A molecular mechanism of STING-mediated NF-κB activation

The stimulator of interferon genes (STING) pathway plays an important and conserved role in antiviral immunity. Human STING (hSTING) has been shown to mediate antiviral immunity by activating the transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). The activation of IRF3 by hSTING involves the C-terminal tail (CTT) of hSTING and TANK-binding kinase 1 (TBK1), and this process is well-described. In contrast, the molecular mechanisms underlying NF-κB activation remain unclear. To elucidate this mechanism, we exploited the conserved Drosophila melanogaster STING (dSTING) pathway to uncover these mechanisms. Similar to the human pathway, dSTING confers antiviral immunity. However, dSTING lacks the CTT and drives the expression of antiviral genes via the NF-κB homolog Relish. Interestingly, there are features of dSTING and hSTING mediated NF-κB signaling which are conserved throughout evolution of animals. To elucidate how STING activate NF-κB signaling, we have developed a proximity labeling approach that enables the specific detection of activity-dependent STING interactors. We demonstrate that IKKγ is recruited by STING upon activation and that the recruitment of IKKγ is essential for STING-mediated activation of Relish. Moreover, studies in human cells indicate the pivotal role of linear ubiquitination in the interaction between IKKγ and STING. Our findings suggest an evolutionarily conserved mechanism of STING-mediated NF-κB activation which existed prior to the evolution of the CTT and the IRF3 pathway. Keywords: NF-κB, STING, signaling mechanism, antiviral immunity, proximity labeling.