Cloning and characterization of the murine promoter for the colony-stimulating factor-1-encoding gene

Rho-kinase regulation of TNF-α-induced nuclear translocation of NF-κB RelA/p65 and M-CSF expression via p38 MAPK in mesangial cells

The small GTPase Rho and its downstream effector, Rho-associated coiled-coil containing protein kinase (Rho-kinase), regulate a number of cellular processes, including organization of the actin cytoskeleton, cell adhesion, and migration. While pharmacological inhibitors of Rho-kinase signaling are known to block renal inflammation, the molecular basis for this effect is unclear. Here, we provide evidence that proinflammatory TNF-α promotes mesangial expression of macrophage colony-stimulating factor (M-CSF), a key regulator for the growth and differentiation of mononuclear phagocytes, in a Rho-kinase-dependent manner. Consistent with this observation, TNF-α-mediated renal expression of M-CSF in insulin-resistant db/db mice was downregulated by Rho-kinase inhibition. Small interfering RNA-facilitated knockdown of Rho-kinase isoforms ROCK1 and ROCK2 indicated that both isoforms make comparable contributions to regulation of M-CSF expression in mesangial cells. From a mechanistic standpoint, Western blotting and EMSA showed that Rho-kinase and its downstream target p38 MAPK regulate nuclear translocation of NF-κB RelA/p65 and subsequent DNA binding activity, with no significant effects on IκBα degradation and RelA/p65 phosphorylation. Moreover, we showed that Rho-kinase-mediated cytoskeletal organization is required for the nuclear uptake of RelA/p65. Collectively, these findings identify Rho-kinase as a critical regulator of chemokine expression and macrophage proliferation.

Intercellular adhesion molecule-1 (ICAM-1) expression correlates with oral cancer progression and induces macrophage/cancer cell adhesion

Intercellular adhesion molecule-1 (ICAM-1) is a transmembrane glycoprotein in the immunoglobulin superfamily, which plays an important role in cell adhesion and signal transduction. Although ICAM-1 is believed to play a role in several malignancies, it is still uncertain whether or not ICAM-1 expression contributes to cancer progression. In this study, we performed clinicopathological and cell biological analyses of ICAM-1 expression in oral squamous cell carcinoma (SCC). First, we examined the ICAM-1 expression in tongue SCC immunohistochemically, and revealed that ICAM-1 was expressed predominantly at the invasive front area of tongue SCC. ICAM-1 expression at the invasive front area was correlated with invasion, lymph node metastasis and increased blood and lymphatic vessel density of the tongue SCC. The relationship between ICAM-1 expression and clinicopathological factors were consistent with the increased proliferation, invasion and cytokine-production activities of ICAM-1-transfected SCC cells. Second, we analyzed the relationship between macrophages and ICAM-1-expressing tongue SCC cells because ICAM-1 is known to act as a ligand for adhesion of immune cells. Increased ICAM-1 expression in tongue SCC was correlated with increased macrophage infiltration within SCC nests. Moreover, macrophage/SCC-cell adhesion through ICAM-1 molecule was revealed using an in vitro cell adhesion and blockade assay. These findings indicate that ICAM-1 plays an important role in tongue SCC progression, which may result from the SCC-cell activity, angiogenic activity, lymphangiogenic activity and macrophage/SCC-cell adhesion.

DNA damage-induced cytotoxicity is mediated by the cooperative interaction of phospho-NF-κB p50 and a single nucleotide in the κB-site

Phosphorylation of the NF-κB subunit, p50, is necessary for cytotoxicity in response to DNA methylation damage. Here, we demonstrate that serine 329 phosphorylation regulates the interaction of p50 with specific NF-κB binding elements based on the identity of a single κB-site nucleotide. Specifically, S329 phosphorylation reduces the affinity of p50 for κB-sites that have a cytosine (C) at the -1 position without affecting binding to sequences with a -1 adenine. The differential interaction between phospho-p50 and the -1 base regulates the downstream transcriptional response and underlies the inhibition of anti-apoptotic gene expression following DNA damage. In genes with multiple κB-sites, the presence of a single -1C κB-site enables inhibition of NF-κB-dependent activity. The data suggest that interaction between phospho-p50 and the -1 κB nucleotide facilitates cytotoxicity in response to DNA damage. Moreover, although conservation of the entire κB-site sequence is not seen across species, the identity of the -1 nt in critical anti-apoptotic genes is conserved such that the overall response to DNA damage is maintained.

Suppression of lipopolysaccharide-induced inflammatory responses in RAW 264.7 murine macrophages by aqueous extract of Clinopodium vulgare L. (Lamiaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

The wild basil Clinopodium vulgare L. is commonly used in Bulgarian folk medicine for treatment of irritated skin, mastitis- and prostatitis-related swelling, as well as for some disorders accompanied with significant degree of inflammation (e.g. gastric ulcers, diabetes, and cancer).

AIM OF STUDY

To determine the effect of aqueous extract of Clinopodium vulgare L. on LPS-induced inflammatory responses of murine RAW 264.7 macrophages.

MATERIALS AND METHODS

Cell cytotoxicity was evaluated by MTT assay. Protein expression levels were monitored by Western blot analysis. Production of NO and PGE(2) was measured by the Griess colorimetric method and enzyme immunoassay, respectively. Activation of MMP-9 was visualized by gelatin zymography. Cytokine levels were determined by BioPlex assay. Intracellular ROS and free radical scavenging potential were measured by DCFH-DA and DPPH method, respectively. Xanthine oxidase activity was evaluated spectrophotometrically.

RESULTS

The extract suppresses NF-kappaB activation by preventing I kappa-B phosphorylation and inhibits the phosphorylation of p38 and SAPK/JNK MAPKs. It down-regulates iNOS expression which manifests as a drastic decrease of NO production, inhibits MMP-9 activation, but does not affect COX-2 protein levels and reduces only slightly the released PGE(2). Secretion of IL-1 beta and Il-10 is greatly reduced, whereas suppression of TNF-alpha and GM-CSF production is less dramatic. The extract has strong free radical scavenging properties and exerts inhibitory effect on xanthine oxidase activity, which lowers the levels of intracellular ROS.

