Oridonin, a diterpenoid isolated from Rabdosia rubescens, has various pharmacological and physiological effects such as anti-inflammation, anti-bacteria, anti-tumor effects [1][2][3] and has been used for the treatment of human cancers, especially esophageal carcinoma. 4) Our previous study showed that oridonin had cytotoxic effects on four tumor cell types, human melanoma A375-S2, human cervical carcinoma HeLa, human breast adenocarcinoma MCF-7, and murine fibrosarcoma L929.5) However, the mechnasim of this antitumor effect remains unclear.Caspases are a family of cysteine proteases, which play key roles in promoting the degradative changes associated with apoptosis and are divided into two classes based on the lengths of their N-terminal prodomains, including up-stream caspases such as caspase-8 and -10 and downstream caspases such as caspase-3, 6 and 7. In general, caspase activation is believed to be involved in apoptosis.6) However, some workers have reported that caspases are required for the protection against tumor necrosis factor-a (TNFa) or CD95-induced L929 cell death, 7,8) suggesting that the effects of caspases on cell death are not limited to the initiation of apoptosis.The Bcl-2 family proteins constitute an important control mechanism in the regulation of apoptosis. Some including Bcl-2 and Bcl-X L suppress apoptosis, and others such as Bax and Bid promote apoptosis, and the balance between these two groups determines the fate of cells in many apoptotic systems.9) In many cell types, the distinct MAPK members have been identified. In these extracellular signalregulated kinases (ERKs), stress-activated protein kinases (SAPKs)/c-Jun NH2-terminal kinases (JNKs), and p38 kinase play important signaling roles in the control of cell proliferation and differentiation. Recent studies suggest that MAPK also regulate the cell cycle, apoptosis, and necrosis.
10-12)The aims of this study were to investigate the effector mechanism(s) of oridonin-induced L929 cell death. We demonstrated that oridonin induced L929 cell death through distinct mechanisms and pathways including apoptosis and necrosis, the mechanism of which is in part due to regulation of Bcl-2 family proteins. Moreover, caspases protected L929 cells against death induced by oridonin. Importantly, modulation of MAPK family members had been first evaluated in oridonin-induced L929 cells death, indicating that oridonininduced cell death is closely correlated with the activation of ERK and inactivation of the p38 signaling pathway.
MATERIALS AND METHODS
MaterialsOridonin was isolated from the aerial parts of Rabdosia rubescens. The 95% ethanol extract of the rabdosia aerial parts was partitioned between water and petroleum ether. The water layer was separated repeatedly by column chromatography on silica gel, and oridonin was then extracted. The structures of the diterpenoids were assigned by comparing the chemical and spectral data ( 1 H-NMR) with those reported in the literature.13) The purity of each compound was tested using an HPLC equipped with...
