May function as an intracellular leucine sensor that negatively regulates the TORC1 signaling pathway (PubMed:25259925). May also regulate the insulin-receptor signaling pathway through activation of TORC2 (PubMed:25377878). This metabolic regulator may also play a role in protection against oxidative and genotoxic stresses (By similarity). May prevent the accumulation of reactive oxygen species (ROS) through the alkylhydroperoxide reductase activity born by the N-terminal domain of the protein (By similarity). a hydroperoxide + L-cysteinyl-[protein] = an alcohol + S-hydroxy-L-cysteinyl-[protein] Interacts with the GATOR2 complex which is composed of MIOS, SEC13, SEH1L, WDR24 and WDR59; the interaction is not regulated by leucine (By similarity). Interacts with RRAGA, RRAGB, RRAGC and RRAGD; may function as a guanine nucleotide dissociation inhibitor for RRAGs and regulate them (PubMed:25259925). Interacts with the TORC2 complex; through RICTOR (PubMed:25377878). Detected in liver and skeletal muscles. The N-terminal domain may have an alkylhydroperoxide reductase activity. The C-terminal domain mediates interaction with GATOR2 through which it regulates TORC1 signaling. Liver-specific Sesn3 knockout mice display insulin resistance and glucose intolerance (PubMed:25377878). Sesn2 and Sesn3 double knockout mice display insulin resistance and glucose intolerance (PubMed:22958918). Triple knockout mice lacking Sesn1, Sesn2 and Sesn3 do not display an embryonic lethal phenotype since they are born at an expected Mendelian ratio. Moreover, they are not distinguishable from their wild-type littermate. However, their survival at 10 days is dramatically affected. This is associated with a constitutive activation of TORC1 signaling in the liver, heart and skeletal muscle during postnatal fasting, that occurs between birth and suckling (PubMed:25259925). Belongs to the sestrin family.