Effect of vesicular stomatitis virus matrix protein on transcription directed by host RNA polymerases I, II, and III

Phylogenetic and phylodynamic analysis of respiratory syncytial virus strains circulating in children less than five years of age in Karachi-Pakistan

BACKGROUND

Respiratory syncytial virus (RSV) is one of the leading causes of infant morbidity and mortality worldwide, especially in Pakistan. To date, few studies have explored RSV epidemiology in different areas of Pakistan. However, none have performed comprehensive phylogenetic and phylodynamic analyses of RSV strains. This study presents a comprehensive genetic and phylodynamic analysis of RSV strains in children less than five years old in Karachi, Pakistan.

METHODS

This study used retrospectively collected nasopharyngeal (swab) samples from 155 children with qPCR-confirmed RSV infection. The samples were used to perform RSV genotyping using PCR employing RSV glycoprotein gene-specific primers. The RSVA and RSVB genotyping was performed using BLAST and Maximum-likelihood (ML) phylogenetic methods. Similarly, the relationship with other RSV strains was analyzed using ML phylogenetic cluster analysis. The RSVA and RSVB mean genetic diversity and coefficient of differentiation were calculated using MEGA7 software. Furthermore, the time to the most common recent ancestor (tMRCA) and effective population size of RSV genotypes A and B were estimated using a Bayesian MCMC analysis. Finally, site selection pressure and glycosylation analyses were performed using FUBAR and NetNGlyc/NetOGlyc tools.

RESULTS

Out of 155, 98 and 57 sequences were RSVA and RSVB, respectively. The tMRCA was estimated to be around 2002 and 2005 for RSVA and RSVB, respectively. RSVA sequences formed two NA1 genotype clusters, comprising 95 and three sequences, respectively. RSVB formed three clusters, where 24 and two sequences clustered with BA9 and BA12 genotypes, respectively, while 31 sequences formed a unique cluster. The RSVA and RSVB glycoprotein gene sequences exhibited N- and O- glycosylation and selection pressure at several sites. RSV B exhibited slightly higher (0.042) nucleotide diversity per site (π) as compared to RSVA (0.019).

CONCLUSIONS

Our results suggest that RSVA and RSVB strains in Pakistan exhibit distinct genotypic clusters and differ in their estimated tMRCA. Additionally, both genotypes showed glycosylation and selection pressure at specific sites, with RSVB exhibiting higher nucleotide divergence per site (π), indicating its potential to undergo further evolutionary changes and adaptation. Overall, this study provides unique insights into RSV molecular epidemiology. The study may also help improve our understanding of RSV evolutionary changes and the emergence of new genotypes in different regions worldwide and within Pakistan.

Respiratory Syncytial Virus (RSV) optimizes the translational landscape during infection

Viral infection often triggers eukaryotic initiator factor 2α (eIF2α) phosphorylation, leading to global 5'-cap-dependent translation inhibition. RSV encodes messenger RNAs (mRNAs) mimicking 5'-cap structures of host mRNAs and thus inhibition of cap-dependent translation initiation would likely also reduce viral translation. We confirmed that RSV limits widespread translation initiation inhibition and unexpectedly found that the fraction of ribosomes within polysomes increases during infection, indicating higher ribosome loading on mRNAs during infection. We found that AU-rich host transcripts that are less efficiently translated under normal conditions become more efficient at recruiting ribosomes, similar to RSV transcripts. Viral transcripts are transcribed in cytoplasmic inclusion bodies, where the viral AU-rich binding protein M2-1 has been shown to bind viral transcripts and shuttle them into the cytoplasm. We further demonstrated that M2-1 is found on polysomes, and that M2-1 might deliver host AU-rich transcripts for translation.

Vesicular Stomatitis Virus Elicits Early Transcriptome Response in Culicoides sonorensis Cells

Viruses that are transmitted by arthropods, or arboviruses, have evolved to successfully navigate both the invertebrate and vertebrate hosts, including their immune systems. Biting midges transmit several arboviruses including vesicular stomatitis virus (VSV). To study the interaction between VSV and midges, we characterized the transcriptomic responses of VSV-infected and mock-infected Culicoides sonorensis cells at 1, 8, 24, and 96 h post inoculation (HPI). The transcriptomic response of VSV-infected cells at 1 HPI was significant, but by 8 HPI there were no detectable differences between the transcriptome profiles of VSV-infected and mock-infected cells. Several genes involved in immunity were upregulated (ATG2B and TRAF4) or downregulated (SMAD6 and TOLL7) in VSV-treated cells at 1 HPI. These results indicate that VSV infection in midge cells produces an early immune response that quickly wanes, giving insight into in vivo C. sonorensis VSV tolerance that may underlie their permissiveness as vectors for this virus.

Oncolytic viruses in hematological malignancies: hijacking disease biology and fostering new promises for immune and cell-based therapies

The increased tropism for malignant cells of some viruses has been highlighted in recent studies, prompting their use as a strategy to modify the transcriptional profile of those cells, while sparing the healthy ones. Likewise, they have been recognized as players modulating microenvironmental immunity, namely through an increase in antigen-presenting, natural-killer, and T CD8+ cytotoxic cells by a cross-priming mechanism elicited by tumor-associated antigens. The immunomodulatory role of the oncolytic virus seems relevant in hematological malignancies, which may relapse as a result of a proliferative burst elicited by an external stimulus in progenitor or neoplastic stem cells. By reprogramming the host cells and the surrounding environment, the potential of virotherapy ranges from the promise to eradicate the minimal measurable disease (in acute leukemia, for example), to the ex vivo purging of malignant progenitor cells in the setting of autologous bone marrow transplantation. In this review, we analyze the recent advances in virotherapy in hematological malignancies, either when administered alone or together with chemotherapeutic agents or other immunomodulators.

Cre-Dependent Anterograde Transsynaptic Labeling and Functional Imaging in Zebrafish Using VSV With Reduced Cytotoxicity

The small size and translucency of larval zebrafish (Danio rerio) have made it a unique experimental system to investigate whole-brain neural circuit structure and function. Still, the connectivity patterns between most neuronal types remain mostly unknown. This gap in knowledge underscores the critical need for effective neural circuit mapping tools, especially ones that can integrate structural and functional analyses. To address this, we previously developed a vesicular stomatitis virus (VSV) based approach called Tracer with Restricted Anterograde Spread (TRAS). TRAS utilizes lentivirus to complement replication-incompetent VSV (VSVΔG) to allow restricted (monosynaptic) anterograde labeling from projection neurons to their target cells in the brain. Here, we report the second generation of TRAS (TRAS-M51R), which utilizes a mutant variant of VSVΔG [VSV(M51R)ΔG] with reduced cytotoxicity. Within the primary visual pathway, we found that TRAS-M51R significantly improved long-term viability of transsynaptic labeling (compared to TRAS) while maintaining anterograde spread activity. By using Cre-expressing VSV(M51R)ΔG, TRAS-M51R could selectively label excitatory (vglut2a positive) and inhibitory (gad1b positive) retinorecipient neurons. We further show that these labeled excitatory and inhibitory retinorecipient neurons retained neuronal excitability upon visual stimulation at 5-8 days post fertilization (2-5 days post-infection). Together, these findings show that TRAS-M51R is suitable for neural circuit studies that integrate structural connectivity, cell-type identity, and neurophysiology.

Advances in viral oncolytics for treatment of multiple myeloma - a focused review

INTRODUCTION

Oncolytic viruses are genetically engineered viruses that target myeloma-affected cells by detecting specific cell surface receptors (CD46, CD138), causing cell death by activating the signaling pathway to induce apoptosis or by immune-mediated cellular destruction.