CONCLUSION

The study provides evidence for the anti-inflammatory potential of Clinopodium vulgare L. aqueous extract.

Macrophage colony stimulating factor expression in human cardiac cells is upregulated by tumor necrosis factor-alpha via an NF-kappaB dependent mechanism

INTRODUCTION

Macrophage colony stimulating factor (M-CSF) is a key factor for monocyte and macrophage survival and proliferation. M-CSF has been implicated in cardiac healing and repair after myocardial infarction.

METHODS AND RESULTS

We show by immunohistochemistry and Western blotting analysis that M-CSF protein is present in human heart tissue. Cultured human adult cardiac myocytes (HACM) and human adult cardiac fibroblasts (HACF) isolated from human myocardial tissue constitutively express M-CSF. When HACM and HACF were treated with tumor necrosis factor-alpha (TNF-alpha) M-CSF protein production and M-CSF mRNA expression, determined by ELISA or by using RT-PCR, respectively, was significantly increased. To determine a possible role of nuclear factor kappaB (NF-kappaB) and activating protein 1 (AP-1) in M-CSF regulation, blockers to both pathways and an adenovirus overexpressing a dominant negative (dn) form of IkappaB kinase 2 (IKK2) were used. Only the NF-kappaB blocker dimethylfumarate and the dn IKK2, but not januskinase inhibitor-1 (JNK-I), were able to block the TNF-alpha-induced increase in M-CSF production in these cells, suggesting that the induction of M-CSF through TNF-alpha is mainly dependent on the activation of the NF-kappaB pathway. The monocyte activation marker CD11b was significantly increased after incubating U937 cells with conditioned medium from HACM or HACF as determined by FACS analysis.

CONCLUSIONS

Our in vitro data taken together with our immunohistochemistry data suggest that human cardiac cells constitutively express M-CSF. This expression of M-CSF in the human heart and its upregulation by TNF-alpha might contribute to monocyte and macrophage survival and differentiation.

Induction of transcription factor Egr-1 gene expression in astrocytoma cells by Murine coronavirus infection

Mouse hepatitis virus (MHV) causes encephalitis and demyelination in the central nervous system (CNS) of susceptible rodents. Astrocytes are one of the major targets for MHV infection in the CNS, and respond to MHV infection by expressing diverse molecules that may contribute to CNS pathogenesis. Here we characterized the activation of an immediate-early transcription factor Egr-1 by MHV infection in an astrocytoma cell line. We found that the expression of Egr-1 was dramatically increased following virus infection. Using various inhibitors of mitogen-activated protein kinases, we identified that the extracellular signal-regulated kinases 1/2 were involved in the activation of Egr-1 transcription by MHV infection. Experiments with ultraviolet light-inactivated virus revealed that the induction of Egr-1 did not require virus replication and was likely mediated during cell entry. We further found that over-expression of Egr-1 suppressed the expression of BNip3, a pro-apoptotic member of the Bcl-2 family. This finding may provide an explanation for our previously observed down-regulation of BNip3 by MHV infection in astrocytoma cells (Cai, Liu, Yu, and Zhang, Virology 316:104-115, 2003). Furthermore, knockdown of Egr-1 by an siRNA inhibited MHV propagation, suggesting the biological relevance of Egr-1 induction to virus replication. In addition, the persistence/demylinating-positive strains (JHM and A59) induced Egr-1 expression, whereas the persistence/demylinating-negative strain (MHV-2) did not. These results indicate a correlation between the ability of MHVs to induce Egr-1 expression and their ability to cause demyelination in the CNS, which may suggest a potential role for the induction of Egr-1 in viral pathogenesis.

Amyloid-beta peptides induce cell proliferation and macrophage colony-stimulating factor expression via the PI3-kinase/Akt pathway in cultured Ra2 microglial cells

Alzheimer's disease is characterized by numerous amyloid-beta peptide (Abeta) plaques surrounded by microglia. Here we report that Abeta induces the proliferation of the mouse microglial cell line Ra2 by increasing the expression of macrophage colony-stimulating factor (M-CSF). We examined signal cascades for Abeta-induced M-CSF mRNA expression. The induction of M-CSF was blocked by a phosphatidylinositol 3 kinase (PI3-kinase) inhibitor (LY294002), a Src family tyrosine kinase inhibitor (PP1) and an Akt inhibitor. Electrophoretic mobility shift assays showed that Abeta enhanced NF-kappaB binding activity to the NF-kappaB site of the mouse M-CSF promoter, which was blocked by LY294002. These results indicate that Abeta induces M-CSF mRNA expression via the PI3-kinase/Akt/NF-kappaB pathway.

Genetic analysis of NF-kappaB/Rel transcription factors defines functional specificities

The NF-kappaB transcription factors consist of dimeric proteins of the Rel homology family. They activate many promoters containing highly divergent kappaB-site sequences. We have generated cell lines lacking individual and multiple NF-kappaB proteins and used them to establish interactions between components of the NF-kappaB-IkappaB signaling system. Functional compensation within the family of dimers was evident in knockout cell lines. Analysis of transiently transfected genes gave an impression of promiscuity that was not borne out by analysis of endogenous genes. Using TNFalpha as an inducer, a panel of endogenous genes showed a wide range of subunit specificities as well as highly variable kinetics of induction. Comparing the function and subunit specificity of genes with the sequence of the kappaB DNA-binding site we found little correlation, indicating that NF-kappaB family member specificity for endogenous promoters is not solely encoded by the kappaB site sequence itself.

