Apoptosis induced by a new member of saponin family is mediated through caspase-8-dependent cleavage of Bcl-2.
OSW-1 is a new member of cholestane saponin family, which is cytotoxic against several types of malignant cells. We reported herein that OSW-1 induced apoptosis of mammalian cells in a concentration- and time-dependent manner. The drug-induced apoptosis was mediated through the mitochondrial pathway, involving the cleavage of Bcl-2. This drug-induced Bcl-2 cleavage in Chinese hamster ovary (CHO) cells could be suppressed either by dominant-negative caspase-8 or by a caspase-8 inhibitor, suggesting that the Bcl-2 cleavage is dependent on caspase-8. In contrast, the Bcl-2 cleavage was independent of caspase-3 activity. The inhibition of caspase-8 activity also resulted in the reduction of apoptotic cells, indicating that Bcl-2 cleavage induced by caspase-8 promotes the progression of apoptosis. The involvement of the caspase-8 activity in the processes of the OSW-1-induced apoptosis was further examined by using caspase-8-deficient Jurkat T cells. It was found that the caspase-8-deficient cells were resistant to OSW-1-induced Bcl-2 cleavage or apoptosis. Furthermore, the small subunit of caspase-8 was found to interact with Bcl-2 as determined by yeast two-hybrid and coimmunoprecipitation assays. Overexpression of caspase-8 small subunit reduced the cleavage of Bcl-2 and inhibited the apoptosis induced by OSW-1. Taken together, these results demonstrate that OSW-1 is capable of inducing apoptosis in mammalian cells, in which the caspase-8-dependent cleavage of Bcl-2 plays an important role.
Zhu
Jianbei
J
Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road., Shanghai 200031, China.
Xiong
Lei
L
Yu
Biao
B
Wu
Jiarui
J
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016466:CHO Cells; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D002783:Cholestenones / Q000494:pharmacology; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D024101:Mitochondrial Proteins / Q000378:metabolism; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012503:Saponins / Q000494:pharmacology*; D020798:Two-Hybrid System Techniques
D002783:Cholestenones; D024101:Mitochondrial Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012503:Saponins; C106408:OSW 1; D053181:Caspase 8; D020169:Caspases