CD155 is a putative therapeutic target in medulloblastoma.

BACKGROUND: Medulloblastoma is the most common pediatric malignant brain tumor, consisting of four molecular subgroups (WNT, SHH, Group 3, Group 4) and 12 subtypes. Expression of the cell surface poliovirus receptor (PVR), CD155, is necessary for entry of the viral immunotherapeutic agent, PVSRIPO, a polio:rhinovirus chimera. CD155, physiologically expressed in the mononuclear phagocytic system, is widely expressed ectopically in solid tumors. The objective of this study is to elucidate CD155 expression as both a receptor for PVSRIPO and a therapeutic target in medulloblastoma. METHODS: PVR mRNA expression was determined in several patient cohorts and human medulloblastoma cell lines. Patient samples were also analyzed for CD155 expression using immunohistochemistry and cell lines were analyzed using Western Blots. CD155 was blocked using a monoclonal antibody and cell viability, invasion, and migration were assessed. RESULTS AND DISCUSSION: PVR mRNA expression was highest in the WNT subgroup and lowest in Group 4. PVR expression in the subgroups of medulloblastoma were similar to other pediatric brain and non-brain tumors. PVR expression was largely not associated with subgroup or subtype. Neither PVR protein expression intensity nor frequency were associated with overall survival. PVR expression was elevated in Group 3 patients with metastases but there was no difference in paired primary and metastatic medulloblastoma. Blocking PVR resulted in dose-dependent cell death, decreased invasion in vitro, and modestly inhibited cell migration. CONCLUSIONS: CD155 is expressed across medulloblastoma subgroups and subtypes. Blocking CD155 results in cell death and decreased cellular invasion. This study provides rationale for CD155-targeting agents including PVSRIPO and antibody-mediated blockade of CD155.

Elusive Trans-Acting Factors Which Operate with Type I (Poliovirus-like) IRES Elements.

The phenomenon of internal initiation of translation was discovered in 1988 on poliovirus mRNA. The prototypic cis-acting element in the 5' untranslated region (5'UTR) of poliovirus mRNA, which is able to direct initiation at an internal start codon without the involvement of a cap structure, has been called an IRES (Internal Ribosome Entry Site or Segment). Despite its early discovery, poliovirus and other related IRES elements of type I are poorly characterized, and it is not yet clear which host proteins (a.k.a. IRES trans-acting factors, ITAFs) are required for their full activity in vivo. Here we discuss recent and old results devoted to type I IRESes and provide evidence that Poly(rC) binding protein 2 (PCBP2), Glycyl-tRNA synthetase (GARS), and Cold Shock Domain Containing E1 (CSDE1, also known as UNR) are major regulators of type I IRES activity.

Essential Domains of Oxysterol-Binding Protein Required for Poliovirus Replication.

Oxysterol-binding protein (OSBP) is a host factor required for enterovirus (EV) replication. OSBP locates at membrane contact site and acts as a lipid exchanger of cholesterol and phosphatidylinositol 4-phosphate (PI4P) between cellular organelles; however, the essential domains required for the viral replication remain unknown. In this study, we define essential domains of OSBP for poliovirus (PV) replication by a functional dominance assay with a series of deletion variants of OSBP. We show that the pleckstrin homology domain (PHD) and the ligand-binding domain, but not the N-terminal intrinsically disordered domain, coiled-coil region, or the FFAT motif, are essential for PV replication. The PHD serves as the primary determinant of OSBP targeting to the replication organelle in the infected cells. These results suggest that not all the domains that support important biological functions of OSBP are essential for the viral replication.

A conserved glutathione binding site in poliovirus is a target for antivirals and vaccine stabilisation.

Strategies to prevent the recurrence of poliovirus (PV) after eradication may utilise non-infectious, recombinant virus-like particle (VLP) vaccines. Despite clear advantages over inactivated or attenuated virus vaccines, instability of VLPs can compromise their immunogenicity. Glutathione (GSH), an important cellular reducing agent, is a crucial co-factor for the morphogenesis of enteroviruses, including PV. We report cryo-EM structures of GSH bound to PV serotype 3 VLPs showing that it can enhance particle stability. GSH binds the positively charged pocket at the interprotomer interface shown recently to bind GSH in enterovirus F3 and putative antiviral benzene sulphonamide compounds in other enteroviruses. We show, using high-resolution cryo-EM, the binding of a benzene sulphonamide compound with a PV serotype 2 VLP, consistent with antiviral activity through over-stabilizing the interprotomer pocket, preventing the capsid rearrangements necessary for viral infection. Collectively, these results suggest GSH or an analogous tight-binding antiviral offers the potential for stabilizing VLP vaccines.

