LST8, a 36-40 kDa intracellular protein, is a novel member of WD-40 protein family. It is a highly conserved cytosolic protein consisting of seven WD-40 repeating motifs. LST8 is a functional component of mTOR signaling complex (TORC1) and positively up-regulates the mTOR pathway. It interacts with the kinase domain of mTOR and stabilizes its interaction with raptor. LST8 participates in regulating cell growth and also in nutrient and growth factor-mediated mTOR signaling to S6K1. Reports suggest up-regulated expression of LST8 due to insulin indicating a possible role of LST8 in intracellular events related to insulin-receptor activation including insulin-stimulated glucose transport and glycogen synthesis. Northern Blot analysis detected a ubiquitous expression of LST8 with highest expression in brain and testis. Part of the mammalian target of rapamycin complex 1 (mTORC1), which is composed of mTOR, regulatory associated protein of mTOR (Raptor), mammalian LST8/G-protein beta-subunit like protein (mLST8/GbetaL) and the recently identified partner PRAS40. This complex is characterized by the classic features of mTOR by functioning as a nutrient/energy/redox sensor and controlling protein synthesis. The activity of this complex is stimulated by insulin, growth factors, serum, phosphatidic acid, amino acids (particularly leucine), and oxidative stress.