Abstract
Viperin is a key antiviral effector in immune responses of vertebrates including the Atlantic cod (Gadus morhua). Using cloning, sequencing and gene expression analyses, we characterized the Atlantic cod viperin at the nucleotide and hypothetical amino acid levels, and its regulating factors were investigated. Atlantic cod viperin cDNA is 1,342 bp long, and its predicted protein contains 347 amino acids. Using in silico analyses, we showed that Atlantic cod viperin is composed of 5 exons, as in other vertebrate orthologs. In addition, the radical SAM domain and C-terminal sequences of the predicted Viperin protein are highly conserved among various species. As expected, Atlantic cod Viperin was most closely related to other teleost orthologs. Using computational modeling, we show that the Atlantic cod Viperin forms similar overall protein architecture compared to mammalian Viperins. qPCR revealed that viperin is a weakly expressed transcript during embryonic development of Atlantic cod. In adults, the highest constitutive expression of viperin transcript was found in blood compared with 18 other tissues. Using isolated macrophages and synthetic dsRNA (pIC) stimulation, we tested various immune inhibitors to determine the possible regulating pathways of Atlantic cod viperin. Atlantic cod viperin showed a comparable pIC induction to other well-known antiviral genes (e.g., interferon gamma and interferon-stimulated gene 15-1) in response to various immune inhibitors. The pIC induction of Atlantic cod viperin was significantly inhibited with 2-Aminopurine, Chloroquine, SB202190, and Ruxolitinib. Therefore, endosomal-TLR-mediated pIC recognition and signal transducers (i.e., PKR and p38 MAPK) downstream of the TLR-dependent pathway may activate the gene expression response of Atlantic cod viperin. Also, these results suggest that antiviral responses of Atlantic cod viperin may be transcriptionally regulated through the interferon-activated pathway.
Highlights
Interferon-stimulated genes (ISGs) play crucial roles as immune effectors and regulators in antiviral immune responses of fishes and other vertebrates [1, 2]
As predicted using SeqBuilder, the Atlantic cod viperin cDNA consisted of a 55 bp 5′-UTR, 1044 bp (347 amino acid (AA)) open reading frame (ORF) and a 243 bp 3′UTR
The sequencing results showed that the Atlantic cod viperin transcript is 1,342-bp long and consists of 6 exons
Summary
Interferon-stimulated genes (ISGs) play crucial roles as immune effectors and regulators in antiviral immune responses of fishes and other vertebrates [1, 2]. Characterization of Atlantic Cod Viperin intracellular Toll-like receptors (TLRs) or RIG-I-like receptors (RLRs), thereby activating transcription factors and enhancing the production of type I and II Interferons (IFNs) [6,7,8,9]. The expression of mammalian viperin is induced via IFN-dependent and independent pathways, both of which may be activated by detection of viruses or dsRNA through a member of the RLR family and activation of transcription factors (e.g., IFN regulatory factor 3, IRF3) [12,13,14]. Viperin expression enhances the TLR-mediated production of type I IFN via forming a signaling complex consisting of Interleukin-1 receptor-associated kinase (IRAK1) and Tumor necrosis factor receptor-associated factor 6 (TRAF6) on lipid bodies and facilitating the nuclear translocation of IRF7 [15]
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