The RIG-I-like receptor (RLR) signaling pathway plays a critical role in the host defense against RNA virus infection. Among the RLR family members, retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are key cytosolic sensors that initiate type I interferon (IFN-I) responses. Their controllable expression, activation, and degradation are essential for maintaining immune homeostasis. However, the precise regulatory mechanisms governing RIG-I and MDA5 function during viral infection remain unclear. Here, we uncover that the E3 ubiquitin ligase RNF20 exerts dual regulatory roles in RLR signaling by modulating the expression and promoting the degradation of RIG-I and MDA5 in a nucleocytoplasmic translocation-dependent manner during viral infection. Under resting conditions, RNF20 resides in the nucleus, where it maintains immune readiness by regulating the basal and inducible transcription of RIG-I and MDA5. Upon RNA virus infection, RNF20 translocates to the cytoplasm via the export receptor CRM1. There, it recognizes the degron motifs of RIG-I and MDA5 through its coiled-coil domain and catalyzes their K27-linked ubiquitination and degradation, thereby preventing excessive antiviral signaling. These findings shed light on the significant and dual regulatory roles of RNF20 in maintaining innate immune homeostasis.
Wang et al. (Thu,) studied this question.