Expression profiling identifies genes that continue to respond to insulin in adipocytes made insulin-resistant by treatment with tumor necrosis factor-alpha

We have employed microarray technology using RNA from normal 3T3-L1 adipocytes and from 3T3-L1 adipocytes made insulin-resistant by treatment with tumor necrosis factor-alpha to identify a new class of insulin-responsive genes. These genes continued to respond normally to insulin even though the adipocytes themselves were metabolically insulin-resistant, i.e. they displayed a significantly decreased rate of insulin-stimulated glucose uptake. Approximately 12,000 genes/expressed sequence tags (ESTs) were screened. Of these, 40 genes/ESTs were identified that became insulin-resistant as expected (e.g. Socs-3, junB, and matrix metalloproteinase-11). However, 61 genes/ESTs continued to respond normally to insulin. Although some of these genes were previously shown to be regulated by insulin (e.g. Glut-1 and beta3-adrenergic receptor), other novel insulin-sensitive genes were also identified (e.g. Egr-1, epiregulin, Fra-1, and ABCA1). Real-time reverse transcription-PCR analysis confirmed the expression patterns of several of the differentially expressed genes. One gene that remained insulin-sensitive in the insulin-resistant adipocytes is the transcription factor Egr-1. Using an antisense strategy, we show that tissue factor and macrophage colony-stimulating factor, two cardiovascular risk factors, are downstream EGR-1 target genes in the adipocyte. Taken together, these data support the hypothesis that some signaling pathways remain insulin-sensitive in metabolically insulin-resistant adipocytes. These pathways may promote abnormal gene expression in hyperinsulinemic states like obesity and type II diabetes and thus may contribute to pathologies associated with these conditions.

Analysis of the mouse CSF-1 gene promoter in a transgenic mouse model

CSF-1 stimulates monocyte and osteoclast populations. However, the molecular mechanisms involved in regulating CSF-1 gene expression are unclear. To identify regulatory regions that control normal CSF-1 gene expression, a -774/+183-bp fragment of the murine CSF-1 promoter was analyzed in vitro and in vivo. Transcriptional activity was high in cultured osteoblasts that express CSF-1 mRNA compared to ARH-77 B cells that lack CSF-1 gene expression. Transient transfection of osteoblasts with promoter deletion constructs showed that the -774-bp fragment conferred the highest transcriptional activity and contained activator and repressor sequences. To assess the ability of the CSF-1 promoter to confer normal tissue expression of CSF-1, transgenic mice containing the -774/+183-bp region driving the E. coli beta-galactosidase (lacZ) reporter gene were generated. beta-Gal analysis of whole tissue extracts showed transgene expression in all tissues tested except liver and kidney. At the cellular level, the pattern of beta-gal expression in the spleen, thymus, bone, lung, and testes of adult transgenic mice mimicked normal endogenous CSF-1 mRNA expression in non-transgenic littermates detected by in situ hybridization. This region also directed appropriate transgene expression to sites in other tissues known to synthesize CSF-1, with the exception of the liver and kidney. These findings indicate that the -774-bp fragment contains cis-acting elements sufficient to direct CSF-1 gene expression in many tissues. CSF-1 promoter/lacZ mice may be useful for studying the transcriptional mechanisms involved in regulating CSF-1 gene expression in tissues throughout development.

Nitric oxide donors inhibit luciferase expression in a promoter-independent fashion

Nitric oxide (NO) is an important molecule with diverse bio-messenger functions including regulation of gene expression. Transcriptional studies using sensitive luciferase reporter systems have suggested that NO inhibits the promoter activity of a variety of genes. Here we report that NO donors (sodium nitroprusside, 2',2'-(hydroxynitrosohydrazono)bis-ethanimine, and (+/-)-(E)-4-ethyl-2-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl-nicotinamide) decrease luciferase activity in a promoter-independent fashion in both viral and eukaryotic promoters, with a reduction to nearly 50% in the presence of 100 microm NO donor. Addition of an SV40 enhancer downstream of the luciferase coding region shifted NO donor inhibition to the right, with inhibition at approximately 300 microm. In contrast, when studied in a chloramphenicol acetyltransferase reporter, two promoters indicating inhibition by NO were unaffected. The decrease in luciferase activity was not caused by NO suppression of the luciferase enzyme. Real-time PCR data showed that luciferase mRNA half-life decreased by nearly half in the presence of NO donor (from 75 to 45 min). The SV40 enhancer prolonged luciferase mRNA half-life and somewhat blunted the NO effect. Our data suggest that exogenous NO inhibits luciferase activity in a dose-dependent manner through decreasing luciferase mRNA stability. Thus, the use of luciferase reporter systems to study transcriptional regulation by NO should be attempted with caution.

Metallothionein is required for zinc-induced expression of the macrophage colony stimulating factor gene

Macrophage colony stimulating factor (M-CSF) plays an important role in the proliferation and differentiation of mononuclear phagocytes. The present study investigates the effect of zinc on M-CSF expression in MC3T3-E1 and L929 cells. Zinc dose-dependently increased M-CSF mRNA levels. The time-course of zinc-induced M-CSF mRNA expression peaked at 6 h. Stability studies of mRNA using actinomycin D revealed that zinc does not affect M-CSF mRNA stability. We examined the function of the M-CSF gene promoter using a luciferase reporter assay. A construct containing the -467/+39 region of the promoter was upregulated by zinc. In the presence of cycloheximide, zinc did not induce a greater increase in the M-CSF mRNA than cycloheximide alone. To confirm the effect of MT on M-CSF mRNA expression, mouse lung fibroblasts (MLFs) were prepared from MT+/+ and MT-/- mice. Zinc induced an increase in the expression of M-CSF in MT+/+ MLFs, but this response was not evident in MT-/- MLFs. Moreover, overexpression of MT upregulated M-CSF mRNA expression as well as M-CSF secretion. Our findings suggest that MT expression mediates zinc regulation of M-CSF gene expression at the transcriptional level.

