Inhibition of vesicular stomatitis virus infection in epithelial cells by alpha interferon-induced soluble secreted proteins

RIG-I-mediated innate immune signaling in tumors reduces the therapeutic effect of oncolytic vesicular stomatitis virus

BACKGROUND

Oncolytic viral therapy is a promising method for tumor treatment. Currently, several oncolytic viruses (OVs) have been used as tumor therapy at different phases of research and clinical trials. OVs not only directly lyse tumor cells due to viral replication but also initiate host antitumor immune responses. Previous studies have primarily focused on how OVs activate adaptive immune responses in immune cells. However, the role of innate immune responses in tumors induced by OVs remains unclear.

METHODS

To determine the innate immune responses induced by vesicular stomatitis virus (VSV), the mutant VSV^ΔM51 strain was used for the infection and quantitative polymerase chain reaction (qPCR) was employed to measure the transcriptional levels of antiviral genes. The knockdown efficiency of RIG-I was examined by qPCR. Viral titers were measured by plaque assays. Tumor models were established by intradermally implanting RIG-I-knockdown and control LLC cells into the flank of wild type C57BL/6J mice. When the tumors reached approximately 50mm³ , they were infected with VSV^ΔM51 via intratumoral injections to examine its therapeutic effect.

RESULTS

Infection with VSV^ΔM51 triggered remarkable innate immune responses in several tumor cell lines through the cytoplasmic RIG-I sensing pathway. Moreover, we found that intratumoral injection of VSV^ΔM51 effectively reduced tumor growth in murine LCC lung cancer model. Importantly, VSV^ΔM51 -induced antitumor therapy was more effective in murine LLC tumor model established using Rig-I-knockdown cells compared with the tumor model established using control cells.

CONCLUSION

RIG-I-mediated innate immune signaling in tumor cells plays a negative role in regulating antitumor therapy with VSV^ΔM51 virus.

Fever-range hyperthermia promotes cGAS-STING pathway and synergizes DMXAA-induced antiviral immunity

Background: Fever-range hyperthermia or fever-range temperature (hereafter FRT) improves survival and shortens disease duration in microbial infections. However, the mechanisms of these beneficial effects still remain elusive. We hypothesized that FRT might enhance cell responsiveness to infections by promoting cGAS-STING signaling to cause enhanced production of IFN-β. Objective: To investigate the effect fever-range hyperthermia on cGAS-STING pathway. Methods: RAW 264.7 and cGAS^-/- RAW 264.7 cells, stimulated with 5μg/ml herring testis DNA (htDNA), were heated to 39.5°C and analyzed for the expression of cGAS, STING, IFN-β, and the synthesis of cGAMP and IRF3 phosphorylation. In vivo, wild type C57BL/6J mice were subjected to whole body hyperthermia (WBH) at 39.5°C. The mice were then challenged with influenza virus and analyzed for antiviral response in term of IFN-β expression, body weight and survival. Results: We found that 39.5°C FRT upregulated the expression of cGAS and STING, and induced the synthesis of cGAMP and production of IFN-β in htDNA-transfected RAW 264.7 cells more potently as compared to 37°C. Moreover, FRT+DMXAA-treated cells were better protected from vesicular stomatitis virus (VSV)-induced cytotoxicity in vitro in contrast to the nonprotected control (no FRT and DMXAA) or DMXAA treatment alone. In vivo, FRT at 39.5°C, co-administered with DMXAA, significantly induced the expression of IFN-β, showed reduced weight loss mice and exhibited 25% more survival over the course of 14 days as compared to DMXAA treated mice 37°C. Conclusion: We conclude that fever-range hyperthermia promotes cGAS-STING pathway to cause increased expression of IFN-β and mediate its antiviral effects.

