A rescued NADC30-like virus by reverse genetic manipulation exhibits moderate virulence and a promising application perspective

The role of major and minor structural proteins of porcine reproductive and respiratory syndrome virus in induction of protective immunity

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV), an economically significant threat to the world pork production, is notoriously known for its heterogeneity, and therefore the current vaccines often fail to provide efficient cross-protection against diverse PRRSV strains.

Methods

By making chimeric viruses using HP-PRRSV-2 lineage 8 (JXwn06) and lineage 1 NADC30-like strains (CHsx1401) as model organisms, the recently results have shown that the viral structural protein-coding region is critical for induction of homologous immunity. In this study, the chimeric viruses were further constructed by exchanging the region coding for the minor (GP2/3/4) or major (GP5/M) structural proteins of JXwn06 on the backbone of CHsx1401 to generate two mutants CHsx1401-GP234JX and CHsx1401-GP5MJX.

Results

The subsequent animal experiment showed that all three chimeras could confer good protective immunity against the lethal challenge by HP-PRRSV strain JXwn06, and the survived pigs had much lower lung lesions, faster viremia clearance, and lower viral tissue load. However, the exchange of SP region as a whole performed better than either GP2/3/4 or GP5/M region alone, as the pigs in the latter groups showed transient fever following challenge and higher viral load in certain tissues, highlighting a synergistic role. Interestingly, as compared to the group CHsx1401-GP234JX, the group CHsx1401-GP5MJX showed excellent viremia clearance, comparable to the SP group.

Discussion

Our results in this report revealed the important role of ORFs2-4 and ORFs5-6 regions in induction of protective immunity and have important implications in understanding viral pathogenesis and further vaccine development.

PSMB1 Inhibits the Replication of Porcine Reproductive and Respiratory Syndrome Virus by Recruiting NBR1 To Degrade Nonstructural Protein 12 by Autophagy

The nonstructural proteins (Nsps) of porcine reproductive and respiratory syndrome virus (PRRSV) play essential roles in virus replication-a multistep process that requires the participation of host factors. It is of great significance for the development of antiviral drugs to characterize the host proteins that interact with PRRSV Nsps and their functions in PRRSV replication. Here, we determined that proteasome subunit β type 1 (PSMB1) interacted with viral Nsp12 to inhibit PRRSV replication in target and permissive cells. PSMB1 could be downregulated by PRRSV infection through interaction with the transcription factor EBF1. Proteasome and autophagy inhibitor assays showed that PSMB1 was regulated by the autophagic pathway to degrade Nsp12. Cotransfection of PSMB1 and Nsp12 increased the level of intracellular autophagy; both molecules were colocated in lysosomes. We also found that the selective autophagy cargo receptor protein NBR1 and E3 ubiquitin ligase STUB1 interacted with PSMB1 and Nsp12, respectively, in the autophagic degradation of Nsp12. Furthermore, the degradation of Nsp12 by PSMB1 was mainly dependent on the ubiquitination of Nsp12 at lysine site 130. Our results indicate for the first time that PSMB1 is an anti-PRRSV host protein that inhibits the replication of PRRSV by degradation of Nsp12 through the selective autophagy pathway. IMPORTANCE PRRS is a major threat to the global pig industry and urgently requires an effective and sustainable control strategy. PRRSV Nsps have important roles in viral RNA synthesis, proteinase activity, induction of replication-associated membrane rearrangements, replicative endoribonuclease activity, determination of virulence, and regulation of host immune response. Research associated with PRRSV Nsps can provide vital guidance to modify the PRRSV genome through reverse genetics in the development of vaccines and diagnostics. The function of Nsp12, which generally plays essential roles in virus replication, remains unclear. We demonstrated that PSMB1 interacted with and degraded Nsp12 through an autophagic pathway to inhibit PRRSV replication. Our data confirmed a novel antiviral function of PSMB1 and allowed us to elaborate on the roles of Nsp12 in PRRSV pathogenesis. These findings suggest a valid and highly conserved candidate target for the development of novel therapies and more effective vaccines and demonstrate the complex cross talk between selective autophagy and PRRSV infection.

Characterization and Pathogenicity of Two Novel PRRSVs Recombined by NADC30-like and NADC34-like Strains in China

Porcine reproductive and respiratory syndrome viruses (PRRSVs) pose a serious threat to the swine industry in China, which has caused great difficulties for porcine reproductive and respiratory syndrome (PRRS) immune prevention and control, due to its easily mutable and recombinant nature. In this study, two novel PRRSV strains, which were named GD-H1 and GD-F1, were isolated and fully sequenced from pig farms in Guangdong province, China. The phylogenetic analysis and recombination analysis revealed that the GD-H1 and GD-F1 were generated by the recombination of NADC30-like and NADC34-like strains which were different from the previously prevalent strain. Further pathogenic studies on piglets and sows found that the recombinant strains could cause piglets high fever, loss of appetite and lung lesions, but no piglets died. However, the recombinant strains could cause acute death and abortion in pregnant sow infection models together with average survival rates of 62.5% and 37.5% abortion rates, respectively. These findings indicated that the recombinant strains were extremely pathogenic to sows. Therefore, we report two clinical novel recombinant strains of PRRSV that are different from the traditional epidemic strains in China, which may provide early warning and support for PRRS immune prevention and control.