Transcription factor Egr-1 activates collagen expression in immortalized fibroblasts or fibrosarcoma cells

Synovial fibroblasts from rheumatoid arthritis patients express elevated levels of the transcription factor Egr-1. The metabolic consequences of Egr-1 overexpression in fibroblasts are not known in detail. Therefore we searched for gene products that are differentially expressed in Egr-1(high) versus Egr-1(low) fibroblasts. Immortalized synovial fibroblasts were transfected with two different Egr-1 expression vectors. Expression of recombinant Egr-1 was confirmed by RT-PCR and immunoblots. Random arbitrarily primed PCR revealed that Egr-1 induces enhanced transcription levels of the alpha1 chain of type I collagen. Increased expression of the alpha2 (I) chain could also be observed. We found enhanced levels of type I collagen propeptide in supernatants and stronger signals of alpha2 (I) protein in extracts of the Egr-1(high) expressing clone versus controls. Additionally, Egr-1 was transiently expressed in fibrosarcoma cells. These cells showed a pronounced elevation of type I collagen (alpha1) transcripts as well. Moreover, we could demonstrate that Egr-1 induces transcription of other genes including type II collagen (alpha1) and plateled-derived growth factor beta1. These data suggest that upregulation of Egr-1 might contribute tofibrosis observed in rheumatoid arthritis synovium by activation of genes encoding the alpha1 and alpha2 chains of type I collagen.

Reactive oxygen species alter gene expression in podocytes: induction of granulocyte macrophage-colony-stimulating factor

It has been suggested that reactive oxygen radicals (ROS) play a crucial role in the pathogenesis of proteinuria and podocyte injury. It was investigated whether changes in gene expression might account for ROS-induced podocyte dysfunction. Differentiated podocytes were incubated with control media or with exogenous ROS from the xanthine/xanthine-oxidase reaction for 4 h. A PCR-based suppressive subtractive hybridization assay was applied to isolate and clone mRNAs that were differentially expressed by exogenous ROS. One differentially expressed clone was identified as the proinflammatory cytokine granulocyte macrophage-colony-stimulating factor (GM-CSF). Regulation of GM-CSF in podocytes was further studied by Northern analysis and enzyme-linked immunosorbent assay. Exogenous ROS caused a concentration-dependent, >10-fold induction of GM-CSF mRNA after 4 h. A >50-fold increase in GM-CSF protein release in podocytes that had been stimulated with ROS could be detected. Induction of GM-CSF protein was inhibited by actinomycin D, which indicated that increased mRNA transcription was involved. The ROS scavengers dimethyl-thio-urea and pyrrolidone-dithio-carbamate strongly inhibited increased GM-CSF production induced by ROS. GM-CSF release was also induced when internal ROS production was triggered with NADH, whereas H2O2 had only a small effect. GM-CSF release by podocytes was also stimulated by lipopolysaccharide (LPS), interleukin-1 (IL-1), and phorbolester (PMA). Dimethyl-thio-urea significantly inhibited the LPS-, IL-1-, and PMA-induced GM-CSF production. Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) but not activator protein-1 was involved in the upregulation of ROS-induced GM-CSF production. The data indicate that GM-CSF is differentially expressed by ROS in podocytes. ROS also partially mediate the effects of PMA and IL-1 on podocyte GM-CSF production. Because GM-CSF can enhance glomerular inflammation and induces mesangial proliferation, these data might provide further insight into the mechanisms of ROS-induced glomerular injury.

Nuclear factor-kappaB p50 is required for tumor necrosis factor-alpha-induced colony-stimulating factor-1 gene expression in osteoblasts

Colony-stimulating factor (CSF)-1 is a hematopoietic growth factor that is released by osteoblasts and is recognized to play a critical role in bone remodeling in vivo and in vitro. We have reported that osteoblasts express CSF-1 constitutively and that tumor necrosis factor (TNF)-alpha, a potent bone-resorbing agent, increases CSF-1 gene expression by a transcriptional mechanism. In the present study, we report that an NF-kappaB site in the CSF-1 promoter is required for TNF-alpha-induced CSF-1 expression in osteoblasts. As determined by electrophoretic mobility shift assays, antiserum against the NF-kappaB-binding protein, p50, retarded the mobility of the inducible complex, whereas antisera against p52, p65, c-Rel, Rel B, IkappaB alpha, IkappaB gamma, and Bcl-3 had no effect. To further confirm that p50 is necessary for TNF-alpha-induced CSF-1 expression in osteoblasts, CSF-1 messenger RNA expression from untreated and TNF-alpha-treated osteoblasts, prepared from wild-type and p50 knock-out mice, was examined by Northern analysis. CSF-1 messenger RNA was increased by TNF treatment in wild-type mice but not in NF-kappaB p50 knock-out mice. Our findings support the conclusion that the NF-kappaB subunit p50 is critical for TNF-induced CSF-1 expression in osteoblasts.

A comparison of macrophage colony-stimulating factor (M-CSF) gene expression in primary and immortalized endothelial cells

M-CSF is produced by a wide variety of cell types, including EC, fibroblasts, and monocyte/macrophages, where it functions as a survival factor and a chemotactic agent for monocytes. An early event in the development of atherosclerosis is the infiltration of monocytes into the artery wall. Local expression of M-CSF by EC lining the blood vessels is thought to promote the growth and survival of lesional monocytes and macrophages, thus enhancing lesion development and disease progression. Primary cultures of EC are difficult to maintain for long periods of time, which complicates their use for biochemical and molecular analysis. As a step toward identifying a representative endothelial-like cell line, serum-dependent and IL-1-dependent changes in M-CSF gene expression in two endothelial-like cell lines were compared to that detected in primary EC cultures. The data presented here demonstrate that the two endothelial-like cell lines, like primary cultures of EC, express the M-CSF gene under basal conditions. In both types of cell cultures, IL-1alpha stimulation increased M-CSF mRNA levels 2-7-fold, whereas serum stimulation elicited a more modest effect (2-3-fold increase). The IL-1alpha-induced change in M-CSF gene expression is mediated at the transcriptional level, and M-CSF promoter activity is, in part, dependent on the activity of the NF-kappaB-inducing kinase. Collectively, our results demonstrate that either endothelial-like cell line would be a representative model in which endothelial-specific changes in M-CSF gene expression could be identified.

