Reactive oxygen species mediate chloroquine-induced expression of chemokines by human astroglial cells

We have previously demonstrated that chloroquine may evoke inflammatory responses in the central nervous system by inducing expression of pro-inflammatory cytokines by astroglial cells. In this study, we further examined the molecular mechanism responsible for chloroquine-induced activation of NF-kappaB and subsequent expression of chemokines by astroglial cells. We observed that (1) chloroquine induced expression of chemokines such as CCL2 and CXCL8 in a dose- and time-dependent manner in human astroglial cells; (2) other lysosomotropic agents such as ammonium chloride and bafilomycin A1 had minimal effects on chemokine expression; (3) inhibition of NF-kappaB by MG-132 and TPCK suppressed chloroquine-induced mRNA expression of chemokines; (4) chloroquine increased the intracellular level of reactive oxygen species (ROS) in a dose- and time-dependent manner by human astroglial cells, but not by monocytic/microglial cells; (5) chloroquine-induced increase of intracellular ROS level was suppressed by pre-incubation with diphenyl iodonium (DPI) and N-acetyl cysteine (NAC); and (6) inhibition of chloroquine-induced ROS production by DPI or NAC suppressed chloroquine-mediated activation of NF-kappaB and subsequent mRNA expression of chemokines in astroglial cells. These results collectively suggest that chloroquine generates ROS, which is responsible for NF-kappaB activation and subsequent expression of pro-inflammatory chemokines in human astroglial cells.

Class II major histocompatibility complex transactivator (CIITA) inhibits matrix metalloproteinase-9 gene expression

Matrix metalloproteinases (MMPs) are a family of structurally related proteins with the collective capability to degrade all components of the extracellular matrix. Although MMP-mediated degradation of the extracellular matrix occurs physiologically, numerous pathological conditions exhibit increased MMP levels and excessive matrix degradation. Previous work from our laboratory has shown that interferon-gamma inhibits MMP-9 expression in a manner dependent upon STAT-1alpha. Here we extend our previous observations and show that the class II major histocompatibility complex transactivator (CIITA), a transcriptional target of STAT-1alpha, is also capable of inhibiting MMP-9 expression. By using stable cell lines that inducibly express CIITA or various mutant forms of CIITA, we show that CIITA requires the ability to bind the CREB-binding protein (CBP) to effectively inhibit MMP-9 expression. Furthermore, we show that CIITA-mediated inhibition of the MMP-9 gene does not rely on the transcriptional capability of CIITA. These findings support a model wherein CIITA inhibits MMP-9 expression by binding to and sequestering CBP, which reduces the levels of CBP at the MMP-9 promoter, inhibits levels of acetylated histone 3 at the MMP-9 promoter, and subsequently inhibits MMP-9 expression.

Coordination of cell signaling, chromatin remodeling, histone modifications, and regulator recruitment in human matrix metalloproteinase 9 gene transcription

Transcriptional activation of eukaryotic genes depends on the precise and ordered recruitment of activators, chromatin modifiers/remodelers, coactivators, and general transcription factors to the promoters of target genes. Using the human matrix metalloproteinase 9 (MMP-9) gene as a model system, we investigated the sequential assembly and dynamic formation of transcription complexes on a human promoter under the influence of mitogen signaling. We find that, coincident with activation of the MMP-9 gene, activators, chromatin remodeling complexes, and coactivators are recruited to the preassembled MMP-9 promoter in a stepwise and coordinated order, which is dependent on activation of MEK-1/extracellular signal-regulated kinase and NF-kappa B signaling pathways. Conversely, corepressor complexes are released from the MMP-9 promoter after transcriptional activation. Histone modifications shift from repressive to permissive modifications concurrent with activation of the MMP-9 gene. Chromatin remodeling induced by Brg-1 is required for MMP-9 gene transcription, which is concomitant with initiation of transcription. Therefore, coordination of cell signaling, chromatin remodeling, histone modifications, and stepwise recruitment of transcription regulators is critical to precisely regulate MMP-9 gene transcription in a temporally and spatially dependent manner. Given the important role of MMP-9 in both normal development and pathological conditions, understanding MMP-9 gene regulation is of great relevance.

