SARS-CoV-2 NSP12 Protein Is Not an Interferon-β Antagonist

The coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is bringing an unprecedented health crisis to the world. To date, our understanding of the interaction between SARS-CoV-2 and host innate immunity is still limited. Previous studies reported that SARS-CoV-2 nonstructural protein 12 (NSP12) was able to suppress interferon-β (IFN-β) activation in IFN-β promoter luciferase reporter assays, which provided insights into the pathogenesis of COVID-19. In this study, we demonstrated that IFN-β promoter-mediated luciferase activity was reduced during coexpression of NSP12. However, we could show NSP12 did not affect IRF3 or NF-κB activation. Moreover, IFN-β production induced by Sendai virus (SeV) infection or other stimulus was not affected by NSP12 at mRNA or protein level. Additionally, the type I IFN signaling pathway was not affected by NSP12, as demonstrated by the expression of interferon-stimulated genes (ISGs). Further experiments revealed that different experiment systems, including protein tags and plasmid backbones, could affect the readouts of IFN-β promoter luciferase assays. In conclusion, unlike as previously reported, our study showed SARS-CoV-2 NSP12 protein is not an IFN-β antagonist. It also rings the alarm on the general usage of luciferase reporter assays in studying SARS-CoV-2. IMPORTANCE Previous studies investigated the interaction between SARS-CoV-2 viral proteins and interferon signaling and proposed that several SARS-CoV-2 viral proteins, including NSP12, could suppress IFN-β activation. However, most of these results were generated from IFN-β promoter luciferase reporter assay and have not been validated functionally. In our study, we found that, although NSP12 could suppress IFN-β promoter luciferase activity, it showed no inhibitory effect on IFN-β production or its downstream signaling. Further study revealed that contradictory results could be generated from different experiment systems. On one hand, we demonstrated that SARS-CoV-2 NSP12 could not suppress IFN-β signaling. On the other hand, our study suggests that caution needs to be taken with the interpretation of SARS-CoV-2-related luciferase assays.

Porcine deltacoronavirus nsp10 antagonizes interferon-β production independently of its zinc finger domains

Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus that causes serious vomiting and diarrhea in piglets. Previous work demonstrated that PDCoV infection inhibits type I interferon (IFN) production. Here, we found that ectopic expression of PDCoV nsp10 significantly inhibited Sendai virus (SeV)-induced IFN-β production by impairing the phosphorylation and nuclear translocation of two transcription factors, IRF3 and NF-κB p65 subunit. Interestingly, experiments with truncated mutants and site-directed mutagenesis revealed that PDCoV nsp10 mutants with missing or destroyed zinc fingers (ZFs) domains also impeded SeV-induced IFN-β production, suggesting that nsp10 does not require its ZF domains to antagonize IFN-β production. Further work found that co-expression of nsp10 with nsp14 or nsp16, two replicative enzymes, significantly enhanced the inhibitory effects of nsp10 on IFN-β. Taken together, our results demonstrate that PDCoV nsp10 antagonizes IFN via a ZF-independent mechanism and has a synergistic effect with nsp14 and nsp16 on inhibiting IFN-β production.

Porcine epidemic diarrhea virus E protein suppresses RIG-I signaling-mediated interferon-β production

Porcine epidemic diarrhea virus (PEDV) encodes many multifunctional proteins that inhibit host innate immune response during virus infection. As one of important structural proteins, PEDV E protein has been found to block the production of type I interferon (IFN) in virus life cycle, but little is known about this process that E protein subverts host innate immune. Thus, in this present study, we initiated the construction of eukaryotic expression vectors to express PEDV E protein. Subsequently, cellular localization analysis was performed and the results showed that the majority of PEDV E protein distributed at cytoplasm and localized in endoplasmic reticulum (ER). Over-expression of PEDV E protein significantly inhibited poly(I:C)-induced IFN-β and IFN-stimulated genes (ISGs) productions. We also found that PEDV E protein remarkably suppressed the protein expression of RIG-I signaling-associated molecules, but all their corresponding mRNA levels remained unaffected and unchanged. Furthermore, PEDV E protein obviously interfered with the translocation of IRF3 from cytoplasm to nucleus through direct interaction with IRF3, which is crucial for the IFN-β production induced by poly(I:C). Taken together, our results suggested that PEDV E protein acts as an IFN-β antagonist through suppression of the RIG-I-mediated signaling. This study will pave the way for the further investigation into the molecular mechanisms by which PEDV E protein evades host innate immune response.

Novel Toscana Virus Reverse Genetics System Establishes NSs as an Antagonist of Type I Interferon Responses

The sand fly-borne Toscana virus (TOSV) is the major cause of human meningoencephalitis in the Mediterranean basin during the summer season. In this work, we have developed a T7 RNA polymerase-driven reverse genetics system to recover infectious particles of a lineage B strain of TOSV. The viral protein pattern and growth properties of the rescued virus (rTOSV) were found to be similar to those of the corresponding wild-type (wt) virus. Using this system, we genetically engineered a TOSV mutant lacking expression of the non-structural protein NSs (rTOSVɸNSs). Unlike rTOSV and the wt virus, rTOSVɸNSs was unable to (i) suppress interferon (IFN)-b messenger RNA induction; and (ii) grow efficiently in cells producing IFN-b. Together, our results highlight the importance of NSs for TOSV in evading the IFN response and provide a comprehensive toolbox to investigate the TOSV life cycle in mammalian and insect host cells, including several novel polyclonal antibodies.

Feline Infectious Peritonitis Virus Nsp5 Inhibits Type I Interferon Production by Cleaving NEMO at Multiple Sites

Feline infectious peritonitis (FIP), caused by virulent feline coronavirus, is the leading infectious cause of death in cats. The type I interferon (type I IFN)-mediated immune responses provide host protection from infectious diseases. Several coronaviruses have been reported to evolve diverse strategies to evade host IFN response. However, whether feline infectious peritonitis virus (FIPV) antagonizes the type I IFN signaling remains unclear. In this study, we demonstrated that FIPV strain DF2 infection not only failed to induce interferon-β (IFN-β) and interferon-stimulated gene (ISG) production, but also inhibited Sendai virus (SEV) or polyinosinic-polycytidylic acid (poly(I:C))-induced IFN-β production. Subsequently, we found that one of the non-structural proteins encoded by the FIPV genome, nsp5, interrupted type I IFN signaling in a protease-dependent manner by cleaving the nuclear factor κB (NF-κB) essential modulator (NEMO) at three sites—glutamine132 (Q132), Q205, and Q231. Further investigation revealed that the cleavage products of NEMO lost the ability to activate the IFN-β promoter. Mechanistically, the nsp5-mediated NEMO cleavage disrupted the recruitment of the TRAF family member-associated NF-κB activator (TANK) to NEMO, which reduced the phosphorylation of interferon regulatory factor 3 (IRF3), leading to the inhibition of type I IFN production. Our research provides new insights into the mechanism for FIPV to counteract host innate immune response.

Chikungunya Virus-Encoded nsP2, E2 and E1 Strongly Antagonize the Interferon-β Signaling Pathway

Chikungunya virus (CHIKV) is a single-stranded positive-sense RNA virus, belonging to the genus Alphavirus of the Togaviridae family. It causes multiple symptoms, including headache, fever, severe joint and muscle pain, and arthralgia. Since CHIKV was first isolated in Tanzania in 1952, there have been multiple outbreaks of chikungunya fever. However, its pathogenesis and mechanisms of viral immune evasion have been poorly understood. In addition, the exact roles of individual CHIKV genes on the host innate immune response remain largely unknown. To investigate if CHIKV-encoded genes modulate the type I interferon (IFN) response, each and every CHIKV gene was screened for its effects on the induction of the IFN-β promoter. Here we report that CHIKV nsP2, E2 and E1 strongly suppressed activation of the IFN-β promoter induced by the MDA5/RIG-I receptor signaling pathway, suggesting that nsP2, E2, and E1 are the major antagonists against induction of IFN-β. Delineation of underlying mechanisms of CHIKV-mediated inhibition of the IFN-β pathway may help develop virus-specific therapeutics and vaccines.

