Porcine Reproductive and Respiratory Syndrome Virus Nonstructural Protein 1 Beta Interacts with Nucleoporin 62 To Promote Viral Replication and Immune Evasion

Porcine reproductive and respiratory syndrome virus (PRRSV) blocks host mRNA nuclear export to the cytoplasm, and nonstructural protein 1 beta (nsp1 beta) of PRRSV has been identified as the protein that disintegrates the nuclear pore complex. In the present study, the molecular basis for the inhibition of host mRNA nuclear export was investigated. Nucleoporin 62 (Nup62) was found to bind to nsp1 beta, and the region representing the C-terminal residues 328 to 522 of Nup62 was determined to be the binding domain for nsp1 beta. The nsp1 beta L126A mutant in the SAP domain did not bind to Nup62, and in L126A-expressing cells, host mRNA nuclear export occurred normally. The vL126A mutant PRRSV generated by reverse genetics replicated at a lower rate, and the titer was lower than for wild-type virus. In nsp1 beta-overexpressing cells or small interfering RNA (siRNA)-mediated Nup62 knockdown cells, viral protein synthesis increased. Notably, the production of type I interferons (IFN-alpha/beta), IFN-stimulated genes (PKR, OAS, Mx1, and ISG15 genes), IFN-induced proteins with tetratricopeptide repeats (IFITs) 1 and 2, and IFN regulatory factor 3 decreased in these cells. As a consequence, the growth of vL126A mutant PRRSV was rescued to the level of wild-type PRRSV. These findings are attributed to nuclear pore complex (NPC) disintegration by nsp1 beta, resulting in increased viral protein production and decreased host protein production, including antiviral proteins in the cytoplasm. Our study reveals a new strategy of PRRSV for immune evasion and enhanced replication during infection. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes PRRS and is known to effectively suppress host innate immunity. The PRRSV nsp1 beta protein blocks host mRNA nuclear export, which has been shown to be one of the viral mechanisms for inhibition of antiviral protein production. nsp1 beta binds to the cellular protein nucleoporin 62 (Nup62), and as a consequence, the nuclear pore complex (NPC) is disintegrated and the nucleocytoplasmic trafficking of host mRNAs and host proteins is blocked. We show the dual benefits of Nup62 and nsp1 beta binding for PRRSV replication: the inhibition of host antiviral protein expression and the exclusive use of host translation machinery by the virus. Our study unveils a novel strategy of PRRSV for immune evasion and enhanced replication during infection.