Herbal (Astragalus) saponins inhibit HepG2 cell growth and promote apoptosis through NF-κB and ERK signaling (Abstract)

We have recently reported that the total saponins of the Chinese medicinal herb Astragalus membranaceus (AST) possess promising anti-tumorigenic effects in human colon cancer cells and tumor xenograft through inhibition of cell proliferation and promotion of apoptosis (Carcinogenesis 28:1347-1355, 2007). In the present study, the anti-carcinogenic effects of AST were further studied in HepG2 human hepatocellular carcinoma cells. We focused on the involvement of both extracellular signal-regulated kinases (ERK) and nuclear factor-kappa B (NF-κB) signaling pathways in AST-induced apoptosis. Our results have shown that AST could suppress HepG2 cell growth, while at the same time downregulate expression of the liver tumor marker α-fetoprotein. Furthermore, apoptosis was induced through caspase 3 activation and subsequent poly(ADP-ribose) polymerase (PARP) cleavage, leading to the appearance of nuclear chromatin condensation. Besides, downregulation of the anti-apoptotic proteins bcl-2 and bcl-x_L were also observed following AST treatment. In order to unveil the underlying mechanism of action, DNA binding activity of the transcription factor NF-κB was examined by electrophoretic mobility shift assay. Data have demonstrated that NF-κB DNA binding activity was significantly decreased after AST treatment. On the other hand, expression of the phosphorylated form of ERK was found to be prominently increased in a dose-dependent manner. Pretreatment of PD98059, a strong inhibitor of ERK, facilitated the cleavage of PARP, indicating an active involvement of the ERK signaling pathway in AST-induced apoptotic activity. Taken together, our findings suggest that AST has the potential to be developed as an effective chemotherapeutic agent in treating liver cancers, with known molecular targets and precise mechanism of action.