The IKK complex and TBK1/IKKε are recruited to STING through distinct mechanisms to activate NF-κB signaling.

Abstract

Stimulator of interferon genes (STING) is a highly conserved signaling molecule that coordinates an antiviral innate immune response through activation of the nuclear factor κB (NF-κB) and interferon regulatory factor 3 (IRF3) signaling pathways. In addition to an antiviral response, STING-mediated NF-κB signaling also leads to an inflammatory response, which can cause substantial pathology. However, the molecular mechanism whereby STING drives inflammation is poorly understood, and this has hindered the development of anti-inflammatory strategies targeting this pathway. Here, we define an evolutionarily conserved mechanism whereby STING activates NF-κB signaling via recruitment of inhibitor of NF-κB kinase subunit γ (IKKγ) in an M1-linked ubiquitin-dependent manner. We also show that the more recently evolved carboxyl-terminal tail of STING cooperates with the IKKγ-IKK complex for NF-κB-dependent expression of pro-inflammatory genes in mammalian cells through the kinases TBK1 (TANK-binding kinase 1)/IKKε. Thus, the expression of the key inflammatory genes CCL3 and CCL4 requires the formation of M1-linked ubiquitin and the activation of NF-κB, but we do not detect a role for IRF3 in STING-driven NF-κB signaling.