DDX6 Represses Aberrant Activation of Interferon-Stimulated Genes

The innate immune system tightly regulates activation of interferon-stimulated genes (ISGs) to avoid inappropriate expression. Pathological ISG activation resulting from aberrant nucleic acid metabolism has been implicated in autoimmune disease; however, the mechanisms governing ISG suppression are unknown. Through a genome-wide genetic screen, we identified DEAD-box helicase 6 (DDX6) as a suppressor of ISGs. Genetic ablation of DDX6 induced global upregulation of ISGs and other immune genes. ISG upregulation proved cell intrinsic, imposing an antiviral state and making cells refractory to divergent families of RNA viruses. Epistatic analysis revealed that ISG activation could not be overcome by deletion of canonical RNA sensors. However, DDX6 deficiency was suppressed by disrupting LSM1, a core component of mRNA degradation machinery, suggesting that dysregulation of RNA processing underlies ISG activation in the DDX6 mutant. DDX6 is distinct among DExD/H helicases that regulate the antiviral response in its singular ability to negatively regulate immunity.

The nucleocapsid proteins of mouse hepatitis virus and severe acute respiratory syndrome coronavirus share the same IFN-β antagonizing mechanism: attenuation of PACT-mediated RIG-I/ MDA5 activation

Coronaviruses (CoVs) are a huge threat to both humans and animals and have evolved elaborate mechanisms to antagonize interferons (IFNs). Nucleocapsid (N) protein is the most abundant viral protein in CoV-infected cells, and has been identified as an innate immunity antagonist in several CoVs, including mouse hepatitis virus (MHV) and severe acute respiratory syndrome (SARS)-CoV. However, the underlying molecular mechanism(s) remain unclear. In this study, we found that MHV N protein inhibited Sendai virus and poly(I:C)-induced IFN-β production by targeting a molecule upstream of retinoic acid-induced gene I (RIG-I) and melanoma differentiation gene 5 (MDA5). Further studies showed that both MHV and SARS-CoV N proteins directly interacted with protein activator of protein kinase R (PACT), a cellular dsRNA-binding protein that can bind to RIG-I and MDA5 to activate IFN production. The N–PACT interaction sequestered the association of PACT and RIG-I/MDA5, which in turn inhibited IFN-β production. However, the N proteins from porcine epidemic diarrhea virus (PEDV) and porcine reproductive and respiratory syndrome virus (PRRSV), which are also classified in the order Nidovirales, did not interact and counteract with PACT. Taken together, our present study confirms that both MHV and SARS-CoV N proteins can perturb the function of cellular PACT to circumvent the innate antiviral response. However, this strategy does not appear to be used by all CoVs N proteins.

Comparative proteomics as a tool for identifying specific alterations within interferon response pathways in human glioblastoma multiforme cells

An acquisition of increased sensitivity of cancer cells to viruses is a common outcome of malignant progression that justifies the development of oncolytic viruses as anticancer therapeutics. Studying molecular changes that underlie the sensitivity to viruses would help to identify cases where oncolytic virus therapy would be most effective. We quantified changes in protein abundances in two glioblastoma multiforme (GBM) cell lines that differ in the ability to induce resistance to vesicular stomatitis virus (VSV) infection in response to type I interferon (IFN) treatment. In IFN-treated samples we observed an up-regulation of protein products of some IFN-regulated genes (IRGs). In total, the proteome analysis revealed up to 20% more proteins encoded by IRGs in the glioblastoma cell line, which develops resistance to VSV infection after pre-treatment with IFN. In both cell lines protein-protein interaction and signaling pathway analyses have revealed a significant stimulation of processes related to type I IFN signaling and defense responses to viruses. However, we observed a deficiency in STAT2 protein in the VSV-sensitive cell line that suggests a de-regulation of the JAK/STAT/IRF9 signaling. The study has shown that the up-regulation of IRG proteins induced by the IFNα treatment of GBM cells can be detected at the proteome level. Similar analyses could be applied for revealing functional alterations within the antiviral mechanisms in glioblastoma samples, accompanying by acquisition of sensitivity to oncolytic viruses. The approach can be useful for discovering the biomarkers that predict a potential sensitivity of individual glioblastoma tumors to oncolytic virus therapy.

