Mammalian target of Rapamycin (mTOR), also known as FKBP12-rapamycin-associated protein (FRAP), is a 280 kDa serine/threonine kinase [1-3]. mTOR kinase activity could be promoted by various extra- and intracellular stimulus like trophic factors, mitogens, hormones, amino acids and cellular stress [4-8]. In response to increased availability of stimuli, mTOR modulates numerous of important cellular processes, e.g. protein translation and autophagy, by phosphorylating its downstream molecules . mTOR is the nuclear catalytic subunit of two complexes: mTORC1 and mTORC2 . mTORC1 is comprised of mTOR, Raptor, mLST8, and PRAS40 (a mTOR inhibitor). This complex presented classic features of mTOR as a nutrient or energy sensor and protein synthesis conditioner [5, 10]. Low level of nutrient levels, growth factor and cellular stress inhibits the activity of mTORC1 [9, 10]. p70-S6 Kinase 1 (S6K1) and the eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1) are the best investigated targets of mTORC1 . The activated mTORC1 showed a negative feedback inhibition on PI3K signaling . mTORC1 could be specifically suppressed by rapamycin, as well as its allosteric ramifications. mTORC2 contains mTOR, Rictor, mLST8, and mSIN1 [12, 13]. Different from mTORC1, activated mTORC2 could induce the phosphorylation of Akt at serine 473 and serving as a positive feedback on PI3K signaling cascade . Although mTORC2 was identified as a rapamycin-insensitive complex previously , an inhibition effect of rapamycin on free mTOR was observed in some cell lines . Recent studies revealed that disordered activity of mTOR is related to some malignant and resistant cancer. The specific inhibitors, such as rapamycin and Temsirolimus(CCI-779), have been developed and trialed as novel anti-cancer agents [16, 17].
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