Research note: duck Tembusu virus non-structural protein 3 induced autophagy through endoplasmic reticulum stress

Duck Tembusu virus (DTMUV) causes severe infectious diseases in poultry. Previous studies have shown that DTMUV induced autophagy and endoplasmic reticulum stress (ERS) in host cells, thereby influencing the virus proliferation. However, the role of ERS in DTMUV-induced autophagy remains unclear. In this study, the relationship between ERS and autophagy activated by DTMUV was first analyzed, and we found that the ERS inhibitor 4-phenylbutyric acid (4-PBA) decreased DTMUV-induced autophagy, suggesting that autophagy induced by DTMUV was ERS-dependent. Further investigation revealed that the NS3 protein of DTMUV played an important role in the activation of ERS, it triggered all three branches of unfolded protein response (UPR) signaling [Protein kinase R-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1ɑ (IRE1ɑ), and activating transcription factor 6 (ATF6)] in duck embryo fibroblast (DEF) cells. Inhibition of PERK and IRE1ɑ pathways reduced the NS3-mediated autophagy. Interestingly, while truncated NS3 mutants still activated ERS via the PERK pathway, they failed to induce autophagy. Mechanistically, NS3 was found to interact with the endoplasmic reticulum chaperone GRP78. This study elucidated ERS was critical for NS3-induced autophagy, laid a foundation for understanding the roles of DTMUV-induced ERS and autophagy in the viral pathogenesis.