Methadone enhances human influenza A virus replication

Growing evidence has indicated that opioids enhance replication of human immunodeficiency virus and hepatitis C virus in target cells. However, it is unknown whether opioids can enhance replication of other clinically important viral pathogens. In this study, the interaction of opioid agonists and human influenza A/WSN/33 (H1N1) virus was examined in human lung epithelial A549 cells. Cells were exposed to morphine, methadone or buprenorphine followed by human H1N1 viral infection. Exposure to methadone differentially enhanced viral propagation, consistent with an increase in virus adsorption, susceptibility to virus infection and viral protein synthesis. In contrast, morphine or buprenorphine did not alter H1N1 replication. Because A549 cells do not express opioid receptors, methadone-enhanced H1N1 replication in human lung cells may not be mediated through these receptors. The interaction of methadone and H1N1 virus was also examined in adult mice. Treatment with methadone significantly increased H1N1 viral replication in lungs. Our data suggest that use of methadone facilitates influenza A viral infection in lungs and might raise concerns regarding the possible consequence of an increased risk of serious influenza A virus infection in people who receive treatment in methadone maintenance programs.

Response of Three Different Viruses to Interferon Priming and Dithiothreitol Treatment of Avian Cells

We have previously shown that the replication of avian reovirus (ARV) in chicken cells is much more resistant to interferon (IFN) than the replication of vesicular stomatitis virus (VSV) or vaccinia virus (VV). In this study, we have investigated the role that the double-stranded RNA (dsRNA)-activated protein kinase (PKR) plays in the sensitivity of these three viruses toward the antiviral action of chicken interferon. Our data suggest that while interferon priming of avian cells blocks vaccinia virus replication by promoting PKR activation, the replication of vesicular stomatitis virus appears to be blocked at a pretranslational step. Our data further suggest that the replication of avian reovirus in chicken cells is quite resistant to interferon priming because this virus uses strategies to downregulate PKR activation and also because translation of avian reovirus mRNAs is more resistant to phosphorylation of the alpha subunit of initiation factor eIF2 than translation of their cellular counterparts. Our results further reveal that the avian reovirus protein sigmaA is able to prevent PKR activation and that this function is dependent on its double-stranded RNA-binding activity. Finally, this study demonstrates that vaccinia virus and avian reovirus, but not vesicular stomatitis virus, express/induce factors that counteract the ability of dithiothreitol to promote eIF2 phosphorylation. Our data demonstrate that each of the three different viruses used in this study elicits distinct responses to interferon and to dithiothreitol-induced eIF2 phosphorylation when infecting avian cells.

IMPORTANCE

Type I interferons constitute the first barrier of defense against viral infections, and one of the best characterized antiviral strategies is mediated by the double-stranded RNA-activated protein kinase R (PKR). The results of this study revealed that IFN priming of avian cells has little effect on avian reovirus (ARV) replication but drastically diminishes the replication of vaccinia virus (VV) and vesicular stomatitis virus (VSV) by PKR-dependent and -independent mechanisms, respectively. Our data also demonstrate that the dsRNA-binding ability of ARV protein sigmaA plays a key role in the resistance of ARV toward IFN by preventing PKR activation. Our findings will contribute to improve the current understanding of the interaction of viruses with the host's innate immune system. Finally, it would be of interest to uncover the mechanisms that allow avian reovirus transcripts to be efficiently translated under conditions (moderate eIF2 phosphorylation) that block the synthesis of cellular proteins.

