Requirements for measles virus induction of RANTES chemokine in human astrocytoma-derived U373 cells

Critical role of TLR activation in viral replication, persistence, and pathogenicity of Theiler's virus

Theiler's murine encephalomyelitis virus (TMEV) establishes persistent viral infections in the central nervous system and induces chronic inflammatory demyelinating disease in susceptible mice. TMEV infects dendritic cells, macrophages, B cells, and glial cells. The state of TLR activation in the host plays a critical role in initial viral replication and persistence. The further activation of TLRs enhances viral replication and persistence, leading to the pathogenicity of TMEV-induced demyelinating disease. Various cytokines are produced via TLRs, and MDA-5 signals linked with NF-κB activation following TMEV infection. In turn, these signals further amplify TMEV replication and the persistence of virus-infected cells. The signals further elevate cytokine production, promoting the development of Th17 responses and preventing cellular apoptosis, which enables viral persistence. Excessive levels of cytokines, particularly IL-6 and IL-1β, facilitate the generation of pathogenic Th17 immune responses to viral antigens and autoantigens, leading to TMEV-induced demyelinating disease. These cytokines, together with TLR2 may prematurely generate functionally deficient CD25-FoxP3+ CD4⁺ T cells, which are subsequently converted to Th17 cells. Furthermore, IL-6 and IL-17 synergistically inhibit the apoptosis of virus-infected cells and the cytolytic function of CD8+ T lymphocytes, prolonging the survival of virus-infected cells. The inhibition of apoptosis leads to the persistent activation of NF-κB and TLRs, which continuously provides an environment of excessive cytokines and consequently promotes autoimmune responses. Persistent or repeated infections of other viruses such as COVID-19 may result in similar continuous TLR activation and cytokine production, leading to autoimmune diseases.

Downregulation of mitochondrial biogenesis by virus infection triggers antiviral responses by cyclic GMP-AMP synthase

In general, in mammalian cells, cytosolic DNA viruses are sensed by cyclic GMP-AMP synthase (cGAS), and RNA viruses are recognized by retinoic acid-inducible gene I (RIG-I)-like receptors, triggering a series of downstream innate antiviral signaling steps in the host. We previously reported that measles virus (MeV), which possesses an RNA genome, induces rapid antiviral responses, followed by comprehensive downregulation of host gene expression in epithelial cells. Interestingly, gene ontology analysis indicated that genes encoding mitochondrial proteins are enriched among the list of downregulated genes. To evaluate mitochondrial stress after MeV infection, we first observed the mitochondrial morphology of infected cells and found that significantly elongated mitochondrial networks with a hyperfused phenotype were formed. In addition, an increased amount of mitochondrial DNA (mtDNA) in the cytosol was detected during progression of infection. Based on these results, we show that cytosolic mtDNA released from hyperfused mitochondria during MeV infection is captured by cGAS and causes consequent priming of the DNA sensing pathway in addition to canonical RNA sensing. We also ascertained the contribution of cGAS to the in vivo pathogenicity of MeV. In addition, we found that other viruses that induce downregulation of mitochondrial biogenesis as seen for MeV cause similar mitochondrial hyperfusion and cytosolic mtDNA-priming antiviral responses. These findings indicate that the mtDNA-activated cGAS pathway is critical for full innate control of certain viruses, including RNA viruses that cause mitochondrial stress.

Viruses exert their pathogenicity by targeting various cellular components in infected cells. In response, host cells have evolved strategies to sense intracellular pathogen-associated molecules, such as nucleic acids derived from infected virus, and trigger subsequent antiviral responses to counteract infection. Measles virus (MeV), the causative agent of human measles, is the most highly contagious virus, killing 300 children per day worldwide; thus MeV has been targeted for eradication by the World Health Organization. In the present study, we found that MeV causes downregulation of mitochondrial biogenesis accompanied with aberrant hyperfusion of mitochondria in the infected cells. Furthermore, we show that cytoplasmic release of mitochondrial DNA activates DNA sensor molecule, cGAS, in addition to the innate immune response induced by the viral component. Importantly, this phenomenon was also observed for viruses, both RNA and DNA, which target mitochondrial biogenesis. Our study provides new insights into the mitochondrial stress by virus infection and an important host defense system to suppress viral propagation.

