Nuclear Cytoskeleton in Virus Infection

The nuclear lamina is the main component of the nuclear cytoskeleton that maintains the integrity of the nucleus. However, it represents a natural barrier for viruses replicating in the cell nucleus. The lamina blocks viruses from being trafficked to the nucleus for replication, but it also impedes the nuclear egress of the progeny of viral particles. Thus, viruses have evolved mechanisms to overcome this obstacle. Large viruses induce the assembly of multiprotein complexes that are anchored to the inner nuclear membrane. Important components of these complexes are the viral and cellular kinases phosphorylating the lamina and promoting its disaggregation, therefore allowing virus egress. Small viruses also use cellular kinases to induce lamina phosphorylation and the subsequent disruption in order to facilitate the import of viral particles during the early stages of infection or during their nuclear egress. Another component of the nuclear cytoskeleton, nuclear actin, is exploited by viruses for the intranuclear movement of their particles from the replication sites to the nuclear periphery. This study focuses on exploitation of the nuclear cytoskeleton by viruses, although this is just the beginning for many viruses, and promises to reveal the mechanisms and dynamic of physiological and pathological processes in the nucleus.

Primary Site of Coxsackievirus B Replication in the Small Intestines: No Proof of Peyer’s Patches Involvement

Background: Enterovirus (EV) infections are associated with a broad range of diseases. Since the first experimental infection of primates with poliovirus (PV), tonsils and the Peyer’s patches (PPs) have been believed to be the primary replication sites of EVs. Our aim was to localize different viral markers in the small intestines (SI) of coxsackievirus B (CVB) orally and intraperitoneally (i.p.) infected mice. Methods: Transverse sections of SIs of both infected and control male outbred mice were collected at different intervals post-infection (p.i) and analyzed for presence of interferon-alpha (IFN-α) and viral protein VP1 by immunohistochemistry and in situ hybridization (ISH). Fluorescent marker, eGFP, was identified in cryosections of mice infected with eGFP-CVB3. Results: In the infected SIs, we observed enlarged germinating centers (GCs) in the PPs; IFN-α was detected in the PPs and mucosal layer of the SIs. However, VP1, viral RNA and the eGFP were absent in the GCs of PPs at all stages of infection irrespective of the virus strains used. Conclusions: Virus was present in the epithelial cells but not in GCs of the PPs of the murine SIs. Our results do not support the hypothesis of EV replication in the PP especially in the GCs.

Virus-Host Interactions of Enteroviruses and Parvovirus B19 in Myocarditis

Viral diseases are a major threat to modern society and the global health system. It is therefore of utter relevance to understand the way viruses affect the host as a basis to find new treatment solutions. The understanding of viral myocarditis (VMC) is incomplete and effective treatment options are lacking. This review will discuss the mechanism, effects, and treatment options of the most frequent myocarditis-causing viruses namely enteroviruses such as Coxsackievirus B3 (CVB3) and Parvovirus B19 (PVB19) on the human heart. Thereby, we focus on: 1. Viral entry: CVB3 use Coxsackievirus-Adenovirus-Receptor (CAR) and Decay Accelerating Factor (DAF) to enter cardiac myocytes while PVB19 use the receptor globoside (Gb4) to enter cardiac endothelial cells. 2. Immune system responses: The innate immune system mediated by activated cardiac toll-like receptors (TLRs) worsen inflammation in CVB3-infected mouse hearts. Different types of cells of the adaptive immune system are recruited to the site of inflammation that have either protective or adverse effects during VMC. 3. Autophagy: CVB3 evades autophagosomal degradation and misuses the autophasomal pathway for viral replication and release. 4. Viral replication sites: CVB3 promotes the formation of double membrane vesicles (DMVs), which it uses as replication sites. PVB19 uses the host cell nucleus as the replication site and uses the host cell DNA replication system. 5. Cell cycle manipulation: CVB3 attenuates the cell cycle at the G1/S phase, which promotes viral transcription and replication. PVB19 exerts cell cycle arrest in the S phase using its viral endonuclease activity. 6. Regulation of apoptosis: Enteroviruses prevent apoptosis during early stages of infection and promote cell death during later stages by using the viral proteases 2A and 3C, and viroporin 2B. PVB19 promotes apoptosis using the non-structural proteins NS1 and the 11 kDa protein. 7. Energy metabolism: Dysregulation of respiratory chain complex expression, activity and ROS production may be altered in CVB3- and PVB19-mediated myocarditis. 8. Ion channel modulation: CVB3-expression was indicated to alter calcium and potassium currents in Xenopus laevis oocytes and rodent cardiomyocytes. The phospholipase 2-like activity of PVB19 may alter several calcium, potassium and sodium channels. By understanding the general pathophysiological mechanisms of well-studied myocarditis-linked viruses, we might be provided with a guideline to handle other less-studied human viruses.

Correction: De Conti et al. Histological Lesions and Replication Sites of PCV3 in Naturally Infected Pigs. Animals 2021, 11, 1520

The authors wish to make the following correction to this paper [...]

