Effect of ceramide on intracellular glutathione determines apoptotic or necrotic cell death of JB6 tumor cells

Selective induction of cell death is a means to remove unwanted cell popula tions from a tissue or organ. Understanding the signaling events responsibl e for mediating cell death by cytokines, such as tumor necrosis factor-alph a (TNF alpha) are key to the development of pharmacologic inducers of this response. Ceramide has been implicated as a secondary messenger for TNF alp ha-induced cell death, but many of the intracellular effects of ceramide ar e not fully understood. Recent reports suggest that ceramide signaling may involve oxidative stress. To explore the relationship between TNF sensitivi ty and ceramide signaling, two genetic variants of mouse JB6 RT101 epiderma l tumor cells, one resistant and one sensitive to TNF alpha- induced cytoto xicity, were treated with C-2-ceramide. Treatment with 20 mu M ceramide ind uced apoptosis and this was quickly followed by oncotic necrosis in the TNF alpha-sensitive JB6 (TNFs) cells. The same concentration of ceramide induc ed apoptosis, but not oncotic necrosis of the TNF alpha resistant JB6 (TNFr ) cells. The basal level of glutathione was significantly higher in TNFr ce lls than in TNFs cells. Treatment with 20 mu M ceramide decreased cellular glutathione in TNFs cells by 50%, in contrast to an insignificant decrease in the TNFr cells. A significant increase in reactive oxygen was noted in T NFs cells treated with 10 or 20 mu M ceramide, Furthermore, pretreatment wi th the antioxidant N-acetylcysteine or with glutathione monoethylester dela yed the onset of ceramide-induced oncotic necrosis, but did not inhibit apo ptosis. Our results suggest that the severity of the decrease in glutathion e appears to determine whether cells undergo just apoptosis or also oncotic necrosis, They also suggest that ceramide-induced oncotic necrosis is modu lated by a decline in cellular glutathione and an elevation of reactive oxy gen. These results suggest that a decrease in cellular redox potential dete rmines susceptibility to ceramide-dependent killing pathways.