USP14 promotes K63-linked RIG-I deubiquitination and suppresses antiviral immune responses

Retinoic acid-inducible gene I (RIG-I) is a critical RNA virus sensor that initiates antiviral immune response through K63-linked ubiquitination. In this study, we demonstrated USP14, a deubiquitinating enzyme, as a negative regulator in antiviral responses by directly deubiquitinating K63-linked RIG-I. USP14 knockdown significantly enhanced RIG-I-triggered type I IFN signaling and inhibited vesicular stomatitis virus (VSV) replication both in mouse peritoneal macrophages and THP1 cells. USP14 overexpression in HeLa cells attenuated RIG-I-triggered IFN-β expression and promoted VSV replication. Besides, USP14-specific inhibitor, IU1, increased RIG-I-mediated type I IFN production and antiviral responses in vitro and in vivo. In addition, USP14 could interact with RIG-I and remove RIG-I K63-linked polyubiquitination chains. This article is the first to report that USP14 acts as a negative regulator in antiviral response through deubiquitinating K63-linked RIG-I. These findings provide insights into a potential new therapy targeting USP14 for RNA virus-related diseases.

Collective Infection of Cells by Viral Aggregates Promotes Early Viral Proliferation and Reveals a Cellular-Level Allee Effect

In addition to the conventional release of free, individual virions, virus dispersal can involve multi-virion assemblies that collectively infect cells. However, the implications of collective infection for viral fitness remain largely unexplored. Using vesicular stomatitis virus, here, we compare the fitness of free versus saliva-aggregated viral particles. We find that aggregation has a positive effect on early progeny production, conferring a fitness advantage relative to equal numbers of free particles in most cell types. The advantage of aggregation resides, at least partially, in increasing the cellular multiplicity of infection. In mouse embryonic fibroblasts, the per capita, short-term viral progeny production peaked for a dose of ca. three infectious particles per cell. This reveals an Allee effect restricting early viral proliferation at the cellular level, which should select for dispersal in groups. We find that genetic complementation between deleterious mutants is probably not the mechanism underlying the fitness advantage of collective infection. Instead, this advantage is cell type dependent and correlates with cellular permissivity to the virus, as well as with the ability of host cells to mount an antiviral innate immune response.

Nitrosporeusine analogue ameliorates Chandipura virus induced inflammatory response in CNS via NFκb inactivation in microglia

Chandipura Virus (CHPV), a negative-stranded RNA virus belonging to the Rhabdoviridae family, has been previously reported to bring neuronal apoptosis by activating several factors leading to neurodegeneration. Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues gets activated and starts secreting chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the effect of CHPV on microglia and the activation of cellular signalling pathways leading to chemokine expression upon CHPV infection. Protein and mRNA expression profiles of chemokine genes revealed that CHPV infection strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. CHPV infection triggered the activation of signalling pathways mediated by mitogen-activated protein kinases, including p38, JNK 1 and 2, and nuclear factor κB (NF-kappaB). CHPV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. Considering the important role of inflammation in neurodegeneration, we have targeted NF-kappaB using a newly synthesised natural product nitrosporeusine analogue and showed incapability of microglial supernatant of inducing apoptosis in neurons after treatment.

The E3 Ubiquitin Ligase TRIM40 Attenuates Antiviral Immune Responses by Targeting MDA5 and RIG-I

Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), including melanoma differentiation-associated gene 5 (MDA5) and RIG-I, are crucial for host recognition of non-self RNAs, especially viral RNA. Thus, the expression and activation of RLRs play fundamental roles in eliminating the invading RNA viruses and maintaining immune homeostasis. However, how RLR expression is tightly regulated remains to be further investigated. In this study, we identified a major histocompatibility complex (MHC)-encoded gene, tripartite interaction motif 40 (TRIM40), as a suppressor of RLR signaling by directly targeting MDA5 and RIG-I. TRIM40 binds to MDA5 and RIG-I and promotes their K27- and K48-linked polyubiquitination via its E3 ligase activity, leading to their proteasomal degradation. TRIM40 deficiency enhances RLR-triggered signaling. Consequently, TRIM40 deficiency greatly enhances antiviral immune responses and decreases viral replication in vivo. Thus, we demonstrate that TRIM40 limits RLR-triggered innate activation, suggesting TRIM40 as a potential therapeutic target for the control of viral infection.

