mTOR stands for mammalian target of rapamycin, which is a fungal derivative that halts protein synthesis by complexing with immunophilin FK-506 binding protein FKBP12 peptide prolyl cis/trans isomerase. The mTOR protein kinase receives stimulatory signals from nutrients as well as Ras and phosphatidylinositol-3-OH kinase (PI3K) downstream from growth factors, so it functions as a signaling molecule and a critical growth-control node.
FRAP1 (mTOR) is an evolutionarily conserved member of the phosphoinositol kinase-related kinase (PIKK) family that includes DNA-PK, ATM, ATR and several other proteins. mTOR participates in the regulation of cell growth through initiation of gene translation in response to nutrients by integratating input from multiple upstream pathways, including growth factors, mitogens, leucine, insulin, and nutrients. mTOR initiates translation by activating the ribosomal p70S6k protein kinase (S6K1) and by inhibiting the eIF4E inhibitor 4E-BP1. FRAP1 is considered to be involved in numerous additional cellular functions including actin organization, membrane trafficking, secretion, protein degradation, protein kinase C signaling, ribosome biogenesis and tRNA synthesis. mTOR may contribute to the regulation of two pathways, referred to as TORC1 and TORC2 (for TOR Complex 1 and 2).