Transcriptional regulation of the expression of macrophage colony stimulating factor

The regulatory regions for transcriptional control of the MCSF gene are unknown. We examined regulatory control in a 774-bp murine MCSF promoter transfected into MC3T3-E1 osteoblast-like and COS-7 cells. Deletion of upstream sequence from -635 increased basal activity of the promoter by at least four-fold, an increase that was maintained when PU.1, NFkappaB and Egr1/Sp1 consensus sequences were subsequently removed. Mutagenesis identified a suppressor element between -635 and -642 from the transcriptional start site and an oligonucleotide representing this sequence was retarded by nuclear cell protein. TNFalpha (1 ng/ml), PTH (5x10(-8) M), and IL-1alpha (100 pg/ml), which increased MCSF protein secretion, failed to enhance the transcriptional rate of the full-length promoter. TNFalpha was able to stimulate transcription of a heterologous reporter transfected into COS-7 containing multiple copies of the murine MCSF NFkappaB site inserted before a minimal promoter. In contrast, deletion of the same NFkappaB response element increased basal activity in the native promoter. Thus, the NFkappaB sequence may act as a negative regulator in the context of the endogenous promoter. Our results indicate that constitutive transcriptional activity conferred by the MCSF promoter may be damped by a suppressor protein. Transcriptional regulation, however, does not appear to be a major stimulatory mechanism for MCSF secretion.

Targeted disruption of CRE-binding factor TREB5 gene leads to cellular necrosis in cardiac myocytes at the embryonic stage

TREB5 (hXBP-1) is a basic region leucine zipper protein which binds to a CRE-like element in both human T-cell leukemia virus type 1 and MHC class II genes. To study the function(s) of TREB5 in normal development, we have generated TREB5 deficient mice by gene targeting. Heterozygous mutant mice have not exhibited any obvious abnormalities; however, homozygous mutant embryos die between embryonic days 10.5 and 14.5. The major defect responsible for lethality is cellular necrosis of cardiac myocytes located at the atrium and the truncus arteriosus with its following ventricle. Necrotic alteration was not observed in either the endocardial cushion or the conotruncal ridge. These results indicate that TREB5 plays an essential role in maintenance and/or growth of cardiac myocytes during cardiogenesis.

Role of NFkappaB in the regulation of macrophage colony stimulating factor by tumor necrosis factor-alpha in ST2 bone stromal cells

Expression of MCSF in bone is important to the regulation of osteoclastogenesis. We show here that tumor necrosis factor-alpha (TNFalpha) increases the production of both soluble (sMCSF) and membrane-bound (mMCSF) macrophage colony stimulating factor by ST2 bone stromal cells. Treatment of ST2 cells with TNFalpha caused sMCSF levels to increase by 394+/-5% from basal; mMCSF rose by 316+/-66% from 30+/-10 per 100,000 cells in the same time. These increases were consistent with increased expression of mRNAs encoding both isoforms. Increases in MCSF mRNA are also seen after stimulation with dexamethasone. To investigate the potential role of NFkappaB in this TNFalpha effect, we treated cells with sodium salicylate (NaS), an inhibitor of NFkappaB translocation. NaS decreased TNFalpha-stimulated NFkappaB activation by 50% as assessed by EMSA. Despite inhibition of NFkappaB signaling, NaS enhanced TNFalpha-stimulated MCSF secretion and did not prevent TNFalpha-stimulated increases in sMCSF mRNA, suggesting that NFkappaB was not involved in TNFalpha effect on the gene. TNFalpha failed to stimulate transcription of a 774 nucleotide MCSF promoter-luciferase reporter transfected into ST2 cells which contained the NFkappaB consensus sequence. Deletion of the seven nucleotides containing the NFkappaB homology response sequence from the MCSF promoter increased basal gene transcription by twofold. TNFalpha thus contributes to an osteoclastogenic environment through upregulation of bone expression of both MCSF isoforms. Our data suggests that NFkappaB is not the major signaling pathway through which this occurs.

Estrogen blocks M-CSF gene expression and osteoclast formation by regulating phosphorylation of Egr-1 and its interaction with Sp-1

Central to the pathogenesis of osteoporosis is the ability of estrogen deficiency to increase osteoclast formation by enhancing stromal cell production of the osteoclastogenic cytokine macrophage colony-stimulating factor (M-CSF). We report that stromal cells from ovariectomized mice exhibit increased casein kinase II-dependent phosphorylation of the nuclear protein Egr-1. Phosphorylated Egr-1 binds less avidly to the transcriptional activator Sp-1 and the resulting higher levels of free Sp-1 stimulate transactivation of the M-CSF gene. Estrogen replacement fails to block M-CSF mRNA expression and osteoclast formation in ovariectomized mice lacking Egr-1, confirming the critical role played by this transcription factor in mediating the antiosteoclastogenic effects of estrogen. Thus, by downregulating formation of a novel Egr-1/Sp-1 complex in stromal cells, estrogen deficiency results in enhanced levels of free Sp-1 and increased M-CSF gene expression and osteoclast formation.