AREAS COVERED

This article summarizes oncolytic virotherapy advancements such as the therapeutic use of viruses by targeting cell surface proteins of myeloma cells as well as the carriers to deliver viruses to the target tissues safely. The major classes of viruses that have been studied for this include measles, myxoma, adenovirus, reovirus, vaccinia, vesicular-stomatitis virus, coxsackie, and others. The measles virus acts as oncolytic viral therapy by binding to the CD46 receptors on the myeloma cells to utilize its surface H protein. These H-protein and CD46 interactions lead to cellular syncytia formation resulting in cellular apoptosis. Vesicular-stomatitis virus acts by downregulation of anti-apoptotic factors (Mcl-2, BCL-2). Based upon the published literature searches till December 2020, we have summarized the data supporting the advances in viral oncolytic for the treatment of MM.

EXPERT OPINION

Oncolytic virotherapy is an experimental approach in multiple myeloma (MM); many issues need to be addressed for safe viral delivery to the target tissue.

Novirhabdoviruses versus fish innate immunity: A review

Novirhabdoviruses belong to the Rhabdoviridae family of RNA viruses. All of the four members are pathogenic for bony fish. Particularly, Infectious hematopoietic necrosis virus (IHNV) and Viral hemorrhagic septicemia virus (VHSV) often cause mass animal deaths and huge economic losses, representing major obstacles to fish farming industry worldwide. The interactions between fish and novirhabdoviruses are becoming better understood. In this review, we will present our current knowledge of fish innate immunity, particularly type I interferon (IFN-I) response, against novirhabdoviral infection, and the evasion strategies exploited by novirhabdoviruses. Members of Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs) appear to be involved in novirhabdovirus surveillance. NF-κB activation and IFN-I induction are primarily triggered for antiviral defense. Autophagy can also be induced by viral glycoprotein (G). Although sensitive to IFN-I, novirhabdoviruses have nucleoprotein (N), matrix protein (M), and non-virion protein (NV) to interfere with host signal transduction and gene expression steps toward antiviral state establishment. Moreover, novirhabdoviruses may exploit some microRNAs for immunosuppression.

Crosstalk between nucleocytoplasmic trafficking and the innate immune response to viral infection

The nuclear pore complex is the sole gateway connecting the nucleoplasm and cytoplasm. In humans, the nuclear pore complex is one of the largest multiprotein assemblies in the cell, with a molecular mass of ∼110 MDa and consisting of 8 to 64 copies of about 34 different nuclear pore proteins, termed nucleoporins, for a total of 1000 subunits per pore. Trafficking events across the nuclear pore are mediated by nuclear transport receptors and are highly regulated. The nuclear pore complex is also used by several RNA viruses and almost all DNA viruses to access the host cell nucleoplasm for replication. Viruses hijack the nuclear pore complex, and nuclear transport receptors, to access the nucleoplasm where they replicate. In addition, the nuclear pore complex is used by the cell innate immune system, a network of signal transduction pathways that coordinates the first response to foreign invaders, including viruses and other pathogens. Several branches of this response depend on dynamic signaling events that involve the nuclear translocation of downstream signal transducers. Mounting evidence has shown that these signaling cascades, especially those steps that involve nucleocytoplasmic trafficking events, are targeted by viruses so that they can evade the innate immune system. This review summarizes how nuclear pore proteins and nuclear transport receptors contribute to the innate immune response and highlights how viruses manipulate this cellular machinery to favor infection. A comprehensive understanding of nuclear pore proteins in antiviral innate immunity will likely contribute to the development of new antiviral therapeutic strategies.

TMT-based quantitative proteomics analysis reveals the attenuated replication mechanism of Newcastle disease virus caused by nuclear localization signal mutation in viral matrix protein

Nuclear localization of cytoplasmic RNA virus proteins mediated by intrinsic nuclear localization signal (NLS) plays essential roles in successful virus replication. We previously reported that NLS mutation in the matrix (M) protein obviously attenuates the replication and pathogenicity of Newcastle disease virus (NDV), but the attenuated replication mechanism remains unclear. In this study, we showed that M/NLS mutation not only disrupted M's nucleocytoplasmic trafficking characteristic but also impaired viral RNA synthesis and transcription. Using TMT-based quantitative proteomics analysis of BSR-T7/5 cells infected with the parental NDV rSS1GFP and the mutant NDV rSS1GFP-M/NLSm harboring M/NLS mutation, we found that rSS1GFP infection stimulated much greater quantities and more expression changes of differentially expressed proteins involved in host cell transcription, ribosomal structure, posttranslational modification, and intracellular trafficking than rSS1GFP-M/NLSm infection. Further in-depth analysis revealed that the dominant nuclear accumulation of M protein inhibited host cell transcription, RNA processing and modification, protein synthesis, posttranscriptional modification and transport; and this kind of inhibition could be weakened when most of M protein was confined outside the nucleus. More importantly, we found that the function of M protein in the cytoplasm effected the inhibition of TIFA expression in a dose-dependent manner, and promoted NDV replication by down-regulating TIFA/TRAF6/NF-κB-mediated production of cytokines. It was the first report about the involvement of M protein in NDV immune evasion. Taken together, our findings demonstrate that NDV replication is closely related to the nucleocytoplasmic trafficking of M protein, which accelerates our understanding of the molecular functions of NDV M protein.

Functional Dissection of the Dominant Role of CD55 in Protecting Vesicular Stomatitis Virus against Complement-Mediated Neutralization

The human complement system is an important part of the innate immune system. Its effector pathways largely mediate virus neutralization. Vesicular stomatitis virus (VSV) activates the classical pathway of the complement, leading to virus neutralization by lysis. Two host-derived membrane-associated regulators of complement activation (RCA), CD55 and CD46, which are incorporated into the VSV envelope during egress, confer protection by delaying/resisting complement-mediated neutralization. We showed previously that CD55 is more effective than CD46 in the inhibition of neutralization. In this study, we identified that, at the protein level, VSV infection resulted in the down-regulation of CD46 but not CD55. The mRNA of both the RCAs was significantly down-regulated by VSV, but it was delayed in the case of CD55. The immunoblot analysis of the levels of RCAs in the progeny virion harvested at three specific time intervals, points to an equal ratio of its distribution relative to viral proteins. Besides reconfirming the dominant role of CD55 over CD46 in shielding VSV from complement, our results also highlight the importance of the subtle modulation in the expression pattern of RCAs in a system naturally expressing them.

Oncolytic Viruses and Hematological Malignancies: A New Class of Immunotherapy Drugs

The use of viruses for tumour treatment has been imagined more than one hundred years ago, when it was reported that viral diseases were occasionally leading to a decrease in neoplastic lesions. Oncolytic viruses (OVs) seem to have a specific tropism for tumour cells. Previously, it was hypothesised that OVs’ antineoplastic actions were mainly due to their ability to contaminate, proliferate and destroy tumour cells and the immediate destructive effect on cells was believed to be the single mechanism of action of OVs’ action. Instead, it has been established that oncolytic viruses operate via a multiplicity of systems, including mutation of tumour milieu and a composite change of the activity of immune effectors. Oncolytic viruses redesign the tumour environment towards an antitumour milieu. The aim of our work is to evaluate the findings present in the literature about the use of OVs in the cure of haematological neoplastic pathologies such as multiple myeloma, acute and chronic myeloid leukaemia, and lymphoproliferative diseases. Further experimentations are essential to recognize the most efficient virus or treatment combinations for specific haematological diseases, and the combinations able to induce the strongest immune response.

