Regulation of STING activation by phosphoinositide and cholesterol.

Stimulator of interferon genes (STING) is an essential adaptor in the cytosolic DNA sensing innate immune pathway. STING is activated by cyclic-GMP-AMP (cGAMP) produced by the DNA sensor cGAMP synthase (cGAS). cGAMP-induced high-order oligomerization and translocation of STING from the endoplasmic reticulum to Golgi and post-Golgi vesicles are critical for STING activation. Recent studies have shown that phosphatidylinositol phosphates (PIPs) and cholesterol also play important roles in STING activation, but the underlying mechanisms remain unclear. Here, we demonstrate that cGAMP-induced high-order oligomerization of STING is enhanced strongly by PI(3,5)P2 and PI(4,5)P2, and by PI(4)P to a less extent. Our cryo-EM structures reveal that PIPs together with cholesterol bind at the interface between STING dimers, directly promoting the high-order oligomerization. The structures also provide an explanation for the preference of the STING oligomer to different PIPs. Mutational and biochemical analyses confirm the binding modes of PIPs and cholesterol and their roles in STING activation. Our findings shed light on the regulatory mechanisms of STING by specific lipids, which may underlie the role of intracellular compartment trafficking in dictating STING signaling.