Sphingolipid-Mediated Apoptosis and Tumor Suppression in Breast Carcinoma.

摘要

In ongoing studies in human breast carcinoma cells in tissue culture, we find that tumor necrosis factor alpha (TNFa) causes apoptosis which is preceded by accumulation of ceramide. This accumulation of ceramide involves activation of ICE-like proteases which are inhibitable by CrmA and by inhibitors of type 1 caspases (YVAD). On the other hand, the addition of ceramide to cells results in the induction of apoptosis which is inhibited by Bcl-2 and by inhibitors of the caspase-3- type proteases (DEVD). In further studies, we have determined that TNFA alpha causes activation of neutral sphingomyelinase. We have isolated this enzyme from breast carcinoma cells and studied its regulation. These studies led to the identification of glutathione (OSH) as an inhibitor of this enzyme in vitro. Studies in cells show that TNFA cc causes a drop in glutathione levels which is coincident with activation of sphingomyelinase and the formation of ceramide. The addition of GSH or N-acetyl cysteine to TNFA alpha treated cells results in replenishment of glutathione levels and prevention of ceramide formation. These studies are beginning to elucidate the mechanisms involved in activation of sphingomyelinase by TNFA alpha in breast carcinoma cells.