Glycoprotein of nonpathogenic rabies viruses is a key determinant of human cell apoptosis

The Interplay Between Viral Infection and Cell Death: A Ping-Pong Effect

Programmed cell death (PCD) is a well-studied cellular mechanism that plays a critical role in immune responses, developmental processes, and the maintenance of tissue homeostasis. However, viruses have developed diverse strategies to bypass or manipulate the host apoptotic machinery to enhance their replication and survival. As a result, the interaction between PCD pathways and viruses has garnered increased interest, leading to many studies being published in recent years. This study aims to provide an overview of the current understanding of PCD pathways and their significance in viral infections. We will discuss various forms of cell death pathways, including apoptosis, autophagy, necroptosis, and pyroptosis, as well as their corresponding molecular mechanisms. In addition, we will show how viruses manipulate host PCD pathways to prevent or delay cell death or facilitate viral replication. This study emphasizes the importance of investigating the mechanisms by which viruses control the host's PCD machinery to gain insight into the evolutionary dynamics of host-pathogen interactions and to develop new approaches for predicting and managing viral threats. Overall, we aimed to highlight new research areas in PCD and viruses, including introduction of new targets for the development of new antiviral drugs to modulate the cellular apoptotic machinery and novel inhibitors of host cell death pathways.

The Immune Escape Strategy of Rabies Virus and Its Pathogenicity Mechanisms

In contrast to most other rhabdoviruses, which spread by insect vectors, the rabies virus (RABV) is a very unusual member of the Rhabdoviridae family, since it has evolved to be fully adapted to warm-blooded hosts and spread directly between them. There are differences in the immune responses to laboratory-attenuated RABV and wild-type rabies virus infections. Various investigations showed that whilst laboratory-attenuated RABV elicits an innate immune response, wild-type RABV evades detection. Pathogenic RABV infection bypasses immune response by antagonizing interferon induction, which prevents downstream signal activation and impairs antiviral proteins and inflammatory cytokines production that could eliminate the virus. On the contrary, non-pathogenic RABV infection leads to immune activation and suppresses the disease. Apart from that, through recruiting leukocytes into the central nervous system (CNS) and enhancing the blood-brain barrier (BBB) permeability, which are vital factors for viral clearance and protection, cytokines/chemokines released during RABV infection play a critical role in suppressing the disease. Furthermore, early apoptosis of neural cells limit replication and spread of avirulent RABV infection, but street RABV strains infection cause delayed apoptosis that help them spread further to healthy cells and circumvent early immune exposure. Similarly, a cellular regulation mechanism called autophagy eliminates unused or damaged cytoplasmic materials and destroy microbes by delivering them to the lysosomes as part of a nonspecific immune defense mechanism. Infection with laboratory fixed RABV strains lead to complete autophagy and the viruses are eliminated. But incomplete autophagy during pathogenic RABV infection failed to destroy the viruses and might aid the virus in dodging detection by antigen-presenting cells, which could otherwise elicit adaptive immune activation. Pathogenic RABV P and M proteins, as well as high concentration of nitric oxide, which is produced during rabies virus infection, inhibits activities of mitochondrial proteins, which triggers the generation of reactive oxygen species, resulting in oxidative stress, contributing to mitochondrial malfunction and, finally, neuron process degeneration.

Induced expression of rabies glycoprotein in the dorsal hippocampus enhances hippocampal dependent memory in a rat model of Alzheimer's disease

The Rabies virus is a neurotropic virus that manipulates the natural cell death processes of its host to ensure its own survival and replication. Studies have shown that the anti-apoptotic effect of the virus is mediated by one of its protein named, rabies glycoprotein (RVG). Alzheimer's disease (AD) is characterized by the loss of neural cells and memory impairment. We aim to examine whether expression of RVG in the hippocampal cells can shield the detrimental effects induced by Aβ. Oligomeric form of Aβ (oAβ) or vehicle was bilaterally microinjected into the dorsal hippocampus of male Wistar rats. One week later, two μl (108 T.U. /ml) of the lentiviral vector carrying RVG gene was injected into their dorsal hippocampus (post-treatment). In another experiment, the lentiviral vector was microinjected one week before Aβ injection (pre-treatment). One week later, the rat's brain was sliced into cross-sections, and the presence of RVG-expressing neuronal cells was confirmed using fluorescent microscopy. Rats were subjected to assessments of spatial learning and memory as well as passive avoidance using the Morris water maze (MWM) and the Shuttle box apparatuses, respectively. Protein expression of AMPA receptor subunit (GluA1) was determined using western blotting technique. In MWM, Aβ treated rats showed decelerated acquisition of the task and impairment of reference memory. RVG expression in the hippocampus prevented and restored the deficits in both pre- and post- treatment conditions, respectively. It also improved inhibitory memory in the oAβ treated rats. RVG increased the expression level of GluA1 level in the hippocampus. Based on our findings, the expression of RVG in the hippocampus has the potential to enhance both inhibitory and spatial learning abilities, ultimately improving memory performance in an AD rat model. This beneficial effect is likely attributed, at least in part, to the increased expression of GluA1-containing AMPA receptors.

Autophagy and Apoptosis in Rabies Virus Replication

Rabies virus (RABV) is a single-stranded negative-sense RNA virus belonging to the Rhabdoviridae family and Lyssavirus genus, which is highly neurotropic and can infect almost all warm-blooded animals, including humans. Autophagy and apoptosis are two evolutionarily conserved and genetically regulated processes that maintain cellular and organismal homeostasis, respectively. Autophagy recycles unnecessary or dysfunctional intracellular organelles and molecules in a cell, whereas apoptosis eliminates damaged or unwanted cells in an organism. Studies have shown that RABV can induce both autophagy and apoptosis in target cells. To advance our understanding of pathogenesis of rabies, this paper reviews the molecular mechanisms of autophagy and apoptosis induced by RABV and the effects of the two cellular events on RABV replication.

The power of mumps virus: Matrix protein activates apoptotic pathways in human colorectal cell lines

New therapeutic approaches can significantly impact the control of colorectal cancer (CRC), which is increasing worldwide. In this study, we investigated the potential of targeting viral proteins to combat cancer cells. Specifically, we examined the anticancer potential of the matrix (M) protein of the mumps virus Hoshino strain in SW480 CRC cell lines. To begin, we individually transfected SW480 cells with pcDNA3 plasmids containing the mumps virus M gene. We then investigated the percentage of cell death, caspase activity, and the expression levels of genes involved in apoptosis pathways. Following this, we performed bioinformatics analysis on the M protein to identify any similarities with Bcl-2 family members and their viral homologs. Our diagnostic methods showed that treatment with the mumps M protein induced apoptosis and upregulated the expression and activity of pro-apoptotic proteins in SW480 CRC cells compared to the control and vector groups. Based on our bioinformatics studies, we proposed that the BH3 motif in the M protein may trigger apoptosis in CRC cells by interacting with cellular Bax. Overall, our study showed for the first time that the mumps virus M protein could be considered as a targeted treatment for CRC by inducing apoptotic pathways.

"Self-inactivating" rabies viruses are susceptible to loss of their intended attenuating modification

Monosynaptic tracing using rabies virus is an important technique in neuroscience, allowing brain-wide labeling of neurons directly presynaptic to a targeted neuronal population. A 2017 article reported the development of a noncytotoxic version-a major advance-based on attenuating the rabies virus by the addition of a destabilization domain to the C terminus of a viral protein. However, this modification did not appear to hinder the ability of the virus to spread between neurons. We analyzed two viruses provided by the authors and show here that both were mutants that had lost the intended modification, explaining the paper's paradoxical results. We then made a virus that actually did have the intended modification in at least the majority of virions and found that it did not spread efficiently under the conditions described in the original paper, namely, without an exogenous protease being expressed in order to remove the destabilization domain. We found that it did spread when the protease was supplied, although this also appeared to result in the deaths of most source cells by 3 wk postinjection. We conclude that the new approach is not robust but that it could become a viable technique given further optimization and validation.

