Emerging molecular mechanisms of cGAS-STING activation and regulation

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway is a crucial component of the innate immune system, responsible for detecting cytosolic double-stranded DNA (dsDNA) from both pathogen invasion and host damage, thereby initiating a robust type I-interferons (IFNs) response. In this review, we summarize the complex and stringent mechanisms governing the activation and regulation of the cGAS-STING pathway. We describe the structural basis of cGAS activation by dsDNA and its catalytic synthesis of 2'3'-cGAMP, and highlight the DNA-independent activation of cGAS by manganese (Mn^2 +), which exhibits a distinct catalytic mechanism. We also discuss recent advances in the regulatory mechanisms of cGAS. The binding of 2'3'-cGAMP triggers STING translocation from the ER to the Golgi apparatus, where sulfated glycosaminoglycans (sGAGs) act as an essential second ligand to promote STING polymerization. Following this, a second translocation from the trans-Golgi network (TGN) to endosomes is required for its full activation. Conversely, supranormal concentrations of 2'3'-cGAMP induce the formation of ER-localized STING biocondensates, which restrict activation and thus prevent an excessive immune response. Dysregulation of the cGAS-STING pathway has been implicated in diverse human health conditions, including infection, autoimmune disorders, neurodegeneration, ageing, and cancer. Understanding these activation and regulatory mechanisms will inform the development of novel therapeutic strategies.