Chicken bromodomain-containing protein 2 interacts with the Newcastle disease virus matrix protein and promotes viral replication

Bromodomain-containing protein 2 (BRD2) is a nucleus-localized serine-threonine kinase that plays pivotal roles in the transcriptional control of diverse genes. In our previous study, the chicken BRD2 (chBRD2) protein was found to interact with the Newcastle disease virus (NDV) matrix (M) protein using a yeast two-hybrid screening system, but the role of the chBRD2 protein in the replication of NDV remains unclear. In this study, we first confirmed the interaction between the M protein and chBRD2 protein using fluorescence co-localization, co-immunoprecipitation and pull-down assays. Intracellular binding studies indicated that the C-terminus (aa 264-313) of the M protein and the extra-terminal (ET) domain (aa 619-683) of the chBRD2 protein were responsible for interactions with each other. Interestingly, although two amino acids (T621 and S649) found in the chBRD2/ET domain were different from those in the human BRD2/ET domain and in that of other mammals, they did not disrupt the BRD2-M interaction or the chBRD2-M interaction. In addition, we found that the transcription of the chBRD2 gene was obviously decreased in both NDV-infected cells and pEGFP-M-transfected cells in a dose-dependent manner. Moreover, small interfering RNA-mediated knockdown of chBRD2 or overexpression of chBRD2 remarkably enhanced or reduced NDV replication by upregulating or downregulating viral RNA synthesis and transcription, respectively. Overall, we demonstrate for the first time that the interaction of the M protein with the chBRD2 protein in the nucleus promotes NDV replication by downregulating chBRD2 expression and facilitating viral RNA synthesis and transcription. These results will provide further insight into the biological functions of the M protein in the replication of NDV.

MAP3K7 and CHD1 Are Novel Mediators of Resistance to Oncolytic Vesicular Stomatitis Virus in Prostate Cancer Cells

A key principle of oncolytic viral therapy is that many cancers develop defects in their antiviral responses, making them more susceptible to virus infection. However, some cancers display resistance to viral infection. Many of these resistant cancers constitutively express interferon-stimulated genes (ISGs). The goal of these experiments was to determine the role of two tumor suppressor genes, MAP3K7 and CHD1, in viral resistance and ISG expression in PC3 prostate cancer cells resistant to oncolytic vesicular stomatitis virus (VSV). MAP3K7 and CHD1 are often co-deleted in aggressive prostate cancers. Silencing expression of MAP3K7 and CHD1 in PC3 cells increased susceptibility to the matrix (M) gene mutant M51R-VSV, as shown by increased expression of viral genes, increased yield of progeny virus, and reduction of tumor growth in nude mice. Silencing MAP3K7 alone had a greater effect on virus susceptibility than did silencing CHD1. Silencing MAP3K7 and CHD1 decreased constitutive expression of ISG mRNAs and proteins, whereas silencing MAP3K7 alone decreased expression of ISG proteins, but actually increased expression of ISG mRNAs. These results suggest a role for the protein product of MAP3K7, transforming growth factor β-activated kinase 1 (TAK1), in regulating translation of ISG mRNAs and a role of CHD1 in maintaining the transcription of ISGs.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

RNA decay during gammaherpesvirus infection reduces RNA polymerase II occupancy of host promoters but spares viral promoters

In mammalian cells, widespread acceleration of cytoplasmic mRNA degradation is linked to impaired RNA polymerase II (Pol II) transcription. This mRNA decay-induced transcriptional repression occurs during infection with gammaherpesviruses including Kaposi’s sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68), which encode an mRNA endonuclease that initiates widespread RNA decay. Here, we show that MHV68-induced mRNA decay leads to a genome-wide reduction of Pol II occupancy at mammalian promoters. This reduced Pol II occupancy is accompanied by down-regulation of multiple Pol II subunits and TFIIB in the nucleus of infected cells, as revealed by mass spectrometry-based global measurements of protein abundance. Viral genes, despite the fact that they require Pol II for transcription, escape transcriptional repression. Protection is not governed by viral promoter sequences; instead, location on the viral genome is both necessary and sufficient to escape the transcriptional repression effects of mRNA decay. We propose a model in which the ability to escape from transcriptional repression is linked to the localization of viral DNA within replication compartments, providing a means for these viruses to counteract decay-induced transcript loss.

While transcription and messenger RNA (mRNA) decay are often considered to be the unlinked beginning and end of gene expression, recent data indicate that alterations to either stage can impact the other. Here we study this connection in the context of lytic gammaherpesvirus infection, which accelerates mRNA degradation through the expression of the viral endonuclease muSOX. We show that RNA polymerase II promoter occupancy is broadly reduced across mammalian promoters in response to infection-induced mRNA decay, and that this phenotype correlates with a reduction in the abundance of several proteins involved in transcription. Notably, gammaherpesviral promoters are resistant to the ensuing transcriptional repression. We show that viral transcriptional escape is conferred by localization of the viral DNA within the protective environment of replication compartments, which are sites of viral genome replication and transcription during infection. Collectively, these findings clarify how mRNA degradation by gammaherpesviruses reshapes the cellular environment and selectively dampens host gene transcription.

Structural Neural Connectivity Analysis in Zebrafish With Restricted Anterograde Transneuronal Viral Labeling and Quantitative Brain Mapping

The unique combination of small size, translucency, and powerful genetic tools makes larval zebrafish a uniquely useful vertebrate system to investigate normal and pathological brain structure and function. While functional connectivity can now be assessed by optical imaging (via fluorescent calcium or voltage reporters) at the whole-brain scale, it remains challenging to systematically determine structural connections and identify connectivity changes during development or disease. To address this, we developed Tracer with Restricted Anterograde Spread (TRAS), a novel vesicular stomatitis virus (VSV)-based neural circuit labeling approach. TRAS makes use of replication-incompetent VSV (VSVΔG) and a helper virus (lentivirus) to enable anterograde transneuronal spread between efferent axons and their direct postsynaptic targets but restricts further spread to downstream areas. We integrated TRAS with the Z-Brain zebrafish 3D atlas for quantitative connectivity analysis and identified targets of the retinal and habenular efferent projections, in patterns consistent with previous reports. We compared retinofugal connectivity patterns between wild-type and down syndrome cell adhesion molecule-like 1 (dscaml1) mutant zebrafish and revealed differences in topographical distribution. These results demonstrate the utility of TRAS for quantitative structural connectivity analysis that would be valuable for detecting novel efferent targets and mapping connectivity changes underlying neurological or behavioral deficits.

Global analysis of polysome-associated mRNA in vesicular stomatitis virus infected cells

Infection of mammalian cells with vesicular stomatitis virus (VSV) results in the inhibition of cellular translation while viral translation proceeds efficiently. VSV RNA synthesis occurs entirely within the cytoplasm, where during transcription the viral polymerase produces 5 mRNAs that are structurally indistinct to cellular mRNAs with respect to their 5′ cap-structure and 3′-polyadenylate tail. Using the global approach of massively parallel sequencing of total cytoplasmic, monosome- and polysome-associated mRNA, we interrogate the impact of VSV infection of HeLa cells on translation. Analysis of sequence reads in the different fractions shows >60% of total cytoplasmic and polysome-associated reads map to the 5 viral genes by 6 hours post-infection, a time point at which robust host cell translational shut-off is observed. Consistent with an overwhelming abundance of viral mRNA in the polysome fraction, the reads mapping to cellular genes were reduced. The cellular mRNAs that remain most polysome-associated following infection had longer half-lives, were typically larger, and were more AU rich, features that are shared with the viral mRNAs. Several of those mRNAs encode proteins known to positively affect viral replication, and using chemical inhibition and siRNA depletion we confirm that the host chaperone heat shock protein 90 (hsp90) and eukaryotic translation initiation factor 3A (eIF3A)—encoded by 2 such mRNAs—support viral replication. Correspondingly, regulated in development and DNA damage 1 (Redd1) encoded by a host mRNA with reduced polysome association inhibits viral infection. These data underscore the importance of viral mRNA abundance in the shut-off of host translation in VSV infected cells and link the differential translatability of some cellular mRNAs with pro- or antiviral function.