Lentiviral Expression of Rabies Virus Glycoprotein in the Rat Hippocampus Strengthens Synaptic Plasticity

Rabies virus (RABV) is a neurotropic virus exclusively infecting neurons in the central nervous system. RABV encodes five proteins. Among them, the viral glycoprotein (RVG) plays a key role in viral entry into neurons and rabies pathogenesis. It was shown that the nature of the C-terminus of the RABV G protein, which possesses a PDZ-binding motif (PBM), modulates the virulence of the RABV strain. The neuronal protein partners recruited by this PBM may alter host cell function. This study was conducted to investigate the effect of RVG on synaptic function in the hippocampal dentate gyrus (DG) of rat. Two μl (108 T.U./ml) of the lentiviral vector containing RVG gene was injected into the DG of rat hippocampus. After 2 weeks, the rat's brain was cross-sectioned and RVG-expressing cells were detected by fluorescent microscopy. Hippocampal synaptic activity of the infected rats was then examined by recording the local field potentials from DG after stimulation of the perforant pathway. Short-term synaptic plasticity was also assessed by double pulse stimulation. Expression of RVG in DG increased long-term potentiation population spikes (LTP-PS), whereas no facilitation of LTP-PS was found in neurons expressing δRVG (deleted PBM). Furthermore, RVG and δRVG strengthened paired-pulse facilitation. Heterosynaptic long-term depression (LTD) in the DG was significantly blocked in RVG-expressing group compared to the control group. This blockade was dependent to PBM motif as rats expressing δRVG in the DG-expressed LTD comparable to the RVG group. Our data demonstrate that RVG expression facilitates both short- and long-term synaptic plasticity in the DG indicating that it may involve both pre- and postsynaptic mechanisms to alter synaptic function. Further studies are needed to elucidate the underlying mechanisms.

A cocktail of human monoclonal antibodies broadly neutralizes North American rabies virus variants as a promising candidate for rabies post-exposure prophylaxis

Human rabies remains a globally significant public health problem. Replacement of polyclonal anti-rabies immunoglobulin (RIG), a passive component of rabies post-exposure prophylaxis (PEP), with a monoclonal antibody (MAb), would eliminate the cost and availability constraints associated with RIG. Our team has developed and licensed a human monoclonal antibody RAB1 (Rabishield^©), as the replacement for RIG where canine rabies is enzootic. However, for the highly diverse rabies viruses of North America, a cocktail containing two or more MAbs targeting different antigenic sites of the rabies glycoprotein should be included to ensure neutralization of all variants of the virus. In this study, two MAb cocktails, R172 (RAB1-RAB2) and R173 (RAB1-CR57), were identified and evaluated against a broad range of rabies variants from North America. R173 was found to be the most potent cocktail, as it neutralized all the tested North American RABV isolates and demonstrated broad coverage of isolates from both terrestrial and bat species. R173 could be a promising candidate as an alternative or replacement for RIG PEP in North America.

[Anti-rabies vaccines applied in the Russian Federation and perspectives for their improvement]

Rabies is almost ubiquitous (except in certain areas) and poses a significant danger to both animals and humans. Every year around 55,000 people die from this disease worldwide. In the Russian Federation alone 400,000- 450,000 patients annually apply for anti-rabies treatment. In the absolute majority of cases human infection is caused by contact with infected animals. In RF, a number of cultured inactivated anti-rabies vaccines for medical and veterinary purposes have been developed, registered and used for specific prevention of rabies. These vaccine preparations have shown high effectiveness in preventing infection in domestic and farm animals. At the same time, the main reservoir of the rabies virus (Mononegavirales: Rhabdoviridae: Lyssavirus) (RV) are wild carnivores (Mammalia: Carnivora). For the purpose of their oral immunization, live virus vaccines from attenuated (fixed) strains of RV that are little resistant in the external environment are used. In Western Europe and North America there is successful experience with recombinant anti-rabies vaccine preparations containing a viral glycoprotein gene (G-protein). Such vaccines are safe for humans and animals. In Russia also had been developed a vector anti-rabies vaccine based on adenovirus (Adenoviridae), which can be used to combat this infection. Currently, in addition to classical rabies, diseases caused by new, previously unknown lyssaviruses (Lyssavirus) are becoming increasingly important. Bats (Mammalia: Microchiroptera) are their vectors. Cases of illness and death after contact with these animals have been described. In the near future, we should expect the development of new vaccines that will provide protection not only against RV, but also against other lyssaviruses.

Glu333 in rabies virus glycoprotein is involved in virus attenuation through astrocyte infection and interferon responses

The amino acid residue at position 333 of the rabies virus (RABV) glycoprotein (G333) is a major determinant of RABV pathogenicity. Virulent RABV strains possess Arg₃₃₃, whereas the attenuated strain HEP-Flury (HEP) possesses Glu₃₃₃. To investigate the potential attenuation mechanism dependent on a single amino acid at G333, comparative analysis was performed between HEP and HEP³³³R mutant with Arg₃₃₃. We examined their respective tropism for astrocytes and the subsequent immune responses in astrocytes. Virus replication and subsequent interferon (IFN) responses in astrocytes infected with HEP were increased compared with HEP³³³R both in vitro and in vivo. Furthermore, involvement of IFN in the avirulency of HEP was demonstrated in IFN-receptor knockout mice. These results indicate that Glu₃₃₃ contributes to RABV attenuation by determining the ability of the virus to infect astrocytes and stimulate subsequent IFN responses.

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Glu₃₃₃ in G protein is responsible for astrocyte infection with RABV HEP strain

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Arg₃₃₃ mutation in G protein decreases astrocyte tropism of RABV HEP

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RABV HEP evokes higher IFN responses in astrocytes than HEP with Arg₃₃₃ mutation

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Glu₃₃₃-dependent astrocyte infection is involved in the attenuation of RABV HEP

G protein-coupled receptor 17 restricts rabies virus replication via BAK-mediated apoptosis

Rabies, caused by rabies virus (RABV), is an ancient zoonotic disease that significantly affects human and animal health throughout the world. RABV causes acute encephalitis in mammals with a high fatality rate in developing countries. G protein-coupled receptor 17 (GPR17) is a vital gene in the central nervous system (CNS) that plays important roles in demyelinating diseases and ischemia brain. However, it is still unclear whether GPR17 participates in the regulation of RABV infection. Here, we found that upregulation or activation of GPR17 can reduce the virus titer; conversely, the inactivation or silence of GPR17 led to increased RABV replication in N2a cells. The recombinant RABV expressing GPR17 (rRABV-GPR17) showed reduced replication capacity compared to the parent virus rRABV. Moreover, overexpression of GPR17 can attenuate RABV pathogenicity in mice. Further study demonstrated that GPR17 suppressed RABV replication via BAK-mediated apoptosis. Our findings uncover an unappreciated role of GPR17 in suppressing RABV infection, where GPR17 mediates cell apoptosis to limit RABV replication and may be an attractive candidate for new therapeutic interventions in the treatment of rabies.

Innate Immune Signaling and Role of Glial Cells in Herpes Simplex Virus- and Rabies Virus-Induced Encephalitis

The environment of the central nervous system (CNS) represents a double-edged sword in the context of viral infections. On the one hand, the infectious route for viral pathogens is restricted via neuroprotective barriers; on the other hand, viruses benefit from the immunologically quiescent neural environment after CNS entry. Both the herpes simplex virus (HSV) and the rabies virus (RABV) bypass the neuroprotective blood-brain barrier (BBB) and successfully enter the CNS parenchyma via nerve endings. Despite the differences in the molecular nature of both viruses, each virus uses retrograde transport along peripheral nerves to reach the human CNS. Once inside the CNS parenchyma, HSV infection results in severe acute inflammation, necrosis, and hemorrhaging, while RABV preserves the intact neuronal network by inhibiting apoptosis and limiting inflammation. During RABV neuroinvasion, surveilling glial cells fail to generate a sufficient type I interferon (IFN) response, enabling RABV to replicate undetected, ultimately leading to its fatal outcome. To date, we do not fully understand the molecular mechanisms underlying the activation or suppression of the host inflammatory responses of surveilling glial cells, which present important pathways shaping viral pathogenesis and clinical outcome in viral encephalitis. Here, we compare the innate immune responses of glial cells in RABV- and HSV-infected CNS, highlighting different viral strategies of neuroprotection or Neuroinflamm. in the context of viral encephalitis.

