Fas activates the JNK pathway in human colonic epithelial cells: lack of adirect role in apoptosis

Fas is expressed constitutively by colonic epithelial cells, and its ligand is expressed by intraepithelial and lamina propria lymphocytes. Fas ligati on induces apoptosis in colonic epithelial cells and is implicated in the e pithelial damage seen in ulcerative colitis. To understand the pleiotropic effects of Fas in the intestinal mucosa, we have examined signaling pathway s activated by Fas in HT-29 colonic epithelial cells. HT-29 cells were stim ulated with anti-Fas in the presence or absence of interferon-gamma (IFN-ga mma). Activation of mitogen-activated protein kinase pathways was assessed by kinase assay, Western blots, and promoter-reporter assays. Electromobili ty shift assays were used to assess activator protein-1 (AP-1) binding acti vity. IFN-gamma increases expression of Fas on HT-29 cells. Signaling via F as receptor, as determined by induction of c-Jun NH2-terminal kinase (JNK) activity and transcriptional activation of AP-1, is enhanced in IFN-gamma-p rimed cells. Dominant-interfering mutants of the JNK pathway do not block F as-mediated apoptosis. Signaling through Fas results in activation of JNK a nd AP-1 binding activity that is increased in the presence of IFN-gamma. In hibition of JNK does not block Fas-mediated apoptosis in these cells. Fas-F as ligand interactions in the intestinal mucosa may lead to complex signal transduction cascades and gene regulation that culminate in apoptosis, cyto kine secretion, or other novel functions.