Modifications of the PI3K/Akt/mTOR axis during FeHV-1 infection in permissive cells

Cell entry of bovine respiratory syncytial virus through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK pathways

Bovine respiratory syncytial virus (BRSV) is an RNA virus with envelope that causes acute, febrile, and highly infectious respiratory diseases in cattle. However, the manner and mechanism of BRSV entry into cells remain unclear. In this study, we aimed to explore the entry manner of BRSV into MDBK cells and its regulatory mechanism. Our findings, based on virus titer, virus copies, western blot and IFA analysis, indicate that BRSV enters MDBK cells through endocytosis, relying on dynamin, specifically via clathrin-mediated endocytosis rather than caveolin-mediated endocytosis and micropinocytosis. We observed that the entered BRSV initially localizes in early endosomes and subsequently localizes in late endosomes. Additionally, our results of western blot, virus titer and virus copies demonstrate that BRSV entry through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK signaling pathways. Overall, our study suggests that BRSV enters MDBK cells through clathrin-mediated endocytosis, entered BRSV is trafficked to late endosome via early endosome, BRSV entry through clathrin-mediated endocytosis is regulated by PI3K-Akt and Src-JNK signaling pathways.

Apoptosis is mediated by FeHV-1 through the intrinsic pathway and interacts with the autophagic process

BACKGROUND

Although FeHV-1 is a primary feline pathogen, little is known about its interactions with host cells. Its relationship with several cellular pathways has recently been described, whereas its interplay with the apoptotic process, unlike other herpesviruses, has not yet been clarified. The aim of this work was to evaluate whether FeHV-1 induces apoptosis in its permissive cells, as well as the pathway involved and the effects of induction and inhibition of apoptosis on viral replication.

METHODS

Monolayers of CRFK cells were infected at different times with different viral doses. A cytofluorimetric approach allowed the quantification of cells in early and late apoptosis. All infections and related controls were also subjected to Western blot analysis to assess the expression of apoptotic markers (caspase 3-8-9, Bcl-2, Bcl-xL, NF-κB). An inhibitor (Z-VAD-FMK) and an inducer (ionomycin) were used to evaluate the role of apoptosis in viral replication. Finally, the expression of autophagy markers during the apoptosis inhibition/induction and the expression of apoptosis markers during autophagy inhibition/induction were evaluated to highlight any crosstalk between the two pathways.

RESULTS

FeHV-1 triggered apoptosis in a time- and dose-dependent manner. Caspase 3 cleavage was evident 48 h after infection, indicating the completeness of the process at this stage. While caspase 8 was not involved, caspase 9 cleavage started 24 h post-infection. The expression of other mitochondrial damage markers also changed, suggesting that apoptosis was induced via the intrinsic pathway. NF- κB was up-regulated at 12 h, followed by a gradual decrease in levels up to 72 h. The effects of apoptosis inhibitors and inducers on viral replication and autophagy were also investigated. Inhibition of caspases resulted in an increase in viral glycoprotein expression, higher titers, and enhanced autophagy, whereas induction of apoptosis resulted in a decrease in viral protein expression, lower viral titer, and attenuated autophagy. On the other hand, the induction of autophagy reduced the cleavage of caspase 3.

CONCLUSIONS

In this study, we established how FeHV-1 induces the apoptotic process, contributing to the understanding of the relationship between FeHV-1 and this pathway.

Seneca Valley Virus Degrades STING via PERK and ATF6-Mediated Reticulophagy

Seneca Valley Virus (SVV), a member of the Picornaviridae family, is an emerging porcine virus that can cause vesicular disease in pigs. However, the immune evasion mechanism of SVV remains unclear, as does its interaction with other pathways. STING (Stimulator of interferon genes) is typically recognized as a critical factor in innate immune responses to DNA virus infection, but its role during SVV infection remains poorly understood. In the present study, we observed that STING was degraded in SVV-infected PK-15 cells, and SVV replication in the cells was affected when STING was knockdown or overexpressed. The STING degradation observed was blocked when the SVV-induced autophagy was inhibited by using autophagy inhibitors (Chloroquine, Bafilomycin A1) or knockdown of autophagy related gene 5 (ATG5), suggesting that SVV-induced autophagy is responsible for STING degradation. Furthermore, the STING degradation was inhibited when reticulophagy regulator 1 (FAM134B), a reticulophagy related receptor, was knocked down, indicating that SVV infection induces STING degradation via reticulophagy. Further study showed that in eukaryotic translation initiation factor 2 alpha kinase 3 (PERK)/activating transcription factor 6 (ATF6) deficient cells, SVV infection failed to induce reticulophagy-medaited STING degradation, indicating that SVV infection caused STING degradation via PERK/ATF6-mediated reticulophagy. Notably, blocking reticulophagy effectively hindered SVV replication. Overall, our study suggested that SVV infection resulted in STING degradation via PERK and ATF6-mediated reticulophagy, which may be an immune escape strategy of SVV. This finding improves the understanding of the intricate interplay between viruses and their hosts and provides a novel strategy for the development of novel antiviral drugs.

Autophagy up-regulation upon FeHV-1 infection on permissive cells

FeHV-1 is a member of the Herpesviridae family that is distributed worldwide and causes feline viral rhinotracheitis (FVR). Since its relationship with the autophagic process has not yet been elucidated, the aim of this work was to evaluate the autophagy mediated by FeHV-1 and to determine its proviral or antiviral role. Our data showed that autophagy is induced by FeHV-1 in a viral dose and time-dependent manner. Phenotypic changes in LC3/p62 axis (increase of LC3-II and degradation of p62) were detected from 12 h post infection using western blot and immuno-fluorescence assays. In a second step, by using late autophagy inhibitors and inducers, the possible proviral role of autophagy during FeHV-1 infection was investigating by assessing the effects of each chemical in terms of viral yield, cytotoxic effects, and expression of viral glycoproteins. Our findings suggest that late-stage autophagy inhibitors (bafilomycin and chloroquine) have a negative impact on viral replication. Interestingly, we observed an accumulation of gB, a viral protein, when cells were pretreated with bafilomycin, whereas the opposite effect was observed when an autophagy inducer was used. The importance of autophagy during FeHV-1 infection was further supported by the results obtained with ATG5 siRNA. In summary, this study demonstrates FeHV-1-mediated autophagy induction, its proviral role, and the negative impact of late autophagy inhibitors on viral replication.