The N protein of spring viremia of carp virus promotes the ubiquitination and degradation of viperin_sv1 to escape from the fish innate immunity

Abstract

Viperin is known as interferon-stimulating genes (ISGs) and plays broad-spectrum antiviral effects during viral infection. Viperin_sv1, a novel viperin splice variant, has recently been identified from SVCV-infected FHM cells with a stronger antiviral effect than viperin by activating IFN signaling pathway. Meanwhile, SVCV infection can suppress the protein level of viperin_sv1 to escape the host immune but the related mechanism remains to be unclear. In this study, the degradation of viperin_sv1 protein was confirmed to be significantly activated by SVCV infection and recovered by MG132 but not NH4Cl or 3-MA. SVCV infection also enhanced the ubiquitination of viperin_sv1, which proved that the viperin_sv1 was degraded through the ubiquitin-proteasome pathway (UPP). Overexpression of SVCV-N protein was able to lead to the degradation of viperin-sv1 while mutating the viperin_sv1 at Lys201 blocked the degradation during SVCV infection or SVCV-N protein overexpression. Besides, the western blot and qRT-PCR tests showed the viperin_sv1-K201R-mediated IFN production is more stable and plays a stronger inhibitory effect on SVCV replication than viperin_sv1. Taken together, this study demonstrates a new defense mechanism of SVCV to dampen the host IFN response by interfering and degrading viperin_sv1.