O-GlcNAc modification of leucyl-tRNA synthetase 1 integrates leucine and glucose availability to regulate mTORC1 and the metabolic fate of leucine

Abstract

All living organisms have the ability to sense nutrient levels to coordinate cellular metabolism. Despite the importance of nutrient-sensing pathways that detect the levels of amino acids and glucose, how the availability of these two types of nutrients is integrated is unclear. Here, we show that glucose availability regulates the central nutrient effector mTORC1 through intracellular leucine sensor leucyl-tRNA synthetase 1 (LARS1). Glucose starvation results in O-GlcNAcylation of LARS1 on residue S1042. This modification inhibits the interaction of LARS1 with RagD GTPase and reduces the affinity of LARS1 for leucine by promoting phosphorylation of its leucine-binding site by the autophagy-activating kinase ULK1, decreasing mTORC1 activity. The lack of LARS1 O-GlcNAcylation constitutively activates mTORC1, supporting its ability to sense leucine, and deregulates protein synthesis and leucine catabolism under glucose starvation. This work demonstrates that LARS1 integrates leucine and glucose availability to regulate mTORC1 and the metabolic fate of leucine.

Integration of O-GlcNAc into Stress Response Pathways

“…O-GlcNAcylation of leucyl-tRNA synthetase 1 (LARS1) has been implicated in the regulation of mTORC1, a negative autophagy regulator [ 293 , 294 ]. Glucose promotes the interaction of LARS1 and the RagD GTPase promoting mTORC1 activation [ 293 , 294 ].…”

“…O-GlcNAcylation of leucyl-tRNA synthetase 1 (LARS1) has been implicated in the regulation of mTORC1, a negative autophagy regulator [ 293 , 294 ]. Glucose promotes the interaction of LARS1 and the RagD GTPase promoting mTORC1 activation [ 293 , 294 ]. Glucose starvation results in the O-GlcNAcylation of LARS1, limiting interaction with RagD and reducing mTORC1 activation by leucine deprivation.…”

“…Glucose starvation results in the O-GlcNAcylation of LARS1, limiting interaction with RagD and reducing mTORC1 activation by leucine deprivation. Overexpression of an O-GlcNAcylation-deficient LARS1 (S1042A) activated mTORC1 signaling under glucose deprivation, highlighting the role of LARS1 O-GlcNAcylation in the anabolism/catabolism switch [ 294 ]. Although autophagy was not directly assessed, it was previously demonstrated that LARS1 binding and phosphorylation by ULK1 was promoted by glucose deprivation and that phosphomimetic mutation at two of the ULK1 phosphorylation sites (Ser2 and Ser720) suppressed LARS1-RagD association and significantly increased autophagosome levels [ 293 ].…”

“…As such, LARS1 Ser720 phosphorylation may be a sufficient marker for ULK1 activation and autophagy upregulation. OGT knockdown not only reduced LARS1 O-GlcNAcylation under glucose deprivation but also suppressed LARS1 ULK1 interaction and S720 phosphorylation [ 294 ]. Loss of ULK1 binding and Ser720 phosphorylation was recapitulated with the O-GlcNAcylation-deficient LARS1, suggesting that pro-autophagic signaling is blunted.…”

Protein O-GlcNAcylation in Metabolic Modulation of Skeletal Muscle: A Bright but Long Way to Go

“…Indeed, autophagy has been considered as an emerging metabolic regulatory pathway in skeletal muscle, and its role in skeletal muscle metabolism and atrophic diseases has been extensively studied [ 212 , 213 ]. In skeletal muscle autophagy signal transduction, mTOR, AMPK, AKT and FoxO3, as important central trophic effectors, regulate autophagy process according to nutritional status, and their interaction with OGT is inseparable [ 214 , 215 , 216 , 217 ]. Given the critical role of O -GlcNAcylation in these processes, O -GlcNAcylation may affect autophagy flux and proteostasis to regulate skeletal muscle mass and proteolysis [ 206 ].…”