Ginsenoside‐Rg1 positively regulates cyclin E‐dependent kinase activity in human hepatoma SK‐HEP‐1 cells

In the present study, we describe that ginsenoside‐Rg1 (G‐Rg1) stimulates the proliferation of cultured human hepatoma SK‐HEP‐1 cells. The incorporation of [3H] thymidine into DNA was increased in the cells in response to G‐Rg1. The stimulatory effect of G‐Rg1 on DNA synthesis in SK‐HEP‐1 cells require newly synthesized proteins, since cycloheximide blocked the DNA synthetic activity stimulated with G‐Rg1. Thus, we examined whether G‐Rg1 induces the intracellular protein levels of regulatory proteins for cell cycle progression using immunoblottings. The results from immunoblottings showed that G‐Rg1 induced the levels of cyclin E and cdk2 proteins in the cells. Furthermore, the results from immuno‐complex kinase assays for cyclin E‐dependent kinase showed that G‐Rg1 up‐regulates the kinase activity in a dose‐dependent manner. These results suggest that G‐Rg1 stimulates cell‐growth of SK‐HEP‐1 cells by inducing the intracellular levels of cyclin E/cdk2 complex, which in turn up‐regulates cyclin E‐dependent kinase activity.