TNF alpha-induced IEC-6 cell apoptosis requires activation of ICE caspaseswhereas complete inhibition of the caspase cascade leads to necrotic cell death

Tumor necrosis factor (TNF)alpha is considered to play a key pathogenetic r ole in inflammatory bowel diseases. In this study we analyzed the mechanism s by which TNF alpha induces intestinal epithelial cell apoptosis. TNF alph a alone, and more potently in combination with IFN gamma, induced a high de gree of IEC-6 cell apoptosis. This effect was more than 100-fold stronger i f both of the TNF-R were stimulated, compared to stimulation of the p55-TNF -R alone, indicating an important apoptosis enhancing effect of the p75-TNF -R. TNF alpha-induced apoptosis required activation of ICE caspases and was completely abolished by its inhibitor, zVAD-fmk. Specific inhibition of ca spase-3 with zDEVD-fmk did not alter the effect of TNF alpha. Western blot analyses confirmed that caspase-3 was not activated in response to TNF alph a. In the presence of complete inhibition of the caspase cascade with zVAD- fmk (greater than or equal to 50 mu M), TNF alpha induced cell necrosis rat her than apoptosis. Our data reveal that TNF alpha can trigger enterocyte c ell death via apoptosis or necrosis, depending upon the activation or block ade of specific caspases. (C) 1999 Academic Press.