Characterization of ISG56 from grass carp ( Ctenopharyngodon idellus ) and its response to two immune stimuli

Interferon (IFN)-stimulated genes (ISGs) 56 is a prominent antiviral agent and negative regulator of the IFN signaling pathway that specifically binds and discriminates viral RNAs in mammals. However, its role in teleosts is still unknown. In the current study, we successfully identified the ISG56 gene from grass carp ( Ctenopharyngodon idellus ) and investigated its immune function response to poly (I:C) and LPS. In addition, the coordinated pattern of multiple typical ISGs was also determined. The open reading frame (ORF) of the CiISG56 gene was 1299 bp in length and encoded a protein of 432 amino acids. The putative amino acid sequence consisted of 10 complete tetratricopeptide repeat motifs (TPRs). Phylogenetic analysis revealed a relatively distant evolutionary relationship between ISG56 and ISG58 in fish, with ISG56 clearly segregating into two distinct clades among freshwater and marine fish. Furthermore, the CiISG56 gene was found to exhibit constitutive expression across all examined tissues in grass carp, with the spleen displaying the highest level of expression. The expression of the CiISG56 gene was markedly increased in the liver, spleen, and kidney at various time points following stimulation with poly (I:C) or LPS. In addition, upon comparing the RNA expression level of CiISG56 following poly (I:C) stimulation with that after LPS stimulation, ISG56 demonstrated the lowest expression level under Poly (I:C) stimulation. Moreover, ISG56 was included among the genes that displayed high expression levels upon LPS stimulation. This finding implies a refined model in which a small subset of “dominant” ISGs may account for the majority of the inhibitory effects on a given immune response triggered by immune-stimulating substances. Furthermore, following stimulation with poly (I:C) or LPS, a high level of consistency and synergy among multiple ISGs was detected. This discovery indicates that in response to the stimulation imposed by immune stimulants, the eight typical ISGs displayed a coordinated pattern. Taken together, our results will contribute to a better understanding of the immune function of the CiISG56 gene in teleost fish, thereby furnishing valuable insights for disease management in grass carp. These findings may contribute to the development of novel immunostimulants for disease control in aquaculture.