Induction of apoptosis in human lung carcinoma cells by the water extract of Panax notoginseng is associated with the activation of caspase-3 through downregulation of Akt

Abstract

The root of Panax notoginseng is highly valued and commonly used in Oriental medicine. Although recent experimental data have revealed the proapoptotic potency of P. notoginseng extracts, the underlying molecular mechanisms of this apoptotic activity have not yet been studied in detail. In the present study, the effects of the water extract of P. notoginseng (WEPN) on the growth of human lung carcinoma cells were investigated. It was found that the exposure of A549 and NIC-H460 cells to WEPN resulted in growth inhibition and the induction of apoptosis in a dose-dependent manner. The WEPN treatment induced the upregulation of pro-apoptotic Bax, downregulation of anti-apoptotic Bcl-2 expression and loss of mitochondrial membrane potential (MMP), which was associated with the proteolytic activation of caspases and the concomitant degradation of poly(ADP ribose) polymerase (PARP) protein. However, the caspase-3-specific inhibitor z-DEVD-fmk blocked PARP degradation and increased the survival rate of WEPN-treated cells. Moreover, the activity of Akt was downregulated in WEPN-treated cells and the phosphatidylinositol-3 kinase (PI3K)/Akt inhibitor LY294002 sensitized the cells to WEPN-induced apoptosis through enhancing the activation of caspase-3 and loss of MMP. The results indicated that the major regulators of WEPN-induced apoptosis in human lung carcinoma cells are the Bcl-2 family and caspase-3, which are associated with mitochondrial dysfunction and dephosphorylation of the Akt signaling pathway.