Prof. Zhengfan Jiang’s group reports that ARMH3 bridges STING and PI4KB to generate PI4P for STING transportation and activation
Source：Zhengfan Jiang
2023-03-31
On March 14, the Cell Press journal IMMUNITY published the research article “ARMH3-mediated recruitment of PI4KB directs Golgi-to-endosome trafficking and activation of the antiviral effector STING”. This study led by Jiang’s group at Peking university, demonstrated that ARMH3 interacts with STING at the Golgi and recruits PI4KB to synthesize PI4P, which directs STING Golgi-to-endosome trafficking via PI4P-binding proteins AP-1 and GGA2.
Phosphoinositides (PIPs) are signaling molecules generated through the phosphorylation of phosphatidylinositol (PI) at the D-3, D-4, and/or D-5 positions of the hydroxyl groups in its inositol ring, and involved in nearly all aspects of cellular functions in eukaryotic cells. Phosphatidylinositol 4-phosphate (PI4P) is the most abundant cellular PIP, being widely distributed in different cellular membranes with the highest abundance at the trans-Golgi network (TGN), where it is required for the final stages of Golgi maturation involving AP-1 vesicle formation. PI4P is not only a precursor for signaling PIPs and a marker for organelles but is also an energy source for lipid-transfer reactions. Intracellular lipids, especially PI4P and cholesterol, are suggested to play a role in the cGAS-STING pathway based on studies showing that mutations of lipid metabolism- or trafficking-related proteins, such as TMEM39A, SCAP, or NPC1, lead to disturbed lipid homeostasis in individuals and the subsequent development of various autoimmune diseases characterized by the overproduction of cytokines, including type I interferons, in the absence of infection. However, the molecular mechanism underlying these important observations remains undefined.
The cGAS-STING pathway detects cytoplasmic DNA from pathogens or damaged cells and is involved in the pathology of various autoimmune-associated diseases. The cytosolic DNA sensor cGAS is activated by DNA binding or Mn2+ to produce the second messenger 2’3’-cGAMP, which binds to and activates the endoplasmic reticulum (ER) membrane adaptor protein STING (also known as MITA, or ERIS). Once activated, STING is transported to the Golgi apparatus where it binds sulfated glycosaminoglycans (sGAGs) and becomes polymerized and subsequently recruits and activates the kinase TBK1 and the transcriptional factor IRF3, leading to cytokine production. Though the transport of STING between the ER and Golgi is well studied, the mechanisms and biological significance underlying STING transport and activation beyond the Golgi apparatus are less understood.
In this study, using a genome-wide CRISPR-Cas9-mediated screen and biochemical analysis, Jiang’s group examined the mechanisms regulating post-Golgi STING transport and activation. They identified the protein Armadillo (ARM)-like helical domain-containing protein 3 (ARMH3) as a key component for STING activation both ex vivo and in vivo. ARMH3 interacted with STING at the Golgi and recruited PI4KB to synthesize PI4P, which promoted STING translocation and activation via two independent mechanisms. On the one hand, PI4P recruits AP-1 and GGA2 to mediate STING trafficking form Golgi to endosome, where the lower pH value makes STING bind sGAGs and undergo polymerization more efficiently. On the other hand, PI4P recruits lipid exchange proteins to construct the lipid environment for STING activation. They also found that aberrantly elevated cellular PI4P level would cause STING autoactivation. As deficiency of the autoimmune-disease risk genes like TMEM39A, SCAP or NPC1 also leads to aberrantly elevated cellular level of PI4P, their finding provides important understanding to the pathogenic mechanism of autoimmune diseases related to these genes.
Prof. Zhengfan Jiang from the School of Life sciences at Peking University is the corresponding author of this work. Drs. Run Fang and Qifei Jiang are co-first authors. The work was funded in part by National Natural Science Foundation of China, the National Key R&D Program of China, Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education and the Peking-Tsinghua Center for Life Sciences.
Links: https://www.cell.com/immunity/fulltext/S1074-7613(23)00078-X
Phosphoinositides (PIPs) are signaling molecules generated through the phosphorylation of phosphatidylinositol (PI) at the D-3, D-4, and/or D-5 positions of the hydroxyl groups in its inositol ring, and involved in nearly all aspects of cellular functions in eukaryotic cells. Phosphatidylinositol 4-phosphate (PI4P) is the most abundant cellular PIP, being widely distributed in different cellular membranes with the highest abundance at the trans-Golgi network (TGN), where it is required for the final stages of Golgi maturation involving AP-1 vesicle formation. PI4P is not only a precursor for signaling PIPs and a marker for organelles but is also an energy source for lipid-transfer reactions. Intracellular lipids, especially PI4P and cholesterol, are suggested to play a role in the cGAS-STING pathway based on studies showing that mutations of lipid metabolism- or trafficking-related proteins, such as TMEM39A, SCAP, or NPC1, lead to disturbed lipid homeostasis in individuals and the subsequent development of various autoimmune diseases characterized by the overproduction of cytokines, including type I interferons, in the absence of infection. However, the molecular mechanism underlying these important observations remains undefined.
The cGAS-STING pathway detects cytoplasmic DNA from pathogens or damaged cells and is involved in the pathology of various autoimmune-associated diseases. The cytosolic DNA sensor cGAS is activated by DNA binding or Mn2+ to produce the second messenger 2’3’-cGAMP, which binds to and activates the endoplasmic reticulum (ER) membrane adaptor protein STING (also known as MITA, or ERIS). Once activated, STING is transported to the Golgi apparatus where it binds sulfated glycosaminoglycans (sGAGs) and becomes polymerized and subsequently recruits and activates the kinase TBK1 and the transcriptional factor IRF3, leading to cytokine production. Though the transport of STING between the ER and Golgi is well studied, the mechanisms and biological significance underlying STING transport and activation beyond the Golgi apparatus are less understood.
In this study, using a genome-wide CRISPR-Cas9-mediated screen and biochemical analysis, Jiang’s group examined the mechanisms regulating post-Golgi STING transport and activation. They identified the protein Armadillo (ARM)-like helical domain-containing protein 3 (ARMH3) as a key component for STING activation both ex vivo and in vivo. ARMH3 interacted with STING at the Golgi and recruited PI4KB to synthesize PI4P, which promoted STING translocation and activation via two independent mechanisms. On the one hand, PI4P recruits AP-1 and GGA2 to mediate STING trafficking form Golgi to endosome, where the lower pH value makes STING bind sGAGs and undergo polymerization more efficiently. On the other hand, PI4P recruits lipid exchange proteins to construct the lipid environment for STING activation. They also found that aberrantly elevated cellular PI4P level would cause STING autoactivation. As deficiency of the autoimmune-disease risk genes like TMEM39A, SCAP or NPC1 also leads to aberrantly elevated cellular level of PI4P, their finding provides important understanding to the pathogenic mechanism of autoimmune diseases related to these genes.
Prof. Zhengfan Jiang from the School of Life sciences at Peking University is the corresponding author of this work. Drs. Run Fang and Qifei Jiang are co-first authors. The work was funded in part by National Natural Science Foundation of China, the National Key R&D Program of China, Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education and the Peking-Tsinghua Center for Life Sciences.
Links: https://www.cell.com/immunity/fulltext/S1074-7613(23)00078-X