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-β production by impairing dsRNA and PACT binding to RIG-I

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that causes watery diarrhea, vomiting and mortality in newborn piglets. Previous studies have suggested that PDCoV infection antagonizes RIG-I-like receptor (RLR)-mediated IFN-β production to evade host innate immune defense, and PDCoV-encoded nonstructural protein nsp5 and accessory protein NS6 are associated with this process. However, whether the structural protein(s) of PDCoV also antagonize IFN-β production remains unclear. In this study, we found that PDCoV nucleocapsid (N) protein, the most abundant viral structural protein, suppressed Sendai virus (SEV)-induced IFN-β production and transcription factor IRF3 activation, but did not block IFN-β production induced by overexpressing RIG-I/MDA5. Furthermore, study revealed that PDCoV N protein interacted with RIG-I and MDA5 in an in vitro overexpression system and evident interactions between N protein and RIG-I could be detected in the context of PDCoV infection, which interfered with the binding of dsRNA and protein activator of protein kinase R (PACT) to RIG-I. Together, our results demonstrate that PDCoV N protein is an IFN antagonist and utilizes diverse strategies to attenuate RIG-I recognition and activation.

Sesamin Catechol Glucuronides Exert Anti-inflammatory Effects by Suppressing Interferon β and Inducible Nitric Oxide Synthase Expression through Deconjugation in Macrophage-like J774.1 Cells

Sesamin, a representative sesame lignan, has health-promoting activities. Sesamin is converted into catechol derivatives and further into their glucuronides or sulfates in vivo, whereas the biological activities of sesamin metabolites remain unclear. We examined the inhibitory effects of sesamin metabolites on the lipopolysaccharide (LPS)-induced nitric oxide (NO) production in mouse macrophage-like J774.1 cells and found that a monocatechol derivative SC1, (7α,7'α,8α,8'α)-3,4-dihydroxy-3',4'-methylenedioxy-7,9':7',9-diepoxylignane, has a much higher activity than sesamin and other metabolites. The inhibitory effects of SC1 glucuronides were time-dependently enhanced, associated with the intracellular accumulation of SC1 and the methylated form. SC1 glucuronides and SC1 attenuated the expression of inducible NO synthase (iNOS) and upstream interferon-β (IFN-β) in the LPS-stimulated macrophages. The inhibitory effects of SC1 glucuronides against NO production were canceled by the β-glucuronidase inhibitor and enhanced by the catechol-O-methyltransferase inhibitor. Our results suggest that SC1 glucuronides exert the anti-inflammatory effects by inhibiting the IFN-β/iNOS signaling through macrophage-mediated deconjugation.

The Nucleoprotein and Phosphoprotein of Peste des Petits Ruminants Virus Inhibit Interferons Signaling by Blocking the JAK-STAT Pathway

Peste des petits ruminants virus (PPRV) is associated with global peste des petits ruminants resulting in severe economic loss. Peste des petits ruminants virus dampens host interferon-based signaling pathways through multiple mechanisms. Previous studies deciphered the role of V and C in abrogating IFN-β production. Moreover, V protein directly interacted with signal transducers and activators of transcription 1 (STAT1) and STAT2 resulting in the impairment of host IFN responses. In our present study, PPRV infection inhibited both IFN-β- and IFN-γ-induced activation of IFN-stimulated response element (ISRE) and IFN-γ-activated site (GAS) element, respectively. Both N and P proteins, functioning as novel IFN response antagonists, markedly suppressed IFN-β-induced ISRE and IFN-γ-induced GAS promoter activation to impair downstream upregulation of various interferon-stimulated genes (ISGs) and prevent STAT1 nuclear translocation. Specifically, P protein interacted with STAT1 and subsequently inhibited STAT1 phosphorylation, whereas N protein neither interacted with STAT1 nor inhibited STAT1 phosphorylation as well as dimerization, suggesting that the N and P protein antagonistic effects were different. Though they differed in their relationship to STAT1, both proteins blocked JAK-STAT signaling, severely negating the host antiviral immune response. Our study revealed a new mechanism employed by PPRV to evade host innate immune response, providing a platform to study the interaction of paramyxoviruses and host response.

PSMB1 Negatively Regulates the Innate Antiviral Immunity by Facilitating Degradation of IKK-ε

Proteasome is a large protein complex, which degrades most intracellular proteins. It regulates numerous cellular processes, including the removal of misfolded or unfolded proteins, cell cycle control, and regulation of apoptosis. However, the function of proteasome subunits in viral immunity has not been well characterized. In this study, we identified PSMB1, a member of the proteasome β subunits (PSMB) family, as a negative regulator of innate immune responses during viral infection. Knockdown of PSMB1 enhanced the RNA virus-induced cytokine and chemokine production. Overexpression of PSMB1 abolished virus-induced activation of the interferon-stimulated response element (ISRE) and interferon beta (IFNβ) promoters. Mechanistically, PSMB1 inhibited the activation of RIG-I-like receptor (RLR) and Toll-like receptor 3 (TLR3) signaling pathways. PSMB1 was induced after viral infection and its interaction with IKK-ε promoted degradation of IKK-ε through the ubiquitin-proteasome system. Collectively, our study demonstrates PSMB1 is an important regulator of innate immune signaling.

Hepatitis E Virus Papain-Like Cysteine Protease Inhibits Type I Interferon Induction by Down-Regulating Melanoma Differentiation-Associated Gene 5

Upon viral infection, the host cell recognizes the invasion through a number of pattern recognition receptors. Melanoma differentiation associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) recognize RNA molecules derived from invading viruses, activating down-stream signaling cascades, culminating in the induction of the type I interferon. On the other hand, viruses have evolved to evade type I interferon-mediated inhibition. Hepatitis E virus has been shown to encode a few antagonists of type I interferon and it is not surprising that viruses encode multiple mechanisms of viral evasion. In the present study, we demonstrated that HEV PCP strongly down-regulates MDA5-mediated activation of interferon β induction in a dose-dependent manner. Interestingly, MDA5 protein expression was almost completely abolished. In addition, polyinosinic polycytidylic acid (poly(I:C))- and Sendai virus-mediated activation of type I interferon responses were similarly abrogated in the presence of HEV PCP. Furthermore, HEV PCP down-regulates several molecules that play critical roles in the induction of type I IFN expression. Taken together, these data collectively suggest that HEV-encoded PCP is a strong antagonist of type I interferon.

Putative endogenous filovirus VP35-like protein potentially functions as an IFN antagonist but not a polymerase cofactor

It has been proposed that some non-retroviral RNA virus genes are integrated into vertebrate genomes. Endogenous filovirus-like elements (EFLs) have been discovered in some mammalian genomes. However, their potential roles in ebolavirus infection are unclear. A filovirus VP35-like element (mlEFL35) is found in the little brown bat (Myotis lucifugus) genome. Putative mlEFL35-derived protein (mlEFL35p) contains nearly full-length amino acid sequences corresponding to ebolavirus VP35. Ebola virus VP35 has been shown to bind double-stranded RNA, leading to inhibition of type I interferon (IFN) production, and is also known as a viral polymerase cofactor that is essential for viral RNA transcription/replication. In this study, we transiently expressed mlEFL35p in human kidney cells and investigated its biological functions. We first found that mlEFL35p was coimmunoprecipitated with itself and ebolavirus VP35s but not with the viral nucleoprotein. Then the biological functions of mlEFL35p were analyzed by comparing it to ebolavirus VP35s. We found that the expression of mlEFL35p significantly inhibited human IFN-β promoter activity as well as VP35s. By contrast, expression of mlEFL35p did not support viral RNA transcription/replication and indeed slightly decrease the reporter gene expression in a minigenome assay. These results suggest that mlEFL35p potentially acts as an IFN antagonist but not a polymerase cofactor.

