NBR1 mediates autophagic degradation of IRF3 to negatively regulate type I interferon production

In the setting of virus infection, autophagy regulates the synthesis of type I interferon (IFN) via multiple mechanisms to prevent adverse overreaction. Interferon regulatory factor (IRF) 3, the dominant transcriptional factor of type I IFN, can be degraded via autophagy-lysosomal pathway. However, the exact regulatory mechanism is not yet well elucidated. IRF3 was targeted into autophagosome by interacting with cargo receptors including p62, NDP52 and NBR1. The recent studies have reported the mechanism of p62 and NDP52 sequestrating IRF3. This work aims to investigate the role of NBR1 in the process of IRF3 degradation. We found that blocking autophagy via ATG3/ATG7 knockout and chemical inhibitors both resulted in the accumulation of IRF3 protein and increased synthesis of type I IFN, while enhancing autophagy activity led to more obvious clearance of IRF3 in HEK293T cells infected with Sendai virus (SeV). Our data suggested that NBR1 bound both unphosphorylated and phosphorylated IRF3 through its ubiquitin-associated domain. Meanwhile, viral infection elevated the expression of NBR1, which sequentially formed a negative feedback loop to promote IRF3 degradation and hence optimized the type I IFN signaling. This study expands the knowledge of molecular mechanisms regulating the IRF3 stability and function during viral infection.