CsIFIT1, an interferon-induced protein with tetratricopeptide repeat, inhibits viral infection in tongue sole (Cynoglossus semilaevis)

• An interferon-induced protein, CsIFIT1, was identified from tongue sole.
• CsIFIT1 expression was found in multiple tissues and upregulated by viral infection.
• Overexpression of CsIFIT1 in tongue sole blocked viral replication in fish tissues.
• Knockdown of CsIFIT1 expression in tongue sole promoted viral replication.
• CsIFIT1 is required for optimal defense against viral infection.

Interferon-induced protein with tetratricopeptide repeats (IFIT) is involved in antiviral immunity in mammalian cells. In fish, the function of this group of proteins is unknown. In this study, we report the identification of an IFIT homologue (named CsIFIT1) from tongue sole (Cynoglossus semilaevis) and examined its antiviral potential. CsIFIT1 is composed of 436 residues and shares 30.9%–58.7% overall sequence identities with the known IFITs of a number of teleost species. In silico analysis identified two tetratricopeptide repeats in CsIFIT1. Quantitative real time RT-PCR analysis showed that CsIFIT1 expression was most abundant in immune relevant organs and upregulated, in a time-dependent manner, by experimental infection with the fish viral pathogen megalocytivirus. When CsIFIT1 was overexpressed in tongue sole before megalocytivirus infection, viral replication in fish tissues was blocked to significant extents. Consistently, when CsIFIT1 expression in tongue sole was knocked down by siRNA, viral replication in fish tissues was significantly enhanced. Taken together, these results indicate that CsIFIT1 is likely a key factor of antiviral immunity and is required for optimal defense against viral infection.