Induction of S Phase Arrest and Apoptosis by Ethyl Acetate Extract from Tetrastigma Hemsleyanum in Human Hepatoma HepG2 Cells

Tetrastigma hemsleyanum, a rare and endangered medicinal plant, has attracted much attention due to antitumor and immunomodulatory activities. In this study, the effect and mechanism of ethyl acetate extract from T. hemsleyanum (EET) on cell cycle and apoptosis in human hepatoma HepG2 cells were investigated. Twenty-five to 200 μg/mL of EET were found to have the antiproliferation effect toward HepG2 cells determined by MTT assay. The morphology of EET-treated HepG2 cells showed evidence of apoptosis that included blebbing and chromatin condensation, nucleic fragmentation, and so on. The DNA laddering assay confirmed that DNA fragmentation had occurred during late apoptosis. The cell-cycle analysis indicated that EET was able to induce S phase arrest and typical subdiploid peak in a dose- and time-dependent manner. The apoptosis rate of 200 μg/mL treatment for 24 h was 42.24 ± 4.90%. The protein expression of Bax and P53 was increased after treatment, while that of Bcl2 was significantly decreased in a dose-dependent manner, which suggested that a high Bax/Bcl2 ratio and an upregulated P53 might contribute to the pro-apoptotic activity of EET via the mitochondria-dependent pathway. The protein expression of cyclin-dependent kinase 1 (CDK1) was decreased in EET-treated HepG2 cells, suggesting that EET evoked S phase arrest possibly through the downregulation of cyclin A-CDK1 complex. In conclusion, the cytotoxicity on HepG2 cells induced by EET is a result of both cell-cycle arrest and apoptosis. Thus, it may have therapeutic potential for the treatment of liver cancer.