Mammalian target of rapamycin (mTOR) plays essential 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 mTORC1. On the other hand, mTORC1 can sense inner-cellular physiological cues such as amino acids and energy states and can indirectly suppress mTORC2 activity in part through phosphorylation of its upstream adaptors, IRS-1 or Grb10, 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 phosphorylation by disrupting the canonical S6K-phoshorylation motif, thereby bypassing Sin1-phosphorylation-mediated suppression of mTORC2 and leading to sustained Akt signaling to promote tumorigenesis. Our work therefore provided physiological and pathological evidence 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.
Adaptor Proteins, Signal Transducing ; metabolism ; Animals ; Humans ; Mechanistic Target of Rapamycin Complex 1 ; Mechanistic Target of Rapamycin Complex 2 ; Models, Biological ; Multiprotein Complexes ; metabolism ; Phosphorylation ; Phosphothreonine ; metabolism ; TOR Serine-Threonine Kinases ; metabolism

BACKGROUND:Bone defects can directly affect the success rate and long-term stability of dental implants.Studies have shown that salidroside has the ability to promote the proliferation and differentiation of osteoblasts,but less is reported on its pathways related to osteogenic differentiation. OBJECTIVE:To investigate the effects of salidroside on the proliferation and differentiation of MC3T3-E1 cells and the expression of related genes and proteins through in vitro cell experiments. METHODS:Cell counting kit-8 test and alkaline phosphatase test were used to determine the optimal concentration of salidroside(0.5,1,5,10,and 50 μmol/L)in promoting the proliferation and differentiation of MC3T3-E1 cells.There were four groups in the experiment:control group,salidroside group,salidroside+LY294002 group,and LY294002 group,which were cultured with osteogenic induction solution,osteogenic induction solution containing 10 μmol/L salidroside,osteogenic induction solution containing 10 μmol/L salidroside+10 μmol/L LY294002,and osteogenic induction solution containing 10 μmol/L LY294002,respectively.The effects of salidroside and LY294002,an inhibitor of the PI3K/Akt signaling pathway,on the expressions of genes and proteins related to osteogenesis were observed. RESULTS AND CONCLUSION:Cell counting kit-8 assay and alkaline phosphatase assay showed that salidroside promoted the proliferation of MC3T3-E1 cells most significantly at 10 μmol/L.Compared with the control group,salidroside could promote mineralization,promote cell adhesion,reduce cell death,increase mRNA expression of Runx-2,osteocalcin and osteopontin(P<0.01),and increase protein expression of Runx-2 and p-Akt(P<0.01).However,the addition of LY294002 reversed the above results.These findings indicate that salidroside can promote the mineralization of MC3T3-E1 cells and the expression of osteogenesis-related genes and proteins,which may be related to the activation of PI3K/Akt signaling pathway.