Mammalian target of rapamycin （mTOR） plays essen- tial roles in cell proliferation, survival and metabolism by forming at least two functional distinct multi-protein complexes, mTORC1 and mTORC2. External growth sig...Mammalian target of rapamycin （mTOR） plays essen- tial roles in cell proliferation, survival and metabolism by forming at least two functional distinct multi-protein complexes, mTORC1 and mTORC2. External growth signals can be received and interpreted by mTORC2 and further transduced to mTORCI. On the other hand, mTORC1 can sense inner-cellular physiological cues such as amino acids and energy states and can indi- rectly suppress mTORC2 activity in part through phosphorylation of its upstream adaptors, IRS-1 or Grbl0, under insulin or IGF-1 stimulation conditions. To date, upstream signaling pathways governing mTORC1 activation have been studied extensively, while the mechanisms modulating mTORC2 activity remain largely elusive. We recently reported that Sin1, an essential mTORC2 subunit, was phosphorylated by either Akt or S6K in a cellular context-dependent manner. More importantly, phosphorylation of Sin1 at T86 and T398 led to a dissociation of Sin1 from the functional mTORC2 holo-enzyme, resulting in reduced Akt activity and sensitizing cells to various apoptotic challenges. Notably, an ovarian cancer patient-derived Sin1-R81T mutation abolished Sin1-T86 phosphoryla- tion by disrupting the canonical S6K-phoshorylation motif, thereby bypassing Sinl-phosphorylation-medi- ated suppression of mTORC2 and leading to sustained Akt signaling to promote tumorigenesis. Our work therefore provided physiological and pathological evi- dence to reveal the biological significance of Sin1 phosphorylation-mediated suppression of the mTOR/ Akt oncogenic signaling, and further suggested that misregulation of this process might contribute to Akt hyper-activation that is frequently observed in human cancers.展开更多
文摘Mammalian target of rapamycin （mTOR） plays essen- tial roles in cell proliferation, survival and metabolism by forming at least two functional distinct multi-protein complexes, mTORC1 and mTORC2. External growth signals can be received and interpreted by mTORC2 and further transduced to mTORCI. On the other hand, mTORC1 can sense inner-cellular physiological cues such as amino acids and energy states and can indi- rectly suppress mTORC2 activity in part through phosphorylation of its upstream adaptors, IRS-1 or Grbl0, under insulin or IGF-1 stimulation conditions. To date, upstream signaling pathways governing mTORC1 activation have been studied extensively, while the mechanisms modulating mTORC2 activity remain largely elusive. We recently reported that Sin1, an essential mTORC2 subunit, was phosphorylated by either Akt or S6K in a cellular context-dependent manner. More importantly, phosphorylation of Sin1 at T86 and T398 led to a dissociation of Sin1 from the functional mTORC2 holo-enzyme, resulting in reduced Akt activity and sensitizing cells to various apoptotic challenges. Notably, an ovarian cancer patient-derived Sin1-R81T mutation abolished Sin1-T86 phosphoryla- tion by disrupting the canonical S6K-phoshorylation motif, thereby bypassing Sinl-phosphorylation-medi- ated suppression of mTORC2 and leading to sustained Akt signaling to promote tumorigenesis. Our work therefore provided physiological and pathological evi- dence to reveal the biological significance of Sin1 phosphorylation-mediated suppression of the mTOR/ Akt oncogenic signaling, and further suggested that misregulation of this process might contribute to Akt hyper-activation that is frequently observed in human cancers.
