Regulation of mTORC1 by amino acids

Abstract

The mechanistic target of rapamycin complex I (mTORC1) is a central regulator of cellular and organismal growth, and hyperactivation of this pathway is implicated in the pathogenesis of many human diseases including cancer and diabetes. mTORC1 promotes growth in response to the availability of nutrients, such as amino acids, which drive mTORC1 to the lysosomal surface, its site of activation. How amino acid levels are communicated to mTORC1 is only recently coming to light by the discovery of a lysosome-based signaling system composed of Rags (Ras-related GTPases) and Ragulator v-ATPase, GATOR (GAP activity towards Rags), and folliculin (FLCN) complexes. Increased understanding of this pathway will not only provide insight into growth control but also into the human pathologies triggered by its deregulation.

Keywords: GATOR complex; Rag GTPases; Ragulator; amino acid sensing; folliculin.

Figure 1. The mTORC1 amino acid sensing pathway

A. Under low amino acid conditions Ragulator is found in an inhibitory state with the v-ATPase and GATOR1 exerts its GAP activity towards RagA, keeping this GTPase in the inactive GDP-bound state that is not sufficient to recruit mTORC1. Insulin signaling inhibits TSC complex translocation to the lysosomal surface where it functions as a GAP for Rheb, inactivating this G protein. B. Upon amino acid stimulation, GATOR1 may be inhibited by GATOR2 and Ragulator and v-ATPase undergo a conformational change unleashing the GEF activity of Ragulator towards RagA, while the folliculin complex promotes RagC GTP hydrolysis. The now active heterodimer, consisting of GTP-bound RagA and GDP-loaded RagC, recruits mTORC1 to the lysosomal surface, where it interacts with and is activated by Rheb.