Viruses co-opt the host translational machinery and frequently suppress host cell protein synthesis. Many positive-strand RNA viruses manipulate initiation factors while bypassing their need for viral protein production using internal ribosome entry sites. Negative-strand RNA viruses and DNA viruses produce mRNAs that contain host-like 5′ cap-structures and 3′ polyadenylate tails. Those similarities necessitate a different mechanism for controlling viral versus host protein synthesis. We infected cells with vesicular stomatitis virus and sequenced polysome-associated mRNAs at 2 and 6 hours post-infection providing 2 snapshots of how infection alters translation. We present evidence that the 5 viral mRNAs outcompete cellular mRNAs for ribosomes and demonstrate that individual host mRNAs vary in the extent to which their polysome association is altered by infection. Host mRNAs that are more abundant, have longer half-lives, greater than average length, and a similar AU content to the viral mRNAs were more likely to be enriched among polysome-associated cellular mRNAs. Several of the enriched mRNAs encode proteins that promote viral replication, whereas mRNAs that exhibit the largest decrease in polysome association include those that encode antiviral functions.

Nuclear localization of Newcastle disease virus matrix protein promotes virus replication by affecting viral RNA synthesis and transcription and inhibiting host cell transcription

Nuclear localization of paramyxovirus proteins is crucial for virus life cycle, including the regulation of viral replication and the evasion of host immunity. We previously showed that a recombinant Newcastle disease virus (NDV) with nuclear localization signal mutation in the matrix (M) protein results in a pathotype change and attenuates viral pathogenicity in chickens. However, little is known about the nuclear localization functions of NDV M protein. In this study, the potential functions of the M protein in the nucleus were investigated. We first demonstrate that nuclear localization of the M protein could not only promote the cytopathogenicity of NDV but also increase viral RNA synthesis and transcription efficiency in DF-1 cells. Using microarray analysis, we found that nuclear localization of the M protein might inhibit host cell transcription, represented by numerous up-regulating genes associated with transcriptional repressor activity and down-regulating genes associated with transcriptional activator activity. The role of representative up-regulated gene prospero homeobox 1 (PROX1) and down-regulated gene aryl hydrocarbon receptor (AHR) in the replication of NDV was then evaluated. The results show that siRNA-mediated knockdown of PROX1 or AHR significantly reduced or increased the viral RNA synthesis and viral replication, respectively, demonstrating the important roles of the expression changes of these genes in NDV replication. Together, our findings demonstrate for the first time that nuclear localization of NDV M protein promotes virus replication by affecting viral RNA synthesis and transcription and inhibiting host cell transcription, improving our understanding of the molecular mechanism of NDV replication and pathogenesis.

Sec13 is a positive regulator of VISA-mediated antiviral signaling

Viral infection triggers the innate antiviral immune response that rapidly produces type I interferons in most cell types to combat viruses invading. Upon viral infection, the cytoplasmic RNA sensors RIG-I/MDA5 recognize viral RNA, and then RIG-I/MDA5 is transported to mitochondria interacting with VISA through the CARD domain. From there, VISA recruits downstream antiviral signaling pathways molecules, such as TRAFs and TBK1. Eventually, IRF3 is phosphorylated and type I IFNs are induced to fight as the first line of defense against viruses. However, it remains unclear how VISA acts as a scaffold to assemble the signalosome in RIG-I-mediated antiviral signaling. Here, we demonstrated Sec13 as a novel component that was involved in VISA-mediated antiviral signaling pathway. The co-immunoprecipitation assays showed that Sec13 specifically interacts with VISA. Overexpression of Sec13 increases VISA's aggregation and ubiquitination and significantly enhances the phosphorylation and dimerization of IRF3, facilitating the IFN-β production. Conversely, the knockdown of Sec13 attenuates Sendai virus-induced and VISA-mediated IRF3 activation and the production of IFNβ, thus weakens antiviral immune activity.

Porcine monocyte-derived dendritic cells can be differentially activated by vesicular stomatitis virus and its matrix protein mutants

Vesicular stomatitis virus (VSV) can cause serious vesicular lesions in pigs, and the matrix (M) protein is its predominant virulence factor. Dendritic cells (DCs) act as the bridge between innate and adaptive immune responses. However, the susceptibility of porcine DCs to VSV infection and the role of M protein in modulating the function of infected DCs are still poorly defined. Thus, this study aimed to determine the ability of virulent wild-type VSV(wtVSV) and two attenuated M protein variants (VSV_ΔM51 and VSV_MT) to induce maturation of porcine monocyte-derived DCs (MoDCs) in vitro. It was found that both wtVSV and the M protein mutant VSVs could productively replicate in porcine MoDCs. Infection with wtVSV resulted in weak proinflammatory cytokine responses and interfered with DC maturation via downregulation of the costimulatory molecule complex CD80/86. Whilst VSV_ΔM51 could activate porcine MoDCs, VSV_MT, a highly attenuated recombinant VSV with triple mutations in the M protein, induced a potent maturation of MoDCs, as evidenced by efficient cytokine induction, and upregulation of CD80/86 and MHC class II. Overall, our findings reveal that porcine MoDCs are differentially activated by VSV, dependent on the presence of a functional M protein. M protein plays a crucial role in modulating porcine DC-VSV interactions. The data further support the potential use of VSV_MT as a vaccine vector for pigs.

Oncotargeting by Vesicular Stomatitis Virus (VSV): Advances in Cancer Therapy

Modern oncotherapy approaches are based on inducing controlled apoptosis in tumor cells. Although a number of apoptosis-induction approaches are available, site-specific delivery of therapeutic agents still remain the biggest hurdle in achieving the desired cancer treatment benefit. Additionally, systemic treatment-induced toxicity remains a major limiting factor in chemotherapy. To specifically address drug-accessibility and chemotherapy side effects, oncolytic virotherapy (OV) has emerged as a novel cancer treatment alternative. In OV, recombinant viruses with higher replication capacity and stronger lytic properties are being considered for tumor cell-targeting and subsequent cell lysing. Successful application of OVs lies in achieving strict tumor-specific tropism called oncotropism, which is contingent upon the biophysical interactions of tumor cell surface receptors with viral receptors and subsequent replication of oncolytic viruses in cancer cells. In this direction, few viral vector platforms have been developed and some of these have entered pre-clinical/clinical trials. Among these, the Vesicular stomatitis virus (VSV)-based platform shows high promise, as it is not pathogenic to humans. Further, modern molecular biology techniques such as reverse genetics tools have favorably advanced this field by creating efficient recombinant VSVs for OV; some have entered into clinical trials. In this review, we discuss the current status of VSV based oncotherapy, challenges, and future perspectives regarding its therapeutic applications in the cancer treatment.

Role of Viral Hemorrhagic Septicemia Virus Matrix (M) Protein in Suppressing Host Transcription

Viral hemorrhagic septicemia virus (VHSV) is a pathogenic fish rhabdovirus found in discrete locales throughout the Northern Hemisphere. VHSV infection of fish cells leads to upregulation of the host's virus detection response, but the virus quickly suppresses interferon (IFN) production and antiviral gene expression. By systematically screening each of the six VHSV structural and nonstructural genes, we identified matrix protein (M) as the virus' most potent antihost protein. Only M of VHSV genotype IV sublineage b (VHSV-IVb) suppressed mitochondrial antiviral signaling protein (MAVS) and type I IFN-induced gene expression in a dose-dependent manner. M also suppressed the constitutively active simian virus 40 (SV40) promoter and globally decreased cellular RNA levels. Chromatin immunoprecipitation (ChIP) studies illustrated that M inhibited RNA polymerase II (RNAP II) recruitment to gene promoters and decreased RNAP II C-terminal domain (CTD) Ser2 phosphorylation during VHSV infection. However, transcription directed by RNAP I to III was suppressed by M. To identify regions of functional importance, M proteins from a variety of VHSV strains were tested in cell-based transcriptional inhibition assays. M of a particular VHSV-Ia strain, F1, was significantly less potent than IVb M at inhibiting SV40/luciferase (Luc) expression yet differed by just 4 amino acids. Mutation of D62 to alanine alone, or in combination with an E181-to-alanine mutation (D62A E181A), dramatically reduced the ability of IVb M to suppress host transcription. Introducing either M D62A or D62A E181A mutations into VHSV-IVb via reverse genetics resulted in viruses that replicated efficiently but exhibited less cytotoxicity and reduced antitranscriptional activities, implicating M as a primary regulator of cytopathicity and host transcriptional suppression.IMPORTANCE Viruses must suppress host antiviral responses to replicate and spread between hosts. In these studies, we identified the matrix protein of the deadly fish novirhabdovirus VHSV as a critical mediator of host suppression during infection. Our studies indicated that M alone could block cellular gene expression at very low expression levels. We identified several subtle mutations in M that were less potent at suppressing host transcription. When these mutations were engineered back into recombinant viruses, the resulting viruses replicated well but elicited less toxicity in infected cells and activated host innate immune responses more robustly. These data demonstrated that VHSV M plays an important role in mediating both virus-induced cell toxicity and viral replication. Our data suggest that its roles in these two processes can be separated to design effective attenuated viruses for vaccine candidates.