Pulmonary edema fluid from patients with early lung injury stimulates fibroblast proliferation through IL-1 beta-induced IL-6 expression

Although the fibroproliferative response to lung injury occurs with a high frequency in patients with clinical acute lung injury, the mechanisms that initiate this response are largely unknown. This study was undertaken first to identify fibroblast mitogenic factors in pulmonary edema fluid, and second to examine the human lung fibroblast's gene expression profile in response to pulmonary edema fluid. The edema fluid obtained from patients with early lung injury has an eightfold higher concentration of IL-1beta and a twofold greater IL-1beta-dependent mitogenic effect than does fluid obtained from control patients with hydrostatic pulmonary edema. Furthermore, fibroblasts responded to acute lung injury patient-derived edema fluid through production of soluble mediators that possess an autocrine mitogenic effect. Gene array analysis reveals that acute lung injury edema fluid induces several inflammation-modulating and proliferation-related genes in fibroblasts, whose inductions are similarly dependent on bioactive IL-1beta. Most notably, the 20-fold induction of IL-6 mRNA and protein was completely blocked by IL-1 receptor antagonist. The combined addition of IL-1beta and IL-6 was mitogenic, and the proliferative response to conditioned medium from IL-1beta-exposed cells was blocked by antagonistically acting Abs to IL-6 or to gp130. These novel findings indicate that soluble IL-1beta bioactivity and autocrine IL-1beta-dependent IL-6 up-regulation are critical initiators of fibroblast activation and proliferation and that they likely play a role in the fibroproliferative response seen in human acute lung injury.

Bis-anthracycline antibiotics inhibit human immunodeficiency virus type 1 transcription

The increasing numbers of human immunodeficiency virus type 1 (HIV-1) strains that exhibit resistance to antiretroviral agents used at present require the development of new effective antiretroviral compounds. Tat transactivation was recognized early on as an attractive target for drug interference. To screen for and analyze the effects of compounds that interfere with Tat transactivation, we developed several cell-based reporter systems in which enhanced green fluorescence protein is a direct and quantitative marker of HIV-1 expression or Tat-dependent long terminal repeat activity. Using these reporter cell lines, we found that the bis-anthracycline WP631, a recently developed DNA intercalator, efficiently inhibits HIV-1 expression at subcytotoxic concentrations. WP631 also abrogated acute HIV-1 replication in peripheral blood mononuclear cells infected with various primary virus isolates. We demonstrate that WP631-mediated HIV-1 inhibition is caused by the inhibition of Tat transactivation. The data presented suggest that WP631 could serve as a lead compound for a new type of HIV-1 inhibitor.

17beta-Estradiol inhibits class II major histocompatibility complex (MHC) expression: influence on histone modifications and cbp recruitment to the class II MHC promoter

Major histocompatibility complex (MHC) class II proteins are important for the initiation of immune responses and are essential for specific recognition of foreign antigens by the immune system. Regulation of class II MHC expression primarily occurs at the transcriptional level. The class II transactivator protein is the master regulator that is essential for both constitutive and interferon-gamma-inducible class II MHC expression. Estrogen [17beta-estradiol (17beta-E2)] has been shown to have immunomodulatory effects. In this study, we show that 17beta-E2 down-regulates interferon-gamma inducible class II MHC protein levels on brain endothelial cells, as well as other cell types (astrocytes, fibrosacroma cells, macrophages). The inhibitory effects of 17beta-E2 on class II MHC expression are not due to changes in class II transactivator mRNA or protein levels, rather, 17beta-E2 mediates inhibition at the level of class II MHC gene expression. We demonstrate that 17beta-E2 attenuates H3 and H4 histone acetylation and cAMP response element binding protein-binding protein association with the class II MHC promoter, suggesting that 17beta-E2 inhibits class II MHC expression by a novel mechanism involving modification of the histone acetylation status of the class II MHC promoter.

