Inhibition of DDX6 enhances autophagy and alleviates endoplasmic reticulum stress in Vero cells under PEDV infection

Porcine epidemic diarrhea (PED), caused by the porcine epidemic diarrhea virus (PEDV), has arisen huge economic losses to the swine industry worldwide. The Asp-Glu-Ala-Asp (DEAD)-box polypeptide 6 (DDX6), a DEAD box RNA helicase family member, acts as a suppressor of autophagy, however, whether it participates in PEDVinduced autophagy remains unclear. Here, we aimed to investigate the potential role of DDX6 during PEDV infection. We found that DDX6 protein expression was down-regulated and mRNA expression was up-regulated in PEDV-infected cells. Overexpression of DDX6 effectively impaired PEDV replication, while knockdown of DDX6 facilitated viral replication. Overexpression of DDX6 facilitated the degradation of autophagy-related gene (ATG) mRNA and partially rescued the dephosphorylation of mammalian target of rapamycin (mTOR) by PEDV infection. We also found that PEDV-triggered endoplasmic reticulum (ER) stress reduced the protein level of DDX6, and conversely, silencing of DDX6 is necessary and sufficient to alleviate ER stress and cell apoptosis. In addition, the loss of RNA helicase activity on DDX6 lost the ability to suppress autophagy and failed to restrict PEDV replication. Taken together, these findings indicated a DDX6-based mechanism that associates ER stress with autophagy activation during PEDV infection. PEDV-triggered ER stress down-regulated the expression of DDX6 to induce autophagy by inhibiting degradation of ATGs and phosphorylation of mTOR signaling, which alleviates ER stress and Promotes cell survival rather than apoptosis. These findings provided new insight into the function of DDX6 in autophagy during PEDV infection and may serve as a therapeutic strategy for controlling PEDV infection.