Nonstructural proteins nsp2TF and nsp2N of porcine reproductive and respiratory syndrome virus (PRRSV) play important roles in suppressing host innate immune responses

Abstract

Recently, we identified a unique -2/-1 ribosomal frameshift mechanism in PRRSV, which yields two truncated forms of nonstructural protein (nsp) 2 variants, nsp2TF and nsp2N. Here, in vitro expression of individual PRRSV nsp2TF and nsp2N demonstrated their ability to suppress cellular innate immune responses in transfected cells. Two recombinant viruses were further analyzed, in which either nsp2TF was C-terminally truncated (vKO1) or expression of both nsp2TF and nsp2N was knocked out (vKO2). Host cellular mRNA profiling showed that a panel of cellular immune genes, in particular those involved in innate immunity, was upregulated in cells infected with vKO1 and vKO2. Compared to the wild-type virus, vKO1 and vKO2 expedited the IFN-α response and increased NK cell cytotoxicity, and subsequently enhanced T cell immune responses in infected pigs. Our data strongly implicate nsp2TF/nsp2N in arteriviral immune evasion and demonstrate that nsp2TF/nsp2N-deficient PRRSV is less capable of counteracting host innate immune responses.

A Nanobody Targeting Viral Nonstructural Protein 9 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication

“…It has a single-stranded, positive-sense RNA genome of approximately 15.4 kb, which contains at least 10 open reading frames (ORFs), including ORF1a, ORF1b, ORF2a, ORF2b, ORF3, ORF4, ORF5, ORF5a, ORF6, and ORF7 (10,11). Viral proteases process polyproteins translated from ORF1a and ORF1b into 16 nonstructural proteins (Nsps): Nsp1␣/␤, Nsp2-6, Nsp7/7␣, Nsp8-12, Nsp2TF, and Nsp2N (12,13). It has been demonstrated that some of the Nsps are assembled with host cell components to form the viral replication and transcription complex (RTC) (14).…”

Hyper-phosphorylation of nsp2-related proteins of porcine reproductive and respiratory syndrome virus

“…Arterivirus nsp2 was also reported to play an important role in the formation of double membrane vesicles (DMVs) that anchor the replication transcription complex (Snijder et al, 2001(Snijder et al, , 2013Posthuma et al, 2008). The identification of two additional frameshifting products, nsp2TF and nsp2N, increases the functional versatility and also the complexity of potential roles played by nsp2 (Snijder et al, 2013;Fang et al, 2012;Li et al, 2014Li et al, , 2018. We observed that all three nsp2-related proteins (nsp2, nsp2TF and nsp2N) are phosphorylated.…”

“…1). However, in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), we observed that the apparent sizes of nsp2-related proteins were substantially larger than the predicted molecular weights Li et al, 2018). We therefore investigated whether post-translational modifications, in particular phosphorylation, affect the mobilities of nsp2-related proteins in SDS-PAGE.…”

The nsp2 Hypervariable Region of Porcine Reproductive and Respiratory Syndrome Virus Strain JXwn06 Is Associated with Viral Cellular Tropism to Primary Porcine Alveolar Macrophages

“…In addition, isoforms exist for PRRSV nsp2 that differ mainly in the C terminus, two of which (nsp2TF and nsp2N) are translated by a frameshift mechanism (16,17). The PLP2 domain contains catalytic sites that are highly conserved among arteriviruses; it possesses both cis-and trans-cleavage activities, which are responsible for nsp2/3 cleavage, and deubiquitinating activity, which likely plays an important role in regulating host innate immunity (14,(18)(19)(20)(21)(22)(23). The C-terminal TMD and CT are highly conserved and are required for PRRSV replication (15).…”