Regulation of mouse colony-stimulating factor-1 gene promoter activity by AP1 and cellular nucleic acid-binding protein

Macrophage colony-stimulating factor (M-CSF; CSF-1) is a member of a complex network of cytokines that regulate monocytic cell development and activity. It is produced in nearly all organs by cell types commonly found in connective tissue, including fibroblasts and monocytes. Whether different cell types share common or have divergent mechanisms for regulating CSF-1 gene expression is not known. To address this question, the identity of cis-acting elements and cognate trans-acting factors was characterized in a region of the CSF-1 promoter known to be more active in monocytes than in fibroblasts. The results of DNase I protection assays performed with fibroblast- or monocyte-derived nuclear extracts revealed a difference in the pattern of DNA-binding proteins. One protected region, common to both fibroblasts and monocytes, spans a putative phorbol ester-responsive element (TRE), and binding to the TRE by AP1 was verified with antibodies directed against c-fos and c-jun family members. Mutational analysis revealed that the TRE is required for CSF-1 gene expression in proliferating fibroblasts and monocytes. Binding of a second putative trans-acting factor, preferentially expressed in fibroblasts, to the region immediately upstream of the TRE was also detected. Screening a mouse expression library with oligonucleotides spanning the putative cis-acting element identified cellular nucleic acid-binding protein (CNBP) as the cognate binding activity, and antiserum to CNBP disrupted the electromobility shift assay complex. Mutational analysis revealed that loss of CNBP binding leads to a decrease in CSF-1 promoter activity in fibroblasts but has no effect on CSF-1 promoter activity in monocytes. Our results demonstrate that control of CSF-1 gene expression in monocytes and fibroblasts is mediated by common and cell type-specific trans-acting factors.

Mutual Education Between Hematopoietic Cells and Bone Marrow Stromal Cells Through Direct Cell-to-Cell Contact: Factors That Determine the Growth of Bone Marrow Stroma-Dependent Leukemic (HB-1) Cells

A stroma-dependent cell line (HB-1) was established from myelogenous leukemic cells of CBA/N mouse. Characterization of the cells showed that HB-1 proliferated on hematopoietic supportive stromal cells (MS-10), but did not survive or proliferate on hematopoietic nonsupportive cells (MS-K). Direct contact between HB-1 and MS-10 appears to be necessary for HB-1 to proliferate on MS-10. We found that interleukin-1α (IL-1α) produced by MS-10 plays a major role in the survival and proliferation of HB-1. IL-11 did not support the proliferation of HB-1 cells by itself, but enhanced the proliferation of HB-1 cells in the presence of IL-1α. The expression of IL-1α and IL-11 was induced in MS-10 by the direct contact with HB-1 cells, and the expression of IL-1 receptor type I (IL-1RI) and interleukin-11 receptor (IL-11R) was induced in HB-1 cells by the attachment of the cells to MS-10. These findings show the existence of two-way interactions between HB-1 and MS-10.

© 1998 by The American Society of Hematology.

Mutual Education Between Hematopoietic Cells and Bone Marrow Stromal Cells Through Direct Cell-to-Cell Contact: Factors That Determine the Growth of Bone Marrow Stroma-Dependent Leukemic (HB-1) Cells

A stroma-dependent cell line (HB-1) was established from myelogenous leukemic cells of CBA/N mouse. Characterization of the cells showed that HB-1 proliferated on hematopoietic supportive stromal cells (MS-10), but did not survive or proliferate on hematopoietic nonsupportive cells (MS-K). Direct contact between HB-1 and MS-10 appears to be necessary for HB-1 to proliferate on MS-10. We found that interleukin-1α (IL-1α) produced by MS-10 plays a major role in the survival and proliferation of HB-1. IL-11 did not support the proliferation of HB-1 cells by itself, but enhanced the proliferation of HB-1 cells in the presence of IL-1α. The expression of IL-1α and IL-11 was induced in MS-10 by the direct contact with HB-1 cells, and the expression of IL-1 receptor type I (IL-1RI) and interleukin-11 receptor (IL-11R) was induced in HB-1 cells by the attachment of the cells to MS-10. These findings show the existence of two-way interactions between HB-1 and MS-10.

© 1998 by The American Society of Hematology.

Identification of alternatively spliced transcripts encoding murine macrophage colony-stimulating factor

We have isolated a novel cDNA encoding macrophage colony-stimulating factor (M-CSF) from a murine stromal cell line, ST2. The cDNA included an entire coding sequence of the M-CSF gene but contained an additional sequence of 140 base pairs (bp). Northern blot analysis demonstrated that other murine cell lines such as a fibroblastic cell line (L) and a stromal cell line (PA6) also expressed the transcripts corresponding to the clone. The nucleotide sequence analyses of the cDNA and the cloned M-CSF genome revealed that the 140-bp insertion sequence was part of intron 1 which separated exon 1 and exon 2: the former contained part of the amino acid residues of the signal sequence and the latter the rest of the signal sequence and the first 22 amino acid residues of the mature protein. The insertion of the 140-bp intron sequence not only changed the amino acid sequence of the signal peptide but also generated an in-frame termination codon. However, instead of the dysfunction of the original initiation codon, the 140-bp insertion sequence contained a putative ATG initiation codon that preserved the original open reading frame. Finally, we found that the cDNA directed the expression of a secreted and biologically active M-CSF protein when it was introduced into COS7 cells and M-CSF activity in the culture supernatants was measured using an M-CSF-dependent cell line. These results indicate the presence of an alternatively spliced M-CSF transcript which utilizes an alternate initiation codon in order to specify active M-CSF protein.