Retrograde axonal transport of poliovirus and EV71 in motor neurons.

Poliovirus (PV) can spread through neural pathway to the central nervous system and replicates in motor neurons, which leads to poliomyelitis. Enterovirus 71 (EV71), which is closely related to PV, is one of the causative agents of hand-foot-and-mouth disease and can cause severe neurological diseases similar to poliomyelitis. Since PV is similar to EV71 in its motor neurotoxicity, we tried to understand if the results obtained with PV are of general applicability to EV71 and other viruses with similar characteristics. Using microfluidic devices, we demonstrated that both PV capsid and the PV genome undergo axonal retrograde transport with human PV receptor (hPVR), and the transported virus replicated in the soma of hPVR-expressing motor neurons. Similar to PV in hPVR-transgenic (Tg) mice, neural pathway ensuring spreading of EV71 has been shown in adult human scavenger receptor class B, member 2 (hSCARB2)-Tg mice. We have validated this finding in microfluidic devices by showing that EV71 is retrogradely transported together with hSCARB2 to the cell body where it replicates in an hSCARB2-dependent manner.

Live-attenuated poliovirus-induced extrinsic apoptosis through Caspase 8 within breast cancer cell lines expressing CD155.

INTRODUCTION: Breast cancer is one of the most common cancers among women in the world. Different therapeutic strategies such as radiotherapy, chemotherapy and surgery have been used either individually or in combination. Oncolytic virotherapy is a rising treatment methodology, which utilizes replicating viruses to eliminate tumor cells. The aim of this study was to investigate the oncolytic activity of live-attenuated poliovirus in breast cancer cell lines. MATERIALS AND METHODS: The CD155 expression level in two human breast cancer cell lines and a normal breast cell line were evaluated using real-time PCR and flow cytometry. Virus titration was assessed by TCID50. The cytotoxicity of poliovirus on cell line and apoptosis response was investigated by MTT and Caspase 8 and Caspase 9 ELISA kits, respectively. RESULTS: This study showed that CD155 gene was expressed significantly (p = 0.001) higher in both human breast cancer cell lines compared to the normal cell line. The protein expression level of CD155 was 98.1%, 96.7%, in MDA_MB231 and MCF_7 cell lines, respectively, whereas the CD155 expression level was 1.3% in MCF_10A. The cytopathic effect of poliovirus in breast cancer cell lines was significantly higher than normal cells (p < 0.05). Extrinsic apoptosis response was more effective than intrinsic apoptosis in both breast cancer cell lines (p < 0.05). CONCLUSION: In summary, administration of live-attenuated poliovirus can be a promising treatment to breast cancer. However, in vitro and in vivo studies will be required to evaluate the safety of this strategy.

A defective viral genome strategy elicits broad protective immunity against respiratory viruses.

RNA viruses generate defective viral genomes (DVGs) that can interfere with replication of the parental wild-type virus. To examine their therapeutic potential, we created a DVG by deleting the capsid-coding region of poliovirus. Strikingly, intraperitoneal or intranasal administration of this genome, which we termed eTIP1, elicits an antiviral response, inhibits replication, and protects mice from several RNA viruses, including enteroviruses, influenza, and SARS-CoV-2. While eTIP1 replication following intranasal administration is limited to the nasal cavity, its antiviral action extends non-cell-autonomously to the lungs. eTIP1 broad-spectrum antiviral effects are mediated by both local and distal type I interferon responses. Importantly, while a single eTIP1 dose protects animals from SARS-CoV-2 infection, it also stimulates production of SARS-CoV-2 neutralizing antibodies that afford long-lasting protection from SARS-CoV-2 reinfection. Thus, eTIP1 is a safe and effective broad-spectrum antiviral generating short- and long-term protection against SARS-CoV-2 and other respiratory infections in animal models.

High-Order Epistasis and Functional Coupling of Infection Steps Drive Virus Evolution toward Independence from a Host Pathway.

