Porcine reproductive and respiratory syndrome virus nsp2-related proteins induce host translational arrest by specifically impairing the mTOR signaling cascade

As obligate parasites, viruses strictly rely on the host translation machinery for progeny production. To compete for host translation resources, the porcine reproductive and respiratory syndrome virus (PRRSV) employs multiple strategies to suppress host protein synthesis. Mechanistically, the mRNA nuclear export and canonical translation initiation are suppressed in cells with PRRSV Infection. Nsp2 was identified to induce host translation shutoff targeting the mTOR signaling pathway. Nsp2TF shares its N-terminal domains with nsp2, while nsp2N is a C-terminal truncation of nsp2. In this study, we investigated the role of nsp2-related proteins in suppressing host protein synthesis, defining their mechanistic impact on translational regulation. In a puromycin incorporation assay, the inactivation of nsp2TF and nsp2N translation attenuated the inhibitory effect of PRRSV Infection on nascent peptide synthesis. PRRSV utilizes a multi-faceted approach to suppress host translation, primarily through modulation of eIF2α phosphorylation before 12 hpi and inhibition of the mTOR signaling pathway at 24 hpi. The nsp2-related proteins (nsp2, nsp2TF, and nsp2N) contribute to the modulation of the mTOR signaling pathway via divergent mechanisms. While nsp2 broadly suppresses mTOR effector proteins (4E-BP1, S6K, and rpS6), nsp2TF and nsp2N mainly downregulate the 4E-BP1 phosphorylation. The activity of mTORC1 may be regulated by additional PRRSV-encoded proteins, suggesting a coordinated viral strategy to hijack host translational machinery. This study provides novel insights into the molecular mechanisms by which nsp2-related proteins subvert host protein synthesis to facilitate viral replication.

Host translational shutoff; MTOR signaling; Nsp2N; Nsp2TF; PRRSV.