Monomeric Intermediates Formed by Vesiculovirus Glycoprotein during Its Low-pH-induced Structural Transition

•Vesiculovirus G is the prototype of class III viral fusion glycoproteins. •The structures of both G pre- and post-fusion conformation have been determined. •The structure of monomeric intermediates reveals the pathway of the transition. •A fusion-loop-exposing antiparallel dimer may initiate the fusion process. •Those data challenge the current model proposed for viral membrane fusion.

Caenorhabditis elegans as an Emerging Model for Virus-Host Interactions

Since 1999, Caenorhabditis elegans has been extensively used to study microbe-host interactions due to its simple culture, genetic tractability, and susceptibility to numerous bacterial and fungal pathogens. In contrast, virus studies have been hampered by a lack of convenient virus infection models in nematodes. The recent discovery of a natural viral pathogen of C. elegans and development of diverse artificial infection models are providing new opportunities to explore virus-host interplay in this powerful model organism.

Integrated modeling and analysis of intracellular and intercellular mechanisms in shaping the interferon response to viral infection

The interferons (IFNs) responses to viral infection are heterogeneous, while the underlying mechanisms for variability among cells are still not clear. In this study, we developed a hybrid model to systematically identify the sources of IFN induction heterogeneity. The experiment-integrated simulation demonstrated that the viral dose/type, the diversity in transcriptional factors activation and the intercellular paracrine signaling could strikingly shape the heterogeneity of IFN expression. We further determined that the IFNβ and IFNλ1 induced diverse dynamics of IFN-stimulated genes (ISGs) production. Collectively, our findings revealed the intracellular and intercellular mechanisms contributing to cell-to-cell variation in IFN induction, and further demonstrated the significant effects of IFN heterogeneity on antagonizing viruses.

Mutational Analysis of Lassa Virus Glycoprotein Highlights Regions Required for Alpha-Dystroglycan Utilization

Lassa virus (LASV) is an enveloped RNA virus endemic to West Africa and responsible for severe cases of hemorrhagic fever. Virus entry is mediated by the glycoprotein complex consisting of a stable-signal peptide, a receptor-binding subunit, GP1, and a viral-host membrane fusion subunit, GP2. Several cellular receptors can interact with the GP1 subunit and mediate viral entry, including alpha-dystroglycan (αDG) and lysosome-associated membrane protein 1 (LAMP1). In order to define the regions within GP1 that interact with the cellular receptors, we implemented insertional mutagenesis, carbohydrate shielding, and alanine scanning mutagenesis. Eighty GP constructs were engineered and evaluated for GP1-GP2 processing, surface expression, and the ability to mediate cell-to-cell fusion after low-pH exposure. To examine virus-to-cell entry, 49 constructs were incorporated onto vesicular stomatitis virus (VSV) pseudoparticles and transduction efficiencies were monitored in HAP1 and HAP1-ΔDAG1 cells that differentially produce the αDG cell surface receptor. Seven constructs retained efficient transduction in HAP1-ΔDAG1 cells yet poorly transduced HAP1 cells, suggesting that they are involved in αDG utilization. Residues H141, N146, F147, and Y150 cluster at the predicted central core of the trimeric interface and are important for GP-αDG interaction. Additionally, H92A-H93A, 150HA, 172HA, and 230HA displayed reduced transduction in both HAP1 and HAP1-ΔDAG1 cells, despite efficient cell-to-cell fusion activity. These mutations may interfere with interactions with the endosomal receptor LAMP1 or interfere at another stage in entry that is common to both cell lines. Insight gained from these data can aid in the development of more-effective entry inhibitors by blocking receptor interactions.IMPORTANCE Countries in which Lassa virus is endemic, such as Nigeria, Sierra Leone, Guinea, and Liberia, usually experience a seasonal outbreak of the virus from December to March. Currently, there is neither a preventative vaccine nor a therapeutic available to effectively treat severe Lassa fever. One way to thwart virus infection is to inhibit interaction with cellular receptors. It is known that the GP1 subunit of the Lassa glycoprotein complex plays a critical role in receptor recognition. Our results highlight a region within the Lassa virus GP1 protein that interacts with the cellular receptor alpha-dystroglycan. This information may be used for future development of new Lassa virus antivirals.

