The Mechanisms Underlying Foot-and-mouth Disease Virus 3C Proteinase Downregulates Protein Kinase PKR To Facilitate Virus Replication

Foot-and-mouth disease is a zoonosis caused by the foot-and-mouth disease virus?FMDV?,which infects domestic livestocks and numerous wild animals.The innate immune systems play significant roles in defending FMDV infection.Immune response is initiated after pathogenic microorganism is recognized by innate immune systems promptly,meanwhile,innate immune also trigger the adaptive immune response and has a dominating regulation to adaptive immune response.Double-strand RNA activated protein kinase?PKR?plays important roles in host defense against viral infection.To exploit the functions and mechanisms of PKR in regulation of FMDV replication in host cells,we constructed a eukaryotic expression plasimd of PKR and performed the overexpression assay,which indicated that FMDV replication was significantly suppressed in PKR up-regulated cells.Meanwhile,we also investigated the state of PKR after FMDV infection,and showed that PKR transcripts were significantly up-regulated in FMDV-infected cells;however,the protein abundances and phosphorylate levels of PKR were significantly down-regulated after FMDV infection.The phosphorylation of eIF2?was also significantly suppressed.A further study revealed that the non-structural protein 3Cpro was responsible for FMDV-induced PKR downregulation and inhibition of PKR phosphorylation.We further performed the co-immunoprecipitation?co-IP?assay,constructed3Cpro mutant,and investigated the protein degradation pathways.Finally,we determined that there was no direct interaction between 3Cpro and PKR;3Cpro induced PKR reduction by regulation of host lysosomal pathway.The mechanisms about how 3Cpro regulates lysosomal pathway remains unkown.In conclusion,we demonstrate the antiviral role of PKR against FMDV,and reveal that FMDV infection significantly downregulates PKR protein expression.Besides,we identify a new antagonistic mechanism of FMDV to suppress host antiviral response:FMDV non-structural protein 3C^pro downregulates PKR expression by lysosome pathway,inhibiting PKR-mediated signaling transduction.This study provides new data to clarify the antagonistic mechanisms induced by FMDV proteins,and paves ways for decrease of immunosuppressive activity of FMDV vaccines.