3 research outputs found
MTORC2 activity disrupts lysosome acidification in systemic lupus erythematosus by impairing caspase-1 cleavage of Rab39a
Lysosomes maintain immune homeostasis through the degradation of phagocytosed apoptotic debris; however, the signaling events regulating lysosomal maturation remain undefined. In this study, we show that lysosome acidification, key to the maturation process, relies on mTOR complex 2 (mTORC2), activation of caspase-1, and cleavage of Rab39a. Mechanistically, the localization of cofilin to the phagosome recruits caspase-11, which results in the localized activation of caspase-1. Caspase-1 subsequently cleaves Rab39a on the phagosomal membrane, promoting lysosome acidification. Although caspase-1 is critical for lysosome acidification, its activation is independent of inflammasomes and cell death mediated by apoptosis-associated speck-like protein containing a caspase recruitment domain, revealing a role beyond pyroptosis. In lupus-prone murine macrophages, chronic mTORC2 activity decouples the signaling pathway, leaving Rab39a intact. As a result, the lysosome does not acidify, and degradation is impaired, thereby heightening the burden of immune complexes that activate FcgRI and sustain mTORC2 activity. This feedforward loop promotes chronic immune activation, leading to multiple lupus-associated pathologies. In summary, these findings identify the key molecules in a previously unappreciated signaling pathway that promote lysosome acidification. It also shows that this pathway is disrupted in systemic lupus erythematosus
Medium-Throughput Screen of Microbially Produced Serotonin via a G‑Protein-Coupled Receptor-Based Sensor
Chemical
biosensors, for which chemical detection triggers a fluorescent
signal, have the potential to accelerate the screening of noncolorimetric
chemicals produced by microbes, enabling the high-throughput engineering
of enzymes and metabolic pathways. Here, we engineer a G-protein-coupled
receptor (GPCR)-based sensor to detect serotonin produced by a producer
microbe in the producer microbe’s supernatant. Detecting a
chemical in the producer microbe’s supernatant is nontrivial
because of the number of other metabolites and proteins present that
could interfere with sensor performance. We validate the two-cell
screening system for medium-throughput applications, opening the door
to the rapid engineering of microbes for the increased production
of serotonin. We focus on serotonin detection as serotonin levels
limit the microbial production of hydroxystrictosidine, a modified
alkaloid that could accelerate the semisynthesis of camptothecin-derived
anticancer pharmaceuticals. This work shows the ease of generating
GPCR-based chemical sensors and their ability to detect specific chemicals
in complex aqueous solutions, such as microbial spent medium. In addition,
this work sets the stage for the rapid engineering of serotonin-producing
microbes
mTORC2 activity disrupts lysosome acidification in systemic lupus erythematosus by impairing caspase-1 cleavage of Rab39a
Lysosomes maintain immune homeostasis through the degradation of phagocytosed apoptotic debris; however, the signaling events regulating lysosomal maturation remain undefined. In this study, we show that lysosome acidification, key to the maturation process, relies on mTOR complex 2 (mTORC2), activation of caspase-1, and cleavage of Rab39a. Mechanistically, the localization of cofilin to the phagosome recruits caspase-11, which results in the localized activation of caspase-1. Caspase-1 subsequently cleaves Rab39a on the phagosomal membrane, promoting lysosome acidification. Although caspase-1 is critical for lysosome acidification, its activation is independent of inflammasomes and cell death mediated by apoptosis-associated speck-like protein containing a caspase recruitment domain, revealing a role beyond pyroptosis. In lupus-prone murine macrophages, chronic mTORC2 activity decouples the signaling pathway, leaving Rab39a intact. As a result, the lysosome does not acidify, and degradation is impaired, thereby heightening the burden of immune complexes that activate FcgRI and sustain mTORC2 activity. This feedforward loop promotes chronic immune activation, leading to multiple lupus-associated pathologies. In summary, these findings identify the key molecules in a previously unappreciated signaling pathway that promote lysosome acidification. It also shows that this pathway is disrupted in systemic lupus erythematosus