The Serendipity of Viral Trans-Neuronal Specificity: More Than Meets the Eye

Trans-neuronal viruses are frequently used as neuroanatomical tools for mapping neuronal circuits. Specifically, recombinant one-step rabies viruses (RABV) have been instrumental in the widespread application of viral circuit mapping, as these viruses have enabled labs to map the direct inputs onto defined cell populations. Within the neuroscience community, it is widely believed that RABV spreads directly between neurons via synaptic connections, a hypothesis based principally on two observations. First, the virus labels neurons in a pattern consistent with known anatomical connectivity. Second, few glial cells appear to be infected following RABV injections, despite the fact that glial cells are abundant in the brain. However, there is no direct evidence that RABV can actually be transmitted through synaptic connections. Here we review the immunosubversive mechanisms that are critical to RABV’s success for infiltration of the central nervous system (CNS). These include interfering with and ultimately killing migratory T cells while maintaining levels of interferon (IFN) signaling in the brain parenchyma. Finally, we critically evaluate studies that support or are against synaptically-restricted RABV transmission and the implications of viral-host immune responses for RABV transmission in the brain.

Rabies virus glycoprotein enhances spatial memory via the PDZ binding motif

Rabies is a life-threatening viral infection of the brain. Rabies virus (RABV) merely infects excitable cells including neurons provoking drastic behaviors including negative emotional memories. RABV glycoprotein (RVG) plays a critical role in RABV pathogenesis. RVG interacts with various cytoplasmic PDZ (PSD-95/Dlg/ZO-1) containing proteins through its PDZ binding motif (PBM). PTZ domains have crucial role in formation and function of signal transduction. Hippocampus is one of the cerebral regions that contain high load of viral antigens. We examined impact of RVG expression in the dorsal hippocampus on aversive as well as spatial learning and memory performance in rats. Two microliter of the lentiviral vector (~10⁸ T.U./ml) encoding RVG or ∆RVG (deleted PBM) genomes was microinjected into the hippocampal CA1. After 1 week, rat's brain was cross-sectioned and RVG/∆RVG-expressing neuronal cells were confirmed by fluorescent microscopy. Passive avoidance and spatial learning and memory were assessed in rats by Shuttle box and Morris water maze (MWM). In the shuttle box, both RVG and ∆RVG decreased the time spent in the dark compartment compared to control (p < 0.05). In MWM, RVG and ∆RVG did not affect the acquisition of spatial task. In the probe test, RVG-expressing rats spent more time in the target quadrant, and also reached the platform position sooner than control group (p < 0.05). Rats expressing ∆RVG significantly swam farther from the hidden platform than RVG group (p < 0.05). Our data indicate RVG expression in the hippocampus strengthens aversive and spatial learning and memory performance. The boosting effect on spatial but not avoidance memory is mediated through PBM.

Chimeric VLPs Based on HIV-1 Gag and a Fusion Rabies Glycoprotein Induce Specific Antibodies against Rabies and Foot-and-Mouth Disease Virus

Foot and mouth disease is a livestock acute disease, causing economic losses in affected areas. Currently, control of this disease is performed by mandatory vaccination campaigns using inactivated viral vaccines. In this work, we describe the development of a chimeric VLP-based vaccine candidate for foot-and-mouth disease virus (FMDV), based on the co-expression of the HIV-1 Gag protein and a novel fusion rabies glycoprotein (RVG), which carries in its N-term the FMDV main antigen: the G-H loop. It is demonstrated by confocal microscopy that both Gag-GFP polyprotein and the G-H loop colocalize at the cell membrane and, that the Gag polyprotein of the HIV virus acts as a scaffold for enveloped VLPs that during the budding process acquires the proteins that are being expressed in the cell membrane. The obtained VLPs were spherical particles of 130 ± 40 nm in diameter (analyzed by TEM, Cryo-TEM and NTA) carrying an envelope membrane that efficiently display the GH-RVG on its surface (analyzed by gold immunolabeling). Immunostainings with a FMDV hyperimmune serum showed that the heterologous antigenic site, genetically fused to RVG, is recognized by specific G-H loop antibodies. Additionally, the cVLPs produced expose the G-H loop to the liquid surrounding (analyzed by specific ELISA). Finally, we confirmed that these FMD cVLPs are able to induce a specific humoral immune response, based on antibodies directed to the G-H loop in experimental animals.

Farr R, Green D, M. Haynes J, Bingham J, O’Brien CM, Dearnley M. Modelling Lyssavirus Infections in Human Stem Cell-Derived Neural Cultures

Rabies is a zoonotic neurological infection caused by lyssavirus that continues to result in devastating loss of human life. Many aspects of rabies pathogenesis in human neurons are not well understood. Lack of appropriate ex-vivo models for studying rabies infection in human neurons has contributed to this knowledge gap. In this study, we utilize advances in stem cell technology to characterize rabies infection in human stem cell-derived neurons. We show key cellular features of rabies infection in our human neural cultures, including upregulation of inflammatory chemokines, lack of neuronal apoptosis, and axonal transmission of viruses in neuronal networks. In addition, we highlight specific differences in cellular pathogenesis between laboratory-adapted and field strain lyssavirus. This study therefore defines the first stem cell-derived ex-vivo model system to study rabies pathogenesis in human neurons. This new model system demonstrates the potential for enabling an increased understanding of molecular mechanisms in human rabies, which could lead to improved control methods.

The Deoptimization of Rabies Virus Matrix Protein Impacts Viral Transcription and Replication

Rabies virus (RABV) matrix (M) protein plays several important roles during RABV infection. Although previous studies have assessed the functions of M through gene rearrangements, this interferes with the position of other viral proteins. In this study, we attenuated M expression through deoptimizing its codon usage based on codon pair bias in RABV. This strategy more objectively clarifies the role of M during virus infection. Codon-deoptimized M inhibited RABV replication during the early stages of infection, but enhanced viral titers at later stages. Codon-deoptimized M also inhibited genome synthesis at early stage of infection and increased the RABV transcription rates. Attenuated M through codon deoptimization enhanced RABV glycoprotein expression following RABV infection in neuronal cells, but had no influence on the cell-to-cell spread of RABV. In addition, codon-deoptimized M virus induced higher levels of apoptosis compared to the parental RABV. These results indicate that codon-deoptimized M increases glycoprotein expression, providing a foundation for further investigation of the role of M during RABV infection.

Structure-based optimization of a PDZ-binding motif within a viral peptide stimulates neurite outgrowth

Protection of neuronal homeostasis is a major goal in the management of neurodegenerative diseases. Microtubule-associated Ser/Thr kinase 2 (MAST2) inhibits neurite outgrowth, and its inhibition therefore represents a potential therapeutic strategy. We previously reported that a viral protein (G-protein from rabies virus) capable of interfering with protein-protein interactions between the PDZ domain of MAST2 and the C-terminal moieties of its cellular partners counteracts MAST2-mediated suppression of neurite outgrowth. Here, we designed peptides derived from the native viral protein to increase the affinity of these peptides for the MAST2-PDZ domain. Our strategy involved modifying the length and flexibility of the noninteracting sequence linking the two subsites anchoring the peptide to the PDZ domain. Three peptides, Neurovita1 (NV1), NV2, and NV3, were selected, and we found that they all had increased affinities for the MAST2-PDZ domain, with K_d values decreasing from 1300 to 60 nm, while target selectivity was maintained. A parallel biological assay evaluating neurite extension and branching in cell cultures revealed that the NV peptides gradually improved neural activity, with the efficacies of these peptides for stimulating neurite outgrowth mirroring their affinities for MAST2-PDZ. We also show that NVs can be delivered into the cytoplasm of neurons as a gene or peptide. In summary, our findings indicate that virus-derived peptides targeted to MAST2-PDZ stimulate neurite outgrowth in several neuron types, opening up promising avenues for potentially using NVs in the management of neurodegenerative diseases.