Measles Virus Matrix Protein Inhibits Host Cell Transcription

Measles virus (MeV) is a highly contagious virus that still causes annual epidemics in developing countries despite the availability of a safe and effective vaccine. Additionally, importation from endemic countries causes frequent outbreaks in countries where it has been eliminated. The M protein of MeV plays a key role in virus assembly and cytopathogenesis; interestingly, M is localised in nucleus, cytoplasm and membranes of infected cells. We have used transient expression of M in transfected cells and in-cell transcription assays to show that only some MeV M localizes to the nucleus, in addition to cell membranes and the cytoplasm as previously described, and can inhibit cellular transcription via binding to nuclear factors. Additionally, MeV M was able to inhibit in vitro transcription in a dose-dependent manner. Importantly, a proportion of M is also localized to nucleus of MeV infected cells at early times in infection, correlating with inhibition of cellular transcription. Our data show, for the first time, that MeV M may play a role early in infection by inhibiting host cell transcription.

VEGF-D-enhanced lymph node metastasis of ovarian cancer is reversed by vesicular stomatitis virus matrix protein

Lymphatic metastasis is a poor prognostic factor in ovarian cancer, which correlates to the majority of cancer deaths. Matrix protein (MP) of vesicular stomatitis virus (VSV) exhibits potent antitumor and antiangiogenic activities through inducing apoptosis and inhibiting angiogenesis. In this study, the antitumor and antimetastatic effects of MP were further investigated. Wild-type SKOV3 (WT-SK) cells were successfully transfected with empty vector pcDNA3.1 plasmid, or pcDNA3.1-VEGF-D recombinant plasmid to construct cell lines named EV-SK, and VEGFD-SK, respectively. Inhibition of VEGFD-SK cell migration and invasion was detected by Transwell and wound healing assay. Then, lymphogenous metastatic model of ovarian cancer was established by injecting VEGFD-SK cells subcutaneously into the left hindlimb claw pad of nude mice. The inducted apoptotic effect of MP on VEGFD-SK cells were assessed by flow analysis and Hoechst-33258 staining, respectively, in vitro. The in vivo antitumor and antiangiogenic activities of MP gene were evaluated with lymphogenous metastatic model of ovarian cancer. Tumor volume and lymphatic metastasis rates were measured. Lymphatic vessels were delineated using Evan's blue and LYVE-1 staining. Expression of VEGF-D and MMP-2 were evaluated by immunostaining. Apoptosis of tumor cells was analyzed by Hoechst-33258 staining. Mice bearing VEGFD-SK tumor cells displayed more rapid tumorigenesis, higher lymphogenous metastatic tendency and increased lymphatic vessel density compared with the mice bearing WT-SK or EV-SK cells. However, VEGF-D-enhanced metastasis was evidently reversed by MP. MP significantly reduced the invasion of VEGFD-SK cells, tumor volume, lymphatic metastasis rates and lymphatic vessel density compared with control groups (P<0.05), accompanied with down-expression of VEGF-D and MMP-2 and increased apoptosis. Our data indicate that MP has strong antitumor and antimetastatic abilities, and it may be a promising therapeutic strategy against the lymphatic metastasis of human ovarian cancer.

Impact of Vesicular Stomatitis Virus M Proteins on Different Cellular Functions

Three different matrix (M) proteins termed M1, M2 and M3 have been described in cells infected with vesicular stomatitis virus (VSV). Individual expression of VSV M proteins induces an evident cytopathic effect including cell rounding and detachment, in addition to a partial inhibition of cellular protein synthesis, likely mediated by an indirect mechanism. Analogous to viroporins, M1 promotes the budding of new virus particles; however, this process does not produce an increase in plasma membrane permeability. In contrast to M1, M2 and M3 neither interact with the cellular membrane nor promote the budding of double membrane vesicles at the cell surface. Nonetheless, all three species of M protein interfere with the transport of cellular mRNAs from the nucleus to the cytoplasm and also modulate the redistribution of the splicing factor. The present findings indicate that all three VSV M proteins share some activities that interfere with host cell functions.

Nucleocytoplasmic transport of nucleocapsid proteins of enveloped RNA viruses

Most viruses with non-segmented single stranded RNA genomes complete their life cycle in the cytoplasm of infected cells. However, despite undergoing replication in the cytoplasm, the structural proteins of some of these RNA viruses localize to the nucleus at specific times in the virus life cycle, primarily early in infection. Limited evidence suggests that this enhances successful viral replication by interfering with or inhibiting the host antiviral response. Nucleocapsid proteins of RNA viruses have a well-established, essential cytoplasmic role in virus replication and assembly. Intriguingly, nucleocapsid proteins of some RNA viruses also localize to the nucleus/nucleolus of infected cells. Their nuclear function is less well understood although significant advances have been made in recent years. This review will focus on the nucleocapsid protein of cytoplasmic enveloped RNA viruses, including their localization to the nucleus/nucleolus and function therein. A greater understanding of the nuclear localization of nucleocapsid proteins has the potential to enhance therapeutic strategies as it can be a target for the development of live-attenuated vaccines or antiviral drugs.

ANP32B is a nuclear target of henipavirus M proteins

Membrane envelopment and budding of negative strand RNA viruses (NSVs) is mainly driven by viral matrix proteins (M). In addition, several M proteins are also known to be involved in host cell manipulation. Knowledge about the cellular targets and detailed molecular mechanisms, however, is poor for many M proteins. For instance, Nipah Virus (NiV) M protein trafficking through the nucleus is essential for virus release, but nuclear targets of NiV M remain unknown. To identify cellular interactors of henipavirus M proteins, tagged Hendra Virus (HeV) M proteins were expressed and M-containing protein complexes were isolated and analysed. Presence of acidic leucine-rich nuclear phosphoprotein 32 family member B (ANP32B) in the complex suggested that this protein represents a direct or indirect interactor of the viral matrix protein. Over-expression of ANP32B led to specific nuclear accumulation of HeV M, providing a functional link between ANP32B and M protein. ANP32B-dependent nuclear accumulation was observed after plasmid-driven expression of HeV and NiV matrix proteins and also in NiV infected cells. The latter indicated that an interaction of henipavirus M protein with ANP32B also occurs in the context of virus replication. From these data we conclude that ANP32B is a nuclear target of henipavirus M that may contribute to virus replication. Potential effects of ANP32B on HeV nuclear shuttling and host cell manipulation by HeV M affecting ANP32B functions in host cell survival and gene expression regulation are discussed.

A quantitative infection assay for human type I, II, and III interferon antiviral activities

Background

Upon virus infection, cells secrete a diverse group of antiviral molecules that signal proximal cells to enter into an antiviral state, slowing or preventing viral spread. These paracrine signaling molecules can work synergistically, so measurement of any one antiviral molecule does not reflect the total antiviral activity of the system.