Multi-virion infectious units arise from free viral particles in an enveloped virus

Many animal viruses are enveloped in a lipid bilayer taken up from cellular membranes. Because viral surface proteins bind to these membranes to initiate infection, we hypothesized that free virions may also be capable of interacting with the envelopes of other virions extracellularly. Here, we demonstrate this hypothesis in the vesicular stomatitis virus (VSV), a prototypic negative-strand RNA virus composed of an internal ribonucleocapsid, a matrix protein and an external envelope1. Using microscopy, dynamic light scattering, differential centrifugation and flow cytometry, we show that free viral particles can spontaneously aggregate into multi-virion infectious units. We also show that, following establishment of these contacts, different viral genetic variants are co-transmitted to the same target cell. Furthermore, virion-virion binding can determine key aspects of viral fitness such as antibody escape. In purified virions, this process is driven by protein-lipid interactions probably involving the VSV surface glycoprotein and phosphatidylserine. Whereas we found that multi-virion complexes occurred unfrequently in standard cell cultures, they were abundant in other fluids such as saliva, a natural VSV shedding route2. Our findings contrast with the commonly accepted perception of virions as passive propagules and show the ability of enveloped viruses to establish collective infectious units, which could in turn facilitate the evolution of virus-virus interactions and of social-like traits3.

ArfGAP Domain-Containing Protein 2 (ADAP2) Integrates Upstream and Downstream Modules of RIG-I Signaling and Facilitates Type I Interferon Production

Transcription of type I interferon genes during RNA virus infection requires signal communication between several pattern recognition receptor (PRR)-adaptor complexes located at distinct subcellular membranous compartments and a central cytoplasmic TBK1-interferon regulatory factor 3 (IRF3) kinase-transcription factor module. However, how the cell integrates signal transduction through spatially distinct modules of antiviral signaling pathways is less defined. RIG-I is a major cytosolic PRR involved in the control of several RNA viruses. Here we identify ArfGAP domain-containing protein 2 (ADAP2) as a key novel scaffolding protein that integrates different modules of the RIG-I pathway, located at distinct subcellular locations, and mediates cellular antiviral type I interferon production. ADAP2 served to bridge the mitochondrial membrane-bound upstream RIG-I adaptor MAVS and the downstream cytosolic complex of NEMO (regulatory subunit of TBK1), TBK1, and IRF3, leading to IRF3 phosphorylation. Furthermore, independently, ADAP2 also functioned as a major orchestrator of the interaction of TBK1 with NEMO and IRF3. Mutational and in vitro cell-free reconstituted RIG-I signaling assay-based analyses identified that the ArfGAP domain of ADAP2 mediates the interferon response. TRAF3 acted as a trigger for ADAP2 to recruit RIG-I pathway component proteins into a single macromolecular complex. This study provides important novel insights into the assembly and integration of different modules of antiviral signaling cascades.