Codon optimization of G protein enhances rabies virus-induced humoral immunity

Rabies, caused by rabies virus (RABV), is a fatal zoonosis, which still poses a threat to public health in most parts of the world. Glycoprotein of RABV is the only viral surface protein, which is critical for the induction of virus-neutralizing antibodies (VNA). In order to improve the production of VNA, recombinant RABVs containing two copies of G gene and codon-optimized G gene were constructed by using reverse genetics, named LBNSE-dG and LBNSE-dOG, respectively. After being inoculated into the mouse brains, LBNSE-dOG induced more apoptosis and recruited more inflammatory cells than LBNSE-dG and LBNSE, resulting in reduced virulence in vivo. After intramuscular (im) immunization in mice, LBNSE-dOG promoted the formation of germinal centres (GCs), the recruitment of GC B cells and the generation of antibody-secreting cells (ASCs) in the draining lymph nodes (LNs). Consistently, LBNSE-dOG boosted the production of VNA and provided better protection against lethal RABV challenge than LBNSE-dG and LBNSE when it was used as both live and inactivated vaccines. Our results demonstrate that the codon-optimized RABV LBNSE-dOG displays attenuated pathogenicity and enhanced immunogenicity, therefore it could be a potential candidate for the next generation of rabies vaccines.

Phenotypic Consequence of Rearranging the N Gene of RABV HEP-Flury

Nucleoprotein (N) is a key element in rabies virus (RABV) replication. To further investigate the effect of N on RABV, we manipulated an infectious cDNA clone of the RABV HEP-Flury to rearrange the N gene from its wild-type position of 1 (N-P-M-G-L) to 2 (P-N-M-G-L), 3 (P-M-N-G-L), or 4 (P-M-G-N-L), using an approach that left the viral nucleotide sequence unaltered. Subsequently, viable viruses were recovered from each of the rearranged cDNA and examined for their gene expression levels, growth kinetics in cell culture, pathogenicity in suckling mice and protection in mice. The results showed that gene rearrangement decreased N mRNA transcription and vRNA replication. As a result, all viruses with rearranged genomes showed worse replication than that of rHEP-Flury in NA cells at a MOI of 0.01, but equivalent or slightly better replication levels at a MOI of 3. Consequently, the lethality in suckling mice infected with N4 was clearly attenuated compared with rHEP-Flury. However, the protection to mice was not enhanced. This study not only gives us insight into the understanding of the phenotype of RABV N gene rearrangement, but also helps with rabies vaccine candidate construction.

Evaluation of apoptosis markers in different cell lines infected with equine arteritis virus

Equine arteritis virus (EAV) induces apoptosis in infected cells. Cell death caused by EAV has been studied mainly using three cell lines, BHK-21, RK-13 and Vero cells. The mechanism of apoptosis varies among cell lines and results cannot be correlated owing to differences in EAV strains used. We evaluated different markers for apoptosis in BHK-21, RK-13 and Vero cell lines using the Bucyrus EAV reference strain. Acridine orange/ethidium bromide staining revealed morphological changes in infected cells, while flow cytometry indicated the extent of apoptosis. We also observed DNA fragmentation, but the DNA ladder was detected at different times post-infection depending on the cell line, i.e., 48, 72 and 96 h post-infection in RK-13, Vero and BHK-21 cells, respectively. Measurement of viral titers obtained with each cell line indicated that apoptosis causes interference with viral replication and therefore decreased viral titers. As an unequivocal marker of apoptosis, we measured the expression of caspase-3 and caspases-8 and -9 as extrinsic and intrinsic markers of apoptosis pathways, respectively. Caspase-8 in BHK-21 cells was the only protease that was not detected at any of the times assayed. We found that Bucyrus EAV strain exhibited a distinctive apoptosis pathway depending on the cell line.

Newcastle disease virus strain AF2240 as an oncolytic virus: A review

The discovery of tumour selective virus-mediated apoptosis marked the birth of an alternative cancer treatment in the form of oncolytic viruses. Even though, its oncolytic efficiency was demonstrated more than 50 years ago, safety concerns which resulted from mild to lethal side effects hampered the progress of oncolytic virus research. Since the classical oncolytic virus studies rely heavily on its natural oncolytic ability, virus manipulation was limited, thereby, restricted efforts to improve its safety. In order to circumvent such restriction, experiments involving non-human viruses such as the avian Newcastle disease virus (NDV) was conducted using cultured cells, animal models and human subjects. The corresponding reports on its significant tumour cytotoxicity along with impressive safety profile initiated immense research interest in the field of oncolytic NDV. The varying degree of oncolytic efficiency and virulency among NDV strains encouraged researchers from all around the world to experiment with their respective local NDV isolates in order to develop an oncolytic virus with desirable characteristics. Such desirable features include high tumour-killing ability, selectivity and low systemic cytotoxicity. The Malaysian field outbreak isolate, NDV strain AF2240, also currently, receives significant research attention. Apart from its high cytotoxicity against tumour cells, this strain also provided fundamental insight into NDV-mediated apoptosis mechanism which involves Bax protein recruitment as well as death receptor engagement. Studies on its ability to selectively induce apoptosis in tumour cells also resulted in a proposed p38 MAPK/NF-κB/IκBα pathway. The immunogenicity of AF2240 was also investigated through PBMC stimulation and macrophage infection. In addition, the enhanced oncolytic ability of this strain under hypoxic condition signifies its dynamic tumour tropism. This review is aimed to introduce and discuss the aforementioned details of the oncolytic AF2240 strain along with its current challenges which outlines the future research direction of this virus.

Recombinant rabies virus expressing interleukin-6 enhances the immune response in mouse brain

Rabies, which is caused by the rabies virus (RABV), is an ancient zoonosis that has a high mortality rate. Previous studies have indicated that recombinant RABV expressing canine interleukin-6 (rHEP-CaIL6), induced more virus-neutralizing antibodies than parental RABV in mice following intramuscular immunization. To investigate the immune response induced in the CNS by rHEP-CaIL6 after intranasal or intracranial administration in mice, the permeability of the blood-brain barrier (BBB), the infiltration of CD3 T cells, and innate immune response-related effector molecules in the CNS were examined. It was observed that infection of rHEP-CaIL6 led to enhanced BBB permeability following intranasal infection. More CD3 T cells infiltrated into the central nervous system (CNS) in mice infected with rHEP-CaIL6 than in those infected with the HEP-Flury strain. Furthermore, rHEP-CaIL6 induced an increased expression of innate immune response-related effector molecules, compared with the parental HEP-Flury strain, within the CNS. Taken together, these findings suggest that rHEP-CaIL6 induced stronger immune responses in mice brains, which is more beneficial for virus clearance. These results may also partly illustrate the role of IL6 in RABV infection.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

Differentiated Human SH-SY5Y Cells Provide a Reductionist Model of Herpes Simplex Virus 1 Neurotropism