The phosphatidylinositol-4 kinase IIIß (PI4KB)/oxysterol-binding protein (OSBP) family I pathway serves as an essential host pathway for the formation of viral replication complex for viral plus-strand RNA synthesis; however, poliovirus (PV) could evolve toward substantial independence from this host pathway with four mutations. Recessive epistasis of the two mutations (3A-R54W and 2B-F17L) is essential for viral RNA replication. Quantitative analysis of effects of the other two mutations (2B-Q20H and 2C-M187V) on each step of infection reveals functional couplings between viral replication, growth, and spread conferred by the 2B-Q20H mutation, while no enhancing effect was conferred by the 2C-M187V mutation. The effects of the 2B-Q20H mutation occur only via another recessive epistasis between the 3A-R54W/2B-F17L mutations. These mutations confer enhanced replication in PI4KB/OSBP-independent infection concomitantly with an increased ratio of viral plus-strand RNA to the minus-strand RNA. This work reveals the essential roles of the functional coupling and high-order, multi-tiered recessive epistasis in viral evolution toward independence from an obligatory host pathway. IMPORTANCE Each virus has a different strategy for its replication, which requires different host factors. Enterovirus, a model RNA virus, requires host factors PI4KB and OSBP, which form an obligatory functional axis to support viral replication. In an experimental evolution system in vitro, virus mutants that do not depend on these host factors could arise only with four mutations. The two mutations (3A-R54W and 2B-F17L) are required for the replication but are not sufficient to support efficient infection. Another mutation (2B-Q20H) is essential for efficient spread of the virus. The order of introduction of the mutations in the viral genome is essential (known as "epistasis"), and functional couplings of infection steps (i.e., viral replication, growth, and spread) have substantial roles to show the effects of the 2B-Q20H mutation. These observations would provide novel insights into an evolutionary pathway of the virus to require host factors for infection.

Interaction of Poliovirus Capsid Proteins with the Cellular Autophagy Pathway.

The capsid precursor P1 constitutes the N-terminal part of the enterovirus polyprotein. It is processed into VP0, VP3, and VP1 by the viral proteases, and VP0 is cleaved autocatalytically into VP4 and VP2. We observed that poliovirus VP0 is recognized by an antibody against a cellular autophagy protein, LC3A. The LC3A-like epitope overlapped the VP4/VP2 cleavage site. Individually expressed VP0-EGFP and P1 strongly colocalized with a marker of selective autophagy, p62/SQSTM1. To assess the role of capsid proteins in autophagy development we infected different cells with poliovirus or encapsidated polio replicon coding for only the replication proteins. We analyzed the processing of LC3B and p62/SQSTM1, markers of the initiation and completion of the autophagy pathway and investigated the association of the viral antigens with these autophagy proteins in infected cells. We observed cell-type-specific development of autophagy upon infection and found that only the virion signal strongly colocalized with p62/SQSTM1 early in infection. Collectively, our data suggest that activation of autophagy is not required for replication, and that capsid proteins contain determinants targeting them to p62/SQSTM1-dependent sequestration. Such a strategy may control the level of capsid proteins so that viral RNAs are not removed from the replication/translation pool prematurely.

The risk of unintentional propagation of poliovirus can be minimized by using human cell lines lacking the functional CD155 gene.

After eradication and containment of wild poliovirus (PV) and cessation of oral polio vaccinations, it is critical to minimize the risk of reintroducing PV into PV-free communities via facilities that handle the virus. The potential risk of unintentional PV propagation through unidentified contaminated materials is a serious issue. This study reports the generation of HeLa and RD-A cells deficient in functional CD155 gene (∆PVR cells); these cells are not susceptible to PV but remain susceptible to other picornaviruses. These ∆PVR cells will minimize the risk of unintentional transmission of PV and support performing the experiments more safely.

Synthetic Genomes.

DNA synthesis technology has progressed to the point that it is now practical to synthesize entire genomes. Quite a variety of methods have been developed, first to synthesize single genes but ultimately to massively edit or write from scratch entire genomes. Synthetic genomes can essentially be clones of native sequences, but this approach does not teach us much new biology. The ability to endow genomes with novel properties offers special promise for addressing questions not easily approachable with conventional gene-at-a-time methods. These include questions about evolution and about how genomes are fundamentally wired informationally, metabolically, and genetically. The techniques and technologies relating to how to design, build, and deliver big DNA at the genome scale are reviewed here. A fuller understanding of these principles may someday lead to the ability to truly design genomes from scratch.