West Nile Virus NS1 Antagonizes Interferon Beta Production by Targeting RIG-I and MDA5

West Nile virus (WNV) is a mosquito-borne flavivirus that causes epidemics of encephalitis and viscerotropic disease worldwide. This virus has spread rapidly and has posed a significant public health threat since the outbreak in New York City in 1999. The interferon (IFN)-mediated antiviral response represents an important component of virus-host interactions and plays an essential role in regulating viral replication. Previous studies have suggested that multifunctional nonstructural proteins encoded by flaviviruses antagonize the host IFN response via various means in order to establish efficient viral replication. In this study, we demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes IFN-β production, most likely through suppression of retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) activation. In a dual-luciferase reporter assay, WNV NS1 significantly inhibited the activation of the IFN-β promoter after Sendai virus infection or poly(I·C) treatment. NS1 also suppressed the activation of the IFN-β promoter when it was stimulated by interferon regulatory factor 3 (IRF3)/5D or its upstream molecules in the RLR signaling pathway. Furthermore, NS1 blocked the phosphorylation and nuclear translocation of IRF3 upon stimulation by various inducers. Mechanistically, WNV NS1 targets RIG-I and melanoma differentiation-associated gene 5 (MDA5) by interacting with them and subsequently causing their degradation by the proteasome. Furthermore, WNV NS1 inhibits the K63-linked polyubiquitination of RIG-I, thereby inhibiting the activation of downstream sensors in the RLR signaling pathway. Taken together, our results reveal a novel mechanism by which WNV NS1 interferes with the host antiviral response.IMPORTANCE WNV Nile virus (WNV) has received increased attention since its introduction to the United States. However, the pathogenesis of this virus is poorly understood. This study demonstrated that the nonstructural protein 1 (NS1) of WNV antagonizes the induction of interferon beta (IFN-β) by interacting with and degrading retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5), which are crucial viral sensors in the host innate immune system. Further experiments suggested that NS1-mediated inhibition of the RIG-I-like receptor (RLR) signaling pathway involves inhibition of RIG-I K63-linked polyubiquitination and that the proteasome plays a role in RIG-I degradation. This study provides new insights into the regulation of WNV NS1 in the RLR signaling pathway and reveals a novel mechanism by which WNV evades the host innate immune response. The novel findings may guide us to discover new therapeutic targets and develop effective vaccines for WNV infections.

Feline Panleucopenia Virus NS2 Suppresses the Host IFN-β Induction by Disrupting the Interaction between TBK1 and STING

Feline panleucopenia virus (FPV) is a highly infectious pathogen that causes severe diseases in pets, economically important animals and wildlife in China. Although FPV was identified several years ago, little is known about how it overcomes the host innate immunity. In the present study, we demonstrated that infection with the FPV strain Philips-Roxane failed to activate the interferon β (IFN-β) pathway but could antagonize the induction of IFN stimulated by Sendai virus (SeV) in F81 cells. Subsequently, by screening FPV nonstructural and structural proteins, we found that only nonstructural protein 2 (NS2) significantly suppressed IFN expression. We demonstrated that the inhibition of SeV-induced IFN-β production by FPV NS2 depended on the obstruction of the IFN regulatory factor 3 (IRF3) signaling pathway. Further, we verified that NS2 was able to target the serine/threonine-protein kinase TBK1 and prevent it from being recruited by stimulator of interferon genes (STING) protein, which disrupted the phosphorylation of the downstream protein IRF3. Finally, we identified that the C-terminus plus the coiled coil domain are the key domains of NS2 that are required for inhibiting the IFN pathway. Our study has yielded strong evidence for the FPV mechanisms that counteract the host innate immunity.

Differential Regulation of Interferon Responses by Ebola and Marburg Virus VP35 Proteins

Suppression of innate immune responses during filoviral infection contributes to disease severity. Ebola (EBOV) and Marburg (MARV) viruses each encode a VP35 protein that suppresses RIG-I-like receptor signaling and interferon-α/β (IFN-α/β) production by several mechanisms, including direct binding to double stranded RNA (dsRNA). Here, we demonstrate that in cell culture, MARV infection results in a greater upregulation of IFN responses as compared to EBOV infection. This correlates with differences in the efficiencies by which EBOV and MARV VP35s antagonize RIG-I signaling. Furthermore, structural and biochemical studies suggest that differential recognition of RNA elements by the respective VP35 C-terminal IFN inhibitory domain (IID) rather than affinity for RNA by the respective VP35s is critical for this observation. Our studies reveal functional differences in EBOV versus MARV VP35 RNA binding that result in unexpected differences in the host response to deadly viral pathogens.

Anti-inflammatory properties of Morus bombycis Koidzumi via inhibiting IFN-β signaling and NLRP3 inflammasome activation

ETHNOPHARMACOLOGICAL RELEVANCE

Morus bombycis Koidzumi (M. bombycis, Moraceae) has been used in Asian countries as a traditional medicine for the treatment of hypertension, diabetes, and inflammation-related disorders.

AIM OF STUDY

Although its anti-inflammatory actions have been partly documented, scientific evidence involving its molecular mechanisms related to inflammasome activation signaling pathways remains unknown.

MATERIALS AND METHODS

Lipopolysaccharide-stimulated RAW 264.7 cells and bone marrow-derived murine macrophages were used to study the in vitro effect of methanolic extract of M. bombycis (MB) on inflammatory responses. A monosodium urate crystal (MSU)-induced peritonitis murine model was used to study the in vivo effects.

RESULTS

MB attenuated the production of nitric oxide and interleukin-6, through the regulation of the interferon-β receptor signaling pathway. MB also inhibited IL-1β secretion via attenuation of NLRP3 inflammasome activation. Furthermore, MB inhibited MSU-induced peritonitis in the in vivo murine model.

CONCLUSIONS

This study provides the key molecular mechanisms involved in the anti-inflammatory effects of M. bombycis, substantiating the traditional claims of its use in the treatment of inflammation-related disorders.

Mir-302c mediates influenza A virus-induced IFNβ expression by targeting NF-κB inducing kinase

Little is known about the role of microRNA during influenza A virus (IAV) infection. We observed that NIK 3'UTR luciferase activity was elevated during IAV infection. Further studies demonstrated that miR-302c reduced NIK expression, resulting in the reduction of IFNβ mRNA expression. We found that miR-302c prevented the translocation of NF-κB from the cytosol to the nucleus. Furthermore, IAV infection downregulated miR-302c expression, leading to the activation of IFNβ expression and the inhibition of viral replication. Compared to miR-302c, miR-520e cannot promote viral replication and production, although the two microRNAs target the same site of the NIK 3'UTR. Collectively, our work defines a novel signaling pathway implicated in the control of IFNβ mRNA expression during IAV infection.

Truncation of the C-terminal region of Toscana Virus NSs protein is critical for interferon-β antagonism and protein stability

Toscana Virus (TOSV) is a Phlebovirus responsible for central nervous system (CNS) injury in humans. The TOSV non-structural protein (NSs), which interacting with RIG-I leads to its degradation, was analysed in the C terminus fragment in order to identify its functional domains. To this aim, two C-terminal truncated NSs proteins, Δ1C-NSs (aa 1-284) and Δ2C-NSs (aa 1-287) were tested. Only Δ1C-NSs did not present any inhibitory effect on RIG-I and it showed a greater stability than the whole NSs protein. Moreover, the deletion of the TLQ aa sequence interposed between the two ΔC constructs caused a greater accumulation of the protein with a weak inhibitory effect on RIG-I, indicating some involvement of these amino acids in the NSs activity. Nevertheless, all the truncated proteins were still able to interact with RIG-I, suggesting that the domains responsible for RIG-I signaling and RIG-I interaction are mapped on different regions of the protein.

Histone deacetylase 6 inhibition enhances oncolytic viral replication in glioma

Oncolytic viral (OV) therapy, which uses genetically engineered tumor-targeting viruses, is being increasingly used in cancer clinical trials due to the direct cytolytic effects of this treatment that appear to provoke a robust immune response against the tumor. As OVs enter tumor cells, intrinsic host defenses have the potential to hinder viral replication and spread within the tumor mass. In this report, we show that histone deacetylase 6 (HDAC6) in tumor cells appears to alter the trafficking of post-entry OVs from the nucleus toward lysosomes. In glioma cell lines and glioma-stem-like cells, HDAC6 inhibition (HDAC6i) by either pharmacologic or genetic means substantially increased replication of oncolytic herpes simplex virus type 1 (oHSV). Moreover, HDAC6i increased shuttling of post-entry oHSV to the nucleus. In addition, electron microscopic analysis revealed that post-entry oHSVs are preferentially taken up into glioma cells through the endosomal pathway rather than via fusion at the cell surface. Together, these findings illustrate a mechanism of glioma cell defense against an incoming infection by oHSV and identify possible approaches to enhance oHSV replication and subsequent lysis of tumor cells.