The neuropathogenic T953 strain of equine herpesvirus-1 inhibits type-I IFN mediated antiviral activity in equine endothelial cells

Equine herpesvirus-1 (EHV-1) infects equine endothelial cells (EECs) lining the small blood vessels in the central nervous system. However, the effect of type I IFN on EHV-1 replication in the EECs is not well studied. Thus, the primary objective of this study was to investigate the effect of type-I IFN on the replication of the neuropathogenic T953 strain of EHV-1 in vitro in EECs. The initial data showed that the EHV-1 was partly resistant to the biological effect of exogenously supplied recombinant equine IFN-α. Subsequent investigation into the mechanism of resistance showed that EHV-1 infection of EECs interfered with the STAT-1 phosphorylation through which type-I IFN exerts its antiviral effect. Immunofluorescence staining showed interference with the translocation of STAT-1 molecules from cytoplasm to nucleus confirming the virus mediated suppression of STAT-1 activation. Downstream of the JAK-STAT signaling, EHV-1 infection inhibited expression of cellular antiviral proteins including IFN-stimulated gene 56 (ISG56) and viperin. Taken together these findings suggest that the neuropathogenic T953 strain of EHV-1 evades the host innate immune response by inhibiting IFN and this may provide some insight into the pathogenesis of EHV-1 infection.

Characterization of the Interaction between the Matrix Protein of Vesicular Stomatitis Virus and the Immunoproteasome Subunit LMP2

The matrix protein (M) of vesicular stomatitis virus (VSV) is involved in virus assembly, budding, gene regulation, and cellular pathogenesis. Using a yeast two-hybrid system, the M globular domain was shown to interact with LMP2, a catalytic subunit of the immunoproteasome (which replaces the standard proteasome catalytic subunit PSMB6). The interaction was validated by coimmunoprecipitation of M and LMP2 in VSV-infected cells. The sites of interaction were characterized. A single mutation of M (I96A) which significantly impairs the interaction between M and LMP2 was identified. We also show that M preferentially binds to the inactive precursor of LMP2 (bearing an N-terminal propeptide which is cleaved upon LMP2 maturation). Furthermore, taking advantage of a sequence alignment between LMP2 and its proteasome homolog, PSMB6 (which does not bind to M), we identified a mutation (L45R) in the S1 pocket where the protein substrate binds prior to cleavage and a second one (D17A) of a conserved residue essential for the catalytic activity, resulting in a reduction of the level of binding to M. The combination of both mutations abolishes the interaction. Taken together, our data indicate that M binds to LMP2 before its incorporation into the immunoproteasome. As the immunoproteasome promotes the generation of major histocompatibility complex (MHC) class I-compatible peptides, a feature which favors the recognition and the elimination of infected cells by CD8 T cells, we suggest that M, by interfering with the immunoproteasome assembly, has evolved a mechanism that allows infected cells to escape detection and elimination by the immune system.

IMPORTANCE

The immunoproteasome promotes the generation of MHC class I-compatible peptides, a feature which favors the recognition and the elimination of infected cells by CD8 T cells. Here, we report on the association of vesicular stomatitis virus (VSV) matrix protein (M) with LMP2, one of the immunoproteasome-specific catalytic subunits. M preferentially binds to the LMP2 inactive precursor. The M-binding site on LMP2 is facing inwards in the immunoproteasome and is therefore not accessible to M after its assembly. Hence, M binds to LMP2 before its incorporation into the immunoproteasome. We suggest that VSV M, by interfering with the immunoproteasome assembly, has evolved a mechanism that allows infected cells to escape detection and elimination by the immune system. Modulating this M-induced immunoproteasome impairment might be relevant in order to optimize VSV for oncolytic virotherapy.

