Induction of apoptosis by the ginsenoside Rh2 by internalization of lipid rafts and caveolae and inactivation of Akt

Abstract

Background and purpose: Lipid rafts and caveolae are membrane microdomains with important roles in cell survival signalling involving the Akt pathway. Cholesterol is important for the structure and function of these microdomains. The ginsenoside Rh2 exhibits anti-tumour activity. Because Rh2 is structurally similar to cholesterol, we investigated the possibility that Rh2 exerted its anti-tumour effect by modulating rafts and caveolae. Experimental approach: A431 cells (human epidermoid carcinoma cell line) were treated with Rh2 and the effects on cell apoptosis, raft localization and Akt activation measured. We also examined the effects of over-expression of Akt and active-Akt on Rh2-induced cell death. Key results: Rh2 induced apoptosis concentration-and time-dependently. Rh2 reduced the levels of rafts and caveolae in the plasma membrane and increased their internalization. Furthermore, Akt activity was decreased and consequently, Aktdependent phosphorylation of Bad, a pro-survival protein, was decreased whereas the pro-apoptotic proteins, Bim and Bax, were increased upon Rh2 treatment. Unlike microdomain internalization induce by cholesterol depletion, Rh2-mediated internalization of rafts and caveolae was not reversed by cholesterol addition. Also, cholesterol addition did not restore Akt activation or rescue cells from Rh2-induced cell death. Rh2-induced cell death was attenuated in MDA-MB-231 cells overexpressing either wild-type or dominant-active Akt. Conclusions and implications: Rh2 induced internalization of rafts and caveolae, leading to Akt inactivation, and ultimately apoptosis. Because elevated levels of membrane rafts and caveolae, and Akt activation have been correlated with cancer development, internalization of these microdomains by Rh2 could potentially be used as an anti-cancer therapy.

Neutral sphingomyelinase 2 modulates cytotoxic effects of protopanaxadiol on different human cancer cells

“…We investigated the possibility that PPD may disrupt lipid rafts as one of cytotoxic mechanisms like Rh2 and aPPD [7,8,12]. K562 and HT29 cells were treated with PPD with or without MβCD, another lipid raft disrupter [6].…”

“…Rh2 also reduces the levels of lipid rafts in plasma membranes by increasing their internalization through unknown mechanisms, leading to Akt inactivation and ensuing apoptosis [8]. 25-hydroxyprotopanaxadiol (25-OH-PPD), another ginsenoside from Panax ginseng demonstrated a potent cytotoxicity against a variety of prostate cancer cells, compared to its related ginsenosides [9].…”

An Essential Role of cAMP Response Element Binding Protein in Ginsenoside Rg1-Mediated Inhibition of Na+/Glucose Cotransporter 1 Gene Expression

“…A recent study demonstrated that Rg3 reduced the expression of fucosyltransferase IV and its synthetic product Lewis Y, thus suppressing fucosylation, which in turn inhibited the activation of the EGFR/mitogenactivated protein kinase pathway and subsequently prevented melanoma growth (Shan et al, 2015). Additionally, Rh2 has been shown to induce internalization of lipid rafts and caveolae, which block EGF-stimulated Akt activation and ultimately induce cancer cell apoptosis (Park et al, 2010). Studies have also shown that the ligand-activated glucocorticoid receptor is essential for the negative regulation of EGFR signaling (Zhang et al, 2007;Lauriola et al, 2014).…”

20(<i>S</i>)-Ginsenoside Rh2 Induces Apoptosis in Human Leukaemia Reh Cells through Mitochondrial Signaling Pathways

“…[25][26][27][28] Moreover, GRh2 can kill colorectal cancer cells and its cytotoxic effect is significantly more potent than GRg3. 29) Our findings are consistent with these previous reports: As shown in Fig.…”