Porcine reproductive and respiratory syndrome virus 3C protease cleaves the mitochondrial antiviral signalling complex to antagonize IFN-β expression

Porcine reproductive and respiratory syndrome, a highly infectious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), has developed various strategies to evade the host innate immune response, including the suppression of type I IFN activation. The mitochondrial antiviral signalling protein (MAVS) is an important bridging adaptor of retinoic acid-inducible gene I/melanoma differentiation-associated protein 5 signalling pathways. Here, we demonstrated that the 3C-like protease (3CLSP) of PRRSV prevented the induction of IFN-β by cleaving MAVS in a proteasome- and caspase-independent manner. Moreover, this cleavage ability was dependent on the protease activity of 3CLSP. Mutations specifically disrupting the cysteine protease activity of 3CLSP eliminated MAVS cleavage and the inhibition of IFN induction. Subsequently, we determined that 3CLSP cleaved MAVS at Glu268. Remarkably, a MAVS point mutation at Glu268 rendered MAVS resistant to 3CLSP cleavage. These results reveal a novel PRRSV mechanism to escape host immunity by directly cleaving MAVS.

Effects of Different Doses of Nucleocapsid Protein from Hantaan Virus A9 Strain on Regulation of Interferon Signaling

Hantaan virus A9 strain (HTNV A9) is an etiologic agent of hemorrhagic fever with renal syndrome in China. The virulence of the pathogenic hantaviruses is determined by their ability to alter key signaling pathways of early interferon (IFN) induction within cells. The potential role of HTNV A9 structural proteins, such as nucleocapsid (N) and envelope glycoproteins (Gn and Gc), in regulating human's innate antiviral immune response has not yet been clarified. In this study, we investigated the effect of HTNV A9 N protein on the regulation of the IFN pathway. We found that A9 N protein can influence the host innate immune response by regulating the activation of IFNβ. The A9 N protein stimulates IFN response in low doses, whereas significantly inhibits IFNβ production at high doses. Furthermore, A9 N protein constitutively inhibits nuclear factor kappa B activation. A high dose of A9 N protein could inhibit either Poly IC-induced IFNβ or vesicular stomatitis virus-induced IFNβ and interferon-stimulated gene production. Our results indicate that HTNV A9 N protein helps virus establish successful infection by downregulating the IFN response and shed new light to the understanding of the interaction between the host innate immunity and virus during Hantaan virus infection.

Immunostimulatory Defective Viral Genomes from Respiratory Syncytial Virus Promote a Strong Innate Antiviral Response during Infection in Mice and Humans

Human respiratory syncytial virus (RSV) is a major cause of severe respiratory illness in children and susceptible adults. RSV blocks the development of the innate antiviral immune response and can grow to high titers in the respiratory tract. Here we demonstrate that immunostimulatory defective viral genomes (iDVGs) that are naturally generated during RSV replication are strong inducers of the innate antiviral response to RSV in mice and humans. In mice, RSV iDVGs stimulated the expression of antiviral genes, restricted viral replication, and prevented weight loss and lung inflammation. In human cells, the antiviral response to RSV iDVGs was dominated by the expression of IFN-λ1 over IFN-β and was driven by rapid intranuclear accumulation of the transcription factor IRF1. RSV iDVGs were detected in respiratory secretions of hospitalized patients, and their amount positively correlated with the level of expression of antiviral genes in the samples. Infection of explanted human lung tissue from different donors revealed that most humans can respond to RSV iDVGs and that the rate of accumulation of iDVGs during infection directly correlates with the quality of the antiviral response. Taken together, our data establish iDVGs as primary triggers of robust antiviral responses to RSV and provide the first evidence for an important biological role for naturally occurring iDVGs during a paramyxovirus infection in humans.

Induction of interferon-induced transmembrane protein 3 gene expression by lipopolysaccharide in astrocytes

Astrocytes are important modulators of the immune and inflammatory reactions in the central nervous system. We have recently demonstrated the role of interferon-induced transmembrane protein 3 (IFITM3) in long-lasting neuronal impairments in mice following neonatal immune challenge by injections of the double-stranded RNA analog polyriboinosinic polyribocytidylic acid. Here, we show that IFITM3 is induced after lipopolysaccharide (LPS) treatment in cultured astrocytes. The induction of IFITM3 by LPS was completely suppressed by the addition of anti-interferon-β (IFN-β) antibody. In addition, neutralization of tumor necrosis factor-α (TNF-α) with its antibody partially inhibited the induction of IFITM3, suggesting that LPS induces IFITM3 through autocrine secretion of IFN-β and TNF-α. Furthermore, experiments using pharmacological inhibitors suggest that LPS induces IFITM3 through activation of TANK-binding kinase 1, p38 mitogen-activated protein kinase, and nuclear factor-κB pathways. Together, these findings may provide new insight into the role of IFITM3 in the pathogenesis of neurodevelopmental diseases associated with immune activation.

Hepatitis A virus 3C protease cleaves NEMO to impair induction of beta interferon

NEMO (NF-κB essential modulator) is a bridging adaptor indispensable for viral activation of interferon (IFN) antiviral response. Herein, we show that hepatitis A virus (HAV) 3C protease (3Cpro) cleaves NEMO at the Q304 residue, negating its signaling adaptor function and abrogating viral induction of IFN-β synthesis via the retinoic acid-inducible gene I/melanoma differentiation-associated protein 5 (RIG-I/MDA5) and Toll-like receptor 3 (TLR3) pathways. NEMO cleavage and IFN antagonism, however, were lost upon ablation of the catalytic activity of 3Cpro. These data describe a novel immune evasion mechanism of HAV.

MAVS protein is attenuated by rotavirus nonstructural protein 1

Rotavirus is the single, most important agent of infantile gastroenteritis in many animal species, including humans. In developing countries, rotavirus infection attributes approximately 500,000 deaths annually. Like other viruses it establishes an intimate and complex interaction with the host cell to counteract the antiviral responses elicited by the cell. Among various pattern recognition receptors (PAMPs) of the host, the cytosolic RNA helicases interact with viral RNA to activate the Mitochondrial Antiviral Signaling protein (MAVS), which regulates cellular interferon response. With an aim to identify the role of different PAMPs in rotavirus infected cell, MAVS was found to degrade in a time dependent and strain independent manner. Rotavirus non-structural protein 1 (NSP1) which is a known IFN antagonist, interacted with MAVS and degraded it in a strain independent manner, resulting in a complete loss of RNA sensing machinery in the infected cell. To best of our knowledge, this is the first report on NSP1 functionality where a signaling protein is targeted unanimously in all strains. In addition NSP1 inhibited the formation of detergent resistant MAVS aggregates, thereby averting the antiviral signaling cascade. The present study highlights the multifunctional role of rotavirus NSP1 and reinforces the fact that the virus orchestrates the cellular antiviral response to its own benefit by various back up strategies.

Interleukin-1 receptor-associated kinase M (IRAK-M) promotes human rhinovirus infection in lung epithelial cells via the autophagic pathway

Human rhinovirus (HRV) is the most common viral etiology in acute exacerbations of asthma. However, the exact mechanisms underlying HRV infection in allergic airways are poorly understood. IL-13 increases interleukin-1 receptor associated kinase M (IRAK-M) and subsequently inhibits airway innate immunity against bacteria. However, the role of IRAK-M in lung HRV infection remains unclear. Here, we provide the first evidence that IRAK-M over-expression promotes lung epithelial HRV-16 replication and autophagy, but inhibits HRV-16-induced IFN-β and IFN-λ1 expression. Inhibiting autophagy reduces HRV-16 replication. Exogenous IFN-β and IFN-λ1 inhibit autophagy and HRV-16 replication. Our data indicate the enhancing effect of IRAK-M on epithelial HRV-16 infection, which is partly through the autophagic pathway. Impaired anti-viral interferon production may serve as a direct or an indirect (e.g., autophagy) mechanism of enhanced HRV-16 infection by IRAK-M over-expression. Targeting autophagic pathway or administrating anti-viral interferons may prevent or attenuate viral (e.g., HRV-16) infections in allergic airways.