Serostatus following polio-containing vaccination before and after liver transplantation.

BACKGROUND: The strategy to eradicate polio is based on preventing infection by immunizing all children until the world is polio-free. However, data regarding efficacy of polio-containing vaccination in immunocompromised patients such as LT recipients are limited. METHODS: We conducted an observational study at the largest pediatric transplant center in Japan from January 2011 to January 2015. LT recipients were enrolled after transplantation, and those who had completed the Japanese polio vaccination program were eligible for the study. Patients' demographics were collected from their medical records. Antibody titers against poliovirus serotypes 1-3 were measured using the neutralization test at the routine follow-up visits after enrollment. Factors associated with seropositivity against each type of poliovirus were evaluated. RESULTS: Sixty-four patients who had received the complete polio vaccination series were enrolled in the study. Of these, 37 patients had received all series of polio-containing vaccination before LT. Median age of the patients was 75 months. Their underlying diseases included the following: 40 (63%) with cholestatic liver diseases and 11 (17%) with metabolic disorders. After a median interval of 43 months after LT, seropositivity rates against poliovirus 1, 2, and 3 were 93.8% (60/64), 92.2% (59/64), and 54.7% (35/64), respectively. Among 32 patients who had received only oral polio vaccine (OPV), seropositivity against poliovirus 3 was particularly low (25.0%). No factors associated with seropositivity against each type of poliovirus were identified. CONCLUSIONS: In the LT recipients, seropositivity for poliovirus 3 was low, suggesting a need for additional inactivated polio-containing vaccination after LT, especially for patients who had received only OPV.

Ribosomal protein RACK1 enhances translation of poliovirus and other viral IRESs.

Viruses have evolved strategies to ensure efficient translation using host cell ribosomes and translation factors. In addition to cleaving translation initiation factors required for host cell translation, poliovirus (PV) uses an internal ribosome entry site (IRES). Recent studies suggest that viruses exploit specific ribosomal proteins to enhance translation of their viral proteins. The ribosomal protein receptor for activated C kinase 1 (RACK1), a protein of the 40S ribosomal subunit, was previously shown to mediate translation from the 5' cricket paralysis virus and hepatitis C virus IRESs. Here we found that translation of a PV dual-luciferase reporter shows a moderate dependence on RACK1. However, in the context of a viral infection we observed significantly reduced poliovirus plaque size and titers and delayed host cell translational shut-off. Our findings further illustrate the involvement of the cellular translational machinery during PV infection and how viruses usurp the function of specific ribosomal proteins.

Structure of MHC-Independent TCRs and Their Recognition of Native Antigen CD155.

During normal T cell development in the thymus, αß TCRs signal immature thymocytes to differentiate into mature T cells by binding to peptide-MHC ligands together with CD4/CD8 coreceptors. Conversely, in MHC and CD4/CD8 coreceptor-deficient mice, the thymus generates mature T cells expressing MHC-independent TCRs that recognize native conformational epitopes rather than linear antigenic-peptides presented by MHC. To date, no structural information of MHC-independent TCRs is available, and their structural recognition of non-MHC ligand remains unknown. To our knowledge in this study, we determined the first structures of two murine MHC-independent TCRs (A11 and B12A) that bind with high nanomolar affinities to mouse adhesion receptor CD155. Solution binding demonstrated the Vαß-domain is responsible for MHC-independent B12A recognition of its ligand. Analysis of A11 and B12A sequences against various MHC-restricted and -independent TCR sequence repertoires showed that individual V-genes of A11 and B12A did not exhibit preference against MHC-restriction. Likewise, CDR3 alone did not discriminate against MHC binding, suggesting VDJ recombination together with Vα/Vß pairing determine their MHC-independent specificity for CD155. The structures of A11 and B12A TCR are nearly identical to those of MHC-restricted TCR, including the conformations of CDR1 and 2. Mutational analysis, together with negative-staining electron microscopy images, showed that the CDR regions of A11 and B12A recognized epitopes on D1 domain of CD155, a region also involved in CD155 binding to poliovirus and Tactile in human. Taken together, MHC-independent TCRs adopt canonical TCR structures to recognize native Ags, highlighting the importance of thymic selection in determining TCR ligand specificity.