Excessive Innate Immunity Steers Pathogenic Adaptive Immunity in the Development of Theiler's Virus-Induced Demyelinating Disease

Several virus-induced models were used to study the underlying mechanisms of multiple sclerosis (MS). The infection of susceptible mice with Theiler’s murine encephalomyelitis virus (TMEV) establishes persistent viral infections and induces chronic inflammatory demyelinating disease. In this review, the innate and adaptive immune responses to TMEV are discussed to better understand the pathogenic mechanisms of viral infections. Professional (dendritic cells (DCs), macrophages, and B cells) and non-professional (microglia, astrocytes, and oligodendrocytes) antigen-presenting cells (APCs) are the major cell populations permissive to viral infection and involved in cytokine production. The levels of viral loads and cytokine production in the APCs correspond to the degrees of susceptibility of the mice to the TMEV-induced demyelinating diseases. TMEV infection leads to the activation of cytokine production via TLRs and MDA-5 coupled with NF-κB activation, which is required for TMEV replication. These activation signals further amplify the cytokine production and viral loads, promote the differentiation of pathogenic Th17 responses, and prevent cellular apoptosis, enabling viral persistence. Among the many chemokines and cytokines induced after viral infection, IFN α/β plays an essential role in the downstream expression of costimulatory molecules in APCs. The excessive levels of cytokine production after viral infection facilitate the pathogenesis of TMEV-induced demyelinating disease. In particular, IL-6 and IL-1β play critical roles in the development of pathogenic Th17 responses to viral antigens and autoantigens. These cytokines, together with TLR2, may preferentially generate deficient FoxP3⁺CD25^- regulatory cells converting to Th17. These cytokines also inhibit the apoptosis of TMEV-infected cells and cytolytic function of CD8⁺ T lymphocytes (CTLs) and prolong the survival of B cells reactive to viral and self-antigens, which preferentially stimulate Th17 responses.

Measles Virus Infection Inactivates Cellular Protein Phosphatase 5 with Consequent Suppression of Sp1 and c-Myc Activities

Measles virus (MeV) causes several unique syndromes, including transient immunosuppression. To clarify the cellular responses to MeV infection, we previously analyzed a MeV-infected epithelial cell line and a lymphoid cell line by microarray and showed that the expression of numerous genes was up- or downregulated in the epithelial cells. In particular, there was a characteristic comprehensive downregulation of housekeeping genes during late stage infection. To identify the mechanism underlying this phenomenon, we examined the phosphorylation status of transcription factors and kinase/phosphatase activities in epithelial cells after infection. MeV infection inactivated cellular protein phosphatase 5 (PP5) that consequently inactivated DNA-dependent protein kinase, which reduced Sp1 phosphorylation levels, and c-Myc degradation, both of which downregulated the expression of many housekeeping genes. In addition, intracellular accumulation of viral nucleocapsid inactivated PP5 and subsequent downstream responses. These findings demonstrate a novel strategy of MeV during infection, which causes the collapse of host cellular functions.

IMPORTANCE

Measles virus (MeV) is one of the most important pathogens in humans. We previously showed that MeV infection induces the comprehensive downregulation of housekeeping genes in epithelial cells. By examining this phenomenon, we clarified the molecular mechanism underlying the constitutive expression of housekeeping genes in cells, which is maintained by cellular protein phosphatase 5 (PP5) and DNA-dependent protein kinase. We also demonstrated that MeV targets PP5 for downregulation in epithelial cells. This is the first report to show how MeV infection triggers a reduction in overall cellular functions of infected host cells. Our findings will help uncover unique pathogenicities caused by MeV.

Phosphorylation of measles virus nucleoprotein affects viral growth by changing gene expression and genomic RNA stability

The measles virus (MV) nucleoprotein associates with the viral RNA genome to form the N-RNA complex, providing a template for viral RNA synthesis. In our previous study, major phosphorylation sites of the nucleoprotein were identified as S479 and S510. However, the functions of these phosphorylation sites have not been clarified. In this study, we rescued recombinant MVs (rMVs) whose phosphorylation sites in the nucleoprotein were substituted (rMV-S479A, rMV-S510A, and rMV-S479A/S510A) by reverse genetics and used them in subsequent analyses. In a one-step growth experiment, rMVs showed rapid growth kinetics compared with wild-type MV, although the peak titer of the wild-type MV was the same as or slightly higher than those of the rMVs. Time course analysis of nucleoprotein accumulation also revealed that viral gene expression of rMV was enhanced during the early phase of infection. These findings suggest that nucleoprotein phosphorylation has an important role in controlling viral growth rate through the regulation of viral gene expression. Conversely, multistep growth curves revealed that nucleoprotein-phosphorylation intensity inversely correlated with viral titer at the plateau phase. Additionally, the phosphorylation intensity of the wild-type nucleoprotein in infected cells was significantly reduced through nucleoprotein-phosphoprotein binding. Excessive nucleoprotein-phosphorylation resulted in lower stability against RNase and faster turnover of viral genomic RNA. These results suggest that nucleoprotein-phosphorylation is also involved in viral genomic RNA stability.

CD46 plasticity and its inflammatory bias in multiple sclerosis

Known as a link to the adaptive immune system, a complement regulator, a "pathogen magnet" and more recently as an inducer of autophagy, CD46 is the human receptor that refuses to be put in a box. This review summarizes the current roles of CD46 during immune responses and highlights the role of CD46 as both a promoter and attenuator of the immune response. In patients with multiple sclerosis (MS), CD46 responses are overwhelmingly pro-inflammatory with notable defects in cytokine and chemokine production. Understanding the role of CD46 as an inflammatory regulator is a distant goal considering the darkness in which its regulatory mechanisms reside. Further research into the regulation of CD46 expression through its internalization and processing will undoubtedly extend our knowledge of how the balance is tipped in favor of inflammation in MS patients.

