Influence of Bax or Bcl-2 overexpression on the ceramide-dependent apoptotic pathway in glioma cells

Ceramide has recently been regarded as a potential mediator of apoptosis, In the present study, the effects of Bcl-2 and Bax on the ceramide-mediated apoptotic pathways mere examined in glioma cells overexpressing Bcl-2 or Bax. Etoposide, cisplatin and tumor necrosis factor-alpha induced apoptosis of C6 rat glioma cells which was associated with ceramide formation due to activation of neutral sphingomyelinase, followed by release of mitochondrial cytochrome c into the cytosol and activation of caspases-9 and -3, The growth of C6 cells stably overexpressing either Bcl-2 or Bax was almost equal to that of the vector-transfected cells. Bas overexpression enhanced etoposide-induced apoptosis through acceleration of cytochrome c release and caspases activation. However, Bax had no effect on ceramide formation, Similar findings mere obtained in C6 cells and U87-MG human glioblastoma cells which mere transiently overexpressed with Bax. In contrast, Bcl-2 overexpression resulted in a retardation of the apoptotic process via prevention of cytochrome c release and caspases activation, and ceramide formation was also blocked when Bcl-2 was highly overexpressed in glioma cells. Tn addition, transient overexpression of Bcl-xL also exerted inhibitory effects on ceramide formation and apoptotic cell death induced by etoposide, These results indicate that Bax promotes apoptosis regardless of ceramide formation and that Bcl-2 or Bcl-xL prevents ceramide formation by repressing neutral sphingomyelinase as well as ceramide-induced cytochrome c release.