Fig. 2

Lysosomes function as an intracellular signal transduction platform. The combination of growth factors and RTKs can activate the PI3K/AKT signaling pathway and negatively regulate TSC1/2, promoting Rheb to become GTP loaded, which can activate mTORC1. Rag GTPases are localized to lysosomes by Ragulator. When nutrients are lacking, mTORC1 is inactive in the cytoplasm, RagA/B is GDP loaded, RagC/D is GTP loaded, and Rag GTPases cannot bind to mTORC1. GATOR1 is a GAP for RagA/B, and its activity can be antagonized by GATOR2. Sestrin, CASTOR, and SAMTOR can sense Leu, Arg and SAM and interact with GATOR1/GATOR2. KICSTOR mediates GATOR1 recruitment to lysosomes and allows RagA/B to become GTP loaded and bind to mTORC1. Then, GTP-loaded Rheb unlocks mTORC1 kinase activity at the lysosome. Moreover, ligands binding to RTKs (e.g., EGFR) can recruit Grb2, which binds to Cbl. RTKs can be ubiquitinated by Cbl and trafficked to lysosomes for degradation