Atlantic Salmon Interferon Genes: Cloning, Sequence Analysis, Expression, and Biological Activity

Abstract

In this work, we report cDNA cloning of two type I interferons (IFNs) from the head kidney of Atlantic salmon, called SasaIFN-alpha1 (829 bp) and SasaIFN-alpha2 (1290 bp). Both translate into 175 amino acid precursor molecules showing 95% amino acid sequence identity. The precursors have a putative 23 amino acid signal peptide, which suggests that the mature Atlantic salmon IFNs contain 152 amino acids (18.2 kDa). Salmon IFN appears to have five alpha-helices, similar to mammalian and avian type I IFNs, and showed 45% sequence identity with zebrafish IFN, up to 29% identity with mammalian IFN-alpha sequences, and 17%-18% sequence identity with mammalian IFN-beta and chicken type I IFNs. Human embryonic kidney 293 cells transfected with the SasaIFN-alpha1 cDNA gene produced high titers of acid-stable antiviral activity, which protected salmonid cells against infectious pancreatic necrosis virus (IPNV) and also induced Mx protein in the cells. Poly(I)-poly(C) induced two IFN transcripts in head kidney of Atlantic salmon. Genomic IFN sequences contained four introns and five exons, which is different from the intronless type I IFN genes of birds and mammals.

Distinct evolution process among type I interferon in mammals

“…Type I IFNs have been identified in zebrafish, Atlantic salmon, grass carp, and Fugurubripes, which several of them display similar activities to their mammal homologs (Altmann et al, 2003;Robertsen et al, 2003). IFNβ is hypothesized to have arisen from birds, and the other type I IFNs are present only in mammals (Sick et al, 1996).IFNζ, also known as limitin, was discovered for its abi lity to arrest the growth of or kill lympho-hematopo ietic cells, and is thought to only exist in mice (Oritani et al, 2000).…”

Fish virus-induced interferon exerts antiviral function through Stat1 pathway

“…Recently virusinduced IFN genes have been characterized in various fish species (Aggad et al, 2009;Altmann et al, 2003;Long et al, 2004;Lutfalla et al, 2003;Robertsen et al, 2003;Zou et al, 2007), and some downstream ISG counterparts have also been identified (Robertsen, 2006;Zhang et al, 2007), strongly indicating that teleost fish possess an IFN antiviral system. In support of this notion, IFN inducible genes including Mx and PKR have been proved to block virus replication in fish (Caipang et al, 2003;Larsen et al, 2004;Zhu et al, 2008), and there exists a conserved RLR (RIG-I-like receptors) pathway responsible for fish IFN induction during virus infection (Biacchesi et al, 2009).…”

“…In support of this notion, IFN inducible genes including Mx and PKR have been proved to block virus replication in fish (Caipang et al, 2003;Larsen et al, 2004;Zhu et al, 2008), and there exists a conserved RLR (RIG-I-like receptors) pathway responsible for fish IFN induction during virus infection (Biacchesi et al, 2009). Fish virus-induced IFNs exhibit more homology to mammalian type I IFN molecules on the basis of protein sequence identity, but they are not clearly an ␣-or ␤-IFN (Robertsen, 2006;Robertsen et al, 2003). However, the genome structure analysis shows that these IFN molecules are more evolutionally similar to type III IFN due to the presence of introns (Lutfalla et al, 2003) and, importantly, no intronless IFN gene has been reported in fish to date.…”

“…Moreover, most conclusions about the antiviral effects of fish virus-induced IFNs are derived from cell protection assays and the ability to upregulate Mx expression, a key hallmark IFN inducible gene (Altmann et al, 2003;Long et al, 2004;Lutfalla et al, 2003;Ooi et al, 2008;Robertsen et al, 2003). Some studies also have made a survey of the expression profile of IFN inducible genes (Martin et al, 2007); however, the physiological relevance of ISG expression is still poorly understood.…”

Gene structures and promoter characteristics of interferon regulatory factor 1 (IRF-1), IRF-2 and IRF-7 from snakehead Channa argus

“…Through the DBD, IRF family members bind to a similar DNA motif, termed interferon stimulating response element (ISRE) and IFN regulatory element (IRF-E) (Tanaka et al, 1993;Darnell et al, 1994). In teleosts, IFN molecules have been cloned and characterized from zebrafish (Danio rerio), pufferfish (Tetraodon nigroviridis), atlantic salmon (Salmo salar) and channel catfish (Ictalurus punctatus) since 2003 (Altmann et al, 2003;Robertsen et al, 2003;Long et al, 2004;Igawa et al, 2006). ISGs and their promoters were identified in rainbow trout (Oncorhynchus mykiss) Mx1 and Vig-2, Goldfish (Carassius auratus) and Atlantic cod (Gadus morhua) ISG15 (Collet and Secombes, 2001;Boudinot et al, 2001;Liu et al, 2002;Seppola et al, 2007).…”