Neuron-virus interactions that occur during herpes simplex virus (HSV) infection are not fully understood. Neurons are the site of lifelong latency and are a crucial target for long-term suppressive therapy or viral clearance. A reproducible neuronal model of human origin would facilitate studies of HSV and other neurotropic viruses. Current neuronal models in the herpesvirus field vary widely and have caveats, including incomplete differentiation, nonhuman origins, or the use of dividing cells that have neuropotential but lack neuronal morphology. In this study, we used a robust approach to differentiate human SH-SY5Y neuroblastoma cells over 2.5 weeks, producing a uniform population of mature human neuronal cells. We demonstrate that terminally differentiated SH-SY5Y cells have neuronal morphology and express proteins with subcellular localization indicative of mature neurons. These neuronal cells are able to support a productive HSV-1 infection, with kinetics and overall titers similar to those seen in undifferentiated SH-SY5Y cells and the related SK-N-SH cell line. However, terminally differentiated, neuronal SH-SY5Y cells release significantly less extracellular HSV-1 by 24 h postinfection (hpi), suggesting a unique neuronal response to viral infection. With this model, we are able to distinguish differences in neuronal spread between two strains of HSV-1. We also show expression of the antiviral protein cyclic GMP-AMP synthase (cGAS) in neuronal SH-SY5Y cells, which is the first demonstration of the presence of this protein in nonepithelial cells. These data provide a model for studying neuron-virus interactions at the single-cell level as well as via bulk biochemistry and will be advantageous for the study of neurotropic viruses in vitroIMPORTANCE Herpes simplex virus (HSV) affects millions of people worldwide, causing painful oral and genital lesions, in addition to a multitude of more severe symptoms such as eye disease, neonatal infection, and, in rare cases, encephalitis. Presently, there is no cure available to treat those infected or prevent future transmission. Due to the ability of HSV to cause a persistent, lifelong infection in the peripheral nervous system, the virus remains within the host for life. To better understand the basis of virus-neuron interactions that allow HSV to persist within the host peripheral nervous system, improved neuronal models are required. Here we describe a cost-effective and scalable human neuronal model system that can be used to study many neurotropic viruses, such as HSV, Zika virus, dengue virus, and rabies virus.

Inhibition of rabies virus replication by interferon-stimulated gene 15 and its activating enzyme UBA7

It was reported that ISG15 and its activating enzyme UBA7 have antiviral functions. However, there is no study to demonstrate whether ISG15 and UBA7 have anti-rabies virus function. In the current study, In vivo and in vitro anti-rabies virus function of ISG15 and UBA7 were investigated using RNAi technology. The results showed that shRNA knock-down of expression of ISG15 and UBA7 increased the titers of RABV in neuroblastoma cell line NA and microglial cell line BV-2 cells and shRNA knockdown of ISG15 conjugation alleviates the IFN-induced inhibition of RABV gene expression in vitro. Lentiviral vector mediated-shRNA knock-down of expression of ISG15 and UBA7 increased the titers of RABV in mouse brains and decreased the survivorship of mice. The study showed that ISG15 and UBA7 inhibit RABV replication in vitro and in vivo. To our knowledge, we for the first time documented the anti-RABV function of ISG15 and UBA7, which may provide a means of understanding the pathogenesis of rabies and improving therapeutic methods.

Phosphoprotein Gene Contributes to the Enhanced Apoptosis Induced by Wild-Type Rabies Virus GD-SH-01 In Vitro

Previous research demonstrated that the matrix protein (M) and glycoprotein (G) of attenuated rabies virus (RABV) strains are involved in the induction of host cell apoptosis. In this work, we show that wild-type (wt) RABV GD-SH-01 induces significantly greater apoptosis than the attenuated strain HEP-Flury. In order to identify the gene(s) accounting for this phenotype, five recombinant RABVs (rRABVs) were constructed by replacing each single gene of HEP-Flury with the corresponding gene of GD-SH-01. By using these rRABVs, we found that not only M and G, but also the phosphoprotein (P) plays an important role in inducing apoptosis. In order to figure out the different role of P gene in inducing apoptosis from the highly divergent background, another rRABV rGDSH-P, which carries the P gene of HEP-Flury in the background of the GD-SH-01 was generated. It was found that infection of NA cells with GD-SH-01 or the recombinant strain rHEP-shP, which carries P gene of GD-SH-01, induced significantly greater apoptosis than HEP-Flury or rGDSH-P in a caspase-dependent pathway that ultimately leads to the activation of the intrinsic apoptotic pathway, which is well characterized with the downregulation of bcl-2, the decrease of mitochondrial membrane potential, the release of mitochondrial cytochrome c, the activation of caspase-9 and caspase-3, and finally the cleavage of poly (ADP-ribose) polymerase. Our results imply that wt P from GD-SH-01 mediates this effect may partly by facilitating viral RNA synthesis but not by viral replication. In sum, we demonstrate a wt RABV strain GD-SH-01 to induce stronger apoptosis than an attenuated RABV HEP-Flury and propose that wt P from GD-SH-01 is involved in this process.

Pathogenicity and Immunogenicity of Recombinant Rabies Viruses Expressing the Lagos Bat Virus Matrix and Glycoprotein: Perspectives for a Pan-Lyssavirus Vaccine

Lagos bat virus (LBV) is a phylogroup II lyssavirus exclusively found in Africa. Previous studies indicated that this virus is lethal to mice after intracranial and intramuscular inoculation. The antigenic composition of LBV differs substantially from that of rabies virus (RABV) and current rabies vaccines do not provide cross protection against phylogroup II lyssaviruses. To investigate the potential role of the LBV matrix protein (M) and glycoprotein (G) in pathogenesis, reverse genetics technology was used to construct recombinant viruses. The genes encoding the glycoprotein, or the matrix and glycoprotein of the attenuated RABV strain SPBN, were replaced with those of LBV resulting in SPBN-LBVG and SPBN-LBVM-LBVG, respectively. To evaluate the immunogenicity of the LBV G, the recombinant RABV SPBNGAS-LBVG-GAS was constructed with the LBV G inserted between two mutated RABV G genes (termed GAS). All the recombinant viruses were lethal to mice after intracranial (i.c.) inoculation although the pathogenicity of SPBNGAS-LBVG-GAS was lower compared to the other recombinant viruses. Following intramuscular (i.m.) inoculation, only SPBN-LBVM-LBVG was lethal to mice, indicating that both the M and G of LBV play a role in the pathogenesis. Most interestingly, serum collected from mice that were inoculated i.m. with SPBNGAS-LBVG-GAS neutralized phylogroup I and II lyssaviruses including RABV, Duvenhage virus (DUVV), LBV, and Mokola virus (MOKV), indicating that this recombinant virus has potential to be developed as a pan-lyssavirus vaccine.

Immunological aspects of rabies: a literature review

Rabies is a lethal disease caused by the neurotropic virus rabies virus (RABV), and it remains an important public health problem globally. It is known that the host immune response is important for control of viral infection and promoting viral clearance. In this context, it is well documented that, in addition to RABV neutralizing antibody, interferons and cell-mediated immunity also have an important role in preventing the establishment of disease. On the other hand, RABV suppresses host immunity through different mechanisms, for example, direct inhibition of host gene expression, sequestration of pathogen-associated molecular patterns, or modification of cytokine signalling pathways, which hinder the protective host immune responses to RABV infection. Here, we review the immunological aspects of rabies, highlighting innate and adaptive immunity, as well as the host evasion immune mechanisms used by the virus. Finally, we briefly discuss how this knowledge can direct new research and be harnessed for future therapeutic strategies.