A Redundant Mechanism of Recruitment Underlies the Remarkable Plasticity of the Requirement of Poliovirus Replication for the Cellular ArfGEF GBF1.

The replication of many positive-strand RNA viruses [(+)RNA viruses] depends on the cellular protein GBF1, but its role in the replication process is not clear. In uninfected cells, GBF1 activates small GTPases of the Arf family and coordinates multiple steps of membrane metabolism, including functioning of the cellular secretory pathway. The nonstructural protein 3A of poliovirus and related viruses has been shown to directly interact with GBF1, likely mediating its recruitment to the replication complexes. Surprisingly, viral mutants with a severely reduced level of 3A-GBF1 interaction demonstrate minimal replication defects in cell culture. Here, we systematically investigated the conserved elements of GBF1 to understand which determinants are important to support poliovirus replication. We demonstrate that multiple GBF1 mutants inactive in cellular metabolism could still be fully functional in the replication complexes. Our results show that the Arf-activating property, but not the primary structure of the Sec7 domain, is indispensable for viral replication. They also suggest a redundant mechanism of recruitment of GBF1 to the replication sites, which is dependent not only on direct interaction of the protein with the viral protein 3A but also on determinants located in the noncatalytic C-terminal domains of GBF1. Such a double-targeting mechanism explains the previous observations of the remarkable tolerance of different levels of GBF1-3A interaction by the virus and likely constitutes an important element of the resilience of viral replication.IMPORTANCE Enteroviruses are a vast group of viruses associated with diverse human diseases, but only two of them could be controlled with vaccines, and effective antiviral therapeutics are lacking. Here, we investigated in detail the contribution of a cellular protein, GBF1, in the replication of poliovirus, a representative enterovirus. GBF1 supports the functioning of cellular membrane metabolism and is recruited to viral replication complexes upon infection. Our results demonstrate that the virus requires a limited subset of the normal GBF1 functions and reveal the elements of GBF1 essential to support viral replication under different conditions. Since diverse viruses often rely on the same cellular proteins for replication, understanding the mechanisms by which these proteins support infection is essential for the development of broad-spectrum antiviral therapeutics.

Essential domains of phosphatidylinositol-4 kinase III ß required for enterovirus replication.

Phosphatidylinositol-4 kinase III ß (PI4KB) is a host factor that is required for enterovirus (EV) replication. In this study, the importance of host proteins that interact with PI4KB in EV replication was analyzed by trans complementation with PI4KB mutants in a PI4KB-knockout cell line. Ectopically expressed PI4KB mutants, which lack binding regions for ACBD3, RAB11, and 14-3-3 proteins, rescued replication of poliovirus and enterovirus 71. These findings suggest that interaction of PI4KB with these host proteins is not essential for EV replication once PI4KB has been expressed and that PI4KB is functionally independent from these host proteins regarding EV replication.

Picornavirus RNA Recombination Counteracts Error Catastrophe.

Template-dependent RNA replication mechanisms render picornaviruses susceptible to error catastrophe, an overwhelming accumulation of mutations incompatible with viability. Viral RNA recombination, in theory, provides a mechanism for viruses to counteract error catastrophe. We tested this theory by exploiting well-defined mutations in the poliovirus RNA-dependent RNA polymerase (RDRP), namely, a G64S mutation and an L420A mutation. Our data reveal two distinct mechanisms by which picornaviral RDRPs influence error catastrophe: fidelity of RNA synthesis and RNA recombination. A G64S mutation increased the fidelity of the viral polymerase and rendered the virus resistant to ribavirin-induced error catastrophe, but only when RNA recombination was at wild-type levels. An L420A mutation in the viral polymerase inhibited RNA recombination and exacerbated ribavirin-induced error catastrophe. Furthermore, when RNA recombination was substantially reduced by an L420A mutation, a high-fidelity G64S polymerase failed to make the virus resistant to ribavirin. These data indicate that viral RNA recombination is required for poliovirus to evade ribavirin-induced error catastrophe. The conserved nature of L420 within RDRPs suggests that RNA recombination is a common mechanism for picornaviruses to counteract and avoid error catastrophe.IMPORTANCE Positive-strand RNA viruses produce vast amounts of progeny in very short periods of time via template-dependent RNA replication mechanisms. Template-dependent RNA replication, while efficient, can be disadvantageous due to error-prone viral polymerases. The accumulation of mutations in viral RNA genomes leads to error catastrophe. In this study, we substantiate long-held theories regarding the advantages and disadvantages of asexual and sexual replication strategies among RNA viruses. In particular, we show that picornavirus RNA recombination counteracts the negative consequences of asexual template-dependent RNA replication mechanisms, namely, error catastrophe.

