Transient high level mammalian reovirus replication in a bat epithelial cell line occurs without cytopathic effect

U5 snRNP Core Proteins Are Key Components of the Defense Response against Viral Infection through Their Roles in Programmed Cell Death and Interferon Induction

The spliceosome is a massive ribonucleoprotein structure composed of five small nuclear ribonucleoprotein (snRNP) complexes that catalyze the removal of introns from pre-mature RNA during constitutive and alternative splicing. EFTUD2, PRPF8, and SNRNP200 are core components of the U5 snRNP, which is crucial for spliceosome function as it coordinates and performs the last steps of the splicing reaction. Several studies have demonstrated U5 snRNP proteins as targeted during viral infection, with a limited understanding of their involvement in virus-host interactions. In the present study, we deciphered the respective impact of EFTUD2, PRPF8, and SNRNP200 on viral replication using mammalian reovirus as a model. Using a combination of RNA silencing, real-time cell analysis, cell death and viral replication assays, we discovered distinct and partially overlapping novel roles for EFTUD2, PRPF8, and SNRNP200 in cell survival, apoptosis, necroptosis, and the induction of the interferon response pathway. For instance, we demonstrated that EFTUD2 and SNRNP200 are required for both apoptosis and necroptosis, whereas EFTUD2 and PRPF8 are required for optimal interferon response against viral infection. Moreover, we demonstrated that EFTUD2 restricts viral replication, both in a single cycle and multiple cycles of viral replication. Altogether, these results establish U5 snRNP core components as key elements of the cellular antiviral response.

[Biological characteristics and permissiveness to viruses of diploid kidney cells strain from the bat Nathusius' pipistrelle (Pipistrellus nathusii Keyserling & Blasius, 1839; Chiroptera: Microchiroptera: Vespertilionidae)]

INTRODUCTION

Bats are an epidemiologically important natural reservoir of viruses of various taxonomic groups, including causative agents of especially dangerous infections of humans and animals. Considering the relevance of arbovirus infections, it seems advisable to study the spectrum of the sensitivity of cells derived from bats inhabiting and migrating on the territory of the Russian Federation to causative agents of vector-borne diseases of animals.The study aimed to obtain a diploid strain of cells from renal tissue of bats Pipistrellus nathusii and to investigate its biological characteristics, as well as to assess its permissiveness for bluetongue (BTV); Rift Valley fever (RVFV); lumpy skin disease (LSDV); rabbit myxoma (Myxomatosis cuniculi); rabbit, or Shope fibroma (RFV); African horse sickness (AHSV) and African swine fever (ASFV) viruses.

MATERIAL AND METHODS

There were 2 clinically healthy male individuals of P. nathusii who taken as donors of organs. To obtain diploid kidney cell culture strain and to study its properties, the level of the 6th passage was investigated by conventional cytological, virological, and molecular methods. The permissiveness of the obtained cell culture for BTV, RVFV, LSDV, Myxomatosis cuniculi, RFV, AHSV and ASFV was determined.

RESULTS

The formation of a confluent monolayer was observed after 72 hours, while the proliferation index was 2.7-3.3. The cell monolayer had been maintained without changing the medium for 45 days (observation period). The stability of the karyotype had been demonstrated in continuous subculturing at the 36th passage. The cell culture named «Diploid cell line Pipistrellus nathusii kidney», and its permissiveness to BTV, RVFV, LSDV and Myxomatosis cuniculi had been demonstrated.

DISCUSSION

The sensitivity of the strain to BTV and RVFV is consistent with the data on the identification of reovirus and RVFV in Egyptian fruit bats (Rousettus aegyptiacus), and its permissiveness for LSDV and rabbits myxoma virus is consistent with the results of detection of poxviruses in big brown bat (Eptesicus fuscus).

CONCLUSION

A diploid kidney cell strain derived from P. nathusii was obtained and certified. Its permissiveness to BTV, RVFV, LSDV and rabbits myxoma viruses makes it possible to use this strain for isolation and studies of these viruses. Reproduction of the viruses in diploid kidney cells strain derived from P. nathusii living and migrating in the European part of the Russian Federation indicates their potential role in the epidemiology of significant infections, especially transmissible ones.

