The Molecular Mechanism Study Of Autophagy Induced By FMDV

Autophagy is a central cytosolic lysosomal-dependent catabolic process that controls protein and organelle degradation,and has essential roles in survival,development and homeostasis.Autophagy is also integral to human health and is involved in physiology,development,lifespan and a wide range of diseases,including cancer,neurodegeneration and viral infection.Autophagy is induced by a variety of stress stimuli,including nutrient and energy stress,ER stress,pathogen-associated molecular patterns(PAMPs)and danger-associated molecular patterns(DAMPs),hypoxia,redox stress,and mitochondrial damage.Foot-and-mouth disease(FMD)is an acute,contagious disease of domestic and wild cloven-hooved animal species and is caused by Foot-and-mouth disease virus(FMDV),the proto-type member of the genus Aphthovirus of the family Picornaviridae.The highly contagious nature of FMDV and the associated productivity losses make it a primary animal health concern worldwide.FMDV has been reported to induce autophagy.However,the exact molecular signaling pathway of autophagy induction and effect of autophagy on FMDV replication are not well understood.We found that LC3B-II expression was significantly upregulated in FMDV-infected PK-15 cells.The results of TEM show that the number of autophagosome-like vesicles markedly increased in the cytoplasm of FMDV-infected PK-15 cells.The level of p62 was significantly decreased and Baf-A1 treatment dramatically recovered green fluorescence puncta and increased yellow puncta at later stages of infection.These data show that FMDV infection not only increases autophagosomes formation,but also enhances autophagic flux.We report that the AKT-m TOR signaling pathway is essential for FMDV-induced autophagy in a swine kidney cell line.FMDV infection inhibited the activity of AKT and mammalian target of rapamycin(m TOR),which resulted in inhibition of Unc-51–like kinase 1(ULK1)S757 and autophagy.We also observed that the EIF2α(eukaryotic translation initiation factor 2α)-ATF4(activating transcription factor 4)pathway of the unfolded protein response(UPR)was activated after FMDV infection,suggesting that FMDV infection led to endoplasmic reticulum(ER)stress.Inhibition of the ER stress decreased autophagy induced by FMDV infection.Further experiments demonstrated that FMDV-induced autophagy via AKT-m TOR pathway depended on the ER stress response.In addition,we observed that alteration of cellular autophagy affected virus production.Inhibition of autophagy by ATG5 knockdown enhanced type I interferon(IFN)response.Overall,our results demonstrate that the activation of EIF2α-ATF4 pathway by FMDV infection inhibited AKT-m TOR pathway and led to autophagy,which blocks innate antiviral immune responses and favors FMDV replication.