Effects of Brazilian green propolis on double-stranded RNA-mediated induction of interferon-inducible gene and inhibition of recruitment of polymorphonuclear cells

BACKGROUND

Propolis is a bee product with various biological properties, including an antiviral activity when taken orally. However, its mechanisms at the cellular and molecular level are not well understood.

RESULTS

We investigated the effect of propolis on antiviral signaling in A549 cells transfected with double-stranded RNA (dsRNA), a model for viral infection. Pretreatment of the cells with propolis inhibited poly I:C (synthetic dsRNA)-induced interferon (IFN)-β expression. Propolis had no effect on the dsRNA-induced expression of RIG-I-like receptors (RLRs), which are known as intracellular viral RNA sensors. As to the effect on antiviral executor genes, propolis enhanced myxovirus resistance 1 (MX1) expression, whereas interferon-inducible gene 6-16 (G1P3) and 2'-5'-oligoadenylate synthetase (OAS) were unaffected. All of these genes belong to the IFN-inducible genes, suggesting that the effect of propolis on antiviral signaling is not necessarily mediated by the autocrine regulation by IFN-β. Propolis pretreatment inhibited dsRNA-induced interleukin-8 (IL8) and CCL5 expression, and consequently lowered polymorphonuclear leukocyte (PMN) chemotactic activity in the cell-conditioned medium.

CONCLUSION

Taken together, these results suggest that propolis may suppress excess inflammatory responses without affecting the innate immunity during viral infection.

ICP27 protein encoded by bovine herpesvirus type 1 (bICP27) interferes with promoter activity of the bovine genes encoding beta interferon 1 (IFN-β1) and IFN-β3

Bovine herpes virus 1 (BHV-1) infection leads to upper respiratory tract infections, conjunctivitis, and the infection predisposes cattle to secondary bacterial infections. The infected cell protein 0 (bICP0) encoded by BHV-1 suppresses antiviral innate immune signaling by interfering with expression of interferon beta (IFN-β). In contrast to humans or mice, cattle contain three IFN-β genes that have distinct transcriptional promoters. We previously cloned and characterized all three bovine IFN-β promoters. In this study, we provide evidence that bICP27; a viral early protein that shuttles between the nucleus and cytoplasm inhibits transcriptional activity of two bovine IFN-β gene promoters (IFN-β1 and IFN-β3). Conversely, the BHV-1 infected cell protein 0 (bICP0) early promoter was not inhibited by bICP27. C-terminal mutants lacking the bICP27 zinc RING finger-like motif did not efficiently inhibit IFN-β3 promoter activity but inhibited IFN-β1 promoter activity as efficiently as wild type bICP27. An N-terminal mutant lacking the nuclear localization signal (NLS) and nucleolar localization signal (NoLS) was localized to the cytoplasm and this mutant had no effect on IFN-β promoter activity. In summary, these studies provided evidence that bICP27 inhibited IFN-β1 and IFN-β3 promoter activity in transiently transfected cells.

[Heat shock protein 27 enhances the inhibitory effect of influenza A virus NS1 on the expression of interferon-beta]

Heat shock protein 27 (HSP27) is a member of the small heat shock proteins (sHSP) and has multiple functions, it also plays an important role in the life cycle of some viruses. To investigate the regulatory effect of HSP27 during influenza virus infection, we cloned and expressed human HSP27 in both prokaryotic and eukaryotic cells, and demonstrated that HSP27 interacted with influenza A virus NS1 protein both in vivo and in vitro. Luciferase assay showed that HSP27 inhibited the expression of interferon-beta (IFN-beta) in infected cells, and independent of its phosphorylation. Moreover, HSP27 enhanced the inhibitory effect of NS1 on the expression of IFN-beta. Further analysis indicated that HSP27 exerted the inhibitory effect probably through influencing MDA5 of the RIG-I like helicase (RLH) pathway. The results suggested that HSP27 play a role in the innate immunity of infected cells, contributed to our understanding of the regulatory effect of host factors during influenza virus infection.

Uterine epithelial cells specifically induce interferon-stimulated genes in response to polyinosinic-polycytidylic acid independently of estradiol

Interferon β (IFNβ) is an antiviral cytokine secreted in response to pathogenic exposure that creates a restrictive intracellular environment through the action of downstream interferon-stimulated genes (ISG). The objective of this study was to examine the expression of IFNβ and ISG in both human uterine epithelial cells (UEC) and the ECC-1 uterine epithelial cell line and determine if expression changes with TLR stimulation and hormone exposure. Stimulation of primary uterine epithelial cells and ECC-1 cells with the TLR3 agonist poly (I:C) induced the mRNA expression of IFNβ, MxA, OAS2 and PKR. Other TLR agonists including imiquimod and CpG had no effect on either IFNβ or ISG expression. In contrast to ECC-1 cell responses which were slower, maximal IFNβ upregulation in UEC occurred 3 hours post-stimulation and preceded the ISG response which peaked approximately 12 hours after poly (I:C) exposure. Unexpectedly, estradiol, either alone or prior to treatment with poly (I:C), had no effect on IFNβ or ISG expression. Blockade of the IFN receptor abrogated the upregulation of MxA, OAS2 and PKR. Furthermore, neutralizing antibodies against IFNβ partially inhibited the upregulation of all three ISG. Estradiol, directly and in the presence of poly (I:C) had no effect on IFNβ and ISG expression. These results indicate that uterine epithelial cells are important sentinels of the innate immune system and demonstrate that uterine epithelial cells are capable of mounting a rapid IFN-mediated antiviral response that is independent of estradiol and is therefore potentially sustained throughout the menstrual cycle to aid in the defense of the uterus against potential pathogens.

Herpes simplex virus type 2 virion host shutoff protein suppresses innate dsRNA antiviral pathways in human vaginal epithelial cells

Viruses that establish persistent infections have evolved numerous strategies to evade host innate antiviral responses. We functionally assessed the role of herpes simplex virus type 2 (HSV-2) virion host shutoff (vhs) protein on innate immune sensing pathways in human vaginal epithelial cells (VK2 ECs). Infection of cells with wild-type (WT) HSV-2 significantly decreased expression of innate immune sensors of viral infection, Toll-like receptor (TLR)2, TLR3, retinoic acid inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (Mda-5), relative to cells infected with a mutant that lacks vhs (vhsB) or mock-infected cells. Transfection with HSV-2 vhs similarly decreased expression of TLR2, TLR3, RIG-I and Mda-5, which was also confirmed in human embryonic kidney (HEK) 293 cells. vhsB infection of VK2 cells caused robust increases in the active form of interferon regulatory factor (IRF)3 and its translocation to the nucleus compared with the WT. Additionally, IRF3 activation by Sendai virus and polyinosinic : polycytidylic acid-induced stimulation of beta interferon (IFN-β) was significantly inhibited in vhs-transfected cells. Overall, our findings provide the first evidence that HSV-2 vhs plays roles in selectively inhibiting TLR3 and RIG-I/Mda-5, as well as TLR2-mediated antiviral pathways for sensing dsRNA and effectively suppresses IFN-β antiviral responses in human vaginal ECs.