Caspase-1 mediates Fas-induced apoptosis and is up-regulated by interferon-gamma in human astrocytoma cells

Resistance to Fas-mediated apoptosis contributes to tumor evasion from the host immune system and enables tumors to mediate alternative responses such as inflammation and angiogenesis. In this study, we investigated the molecular mechanisms of the resistance to Fas-mediated apoptosis and sensitization to Fas-induced cell death by IFN-gamma in human astrocytoma cells. To address this, we investigated the expression of thirty-three genes related to the Fas signal transduction pathways using RNase protection assay in five different human astrocytoma cells. Patterns of expression of these genes were similar between different cell lines and did not correlate with sensitivity to Fas-mediated cell death. Treatment with IFN-gamma increased the mRNA expression of caspases-1, -4 and -7 in addition to those of Fas and TRAIL in a time- and dose-dependent manner. Studies using specific caspase inhibitors showed that Fas-induced cell death was mediated by caspases-1, -3 and 8 in the Fas-sensitive human astrocytoma cell lines, CRT-J and U87-MG. We further demonstrated that these caspases were proteolytically cleaved upon Fas ligation in these cells. Interestingly, caspase-1 protein expression but not that of caspase-3 nor -8 was up-regulated by IFN-gamma only in Fas-sensitive CRT-J cells but not in Fas-resistant U373-MG cells. These results collectively suggest that caspase-1, along with caspases-3 and -8, mediate Fas-induced cell death in human astrocytoma cells, and post-transcriptional regulation of caspase-1 may determine the responsiveness to IFN-gamma-induced sensitization to Fas-mediated apoptosis.

STAT-1 alpha and IFN-gamma as modulators of TNF-alpha signaling in macrophages: regulation and functional implications of the TNF receptor 1:STAT-1 alpha complex

TNF-alpha and IFN-gamma cooperate in the activation of macrophages. TNF-alpha-dependent activation of NF-kappaB is stronger in the presence of IFN-gamma. STAT-1alpha associates with TNFR1 in TNF-alpha-treated cells, and this association attenuates TNF-alpha-mediated NF-kappaB activation. We hypothesized that nuclear localization of STAT-1alpha due to IFN-gamma signaling would preclude it from being recruited to the TNFR1 and therefore enhance TNF-alpha-induced NF-kappaB activation. In the RAW264.7 macrophage cell line, TNF-alpha treatment indeed recruits STAT-1alpha to the TNFR1, and this association is abrogated when cells are exposed to IFN-gamma. TNF-alpha treatment induces a more robust activation of NF-kappaB in STAT-1alpha-deficient cells, and restoration of STAT-1alpha inhibits TNF-alpha-dependent NF-kappaB activation. Our results suggest that a receptor-proximal level of cross-talk exists between these two cytokine pathways: IFN-gamma limits STAT-1alpha availability to the TNFR1 by depleting STAT-1alpha from the cytoplasm, thus allowing for optimal NF-kappaB activation upon TNF-alpha ligation.

Induction of intercellular adhesion molecule-1 by Fas ligation: proinflammatory roles of Fas in human astroglioma cells

FasL has been shown to induce angiogenesis in vivo, however, the mechanism remains to be determined. We have previously shown that Fas ligation induces expression of chemokines such as interleukin-8 by human astrogliomas, which may partially explain the in vivo angiogenic property of FasL. Intercellular adhesion molecule (ICAM)-1 is increased in various human tumors, and is thought to be involved in the processes of metastasis and angiogenesis. We demonstrate that Fas ligation induces ICAM-1 expression at the mRNA and protein levels in human astroglioma cells. Studies using Boc-D-Fmk, a pharmacological inhibitor, show that caspase activation is required for Fas-mediated ICAM-1 induction. To study the in vivo expression of Fas and ICAM-1, human low-grade astrogliomas and glioblastoma multiforme (GBM) samples were examined by ELISA for Fas and ICAM-1. Human GBM samples express higher levels of Fas compared to normal control brain, which correlates with increased ICAM-1 expression. These findings suggest that Fas ligation on human glioma cells leads to the induction of ICAM-1 expression, which involves caspase cascade signaling pathways.

