Conggang Zhang Group Reveals Novel Inhibitors and Regulation Mechanisms of the cGAS-STING Signaling
Source：Conggang Zhang
2023-12-21
On Nov. 14th, the Cell Press journal IMMUNITY published the research article entitled “SMPDL3A is a cGAMP-degrading enzyme induced by LXR-mediated lipid metabolism to restrict cGAS-STING DNA sensing”. The authors identified a new class of inhibitors of the cGAS-STING signaling pathway. Moreover, they found that the inhibitors activated LXR pathway to induce the expression of SMPDL3A, which is a new cGAMP-degrading enzyme to restrict cGAS-STING signaling.
Lipid metabolism has been associated with cGAS-STING signaling pathway, but our understanding of how these signals is integrated into a cohesive immunometabolism program is lacking. Liver X receptor (LXR)-stimulated lipid metabolism and anti-inflammatory effects have been a particular focus. How LXR-mediated anti-inflammation and lipid metabolism occur, and which key effectors of lipid metabolism suppress cGAMP-STING immune response, remain largely unclear. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as the major DNA-sensing pathway. Abnormal activation of the cGAS-STING pathway could cause inflammation. Therefore, the activation of cGAS-STING signaling is negatively regulated to avoid sustained innate immune response induction, and precise regulators that restrain cGAS-STING activation are important for preventing detrimental autoinflammation.
In this study, the authors employed a cell-based phenotypic assay combined with a high-throughput chemical screen to search for inhibitors of STING signaling. They demonstrated for the first time that LXR agonist, T0901317, specifically inhibited 2’3’-cGAMP-mediated STING signaling. Further study confirmed that T09 specifically suppressed cGAMP-induced immune responses but not the immune response induced by other STING agonists, including 3’3’-cGAMP、c-di-AMP、c-di-GMP、SR-717、DMXAA. Collectively, the authors identified that T09 was a highly selective small-molecule inhibitor of the cGAMP-STING signaling. This is the first small-molecule inhibitor that specifically targets cGAMP to suppress STING signaling.
The authors hypothesized that T09 might induce expression of the cGAMP-degrading enzymes to suppress cGAMP-STING signaling. The authors employed multiple approaches, including selective pull-down system, mass spectrometry, thin-layer chromatography (TLC), Mono Q chromatography, cGAMP ELISA analysis, and cell-based functional assay, to identify and confirm that SMPDL3A is the cGAMP-degrading enzyme induced by T09. The authors revealed that the dimerization of SMPDL3A and a proline-containing loop in the catalytic pocket play critical roles in SMPDL3A activity on cGAMP degradation. The authors continued to characterize the mechanism and function of SMPDL3A. They showed that SMPDL3A was stimulated by LXR lipid metabolism to restrict cGAMP-STING signaling in vitro and in vivo. The relevance of LXR-SMPDL3A module was also verified in related disease model.
Together, the results show that LXR signaling induces expression of SMPDL3A, which is a specific 2′3′-cGAMP-degrading enzyme that inhibits inflammatory signaling through STING. The authors identified a new class of inhibitors and a new regulation mechanism of the cGAS-cGAMP-STING signaling. The study deepens our understanding of the regulatory connections between lipid metabolism and innate immunity and suggests that targeting this signaling axis could be a potential therapeutic strategy to modulate inflammatory responses.
This work was supported by grants from the National Natural Science Foundation of China, grants from Tsinghua-Peking Center for Life Sciences, and grants from Beijing Natural Science Foundation.
Links：https://www.cell.com/immunity/fulltext/S1074-7613(23)00441-7
Lipid metabolism has been associated with cGAS-STING signaling pathway, but our understanding of how these signals is integrated into a cohesive immunometabolism program is lacking. Liver X receptor (LXR)-stimulated lipid metabolism and anti-inflammatory effects have been a particular focus. How LXR-mediated anti-inflammation and lipid metabolism occur, and which key effectors of lipid metabolism suppress cGAMP-STING immune response, remain largely unclear. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as the major DNA-sensing pathway. Abnormal activation of the cGAS-STING pathway could cause inflammation. Therefore, the activation of cGAS-STING signaling is negatively regulated to avoid sustained innate immune response induction, and precise regulators that restrain cGAS-STING activation are important for preventing detrimental autoinflammation.
In this study, the authors employed a cell-based phenotypic assay combined with a high-throughput chemical screen to search for inhibitors of STING signaling. They demonstrated for the first time that LXR agonist, T0901317, specifically inhibited 2’3’-cGAMP-mediated STING signaling. Further study confirmed that T09 specifically suppressed cGAMP-induced immune responses but not the immune response induced by other STING agonists, including 3’3’-cGAMP、c-di-AMP、c-di-GMP、SR-717、DMXAA. Collectively, the authors identified that T09 was a highly selective small-molecule inhibitor of the cGAMP-STING signaling. This is the first small-molecule inhibitor that specifically targets cGAMP to suppress STING signaling.
The authors hypothesized that T09 might induce expression of the cGAMP-degrading enzymes to suppress cGAMP-STING signaling. The authors employed multiple approaches, including selective pull-down system, mass spectrometry, thin-layer chromatography (TLC), Mono Q chromatography, cGAMP ELISA analysis, and cell-based functional assay, to identify and confirm that SMPDL3A is the cGAMP-degrading enzyme induced by T09. The authors revealed that the dimerization of SMPDL3A and a proline-containing loop in the catalytic pocket play critical roles in SMPDL3A activity on cGAMP degradation. The authors continued to characterize the mechanism and function of SMPDL3A. They showed that SMPDL3A was stimulated by LXR lipid metabolism to restrict cGAMP-STING signaling in vitro and in vivo. The relevance of LXR-SMPDL3A module was also verified in related disease model.
Together, the results show that LXR signaling induces expression of SMPDL3A, which is a specific 2′3′-cGAMP-degrading enzyme that inhibits inflammatory signaling through STING. The authors identified a new class of inhibitors and a new regulation mechanism of the cGAS-cGAMP-STING signaling. The study deepens our understanding of the regulatory connections between lipid metabolism and innate immunity and suggests that targeting this signaling axis could be a potential therapeutic strategy to modulate inflammatory responses.
This work was supported by grants from the National Natural Science Foundation of China, grants from Tsinghua-Peking Center for Life Sciences, and grants from Beijing Natural Science Foundation.
Links：https://www.cell.com/immunity/fulltext/S1074-7613(23)00441-7