Measles virus induces cell-type specific changes in gene expression

Measles virus (MV) causes various responses including the induction of immune responses, transient immunosuppression and establishment of long-lasting immunity. To obtain a comprehensive view of the effects of MV infection on target cells, DNA microarray analyses of two different cell-types were performed. An epithelial (293SLAM; a 293 cell line stably expressing SLAM) and lymphoid (COBL-a) cell line were inoculated with purified wild-type MV. Microarray analyses revealed significant differences in the regulation of cellular gene expression between these two different cells. In 293SLAM cells, upregulation of genes involved in the antiviral response was rapidly induced; in the later stages of infection, this was followed by regulation of many genes across a broad range of functional categories. On the other hand, in COBL-a cells, only a limited set of gene expression profiles was modulated after MV infection. Since it was reported that V protein of MV inhibited the IFN signaling pathway, we performed a microarray analysis using V knockout MV to evaluate V protein's effect on cellular gene expression. The V knockout MV displayed a similar profile to that of parental MV. In particular, in COBL-a cells infected with the virus, no alteration of cellular gene expression, including IFN signaling, was observed. Furthermore, IFN signaling analyzed in vitro was completely suppressed by MV infection in the COBL-a cells. These results reveal that MV induces different cellular responses in a cell-type specific manner. Microarray analyses will provide us useful information about potential mechanisms of MV pathogenesis.

Stem cells tropism for malignant gliomas

Various studies have demonstrated the tremendous tropism of stem cells for malignant gliomas, making these cells a potential vehicle for delivery of therapeutic genes to disseminated glioma cells. However, little is known about the mechanisms underlying the glioma-induced tropism of stem cells. Soluble factors including chemokines or growth factors released and expressed by glioma cells at least mediate the tropism of stem cells for gliomas. Here we review the possible mechanisms of stem cells tropism for malignant gliomas.

Retinoic acid-inducible gene-I mediates RANTES/CCL5 expression in U373MG human astrocytoma cells stimulated with double-stranded RNA

Retinoic acid-inducible gene-I (RIG-I) mediates part of the cell signaling in response to viral infection. Polyinosinic-polycytidilic acid (poly IC) is a synthetic double-stranded RNA (dsRNA) and mimics viral infection when applied to cell cultures. The CC chemokine, RANTES (regulated on activation, normal T-cell expressed and secreted), is a potent attractant for inflammatory cells such as memory T-lymphocytes, monocytes and eosinophils. In the present study, we demonstrated that poly IC enhances the expression of RIG-I in U373MG human astrocytoma cells. The RNA interference of RIG-I resulted in the suppression of the poly IC-induced RANTES expression. Pretreatment of the cells with SB203580, an inhibitor of p38 mitogen-activated protein kinase, and dexamethasone inhibited the poly IC-induced expression of RIG-I. Furthermore, poly IC upregulated RIG-I in normal human astrocytes in culture and the in vivo injection of poly IC into the striatum of the mouse brain induced the expression of RIG-I in astrocytes. We conclude that RIG-I may be involved in immune reactions against viral infection, at least in part, through the regulation of RANTES expression in astrocytes.

Variants of the paramyxovirus Simian virus 5 with accelerated or delayed viral gene expression activate proinflammatory cytokine synthesis

Our previous results have shown that the parainfluenza virus SV5 is a poor inducer of proinflammatory cytokines interleukin-8 (IL-8) and macrophage chemoattractant protein 1 (MCP-1). By contrast, an engineered P/V mutant rSV5-P/V-CPI- and a naturally-occurring variant WF-PIV (Wake Forest-Parainfluenza Virus) are both potent activators of IL-8 and MCP-1. In the present study, we addressed the question of why rSV5-WT is such a poor inducer of host cytokine responses relative to the two SV5 variants, and we used the CC chemokine RANTES as a measure of host responses. Time course experiments showed high-level secretion of IL-6 and RANTES following infections of human A549 lung epithelial cells with the P/V-CPI- mutant and WF-PIV. By contrast, SV5-WT induced very low cytokine responses, with the notable exception of moderate induction of RANTES. The mechanism of RANTES induction by the two SV5 variants shared common properties, since RANTES secretion from infected cells had similar kinetics, depended on virus replication, correlated with increased RANTES mRNA levels and promoter activation, and was reduced by inhibitors of the p38 MAPK, ERK, and PI3K pathways. Despite the similar mechanisms of RANTES induction, the two SV5 variants differed dramatically in their growth and gene expression kinetics. By comparison to the P/V mutant rSV5-P/V-CPI- which has accelerated viral gene expression, WF-PIV infection showed a prolonged delay in viral replication, and infected cells did not show high-level viral RNA and protein expression until approximately 12-24 hpi. Sequence analysis revealed that the N, P, V, and M genes from WF-PIV differed by 3, 8, 5, and 10 amino acids compared to rSV5-WT, respectively. Chimeric viruses harboring the WF-PIV P/V or M genes in the context of the other rSV5 genes had growth properties similar to rSV5-WT but had a RANTES-inducing phenotype similar to that of the bone fide WF-PIV virus. Our data indicate a role for both the P/V and the M gene products as determinants of RANTES induction in response to SV5 infection.

