Amino acids stimulate the mTOR pathway, and amino acid pools rely on glutamine to be maintained. Specifically, arginine and leucine are two amino acids that can together almost fully stimulate mTOR complex 1 (mTORC1) through activation of the RAS-related GTPase (RAG) complex, which in turn recruits mTORC1 to the lysosome and stimulates its activity , , . Glutamine can contribute to mTORC1 activation by being exchanged for essential amino acids, including leucine, through the large neutral amino acid transporter 1 (LAT1; a heterodimer of SLC7A5 and SLC3A2) transporter . This RAG-dependent regulation of mTOR is likely dependent on the lysosomal amino acid transporter SLC38A9, which transports glutamine, arginine, and leucine as substrates, , , as well as the leucine sensor sestrin 2 (not shown in Figure) , . Although the mechanism is not well understood, α-ketoglutarate (α-KG) may regulate RAGB activity and mTOR activation downstream of glutamine metabolism . Several RAG-independent pathways of mTOR regulation by glutamine have also been identified. Glutamine promotes mTOR localization to the lysosome (and thus activity) through the RAS-family member ADP ribosylation factor 1 (ARF1) in a poorly understood mechanism, as well as the TTT-RUVBL1/2 complex (not shown in Figure) , . GLS, kidney-type glutaminase; GLS2, liver-type glutaminase; GLUD, glutamate dehydrogenase.