NF-κB1 inhibits TLR-induced IFN-β production in macrophages through TPL-2-dependent ERK activation

Although NF-κB1 p50/p105 has critical roles in immunity, the mechanism by which NF-κB1 regulates inflammatory responses is unclear. In this study, we analyzed the gene expression profile of LPS-stimulated Nfkb1(-/-) macrophages that lack both p50 and p105. Deficiency of p50/p105 selectively increased the expression of IFN-responsive genes, which correlated with increased IFN-β expression and STAT1 phosphorylation. IFN Ab-blocking experiments indicated that increased STAT1 phosphorylation and expression of IFN-responsive genes observed in the absence of p50/p105 depended upon autocrine IFN-β production. Markedly higher serum levels of IFN-β were observed in Nfkb1(-/-) mice than in wild-type mice following LPS injection, demonstrating that Nfkb1 inhibits IFN-β production under physiological conditions. TPL-2, a mitogen-activated protein kinase kinase kinase stabilized by association with the C-terminal ankyrin repeat domain of p105, negatively regulates LPS-induced IFN-β production by macrophages via activation of ERK MAPK. Retroviral expression of TPL-2 in Nfkb1(-/-) macrophages, which are deficient in endogenous TPL-2, reduced LPS-induced IFN-β secretion. Expression of the C-terminal ankyrin repeat domain of p105 in Nfkb1(-/-) macrophages, which rescued LPS activation of ERK, also inhibited IFN-β expression. These data indicate that p50/p105 negatively regulates LPS-induced IFN signaling in macrophages by stabilizing TPL-2, thereby facilitating activation of ERK.

Influenza C virus NS1 protein counteracts RIG-I-mediated IFN signalling

The nonstructural proteins 1 (NS1) from influenza A and B viruses are known as the main viral factors antagonising the cellular interferon (IFN) response, inter alia by inhibiting the retinoic acid-inducible gene I (RIG-I) signalling. The cytosolic pattern-recognition receptor RIG-I senses double-stranded RNA and 5'-triphosphate RNA produced during RNA virus infections. Binding to these ligands activates RIG-I and in turn the IFN signalling. We now report that the influenza C virus NS1 protein also inhibits the RIG-I-mediated IFN signalling. Employing luciferase-reporter assays, we show that expression of NS1-C proteins of virus strains C/JJ/50 and C/JHB/1/66 considerably reduced the IFN-β promoter activity. Mapping of the regions from NS1-C of both strains involved in IFN-β promoter inhibition showed that the N-terminal 49 amino acids are dispensable, while the C-terminus is required for proper modulation of the IFN response. When a mutant RIG-I, which is constitutively active without ligand binding, was employed, NS1-C still inhibited the downstream signalling, indicating that IFN inhibitory properties of NS1-C are not necessarily linked to an RNA binding mechanism.

Phenylmethimazole blocks palmitate-mediated induction of inflammatory cytokine pathways in 3T3L1 adipocytes and RAW 264.7 macrophages

Visceral adipocytes and associated macrophages produce and release excessive amounts of biologically active inflammatory cytokines via the portal and systemic vascular system, which induce insulin resistance in insulin target tissues such as fat, liver, and muscle. Free fatty acids (FFAs) absorbed via the portal system or released from adipocytes also induce insulin resistance. In this report, we show that phenylmethimazole (C10) blocks basal IL6 and leptin production as well as basal Socs-3 expression in fully differentiated 3T3L1 cells (3T3L1 adipocytes) without affecting insulin-stimulated AKT signaling. In addition, C10 inhibits palmitate-induced IL6 and iNos up-regulation in both 3T3L1 adipocytes and RAW 264.7 macrophages, LPS-induced NF-κB and IFN-β activation in 3T3L1 cells, and LPS-induced iNos, Ifn-β, Il1β, Cxcl10, and Il6 expression in RAW 264.7 macrophages. C10 also blocks palmitate-induced Socs-3 up-regulation and insulin receptor substrate-1 (IRS-1) serine 307 phosphorylation in 3T3L1 adipocytes. Additionally, we show for the first time that although palmitate increases IRS-1 serine 307 phosphorylation in 3T3L1 adipocytes, AKT serine 473 phosphorylation is enhanced, not reduced, by palmitate. These results suggest that through inhibition of FFA-mediated signaling in adipocytes and associated macrophages, as well as possibly other insulin target cells/tissues (i.e. non-immune cells), C10 might be efficacious to prevent or reverse cytokine-induced insulin resistance seen in obesity-related insulin resistance and type 2 diabetes mellitus.

Epstein-Barr virus BRLF1 inhibits transcription of IRF3 and IRF7 and suppresses induction of interferon-beta

Activation of interferon regulatory factors (IRFs) 3 and 7 is essential for the induction of Type I interferons (IFN) and innate antiviral responses, and herpesviruses have evolved mechanisms to evade such responses. We previously reported that Epstein-Barr virus BZLF1, an immediate-early (IE) protein, inhibits the function of IRF7, but the role of BRLF1, the other IE transactivator, in IRF regulation has not been examined. We now show that BRLF1 expression decreased induction of IFN-beta, and reduced expression of IRF3 and IRF7; effects were dependent on N- and C-terminal regions of BRLF1 and its nuclear localization signal. Endogenous IRF3 and IRF7 RNA and protein levels were also decreased during cytolytic EBV infection. Finally, production of IFN-beta was decreased during lytic EBV infection and was associated with increased susceptibility to superinfection with Sendai virus. These data suggest a new role for BRLF1 with the ability to evade host innate immune responses.

Oncogenic Ras promotes reovirus spread by suppressing IFN-beta production through negative regulation of RIG-I signaling

Reovirus is the first naturally occurring human virus reported to exploit activated Ras signaling in the host cell for infection, and is currently undergoing clinical trials as a cancer therapeutic. Recent evidence suggests that Ras transformation promotes three reoviral replication steps during the first round of infection: uncoating of the incoming virion, generation of progeny viruses with enhanced infectivity, and virus release through enhanced apoptosis. Whether oncogenic Ras also enhances reovirus spread in subsequent rounds of infection through other mechanisms has not been examined. Here, we show that compared with nontransformed cells, Ras-transformed cells are severely compromised not only in their response to IFN-beta, but also in the induction of IFN-beta mRNA following reovirus infection. Defects in both IFN-beta production and response allow for efficient virus spread in Ras-transformed cells. We show that the MEK/ERK pathway downstream of Ras is responsible for inhibiting IFN-beta expression by blocking signaling from the retinoic acid-inducible gene I (RIG-I) which recognizes viral RNAs. Overexpression of wild-type RIG-I restores INF-beta expression in reovirus-infected Ras-transformed cells. In vitro-synthesized viral mRNAs also invoke robust RIG-I-mediated IFN-beta production in transfected nontransformed cells, but not in Ras-transformed cells. Collectively, our data suggest that oncogenic Ras promotes virus spread by suppressing viral RNA-induced IFN-beta production through negative regulation of RIG-I signaling.

Human respiratory syncytial virus nonstructural protein NS2 antagonizes the activation of beta interferon transcription by interacting with RIG-I

A wide variety of RNA viruses have been shown to produce proteins that inhibit interferon (IFN) production and signaling. For human respiratory syncytial virus (RSV), the nonstructural NS1 and NS2 proteins have been shown to block IFN signaling by causing the proteasomal degradation of STAT2. In addition, recombinant RSVs lacking either NS1 or NS2 induce more IFN production than wild-type (wt) RSV in infected cells. However, the mechanisms by which the NS proteins perform this function are unknown. In this study, we focused on defining the mechanism by which NS2 inhibits the induction of IFN transcription. We find that NS2 is required for the early inhibition of IFN transcription since the infection of cells with NS2-deletion RSV resulted in a higher level of IRF3 activation at early time points postinfection compared with that of wt or NS1-deletion RSV infection. In addition, NS2 expression inhibits IFN transcription induced by both the RIG-I and TLR3 pathways. Furthermore, we show that NS2 inhibits RIG-I-mediated IFN promoter activation by binding to the N-terminal CARD of RIG-I and inhibiting its interaction with the downstream component MAVS (IPS-1, VISA, Cardif). Thus, the RSV NS2 protein is a multifunctional IFN antagonist that targets specific components of both the IFN induction and IFN signaling pathways.

