Effect of the viral hemorrhagic septicemia virus nonvirion protein on translation via the PERK – eIF2alpha pathway

Authors: KESTERSON, POWELL - University Of Toledo; RINGIESN, JEFF - Wright State University; VAHARIA, VIKRAM - University Of Baltimore; Shepherd, Brian; LEAMAN, DOUGLAS - Wright State University; KRISHNAMURTHY, MALATHI - University Of Toledo

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2020
Publication Date: 4/30/2020
Citation: Kesterson, S.P., Ringiesn, J., Vaharia, V.N., Shepherd, B.S., Leaman, D.W., Krishnamurthy, M. 2020. Effect of the viral hemorrhagic septicemia virus nonvirion protein on translation via the PERK – eIF2alpha pathway. Viruses. 12(5), 499. https://doi.org/10.3390/v12050499.
DOI: https://doi.org/10.3390/v12050499

Interpretive Summary: Viral Hemorrhagic Septicemia virus (VHSv) is one of the most deadly infectious fish pathogens posing a serious threat to the aquaculture industry. As with related viruses, the Great Lakes VHSv contains a unique and highly variable nonvirion (NV) gene, which is thought to enable infection of host cells and its ability to evade the host immune response. Using a fish cell-line (EPC), we observed that the native Great Lakes type of VHS virus suppressed the host antiviral response by inhibiting production of most new proteins within the cells, except for production of viral proteins. Infection of EPC fish cells with a Great Lakes VHS virus, not containing the NV region, exhibited lower levels of viral protein synthesis despite increased levels of viral messenger ribonucleic acid (increased viral gene abundance). These findings show a subtle role for the NV region in Great Lakes type of VHS virus mediated pathogenesis via alteration of host protein shutoff. Information from this work may enable identification of new viral targets that modulate the host-pathogen interaction, and immunogenicity, which could be adopted to design more efficient vaccination strategies.

Technical Abstract: Viral Hemorrhagic Septicemia virus (VHSv) is one of the most deadly infectious fish pathogens posing a serious threat to the aquaculture industry. In this work, we continued our assessment of how protein regions of the VHSv pathogen modulate the immune responses using the EPC (fathead minnow) fish cell-line as a host model system. Previous work showed that Great Lakes type VHS virus suppresses the host innate immune responses in various fish cell-lines, but the exact mechanism by which this virus inhibits the host antiviral response is not understood. As with related viruses, the Great Lakes VHSv-type contains a unique and highly variable nonvirion (NV) gene, which is implicated in facilitating viral replication, affecting interferon production and inducing cell death of the host cells. INF production is what helps the cell respond to a pathogen, by inducing a virus resistant state, so affecting its production allows the virus to take over the host for viral replication. Using the EPC cell-line, we observed that the native Great Lakes type of VHS virus, or a mutant VHSv lacking a functional NV region, reduced interferon (IFN) expression and compromised the innate immune response of the host cells by inhibiting production of new proteins in the cells. By contrast, infection with the native Great Lakes VHS virus resulted in increased levels of an important phosphorylated protein called eukaryotic initiation factor 2a (p-eIF2a), which resulted the shutoff of new protein production (defense proteins) by the host cell with exception of synthesis of viral proteins needed for production of more virus. Here, virus protein synthesis proceeded despite increasing phosphorylation of eIF2a. To examine how eIF2a phosphorylation and viral protein production occurs despite shut-down of host protein production, we determined that another protein called PKR-like endoplasmic reticulum kinase (PERK) was involved with efficient viral protein production, but inhibition of host protein production and interferon signaling was independent of p-eIF2a. Similarly, infection of EPC cells with the Great Lakes, NV null, VHS virus induced less p-eIF2a, but exhibited decreased viral protein synthesis despite increased levels of viral messenger ribonucleic acid (increased viral gene abundance). These findings show a role for NV region of Great Lakes type of VHS virus pathogenesis by utilizing the PERK-eIF2a pathway for viral mediated host protein shutoff and interferon signaling to regulate host cell response in favor of greater virus replication. Information from this work may enable identification of new viral targets that modulate the host-pathogen interaction, and immunogenicity, which could be adopted to design more efficient vaccination strategies.