Acts as a lysosomal membrane arginine sensor (By similarity). Forms a complex with MTOR and SLC38A9 on lysosomal membranes in an arginine-regulated manner, leading to arginine efflux which enables the activation of mTORC1 which subsequently leads to RPS6KB1 and EIF4EBP1 phosphorylations (By similarity). Facilitates cell cycle G1/S phase progression and the translocation of the CDK4-CCND1 complex into the nucleus (By similarity). CDKN1B and RHOA/ROCK signaling activity are involved in TM4SF5-mediated acceleration of G1/S phase progression (By similarity). Interacts with MTOR; the interaction is positively regulated by arginine and is negatively regulated by leucine (By similarity). Interacts with SLC38A9 (By similarity). Interacts with SLC7A1; the interaction is negatively regulated by arginine (By similarity). Interacts with CASTOR1; the interaction is positively regulated by leucine and is negatively regulated by arginine (By similarity). Localization to cell membrane increases during conditions of arginine depletion and translocation to lysosome membrane seen upon arginine repletion. Belongs to the L6 tetraspanin family.