The chemokine GRO-alpha (CXCL1) confers increased tumorigenicity to glioma cells

The chemokine GRO-alpha (CXCL1) has been found to mediate the proliferation of glia progenitor cells during neural development. As malignant gliomas are thought to arise from glia progenitors or their differentiated counterparts, astrocytes or oligodendrocytes, we have investigated whether GRO-alpha regulates the tumor characteristics of glioma cells. We found first that resected glioma specimens were strongly immunoreactive for GRO-alpha expression in cells with the morphology of tumor cells. In culture, the U251 glioma line transfected to overexpress GRO-alpha had elevated levels of motility and invasiveness. GRO-alpha transfectants increased their expression of several proteins associated with migratory behavior, including matrix metalloproteinase-2, beta1-integrin and SPARC. The implantation of GRO-alpha glioma clones into the brain of nude mice caused the early demise of mice and this was associated with the formation of larger intracerebral tumors when compared with mice implanted with vector control lines. These results implicate GRO-alpha in gliomas and suggest that the dysregulation of a glia proliferative factor contributes to tumorigenesis. Targeting GRO-alpha may be a useful therapeutic tool to control brain tumor biology.

Innate immune response induced by Theiler's murine encephalomyelitis virus infection

Although the causative agents of human multiple sclerosis (MS) are not known, it is suspected that a viral infection may be associated with the initiation of the disease. Several viral disease models in mice have been studied to understand the pathogenesis of demeylination. In particular, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) has been extensively studied as a relevant model. Various cytokines and chemokines are produced upon viral infection by different cell types, including antigen-presenting cells (APCs) such as macrophages; dendritic cells (DCs); and glial cells, such as astrocytes, microglia, and oligoden-drocytes. The upregulation of the corresponding molecules are also found in MS and are likely to play an important role in the protection and/or pathogenesis of chronic inflammatory demyelinating disease. In this review, the type of cells and molecules, gene-activation mechanisms as well as their potential roles in protection and pathogenesis will be discussed.

The cytokine IL-1beta activates IFN response factor 3 in human fetal astrocytes in culture

The cytokine IL-1beta is a major activator of primary human fetal astrocytes in culture, leading to the production of a wide range of cytokines and chemokines important in the host defense against pathogens. IL-1beta, like TLR4, signals via the MyD88/IL-1betaR-associated kinase-1 pathway linked to activation of NF-kappaB and AP-1. Recent studies have shown that TLR4 also signals independently of MyD88, resulting in the activation of IFN regulatory factor 3 (IRF3), a transcription factor required for the production of primary antiviral response genes such as IFN-beta. Using a functional genomics approach, we observed that IL-1beta induced in astrocytes a group of genes considered to be IFN-stimulated genes (ISG), suggesting that IL-1beta may also signal via IRF3 in these cells. We now show, using real-time PCR, that in astrocytes IL-1beta induces the expression of IFN-beta, IRF7, CXCL10/IFN-gamma-inducible protein-10, and CCL5/RANTES. Chemokine expression was confirmed by ELISA. We also show that IL-1beta induces phosphorylation and nuclear translocation of IRF3 and delayed phosphorylation of STAT1. The dependency of IFN-beta, IRF7, and CXCL10/IFN-gamma-inducible protein-10 gene expression on IRF3 was confirmed using a dominant negative IRF3-expressing adenovirus. The robust induction by IL-1beta of additional ISG noted on the microarrays, such as STAT1, 2'5'-oligoadenylate synthetase 2, and ISG15, also supports an active signaling role for IL-1beta via this pathway in human fetal astrocytes. These data are the first to show that IL-1beta, in addition to TLRs, can stimulate IRF3, implicating this cytokine as an activator of genes involved in innate antiviral responses in astrocytes.

CD46: A complement regulator and pathogen receptor that mediates links between innate and acquired immune function

In the last 10 years, the human cell-surface molecule, CD46, has evolved from 'just another complement regulator' to a receptor for a striking array of pathogens. CD46 not only protects cells from complement-mediated attack and facilitates infection by a large number of pathogens, but also exerts complex effects on cellular immune function. It has been proposed that CD46 links innate and adaptive immunity by affecting cellular immune function in response to complement binding, and the role of CD46 in the pathogenesis of many infectious pathogens is now the subject of intense investigation. So far, the flood of information that implicates CD46 in modifying a host response to measles, Neisseria, human herpes virus 6, and pathogens that activate complement has not yet been matched with a comprehensive understanding of the molecular mechanisms by which CD46 affects immune function. This review summarizes the evidence that points to a significant role for CD46 in a range of pathological processes and describes how CD46 might exert its effects by altering signal transduction and antigen presentation pathways.