TRADD interacts with STAT1-alpha and influences interferon-gamma signaling

Tumor necrosis factor receptor 1 (TNFR1)-associated death domain protein (TRADD) is essential in recruiting signaling molecules to the TNFR1 receptor complex. Interferon-gamma (IFN-gamma) is a potent activator of macrophages and uses signal transducer and activator of transcription 1-alpha (STAT1-alpha) for signal transduction. Here we demonstrate that IFN-gamma induces the formation of a nuclear-localized TRADD-STAT1-alpha complex. IFN-gamma-mediated STAT1-alpha phosphorylation was prolonged in cells with reduced TRADD expression. Moreover, we noted an increase in IFN-gamma-mediated STAT1-alpha DNA-binding activity, nuclear presence and transcriptional potential in the TRADD knockdown cells. These data indicate that TRADD may be involved in IFN-gamma signaling by forming a complex with STAT1-alpha within the nucleus and regulating IFN-gamma-mediated STAT1-alpha activation.

Fas ligand/Fas system in the brain: regulator of immune and apoptotic responses

Apoptosis, also known as programmed cell death, is the major type of cell death involved in normal development, regeneration, proliferation and pathologic degeneration in the central nervous system (CNS). The apoptotic process can be divided further into two pathways depending on the involvement of mitochondria and related biochemical cascades. The internal pathway of apoptosis is initiated by a variety of cytotoxic stimuli and mediated by the release of cytochrome c and subsequent activation of downstream caspases. The external pathway is mainly triggered by ligation of death receptors such as Fas, tumor necrosis factor (TNF)-related apoptosis inducing ligand-R1 (TRAIL-R1), TRAIL-R2 and TNFRp55, and mediated by direct activation of upstream caspases. The Fas-FasL system has been known as a prototypic inducer of extrinsic cell death responsible for cell-mediated cytotoxicity, peripheral immune regulation, immune privilege and "counterattack" of malignant tumor cells against the host immune system. Fas and FasL are expressed in the normal CNS, and expression increases in inflamed and degenerated brains. Like other specialized tissues such as the eye and testis, the Fas-FasL system is thought to be involved in immune suppressed status in the CNS. Expression of Fas and FasL is significantly elevated in a variety of the neurologic disorders, suggesting the possibility that this system may play roles in degenerative and inflammatory responses in the CNS. Therefore, the FasL-Fas system should be considered as a double-edged sword in the CNS: maintaining the immune suppressed status in normal brain and inducing neuronal cell death and inflammation in a variety of neurologic disorders.

Molecular regulation of CD40 gene expression in macrophages and microglia

Inflammatory events in the central nervous system (CNS) contribute to the disease process in a variety of neuroinflammatory diseases such as multiple sclerosis (MS), Alzheimer's Disease (AD), and cerebral ischemia, and activated macrophages/microglia are central to this response. Immunological activation of these cells leads to the production of a wide array of cytokines, chemokines, matrix metalloproteinases and neurotoxins, and ultimately to glial/neuronal injury and death. The CD40 molecule has an important role in promoting inflammatory responses by macrophages/microglia, since interaction with its cognate ligand, CD154, leads to secretion of cytokines and neurotoxins. Aberrant CD40 expression by macrophages/microglia, induced by cytokines such as IFN-gamma and TNF-alpha, contributes to neuroimmunologic cascades in the CNS. Strategies to suppress CD40 expression may attenuate inflammation and neuronal damage within the CNS, which will ultimately be of benefit in neuroinflammatory diseases. The mediators that regulate expression of CD40 in macrophages/microglia (both induction and inhibition) function at the level of gene transcription. In this review, we present an overview of the molecular basis of CD40 expression in macrophages/microglia. The signal transduction pathways and transcription factors employed by IFN-gamma and TNF-alpha to induce CD40 expression are described, as are the cis-elements in the CD40 promoter that are critical for CD40 transcription. Information is provided on the mechanism(s) underlying suppression of CD40 in macrophages/microglia by immunomodulatory agents such as IL-4, TGF-beta, neuropeptides, neurotrophins, and statins. A comprehensive assessment of CD40 production and function in macrophages/microglia will establish the foundation for future therapeutic manipulation of this critical immunoregulatory protein.