Long Non-Coding RNA BST2/BISPR is Induced by IFN and Regulates the Expression of the Antiviral Factor Tetherin

Many long non-coding RNAs (lncRNAs) are expressed in cells but only a few have been well characterized. In these cases, lncRNAs have been shown to be key regulators of several cellular processes. Therefore, there is a great need to understand the function of more lncRNAs and their regulation in response to stimuli. Interferon (IFN) is a key molecule in the cellular antiviral response. IFN binding to its receptor activates transcription of several IFN-stimulated genes (ISGs) that function as potent antivirals. In addition, several ISGs are positive or negative regulators of the IFN pathway. This is essential to ensure a strong antiviral response and a later return of the cell to homeostasis. As the ISGs described to date are coding genes, we sought to determine whether IFN also regulates the expression of long non-coding ISGs. To this aim, we used RNA sequencing to analyze the transcriptome of control and HuH7 cells treated with IFNα2. The results show that IFN-treatment regulates the expression of several unknown non-coding transcripts. We have validated two lncRNAs upregulated after treatment with different doses of type I IFNα2 in different cells or with type III IFNλ. These lncRNAs were also induced by influenza and vesicular stomatitis virus mutants unable to block the IFN response, but not by several wild-type lytic viruses tested. These lncRNA genes were named lncISG15 and lncBST2 as they are located close to ISGs ISG15 and BST2, respectively. Interestingly, inhibition experiments showed that lncBST2 is a positive regulator of BST2. Therefore lncBST2 has been renamed BISPR, from BST2 IFN-stimulated positive regulator. Our results may have therapeutic implications as lncBST2/BISPR, but also lncISG15 and their coding neighbors, are increased in cells infected with hepatitis C virus and in the liver of infected patients. These results allow us to hypothesize that several lncRNAs could be activated by IFN to control the potency of the antiviral IFN response.

In vitro assessment of the biologic activity of interferon beta formulations used for the treatment of relapsing multiple sclerosis

A new formulation (NF) of subcutaneous (sc) interferon (IFN) β-1a was developed in an attempt to improve injection tolerability and immunogenicity. We compared antiviral and IFNβ-stimulated gene (ISG) activities of IFNβ-1a sc NF with IFNβ-1a sc original formulation and IFNβ-1b sc. When equivalent unit amounts were compared, the IFNβ formulations demonstrated similar antiviral activity and induced similar levels of ISG mRNA. However, on a weight basis (ng/mL), significantly more IFNβ-1b sc was needed to equal the antiviral activity of either IFNβ-1a sc formulation, and both IFNβ-1a sc formulations induced significantly higher levels of ISG mRNA than IFNβ-1b sc.

Potential applications for antiviral therapy and prophylaxis in bovine medicine

Viral disease is one of the major causes of financial loss and animal suffering in today's cattle industry. Increases in global commerce and average herd size, urbanization, vertical integration within the industry and alterations in global climate patterns have allowed the spread of pathogenic viruses, or the introduction of new viral species, into regions previously free of such pathogens, creating the potential for widespread morbidity and mortality in naïve cattle populations. Despite this, no antiviral products are currently commercially licensed for use in bovine medicine, although significant progress has been made in the development of antivirals for use against bovine viral diarrhea virus (BVDV), foot and mouth disease virus (FMDV) and bovine herpesvirus (BHV). BVDV is extensively studied as a model virus for human antiviral studies. Consequently, many compounds with efficacy have been identified and a few have been successfully used to prevent infection in vivo although commercial development is still lacking. FMDV is also the subject of extensive antiviral testing due to the importance of outbreak containment for maintenance of export markets. Thirdly, BHV presents an attractive target for antiviral development due to its worldwide presence. Antiviral studies for other bovine viral pathogens are largely limited to preliminary studies. This review summarizes the current state of knowledge of antiviral compounds against several key bovine pathogens and the potential for commercial antiviral applications in the prevention and control of several selected bovine diseases.

