Rubicon Modulates Antiviral Type I Interferon (IFN) Signaling by Targeting IFN Regulatory Factor 3 Dimerization

Rubicon is part of a Beclin-1-Vps34-containing autophagy complex. Rubicon induces antimicrobial responses upon Toll-like receptor (TLR) stimulation and functions as a feedback inhibitor to prevent unbalanced proinflammatory responses depending on dectin-1 signaling. However, the role played by Rubicon during antiviral immune responses, particularly the type I interferon (IFN) responses, remains largely unknown. Here, we report that Rubicon acts as a negative regulator for virus-triggered IFN signaling. Knockdown of Rubicon promoted type I interferon signaling and inhibited virus replication, while overexpression of Rubicon had the opposite effect. Rubicon specifically interacts with the interferon regulatory factor (IRF) association domain (IAD) of IRF3, and this interaction leads to inhibition of the dimerization of IRF3, which negatively regulates IFN-mediated antiviral response. Thus, our findings suggest the novel additional role of Rubicon as a negative regulator that inhibits the IFN signaling and cellular antiviral responses, providing a novel cellular mechanism of IRF3 inhibition. IMPORTANCE The type I IFN system is a critical innate immune response that protects organisms against virus infection. However, type I IFN signaling must be tightly regulated to avoid excessive production of IFNs. Hence, negative regulatory mechanisms for type I IFN signaling are important, and to date, several related molecules have been identified. Here, we show that Rubicon is a major negative regulator of type I IFN signaling, and unlike previous reports of cellular molecules that inhibit IRF3 activation via proteasomal degradation or dephosphorylation of IRF3, we show that Rubicon interacts with IRF3 and that ultimately this interaction leads to inhibition of the dimerization of IRF3. Thus, we identified a novel negative regulator of type I IFN signaling pathways and a novel cellular mechanism of IRF3 inhibition. The results of this study will increase our understanding of the role of negative-feedback mechanisms that regulate type I IFN signaling and maintain immune homeostasis.