DDX19 inhibits RLR/IRF3 mediated type I interferon signaling of black carp Mylopharyngodon piceus by restricting IRF3 from entering nucleus

Members of DExD/H-box helicase family are important receptors for detecting viral nucleic acids. Mammalian DExD/H-box RNA helicase 19 (DDX19) has been reported to play as a negative regulator of type I interferon (IFN). However, the role of teleost DDX19 during the innate immune response is still obscure. In this study, the DDX19 homolog of black carp (bcDDX19) has been cloned and characterized. The open reading frame (ORF) of bcDDX19 consists of 1440 nucleotides and encodes contains 479 amino acids. bcDDX19 migrates around 54 kDa in immunoblotting assay and is identified as a cytosolic protein by immunofluorescence staining. The qPCR results show that the transcription of bcDDX19 in host cells rises in response to Lipopolysaccharide (LPS), Poly (I: C), spring viremia of carp virus (SVCV) or grass carp reovirus (GCRV) stimulation. In the report assay, bcDDX19 suppressed bcIRF3-, but not bcIRF7-mediated transcription activities of bcIFNa and DrIFN phi l promoter. Co-immunoprecipitation assays identify that bcDDX19 interacts with bcIRF3 but not bcIRF7. According, plaque assay results demonstrate that bcDDX19 dampens bcIRF3- but not bcIRF7-induced antiviral activity of EPC cells. Knockdown of bcDDX19 offers host cells the increase of mRNA levels of bcIFNa, bcMx1 and bcViperin, and the improved antiviral ability against SVCV. In addition, the nuclear translocation of bcIRF3 is dampened when co-expressed with bcDDX19. All of these findings demonstrate that bcDDX19 negatively regulates RLR/IRF3 mediated type I IFN signaling in the innate immune activation through restricting IRF3 from entering nucleus.