Oncostatin-M induction of vascular endothelial growth factor expression in astroglioma cells

Oncostatin-M (OSM), a hematopoietic cytokine, and vascular endothelial growth factor (VEGF), a quintessential angiogenic signal, are coexpressed in development, cancer and inflammation. Here, we report that OSM treatment of human astroglioma cell lines increases VEGF levels by approximately threefold. Interleukin-1beta (IL-1beta), in combination with OSM, induces up to sevenfold higher VEGF expression, without significantly inducing VEGF on its own. Specifically examining the OSM contribution to VEGF expression, neutralizing antibodies to OSM receptor subunits gp130 and OSMRbeta, but not LIFRbeta, inhibited OSM induction of VEGF, indicating that the OSM-specific receptor OSMRbeta/gp130 transduces the OSM signal for VEGF synthesis. OSM induction of VEGF promoter activity maps to the (-1171, -786) region of the VEGF promoter, which contains a STAT-3-binding site. STAT-3 is indeed essential for this response, since overexpression of a dominant-negative STAT-3 blocks OSM induction of VEGF promoter activity, as well as endogenous VEGF expression. Finally, we demonstrate that OSM is expressed in glioblastoma multiforme tumor biopsies, a particularly malignant form of brain tumor. This novel mechanism of VEGF regulation in astroglioma cells may be active in pathophysiological states where both OSM and IL-1beta are present.

CD154-CD40-induced reactivation of latent HIV-1 infection

Reservoirs of latent HIV-1 in T cells and macrophages pose one of the major obstacles that hamper final eradication of HIV-1 from infected patients. Targeting costimulatory molecules expressed on cell types harboring latent HIV-1 to achieve reactivation may provide a new approach to overcome this problem. One such molecule is CD40, a member of the tumor necrosis factor (TNF)-receptor family. Using THP89GFP cells as a model for latently infected macrophages, we demonstrate that trimeric forms of recombinant CD154 allow for the direct reactivation of latent HIV-1 infection. Reactivation is augmented by the release of TNF-alpha. The presence of TNF-alpha is also crucial for the expression of late structural genes such as p24 Gag. In addition, levels of secreted TNF-alpha are sufficiently high to reactivate latent HIV-1 in a latently HIV-1-infected T-cell line (J89GFP). Taken together, our results demonstrate that costimulatory molecules may be attractive targets to reactivate latent HIV-1 in infected patients.

Oncostatin M enhances the expression of prostaglandin E2 and cyclooxygenase-2 in astrocytes: synergy with interleukin-1beta, tumor necrosis factor-alpha, and bacterial lipopolysaccharide

Oncostatin M (OSM), a cytokine of the interleukin-6 family, is expressed in rheumatoid arthritis, multiple sclerosis, multiple myeloma, and other inflammatory and neoplastic conditions. Prostaglandin E(2) (PGE(2)), an eicosanoid also associated with inflammation and cancer, has recently been shown to induce OSM expression. We report here that OSM in turn induces PGE(2) production by astrocytes and astroglioma cells. More importantly, in combination with the inflammatory mediators IL-1beta, tumor necrosis factor-alpha, and lipopolysaccharide, OSM exhibits a striking synergy, resulting in up to 50-fold higher PGE(2) production by astrocytes, astroglioma, and neuroblastoma cell lines. Enhanced PGE(2) production by OSM and IL-1beta treatment is explained by their effect on cyclooxygenase-2 (COX-2), an enzyme that catalyzes the committed step in PGE(2) synthesis. Of the enzymes involved in PGE(2) biosynthesis, only COX-2 mRNA and protein levels are synergistically amplified by OSM and IL-1beta. Nuclear run-on assays demonstrate that OSM and IL-1beta synergistically upregulate transcription of the COX-2 gene, and the mRNA stability assay indicates that COX-2 mRNA is posttranscriptionally stabilized by OSM and IL-1beta. To effect synergy on the PGE(2) level, OSM signals in part through its gp130/OSMRbeta receptor, since neutralizing antibodies against gp130 and OSMRbeta, but not LIFRbeta, decrease PGE(2) production in response to OSM plus IL-1beta. SB202190 and U0126, inhibitors of p38 MAPK and ERK1/2 activation, respectively, inhibit IL-1beta and OSM upregulation of COX-2 and PGE(2), indicating that these MAPK cascades are utilized by both stimuli. This mechanism of PGE(2) amplification may be active in brain pathologies where both OSM and IL-1beta are present, such as glioblastomas and multiple sclerosis.