Deconstructing virus condensation

Viruses have evolved precise mechanisms for using the cellular physiological pathways for their perpetuation. These virus-driven biochemical events must be separated in space and time from those of the host cell. In recent years, granular structures, known for over a century for rabies virus, were shown to host viral gene function and were named using terms such as viroplasms, replication sites, inclusion bodies, or viral factories (VFs). More recently, these VFs were shown to be liquid-like, sharing properties with membrane-less organelles driven by liquid–liquid phase separation (LLPS) in a process widely referred to as biomolecular condensation. Some of the best described examples of these structures come from negative stranded RNA viruses, where micrometer size VFs are formed toward the end of the infectious cycle. We here discuss some basic principles of LLPS in connection with several examples of VFs and propose a view, which integrates viral replication mechanisms with the biochemistry underlying liquid-like organelles. In this view, viral protein and RNA components gradually accumulate up to a critical point during infection where phase separation is triggered. This yields an increase in transcription that leads in turn to increased translation and a consequent growth of initially formed condensates. According to chemical principles behind phase separation, an increase in the concentration of components increases the size of the condensate. A positive feedback cycle would thus generate in which crucial components, in particular nucleoproteins and viral polymerases, reach their highest levels required for genome replication. Progress in understanding viral biomolecular condensation leads to exploration of novel therapeutics. Furthermore, it provides insights into the fundamentals of phase separation in the regulation of cellular gene function given that virus replication and transcription, in particular those requiring host polymerases, are governed by the same biochemical principles.

In situ structures of membrane-assisted assembly and selective autophagy of enteroviruses

SummaryEnteroviruses are non-enveloped positive-sense RNA viruses that cause diverse diseases in humans. Their rapid multiplication depends on remodeling of cytoplasmic membranes for viral genome replication. New virions are thought to be assembled near the genome replication sites and are released in vesicles through secretory autophagy. Here, we use cryo-electron tomography to show that poliovirus assembles directly on replication membranes. Assembly progression beyond a membrane-bound half-capsid intermediate requires the host lipid kinase VPS34, whereas inhibition of ULK1, the initiator of canonical autophagy, leads to accumulation of virions in vast intracellular arrays followed by an increased release at later time points. We further identify multiple layers of selectivity in virus-induced autophagy, with a strong selection for RNA-loaded virions over empty capsids and the segregation of virions from a second class of autophagic membranes containing protein filaments bundles. These findings provide an integrated structural framework for multiple stages of the poliovirus life cycle.

Pharmacological perturbation of intracellular dynamics as a SARS-CoV-2 antiviral strategy

SARS-CoV-2 (CoV2) is the viral agent responsible for the pandemic of the coronavirus disease 2019 (COVID-19). Vaccines are being deployed all over the world with good efficacy, but there is no approved antiviral treatment to date. This is particularly needed since the emergence of variants and the potential immune escape may prolong pandemic spreading of the infection for much longer than anticipated. Here, we developed a series of small molecules and identified RG10 as a potent antiviral compound against SARS-CoV-2 in cell lines and human airway epithelia (HAE). RG10 localizes to endoplasmic reticulum (ER) membranes, perturbing ER morphology and inducing ER stress. Yet, RG10 does not associate with SARS-CoV-2 replication sites although preventing virus replication. To further investigate the antiviral properties of our compound, we developed fluorescent SARS-CoV-2 viral particles allowing us to track virus arrival to ER membranes. Live cell imaging of replication-competent virus infection revealed that RG10 stalls the intracellular virus-ER dynamics. Finally, we synthesized RG10b, a stable version of RG10, that showed increased potency in vitro and in HAE with a pharmacokinetic half-life greater than 2 h. Together, our work reports on a novel fluorescent virus model and innovative antiviral strategy consisting of the perturbation of ER/virus dynamics, highlighting the promising antiviral properties of RG10 and RG10b.

Cross Talk between Viruses and Insect Cells Cytoskeleton

Viruses are excellent manipulators of host cellular machinery, behavior, and life cycle, with the host cell cytoskeleton being a primordial viral target. Viruses infecting insects generally enter host cells through clathrin-mediated endocytosis or membrane fusion mechanisms followed by transport of the viral particles to the corresponding replication sites. After viral replication, the viral progeny egresses toward adjacent cells and reaches the different target tissues. Throughout all these steps, actin and tubulin re-arrangements are driven by viruses. The mechanisms used by viruses to manipulate the insect host cytoskeleton are well documented in the case of alphabaculoviruses infecting Lepidoptera hosts and plant viruses infecting Hemiptera vectors, but they are not well studied in case of other insect–virus systems such as arboviruses–mosquito vectors. Here, we summarize the available knowledge on how viruses manipulate the insect host cell cytoskeleton, and we emphasize the primordial role of cytoskeleton components in insect virus motility and the need to expand the study of this interaction.

Endomembrane targeting of human OAS1 p46 augments antiviral activity

Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from cellular innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flaviviruses, picornaviruses, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform correlates with protection from severe COVID-19. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests that early control of SARS-CoV-2 replication through OAS1-p46 is an important determinant of COVID-19 severity.

Presentation of a new method based on modern multivariate approaches for big data replication in distributed environments

As the amounts of data and use of distributed systems for data storage and processing have increased, reducing the number of replications has turned into a crucial requirement in these systems, which has been addressed by plenty of research. In this paper, an algorithm has been proposed to reduce the number of replications in big data transfer and, eventually to lower the traffic load over the grid by classifying data efficiently and optimally based on the sent data types and using VIKOR as a method of multivariate decision-making for ranking replication sites. Considering different variables, the VIKOR method makes it possible to take all the parameters effective in the assessment of site ranks into account. According to the results and evaluations, the proposed method has exhibited an improvement by about thirty percent in average over the LRU, LFU, BHR, and Without Rep. algorithms. Furthermore, it has improved the existing multivariate methods through different approaches to replication by thirty percent, as it considers effective parameters such as time, the number of replications, and replication site, causing replication to occur when it can make an improvement in terms of access.