PEDV infection in neonatal piglets through the nasal cavity is mediated by subepithelial CD3+ T cells

Porcine epidemic diarrhea virus (PEDV) primarily infects neonatal piglets causing catastrophic effects on the global pig farming industry. PEDV infects piglets through the nasal cavity, a process in which dendritic cells (DCs) play an important role. However, neonatal piglets have fewer nasal DCs. This study found that subepithelial CD3⁺ T cells mediated PEDV invasion through the nasal cavity in neonatal piglets. PEDV could replicate in the nasal epithelial cells (NECs) isolated from the nasal cavity of neonatal piglets. Infection of NECs with PEDV could induce antiviral and inflammatory cytokines at the late stage. The infected NECs mediated transfer of virus to CD3⁺ T cells distributed in the subepithelial of the nasal cavity via cell-to-cell contact. The infected CD3⁺ T cells could migrate to the intestine via blood circulation, causing intestinal infection in neonatal piglets. Thus, the findings of this study indicate the importance of CD3⁺T cells in the dissemination of PEDV from the nasal cavity to the intestinal mucosa in neonatal piglets.

Role of pattern recognition receptors and interferon-beta in protecting bat cell lines from encephalomyocarditis virus and Japanese encephalitis virus infection

Bats are potential natural hosts of Encephalomyocarditis virus (EMCV) and Japanese encephalitis virus (JEV). Bats appear to have some unique features in their innate immune system that inhibit viral replication causing limited clinical symptoms, and thus, contributing to the virus spill over to humans. Here, kidney epithelial cell lines derived from four bat species (Pteropus dasymallus, Rousettus leschenaultii, Rhinolophus ferrumequinum, and Miniopterus fuliginosus) and two non-bat species (Homo sapiens and Mesocricetus auratus) were infected with EMCV and JEV. The replication of EMCV and JEV was lower in the bat cell lines derived from R. leschenaultii, R. ferrumequinum, and M. fuliginosus with a higher expression level of pattern recognition receptors (PRRs) (TLR3, RIG-I, and MDA5) and interferon-beta (IFN-β) than that in the non-bat cell lines and a bat cell line derived from P. dasymallus. The knockdown of TLR3, RIG-I, and MDA5 in Rhinolophus bat cell line using antisense RNA oligonucleotide led to decrease IFN-β expression and increased viral replication. These results suggest that TLR3, RIG-I, and MDA5 are important for antiviral response against EMCV and JEV in Rhinolophus bats.

Bat lung epithelial cells show greater host species-specific innate resistance than MDCK cells to human and avian influenza viruses

Background

With the recent discovery of novel H17N10 and H18N11 influenza viral RNA in bats and report on high frequency of avian H9 seroconversion in a species of free ranging bats, an important issue to address is the extent bats are susceptible to conventional avian and human influenza A viruses.

Method

To this end, three bat species (Eidolon helvum, Carollia perspicillata and Tadarida brasiliensis) of lung epithelial cells were separately infected with two avian and two human influenza viruses to determine their relative host innate immune resistance to infection.

Results

All three species of bat cells were more resistant than positive control Madin-Darby canine kidney (MDCK) cells to all four influenza viruses. TB1-Lu cells lacked sialic acid α2,6-Gal receptors and were most resistant among the three bat species. Interestingly, avian viruses were relatively more replication permissive in all three bat species of cells than with the use of human viruses which suggest that bats could potentially play a role in the ecology of avian influenza viruses. Chemical inhibition of the JAK-STAT pathway in bat cells had no effect on virus production suggesting that type I interferon signalling is not a major factor in resisting influenza virus infection.

Conclusion

Although all three species of bat cells are relatively more resistant to influenza virus infection than control MDCK cells, they are more permissive to avian than human viruses which suggest that bats could have a contributory role in the ecology of avian influenza viruses.

Tools to study pathogen-host interactions in bats

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Bats are important reservoir hosts for emerging zoonotic viruses.

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Viruses detected in bats are difficult to isolate using traditional cell lines.

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Bat cell lines provide critical tools to dissect host pathogen interactions.

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Little is known about immune cell populations and their responses in bats.

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Sharing reagents and cell lines will accelerate research and virus discovery.

