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

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, Akt-dependent 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 over-expressing 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.Musende AG, 2009, CANCER CHEMOTH PHARM, V64, P1085, DOI 10.1007/s00280-009-0965-1Park EK, 2009, J PATHOL, V218, P337, DOI 10.1002/path.2531Royer MC, 2009, J BIOL CHEM, V284, P15826, DOI 10.1074/jbc.M808641200YI JS, 2009, BIOCHEM BIOPH RES CO, V24, P154Franke TF, 2008, ONCOGENE, V27, P6473, DOI 10.1038/onc.2008.313Lasserre R, 2008, NAT CHEM BIOL, V4, P538, DOI 10.1038/nchembio.103Tarahovsky YS, 2008, MOL CELL BIOCHEM, V314, P65, DOI 10.1007/s11010-008-9766-9Giannoni E, 2008, CELL DEATH DIFFER, V15, P867, DOI 10.1038/cdd.2008.3Patra SK, 2008, BBA-REV CANCER, V1785, P182, DOI 10.1016/j.bbcan.2007.11.002Youle RJ, 2008, NAT REV MOL CELL BIO, V9, P47, DOI 10.1038/nrm2308McCubrey JA, 2007, BBA-MOL CELL RES, V1773, P1263, DOI 10.1016/j.bbamcr.2006.10.001Adam RM, 2007, CANCER RES, V67, P6238, DOI 10.1158/008-5472.CAN-07-0288Schley PD, 2007, J NUTR, V137, P548Jacobson K, 2007, NAT CELL BIOL, V9, P7, DOI 10.1038/ncb0107-7YUE PY, 2007, CHIN MED, V2, P6Ham YM, 2006, J PHARMACOL EXP THER, V319, P1276, DOI 10.1124/jpet.106.109926Hancock JF, 2006, NAT REV MOL CELL BIO, V7, P456, DOI 10.1038/nrm1925Li YC, 2006, AM J PATHOL, V168, P1107, DOI 10.2353/ajpath.2006.050959LI YC, 2006, AM J PATHOL, V168, P1404del Pozo MA, 2005, NAT CELL BIOL, V7, P901, DOI 10.1038/ncb1293Cheng CC, 2005, CANCER CHEMOTH PHARM, V55, P531, DOI 10.1007/s00280-004-0919-6Zhuang LY, 2005, J CLIN INVEST, V115, P959Uriarte SM, 2005, CELL DEATH DIFFER, V12, P233, DOI 10.1038/sj.cdd.4401549Kim YS, 2004, ARCH PHARM RES, V27, P834Pike LJ, 2004, BIOCHEM J, V378, P281, DOI 10.1042/BJ20031672Ham YM, 2003, J BIOL CHEM, V278, P50330, DOI 10.1074/jbc.M302997200Rubio CA, 2003, EUR J CLIN INVEST, V33, P406Zhuang LY, 2002, CANCER RES, V62, P2227Kim YN, 2000, J BIOL CHEM, V275, P7481Attele AS, 1999, BIOCHEM PHARMACOL, V58, P1685, DOI 10.1016/S0006-2952(99)00212-9Nakata H, 1998, JPN J CANCER RES, V89, P733Salvioli S, 1997, FEBS LETT, V411, P77TODE T, 1993, J CANCER RES CLIN, V120, P24