Involvement of a Nonstructural Protein in Poliovirus Capsid Assembly

Wide circulation of type 1 vaccine-derived poliovirus strains in clinical specimens from suspected cases of poliomyelitis, their contacts and in wastewater in Madagascar since late 2020

Madagascar has faced three major outbreaks of vaccine-derived polioviruses (VDPVs) in recent decades, with VDPV type 1 reemerging in late 2020. Here, we report the molecular characterization of these cVDPV1 strains. WHO protocols were used for poliovirus detection in stool and wastewater samples. Molecular genotyping was based on the 5' non-coding (5'NC), VP1, and 3Dpol regions. From 2020 to 2022, 92 of 5690 stool samples and 129 of 1046 wastewater samples tested positive for cVDPV1. Genetic analysis of the VP1 gene revealed 1.3%-6.1% variability compared to the Sabin strain. Most sequences showed mutations at neurovirulence attenuation sites. Phylogenetic analysis distributed strains into four genogroups originating from Southern Madagascar. All analyzed cVDPV1 strains were recombinant, containing mutated oral polio vaccine sequences in VP1 and type C enterovirus sequences in other regions. This study demonstrated that all strains were closely related during this epidemic.

Thrombin cleavage of the hepatitis E virus polyprotein at multiple conserved locations is required for genome replication

The genomes of positive-sense RNA viruses encode polyproteins that are essential for mediating viral replication. These viral polyproteins must undergo proteolysis (also termed polyprotein processing) to generate functional protein units. This proteolysis can be performed by virally-encoded proteases as well as host cellular proteases, and is generally believed to be a key step in regulating viral replication. Hepatitis E virus (HEV) is a leading cause of acute viral hepatitis. The positive-sense RNA genome is translated to generate a polyprotein, termed pORF1, which is necessary and sufficient for viral genome replication. However, the mechanism of polyprotein processing in HEV remains to be determined. In this study, we aimed to understand processing of this polyprotein and its role in viral replication using a combination of in vitro translation experiments and HEV sub-genomic replicons. Our data suggest no evidence for a virally-encoded protease or auto-proteolytic activity, as in vitro translation predominantly generates unprocessed viral polyprotein precursors. However, seven cleavage sites within the polyprotein (suggested by bioinformatic analysis) are susceptible to the host cellular protease, thrombin. Using two sub-genomic replicon systems, we demonstrate that mutagenesis of these sites prevents replication, as does pharmacological inhibition of serine proteases including thrombin. Overall, our data supports a model where HEV uses host proteases to support replication and could have evolved to be independent of a virally-encoded protease for polyprotein processing.

Thermal stabilization of enterovirus A 71 and production of antigenically stabilized empty capsids

Enterovirus A71 (EVA71) infection can result in paralysis and may be fatal. In common with other picornaviruses, empty capsids are produced alongside infectious virions during the viral lifecycle. These empty capsids are antigenically indistinguishable from infectious virus, but at moderate temperatures they are converted to an expanded conformation. In the closely related poliovirus, native and expanded antigenic forms of particle have different long-term protective efficacies when used as vaccines. The native form provides long-lived protective immunity, while expanded capsids fail to generate immunological protection. Whether this is true for EVA71 remains to be determined. Here, we selected an antigenically stable EVA71 virus population using successive rounds of heating and passage and characterized the antigenic conversion of both virions and empty capsids. The mutations identified within the heated passaged virus were dispersed across the capsid, including at key sites associated with particle expansion. The data presented here indicate that the mutant sequence may be a useful resource to address the importance of antigenic conformation in EVA71 vaccines.

Detection methods targeting the positive- and negative-sense RNA transcripts from plus-stranded RNA viruses

The largest group of viruses in the Baltimore classification system comprises viruses with a positive-sense, single-stranded RNA genome. Once the viral genome is released into the cytoplasm of a specific host cell following virus entry, it functions directly as a mRNA and the virus-encoded proteins that are essential for genome replication, are produced by the translation apparatus of the host cell. The positive-sense genome is replicated in two stages, initially the positive strand is copied to make a negative-sense RNA, which then functions as the template for transcription of many new positive-sense genomes. Virus infections can be detected at different stages throughout the infection cycle for diagnostic and scientific purposes. Here, the advantages and disadvantages of some of the relevant methods for genome detection will be briefly reviewed with special emphasis on techniques allowing strand-specific RNA detection. Furthermore, tools of the future are considered.

CD155: A Key Receptor Playing Diversified Roles

Cluster of differentiation (CD155), formerly identified as poliovirus receptor (PVR) and later as immunoglobulin molecule involved in cell adhesion, proliferation, invasion and migration. It is a surface protein expressed mostly on normal and transformed malignant cells. The expression of the receptor varies based on the origin of tissue. The expression of the protein is determined by factors involved in sonic hedgehog pathway, Ras-MEK-ERK pathway and during stress conditions like DNA damage response. The protein uses alternate splicing mechanism, producing four isoforms - two being soluble (CD155β and CD155γ) and two being transmembrane protein (CD155α and CD155δ). Apart from being a viral receptor, researchers have identified CD155 having important roles in cancer research and cell signaling field. The receptor is recognized as biomarker for identifying cancerous tissue. The receptor interacts with molecules involved in cells defense mechanism. The immune-surveillance role of CD155 is being deciphered to understand the mechanistic approach it utilizes as onco-immunologic molecule. CD155 is a non-MHC-I ligand which helps in identifying non-self to NK cells via an inhibitory TIGIT ligand. The TIGIT-CD155 pathway is a novel MHC-I-independent education mechanism for cell tolerance and activation of NK cell. The receptor also has a role in metastasis of cancer and trans endothelial mechanism. In this review, authors discuss the virus-host interaction that occurs via single transmembrane receptor, the poliovirus infection pathway, which is being exploited as therapeutic pathway. The oncolytic virotherapy is now promising way for curing cancer.

Functional advantages of triplication of the 3B coding region of the FMDV genome

For gene duplication to be maintained, particularly in the small genomes of RNA viruses, this should offer some advantages. We have investigated the functions of a small protein termed VPg or 3B, which acts as a primer in the replication of foot-and-mouth disease virus (FMDV). Many related picornaviruses encode a single copy but uniquely the FMDV genome includes three (nonidentical) copies of the 3B coding region. Using sub-genomic replicons incorporating nonfunctional 3Bs and 3B fusion products in competition and complementation assays, we investigated the contributions of individual 3Bs to replication and the structural requirements for functionality. We showed that a free N-terminus is required for 3B to function as a primer and although a single 3B can support genome replication, additional copies provide a competitive advantage. However, a fourth copy confers no further advantage. Furthermore, we find that a minimum of two 3Bs is necessary for trans replication of FMDV replicons, which is unlike other picornaviruses where a single 3B can be used for both cis and trans replication. Our data are consistent with a model in which 3B copy number expansion within the FMDV genome has allowed evolution of separate cis and trans acting functions, providing selective pressure to maintain multiple copies of 3B.

Multifunctionality of structural proteins in the enterovirus life cycle

Members of the genus Enterovirus have a significant effect on human health, especially in infants and children. Since the viral genome has limited coding capacity, Enteroviruses subvert a range of cellular processes for viral infection via the interaction of viral proteins and numerous cellular factors. Intriguingly, the capsid-receptor interaction plays a crucial role in viral entry and has significant implications in viral pathogenesis. Moreover, interactions between structural proteins and host factors occur directly or indirectly in multiple steps of viral replication. In this review, we focus on the current understanding of the multifunctionality of structural proteins in the viral life cycle, which may constitute valuable targets for antiviral and therapeutic interventions.