Involvement of PRRSV NSP3 and NSP5 in the autophagy process.

BACKGROUND: Autophagy is an essential process in eukaryotic cells in which autophagosomes form to deliver cellular organelles and long-lived proteins to lysosomes for degradation. Many studies have recently identified the regulatory mechanisms involved in the interaction between viral infection and autophagy. METHODS: LC3 turnover and the proteins in the endoplasmic reticulum (ER) stress pathway were investigated using western blot analysis. The formation and degradation of autophagosomes were detected using immunofluorescence staining. RESULTS: Autophagy was activated by porcine reproductive and respiratory syndrome virus (PRRSV) NSP3, NSP5 and NSP9, which are two transmembrane proteins and an RNA-dependent RNA polymerase, respectively. The formation of autophagosomes was induced by NSP3 and NSP5 and developed from the ER; the fusion of these autophagosomes with lysosomes was limited. Although NSP3 and NSP5 are ER transmembrane proteins, these proteins did not activate the ER stress signaling pathways. In addition, the cytoplasmic domain of NSP3 plays a pivotal role in activating autophagy. CONCLUSIONS: The data presented in this study reveal an important relationship between PRRSV NSPs and autophagy and provide new insights that improve our understanding of the involvement of PRRSV NSPs in the autophagy process.