Chloroquine induces activation of nuclear factor-kappaB and subsequent expression of pro-inflammatory cytokines by human astroglial cells

Chloroquine, an antimalarial lysosomotropic base, is known for its anti-inflammatory effects and therefore used for treatment of autoimmune diseases. Given its anti-inflammatory effects, it has been under clinical trials to modify neurodegenerative processes. In this study, we examined whether chloroquine has an anti-inflammatory effect in the CNS by determining the in vitro effects of chloroquine on LPS-induced expression of cytokines by glial cells. We observed that (i) chloroquine augmented LPS-induced expression of pro-inflammatory cytokines such as lymphotoxin (LT)-beta, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1alpha, IL-1beta and IL-6 in human astroglial cells, while the same treatment suppressed LPS-induced expression of cytokines in monocytic and microglial cells; (ii) chloroquine alone induced expression of pro-inflammatory cytokines in a dose- and time-dependent manner in astroglial cells; (iii) other lysosomotropic agents such as ammonium chloride and bafilomycin A1 had minimal effects on cytokine expression; and (iv) chloroquine induced the activation of nuclear factor-kappa B in astroglial cells, which is a required component of chloroquine induction of cytokines. These results suggest that chloroquine may evoke either anti- or pro-inflammatory responses in the CNS depending on the cellular context.

Regulation and function of class II major histocompatibility complex, CD40, and B7 expression in macrophages and microglia: Implications in neurological diseases

The ability of microglia, the brain's resident macrophage, to present antigen through the class II major histocompatibility complex (MHC) to T cells allows these normally quiescent cells to play a critical role in shaping the outcome of many neurological diseases. The expression of class II MHC antigens and the costimulatory molecules CD40 and B7 on microglia and infiltrating macrophages is regulated through a complex network of cytokines in the inflamed brain. In this review, we describe the molecular mechanisms underlying class II MHC, CD40 and B7 regulation in microglia and macrophages. Our focus is on the cis-elements in the promoters of their genes and the transcription factors activated by cytokines that bind them. The functional implications of aberrant class II MHC, CD40 and B7 expression by microglia and macrophages as related to the diseases of Multiple Sclerosis and Alzheimer's Disease are discussed.

Direct and quantitative single-cell analysis of human immunodeficiency virus type 1 reactivation from latency

The ability of human immunodeficiency virus type 1 (HIV-1) to establish latent infections in cells has received renewed attention owing to the failure of highly active antiretroviral therapy to eradicate HIV-1 in vivo. Despite much study, the molecular bases of HIV-1 latency and reactivation are incompletely understood. Research on HIV-1 latency would benefit from a model system that is amenable to rapid and efficient analysis and through which compounds capable of regulating HIV-1 reactivation may be conveniently screened. We describe a novel reporter system that has several advantages over existing in vitro systems, which require elaborate, expensive, and time-consuming techniques to measure virus production. Two HIV-1 molecular clones (NL4-3 and 89.6) were engineered to express enhanced green fluorescent protein (EGFP) under the control of the viral long terminal repeat without removing any viral sequences. By using these replication-competent viruses, latently infected T-cell (Jurkat) and monocyte/macrophage (THP-1) lines in which EGFP fluorescence and virus expression are tightly coupled were generated. Following reactivation with agents such as tumor necrosis factor alpha, virus expression and EGFP fluorescence peaked after 4 days and over the next 3 weeks each declined in a synchronized manner, recapitulating the establishment of latency. Using fluorescence microscopy, flow cytometry, or plate-based fluorometry, this system allows immediate, direct, and quantitative real-time analysis of these processes within single cells or in bulk populations of cells. Exploiting the single-cell analysis abilities of this system, we demonstrate that cellular activation and virus reactivation following stimulation with proinflammatory cytokines can be uncoupled.