Induction of chemokines in human astrocytes by picornavirus infection requires activation of both AP-1 and NF-kappa B

Infection with different picornaviruses can cause meningitis/encephalitis in humans and experimental animals. To investigate the mechanisms of such inflammatory diseases, potential chemokine gene activation in human astrocytes was investigated following infection with Theiler's murine encephalomyelitis virus (TMEV), coxsackievirus B3 (CVB3), or coxsackievirus B4 (CVB4). We report that all these viruses are potent inducers for the expression of interleukin‐8 (IL‐8) and monocyte chemoattractant protein‐1 (MCP‐1) genes in primary human astrocytes, as well as in an established astrocyte cell line (U‐373MG). Further studies indicated that both activator protein‐1 (AP‐1) and NF‐κB transcription factors are required in the activation of chemokine genes in human astrocytes infected with various picornaviruses. Interestingly, the pattern of activated chemokine genes in human astrocytes is quite restricted compared to that in mouse astrocytes infected with the same viruses, suggesting species differences in gene activation. This may result in potential differences in the pathogenic outcome in each species. © 2003 Wiley‐Liss, Inc.

Measles Virus 1998–2002: Progress and Controversy

Despite the extensive media exposure that viruses such as West Nile, Norwalk, and Ebola have received lately, and the emerging threat that old pathogens may reappear as new agents of terrorism, measles virus (MV) persists as one of the leading causes of death by infectious agents worldwide, approaching the annual mortality rate of human immunodeficiency virus (HIV)-1. For most MV victims, fatality is indirect: Virus-induced transient immunosuppression predisposes the individual to opportunistic infections that, left untreated, can result in mortality. In rare cases, MV may also cause progressive neurodegenerative disease. During the past five years (1998-2002), development of animal models and the application of reverse genetics and immunological assays have collectively contributed to major progress in our understanding of MV biology and pathogenesis. Nevertheless, questions and controversies remain that are the basis for future research. In this review, major advances and current debates are discussed, including MV receptor usage, the cellular basis of immunosuppression, the suspected role of MV in "nonviral" diseases such as multiple sclerosis and Paget's disease, and the controversy surrounding MV vaccine safety.

Innate immunity in th e cornea: a putative role for keratocytes in the chemokine response to viral infection of the human corneal stroma

Existing evidence suggests that chemokine expression by virus-infected cells is a common response to viral infection. By such a mechanism, non-immunologic cells may participate in the generation of an early innate immune response to infection. In the absence of classic immunologic cells in the corneal stroma, keratocytes may play a similar role in the corneal responses to viral infection.

Mumps virus decreases testosterone production and gamma interferon-induced protein 10 secretion by human leydig cells

Mumps virus is responsible for sterility. Here, we show that the mumps virus infects Leydig cells in vitro and totally inhibits testosterone secretion and that ribavirin in mumps virus-infected Leydig cell cultures completely restores testosterone production. Moreover, we show that gamma interferon-induced protein 10 (IP-10) is highly expressed by mumps virus-infected Leydig cells and that ribavirin does not block IP-10 production.

CXCR4 is a major chemokine receptor on glioma cells and mediates their survival

Chemokines were described originally in the context of providing migrational cues for leukocytes. They are now known to have broader activities, including those that favor tumor growth. We addressed whether and which chemokines may be important promoters of the growth of the incurable brain neoplasm, malignant gliomas. Analyses of 16 human glioma lines for the expression of chemokine receptors belonging to the CXCR and CCR series revealed low to negligible levels of all receptors, with the exception of CXCR4 that was expressed by 13 of 16 lines. All six resected human glioma specimens showed similarly high CXCR4 expression. The CXCR4 on glioma lines is a signaling receptor in that its agonist, stromal cell-derived factor-1 (SDF-1; CXCL12), produced rapid phosphorylation of mitogen-activated protein kinases. Furthermore, SDF-1 induced the phosphorylation of Akt (protein kinase B), a kinase associated with survival, and prevented the apoptosis of glioma cells when serum was withdrawn from the culture medium. SDF-1 also mediated glioma chemotaxis, in accordance with this better known role of chemokines. We conclude that glioma cells express a predominant chemokine receptor, CXCR4, and that this functions to regulate survival in part through activating pathways such as Akt.

