Molecular Mechanism Of Interferon Antiviral Response Regulated By FTR67 And FTR100 In Yellow Catfis

When vertebrates are infected by virus,host pattern-recognition receptors(PRRs)can recognize pathogen-associated molecular patterns(Pathogen-associated molecular patterns,PAMPs)such as viral nucleic acids through,and subsequently activate signal transduction pathways to induce interferon(Interferon,IFN)expression.The secreted interferon binds to the cognate cellular receptor to activate the JAK-STAT signaling pathway(Janus kinase-signal transducer and activator of transcription pathway),thus inducing the expression of hundreds of interferon-stimulated genes(ISGs)to inhibit virus invasion.Insufficient interferon is difficult to clear the invading virus in cells,while overproduction to IFN might result in the development of immunopathological conditions.Thus,cellular IFN responses in vertebrates must be fine-tuned.Mammalian TRIM(Tripartite motif)proteins,as E3 ubiquitin ligases,play a direct antiviral role or a regulatory function in host antiviral response.In addition to those conserved in mammals,fish has a fish-specific TRIM subfamily called finTRIM(fish novel TRIM,FTR).Recently,our laboratory has identified a species-specific fintrim gene in crucian carp,named ftrca1.Functional studies reveal that FTRCA1 negatively regulates IFN antiviral immune response.In order to study whether there are functional genes homologous to ftrca1 in Pelteobagrus fulvidraco,this study reports the identification and function of two genes from Pelteobagrus fulvidraco,which are homologous to ftrca1.1.Molecular cloning and functional identification of fintrim67 gene from yellow catfishWe first cloned a Pelteobagrus fulvidraco fintrim gene with the highest homology to zebrafish(Danio rerio)ftr67,so this gene is named pfftr67(Pelteobagrus fulvidraco FTR67).Although only one copy of ftr67 is identified in yellow catfish,three copies are found in goldfish,suggesting that the ftr67 gene number may have been increased due to whole genome duplication in some fish species.pfftr67 is not induced by SVCV and is therefore a constitutively expressed gene.Overexpression of Pf FTR67 inhibits fish IFN response induced by poly(I:C)and RLR signaling molecules,and concomitantly promotes virus replication,indicating that Pf FTR67 plays a negative regulatory role in the constitutive expression of IFN.Given that the expression characteristics and function features of yellow catfish FTR67 are different from those of zebrafish FTR67,the data in the current study suggest that fish FTR67 has undergone gene duplication and functional diversification after radiation of fish species.2.Molecular cloning and functional identification of fintrim100 gene from yellow catfishWe also clone an unannotated fintrim gene from yellow catfish genome,named Pf FTR100.Because fish finTRIM gene family has undergone lineage-specific expansion and even species-specific expansion,we develop a nomenclature for newly cloned fintrim genes from different fish species.Genome-wide analyses reveal that FTR100 is unique to Otomorpha fish,with a single copy in spite of additional genome duplication in some fish species.pfftr100 m RNA is not induced by virus infection,but there is a high level of constitutive expression,even comparable to the expression level of IFN induced by virus.However,ectopically-expressed Pf FTR100 protein is attenuated in virally-infected cells through the proteasomal-dependent pathway.Functional studies reveal that Pf FTR100 promotes SVCV replication by downregulating the constitutive and inducible IFN response via a mechanism by which Pf FTR100 targets irf3 and irf7 to attenuate their m RNA levels rather than their protein levels.The above results indicate that Pf FTR100 is essential for homeostatic regulation of fish tonic IFN response.