Suppressor of cytokine signaling 1 inhibits cytokine induction of CD40 expression in macrophages

CD40 is a type I membrane-bound molecule belonging to the TNFR superfamily that is expressed on various immune cells including macrophages and microglia. The aberrant expression of CD40 is involved in the initiation and maintenance of various human diseases including multiple sclerosis, arthritis, atherosclerosis, and Alzheimer's disease. Inhibition of CD40 signaling has been shown to provide a significant beneficial effect in a number of animal models of human diseases including the aforementioned examples. We have previously shown that IFN-gamma induces CD40 expression in macrophages and microglia. IFN-gamma leads to STAT-1alpha activation directly and up-regulation of NF-kappaB activity due to the secretion and subsequent autocrine signaling of TNF-alpha. However, TNF-alpha alone is not capable of inducing CD40 expression in these cells. Suppressor of cytokine signaling 1 protein (SOCS-1) is a cytokine-inducible Src homology 2-containing protein that regulates cytokine receptor signaling by inhibiting STAT-1alpha activation via a specific interaction with activated Janus kinase 2. Given the important role of CD40 in inflammatory events in the CNS as well as other organ systems, it is imperative to understand the molecular mechanisms contributing to both CD40 induction and repression. We show that ectopic expression of SOCS-1 abrogates IFN-gamma-induced CD40 protein expression, mRNA levels, and promoter activity. Additionally, IFN-gamma-induced TNF-alpha secretion, as well as STAT-1alpha and NF-kappaB activation, are inhibited in the presence of SOCS-1. We conclude that SOCS-1 inhibits cytokine-induced CD40 expression by blocking IFN-gamma-mediated STAT-1alpha activation, which also then results in suppression of IFN-gamma-induced TNF-alpha secretion and subsequent NF-kappaB activation.

Cloning of rat calcium-modulating cyclophilin ligand

Rat calcium-modulating cyclophilin ligand (CAML) cDNA was cloned and sequenced. It has a predicted open reading frame of 294 amino acids. The CAML gene is highly conserved throughout species, showing 85, 89 and 69% amino acid sequence identity to the human, mouse, and chicken genes, respectively. Gene expression data using astrocytes, microglia and neurons show that CAML mRNA and protein is constitutively expressed in these cell types of the central nervous system. The cloning of rat CAML will facilitate further investigations on the function of this molecule.

Critical role of tumor necrosis factor-alpha and NF-kappa B in interferon-gamma -induced CD40 expression in microglia/macrophages

CD40 is a member of the tumor necrosis factor (TNF) receptor superfamily. CD40 expression on antigen-presenting cells (including macrophages and microglia) is crucial for T-cell activation. Aberrant expression of CD40 has been associated with autoimmune inflammatory diseases such as multiple sclerosis and rheumatoid arthritis. We have recently shown that the cytokine interferon (IFN)-gamma is the most potent inducer of CD40 expression in macrophages and microglia, and this induction is mediated by the IFN-gamma-activated transcription factor STAT-1alpha and constitutively expressed PU.1 and/or Spi-B. In this study, we have discovered that a major component of IFN-gamma-induced CD40 expression involves the endogenous production of the cytokine TNF-alpha. The inclusion of anti-TNF-alpha-neutralizing antibody significantly inhibits IFN-gamma-induced CD40 mRNA and CD40 promoter activity. IFN-gamma-induced CD40 protein expression is attenuated in TNF-alpha-deficient microglia and can be restored with exogenous TNF-alpha. Site-directed mutagenesis studies demonstrate that three of the four NF-kappaB elements in the CD40 promoter are required for IFN-gamma-induced CD40 promoter activity. IFN-gamma treatment leads to the activation of NF-kappaB in a time-dependent manner, which is inhibited in the presence of anti-TNF-alpha-neutralizing antibody. These results indicate that IFN-gamma-induced TNF-alpha production and subsequent NF-kappaB activation are integral parts of the mechanism of IFN-gamma-induced CD40 expression.

