Elucidating the mechanisms that allow cells to survive under adverse growth conditions is crucial for understanding how cancer cells arise and persist. The mammalian target of rapamycin (mTOR) is a protein kinase that is inhibited by the potential anti-cancer drug, rapamycin, and plays a central role in growth and proliferation. Recently, we discovered that mTOR is part of two distinct protein complexes and that mTORC2 (mTOR Complex 2) performs a novel function in cell survival that is not inhibited by rapamycin. This novel function of mTORC2 involves phosphorylation of Akt/PKB and is critical only under stress conditions. We have identified SIN1 as an integral component of mTORC2. We found that SIN1 is required for phosphorylation of Akt. Using SIN1 knockout cells, our initial studies indicate that when Akt phosphorylation is abolished at the mTORC2-mediated site, phosphorylation of the pro- apoptotic targets of Akt is defective and cells become susceptible to stress-induced apoptosis. We will now elucidate the mechanism of how Akt regulation by mTORC2 can promote cell survival. We have preliminary findings that in the absence of SIN1, Akt is destabilized more readily upon stress induction. We now hypothesize that mTORC2 regulates protein stability and that this novel function of mTORC2 is required specifically for cell survival under stress conditions. First, we will examine Akt turnover and degradation in the absence of SIN1. Second, we will investigate if mTORC2 can regulate Akt by phosphorylation or if SIN1 serves as a scaffold to allow Akt phosphorylation. Third, we will elucidate how Akt stabilization by mTORC2-mediated phosphorylation can promote cell survival. These studies will advance our knowledge on how mTOR can regulate cell growth and survival pathways and will provide clues as to how mTORC2 can be exploited as a drug target to specifically inhibit the survival of cancer cells.
Cancer is characterized by uncontrolled growth and proliferation and the increased viability of these abnormal cells despite hostile conditions. Our studies will examine the mechanisms of how the mammalian target of rapamycin (mTOR) can enhance survival capacity of cancer cells via upregulation of Akt, a protein that is found mutated in a number of tumors.
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