another TNF-alpha-responsive transcription factor, NF-kappa B, by several criteria. Firstly, several NF-kappa B-binding sites, although having sequence similarity with the CK-1 sequence, cannot compete efficiently for NF-GMa binding to CK-1. Secondly, the CK-1 sequence from both G-CSF and GM-CSF does not respond to phorbol ester treatment as would an NF-kappa B-binding element. These results demonstrate that NF-GMa is a novel transcription factor inducible by TNF-alpha and binds to a common element in HGF gene promoters.

Regulatory elements responsible for inducible expression of the granulocyte colony-stimulating factor gene in macrophages

Granulocyte colony-stimulating factor (G-CSF) plays an essential role in granulopoiesis during bacterial infection. Macrophages produce G-CSF in response to bacterial endotoxins such as lipopolysaccharide (LPS). To elucidate the mechanism of the induction of G-CSF gene in macrophages or macrophage-monocytes, we have examined regulatory cis elements in the promoter of mouse G-CSF gene. Analyses of linker-scanning and internal deletion mutants of the G-CSF promoter by the chloramphenicol acetyltransferase assay have indicated that at least three regulatory elements are indispensable for the LPS-induced expression of the G-CSF gene in macrophages. When one of the three elements was reiterated and placed upstream of the TATA box of the G-CSF promoter, it mediated inducibility as a tissue-specific and orientation-independent enhancer. Although this element contains a conserved NF-kappa B-like binding site, the gel retardation assay and DNA footprint analysis with nuclear extracts from macrophage cell lines demonstrated that nuclear proteins bind to the DNA sequence downstream of the NF-kappa B-like element, but not to the conserved element itself. The DNA sequence of the binding site was found to have some similarities to the LPS-responsive element which was recently identified in the promoter of the mouse class II major histocompatibility gene.

Regulatory elements responsible for inducible expression of the granulocyte colony-stimulating factor gene in macrophages

Granulocyte colony-stimulating factor (G-CSF) plays an essential role in granulopoiesis during bacterial infection. Macrophages produce G-CSF in response to bacterial endotoxins such as lipopolysaccharide (LPS). To elucidate the mechanism of the induction of G-CSF gene in macrophages or macrophage-monocytes, we have examined regulatory cis elements in the promoter of mouse G-CSF gene. Analyses of linker-scanning and internal deletion mutants of the G-CSF promoter by the chloramphenicol acetyltransferase assay have indicated that at least three regulatory elements are indispensable for the LPS-induced expression of the G-CSF gene in macrophages. When one of the three elements was reiterated and placed upstream of the TATA box of the G-CSF promoter, it mediated inducibility as a tissue-specific and orientation-independent enhancer. Although this element contains a conserved NF-kappa B-like binding site, the gel retardation assay and DNA footprint analysis with nuclear extracts from macrophage cell lines demonstrated that nuclear proteins bind to the DNA sequence downstream of the NF-kappa B-like element, but not to the conserved element itself. The DNA sequence of the binding site was found to have some similarities to the LPS-responsive element which was recently identified in the promoter of the mouse class II major histocompatibility gene.

Transcriptional and posttranscriptional regulation of macrophage-specific colony stimulating factor gene expression by tumor necrosis factor. Involvement of arachidonic acid metabolites