Increased transgene expression level of rabies virus vector for transsynaptic tracing

Viral vectors that can infect neurons transsynaptically and can strongly express foreign genes are useful for investigating the organization of neural circuits. We previously developed a propagation-competent rabies virus (RV) vector based on a highly attenuated HEP-Flury strain (rHEP5.0-CVSG), which selectively infects neurons and propagates between synaptically connected neurons in a retrograde direction. Its relatively low level of transgene expression, however, makes immunostaining necessary to visualize the morphological features of infected neurons. To increase the transgene expression level of this RV vector, in this study we focused on two viral proteins: the large protein (L) and matrix protein (M). We first attempted to enhance the expression of L, which is a viral RNA polymerase, by deleting the extra transcription unit and shortening the intergenic region between the G and L genes. This viral vector (rHEP5.0-GctL) showed increased transgene expression level with efficient transsynaptic transport. We next constructed an RV vector with a rearranged gene order (rHEP5.0-GML) with the aim to suppress the expression of M, which plays a regulatory role in virus RNA synthesis. Although this vector showed high transgene expression level, the efficiency of transsynaptic transport was low. To further evaluate the usability of rHEP5.0-GctL as a transsynaptic tracer, we inserted a fluorescent timer as a transgene, which changes the color of its fluorescence from blue to red over time. This viral vector enabled us the differentiation of primary infected neurons from secondary infected neurons in terms of the fluorescence wavelength. We expect this propagation-competent RV vector to be useful for elucidating the complex organization of the central nervous system.

Comparison of G protein sequences of South African street rabies viruses showing distinct progression of the disease in a mouse model of experimental rabies

Rabies is a fatal zoonotic disease and infections generally lead to a fatal encephalomyelitis in both humans and animals. In South Africa, domestic (dogs) and the wildlife (yellow mongoose) host species maintain the canid and mongoose rabies variants respectively. In this study, pathogenicity differences of South African canid and mongoose rabies viruses were investigated in a murine model, by assessing the progression of clinical signs and survivorship. Comparison of glycoprotein gene sequences revealed amino acid differences that may underpin the observed pathogenicity differences. Cumulatively, our results suggest that the canid rabies virus may be more neurovirulent in mice than the mongoose rabies variant.

Investigation of rabies virus glycoprotein carboxyl terminus as an in vitro predictive tool of neurovirulence. A 3R approach

In the field of live viral vaccines production, there is an unmet need for in vitro tests complying a 3R approach (Refine, Replace and Reduce the use of animal experimentation) to replace the post-licensing safety tests currently assayed in animals. Here, we performed a pilot study evaluating whether virulence of rabies virus, RABV, can be forecast by an in vitro test of neurite outgrowth. The rationale to use neurite outgrowth as a read-out for this test is based on the salient property of the cytoplasmic domain of the G-protein (Cyto-G) of virulent RABV strains - not of attenuated RABV strains - to stimulate neurite outgrowth in vitro. We observed that neurite elongation triggered by the Cyto-Gs encoded by different RABV field isolates correlate with the distinct virulence scores obtained in a mouse model of experimental rabies. Our results cast the idea that it could be feasible to predict RABV virulence by testing the in vitro property of a RABV strain to promote neurite outgrowth without the use of animal experimentation.

Phenotypic Consequences In vivo and In vitro of Rearranging the P Gene of RABV HEP-Flury

Phosphoprotein (P) of the Rabies virus (RABV) is critically required for viral replication and pathogenicity. Here we manipulated infectious cDNA clones of the RABV HEP-Flury to translocate the P gene from its wild-type position 2 to 1, 3, or 4 in gene order, using an approach which left the viral nucleotide sequence unaltered. The recovered viruses were evaluated for the levels of gene expression, growth kinetics in cell culture, lethality in suckling mice and protection of mice. The results showed that viral replication was affected by the absolute value of N protein which was regulated by P protein. Viral lethality in suckling mice was consistent with the ratio of P mRNA in one complete transcription. The protection of mice induced by viruses was related to the antibody titer 5 weeks post-infection which might be regulated by G protein. However, the ability to induce cell apoptosis and viral spread were not only related to the viral replication but also to the ratio of related gene which affected by the gene position. These findings might not only improve the understanding of phenotype of RABV and P gene rearrangement, but also help rabies vaccine candidate construction.

Systems Biomedicine of Rabies Delineates the Affected Signaling Pathways

The prototypical neurotropic virus, rabies, is a member of the Rhabdoviridae family that causes lethal encephalomyelitis. Although there have been a plethora of studies investigating the etiological mechanism of the rabies virus and many precautionary methods have been implemented to avert the disease outbreak over the last century, the disease has surprisingly no definite remedy at its late stages. The psychological symptoms and the underlying etiology, as well as the rare survival rate from rabies encephalitis, has still remained a mystery. We, therefore, undertook a systems biomedicine approach to identify the network of gene products implicated in rabies. This was done by meta-analyzing whole-transcriptome microarray datasets of the CNS infected by strain CVS-11, and integrating them with interactome data using computational and statistical methods. We first determined the differentially expressed genes (DEGs) in each study and horizontally integrated the results at the mRNA and microRNA levels separately. A total of 61 seed genes involved in signal propagation system were obtained by means of unifying mRNA and microRNA detected integrated DEGs. We then reconstructed a refined protein–protein interaction network (PPIN) of infected cells to elucidate the rabies-implicated signal transduction network (RISN). To validate our findings, we confirmed differential expression of randomly selected genes in the network using Real-time PCR. In conclusion, the identification of seed genes and their network neighborhood within the refined PPIN can be useful for demonstrating signaling pathways including interferon circumvent, toward proliferation and survival, and neuropathological clue, explaining the intricate underlying molecular neuropathology of rabies infection and thus rendered a molecular framework for predicting potential drug targets.

Subversion of the Immune Response by Rabies Virus

Rabies has affected mankind for several centuries and is one of the oldest known zoonoses. It is peculiar how little is known regarding the means by which rabies virus (RABV) evades the immune response and kills its host. This review investigates the complex interplay between RABV and the immune system, including the various means by which RABV evades, or advantageously utilizes, the host immune response in order to ensure successful replication and spread to another host. Different factors that influence immune responses—including age, sex, cerebral lateralization and temperature—are discussed, with specific reference to RABV and the effects on host morbidity and mortality. We also investigate the role of apoptosis and discuss whether it is a detrimental or beneficial mechanism of the host’s response to infection. The various RABV proteins and their roles in immune evasion are examined in depth with reference to important domains and the downstream effects of these interactions. Lastly, an overview of the means by which RABV evades important immune responses is provided. The research discussed in this review will be important in determining the roles of the immune response during RABV infections as well as to highlight important therapeutic target regions and potential strategies for rabies treatment.

Rabies virus matrix protein induces apoptosis by targeting mitochondria

Apoptosis, as an innate antiviral defense, not only functions to limit viral replication by eliminating infected cells, but also contribute to viral dissemination, particularly at the late stages of infection. A highly neurotropic CVS strain of rabies virus induces apoptosis both in vitro and in vivo. However, the detailed mechanism of CVS-mediated neuronal apoptosis is not entirely clear. Here, we show that CVS induces apoptosis through mitochondrial pathway by dissipating mitochondrial membrane potential, release of cytochrome c and AIF. CVS blocks Bax activation at the early stages of infection; while M protein partially targets mitochondria and induces mitochondrial apoptosis at the late stages of infection. The α-helix structure spanning 67-79 amino acids of M protein is essential for mitochondrial targeting and induction of apoptosis. These results suggest that CVS functions on mitochondria to regulate apoptosis at different stages of infection, so as to for viral replication and dissemination.

Intrinsic, extrinsic and endoplasmic reticulum stress-induced apoptosis in RK13 cells infected with equine arteritis virus

The modulation of the expression of caspases by viruses influences the cell survival of different cell types. Equine arteritis virus (EAV) induces apoptosis of BHK21 and Vero cell lines, but it is not known whether EAV induces apoptosis in RK13 cells, a common cell line routinely used in EAV diagnosis and research. In this study, we determined that caspase-3 expression was triggered after infection of RK13 cells with EAV in a time- and dose-dependent manner. We also detected caspase-8 and caspase-9 activation, indicating the stimulation of both extrinsic and intrinsic apoptosis pathways. Finally, we found caspase-12 activation, an indicator of endoplasmic reticulum stress-induced apoptosis. The variability observed in the apoptotic response in the different cell lines demonstrates that apoptosis depends on the distinctive sensitivity of each cell line used for investigation.