Bats are natural reservoirs for a variety of emerging viruses that cause significant disease in humans and domestic animals yet rarely cause clinical disease in bats. The co-evolutionary history of bats with viruses has been hypothesized to have shaped the bat-virus relationship, allowing both to exist in equilibrium. Progress in understanding bat-virus interactions and the isolation of bat-borne viruses has been accelerated in recent years by the development of susceptible bat cell lines. Viral sequences similar to severe acute respiratory syndrome corona virus (SARS-CoV) have been detected in bats, and filoviruses such as Marburg virus have been isolated from bats, providing definitive evidence for the role of bats as the natural host reservoir. Although viruses can be readily detected in bats using molecular approaches, virus isolation is far more challenging. One of the limitations in using traditional culture systems from non-reservoir species is that cell types and culture conditions may not be compatible for isolation of bat-borne viruses. There is, therefore, a need to develop additional bat cell lines that correspond to different cell types, including less represented cell types such as immune cells, and culture them under more physiologically relevant conditions to study virus host interactions and for virus isolation. In this review, we highlight the current progress in understanding bat-virus interactions in bat cell line systems and some of the challenges and limitations associated with cell lines. Future directions to address some of these challenges to better understand host-pathogen interactions in these intriguing mammals are also discussed, not only in relation to viruses but also other pathogens carried by bats including bacteria and fungi.

Multiple proteins differing between laboratory stocks of mammalian orthoreoviruses affect both virus sensitivity to interferon and induction of interferon production during infection

In the course of previous works, it was observed that the virus laboratory stock (T3D^S) differs in sequence from the virus encoded by the ten plasmids currently in use in many laboratories (T3D^K), and derived from a different original virus stock. Seven proteins are affected by these sequence differences. In the present study, replication of T3D^K was shown to be more sensitive to the antiviral effect of interferon. Infection by the T3D^K virus was also shown to induce the production of higher amount of β and α-interferons compared to T3D^S. Two proteins, the μ2 and λ2 proteins, were found to be responsible for increased sensitivity to interferon while both μ2 and λ1 are responsible for increased interferon secretion. Altogether this supports the idea that multiple reovirus proteins are involved in the control of induction of interferon and virus sensitivity to the interferon-induced response. While interrelated, interferon induction and sensitivity can be separated by defined gene combinations. While both μ2 and λ2 were previously suspected of a role in the control of the interferon response, other proteins are also likely involved, as first shown here for λ1. This also further stresses that due caution should be exerted when comparing different virus isolates with different genetic background.

Serotype-Specific Killing of Large Cell Carcinoma Cells by Reovirus

Reovirus is under development as a therapeutic for numerous types of cancer. In contrast to other oncolytic viruses, the safety and efficacy of reovirus have not been improved through genetic manipulation. Here, we tested the oncolytic capacity of recombinant strains (rs) of prototype reovirus laboratory strains T1L and T3D (rsT1L and rsT3D, respectively) in a panel of non-small cell lung cancer (NSCLC) cell lines. We found that rsT1L was markedly more cytolytic than rsT3D in the large cell carcinoma cell lines tested, whereas killing of adenocarcinoma cell lines was comparable between rsT1L and rsT3D. Importantly, non-recombinant T1L and T3D phenocopied the kinetics and magnitude of cell death induced by recombinant strains. We identified gene segments L2, L3, and M1 as viral determinants of strain-specific differences cell killing of the large cell carcinoma cell lines. Together, these results indicate that recombinant reoviruses recapitulate the cell killing properties of non-recombinant, tissue culture-passaged strains. These studies provide a baseline for the use of reverse genetics with the specific objective of engineering more effective reovirus oncolytics. This work raises the possibility that type 1 reoviruses may have the capacity to serve as more effective oncolytics than type 3 reoviruses in some tumor types.

A single amino acid substitution in the mRNA capping enzyme λ2 of a mammalian orthoreovirus mutant increases interferon sensitivity

In the last few years, the development of a plasmid-based reverse genetics system for mammalian reovirus has allowed the production and characterization of mutant viruses. This could be especially significant in the optimization of reovirus strains for virotherapeutic applications, either as gene vectors or oncolytic viruses. The genome of a mutant virus exhibiting increased sensitivity to interferon was completely sequenced and compared with its parental virus. Viruses corresponding to either the parental or mutant viruses were then rescued by reverse genetics and shown to exhibit the expected phenotypes. Systematic rescue of different viruses harboring either of the four parental genes in a mutant virus backbone, or reciprocally, indicated that a single amino acid substitution in one of λ2 methyltransferase domains is the major determinant of the difference in interferon sensitivity between these two viruses.

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An interferon sensitive reovirus harbors amino acids substitutions in four proteins.

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Wild-type laboratory stock and mutant viruses were reconstructed by reverse genetics.

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Each mutant gene was substituted by its wild-type counterpart and reciprocally.

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Interferon sensitivity was assigned to a substitution in mRNA capping protein λ2.