Results

We have developed an antiviral assay based on replication inhibition of an engineered fluorescent vesicular stomatitis virus reporter strain on A549 human lung epithelial cells. Our assay provides a quantitative functional readout of human type I, II, and III interferon activities, and it provides better sensitivity, intra-, and inter-assay reproducibility than the traditional crystal violet based assay. Further, it eliminates cell fixation, rinsing, and staining steps, and is inexpensive to implement.

Conclusions

A dsRed2-strain of vesicular stomatitis virus that is sensitive to type I, II, and III interferons was used to develop a convenient and sensitive assay for interferon antiviral activity. We demonstrate use of the assay to quantify the kinetics of paracrine antiviral signaling from human prostate cancer (PC3) cells in response to viral infection. The assay is applicable to high-throughput screening for anti-viral compounds as well as basic studies of cellular antiviral signaling.

High-throughput virtual screening and docking studies of matrix protein vp40 of ebola virus

Ebolavirus, a member of the Filoviridae family of negative-sense RNA viruses, causes severe haemorrhagic fever leading up to 90% lethality. Ebolavirus matrix protein VP40 is involved in the virus assembly and budding process. The RNA binding pocket of VP40 is considered as the drug target site for structure based drug design. High Throughput Virtual Screening and molecular docking studies were employed to find the suitable inhibitors against VP40. Ten compounds showing good glide score and glide energy as well as interaction with specific amino acid residues were short listed as drug leads. These small molecule inhibitors could be potent inhibitors for VP40 matrix protein by blocking virus assembly and budding process.

Matrix protein of vesicular stomatitis virus: a potent inhibitor of vascular endothelial growth factor and malignant ascites formation

Malignant ascites is common in various types of cancers and is difficult to manage. Vascular endothelial growth factor (VEGF) has a pivotal role in malignant ascites. The matrix protein of vesicular stomatitis virus (VSVMP) has been shown to inhibit host gene expression and induce the apoptosis of cancer cells. The present study was designed to determine whether VSVMP suppresses the formation of ascites in ascites-producing peritoneal carcinomatosis. BALB/c female mice, 6-8 weeks old, bearing peritoneal tumors of H22 or MethA cells received an intraperitoneal administration of 50 μg VSVMP/250 μg liposome complexes, 50 μg empty plasmid/250 μg liposome complexes or 0.9% NaCl solution, respectively, every 2 days for 3 weeks. Administration of VSVMP resulted in a significant inhibition in ascites formation, improvement in health condition and prolonged survival of the treated mice. Decreased peritoneum osmolarity and reduced tumor vascularity coincided with dramatic reductions in the VEGF level in ascites fluid and plasma. Examination of floating tumor cells collected from the peritoneal wash revealed an apparently increased number of apoptotic cells and profound downregulation of VEGF mRNA in the VSVMP-treated mice. Our data indicate for the first time that in BALB/c mice bearing H22 or MethA cell peritoneal tumors, VSVMP may inhibit VEGF production and suppress angiogenesis, consequently abolishing ascites formation.

[Vesicular stomatitis virus in the fight against cancer]

Cancer is a complex disease that affects more and more people around the world. Unfortunately, existing treatments are only partially efficient and often induce major side effects. Thus, the use of viruses to selectively kill cancer cells is a new promising therapeutic approach. Recently, VSV has been used in oncolytic virotherapy because of its capacity to preferentially infect most human tumor cells. However, despite the availability of good oncolytic VSV mutants, the large variability of tumor cell types and the multiple ways in which they can evade viral infection suggests that therapeutic combinations of various viruses will be necessary to efficiently treat most cancers. A better understanding of the infection mechanisms and immune system recruitment by oncolytic viruses will be of great value for the development of safe and efficient strategies for cancer treatment.

Vesicular stomatitis virus with the rabies virus glycoprotein directs retrograde transsynaptic transport among neurons in vivo

Defining the connections among neurons is critical to our understanding of the structure and function of the nervous system. Recombinant viruses engineered to transmit across synapses provide a powerful approach for the dissection of neuronal circuitry in vivo. We recently demonstrated that recombinant vesicular stomatitis virus (VSV) can be endowed with anterograde or retrograde transsynaptic tracing ability by providing the virus with different glycoproteins. Here we extend the characterization of the transmission and gene expression of recombinant VSV (rVSV) with the rabies virus glycoprotein (RABV-G), and provide examples of its activity relative to the anterograde transsynaptic tracer form of rVSV. rVSV with RABV-G was found to drive strong expression of transgenes and to spread rapidly from neuron to neuron in only a retrograde manner. Depending upon how the RABV-G was delivered, VSV served as a polysynaptic or monosynaptic tracer, or was able to define projections through axonal uptake and retrograde transport. In animals co-infected with rVSV in its anterograde form, rVSV with RABV-G could be used to begin to characterize the similarities and differences in connections to different areas. rVSV with RABV-G provides a flexible, rapid, and versatile tracing tool that complements the previously described VSV-based anterograde transsynaptic tracer.

A ribosome-specialized translation initiation pathway is required for cap-dependent translation of vesicular stomatitis virus mRNAs

Initiation is the primary target of translational control for all organisms. Regulation of eukaryotic translation is traditionally thought to occur through initiation factors and RNA structures. Here, we characterize a transcript-specific translation initiation mechanism that is mediated by the ribosome. By studying vesicular stomatitis virus (VSV), we identify the large ribosomal subunit protein rpL40 as requisite for VSV cap-dependent translation but not bulk cellular or internal ribosome entry site-driven translation. This requirement is conserved among members of the order Mononegavirales, including measles virus and rabies virus. Polysome analyses and in vitro reconstitution of initiation demonstrate that rpL40 is required for 80S formation on VSV mRNAs through a cis-regulatory element. Using deep sequencing, we further uncover a subset of cellular transcripts that are selectively sensitive to rpL40 depletion, suggesting VSV may have usurped an endogenous translation pathway. Together, these findings demonstrate that the ribosome acts as a translational regulator outside of its catalytic role during protein synthesis.

Chandipura Virus: an emerging tropical pathogen

Chandipura Virus (CHPV), a member of Rhabdoviridae, is responsible for an explosive outbreak in rural areas of India. It affects mostly children and is characterized by influenza-like illness and neurologic dysfunctions. It is transmitted by vectors such as mosquitoes, ticks and sand flies. An effective real-time one step reverse-transcriptase PCR assay method is adopted for diagnosis of this virus. CHPV has a negative sense RNA genome encoding five different proteins (N, P, M, G, and L). P protein plays a vital role in the virus's life cycle, while M protein is lethal in nature. There is no specific treatment available to date, symptomatic treatment involves use of mannitol to reduce brain edema. A Vero cell based vaccine candidate against CHPV was evaluated efficiently as a preventive agent against it. Prevention is the best method to suppress CHPV infection. Containment of disease transmitting vectors, maintaining good nutrition, health, hygiene and awareness in rural areas will help in curbing the menace of CHPV. Thus, to control virus transmission some immense preventive measures need to be attempted until a good anti-CHPV agent is developed.