Induction of antiviral genes by the tumor microenvironment confers resistance to virotherapy

Oncolytic viruses obliterate tumor cells in tissue culture but not against the same tumors in vivo. We report that macrophages can induce a powerfully protective antiviral state in ovarian and breast tumors, rendering them resistant to oncolytic virotherapy. These tumors have activated JAK/STAT pathways and expression of interferon-stimulated genes (ISGs) is upregulated. Gene expression profiling (GEP) of human primary ovarian and breast tumors confirmed constitutive activation of ISGs. The tumors were heavily infiltrated with CD68+ macrophages. Exposure of OV-susceptible tumor cell lines to conditioned media from RAW264.7 or primary macrophages activated antiviral ISGs, JAK/STAT signaling and an antiviral state. Anti-IFN antibodies and shRNA knockdown studies show that this effect is mediated by an extremely low concentration of macrophage-derived IFNβ. JAK inhibitors reversed the macrophage-induced antiviral state. This study points to a new role for tumor-associated macrophages in the induction of a constitutive antiviral state that shields tumors from viral attack.

DAMP molecule S100A9 acts as a molecular pattern to enhance inflammation during influenza A virus infection: role of DDX21-TRIF-TLR4-MyD88 pathway

Pathogen-associated molecular patterns (PAMPs) trigger host immune response by activating pattern recognition receptors like toll-like receptors (TLRs). However, the mechanism whereby several pathogens, including viruses, activate TLRs via a non-PAMP mechanism is unclear. Endogenous “inflammatory mediators” called damage-associated molecular patterns (DAMPs) have been implicated in regulating immune response and inflammation. However, the role of DAMPs in inflammation/immunity during virus infection has not been studied. We have identified a DAMP molecule, S100A9 (also known as Calgranulin B or MRP-14), as an endogenous non-PAMP activator of TLR signaling during influenza A virus (IAV) infection. S100A9 was released from undamaged IAV-infected cells and extracellular S100A9 acted as a critical host-derived molecular pattern to regulate inflammatory response outcome and disease during infection by exaggerating pro-inflammatory response, cell-death and virus pathogenesis. Genetic studies showed that the DDX21-TRIF signaling pathway is required for S100A9 gene expression/production during infection. Furthermore, the inflammatory activity of extracellular S100A9 was mediated by activation of the TLR4-MyD88 pathway. Our studies have thus, underscored the role of a DAMP molecule (i.e. extracellular S100A9) in regulating virus-associated inflammation and uncovered a previously unknown function of the DDX21-TRIF-S100A9-TLR4-MyD88 signaling network in regulating inflammation during infection.

The lung disease severity following influenza A virus (IAV) infection is dependent on the extent of inflammation in the respiratory tract. Severe inflammation in the lung manifests in development of pneumonia. Therefore, it is very critical to identify cellular factors and dissect the molecular/cellular mechanism controlling inflammation in the respiratory tract during IAV infection. Knowledge derived from these studies will be instrumental in development of therapeutics to combat the lung disease associated with IAV infection. Towards that end, in the current study we have identified a cellular factor S100A9 which is responsible for enhanced inflammation during IAV infection. In addition, we have characterized a signal transduction pathway involving various cellular receptors and signaling adaptors that are involved in mediating S100A9-dependent inflammatory response. Thus, our studies have illuminated a cellular/molecular mechanism that can be intervened by therapeutics to reduce and control IAV-associated lung inflammatory disease like pneumonia.

Understanding and altering cell tropism of vesicular stomatitis virus

Vesicular stomatitis virus (VSV) is a prototypic nonsegmented negative-strand RNA virus. VSV's broad cell tropism makes it a popular model virus for many basic research applications. In addition, a lack of preexisting human immunity against VSV, inherent oncotropism and other features make VSV a widely used platform for vaccine and oncolytic vectors. However, VSV's neurotropism that can result in viral encephalitis in experimental animals needs to be addressed for the use of the virus as a safe vector. Therefore, it is very important to understand the determinants of VSV tropism and develop strategies to alter it. VSV glycoprotein (G) and matrix (M) protein play major roles in its cell tropism. VSV G protein is responsible for VSV broad cell tropism and is often used for pseudotyping other viruses. VSV M affects cell tropism via evasion of antiviral responses, and M mutants can be used to limit cell tropism to cell types defective in interferon signaling. In addition, other VSV proteins and host proteins may function as determinants of VSV cell tropism. Various approaches have been successfully used to alter VSV tropism to benefit basic research and clinically relevant applications.