Role of the glycoprotein G in lyssavirus pathogenicity

Rabies is a fatal zoonotic disease caused by the highly neurotropic members of the Lyssavirus genus (Rhabdoviridae family). These viruses contain an RNA genome that encodes information for five viral proteins: the nucleoprotein (N), the glycoprotein (G), the phosphoprotein (P), matrix (M) and an RNA-dependent RNA polymerase (L). The glycoprotein is the major contributor of viral pathogenicity. However, nucleotide changes in specific regions of the G-protein influence the ability of the rabies virus to cause death in experimental animals but also the ability to move within the neuronal network. In addition to the glycoprotein, other regions of the viral genome may also contribute to pathogenicity, underlining the multigenic nature of the lyssavirus.

Deciphering the unconventional peptide binding to the PDZ domain of MAST2

Peptide binding on to microtubule-associated serine threonine kinase 2 (MAST2)—PDZ (PSD-95, Dlg1, Zo-1) prevents dimerization of the domain without directly competing with the monomer interface. Peptide binding affects positions distal from the binding groove through a network of residues undergoing subtle changes of conformation and dynamics.

Autophagy is involved in recombinant Newcastle disease virus (rL-RVG)-induced cell death of stomach adenocarcinoma cells in vitro

Oncolytic viruses can kill malignant cells while sparing normal cells. Multiple pathways are involved in this action. The antitumor effects of viral infection on SGC-7901 and AGS cells were investigated. We measured endoplasmic reticulum stress and autophagy caused by the recombinant avirulent Newcastle disease virus (NDV) LaSota strain expressing the rabies virus glycoprotein (rL-RVG) and the NDV wild-type strain. The dose-response curves were analyzed using the MTT assay. The expression of RVG was detected by western blotting, RT-PCR and immunofluorescence analyses. Cell death and autophagy were observed using transmission electron microscopy, TUNEL and western blotting. Endoplasmic reticulum stress and the mitochondrial transmembrane potential were detected by western blotting and immunofluorescence, respectively. Immunofluorescence, western blot and RT-PCR analyses indicated that RVG gene and protein were expressed in SGC-7901 and AGS cells infected by rL-RVG. MTT and TUNEL analyses showed that the growth of SGC-7901 and AGS cells in the rL-RVG-infected group was significantly inhibited compared with the wild-type NDV-infected group (p<0.05). Western blot analysis indicated that rL-RVG and NDV induced increases in apoptosis, endoplasmic reticulum stress, and autophagy in the SGC-7901 and AGS cells. However, apoptosis and autophagy decreased in these cells after the application of the autophagy pathway inhibitor 3-MA or ATG-5-specific siRNA. Immunofluorescence analysis showed that the mitochondrial membrane potential collapsed. Taken together, these results indicate that the rL-RVG virus group is much more powerful compared with the NDV-infected group (p<0.05). rL-RVG and NDV are potent antitumor agents that induce autophagy.

Effects of G-gene Deletion and Replacement on Rabies Virus Vector Gene Expression

The glycoprotein-gene (G gene) -deleted rabies virus (RV) vector is a powerful tool to examine the function and structure of neural circuits. We previously reported that the deletion of the G gene enhances the transgene expression level of the RV vector. However, the mechanism of this enhancement remains to be clarified. We presume that there are two possible factors for this enhancement. The first factor is the glycoprotein of RV, which shows cytotoxicity; thus, may cause a dysfunction in the translation process of infected cells. The second possible factor is the enhanced expression of the L gene, which encodes viral RNA polymerase. In the RV, it is known that the gene expression level is altered depending on the position of the gene. Since G-gene deletion displaces the L gene in the genome, the expression of the L gene and viral transcription may be enhanced. In this study, we compared the transgene expression level and viral transcription of three recombinant RV vectors. The effect of glycoprotein was examined by comparing the viral gene expression of G-gene-intact RV and G-gene-replaced RV. Despite the fact that the L-gene transcription level of these two RV vectors was similar, the G-gene-replaced RV vector showed higher viral transcription and transgene expression level than the G-gene-intact RV vector. To examine the effect of the position of the L gene, we compared the viral gene expression of the G-gene-deleted RV and G-gene-replaced RV. The G-gene-deleted RV vector showed higher L-gene transcription, viral transcription, and transgene expression level than the G-gene-replaced RV vector. These results indicate that G-gene deletion enhances the transgene expression level through at least two factors, the absence of glycoprotein and enhancement of L-gene expression. These findings enable investigators to design a useful viral vector that shows a controlled desirable transgene expression level in applications.

Association between RABV G Proteins Transported from the Perinuclear Space to the Cell Surface Membrane and N-Glycosylation of the Sequon Asn(204)

In this study, G proteins of the rabies virus (RABV) Kyoto strain were detected in the cytoplasm but not distributed at the cell membrane of mouse neuroblastoma (MNA) cells. G proteins of CVS-26 were detected in both the cell membrane and perinuclear space of MNA cells. We found that N-glycosylation of street RABV G protein by the insertion of the sequon Asn(204) induced the transfer of RABV G proteins to the cell surface membrane. Fixed RABV budding from the plasma membrane has been found to depend not only on G protein but also on other structural proteins such as M protein. However, the differing N-glycosylation of G protein could be associated with the distinct budding and antigenic features of RABV in street and fixed viruses. Our study of the association of N-glycan of G protein at Asn(204) with the transport of RABV G protein to the cell surface membrane contributes to the understanding of the evolution of fixed virus from street virus, which in turn would help for determine the mechanism underlying RABV budding and enhanced host immune responses.

A recombinant canine distemper virus expressing a modified rabies virus glycoprotein induces immune responses in mice

Canine distemper virus (CDV) and rabies virus (RV) are two important pathogens of the dog. CDV, a member of the morbillivirus genus, has shown promise as an expression vector. The glycoprotein from RV is a main contributor to protective immunity and capable of eliciting the production of virus-neutralizing antibodies. In this study, we recovered an attenuated strain of canine distemper virus and constructed a recombinant virus, rCDV-RV-G, expressing a modified (R333Q) rabies virus glycoprotein (RV-G) of RV Flury strain LEP. RV-G expression by the recombinant viruses was confirmed. Furthermore, G was proved to be incorporated into the surface of CDV particles. While replication of the recombinant virus was slightly reduced compared with the parental CDV, it stably expressed the RV-G over ten serial passages. Inoculation of mice induced specific neutralizing antibodies against both RV-G and CDV. Therefore, the rCDV-RV-G has the potential as a vaccine that may be used to control rabies virus infection in dogs and other animals.

Strategies to interfere with PDZ-mediated interactions in neurons: What we can learn from the rabies virus

PDZ (PSD-95/Dlg/ZO-1) domains play a major role in neuronal homeostasis in which they act as scaffold domains regulating cellular trafficking, self-association and catalytic activity of essential proteins such as kinases and phosphatases. Because of their central role in cell signaling, cellular PDZ-containing proteins are preferential targets of viruses to hijack cellular function to their advantage. Here, we describe how the viral G protein of the rabies virus specifically targets the PDZ domain of neuronal enzymes during viral infection. By disrupting the complexes formed by cellular enzymes and their ligands, the virus triggers drastic effect on cell signaling and commitment of the cell to either survival (virulent strains) or death (vaccinal strains). We provide structural and biological evidences that the viral proteins act as competitors endowed with specificity and affinity in an essential cellular process by mimicking PDZ binding motif of cellular partners. Disruption of critical endogenous protein-protein interactions by viral protein drastically alters intracellular protein trafficking and catalytic activity of cellular proteins that control cell homeostasis. This work opens up many perspectives to mimic viral sequences and developing innovative therapies to manipulate cellular homeostasis.

