Aster‐C coordinates with COP I vesicles to regulate lysosomal trafficking and activation of mTORC1

Nutrient sensing by the mTOR complex 1 (mTORC1) requires its translocation to the lysosomal membrane. Upon amino acids removal, mTORC1 becomes cytosolic and inactive, yet its precise subcellular localization and the mechanism of inhibition remain elusive. Here, we identified Aster‐C as a negative regulator of mTORC1 signaling. Aster‐C earmarked a special rough ER subdomain where it sequestered mTOR together with the GATOR2 complex to prevent mTORC1 activation during nutrient starvation. Amino acids stimulated rapid disassociation of mTORC1 from Aster‐C concurrently with assembly of COP I vesicles which escorted mTORC1 to the lysosomal membrane. Consequently, ablation of Aster‐C led to spontaneous activation of mTORC1 and dissociation of TSC2 from lysosomes, whereas inhibition of COP I vesicle biogenesis or actin dynamics prevented mTORC1 activation. Together, these findings identified Aster‐C as a missing link between lysosomal trafficking and mTORC1 activation by revealing an unexpected role of COP I vesicles in mTORC1 signaling. Synopsis This study identifies Aster‐C as a negative regulator of mTORC1 by sequestering mTOR and the GATOR2 complex on rough ER during nutrient starvation. Upon amino acids stimulation, Aster‐C releases the mTORC1 complex which is assorted by COP I vesicles to lysosomal surface for activation. Aster‐C sequesters mTOR together with the GATOR2 complex on rough ER during nutrient starvation. Aster‐C deficiency leads to constitutive activation of mTORC1. Depletion of Aster‐C prevents lysosomal association of TSC2 during nutrient starvation. Aster‐C coordinates COP I vesicle biogenesis with the remodeling of non‐muscle myosin to regulate lysosomal trafficking mTORC1. Graphical Abstract This study identifies Aster‐C as a negative regulator of mTORC1 by sequestering mTOR and the GATOR2 complex on rough ER during nutrient starvation. Upon amino acids stimulation, Aster‐C releases the mTORC1 complex which is assorted by COP I vesicles to lysosomal surface for activation.