Measured Neutralizing Titers of IFN-β Neutralizing Antibodies (NAbs) Can Depend on the Preparations of IFN-β Used in the Assay

An immune response to recombinant human protein therapeutics, including type I interferons (IFNs), has the potential to have a serious negative impact on safety and efficacy. Monitoring of patients for neutralizing antibodies (NAbs) often is advisable. In the case of IFN-beta therapy for multiple sclerosis (MS), we obtained reproducible quantitative titers of NAbs using an improved and well-characterized assay based on a 10-fold reduction of a challenge dose of IFN-beta. However, the observed titer was significantly affected by the preparation of IFN-beta used as the assay challenge. NAb titers obtained using IFN-beta1b averaged 3-5-fold lower than titers of the same sample assayed using either IFN-beta1a or human fibroblast-derived IFN-beta. This was the case whether neutralizing serum was obtained from patients on therapy with IFN-beta1a or IFN-beta1b. The reason for this apparent titer difference is not fully understood but appears to be related to protein folding or other structural properties that differentiate the IFN-beta1b both from commercial IFN-beta1a preparations and from human fibroblast-derived IFN-beta.

Effects of type I interferons on the adjuvant properties of plasmid granulocyte-macrophage colony-stimulating factor in vivo

While administration of granulocyte-macrophage colony-stimulating factor (GM-CSF) can induce the local recruitment of activated antigen-presenting cells at the site of vaccine inoculation, this cellular recruitment is associated with a paradoxical decrease in local vaccine antigen expression and vaccine-elicited CD8+ T-cell responses. To clarify why this cytokine administration does not potentiate immunization, we examined the recruited cells and expressed inflammatory mediators in muscles following intramuscular administration of plasmid GM-CSF in mice. While large numbers of dendritic cells and macrophages were attracted to the site of plasmid GM-CSF inoculation, high concentrations of type I interferons were also detected in the muscles. As type I interferons have been reported to damp foreign gene expression in vivo, we examined the possibility that these local innate mediators might decrease plasmid DNA expression and therefore the immunogenicity of plasmid DNA vaccines. In fact, we found that coadministration of an anti-beta interferon monoclonal antibody with the plasmid DNA immunogen and plasmid GM-CSF restored both the local antigen expression and the CD8+ T-cell immunogenicity of the vaccine. These data demonstrate that local innate immune responses can change the ability of vaccines to generate robust adaptive immunity.

Replacement of the respiratory syncytial virus nonstructural proteins NS1 and NS2 by the V protein of parainfluenza virus 5

Paramyxoviruses have been shown to produce proteins that inhibit interferon production and signaling. For human respiratory syncytial virus (RSV), the nonstructural NS1 and NS2 proteins have been shown to have interferon antagonist activity through an unknown mechanism. To understand further the functions of NS1 and NS2, we generated recombinant RSV in which both NS1 and NS2 were replaced by the PIV5 V protein, which has well-characterized IFN antagonist activities (DeltaNS1/2-V). Expression of V was able to partially inhibit IFN responses in DeltaNS1/2-V-infected cells. In addition, the replication kinetics of DeltaNS1/2-V were intermediate between DeltaNS1/2 and wild-type (rA2) in A549 cells. However, expression of V did not affect the ability of DeltaNS1/2-V to activate IRF3 nuclear translocation and IFNbeta transcription. These data indicate that V was able to replace some of the IFN inhibitory functions of the RSV NS1 and NS2 proteins, but also that NS1 and NS2 have functions in viral replication beyond IFN antagonism.

Bovine parainfluenza virus type 3 accessory proteins that suppress beta interferon production

The paramyxovirus P gene encodes accessory proteins antagonistic to interferon (IFN). Viral proteins responsible for the IFN antagonism, however, are distinct among paramyxoviruses. Here we determine bovine parainfluenza virus type 3 (bPIV3) IFN antagonists that suppress IFN-beta production, and investigate the underlying molecular mechanism. Of bPIV3 P gene products, C and V proteins were found to suppress double-stranded RNA-stimulated IFN-beta production. The V protein of bPIV3 and Sendai virus in the same genus Respirovirus significantly inhibits double-stranded RNA-stimulated IFN-beta production and the IFN-beta promoter activation enhanced by overexpression of MDA5 but not RIG-I, and yet does not suppress IFN-beta production induced by TRIF, TBK1, and IKKi. The V protein of both viruses specifically binds to MDA5 but not RIG-I. These results suggest that the V protein targets MDA5 for blockage of the IFN-beta gene activation signal. On the other hand, both bPIV3 and Sendai virus C proteins modestly inhibited IFN-beta production irrespective of a species of the signaling molecules used as an inducer. Interestingly, reporter gene expression driven by various promoters was also suppressed by the C proteins irrespective of the promoter species. These results demonstrate that the target of the respirovirus C protein is undoubtedly different from that of the V protein.

Inhibition of transcription of the beta interferon gene by the human herpesvirus 6 immediate-early 1 protein

Human herpesviruses (HHV) are stealth pathogens possessing several decoy or immune system evasion mechanisms favoring their persistence within the infected host. Of these viruses, HHV-6 is among the most successful human parasites, establishing lifelong infections in nearly 100% of individuals around the world. To better understand this host-pathogen relationship, we determined whether HHV-6 could interfere with the development of the innate antiviral response by affecting interferon (IFN) biosynthesis. Using inducible cell lines and transient transfection assays, we have identified the immediate-early 1 (IE1) protein as a potent inhibitor of IFN-beta gene expression. IE1 proteins from both HHV-6 variants were capable of suppressing IFN-beta gene induction. IE1 prevents IFN-beta gene expression triggered by Sendai virus infection, double-stranded RNA (dsRNA) and dsDNA transfection, or the ectopic expression of IFN-beta gene activators such as retinoic inducible gene I protein, mitochondrial antiviral signaling protein, TBK-1, IkappaB kinase epsilon (IKKepsilon), and IFN regulatory factor 3 (IRF3). While the stability of IFN-beta mRNA is not affected, IE1-expressing cells have reduced levels of dimerized IRF3 and nucleus-translocated IRF3 in response to activation by TBK-1 or IKKepsilon. Using nuclear extracts and gel shift experiments, we could demonstrate that in the presence of IE1, IRF3 does not bind efficiently to the IFN-beta promoter sequence. Overall, these results indicate that the IE1 protein of HHV-6, one of the first viral proteins synthesized upon viral entry, is a potent suppressor of IFN-beta gene induction and likely contributes to favor the establishment of and successful infection of cells with this virus.

Multiple anti-interferon actions of the influenza A virus NS1 protein

The replication and pathogenicity of influenza A virus (FLUAV) are controlled in part by the alpha/beta interferon (IFN-alpha/beta) system. This virus-host interplay is dependent on the production of IFN-alpha/beta and on the capacity of the viral nonstructural protein NS1 to counteract the IFN system. Two different mechanisms have been described for NS1, namely, blocking the activation of IFN regulatory factor 3 (IRF3) and blocking posttranscriptional processing of cellular mRNAs. Here we directly compare the abilities of NS1 gene products from three different human FLUAV (H1N1) strains to counteract the antiviral host response. We found that A/PR/8/34 NS1 has a strong capacity to inhibit IRF3 and activation of the IFN-beta promoter but is unable to suppress expression of other cellular genes. In contrast, the NS1 proteins of A/Tx/36/91 and of A/BM/1/18, the virus that caused the Spanish influenza pandemic, caused suppression of additional cellular gene expression. Thus, these NS1 proteins prevented the establishment of an IFN-induced antiviral state, allowing virus replication even in the presence of IFN. Interestingly, the block in gene expression was dependent on a newly described NS1 domain that is important for interaction with the cleavage and polyadenylation specificity factor (CPSF) component of the cellular pre-mRNA processing machinery but is not functional in A/PR/8/34 NS1. We identified the Phe-103 and Met-106 residues in NS1 as being critical for CPSF binding, together with the previously described C-terminal binding domain. Our results demonstrate the capacity of FLUAV NS1 to suppress the antiviral host defense at multiple levels and the existence of strain-specific differences that may modulate virus pathogenicity.