Gamma-aminobutyric acid transporter (BGT-1) expressed in human astrocytoma U373 MG cells: pharmacological and molecular characterization and phorbol ester-induced inhibition

The properties of a transport system specific for gamma-aminobutyric acid (GABA) expressed in human U373 MG astrocytoma cells were examined. The uptake of [(3)H]GABA was dependent on both extracellular Na(+) and Cl(-) ions and was inhibited by (+/-)-nipecotic acid, guvacine, and beta-alanine, with a pharmacological profile corresponding to that reported for the human homologue of the GABA/betaine transporter (BGT-1). Accordingly, [(3)H]GABA uptake was also inhibited by betaine, and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of total RNA from U373 MG cells with specific BGT-1 primers resulted in the amplification of a 440 bp fragment that was further characterized by restriction analysis and sequencing. In addition, Western blot analysis with anti-BGT-1 antiserum revealed the presence of a characteristic 60 kDa band. The primary structure of the human BGT-1 protein predicts two putative phosphorylation sites for the Ca(2+)/diacylglicerol-dependent protein kinase (PKC), and treatment of U373 MG cells with the PKC activator phorbol 12-myristate-13-acetate (TPA) led to a concentration- and time-dependent decrease in [(3)H]GABA uptake. The maximal effect was detected at 2 hr of incubation, to disappear after 4 hr. TPA-induced reduction in [(3)H]GABA uptake was reversed by preincubation with staurosporine. Taken together, these results indicate that U373 MG cells express a GABA transporter of the BGT-1 subtype whose function is regulated by phosphorylation events through PKC.

Activity of polymerase proteins of vaccine and wild-type measles virus strains in a minigenome replication assay

The relative activities of five measles virus (MV) polymerase (L) proteins were compared in an intracellular, plasmid-based replication assay. When coexpressed with N and P proteins from an attenuated strain, L proteins from two attenuated viruses directed the production of up to eight times more reporter protein from an MV minigenome than the three wild-type L proteins. Northern blot analysis demonstrated that the differences in reporter protein production correlated with mRNA transcription levels. Increased activity of polymerases from attenuated viruses equally affected mRNA transcription and minigenome replication. The higher level of transcription may be a consequence of increased template availability or may be an independent effect of the elevated activity of the attenuated polymerases. Coexpression of wild-type L proteins with homologous N and P proteins did not affect the activity of the wild-type polymerases, indicating that the differential activity was a function of the L proteins alone. Use of a minigenome that incorporated two nucleotide changes found in the genomic leader of the three wild-type viruses did not raise the activity of the wild-type L proteins. These data demonstrate that increased polymerase activity differentiates attenuated from wild-type viruses and suggest that functions involved in RNA synthesis contribute to the attenuated phenotype of MV vaccine strains.

The interferon antiviral response: from viral invasion to evasion

One of the initial responses of an organism to infection by pathogenic viruses is the synthesis of antiviral cytokines such as the type I interferons (interferon-alpha/beta), interleukins, and other proinflammatory cytokines and chemokines. Interferons provide a first line of defence against virus infections by generating an intracellular environment that restricts virus replication and signals the presence of a viral pathogen to the adaptive arm of the immune response. Interferons stimulate cells in the local environment to activate a network of interferon-stimulated genes, which encode proteins that have antiviral, antiproliferative and immunomodulatory activities. The present review focuses on recent reports that describe the activation of multiple signalling pathways following virus infection, new candidate genes that are implicated in the establishment of the antiviral state, and the strategies used by viruses and their specific viral products to antagonize and evade the host antiviral response.

Recognition of the measles virus nucleocapsid as a mechanism of IRF-3 activation

The mechanisms of cellular recognition for virus infection remain poorly understood despite the wealth of information regarding the signaling events and transcriptional responses that ensue. Host cells respond to viral infection through the activation of multiple signaling cascades, including the activation of NF-kappaB, c-Jun/ATF-2 (AP-1), and the interferon regulatory factors (IRFs). Although viral products such as double-stranded RNA (dsRNA) and the processes of viral binding and fusion have been implicated in the activation of NF-kappaB and AP-1, the mechanism(s) of IRF-1, IRF-3, and IRF-7 activation has yet to be fully elucidated. Using recombinant measles virus (MeV) constructs, we now demonstrate that phosphorylation-dependent IRF-3 activation represents a novel cellular detection system that recognizes the MeV nucleocapsid structure. At low multiplicities of infection, IRF-3 activation is dependent on viral transcription, since UV cross-linking and a deficient MeV containing a truncated polymerase L gene failed to induce IRF-3 phosphorylation. Expression of the MeV nucleocapsid (N) protein, without the requirement for any additional viral proteins or the generation of dsRNA, was sufficient for IRF-3 activation. In addition, the nucleocapsid protein was found to associate with both IRF-3 and the IRF-3 virus-activated kinase, suggesting that it may aid in the colocalization of the kinase and the substrate. Altogether, this study suggests that IRF-3 recognizes nucleocapsid structures during the course of an MeV infection and triggers the induction of interferon production.