Monitoring drug pharmacokinetics and immunologic biomarkers in dermal interstitial fluid using a microneedle patch.

Minimally invasive point-of-care diagnostic devices are of great interest for rapid detection of biomarkers in diverse settings. Although blood is the most common source of biomarkers, interstitial fluid (ISF) is an alternate body fluid that does not clot or contain red blood cells that often complicate analysis. However, ISF is difficult to collect. In this study, we assessed the utility of a microneedle patch to sample microliter volumes of ISF in a simple and minimally invasive manner. We demonstrated the use of ISF collected in this way for therapeutic drug monitoring by showing similar vancomycin pharmacokinetic profiles in ISF and serum from rats. We also measured polio-specific neutralizing antibodies and anti-polio IgG in ISF similar to serum in rats immunized with polio vaccine. These studies demonstrate the potential utility of ISF collected by microneedle patch in therapeutic drug monitoring and immunodiagnostic applications.

Involvement of a Nonstructural Protein in Poliovirus Capsid Assembly.

Virus capsid proteins must perform a number of roles. These include self-assembly and maintaining stability under challenging environmental conditions, while retaining the conformational flexibility necessary to uncoat and deliver the viral genome into a host cell. Fulfilling these roles could place conflicting constraints on the innate abilities encoded within the protein sequences. In a previous study, we identified a number of mutations within the capsid-coding sequence of poliovirus (PV) that were established in the population during selection for greater thermostability by sequential treatment at progressively higher temperatures. Two mutations in the VP1 protein acquired at an early stage were maintained throughout this selection procedure. One of these mutations prevented virion assembly when introduced into a wild-type (wt) infectious clone. Here we show, by sequencing beyond the capsid-coding region of the heat-selected virions, that two mutations had arisen within the coding region of the 2A protease. Both mutations were maintained throughout the selection process. Introduction of these mutations into a wt infectious clone by site-directed mutagenesis considerably reduced replication. However, they permitted a low level of assembly of infectious virions containing the otherwise lethal mutation in VP1. The 2Apro mutations were further shown to slow the kinetics of viral polyprotein processing, and we suggest that this delay improves the correct folding of the mutant capsid precursor protein to permit virion assembly.IMPORTANCE RNA viruses, including poliovirus, evolve rapidly due to the error-prone nature of the polymerase enzymes involved in genome replication. Fixation of advantageous mutations may require the acquisition of complementary mutations which can act in concert to achieve a favorable phenotype. This study highlights a compensatory role of a nonstructural regulatory protein, 2Apro, for an otherwise lethal mutation of the structural VP1 protein to facilitate increased thermal resistance. Studying how viruses respond to selection pressures is important for understanding mechanisms which underpin emergence of resistance and could be applied to the future development of antiviral agents and vaccines.

Hsp90 shapes protein and RNA evolution to balance trade-offs between protein stability and aggregation.

Acquisition of mutations is central to evolution; however, the detrimental effects of most mutations on protein folding and stability limit protein evolvability. Molecular chaperones, which suppress aggregation and facilitate polypeptide folding, may alleviate the effects of destabilizing mutations thus promoting sequence diversification. To illuminate how chaperones can influence protein evolution, we examined the effect of reduced activity of the chaperone Hsp90 on poliovirus evolution. We find that Hsp90 offsets evolutionary trade-offs between protein stability and aggregation. Lower chaperone levels favor variants of reduced hydrophobicity and protein aggregation propensity but at a cost to protein stability. Notably, reducing Hsp90 activity also promotes clusters of codon-deoptimized synonymous mutations at inter-domain boundaries, likely to facilitate cotranslational domain folding. Our results reveal how a chaperone can shape the sequence landscape at both the protein and RNA levels to harmonize competing constraints posed by protein stability, aggregation propensity, and translation rate on successful protein biogenesis.