Complexes of vesicular stomatitis virus matrix protein with host Rae1 and Nup98 involved in inhibition of host transcription

Vesicular stomatitis virus (VSV) suppresses antiviral responses in infected cells by inhibiting host gene expression at multiple levels, including transcription, nuclear cytoplasmic transport, and translation. The inhibition of host gene expression is due to the activity of the viral matrix (M) protein. Previous studies have shown that M protein interacts with host proteins Rae1 and Nup98 that have been implicated in regulating nuclear-cytoplasmic transport. However, Rae1 function is not essential for host mRNA transport, raising the question of how interaction of a viral protein with a host protein that is not essential for gene expression causes a global inhibition at multiple levels. We tested the hypothesis that there may be multiple M protein-Rae1 complexes involved in inhibiting host gene expression at multiple levels. Using size exclusion chromatography and sedimentation velocity analysis, it was determined that Rae1 exists in high, intermediate, and low molecular weight complexes. The intermediate molecular weight complexes containing Nup98 interacted most efficiently with M protein. The low molecular weight form also interacted with M protein in cells that overexpress Rae1 or cells in which Nup98 expression was silenced. Silencing Rae1 expression had little if any effect on nuclear accumulation of host mRNA in VSV-infected cells, nor did it affect VSV's ability to inhibit host translation. Instead, silencing Rae1 expression reduced the ability of VSV to inhibit host transcription. M protein interacted efficiently with Rae1-Nup98 complexes associated with the chromatin fraction of host nuclei, consistent with an effect on host transcription. These results support the idea that M protein-Rae1 complexes serve as platforms to promote the interaction of M protein with other factors involved in host transcription. They also support the idea that Rae1-Nup98 complexes play a previously under-appreciated role in regulation of transcription.

All viruses have mechanisms to suppress or evade host antiviral responses. These mechanisms are critical for viral pathogenicity. Vesicular stomatitis virus (VSV) suppresses antiviral responses by global inhibition of host gene expression mediated by the viral matrix (M) protein. M protein interacts with the host protein Rae1 in a complex with the nucleoporin Nup98. It had been thought that interaction of M protein with Rae1 blocks nuclear-cytoplasmic mRNA transport. However, other data show that Rae1 is not essential for mRNA transport. With this discrepancy in mind, we re-examined the interaction of M protein with Rae1 and Nup98 and the level of host gene expression in which they are involved. A key result was that silencing Rae1 expression did not affect host gene expression, but instead increased cellular resistance to inhibition by M protein. Furthermore, silencing Rae1 expression primarily affected the inhibition of host transcription with no significant effect on nuclear accumulation of mRNA. These results support a model in which Rae1 serves as a “platform” to promote interaction of M protein with cellular targets involved in host transcription. This illustrates a general principle that viral proteins can have multiple cellular effects by interacting with host proteins that are themselves multi-functional.

Cytopathogenesis of vesicular stomatitis virus is regulated by the PSAP motif of M protein in a species-dependent manner

Vesicular stomatitis virus (VSV) is an important vector-borne pathogen of bovine and equine species, causing a reportable vesicular disease. The matrix (M) protein of VSV is multifunctional and plays a key role in cytopathogenesis, apoptosis, host protein shut-off, and virion assembly/budding. Our previous findings indicated that mutations of residues flanking the ₃₇PSAP₄₀ motif within the M protein resulted in VSV recombinants having attenuated phenotypes in mice. In this report, we characterize the phenotype of VSV recombinant PS > A4 (which harbors four alanines (AAAA) in place of the PSAP motif without disruption of flanking residues) in both mice, and in Aedes albopictus C6/36 mosquito and Culicoides sonorensis KC cell lines. The PS > A4 recombinant displayed an attenuated phenotype in infected mice as judged by weight loss, mortality, and viral titers measured from lung and brain samples of infected animals. However, unexpectedly, the PS > A4 recombinant displayed a robust cytopathic phenotype in insect C6/36 cells compared to that observed with control viruses. Notably, titers of recombinant PS > A4 were approximately 10-fold greater than those of control viruses in infected C6/36 cells and in KC cells from Culicoides sonorensis, a known VSV vector species. In addition, recombinant PS > A4 induced a 25-fold increase in the level of C3 caspase activity in infected C6/36 cells. These findings indicate that the PSAP motif plays a direct role in regulating cytopathogenicity in a species-dependent manner, and suggest that the intact PSAP motif may be important for maintaining persistence of VSV in an insect host.

Immunity to fish rhabdoviruses

Members of the family Rhabdoviridae are single-stranded RNA viruses and globally important pathogens of wild and cultured fish and thus relatively well studied in their respective hosts or other model systems. Here, we review the protective immune mechanisms that fish mount in response to rhabdovirus infections. Teleost fish possess the principal components of innate and adaptive immunity found in other vertebrates. Neutralizing antibodies are critical for long-term protection from fish rhabdoviruses, but several studies also indicate a role for cell-mediated immunity. Survival of acute rhabdoviral infection is also dependent on innate immunity, particularly the interferon (IFN) system that is rapidly induced in response to infection. Paradoxically, rhabdoviruses are sensitive to the effects of IFN but virulent rhabdoviruses can continue to replicate owing to the abilities of the matrix (M) protein to mediate host-cell shutoff and the non‑virion (NV) protein to subvert programmed cell death and suppress functional IFN. While many basic features of the fish immune response to rhabdovirus infections are becoming better understood, much less is known about how factors in the environment affect the ecology of rhabdovirus infections in natural populations of aquatic animals.

Potential of vesicular stomatitis virus as an oncolytic therapy for recurrent and drug-resistant ovarian cancer

In the last decade, we have gained significant understanding of the mechanism by which vesicular stomatitis virus (VSV) specifically kills cancer cells. Dysregulation of translation and defective innate immunity are both thought to contribute to VSV oncolysis. Safety and efficacy are important objectives to consider in evaluating VSV as a therapy for malignant disease. Ongoing efforts may enable VSV virotherapy to be considered in the near future to treat drug-resistant ovarian cancer when other options have been exhausted. In this article, we review the development of VSV as a potential therapeutic approach for recurrent or drug-resistant ovarian cancer.

Interplay between innate immunity and negative-strand RNA viruses: towards a rational model

The discovery of a new class of cytosolic receptors recognizing viral RNA, called the RIG-like receptors (RLRs), has revolutionized our understanding of the interplay between viruses and host cells. A tremendous amount of work has been accumulating to decipher the RNA moieties required for an RLR agonist, the signal transduction pathway leading to activation of the innate immunity orchestrated by type I interferon (IFN), the cellular and viral regulators of this pathway, and the viral inhibitors of the innate immune response. Previous reviews have focused on the RLR signaling pathway and on the negative regulation of the interferon response by viral proteins. The focus of this review is to put this knowledge in the context of the virus replication cycle within a cell. Likewise, there has been an expansion of knowledge about the role of innate immunity in the pathophysiology of viral infection. As a consequence, some discrepancies have arisen between the current models of cell-intrinsic innate immunity and current knowledge of virus biology. This holds particularly true for the nonsegmented negative-strand viruses (Mononegavirales), which paradoxically have been largely used to build presently available models. The aim of this review is to bridge the gap between the virology and innate immunity to favor the rational building of a relevant model(s) describing the interplay between Mononegavirales and the innate immune system.

The protease-sensitive loop of the vesicular stomatitis virus matrix protein is involved in virus assembly and protein translation

To study the contribution of the protease-sensitive loop of the VSV M protein in virus assembly we recovered recombinant VSV (rVSV) with mutations in this region and examined virus replication. Mutations in the highly conserved LXD motif (aa 123-125) resulted in reduced virion budding, reduced virus titers and enhanced M protein exchange with M-ribonucleocapsid complexes (M-RNPs), suggesting that the mutant M proteins were less tightly associated with RNP skeletons. In addition, viral protein synthesis began to decrease at 4h post-infection (hpi) and was reduced by ~80% at 8 hpi for the mutant rVSV-D125A. The reduced protein synthesis was not due to decreased VSV replication or transcription; however, translation of a reporter gene with an EMCV IRES was not reduced, suggesting that cap-dependent, but not cap-independent translation initiation was affected in rVSV-D125A infected cells. These results indicate that the LXD motif is involved in both virus assembly and VSV protein translation.