Post-genomic virology: the impact of bioinformatics, microarrays and proteomics on investigating host and pathogen interactions

Post-genomic research encompasses many diverse aspects of modern science. These include the two broad subject areas of computational biology (bioinformatics) and functional genomics. Laboratory based functional genomics aims to measure and assess either the messenger RNA (mRNA) levels (transcriptome studies) or the protein content (proteome studies) of cells and tissues. All of these methods have been applied recently to the study of host and pathogen interactions for both bacteria and viruses. A basic overview of the technology is given in this review together with approaches to data analysis. The wealth of information produced from even these preliminary studies has shown the generalities, subtleties and specificities of host-pathogen interactions. Such research should ultimately result in new methods for diagnosing and treating infectious diseases.

Induction of selected chemokines in glial cells infected with Theiler's virus

To elucidate the early events in Theiler's virus-induced demyelination, a model for human multiple sclerosis (MS), chemokine gene activation in the central nervous system (CNS) resident cells upon viral infection was investigated. Viral infection selectively upregulated RANTES and IP-10 gene expression in primary astrocyte cultures and broader chemokine genes in oligodendrocyte and microglia cultures. Both RANTES and IP-10 were stimulated by proinflammatory cytokine interferon-gamma (IFNgamma), but only RANTES by tumor necrosis factor alpha (TNFalpha), suggesting that virus infection induces chemokines overlapping with those inducible by proinflammatory cytokines. These results suggest that glial cells, astrocytes in particular, may be critical for early recruitment of inflammatory cells in the initiation of virus-induced, immune-mediated demyelination.

Glatiramer acetate inhibition of tumor necrosis factor-alpha-induced RANTES expression and release from U-251 MG human astrocytic cells

Glatiramer acetate is an approved drug for the treatment of multiple sclerosis (MS). RANTES is a beta-family chemokine that manifests chemoattractant activity for T lymphocytes and monocytes/macrophages implicated in the pathogenesis of MS lesions. However, the effect of glatiramer acetate on the regulation of RANTES secretion in glial cells is unknown. In the present study, we demonstrate for the first time that treatment of human U-251 MG astrocytic cells with glatiramer acetate blocks tumor necrosis factor-alpha (TNF-alpha)-induced RANTES mRNA and protein in a dose- and time-dependent manner. This effect is attributed to inhibition of transcription and a 40% decrease in transcript stability. Furthermore, our electrophoretic mobility shift assays of nuclear extracts from TNF-alpha-treated cells reveal an increase in DNA-binding activity specific for the nuclear factor-kappa B (NF-kappaB) binding site, in the 5'-flanking promoter region of the human RANTES gene, and that this increase in NF-kappaB binding activity is prevented by pretreatment with glatiramer acetate or the NF-kappaB inhibitors. These findings suggest that glatiramer acetate may exert its therapeutic effect in MS partially through inhibiting NF-kappaB activation and chemokine production.

Glatiramer acetate blocks interleukin-1-dependent nuclear factor-kappaB activation and RANTES expression in human U-251 MG astroglial cells

RANTES is a basic 8-kDa polypeptide of the C-C chemokine subfamily with strong chemoattractant activity for T lymphocytes and monocytes/macrophages that are implicated in the pathogenesis of multiple sclerosis (MS) lesions. Glatiramer acetate is a drug recently approved for the treatment of MS. We therefore investigated the effect of glatiramer acetate on RANTES expression in glial cells in vitro. Treatment of human U-251 MG astroglial cells with glatiramer acetate blocks IL-1beta-induced RANTES chemokine production in a dose- and time-dependent manner. Glatiramer acetate also decreased steady-state levels of RANTES mRNA in these cells, which was attributable to reduced transcription, as assessed by nuclear run-on assays. In addition, we showed that NF-kappaB may be the transcriptional activator responsible for the IL-1beta-mediated RANTES gene expression in this system. Our data indicated that the IL-1beta-induced increase in RANTES was associated with an increase in in vitro nuclear extract binding activity specific for the NF-kappaB site in the promoter region of the RANTES gene. The increases in RANTES mRNA and protein expression were suppressed by the NF-kappaB inhibitors gliotoxin, isohelenin, and pyrrolidine dithiocarbamate (PDTC). Furthermore, we demonstrated that the increase in NF-kappaB DNA-binding activity was prevented by pretreatment with glatiramer acetate or the NF-kappaB inhibitors. Our results suggest that glatiramer acetate may inhibit IL-1beta-stimulated RANTES expression in human glial cells by blocking NF-kappaB activation, thus identifying part of the molecular basis for its anti-inflammatory and immunosuppressive effects in demyelinating diseases.