A genetic screen identifies interferon-α effector genes required to suppress hepatitis C virus replication

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection is a leading cause of end-stage liver disease. Interferon-α (IFNα) is an important component of anti-HCV therapy; it up-regulates transcription of IFN-stimulated genes, many of which have been investigated for their antiviral effects. However, all of the genes required for the antiviral function of IFNα (IFN effector genes [IEGs]) are not known. IEGs include not only IFN-stimulated genes, but other nontranscriptionally induced genes that are required for the antiviral effect of IFNα. In contrast to candidate approaches based on analyses of messenger RNA (mRNA) expression, identification of IEGs requires a broad functional approach.

METHODS

We performed an unbiased genome-wide small interfering RNA screen to identify IEGs that inhibit HCV. Huh7.5.1 hepatoma cells were transfected with small interfering RNAs incubated with IFNα and then infected with JFH1 HCV. Cells were stained using HCV core antibody, imaged, and analyzed to determine the percent infection. Candidate IEGs detected in the screen were validated and analyzed further.

RESULTS

The screen identified 120 previously unreported IEGs. From these, we more fully evaluated the following: asparagine-linked glycosylation 10 homolog (yeast, α-1,2-glucosyltransferase); butyrylcholinesterase; dipeptidyl-peptidase 4 (CD26, adenosine deaminase complexing protein 2); glucokinase (hexokinase 4) regulator; guanylate cyclase 1, soluble, β 3; MYST histone acetyltransferase 1; protein phosphatase 3 (formerly 2B), catalytic subunit, β isoform; peroxisomal proliferator-activated receptor-γ-DBD-interacting protein 1; and solute carrier family 27 (fatty acid transporter), member 2; and demonstrated that they enabled IFNα-mediated suppression of HCV at multiple steps of its life cycle. Expression of these genes had more potent effects against flaviviridae because a subset was required for IFNα to suppress dengue virus but not influenza A virus. In addition, many of the host genes detected in this screen (92%) were not transcriptionally stimulated by IFNα; these genes represent a heretofore unknown class of non-IFN-stimulated gene IEGs.

CONCLUSIONS

We performed a whole-genome loss-of-function screen to identify genes that mediate the effects of IFNα against human pathogenic viruses. We found that IFNα restricts HCV via actions of general and specific IEGs.

Cholesterol-rich lipid rafts are required for release of infectious human respiratory syncytial virus particles

Cholesterol and sphingolipid enriched lipid raft micro-domains in the plasma membrane play an important role in the life-cycle of numerous enveloped viruses. Although human respiratory syncytial virus (RSV) proteins associate with the raft domains of infected cells and rafts are incorporated in RSV virion particles, the functional role of raft during RSV infection was unknown. In the current study we have identified rafts as an essential component of host cell that is required for RSV infection. Treatment of human lung epithelial cells with raft disrupting agent methyl-beta-cyclodextrin (MBCD) led to drastic loss of RSV infectivity due to diminished release of infectious progeny RSV virion particles from raft disrupted cells. RSV infection of raft deficient Niemann-Pick syndrome type C human fibroblasts and normal human embryonic lung fibroblasts revealed that during productive RSV infection, raft is required for release of infectious RSV particles.

Pharmacologic activation of the innate immune system to prevent respiratory viral infections