The Antiviral RNA Interference Response Provides Resistance to Lethal Arbovirus Infection and Vertical Transmission in Caenorhabditis elegans

The recent discovery of the positive-sense single-stranded RNA (ssRNA) Orsay virus (OV) as a natural pathogen of the nematode Caenorhabditis elegans has stimulated interest in exploring virus-nematode interactions. However, OV infection is restricted to a small number of intestinal cells, even in nematodes defective in their antiviral RNA interference (RNAi) response, and is neither lethal nor vertically transmitted. Using a fluorescent reporter strain of the negative-sense ssRNA vesicular stomatitis virus (VSV), we show that microinjection of VSV particles leads to a dose-dependent, muscle tissue-tropic, lethal infection in C. elegans. Furthermore, we find nematodes deficient for components of the antiviral RNAi pathway, such as Dicer-related helicase 1 (DRH-1), to display hypersusceptibility to VSV infection as evidenced by elevated infection rates, virus replication in multiple tissue types, and earlier mortality. Strikingly, infection of oocytes and embryos could also be observed in drh-1 mutants. Our results suggest that the antiviral RNAi response not only inhibits vertical VSV transmission but also promotes transgenerational inheritance of antiviral immunity. Our study introduces a new, in vivo virus-host model system for exploring arbovirus pathogenesis and provides the first evidence for vertical pathogen transmission in C. elegans.

Neuropathogenesis by Chandipura virus: An acute encephalitis syndrome in India

Chandipura virus (CHPV) has been contributing to the rising number of premature deaths due to acute encephalitis syndrome for over a decade in India. CHPV belongs to the family Rhabdoviridae. Neuropathogenesis of CHPV has been well established but the exact route of entry into the central nervous system (CNS) and the triggering factor for neuronal death are still unknown. Rabies virus and vesicular stomatitis virus, which are related closely to CHPV, enter the CNS retrogradely from peripheral or olfactory neurons. Disruption of the blood-brain barrier has also been connoted in the entry of CHPV into the CNS. CHPV upon entering the neurons triggers cellular stress factors and release of reactive oxygen species (ROS). The stress granules produced in response to cellular stress have been implicated in viral replication and ROS generation, which stimulates neuronal death. Both these phenomena cohesively explain the neuropathogenesis and neurodegeneration following CHPV infection.

Novel biomarkers of resistance of pancreatic cancer cells to oncolytic vesicular stomatitis virus

Vesicular stomatitis virus (VSV) based recombinant viruses (such as VSV-ΔM51) are effective oncolytic viruses (OVs) against a majority of pancreatic ductal adenocarcinoma (PDAC) cell lines. However, some PDAC cell lines are highly resistant to VSV-ΔM51. We recently showed that treatment of VSV-resistant PDAC cells with ruxolitinib (JAK1/2 inhibitor) or TPCA-1 (IKK-β inhibitor) breaks their resistance to VSV-ΔM51. Here we compared the global effect of ruxolitinib or TPCA-1 treatment on cellular gene expression in PDAC cell lines highly resistant to VSV-ΔM51. Our study identified a distinct subset of 22 interferon-stimulated genes (ISGs) downregulated by both ruxolitinib and TPCA-1. Further RNA and protein analyses demonstrated that 4 of these genes (MX1, EPSTI1, XAF1, and GBP1) are constitutively co-expressed in VSV-resistant, but not in VSV-permissive PDACs, thus serving as potential biomarkers to predict OV therapy success. Moreover, shRNA-mediated knockdown of one of such ISG, MX1, showed a positive effect on VSV-ΔM51 replication in resistant PDAC cells, suggesting that at least some of the identified ISGs contribute to resistance of PDACs to VSV-ΔM51. As certain oncogene and tumor suppressor gene variants are often associated with increased tropism of OVs to cancer cells, we also analyzed genomic DNA in a set of PDAC cell lines for frequently occurring cancer associated mutations. While no clear correlation was found between such mutations and resistance of PDACs to VSV-ΔM51, the analysis generated valuable genotypic data for future studies.