Tumor necrosis factor-related apoptosis-inducing ligand induces caspase-dependent interleukin-8 expression and apoptosis in human astroglioma cells

Among the tumor necrosis factor (TNF) family of cytokines, FasL and TNF-related apoptosis-inducing ligand (TRAIL) are known to induce cell death via caspase activation. Recently, other biological functions of these death ligands have been postulated in vitro and in vivo. It was previously shown that Fas ligation induces chemokine expression in human glioma cells. In this study, we investigated whether the TRAIL-DR5 system transduces signals similar to those induced by other TNF family ligands and receptors. To address this issue, two human glioma cell lines, CRT-MG and U87-MG, were used, and an agonistic antibody against DR5 (TRA-8) and human recombinant TRAIL were used to ligate DR5. We demonstrate that DR5 ligation by either TRAIL or TRA-8 induces two functional outcomes, apoptosis and expression of the chemokine interleukin-8 (IL-8); the nonspecific caspase inhibitor Boc-D-Fmk blocks both TRAIL-mediated cell death and IL-8 production; the caspase 3-specific inhibitor z-DEVD-Fmk suppresses TRAIL-mediated apoptosis but not IL-8 induction; caspase 1- and 8-specific inhibitors block both TRAIL-mediated cell death and IL-8 production; and DR5 ligation by TRAIL mediates AP-1 and NF-kappaB activation, which can be inhibited by caspase 1- and 8-specific inhibitors. These findings collectively indicate that DR5 ligation on human glioma cells leads to apoptosis and that the activation of AP-1 and NF-kappaB leads to the induction of IL-8 expression; these responses are dependent on caspase activation. Therefore, the TRAIL-DR5 system has a role not only as an inducer of apoptotic cell death but also as a transducer for proinflammatory and angiogenic signals in human brain tumors.

Fas engagement increases expression of interleukin-6 in human glioma cells

Although Fas (APO-1/CD95) is expressed ubiquitously and induces cell death, it is also known to mediate other responses such as inflammation and angiogenesis in vivo. Previously, we have reported that Fas ligation induces selective expression of chemokines (IL-8 and MCP-1) in human astroglioma cells in vitro. In this study, we investigated whether Fas ligation can induce expression of other cytokines. Expression of IL-1alpha, IL-1beta, IL-6, IL-10, IL-12, IFN-beta, IFN-gamma, LT-beta, TGF-beta, TNF-a and TNF-beta mRNA levels in CRT-MG human astroglioma cells upon Fas ligation was investigated using RNase protection assay (RPA). We found that IL-6 mRNA is selectively induced upon Fas ligation, and IL-6 mRNA and protein expression was further investigated using single probe RPA and ELISA. To investigate the in vivo expression of IL-6, human brain specimens were homogenized and ELISA was performed for IL-6 expression. Herein, we demonstrate that: (1) Among these cytokines, only IL-6 was induced upon Fas ligation in a dose- and time-dependent manner; (2) A selective p38 MAP kinase inhibitor, SB202190, and a MEK inhibitor, U0126, suppressed induction of IL-6 mRNA and protein expression by Fas ligation; and (3) Glioblastoma multiforme samples (n = 11) contain significantly higher levels of IL-6 compared to those of control brains (n = 5), which correlate with increased levels of Fas. These results suggest that the Fas-FasL system may play a role in the regulation of tumor growth and survival by inducing the pleiotropic cytokine IL-6.