Oxidants as stimulators of signal transduction

Redox (oxidation-reduction) reactions regulate signal transduction. Oxidants such as superoxide, hydrogen peroxide, hydroxyl radicals, and lipid hydroperoxides (i.e., reactive oxygen species) are now realized as signaling molecules under subtoxic conditions. Nitric oxide is also an example of a redox mediator. Reactive oxygen species induce various biological processes such as gene expression by stimulating signal transduction components such as Ca(2+)-signaling and protein phosphorylation. Various oxidants increase cytosolic Ca2+; however, the exact origin of Ca2+ is controversial. Ca2+ may be released from the endoplasmic reticulum, extracellular space, or mitochondria in response to oxidant-influence on Ca2+ pumps, channels, and transporters. Alternatively, oxidants may release Ca2+ from Ca2+ binding proteins. Various oxidants stimulate tyrosine as well as serine/threonine phosphorylation, and direct stimulation of protein kinases and inhibition of protein phosphatases by oxidants have been proposed as mechanisms. The oxidant-stimulation of the effector molecules such as phospholipase A2 as well as the activation of oxidative stress-responsive transcription factors may also depend on the oxidant-mediated activation of Ca(2+)-signaling and/or protein phosphorylation. In addition to the stimulation of signal transduction by oxidants, the observations that ligand-receptor interactions produce reactive oxygen species and that antioxidants block receptor-mediated signal transduction led to a proposal that reactive oxygen species may be second messengers for transcription factor activation, apoptosis, bone resorption, cell growth, and chemotaxis. Physiological significance of the role of biological oxidants in the regulation of signal transduction as well as the mechanisms of the oxidant-stimulation of signal transduction are discussed.

Transcriptional regulation of the mouse CSF-1 gene

Research in our laboratory is aimed at understanding the cellular and molecular mechanisms that govern colony stimulating factor-1 (CSF-1) gene expression. Our hypothesis is that a basal set of trans-acting factors is bound to the CSF-1 gene during fibroblast proliferation, resulting in constitutive CSF-1 gene expression. Modulation of CSF-1 gene transcription by growth-arrest (decrease) or stimulation of growth-arrested fibroblasts (re-initiate) is mediated by changes in the basal set of factors bound and/or by the addition of stimulus-specific factors. We have extended our hypothesis to include other cell types (monocytes) to determine if mechanisms used to control CSF-1 gene expression in fibroblasts are unique or represent common nontissue-specific regulatory mechanisms. Analysis of CSF-1-CAT reporter constructs in transiently transfected fibroblasts and monocytes was used to identify CSF-1 genomic sequences that affect transcriptional activity. DNase I protection, electrophoretic mobility shift, and methylation interference assays were used to identify the putative cis-acting elements. Results of our study suggest multiple trans-acting factors may regulate CSF-1 gene expression; some may be tissue specific, while others, such as AP1, CTF/NF1, Sp1, and Sp3, are shared in common.

Estrogen deficiency increases the ability of stromal cells to support murine osteoclastogenesis via an interleukin-1and tumor necrosis factor-mediated stimulation of macrophage colony-stimulating factor production

To analyze how estrogen blocks osteoclastogenesis, we investigated the effects of ovariectomy on osteoclast (OC) formation in co-cultures of purified OC precursors and purified stromal cells (SC). OC formation was higher in co-cultures containing SC from ovariectomized mice than in those containing SC from sham-operated mice, thus suggesting that estrogen regulates osteoclastogenesis by targeting SC. Ovariectomy also increased the mononuclear cell secretion of interleukin (IL)-1) and tumor necrosis factor (TNF) and the SC production of macrophage colony-stimulating factor (MCSF). Osteoclastogenesis and SC production of M-CSF were not blocked by in vitro estrogen treatment but were decreased by in vivo treatment of donor mice with either estrogen or a combination of the IL-1 inhibitor, IL-1 receptor antagonist, and the TNF inhibitor, TNF binding protein. IL-1 and TNF production were also blocked by in vivo estrogen treatment, demonstrating that the increased bone marrow levels of IL-1 and TNF characteristic of ovariectomized mice induce the formation of a SC population characterized by a high production of M-CSF and increased pro-osteoclastogenic activity. Since in co-cultures of SC and OC precursors M-CSF levels correlated with OC production (r = 0.7, p < 0.0001), the data also indicate that the pro-osteoclastogenic activity of SC is proportional to their secretion of M-CSF. The ability of estrogen to decrease SC production of M-CSF and the pro-osteoclastogenic activity of these cells by regulating IL-1 and TNF production is a previously undescribed mechanism by which estrogen down-regulates osteoclastogenesis.

Binding of a CTF/NF1-like protein to the mouse colony-stimulating factor-1 gene promoter

Circulating and tissue-specific monocytes/macrophages, through production of hydrolytic enzymes and growth factors, can dramatically affect the local tissue environment. Colony-stimulating factor-1 (CSF-1) is a key regulator of monocyte/macrophage cell activity. CSF-1 is produced by stromal elements, including fibroblasts, which are found in all tissues. To understand at the molecular level how changes in CSF-1 gene transcription are initiated in fibroblasts, we set out to identify the cis-acting elements and cognate trans-acting factor(s) that bind regulatory regions of the mouse CSF-1 gene. Analysis of heterologous reporter constructs containing the mouse CSF-1 promoter linked to the bacterial chloramphenicol acetyltransferase (CAT) gene in transiently transfected fibroblasts identified a cis-acting element located between base pairs -88 and -43 of the CSF-1 gene. Electrophoretic mobility-shift assays (EMSAs) and DNase I protection assays with nuclear extracts isolated from proliferating fibroblasts revealed distinct protein binding to the region spanning base pairs -90 to -68. Results from methylation interference assays suggest CTF/NF1 or a CTF/NF1-like factor is the cognate trans-acting factor. Mutation of the putative CTF/NF1 binding site in the CSF-1 promoter lead to a modest decrease in promoter activity in transiently transfected fibroblasts and monocytes. Therefore, we have demonstrated that CTF/NF1 or a CTF/NF1-like protein binds to the CSF-1 gene promoter; however, binding of the CTF/NF1-like protein alone does not significantly effect changes in CSF-1 gene promoter activity.

