STING COPII ER Export Trafficking and Signaling Primed by Phosphorylation Switches.

Abstract

Despite advances in understanding the STING signaling pathway, mechanisms governing cyclic GMP-AMP (cGAMP)-induced STING trafficking out of the endoplasmic reticulum (ER) remain unclear. This study reveals that STING localization is regulated by the balance between coat protein II (COPII)- and coat protein I (COPI)-mediated trafficking, maintaining ER residency in the inactive state or promoting transport to the cis-Golgi via enhanced COPII-mediated export upon activation. Two novel TANK-binding kinase 1 (TBK1)-regulated phosphorylated COPII sorting signals on STING-a conserved pSGME motif and a primate-specific pFS motif-are biochemically and structurally identified. These cGAMP-induced signals drive activated STING toward the ER-Golgi intermediate compartment (ERGIC) and the cis-Golgi complex. Using a cell-free COPII vesicle reconstitution system, TBK1 activation is shown to occur on COPII vesicles, while IRF3 phosphorylation is confined to the ERGIC or the cis-Golgi complex post-uncoating, due to the competitive binding of COPII Sec24 and IRF3 to phosphorylated STING. A class of compounds is also identified that attenuates IRF3 phosphorylation by inhibiting phosphorylated STING packaging into COPII vesicles. These findings elucidate STING trafficking mechanisms and offer therapeutic potential for diseases linked to dysregulated STING activation.