The mammalian target of rapamycin (mTOR) is a master regulator of many cellular processes like cell growth, biosynthesis, and metabolism. mTOR is the enzymatic component of two different signaling complexes: mTORC1, which contains the regulatory unit Raptor, and mTORC2, which contains the rapamycin-insensitive regulatory unit Rictor. Growth factors and insulin can activate mTORC1 through Ras and Akt signaling, which inhibit the inhibitory factors TSC1/2. In contrast, signals like oxygen stress can halt mTORC1 signaling through REDD1, which promotes TSC2's inhibitory function. Activated mTORC1 drives protein and lipid synthesis for cell growth, while limiting autophagy. Though upstream signals of mTORC2 are less clear, it is known to promote signaling through AKT and other factors that regulate cell survival and cytoskeleton organization.
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