Lipopolysaccharide suppresses human immunodeficiency virus 1 reverse transcription in macrophages

HIV-1-infected macrophages are long-lived and act as human immunodeficiency virus 1 (HIV-1) virus reservoirs. Lipopolysaccharide (LPS) has been demonstrated to suppress HIV-1 replication in macrophages, but the mechanism is not clear. Previous research suggested that downregulation of CD4 and CCR5 as well as blockage of the interaction of HIV-1 with cells are major causes of inhibition of HIV-1 replication in macrophages by LPS. In order to study whether LPS blocks the post-entry event of HIV-1 replication, we developed a macrophage HIV-1 infection model by using VSV-G pseudotyped HIV-1-luciferase virus to infect THP-1 differentiated macrophage-like cells. We found that LPS can suppress HIV-1 replication at post-entry steps. Further study suggested that HIV-1 reverse transcription was blocked by LPS, but addition of exogenous deoxyribonucleosides led to only partial recovery of HIV-1 replication. However, the inhibition of pro-inflammatory pathway completely rescued HIV-1 replication. Thus, our study shows that LPS can suppress the events of HIV-1 replication post-entry, including reverse transcription, and this restriction is mediated by more than one mechanism.

HSP90 Chaperoning in Addition to Phosphoprotein Required for Folding but Not for Supporting Enzymatic Activities of Measles and Nipah Virus L Polymerases

Nonsegmented negative-stranded RNA viruses, or members of the order Mononegavirales, share a conserved gene order and the use of elaborate transcription and replication machinery made up of at least four molecular partners. These partners have coevolved with the acquisition of the permanent encapsidation of the entire genome by the nucleoprotein (N) and the use of this N-RNA complex as a template for the viral polymerase composed of the phosphoprotein (P) and the large enzymatic protein (L). Not only is P required for polymerase function, but it also stabilizes the L protein through an unknown underlying molecular mechanism. By using NVP-AUY922 and/or 17-dimethylaminoethylamino-17-demethoxygeldanamycin as specific inhibitors of cellular heat shock protein 90 (HSP90), we found that efficient chaperoning of L by HSP90 requires P in the measles, Nipah, and vesicular stomatitis viruses. While the production of P remains unchanged in the presence of HSP90 inhibitors, the production of soluble and functional L requires both P and HSP90 activity. Measles virus P can bind the N terminus of L in the absence of HSP90 activity. Both HSP90 and P are required for the folding of L, as evidenced by a luciferase reporter insert fused within measles virus L. HSP90 acts as a true chaperon; its activity is transient and dispensable for the activity of measles and Nipah virus polymerases of virion origin. That the cellular chaperoning of a viral polymerase into a soluble functional enzyme requires the assistance of another viral protein constitutes a new paradigm that seems to be conserved within the Mononegavirales order.

IMPORTANCE

Viruses are obligate intracellular parasites that require a cellular environment for their replication. Some viruses particularly depend on the cellular chaperoning apparatus. We report here that for measles virus, successful chaperoning of the viral L polymerase mediated by heat shock protein 90 (HSP90) requires the presence of the viral phosphoprotein (P). Indeed, while P protein binds to the N terminus of L independently of HSP90 activity, both HSP90 and P are required to produce stable, soluble, folded, and functional L proteins. Once formed, the mature P+L complex no longer requires HSP90 to exert its polymerase functions. Such a new paradigm for the maturation of a viral polymerase appears to be conserved in several members of the Mononegavirales order, including the Nipah and vesicular stomatitis viruses.

Autophagy induced by snakehead fish vesiculovirus inhibited its replication in SSN-1 cell line

Autophagy plays an important role in host protection against pathogen infection through activating innate and adaptive immunity. In the present study, we observed that the infection of snakehead fish vesiculovirus (SHVV) could induce apparent autophagy in striped snakehead fish cell line (SSN-1), including clear double-membrane vesicles, fluorescent punctate pattern of microtubule-associated protein 1 light chain 3B (SSN-LC3B) and the conversion of SSN-LC3B-Ⅰ to SSN-LC3B-Ⅱ. Furthermore, we verified that autophagy inhibited the replication of SHVV by assessing mRNA and protein level of nucleoprotein as well as virus titer in the supernatant. These results will shed a new light on the prevention of the infection of SHVV.

