Porcine Reproductive and Respiratory Syndrome Virus Infection Induces both eIF2α Phosphorylation-Dependent and -Independent Host Translation Shutoff

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is an that has caused tremendous economic losses in the global swine industry since it was discovered in the late 1980s. Inducing host translation shutoff is a strategy used by many viruses to optimize their replication and spread. Here, we demonstrate that PRRSV infection causes host translation suppression, which is strongly dependent on viral replication. By screening PRRSV-encoded nonstructural proteins (nsps), we found that nsp2 participates in the induction of host translation shutoff and that its transmembrane (TM) domain is required for this process. nsp2-induced translation suppression is independent of protein degradation pathways and the phosphorylation of eukaryotic initiation factor 2α (eIF2α). However, the overexpression of nsp2 or its TM domain significantly attenuated the mammalian target of rapamycin (mTOR) signaling pathway, an alternative pathway for modulating host gene expression. PRRSV infection also attenuated the mTOR signaling pathway, and PRRSV-induced host translation shutoff could be partly reversed when the attenuated mTOR phosphorylation was reactivated by an activator of the mTOR pathway. PRRSV infection still negatively regulated the host translation when the effects of eIF2α phosphorylation were completely reversed. Taken together, our results demonstrate that PRRSV infection induces host translation shutoff and that nsp2 is associated with this process. Both eIF2α phosphorylation and the attenuation of the mTOR signaling pathway contribute to PRRSV-induced host translation arrest. Viruses are obligate parasites, and the production of progeny viruses relies strictly on the host translation machinery. Therefore, the efficient modulation of host mRNA translation benefits viral replication, spread, and evolution. In this study, we provide evidence that porcine reproductive and respiratory syndrome virus (PRRSV) infection induces host translation shutoff and that the viral nonstructural protein nsp2 is associated with this process. Many viruses induce host translation shutoff by phosphorylating eukaryotic initiation factor 2α (eIF2α). However, PRRSV nsp2 does not induce eIF2α phosphorylation but attenuates the mTOR signaling pathway, another pathway regulating the host cell translational machinery. We also found that PRRSV-induced host translation shutoff was partly reversed by eliminating the effects of eIF2α phosphorylation or reactivating the mTOR pathway, indicating that PRRSV infection induces both eIF2α phosphorylation-dependent and -independent host translation shutoff.

Pathogens MenTORing Macrophages and Dendritic Cells: Manipulation of mTOR and Cellular Metabolism to Promote Immune Escape

“…This downregulation of IFITM proteins has already been shown to promote influenza virus A infection in HeLa cells and HFFs [180]. Interestingly, viruses employing internal ribosome entry sites (IRESs) for translation of their mRNAs may benefit from the inhibition of mTORC1, since those viruses do not depend on mTOR-driven cap-dependent translation [23,161,[181][182][183].…”

“…T. gondii [177,178] Cleavage of mTOR via the protease GP63 in B10R macrophages to prevent IFN type I production and iNOS translation L. major [23] Mediates shut off of host translation which leads to a decreased translation of innate cytokines in U937 cells HSV-1 [179] Shut off of host translation to favor replication of own genome and to downregulate IFITM proteins Viruses relying on IRES-dependent translation [23,161,[180][181][182][183] Innate Cytokines…”

Integrin β3, a RACK1 interacting protein, is required for porcine reproductive and respiratory syndrome virus infection and NF-κB activation in Marc-145 cells

“…We speculate that some other signal pathways may be involved in and indispensable for PRRSV infection. Indeed, there have been a number of studies illustrating the relationship between PRRSV infection and mTOR signaling pathway (53), MyD88/ERK/AP-1 and NLRP3 inflammasome (54), ERK1/2-p-C/EBP-β Pathway (55) and Wnt/β-catenin pathway (56). Simultaneously deactivating the above-mentioned signal pathways probably will further block the PRRSV infection.…”

Porcine Reproductive and Respiratory Syndrome Virus E Protein Degrades Porcine Cholesterol 25-Hydroxylase via the Ubiquitin-Proteasome Pathway

“…The results showed that the PRRSV E protein did not significantly change the mRNA expression of GRP78 and GRP94 (data not shown), indicating that PRRSV E protein does not induce ER stress and subsequent degradation through the ERAD response. In addition, a previous study showed that PRRSV infection downregulated host protein expression by inducing host translation shutoff but UV-inactivated PRRSV did not (56). To test whether PRRSV E protein induces host translation shutoff, resulting in the degradation of pCH25H, we determined the levels of puromycin in 3D4/21 cells transfected with PRRSV E protein or cotransfected with PRRSV E protein and pCH25H.…”