Induction of apoptosis by an ethanol extract of Poria cocos Wolf. in human leukemia U937 cells

Abstract

Poria cocos Wolf., which belongs to the Polyporaceae family, has been widely used as an Oriental traditional herbal medicine for centuries. Its sclerotium has been reported to possess a wide spectrum of pharmacological activities, including free-radical scavenging, anti-viral, anti-microbial, anti-inflammatory and anticancer activities. However, the cellular and molecular mechanisms of apoptosis induction by P. cocos in human cancer cells are poorly understood. In the present study, we investigated the pro-apoptotic potential of an ethanol extract of P. cocos sclerotium (EEPC) in human leukemia U937 cells in vitro. We found that EEPC induced anti-proliferative effects in U937 cells in a concentration- and time-dependent manner, which was due to apoptotic induction, as evident from morphological changes and flow cytometric assays. EEPC-induced apoptosis of U937 cells was associated with an increase in the Bax:Bcl-2 ratio, the release of cytochrome c to the cytosol, and a decrease in the expression of an inhibitor of the apoptosis family of proteins. The events were accompanied by activation of caspase-8, -9 and -3, and cleaved poly(ADP-ribose) polymerase, suggesting the involvement of both the intrinsic and extrinsic apoptotic cascades. In addition, the overexpression of Bcl-2 caused a significant attenuation of EEPC-induced caspase activation, degradation of PARP, and the collapse of mitochondrial membrane potential, and thereby reversed EEPC-induced cell apoptosis and growth inhibition. Collectively, these data provide insights into the molecular mechanisms underlying EEPC-induced apoptosis in U937 cells, suggesting that EEPC may be a new therapeutic option for the treatment of leukemia.