Abstract
Viruses have evolved multiple strategies to manipulate their host’s translational machinery for the synthesis of viral proteins. A common viral target is the alpha subunit of eukaryotic initiation factor 2 (eIF2α). In this study, we show that global protein synthesis was increased but the eIF2α phosphorylation level was markedly decreased in porcine kidney 15 (PK15) cells infected with pseudorabies virus (PRV), a swine herpesvirus. An increase in the eIF2α phosphorylation level by salubrinal treatment or transfection of constructs expressing wild-type eIF2α or an eIF2α phosphomimetic [eIF2α(S51D)] attenuated global protein synthesis and suppressed PRV replication. To explore the mechanism involved in the inhibition of eIF2α phosphorylation during PRV infection, we examined the phosphorylation status of protein kinase R-like endoplasmic reticulum kinase (PERK) and double-stranded RNA-dependent protein kinase R (PKR), two kinases that regulate eIF2α phosphorylation during infection with numerous viruses. We found that the level of neither phosphorylated (p)-PERK nor p-PKR was altered in PRV-infected cells or the lungs of infected mice. However, the expression of growth arrest and DNA damage-inducible protein 34 (GADD34), which promotes eIF2α dephosphorylation by recruiting protein phosphatase 1 (PP1), was significantly induced both in vivo and in vitro. Knockdown of GADD34 and inhibition of PP1 activity by okadaic acid treatment led to increased eIF2α phosphorylation but significantly suppressed global protein synthesis and inhibited PRV replication. Collectively, these results demonstrated that PRV induces GADD34 expression to promote eIF2α dephosphorylation, thereby maintaining de novo protein synthesis and facilitating viral replication.
Highlights
Viruses lack biosynthetic capabilities and depend on the host machinery to synthesize viral proteins
The results showed that global protein synthesis remained unaffected up to 9 h post-infection; a significant increase in protein synthesis was observed from 12 to 24 hpi at an multiplicity of infection (MOI) of 0.1 (Figure 1A); densitometric analysis of the bands corresponding to puromycin-labelled proteins showed a 1.42–1.72-fold increase in the translation rate at 12–24 hpi in pseudorabies virus (PRV)-infected cells compared with mock-infected cells
We found that global protein synthesis was increased during PRV replication
Summary
Viruses lack biosynthetic capabilities and depend on the host machinery to synthesize viral proteins. EIF2α is known to be phosphorylated by at least four different kinases, namely, general control nonderepressible-2 (GCN-2), protein kinase R-like endoplasmic reticulum kinase (PERK), double-stranded RNA (dsRNA)-dependent protein kinase R (PKR), and haemregulated inhibitor (HRI), in response to a variety of stress conditions [6, 7]. Among these kinases, PERK and PKR play critical roles in viral infection via phosphorylation of eIF2α. It is known that the E2 protein of hepatitis C virus binds to PERK and inhibits its activation, thereby reversing PERK-mediated translational repression and promoting persistent viral infection [18]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
