Antiviral Activity Of IFN-inducible Porcine 2'-5'-Oligoadenylate Synthase-Like Protein Against Classical Swine Fever Virus

Classical swine fever virus?CSFV?is the causative agent of classical swine fever?CSF?,which poses a serious threat to pig industry in many countries.Interferon?IFN?and IFN-stimulated genes?ISGs?play a key role in host antiviral defense,which are the first line of defense for animals.CSFV triggers the type I IFN signaling pathway upon infection,resulting in the transcription of hundreds of ISGs and then ISGs exert the antiviral activities.Up to now,the anti-CSFV ISGs and their antiviral molecular mechanisms have been poorly documented.Therefore,it is important to screen anti-CSFV ISGs and analyze their antiviral mechanisms.We have previously screened the porcine2'-5'-oligoadenylate synthase-like protein?pOASL?as a potential anti-CSFV ISG using a reporter CSFV in lentivirus-delivered,ISGs-overexpressing PK-15 cells.This study aimed to clarify the antiviral effect of pOASL against CSFV.We confirmed that CSFV replication was significantly suppressed in lentivirus-delivered,pOASL-overexpressing PK-15 cells at different multiplicity of infection?MOIs?and different time points by testing the virus titers,the genome RNA copies and the expression of nonstructural protein N^pro.The results showed that the inhibition of CSFV at an MOI of 1 by pOASL started from 6 h postinfection?hpi?,reached a peak at 12 hpi and decreased thereafter.In addition,silencing the expression of endogenous pOASL by small interfering RNAs markedly enhanced CSFV growth using the above-mentioned tests.These indicated that pOASL is an anti-CSFV ISG.Moreover,we attempted to confirm the effects of CSFV infection on the expression of pOASL.The results demonstrated that the transcriptional level of p OASL mRNA was upregulated at MOI of 0.1 at 3,6,12,24,36 and 48 hpi,as well as at MOI of 0.1 and 1 at 6 hpi.pOASL is a member of the OAS family and it contains an OAS domain.Maybe pOASL exerts an anti-CSFV activity depending on canonical RNase L pathway.Interestingly,pOASL still has the anti-CSFV activity after silencing endogenous RNase L.Furthermore,we examined that whether pOASL exerts anti-CSFV activity depending on the IFN signaling pathway or not.The results showed that pOASL can enhance IFN signaling pathway.Taken together,pOASL is an anti-CSFV ISG and exerts antiviral activity depending on type I IFN signaling but not canonical RNase L pathway.