Activation and attenuation of transcription factor NF-kB in mouse glomerular mesangial cells in response to tumor necrosis factor-alpha, immunoglobulin G, and adenosine 3':5'-cyclic monophosphate. Evidence for involvement of reactive oxygen species

The transcription factor NF-kB may play an important role in the response to tissue injury and activation of cytokines. We therefore examined the regulation of NF-kB in mesangial cells. Treatment of mesangial cells with TNF-alpha increased nuclear proteins that bound to an NF-kB-specific DNA oligonucleotide. IgG aggregates also increased nuclear NF-kB demonstrating Fc-tau receptor-mediated activation of NF-kB. Treatment of a cytosolic preparation with the detergent deoxycholate also activated NF-kB. The binding characteristics were typical for NF-kB transcription factors as determined by competition experiments with NF-kB-binding wild type kB DNA oligonucleotides or mutated oligonucleotides. Furthermore, a monoclonal antibody against the p65 subunit of NF-kB prevented the binding of NF-kB to the kB oligonucleotide. To evaluate the potential role of reactive oxygen intermediates in the activation of NF-kB, we used PDTC as a scavenger and HMAP as an inhibitor of NADPH-dependent oxidase. Both PDTC and HMAP attenuated the increase in nuclear NF-kB in response to either TNF-alpha or IgG complexes. Finally, generation of superoxide anion by xanthine oxidase activated NF-kB, an effect also mitigated by PDTC. In contrast, exogenous H2O2 did not activate NF-kB. Preincubation of cells with 8 br-cAMP, forskolin, or PGE2 attenuated the increase in nuclear NF-kB in response to TNF-alpha, aggregated IgG, or superoxide anion. Our results provide support for a role of reactive oxygen intermediates as mediators for activation of NF-kB in MC after stimulation with TNF-alpha or IgG aggregates. As an unexpected novel finding we report that cAMP can inhibit activation of NF-kB in MC. These observations may help to explain effects of TNF-alpha, IgG aggregates and cAMP on generation of cytokines by mesangial cells and the resulting glomerular pathophysiology.

Basal expression of the human macrophage colony-stimulating factor (M-CSF) gene in K562 cells

Macrophage colony-stimulating factor (M-CSF) functions in hematopoiesis and regulates mature monocytes. Untreated K562 leukemic cells transcribe M-CSF. Elements between bases -43 and -77 (NF-KB enhancer) and between -129 and -180 (Sp1 enhancer) of the M-CSF promoter were important for basal transcription. Gel Shift assays and ultraviolet crosslinking experiments showed a 50 kDa protein bound to the NF-KB element at -65 in a GTP-dependent fashion. Additionally, a K562 nuclear protein, specifically bound the Sp1 enhancer. Run-off transcription and half-life studies showed that M-CSF is regulated primarily at the post-transcriptional level.

Effects of gamma-irradiation on the M-CSF-promoter linked to a chloramphenicol aminoacyl transferase reporter gene expressed in a clonal murine bone marrow stromal cell line

The effects of cytokines produced by bone marrow stromal cells on closely associated hematopoietic cells constitute a major component of the physiology of the hematopoietic microenvironment. A major cytokine produced by marrow stromal cells is macrophage colony-stimulating factor (M-CSF). To determine the effect of gamma-irradiation on the M-CSF promoter in bone marrow stromal cells, we selected a clonal cell line from the C3H/HeJ mouse marrow stromal cell line D2XRII and stably transfected a reporter construct containing the murine M-CSF-promoter linked to a chloramphenicol aminoacyl transferase (CAT) gene. CAT activity was measured at serial time points after gamma-irradiation in vitro to doses between 500 and 10,000 cGy at a dose rate of 116 cGy/min. D2XRII marrow stromal cells treated with phorbol myristate acetate (40 micrograms/ml, four h), demonstrated a significant two-fold increase in CAT activity. In contrast, CAT activity measured immediately, 24 h, 72 h or 1 week after gamma-irradiation, showed no significant increase or decrease in CAT activity. An increase in CAT activity was detected 48 h after irradiation with cells that received 5,000 cGy. Thus, single fraction gamma-irradiation of plateau phase bone marrow stromal cells did not decrease M-CSF-promoter activity. These results are consistent with prior experimental data demonstrating stable levels of release of M-CSF protein following gamma-irradiation of bone marrow stromal cells and imply that the stability of transcription of the gene for this important cytokine is protected from irradiation.

Oxygen radicals as second messengers for expression of the monocyte chemoattractant protein, JE/MCP-1, and the monocyte colony-stimulating factor, CSF-1, in response to tumor necrosis factor-alpha and immunoglobulin G. Evidence for involvement of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent oxidase

The potential involvement of reactive oxygen species in the expression of genes involved in immune response was examined in mesangial cells. Tumor necrosis factor (TNF-alpha) and aggregated (aggr.) IgG increased mRNA levels for the monocyte chemoattractant protein, JE/MCP-1, and the colony-stimulating factor, CSF-1. Scavengers for free radicals such as di- and tetra-methylthiourea (DMTU and TMTU) attenuated the increase in mRNA levels in response to TNF-alpha and aggr. IgG. Generation of superoxide anion by xanthine oxidase and hypoxanthine increased mRNA levels of these genes, but exogenous H2O2 did not. Addition of NADPH to activate a membrane-bound NADPH-oxidase generated superoxide and caused a dose-dependent increase in mRNA levels and further enhanced the stimulation by TNF-alpha or aggr. IgG. An inhibitor of NADPH-dependent oxidase 4'-hydroxy-3'-methoxy-acetophenone attenuated the rise in mRNA levels in response to TNF-alpha and aggr. IgG. By nuclear run-on experiments TNF-alpha, aggr. IgG and NADPH increased the transcription rates for JE/MCP-1 and CSF-1, effects inhibited by TMTU. We conclude that generation of reactive oxygen species, possibly by NADPH-dependent oxidase, are involved in the induction of the JE/MCP-1 and CSF-1 genes by TNF-alpha and IgG complexes. The concerted expression of leukocyte-directed cytokines represents a general response to tissue injury.