mTORC1 activity licenses its own release from the lysosomal surface

Abstract

Nutrient signaling converges on mTORC1, which, in turn, orchestrates a physiological cellular response. A key determinant of mTORC1 activity is its shuttling between the lysosomal surface and the cytoplasm, with nutrients promoting its recruitment to lysosomes by the Rag GTPases. Active mTORC1 regulates various cellular functions by phosphorylating distinct substrates at different subcellular locations. Importantly, how mTORC1 that is activated on lysosomes is released to meet its non-lysosomal targets and whether mTORC1 activity itself impacts its localization remain unclear. Here, we show that, in human cells, mTORC1 inhibition prevents its release from lysosomes, even under starvation conditions, which is accompanied by elevated and sustained phosphorylation of its lysosomal substrate TFEB. Mechanistically, "inactive" mTORC1 causes persistent Rag activation, underlining its release as another process actively mediated via the Rags. In sum, we describe a mechanism by which mTORC1 controls its own localization, likely to prevent futile cycling on and off lysosomes.

Keywords: GATOR1; Rag GTPases; Rheb; TFE3; TFEB; Torin1; lysosomes; mTORC1; rapamycin.