Th1 cytokines stimulate RANTES chemokine secretion by human astroglial cells depending on de novo transcription

Beta-chemokines induce the directional migration of monocytes and T lymphocytes that are implicated in the pathogenesis of multiple sclerosis (MS) lesions. RANTES is a member of the beta-chemokine family that has been detected in the lesions of MS patients. However, the cellular sources of RANTES message and the molecular basis for the regulation of its production in MS lesions are not well understood. Glial cells may be a major source of RANTES in vivo and have been shown to produce RANTES in vitro. Thus, the objective of this study was to establish a model system for studying the regulation of RANTES expression by cytokines in cultured human glial cells, and to determine the mechanism involved in the process. We show that the Th1 cytokines TNF-alpha and IL-1beta independently induce RANTES mRNA and chemokine levels in human U-251 MG astroglial cells, and that these effects are time- and concentration-dependent. In addition, we demonstrate that both cytokines increased the rate of transcription of the RANTES gene, as estimated by in vitro nuclear transcript elongation assays. The transcriptional activity in TNF-alpha-treated U-251 MG cells started to increase at 2 h and peaked at 8 h, with levels more than 14 times greater than controls. We further show that NF-kappaB may play a critical role in the up-regulation of human RANTES gene expression in this system. Gel shift assays revealed an induction of in vitro nuclear extract binding activity to the NF-kappaB element of RANTES in cells incubated with the Th1 cytokines. These observations suggest that human astroglia, within diseased brain, may be stimulated to produce RANTES chemokine in response to TNF-alpha and IL-1beta, and that this effect of the Th1 cytokines is attributed to increase of transcription.

Herpes simplex virus triggers and then disarms a host antiviral response

Virus infection induces an antiviral response that is predominantly associated with the synthesis and secretion of soluble interferon. Here, we report that herpes simplex virus type 1 virions induce an interferon-independent antiviral state in human embryonic lung cells that prevents plaquing of a variety of viruses. Microarray analysis of 19,000 human expressed sequence tags revealed induction of a limited set of host genes, the majority of which are also induced by interferon. Genes implicated in controlling the intracellular spread of virus and eliminating virally infected cells were among those induced. Induction of the cellular response occurred in the absence of de novo cellular protein synthesis and required viral penetration. In addition, this response was only seen when viral gene expression was inhibited, suggesting that a newly synthesized viral protein(s) may function as an inhibitor of this response.

Involvement of oxidative stress, NF-IL-6, and RANTES expression in dengue-2-virus-infected human liver cells

The liver has been suspected to be one of the major targets of dengue virus infection. Here, we detected increasing secretion of the chemokine RANTES (regulated upon activation, normal T cell expressed and secreted), which functions to recruit the immune cells, in dengue-virus-infected liver cells and patients. Three luciferase reporter genes with various deletions at the 5'-end of the RANTES promoter were constructed to explore the RANTES activation mechanism in human liver cells. The reporter gene was optimally activated by dengue-2 virus when the RANTES promoter contains the region from the transcription starting site (+1) to the nucleotide at the -181 position. NF-IL-6 and an undefined factor forming DNA-protein complexes in the RANTES promoter E and A/B regions in the infected cells were demonstrated by electrophoretic mobility shift assay. Further analysis showed that oxidative stress was an upstream inducer of NF-IL-6 and RANTES signaling in dengue-virus-infected liver cells. This finding was demonstrated by three antioxidants (N-acetyl-l-cysteine, nitro-l-arginine methyl ester, and pyrrolidine dithiocarbamate) used to suppress the activation. In contrast, the DNA binding activity of the undefined factor was not affected by the antioxidant treatment, indicating the existence of an oxidant-independent pathway. We hypothesize that dengue virus infection of the liver cells may trigger both an oxidant-dependent and an oxidant-independent pathway to up-regulate RANTES mRNA expression through activating NF-IL-6 and an undefined factor, respectively. In conclusion, the present study suggests a new direction for the study of liver pathogenesis involving RANTES in host immune responses during dengue virus infection.

Regulation of RANTES chemokine gene expression requires cooperativity between NF-kappa B and IFN-regulatory factor transcription factors

Virus infection of host cells activates a set of cellular genes, including cytokines, IFNs, and chemokines, involved in antiviral defense and immune activation. Previous studies demonstrated that virus-induced transcriptional activation of a member of the human CC-chemokine RANTES required activation of the latent transcription factors IFN-regulatory factor (IRF)-3 and NF-kappa B via posttranslational phosphorylation. In the present study, we further characterized the regulatory control of RANTES transcription during virus infection using in vivo genomic footprinting analyses. IRF-3, the related IRF-7, and NF-kappa B are identified as important in vivo binding factors required for the cooperative induction of RANTES transcription after virus infection. Using fibroblastic or myeloid cells, we demonstrate that the kinetics and strength of RANTES virus-induced transcription are highly dependent on the preexistence of IRFs and NF-kappa B. Use of dominant negative mutants of either I kappa B-alpha or IRF-3 demonstrate that disruption of either pathway dramatically abolishes the ability of the other to bind and activate RANTES expression. Furthermore, coexpression of IRF-3, IRF-7, and p65/p50 leads to synergistic activation of RANTES promoter transcription. These studies reveal a model of virus-mediated RANTES promoter activation that involves cooperative synergism between IRF-3/IRF-7 and NF-kappa B factors.