Apoptotic induction of lung adenocarcinoma A549 cells infected by recombinant RVG Newcastle disease virus (rL-RVG) in vitro

Newcastle disease virus (NDV) is a member of the genus Avulavirus in the Paramyxoviridae family and its antitumor properties depend on its ability to kill malignant cells while not affecting normal cells. The present study investigated a recombinant avirulent NDV LaSota strain (wild-type NDV strain) expressing the rabies virus glycoprotein (rL-RVG), examined its oncolytic effect on the lung adenocarcinoma A549 cell line and evaluated its potential to serve as a vaccine against lung cancer. A549 cells were infected with the rL-RVG virus and analyzed by MTT, western blot, polymerase chain reaction (PCR), immunofluorescence, terminal deoxynucleotidyl transferase dUTP nick end labeling and flow-cytometric analyses. PCR, western blot and immunofluorescence showed that the RVG gene and protein were stably expressed in A549 cells following infection with rL-RVG. The growth of A549 cells in the rL-RVG group was inhibited more effectively compared to those infected with the wild-type NDV strain. MTT results showed that cell growth inhibition rates in the rL-RVG group were significantly higher than those in the NDV group (P<0.05). Early apoptosis in the rL-RVG group was also more evident, with the apoptotic index being increased in rL-RVG group. The expression of the pro-apoptotic proteins caspase-3, -8 and -9 increased. The expression of caspase-3 decreased following application of the broad-specificity caspase inhibitor Z-VAD-FMK. However, the expression of the inhibitory apoptosis protein B-cell lymphoma 2 (bcl-2) did not change, but bcl-2-associated X/bcl-2 ratio was higher in the rL-RVG group than that in the NDV group. The rL-RVG strain was able to suppress lung cancer cell growth and promote lung cancer cell apoptosis to a greater extent than the wild-type NDV strain. Therefore, the rL-RVG strain is a potent antitumor agent.

Multigenic Relation to the Attenuation of Rabies Virus

Rabies virus Nishigahara strain causes lethal infection in adult mice after intracerebral inoculation. On the other hand, the RC-HL strain, derived from the Nishigahara strain, does not cause lethal infection in adult mice. We previously demonstrated that a chimeric virus, R(G), with the open reading frame of the G gene (G-ORF) from the Nishigahara strain in the background of the RC-HL genome, is virulent. Reversely, in order to demonstrate that the G gene of the RC-HL strain is related to the attenuated phenotype, we established a reverse genetics system of the Nishigahara strain and generated a chimeric virus, Ni(G), with the G-ORF from RC-HL in the background of the Nishigahara genome. Contrary to our prediction, Ni(G) killed adult mice after intracerebral inoculation with neuropathic symptoms like those of Nishigahara strain infection. Therefore, the G-ORF of the RC-HL strain is not the sole determinant of the attenuated phenotype. In additional investigation, we examined other genes, including N, P, M and L genes, and generated chimeric viruses exhaustively. We found that chimeric viruses with a single gene from the RC-HL were not attenuated and that chimeric viruses with the G-ORF and at least one other ORF from the RC-HL were attenuated. In conclusion, attenuation from the Nishigahara to RC-HL strain is multigenic.

Rabies virus vector transgene expression level and cytotoxicity improvement induced by deletion of glycoprotein gene

The glycoprotein (G) of rabies virus (RV) is required for binding to neuronal receptors and for viral entry. G-deleted RV vector is a powerful tool for investigating the organization and function of the neural circuits. It gives the investigator the ability to genetically target initial infection to particular neurons and to control trans-synaptic propagation. In this study we have quantitatively evaluated the effect of G gene deletion on the cytotoxicity and transgene expression level of the RV vector. We compared the characteristics of the propagation-competent RV vector (rHEP5.0-CVSG-mRFP) and the G-deleted RV vector (rHEP5.0-ΔG-mRFP), both of which are based on the attenuated HEP-Flury strain and express monomeric red fluorescent protein (mRFP) as a transgene. rHEP5.0-ΔG-mRFP showed lower cytotoxicity than rHEP5.0-CVSG-mRFP, and within 16 days of infection we found no change in the basic electrophysiological properties of neurons infected with the rHEP5.0-ΔG-mRFP. The mRFP expression level of rHEP5.0-ΔG-mRFP was much higher than that of rHEP5.0-CVSG-mRFP, and 3 days after infection the retrogradely infected neurons were clearly visualized by the expressed fluorescent protein without any staining. This may be due to the low cytotoxicity and/or the presumed change in the polymerase gene (L) expression level of the G-deleted RV vector. Although the mechanisms remains to be clarified, the results of this study indicate that deletion of the G gene greatly improves the usability of the RV vector for studying the organization and function of the neural circuits by decreasing the cytotoxicity and increasing the transgene expression level.

Evaluation of single and dual siRNAs targeting rabies virus glycoprotein and nucleoprotein genes for inhibition of virus multiplication in vitro

Small interfering RNAs (siRNAs) targeting rabies virus (RV) glycoprotein (G) and nucleoprotein (N) genes were evaluated as antiviral agents against rabies virus in vitro in BHK-21 cells. To select effective siRNAs targeting RV-G, a plasmid-based transient co-transfection approach was used. In this, siRNAs were expressed as short hairpin RNAs (shRNAs), and their ability to inhibit RV-G gene expression was evaluated in cells transfected with a plasmid expressing RV-G. The nine different siRNAs designed to target RV-G exhibited varying degrees of knockdown of RV-G gene expression. One siRNA (si-G7) with considerable effect in knockdown of RV-G expression also demonstrated significant inhibition of RV multiplication in BHK-21 cells after in vitro challenge with the RV Pasteur virus-11 (PV-11) strain. A decrease in the number of fluorescent foci in siRNA-treated cells and a reduction (86.8 %) in the release of RV into infected cell culture supernatant indicated the anti-rabies potential of siRNA. Similarly, treatment with one siRNA targeting RV-N resulted in a decrease in the number of fluorescent foci and a reduction (85.9 %) in the release of RV. As a dual gene silencing approach where siRNAs targeting RV-G and RV-N genes were expressed from single construct, the anti-rabies-virus effect was observed as an 87.4 % reduction in the release of RV. These results demonstrate that siRNAs targeting RV-G and N, both in single and dual form, have potential as antiviral agent against rabies.

Involvement of the rabies virus phosphoprotein gene in neuroinvasiveness

Rabies virus (RABV), which is transmitted via a bite wound caused by a rabid animal, infects peripheral nerves and then spreads to the central nervous system (CNS) before causing severe neurological symptoms and death in the infected individual. Despite the importance of this ability of the virus to spread from a peripheral site to the CNS (neuroinvasiveness) in the pathogenesis of rabies, little is known about the mechanism underlying the neuroinvasiveness of RABV. In this study, to obtain insights into the mechanism, we conducted comparative analysis of two fixed RABV strains, Nishigahara and the derivative strain Ni-CE, which cause lethal and asymptomatic infections, respectively, in mice after intramuscular inoculation. Examination of a series of chimeric viruses harboring the respective genes from Nishigahara in the genetic background of Ni-CE revealed that the Nishigahara phosphoprotein (P) gene plays a major role in the neuroinvasiveness by mediating infection of peripheral nerves. The results obtained from both in vivo and in vitro experiments strongly suggested that the Nishigahara P gene, but not the Ni-CE P gene, is important for stable viral replication in muscle cells. Further investigation based on the previous finding that RABV phosphoprotein counteracts the host interferon (IFN) system demonstrated that the Nishigahara P gene, but not the Ni-CE P gene, functions to suppress expression of the beta interferon (IFN-β) gene (Ifn-β) and IFN-stimulated genes in muscle cells. In conclusion, we provide the first data strongly suggesting that RABV phosphoprotein assists viral replication in muscle cells by counteracting the host IFN system and, consequently, enhances infection of peripheral nerves.