The effects of tumor necrosis factor (TNF) on the regulation of macrophage-specific colony stimulating factor (CSF-1) gene expression have been studied in HL-60 cells during monocytic differentiation. CSF-1 transcripts were undetectable in uninduced HL-60 cells, reached maximal levels by 3 h of exposure to TNF, and returned to that of control cells by 24 h. Transcriptional run-on analysis demonstrated that exposure to TNF stimulated the rate of CSF-1 gene transcription by 6.4-fold. The combination of a protein synthesis inhibitor, cycloheximide, and TNF increased levels of CSF-1 mRNA compared with treatment by TNF alone. We also studied the signal transduction mechanisms responsible for regulating TNF-induced CSF-1 mRNA levels. Both 4-bromophenacyl bromide and quinacrine, inhibitors of phospholipase A2 activity, blocked TNF-induced increases in CSF-1 transcripts in a concentration-dependent manner, while caffeic acid and nordihydroguaiaretic acid, inhibitors of the 5-lipoxygenase pathway, had no detectable effect on induction of CSF-1 RNA. PGE2 or dibutyryl cAMP treatment of HL-60 cells in the presence of TNF blocked the expression of CSF-1 mRNA in a dose-dependent manner. These findings suggest that the increase in CSF-1 RNA observed during TNF treatment is regulated, at least in part, by both transcriptional and posttranscriptional mechanisms, and that PGE2 and cAMP regulate transcriptional activation of the CSF-1 gene by TNF.

Role of lymphotoxin in expression of interleukin 6 in human fibroblasts. Stimulation and regulation

IL-6 is a cytokine with a number of biological functions, including stimulation of immunoglobulin synthesis and proliferation of early hematopoietic stem cells. We showed that lymphotoxin stimulated accumulation of IL-6 mRNA in human fibroblasts (W138) in a dose-responsive fashion; tumor necrosis factor-alpha (TNF-alpha) was about threefold more potent than lymphotoxin. Further experiments suggested that stimulation by lymphotoxin was independent of protein kinase C activity, did not require new protein synthesis, and was at least in part a result of increased stabilization of IL-6 mRNA. t1/2 of the IL-6 transcripts increased from 0.3 h in unstimulated cells to 0.85 h in cells stimulated with lymphotoxin. In addition, stimulators of protein kinase C, including phorbol esters and teleocidin, enhanced accumulation of IL-6 mRNA. Cycloheximide (CHX), inhibitor of protein synthesis, also markedly increased levels of IL-6 mRNA. Both CHX and activators of protein kinase C increased by greater than 16-fold the stability of IL-6 mRNA. Further, dose-response studies showed that sodium fluoride (NaF), activator of G-binding proteins, and ouabain, inhibitor of Na+/H+ pump, increased levels of IL-6 mRNA. NaF stimulated IL-6 mRNA levels independent of protein kinase C activity. These results suggest that stimulators of several pathways of signal transduction increase levels of IL-6 mRNA and posttranscriptional stabilization is, in part, the mechanism that many of these signals, including lymphotoxin, use to increase levels of IL-6 RNA.

Regulation of interleukin 3 mRNA expression in mast cells occurs at the posttranscriptional level and is mediated by calcium ions

Interleukin 3 (IL-3) is transiently produced by murine bone marrow-derived mast cells in response to antigen stimulation of the high-affinity immunoglobulin E receptors. We have studied the postreceptor signaling pathways involved in regulating expression of the IL-3 gene in the murine mast cell line PB-3c. Large amounts of IL-3 mRNA accumulated after exposure of cells to calcium ionophore A23187, a reagent that increases intracellular Ca2+. Phorbol 12-myristate 13-acetate, which stimulates protein kinase C, did not induce IL-3 mRNA accumulation, although it did potentiate the effect of A23187. Nuclear run-on analysis showed that the IL-3 gene is constitutively transcribed in unstimulated cells and that treatment with A23187 and/or phorbol ester has no influence on its transcription rate. The effect of A23187 was found to be due to stabilization of the IL-3 mRNA. In cells maintained in the presence of A23187 the IL-3 mRNA was stable during 3 hr of incubation with actinomycin D, whereas removal of A23187 under the same conditions resulted in rapid degradation of the mRNA. These results indicate that control of expression of the IL-3 gene in mast cells is primarily at the posttranscriptional level and that the Ca2(+)-dependent signal-transduction pathway plays an important role in this process. Synthesis of granulocyte/macrophage colony-stimulating factor mRNA in response to A23187 and phorbol ester was found to be subject to both transcriptional and posttranscriptional regulation.