PPM1A silences cytosolic RNA sensing and antiviral defense through direct dephosphorylation of MAVS and TBK1

Cytosolic RNA sensing is a prerequisite for initiation of innate immune response against RNA viral pathogens. Signaling through RIG-I (retinoic acid-inducible gene I)-like receptors (RLRs) to TBK1 (Tank-binding kinase 1)/IKKε (IκB kinase ε) kinases is transduced by mitochondria-associated MAVS (mitochondrial antiviral signaling protein). However, the precise mechanism of how MAVS-mediated TBK1/IKKε activation is strictly controlled still remains obscure. We reported that protein phosphatase magnesium-dependent 1A (PPM1A; also known as PP2Cα), depending on its catalytic ability, dampened the RLR-IRF3 (interferon regulatory factor 3) axis to silence cytosolic RNA sensing signaling. We demonstrated that PPM1A was an inherent partner of the TBK1/IKKε complex, targeted both MAVS and TBK1/IKKε for dephosphorylation, and thus disrupted MAVS-driven formation of signaling complex. Conversely, a high level of MAVS can dissociate the TBK1/PPM1A complex to override PPM1A-mediated inhibition. Loss of PPM1A through gene ablation in human embryonic kidney 293 cells and mouse primary macrophages enabled robustly enhanced antiviral responses. Consequently, Ppm1a(-/-) mice resisted to RNA virus attack, and transgenic zebrafish expressing PPM1A displayed profoundly increased RNA virus vulnerability. These findings identify PPM1A as the first known phosphatase of MAVS and elucidate the physiological function of PPM1A in antiviral immunity on whole animals.

Hepatitis C virus core protein enhances hepatocellular carcinoma cells to be susceptible to oncolytic vesicular stomatitis virus through down-regulation of HDAC4

Since hepatitis C virus (HCV) core protein is known to possess potential oncogenic activity, we explored whether oncolytic vesicular stomatitis virus (VSV) could efficiently induce cytolysis in hepatocellular carcinoma cells stably expressing HCV core protein (Hep3B-Core). We found that Hep3B-Core cells were more susceptible to VSV as compared to control (Hep3B-Vec) cells owing to core-mediated inactivation of STAT1 and STAT2 proteins. Core expression induced lower phosphorylation levels of type I IFN signaling proteins such as Tyk2 and Jak1, and a reduced response to exogenous IFN-α, which resulted in susceptibility to VSV. Furthermore, as STAT1 acetylation by switching phosphorylation regulated its activity, the role of STAT1 acetylation in susceptibility of Hep3B-Core cells to VSV was investigated. Treatment with trichostatin A, an inhibitor of histone deacetylase (HDAC), increased STAT1 acetylation but blocked IFN-α-induced phosphorylation of STAT1, leading to increase of susceptibility to VSV. Interestingly, the core protein decreased HDCA4 transcript levels, leading to down-regulation of HDAC4 protein. However, ectopic expression of HDAC4 conversely enforced phosphorylation of STAT1 and hindered VSV replication, indicating that core-mediated reduction of HDAC4 provides a suitable intracellular circumstance for VSV replication. Collectively, we suggest that VSV treatment will be a useful therapeutic strategy for HCV-infected hepatocellular carcinoma cells because HCV core protein suppresses the anti-viral threshold by down-regulation of the STAT1-HDAC4 signaling axis.

Cellular microRNAs Repress Vesicular Stomatitis Virus but Not Theiler's Virus Replication

