PRRSV degrades MDA5 via dual autophagy receptors P62 and CCT2 to evade antiviral innate immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economically devastating pathogen that has evolved various strategies to evade innate immunity. Downregulation of Antiviral interferon largely contributes to PRRSV immunoevasion through cytoplasmic melanoma differentiation-associated gene 5 (MDA5), a receptor that senses viral RNA. In this study, the downregulated transcription and expression levels of porcine MDA5 in PRRSV Infection were observed, but the detailed mechanisms remain unclear. The interaction between p62 and MDA5 was strengthened due to the phosphorylation modification of the autophagic receptor p62 by the upregulated kinase CK2α and the K63 ubiquitination of porcine MDA5 catalyzed by the E3 ubiquitinase TRIM21 in PRRSV-infected cells, thus triggering the classic P62-mediated Autophagy. Additionally, porcine MDA5 interacted with the chaperonin containing TCP1 subunit 2 (CCT2) and was enhanced by PRRSV nsp3, facilitating the aggregate formation and autophagic clearance of MDA5-CCT2-nsp3 independently of ubiquitin. Enhanced MDA5 degradation occurs in PRRSV Infection via two autophagic pathways, including the binding of MDA5 with the Autophagy receptor p62 and the aggrephagy receptor CCT2, triggering intense innate immune suppression. The research reveals a novel mechanism of immune evasion in PRRSV Infection and provides fundamental insights for the development of new vaccines or therapeutic strategies.

MDA5; Porcine reproductive and respiratory syndrome virus (PRRSV); autophagy; nsp3.