Cytokine regulation of human intestinal primary epithelial cell susceptibility to Fas-mediated apoptosis

The regulatory mechanisms of nontransformed intestinal epithelial cell apoptosis have not been thoroughly investigated. We determined the susceptibility and mechanism of Fas-mediated apoptosis in nontransformed human intestinal epithelial cells (HIPEC) in the presence and absence of inflammatory cytokines. Despite ample expression of Fas, HIPEC were relatively insensitive to Fas-mediated apoptosis in that agonist anti-Fas antibody (CH11) induced a <25% increase in HIPEC apoptosis. Pretreatment of HIPEC with interferon (IFN)-gamma, but not tumor necrosis factor-alpha or granulocyte-macrophage colony-stimulating factor, significantly increased CH11-induced apoptosis of these cells without increasing Fas expression. Increased apoptosis correlated with increased caspase 3 activation but not expression of procaspase 3. Also, there was a significant delay in the onset of Fas-mediated apoptosis in HIPEC, which correlated with the generation of an activated caspase 3 p22/20 subunit. HIPEC required both initiator caspases 8 and 9 activity but expressed significantly less of the zymogen form of these caspases than did control cells. IFN-gamma-mediated sensitization of HIPEC occurred upstream of caspase 9 activation and correlated with a small increase in procaspase 8 expression (<1-fold increase) and a significant increase in expression of an intermediate form (p35) of caspase 4 (3.3-fold increase).