RNA Interference Targeting Nucleocapsid Protein Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication in Marc-145 Cells

Porcine reproductive and respiratory syndrome (PRRS) is an important disease, which leads to severe economic losses in swine-producing areas of the world. However, current antiviral strategies cannot provide highly effective protection. In this study, three theoretically effective interference target sites (71-91, 144-164,218-238) targeting the nucleocapsid (N) gene of PRRSV were designed and selected, and then three siRNA-expressing plasmids were constructed, respectively named p2.1-N71, p2.1-N144, and p2.1-N218. The recombinant siRNA-expressing plasmids were transfected into Marc-145 cells; then the cells were infected with PRRSV (JL07SW strain); finally, after incubation for 48 h, the antiviral activity of those siRNA-expressing plasmids in Marc-145 cells was assessed by cytopathic effects, virus titers, indirect immunofluorescence, and quantitative real-time PCR. Experimental results demonstrated that these three siRNA-expressing plasmids could effectively and significantly inhibit the replication of PRRSV by 93.2%, 83.6%, and 89.2% in Marc-145 cells, respectively. Among these three siRNA-expressing plasmids, p2.1-N71 was found to be most effective, while p2.1-N144 and p2.1-N218 displayed relatively weak inhibition of virus replication. The results indicated that siRNA-expressing plasmids targeting the N gene of PRRSV could significantly inhibit PRRSV replication in Marc-145 cells. Based on our experimental results and previous reports, the 71-91, 179-197, and 234-252 sites of the N gene are good choices to effectively inhibit the replication of PRRSV, and this RNA interference technique can be a potential anti-PRRSV strategy.