Human STING oligomer function is governed by palmitoylation of an evolutionarily conserved cysteine

Abstract

Autoimmune disorders are frequently exacerbated by aberrant STING signaling. While STING inhibitors are highly sought after, no viable therapeutic strategies have been reported. When stimulated, STING undergoes a multi-step mechanism to activate downstream interferon-stimulated genes (ISGs), including palmitoylation, translocation from the ER to the Golgi, and oligomerization, but it remains unclear which step(s) are strictly required and therefore should be targeted by potential STING inhibitors. Here, we comprehensively established the order and determined the necessity of each STING activation step. We find that ER-to-Golgi translocation is dispensable for downstream ISG activation, and a previously studied palmitoylation site, C91, is not required for activation in all contexts. Cysteine reactivity mapping and metabolic labeling identified a new palmitoylation site, C64, that is basally palmitoylated and required for STING activation, but is not druggable due to poor solvent accessibility. We confirm that the oligomerization step of STING activation is strictly required, and therefore developed a short peptide mimicking its natural autoinhibitory domain that effectively inhibits STING activation: a proof of concept for the first viable strategy for developing STING inhibitors.