Picornavirus’ genomic RNA is a positive-stranded RNA sequence that also serves as a template for translation and replication. Cellular microRNAs were reported to interfere to different extents with the replication of specific picornaviruses, mostly acting as inhibitors. However, owing to the high error rate of their RNA-dependent RNA-polymerases, picornavirus quasi-species are expected to evolve rapidly in order to lose any detrimental microRNA target sequence. We examined the genome of Theiler’s murine encephalomyelitis virus (TMEV) for the presence of under-represented microRNA target sequences that could have been selected against during virus evolution. However, little evidence for such sequences was found in the genome of TMEV and introduction of the most under-represented microRNA target (miR-770-3p) in TMEV did not significantly affect viral replication in cells expressing this microRNA. To test the global impact of cellular microRNAs on viral replication, we designed a strategy based on short-term Dicer inactivation in mouse embryonic fibroblasts. Short-term Dicer inactivation led to a >10-fold decrease in microRNA abundance and strongly increased replication of Vesicular stomatitis virus (VSV), which was used as a microRNA-sensitive control virus. In contrast, Dicer inactivation did not increase TMEV replication. In conclusion, cellular microRNAs appear to exert little influence on Theiler’s virus fitness.

CARMA3 Is a Host Factor Regulating the Balance of Inflammatory and Antiviral Responses against Viral Infection

Host response to RNA virus infection is sensed by RNA sensors such as RIG-I, which induces MAVS-mediated NF-κB and IRF3 activation to promote inflammatory and antiviral responses, respectively. Here, we have found that CARMA3, a scaffold protein previously shown to mediate NF-κB activation induced by GPCR and EGFR, positively regulates MAVS-induced NF-κB activation. However, our data suggest that CARMA3 sequesters MAVS from forming high-molecular-weight aggregates, thereby suppressing TBK1/IRF3 activation. Interestingly, following NF-κB activation upon virus infection, CARMA3 is targeted for proteasome-dependent degradation, which releases MAVS to activate IRF3. When challenged with vesicular stomatitis virus or influenza A virus, CARMA3-deficient mice showed reduced disease symptoms compared to those of wild-type mice as a result of less inflammation and a stronger ability to clear infected virus. Altogether, our results reveal the role of CARMA3 in regulating the balance of host antiviral and pro-inflammatory responses against RNA virus infection.

Perfusion Pressure Is a Critical Determinant of the Intratumoral Extravasation of Oncolytic Viruses

Antitumor efficacy of oncolytic virotherapy is determined by the density and distribution of infectious centers within the tumor, which may be heavily influenced by the permeability and blood flow in tumor microvessels. Here, we investigated whether systemic perfusion pressure, a key driver of tumor blood flow, could influence the intratumoral extravasation of systemically administered oncolytic vesicular stomatitis virus (VSV) in myeloma tumor-bearing mice. Exercise was used to increase mean arterial pressure, and general anesthesia to decrease it. A recombinant VSV expressing the sodium iodide symporter (NIS), which concentrates radiotracers at sites of infection, was administered intravenously to exercising or anesthetized mice, and nuclear NIS reporter gene imaging was used to noninvasively track the density and spatial distribution of intratumoral infectious centers. Anesthesia resulted in decreased intratumoral infection density, while exercise increased the density and uniformity of infectious centers. Perfusion state also had a significant impact on the antitumor efficacy of the VSV therapy. In conclusion, quantitative dynamic radiohistologic imaging was used to noninvasively interrogate delivery of oncolytic virotherapy, highlighting the critical importance of perfusion pressure as a driver of intratumoral delivery and efficacy of oncolytic viruses.

High-Throughput Single-Cell Kinetics of Virus Infections in the Presence of Defective Interfering Particles

Defective interfering particles (DIPs) are virus mutants that lack essential genes for growth. In coinfections with helper virus, the diversion of viral proteins to the replication and packaging of DIP genomes can interfere with virus production. Mounting cases of DIPs and DIP-like genomes in clinical and natural isolates, as well as growing interest in DIP-based therapies, underscore a need to better elucidate how DIPs work. DIP activity is primarily measured by its inhibition of virus infection yield, an endpoint that masks the dynamic and potentially diverse individual cell behaviors. Using vesicular stomatitis virus (VSV) as a model, we coinfected BHK cells with VSV DIPs and recombinant helper virus carrying a gene encoding a red fluorescent protein (RFP) whose expression correlates with the timing and level of virus release. For single cells within a monolayer, 10 DIPs per cell suppressed the reporter expression in only 1.2% of the cells. In most cells, it slowed and reduced viral gene expression, manifested as a shift in mean latent time from 4 to 6 h and reduced virus yields by 10-fold. For single cells isolated in microwells, DIP effects were more pronounced, reducing virus yields by 100-fold and extending latent times to 12 h, including individual instances above 20 h. Together, these results suggest that direct or indirect cell-cell interactions prevent most coinfected cells from being completely suppressed by DIPs. Finally, a gamma distribution model captures well how the infection kinetics quantitatively depends on the DIP dose. Such models will be useful for advancing a predictive biology of DIP-associated virus growth and infection spread.