Drugs that can rapidly inhibit respiratory infection from influenza or other respiratory pathogens are needed. One approach is to engage primary innate immune defenses against viral infection, such as activating the IFN pathway. In this study, we report that a small, cell-permeable compound called 5,6-di-methylxanthenone-4-acetic acid (DMXAA) can induce protection against vesicular stomatitis virus in vitro and H1N1 influenza A virus in vitro and in vivo through innate immune activation. Using the mouse C10 bronchial epithelial cell line and primary cultures of nasal epithelial cells, we demonstrate DMXAA activates the IFN regulatory factor-3 pathway leading to production of IFN-β and subsequent high-level induction of IFN-β-dependent proteins, such as myxovirus resistance 1 (Mx1) and 2',5'-oligoadenylate synthetase 1 (OAS1). Mice treated with DMXAA intranasally elevate mRNA/protein expression of Mx1 and OAS1 in the nasal mucosa, trachea, and lung. When challenged intranasally with a lethal dose of H1N1 influenza A virus, DMXAA reduced viral titers in the lungs and protected 80% of mice from death, even when given at 24 hours before infection. These data show that agents, like DMXAA, that can directly activate innate immune pathways, such as the IFN regulatory factor-3/IFN-β system, in respiratory epithelial cells can be used to protect from influenza pneumonia and potentially in other respiratory viral infections. Development of this approach in humans could be valuable for protecting health care professionals and "first responders" in the early stages of viral pandemics or bioterror attacks.

Retinoic acid inducible gene I activates innate antiviral response against human parainfluenza virus type 3

Human parainfluenza virus type 3 (HPIV3) is a respiratory paramyxovirus that infects lung epithelial cells to cause high morbidity among infants and children. To date, no effective vaccine or antiviral therapy exists for HPIV3 and therefore, it is important to study innate immune antiviral response induced by this virus in infected cells. Type-I interferons (IFN, interferon-alpha/beta) and tumor necrosis factor-alpha (TNFalpha activated by NFkappaB) are potent antiviral cytokines that play an important role during innate immune antiviral response. A wide-spectrum of viruses utilizes pattern recognition receptors (PRRs) like toll-like receptors (TLRs) and RLH (RIG like helicases) receptors such as RIGI (retinoic acid inducible gene -I) and Mda5 to induce innate antiviral response. Previously it was shown that both TNFalpha and IFNbeta are produced from HPIV3 infected cells. However, the mechanism by which infected cells activated innate response following HPIV3 infection was not known. In the current study, we demonstrated that RIGI serves as a PRR in HPIV3 infected cells to induce innate antiviral response by expressing IFNbeta (via activation of interferon regulatory factor-3 or IRF3) and TNFalpha (via activation of NF-kappaB).

Role of human beta-defensin-2 during tumor necrosis factor-alpha/NF-kappaB-mediated innate antiviral response against human respiratory syncytial virus

Human respiratory syncytial virus (RSV) constitutes a highly pathogenic virus that infects lung epithelial cells to cause a wide spectrum of respiratory diseases. Our recent studies have revealed the existence of an interferon-alpha/beta-independent, innate antiviral response against RSV that was dependent on activation of NF-kappaB. We demonstrated that NF-kappaB inducing pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF) confers potent antiviral function against RSV in an NF-kappaB-dependent fashion, independent of interferon-alpha/beta. During our efforts to study this pathway, we identified HBD2 (human beta-defensin-2), a soluble secreted cationic protein as an antiviral factor induced during NF-kappaB-dependent innate antiviral activity in human lung epithelial cells. Our results demonstrated that HBD2 is induced by TNF and RSV in an NF-kappaB-dependent manner. Induction of HBD2 in infected cells was mediated by the paracrine/autocrine action of TNF produced upon RSV infection. HBD2 plays a critical role during host defense, because purified HBD2 drastically inhibited RSV infection. We also show that the antiviral mechanism of HBD2 involves blocking of viral cellular entry possibly because of destabilization/disintegration of the viral envelope. The important role of HBD2 in the innate response was also evident from loss of antiviral activity of TNF upon HBD2 silencing by short interfering RNA. The in vivo physiological relevance of HBD2 in host defense was apparent from induction of murine beta-defensin-4 (murine counterpart of HBD2) in lung tissues of RSV-infected mice. Thus, HBD2 functions as an antiviral molecule during NF-kappaB-dependent innate antiviral immunity mediated by the autocrine/paracrine action of TNF.