Onia, L. | bioRxiv Science

bioRxiv2022

STING activation depends on ACBD3 and other phosphatidylinositol 4-phosphate-regulating proteins

STING induces transcription of pro-inflammatory genes upon activation at the Golgi apparatus. Many of the regulators involved in STING activation are unknown. We found that ACBD3 and other phosphatidylinositol 4-phosohate (PI4P) regulating proteins play a critical role in STING activation. We show that proper STING localization and activation at the Golgi depended on ACBD3 and PI4KB expression. Furthermore, depleting PI4P by inactivating PI4KB or overexpressing Sac1 diminished STING activation. STING signalling was also regulated by the lipid-shuttling protein OSBP, which removes PI4P from the Golgi. OSBP inhibition by the FDA-approved antifungal itraconazole and other OSBP inhibitors greatly enhanced STING activation by increasing the levels of STING-activating phospholipids. Itraconazole-enhanced STING activation resulted in a hundred to thousand-fold increased expression of interferon-beta and other cytokines. In conclusion, the phospholipid PI4P is critical for STING activation and manipulating PI4P levels is a promising therapeutic strategy to alter the STING immune response.

immunology↗

bioRxiv2019

SLC19A1 is a cyclic dinucleotide transporter

The accumulation of DNA in the cytosol serves as a key immunostimulatory signal associated with infections, cancer and genomic damage1,2. Cytosolic DNA triggers immune responses by activating the cGAS/STING pathway3. The binding of DNA to the cytosolic enzyme cGAMP synthase (cGAS), activates its enzymatic activity, leading to the synthesis of a second messenger, cyclic[G(2,5)pA(3,5)] (23-cGAMP)4-8. 23-cGAMP, a cyclic dinucleotide (CDN), activates the protein stimulator of interferon genes (STING)9, which in turn activates the transcription factors IRF3 and NF-{kappa}B promoting the transcription of genes encoding type I interferons and other cytokines and mediators that stimulate a broader immune response. Exogenous 23-cGAMP and other CDNs, including CDNs produced by bacteria and synthetic CDNs used in cancer immunotherapy, must traverse the cell membrane to activate STING in target cells. How these charged CDNs pass through the lipid bilayer is unknown. Here we used a genome-wide CRISPR interference screen to identify the reduced folate carrier SLC19A1 as the major CDN transporter for uptake of synthetic and naturally occurring CDNs. CDN uptake and functional responses are inhibited by depleting SLC19A1 from cells and enhanced by overexpressing SLC19A1. In both cell lines and primary cells ex vivo, CDN uptake is inhibited competitively by folate and blocked by the SLC19A1 inhibitor sulfasalazine, a medication approved for the treatment of inflammatory diseases. The identification of SLC19A1 as the major transporter of CDNs into cells has far reaching implications for the immunotherapeutic treatment of cancer10, transport of 23-cGAMP from tumor cells to other immune cells to trigger the anti-tumor immune response11, host responsiveness to CDN-producing pathogenic microorganisms12, and potentially in certain inflammatory diseases.

immunology↗