Acts as a lysosomal membrane arginine sensor (PubMed:30956113). 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 (PubMed:30956113). Facilitates cell cycle G1/S phase progression and the translocation of the CDK4-CCND1 complex into the nucleus (PubMed:20399237). CDKN1B and RHOA/ROCK signaling activity are involved in TM4SF5-mediated acceleration of G1/S phase progression (PubMed:20399237). Interacts with MTOR; the interaction is positively regulated by arginine and is negatively regulated by leucine (PubMed:30956113). Interacts with SLC38A9 (PubMed:30956113). Interacts with SLC7A1; the interaction is negatively regulated by arginine (PubMed:30956113). Interacts with CASTOR1; the interaction is positively regulated by leucine and is negatively regulated by arginine (PubMed:30956113). Localization to cell membrane increases during conditions of arginine depletion and translocation to lysosome membrane seen upon arginine repletion. Intestine. Overexpressed in pancreatic cancers. Belongs to the L6 tetraspanin family.