Porcine epidemic diarrhea virus (PEDV) is a globally distributed alphacoronavirus that has reemerged lately, resulting in large economic losses. During viral infection, type I interferon (IFN-I) plays a vital role in the antiviral innate immunity. However, PEDV has evolved strategies to limit IFN-I production. To suppress virus replication, the host must activate IFN-stimulated genes and some host restriction factors to circumvent viral replication. This study observed that PEDV infection induced early growth response gene 1 (EGR1) expression in PEDV-permissive cells. EGR1 overexpression remarkably suppressed PEDV replication. In contrast, depletion of EGR1 led to a significant increase in viral replication. EGR1 suppressed PEDV replication by directly binding to the IFN-regulated antiviral (IRAV) promoter and upregulating IRAV expression. A detailed analysis revealed that IRAV interacts and colocalizes with the PEDV nucleocapsid (N) protein, inducing N protein degradation via the E3 ubiquitin ligase MARCH8 to catalyze N protein ubiquitination. Knockdown of endogenous MARCH8 significantly reversed IRAV-mediated N protein degradation. The collective findings demonstrate a new mechanism of EGR1-mediated viral restriction, in which EGR1 upregulates the expression of IRAV to degrade PEDV N protein through MARCH8. IMPORTANCE PEDV is a highly contagious enteric coronavirus that has rapidly emerged worldwide and has caused severe economic losses. No currently available drugs or vaccines can effectively control PEDV. PEDV has evolved many strategies to limit IFN-I production. We identified EGR1 as a novel host restriction factor and demonstrated that EGR1 suppresses PEDV replication by directly binding to the IRAV promoter and upregulating the expression of IRAV, which interacts with and degrades the PEDV N protein via the E3 ubiquitin ligase MARCH8 to catalyze nucleocapsid protein ubiquitination, which adds another layer of complexity to the innate antiviral immunity of this newly identified restriction factor. A better understanding of the innate immune response to PEDV infection will aid the development of novel therapeutic targets and more effective vaccines against virus infection.
Keywords: EGR1; IRAV; PEDV; antiviral response; nucleocapsid protein; viral replication.