STING signals to NF-κB from late endolysosomal compartments using IRF3 as an adaptor.

NF-κB is central for activation of immune responses. Cytosolic DNA activates the cGAS-STING pathway to induce type I interferons (IFNs) and signaling through NF-κB, thus instigating host defenses and pathological inflammation. However, the mechanism underlying STING-induced NF-κB activation is unknown. Here we report that STING activates NF-κB in a delayed manner, following exit from the Golgi to endolysosomal compartments. Activation of NF-κB is dependent on the IFN-inducing transcription factor IRF3 but is independent of type I IFN signaling. This activation pattern is evolutionarily conserved in tetrapods. Mechanistically, the monomer IRF3 is recruited to STING pS358, with delayed kinetics relative to IRF3 recruitment to STING pS366, which promotes type I IFN responses. IRF3 engagement with STING pS358 induces trafficking to late endolysosomal compartments, supporting recruitment of TRAF6 and activation of NF-κB. We identify a TRAF6 binding motif in IRF3 that facilitates recruitment of TRAF6. This work defines a signaling surface on STING and a function for IRF3 as an adaptor in immune signaling. These findings indicate that STING signaling to NF-κB is enabled only within a short time window between exit from the Golgi and lysosomal degradation, possibly limiting inflammation under homeostatic and danger-sensing conditions.