Mutations in the glycoprotein of vesicular stomatitis virus affect cytopathogenicity: potential for oncolytic virotherapy

Vesicular stomatitis virus (VSV) has been widely used to characterize cellular processes, viral resistance, and cytopathogenicity. Recently, VSV has also been used for oncolytic virotherapy due to its capacity to selectively lyse tumor cells. Mutants of the matrix (M) protein of VSV have generally been preferred to the wild-type virus for oncolysis because of their ability to induce type I interferon (IFN) despite causing weaker cytopathic effects. However, due to the large variability of tumor types, it is quite clear that various approaches and combinations of multiple oncolytic viruses will be needed to effectively treat most cancers. With this in mind, our work focused on characterizing the cytopathogenic profiles of four replicative envelope glycoprotein (G) VSV mutants. In contrast to the prototypic M mutant, VSV G mutants are as efficient as wild-type virus at inhibiting cellular transcription and host protein translation. Despite being highly cytopathic, the mutant G(6R) triggers type I interferon secretion as efficiently as the M mutant. Importantly, most VSV G mutants are more effective at killing B16 and MC57 tumor cells in vitro than the M mutant or wild-type virus through apoptosis induction. Taken together, our results demonstrate that VSV G mutants retain the high cytopathogenicity of wild-type VSV, with G(6R) inducing type I IFN secretion at levels similar to that of the M mutant. VSV G protein mutants could therefore prove to be highly valuable for the development of novel oncolytic virotherapy strategies that are both safe and efficient for the treatment of various types of cancer.

Dominant inhibition of Akt/protein kinase B signaling by the matrix protein of a negative-strand RNA virus

Vesicular stomatitis virus (VSV) is a rhabdovirus that alters host nuclear and cytoplasmic function upon infection. We have investigated the effect of VSV infection on cellular signaling through the phosphatidylinositol-3 kinase (PI3k)/Akt signaling pathway. Akt phosphorylation at both threonine 308 (Thr308) and serine 473 (Ser473) was inhibited in cells infected with VSV. This inhibition was rapid (beginning within the first 2 to 3 h postinfection) and correlated with the dephosphorylation of downstream effectors of Akt, such as glycogen synthase kinase 3β (GSK3β) and mammalian target of rapamycin (mTOR). The dephosphorylation of Akt occurred in the presence of growth factor stimulation and was not overcome through constitutive membrane targeting of Akt or high levels of phosphatidylinositol-3,4,5-triphosphate (PIP3) accumulation in the membrane. Akt dephosphorylation was not a result of alterations in PDK1 phosphorylation or activity, changes in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) levels, or the downregulation of PI3k signaling. Inactivation of Akt was caused by the expression of the viral M protein in the absence of other viral components, and an M protein mutant that does not inhibit RNA polymerase II (Pol II) transcription and nuclear/cytoplasmic transport was also defective in inhibiting Akt phosphorylation. These data illustrate that VSV utilizes a novel mechanism to alter this central player in cell signaling and oncogenesis. It also suggests an inside-out model of signal transduction where VSV interruption of nuclear events has a rapid and significant effect on membrane signaling events.

Fusion-active glycoprotein G mediates the cytotoxicity of vesicular stomatitis virus M mutants lacking host shut-off activity

The cytopathogenicity of vesicular stomatitis virus (VSV) has been attributed mainly to the host shut-off activity of the viral matrix (M) protein, which inhibits both nuclear transcription and nucleocytoplasmic RNA transport, thereby effectively suppressing the synthesis of type I interferon (IFN). The M protein from persistently VSV-infected cells was shown to harbour characteristic amino acid substitutions (M51R, V221F and S226R) implicated in IFN induction. This study demonstrates that infection of human fibroblasts with recombinant VSV containing the M51R substitution resulted in IFN induction, whereas neither the V221F nor the S226R substitution effected an IFN-inducing phenotype. Only when V221F was combined with S226R were the host shut-off activity of the M protein abolished and IFN induced, independently of M51R. The M33A substitution, previously implicated in VSV cytotoxicity, did not affect host shut-off activity. M-mutant VSV containing all four amino acid substitutions retained cytotoxic properties in both Vero cells and IFN-competent primary fibroblasts. Infected-cell death was associated with the formation of giant polynucleated cells, suggesting that the fusion activity of the VSV G protein was involved. Accordingly, M-mutant VSV expressing a fusion-defective G protein or with a deletion of the G gene showed significantly reduced cytotoxic properties and caused long-lasting infections in Vero cells and mouse hippocampal slice cultures. In contrast, a G-deleted VSV expressing wild-type M protein remained cytotoxic. These findings indicate that the host shut-off activity of the M protein dominates VSV cytotoxicty, whilst the fusion-active G protein is mainly responsible for the cytotoxicity remaining with M-mutant VSV.

Induction of interferon and interferon signaling pathways by replication of defective interfering particle RNA in cells constitutively expressing vesicular stomatitis virus replication proteins

We show here that replication of defective interfering (DI) particle RNA in HEK293 cells stably expressing vesicular stomatitis virus (VSV) replication proteins potently activates interferon (IFN) and IFN signaling pathways through upregulation of IFN-beta promoter, IFN-stimulated response element (ISRE) promoter, and NF-kappaB promoter activities. Replication of DI particle RNA, not mere expression of the viral replication proteins, was found to be critical for induction of IFN and IFN signaling. The stable cells supporting replication of DI RNA described in this report will be useful in further examining the innate immune signaling pathways and the host cell functions in viral genome replication.

Intracranial administration of P gene siRNA protects mice from lethal Chandipura virus encephalitis

Background

In parts of India, Chandipura Virus (CHPV) has emerged as an encephalitis causing pathogen in both epidemic and sporadic forms. This pediatric disease follows rapid course leading to 55–75% mortality. In the absence of specific treatment, effectiveness of RNA interference (RNAi) was evaluated.

Methods and Findings

Efficacy of synthetic short interfering RNA (siRNA) or short hairpin RNA (shRNA) in protecting mice from CHPV infection was assessed. The target genes were P and M genes primarily because important role of the former in viral replication and lethal nature of the latter. Real time one step RT-PCR and plaque assay were used for the assessment of gene silencing. Using pAcGFP1N1-CHPV-P, we showed that P-2 siRNA was most efficient in reducing the expression of P gene in-vitro. Both quantitative assays documented 2logs reduction in the virus titer when P-2, M-5 or M-6 siRNAs were transfected 2hr post infection (PI). Use of these siRNAs in combination did not result in enhanced efficiency. P-2 siRNA was found to tolerate four mismatches in the center. As compared to five different shRNAs, P-2 siRNA was most effective in inhibiting CHPV replication. An extended survival was noted when mice infected intracranially with 100 LD₅₀ CHPV were treated with cationic lipid complexed 5 µg P-2 siRNA simultaneously. Infection with 10LD₅₀ and treatment with two doses of siRNA first, simultaneously and second 24 hr PI, resulted in 70% survival. Surviving mice showed 4logs less CHPV titers in brain without histopathological changes or antibody response. Gene expression profiles of P-2 siRNA treated mice showed no interferon response. First dose of siRNA at 2hr or 4hr PI with second dose at 24hr resulted in 40% and 20% survival respectively suggesting potential application in therapy.

Conclusions

The results highlight therapeutic potential of siRNA in treating rapid and fatal Chandipura encephalitis.

Interferon response and viral evasion by members of the family rhabdoviridae

Like many animal viruses, those of the Rhabdoviridae family, are able to antagonize the type I interferon response and cause disease in mammalian hosts. Though these negative-stranded RNA viruses are very simple and code for as few as five proteins, they have been seen to completely abrogate the type I interferon response early in infection. In this review, we will discuss the viral organization and type I interferon evasion of rhabdoviruses, focusing on vesicular stomatitis virus (VSV) and rabies virus (RABV). Despite their structural similarities, VSV and RABV have completely different mechanisms by which they avert the host immune response. VSV relies on the matrix protein to interfere with host gene transcription and nuclear export of anti-viral mRNAs. Alternatively, RABV uses its phosphoprotein to interfere with IRF-3 phosphorylation and STAT1 signaling. Understanding the virus-cell interactions and viral proteins necessary to evade the immune response is important in developing effective vaccines and therapeutics for this viral family.