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.