IMPORTANCE

During the last century, basic studies in virology have focused on developing a molecular mechanistic understanding of how infectious viruses reproduce in their living host cells. However, over the last 10 years, the advent of deep sequencing and other powerful technologies has revealed in natural and patient infections that viruses do not act alone. Instead, viruses are often accompanied by defective virus-like particles that carry large deletions in their genomes and fail to replicate on their own. Coinfections of viable and defective viruses behave in unpredictable ways, but they often interfere with normal virus growth, potentially enabling infections to evade host immune surveillance. In the current study, controlled levels of defective viruses are coinfected with viable viruses that have been engineered to express a fluorescent reporter protein during infection. Unique profiles of reporter expression acquired from thousands of coinfected cells reveal how interference acts at multiple stages of infection.

Identification and Characterization of MicroRNAs in Snakehead Fish Cell Line upon Snakehead Fish Vesiculovirus Infection

MicroRNAs (miRNAs) play important roles in mediating multiple biological processes in eukaryotes and are being increasingly studied to evaluate their roles associated with cellular changes following viral infection. Snakehead fish Vesiculovirus (SHVV) has caused mass mortality in snakehead fish during the past few years. To identify specific miRNAs involved in SHVV infection, we performed microRNA deep sequencing on a snakehead fish cell line (SSN-1) with or without SHVV infection. A total of 205 known miRNAs were identified when they were aligned with the known zebrafish miRNAs, and nine novel miRNAs were identified using MiRDeep2 software. Eighteen and 143 of the 205 known miRNAs were differentially expressed at three and 24 h post-infection (poi), respectively. From the differentially-expressed miRNAs, five were randomly selected to validate their expression profiles using quantitative reverse transcription polymerase chain reaction (qRT-PCR), and their expression profiles were consistent with the microRNA sequencing results. In addition, the target gene prediction of the SHVV genome was performed for the differentially-expressed host miRNAs, and a total of 10 and 58 differentially-expressed miRNAs were predicted to bind to the SHVV genome at three and 24 h poi, respectively. The effects of three selected miRNAs (miR-130-5p, miR-214 and miR-216b) on SHVV multiplication were evaluated using their mimics and inhibitors via qRT-PCR and Western blotting. The results showed that all three miRNAs were able to inhibit the multiplication of SHVV; whereas the mechanisms underlying the SHVV multiplication inhibited by the specific miRNAs need to be further characterized in the future.

Characterization of the glycoproteins of bat-derived influenza viruses

Recently found bat-derived influenza viruses (BatIVs) have hemagglutinin (HA) and neuraminidase (NA) gene segments distinct from those of previously known influenza A viruses. However, pathogenicities of these BatIVs remain unknown since infectious virus strains have not been isolated yet. To gain insight into the biological properties of BatIVs, we generated vesicular stomatitis viruses (VSVs) pseudotyped with the BatIV HA and NA. We found that VSVs pseudotyped with BatIV HAs and NAs efficiently infected particular bat cell lines but not those derived from primates, and that proteolytic cleavage with a trypsin-like protease was necessary for HA-mediated virus entry. Treatment of the susceptible bat cells with some enzymes and inhibitors revealed that BatIV HAs might recognize some cellular glycoproteins as receptors rather than the sialic acids used for the other known influenza viruses. These data provide fundamental information on the mechanisms underlying the cellular entry and host restriction of BatIVs.