title: Subcellular localization and functional characterization of a fish IRF9 from crucian carp Carassius auratus.
abstract: Mammalian interferon (IFN) regulatory factor 9 (IRF-9) has long been recognized as the DNA sequence recognition subunit of IFN-stimulated gene factor 3 (ISGF3) complex, which is critical for type I IFN to induce the expression of IFN-stimulated genes (ISGs) against viral infection. Recent studies have shown that fish IFN exerts antiviral effects by induction of a number of ISGs and also of itself; however, little is known about the role of fish IRF9 in IFN signaling. Here we identify a fish IRF9 orthologue (CaIRF9) from IFN-producing cell line, crucian carp Carassius auratus blastulae embryonic (CAB) cells. Analysis of subcellular distribution of CaIRF9-green fluorescent protein indicates that CaIRF9 is constitutively present in the nucleus, which is driven by two nuclear localization signals (NLS), one locating within DNA-binding domain (DBD) of CaIRF9 and the other immediately behind DBD, although human IRF9 contains only one NLS analogous to the former of CaIRF9. Overexpression of CaIRF9 together with CaSTAT2 not only activates ISRE-containing promoter but also upregulates the expression of fish ISGs. Strikingly, CaIRF9 together with CaSTAT2 also exhibits an ability to activate crucian carp IFN promoter, and blockade of cellular CaIRF9 attenuates IFN itself-induced activation of crucian carp IFN promoter. Taken together, these data suggest that crucian carp IFN induces the expression of ISGs and also of itself possibly by the JAK-STAT signaling pathway that is conserved from fish to mammals.
authors.affiliation: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Wuhan, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Shi
authors.forename: Yi-Bing
authors.initials: YB
authors.lastname: Zhang
authors.forename: Ting-Kai
authors.initials: TK
authors.lastname: Liu
authors.forename: Fan
authors.initials: F
authors.lastname: Sun
authors.forename: Jian-Fang
authors.initials: JF
authors.lastname: Gui
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006054:Goldfish / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit / Q000235:genetics / Q000378:metabolism*; D007372:Interferons / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029941:Fish Proteins; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D011994:Recombinant Proteins; D007372:Interferons