Objective      To investigate the effect of Panax notoginseng saponins (PNS) on the expression and activity of mTOR signaling pathway related molecules in K562 cells in vitro.        Methods      K562 cells were treated with different concentrations (50-800 μg/mL) of PNS for different periods of time (24-72 h). The cell proliferation was measured by MTT assay

and the cell death and apoptosis were observed by AO/EB double fluorescence staining. The mRNA expression of

mTOR

p70S6K and 4E-BP1 was examined by RT-PCR

and the protein expression of mTOR

p70S6K

4E-BP1 and their phosphorylated proteins (p-mTOR

p-p70S6K and p-4E-BP1) was detected by Western blotting.        Results      PNS (100-800 μg/mL) inhibited the proliferation of K562 cells (P0.05) and promoted cell apoptosis and death (P0.05)

and 72-h IC

50

was (229.07±2.36) μg/mL. After PNS (100

200 and 400 μg/mL) was applied to K562 cells for 72 h

the mRNA and protein expressions levls of mTOR were dose-dependently reduced (P0.05). In addition

the expression of p-mTOR (Ser2448)

p-p70S6K (Thr229/389) and p-4E-BP1 (Thr37/46) proteins was also decreased in a dose-dependent manner (P0.05).        Conclusion      PNS can inhibit the activity of mTOR signaling pathway in K562 cells

and this may be one of PNS-mediated cell proliferation inhibition mechanisms.