Objective       To determine the eff

ect of total saponins of panax ginseng (TSPG) separately or jointly with erythropoietin (EPO) on the proliferation of human leukemia cell line KG1-α and investigate the possible underlying mechanism.       Methods       The KG1-α cells were respectively treated by 25

50

100

200 and 400 mg/L TSPG in presence or absence of 0.5 U/L EPO. The cells cultured in normal condition served as control. CCK-8 assay was utilized to detect the proliferation of KG1-α cells in 3

7 and 14 d after treatment. Real-time PCR was employed to detect the mRNA expression of EPO/ EPO receptor (EPOR) pathway related genes

such as EPOR

STAT5

Jak2

and AKT. Western blot analysis was used to measure the expression of apoptosis related proteins

Bcl-2

Bax

Cleaved Caspase-3

P53

P16 and EPOR.       Results       TSPG significantly inhibited the proliferation in KG1-α cells

with 100 μmol/L as optimal concentration and 7 d as best treatment period. In the presence of 0.5 U/L EPO

its optimal concentration was decreased to 75 mg/L. Compared with the control

TSPG significantly arrested the cell cycle at G

0

/G

1

phase in the presence of EPO

but without the EPO

TSPG had no effect on cell cycle. Real-time PCR analysis showed that the expression of the genes related to EPOR-mediated Jak-STAT signaling pathway

such as EPOR

Jak2 and STAT5 genes were in a negatively dose-dependent manner with TSPG in KG1-α cells

especially in the cells treated by high dose TSPG (P0.05). Western blotting indicated that the expression of EPOR

p-EPOR

Jak2

STAT5

p-STAT5 and Bcl-2 was down-regulated

while that of Bax and Cleaved Caspase-3 proteins was increased

and that of P53 and P16 had no change in the KG1-α cells treated by TSPG in absence of EPO. However in the presence of EPO

the expression of p-EPOR

Jak2

p-STAT5

P53 and P16 was significantly increased

while Bcl-2

Bax and Cleaved Caspase-3 had no change in expression.       Conclusion       TSPG down-regulates the expression of EPOR and related proteins in Jak-STAT pathway

mediated by EPOR

decreases the activity of EPOR

then reduces the expression of Bcl-2 protein

and increases the expression of Bax and Cleaved Caspase-3 proteins to promote the cell apoptosis in the KG1-α cells. While

when combining EPO

these effects are antagonized. The inhibition of cell proliferation is induced by increasing the expression of P53 and P16 and promoting cell senescence.