Neutralizing antibodies to interferon beta: Assessment of their clinical and radiographic impact: An evidence report: Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology

The clinical and radiologic impact of developing neutralizing antibodies (NAbs) to interferon beta (IFNbeta) while on this therapy for multiple sclerosis (MS) is assessed. On the basis of Class II and III evidence, it is concluded that treatment of patients with MS with IFNbeta (Avonex, Betaseron, or Rebif) is associated with the production of NAbs (Level A). NAbs in the serum are probably associated with a reduction in the radiographic and clinical effectiveness of IFNbeta treatment (Level B). In addition, the rate of NAb production is probably less with IFNbeta-1a treatment than with IFNbeta-1b treatment, although the magnitude and persistence of this difference is difficult to determine (Level B). Finally, it is probable that there is a difference in seroprevalence due to variability in the dose of IFNbeta injected or in the frequency or route of its administration (Level B). Regardless of the explanation, it seems clear that IFNbeta-1a (as it is currently formulated for IM injection) is less immunogenic than the current IFNbeta preparations (either IFNbeta-1a or IFNbeta-1b) given multiple times per week subcutaneously (Level A). However, because NAbs disappear in some patients even with continued IFNbeta treatment (especially in patients with low titers), the persistence of this difference is difficult to determine (Level B). Although the finding of sustained high-titer NAbs (>100 to 200 NU/mL) is associated with a reduction in the therapeutic effects of IFNbeta on radiographic and clinical measures of MS disease activity, there is insufficient information on the utilization of NAb testing to provide specific recommendations regarding when to test, which test to use, how many tests are necessary, or which cutoff titer to apply (Level U).

Inhibition of retinoic acid-inducible gene I-mediated induction of beta interferon by the NS1 protein of influenza A virus

The retinoic acid-inducible gene I product (RIG-I) has been identified as a cellular sensor of RNA virus infection resulting in beta interferon (IFN-beta) induction. However, many viruses are known to encode viral products that inhibit IFN-beta production. In the case of influenza A virus, the viral nonstructural protein 1 (NS1) prevents the induction of the IFN-beta promoter by inhibiting the activation of transcription factors, including IRF-3, involved in IFN-beta transcriptional activation. The inhibitory properties of NS1 appear to be due at least in part to its binding to double-stranded RNA (dsRNA), resulting in the sequestration of this viral mediator of RIG-I activation. However, the precise effects of NS1 on the RIG-I-mediated induction of IFN-beta have not been characterized. We now report that the NS1 of influenza A virus interacts with RIG-I and inhibits the RIG-I-mediated induction of IFN-beta. This inhibition was apparent even when a mutant RIG-I that is constitutively activated (in the absence of dsRNA) was used to trigger IFN-beta production. Coexpression of RIG-I, its downstream signaling partner, IPS-1, and NS1 resulted in increased levels of RIG-I and NS1 within an IPS-1-rich, solubilization-resistant fraction after cell lysis. These results suggest that RIG-I, IPS-1, and NS1 become part of the same complex. Consistent with this idea, NS1 was also found to inhibit IFN-beta promoter activation by IPS-1 overexpression. Our results indicate that, in addition to sequestering dsRNA, the NS1 of influenza A virus binds to RIG-I and inhibits downstream activation of IRF-3, preventing the transcriptional induction of IFN-beta.

Interferon inhibitory activity in patients with multiple sclerosis

BACKGROUND

Interferon inhibitory activity (IIA) is a logical candidate for explaining neutralizing antibody-negative partial responsiveness to interferon beta in multiple sclerosis (MS), but its role has not been evaluated.

OBJECTIVE

To investigate the role of IIA and soluble interferon-alpha/beta receptor (sIFNR) in determining response of patients with MS to interferon beta therapy.

DESIGN

Parallel-group, open-label study.

SETTING

Baird Multiple Sclerosis Center, Buffalo, NY. Patients Blood was obtained before and 24 hours after injection of interferon beta-1a from 38 anti-interferon beta neutralizing antibody-negative patients with relapsing-remitting MS and 16 untreated healthy controls. On the basis of clinical parameters of response to interferon beta therapy, the patients were divided into stable or good-responder (n = 20) and active or partial-responder (n = 18) groups.

MAIN OUTCOME MEASURES

Quantitative analyses of magnetic resonance imaging were obtained; the IIA and sIFNR levels were measured using bioassay and enzyme-linked immunosorbent assay, respectively.

RESULTS

The IIA and sIFNR levels were elevated in MS patients compared with controls (P<.001). The IIA levels were higher in active or partial responders compared with stable or good responders (P<.001); the sIFNR levels were not different between groups. The Extended Disability Status Score and T2 lesion volumes were higher in the active or partial-responder group compared with the stable or good-responder group. Interferon beta-1a did not have short-term effects on the IIA and sIFNR levels. In univariate general linear model and stepwise regression analyses, IIA levels were associated with T2 lesion volume.

CONCLUSION

The levels of IIA are associated with increased MS disease activity and with responsiveness to interferon beta therapy in anti-interferon beta neutralizing antibody-negative MS patients.

Severe acute respiratory syndrome coronavirus open reading frame (ORF) 3b, ORF 6, and nucleocapsid proteins function as interferon antagonists

The severe acute respiratory syndrome coronavirus (SARS-CoV) is highly pathogenic in humans, with a death rate near 10%. This high pathogenicity suggests that SARS-CoV has developed mechanisms to overcome the host innate immune response. It has now been determined that SARS-CoV open reading frame (ORF) 3b, ORF 6, and N proteins antagonize interferon, a key component of the innate immune response. All three proteins inhibit the expression of beta interferon (IFN-beta), and further examination revealed that these SARS-CoV proteins inhibit a key protein necessary for the expression of IFN-beta, IRF-3. N protein dramatically inhibited expression from an NF-kappaB-responsive promoter. All three proteins were able to inhibit expression from an interferon-stimulated response element (ISRE) promoter after infection with Sendai virus, while only ORF 3b and ORF 6 proteins were able to inhibit expression from the ISRE promoter after treatment with interferon. This indicates that N protein inhibits only the synthesis of interferon, while ORF 3b and ORF 6 proteins inhibit both interferon synthesis and signaling. ORF 6 protein, but not ORF 3b or N protein, inhibited nuclear translocation but not phosphorylation of STAT1. Thus, it appears that these three interferon antagonists of SARS-CoV inhibit the interferon response by different mechanisms.

Neutralizing antibodies hamper IFN bioactivity and treatment effect on MRI in patients with MS

We measured neutralizing antibodies (NABs) and the in vivo biologic response to interferon-beta on neopterin and beta(2)-microglobulin blood levels. All NAB-negative patients had an in vivo biologic response (full or partial), whereas all high-level positive patients had no response. High-level NAB patients had more MRI activity than NAB-negative patients (p = 0.031). Patients with a full response had less MRI activity than patients without biologic response (p = 0.032).

A role for Stat1 in the regulation of lipopolysaccharide-induced interleukin-1beta expression

Because the induction of interleukin-1beta (IL-1beta) is critical to antibacterial host defenses and its excessive generation is a prominent component of sepsis, regulation of this proinflammatory cytokine is a critical factor in the immune response to lipopolysaccharide (LPS). We previously showed that LPS-induced IL-1beta expression was regulated by a Stat1-dependent, nitric oxide (NO)-mediated mechanism. Subsequent in vivo studies showed that whereas Stat1 had a role in the downregulation of IL-1beta expression, it had a more significant effect on its initial induction. Although both interferon-beta (IFN-beta) and IFN-gamma activate Stat1, the early appearance of IFN-beta in the circulation after LPS administration suggested its pivotal role in Stat1-mediated IL-1beta expression in vivo. Further in vitro analysis of peritoneal macrophages from IFN-beta (/), Stat1(/), and caspase-1(/) mice and their wild-type controls following LPS stimulation demonstrated that IL-1beta mRNA was expressed in these mice but not in macrophages from MyD88(/) mice. Despite the presence of IL-1beta mRNA, IL-1beta protein was markedly reduced in the absence of Stat1 activation in macrophages derived from IFN-beta (/) and Stat1(/) mice or in the absence of caspase-1 activity, which itself was dependent on Stat1 activation. These studies support the hypothesis that the expression of IL-1beta requires both the MyD88-dependent induction of IL-1beta mRNA and pro-IL-1beta as well as the MyD88-independent, Stat1-mediated processing of that gene product into active cytokine.