Fas activates the JNK pathway in human colonic epithelial cells: lack of a direct role in apoptosis.

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

A role for TNF-alpha and mucosal T helper-1 cytokines in the pathogenesis of Crohn's disease.

Recent clinical studies of Crohn's disease patients demonstrated dramatic clinical responses following one i.v. infusion of a chimeric mAb to TNF-alpha (cA2). To assess the role of TNF-alpha in mucosal cytokine regulation, the effects of TNF-alpha on lamina propria mononuclear cell (LPMC) Th1 production were determined. Increased IFN-gamma production was demonstrated in anti-CD2-stimulated LPMC cultured in TNF-alpha. To determine the effects of cA2 on cytokine production, TNF-alpha- and IFN-gamma-producing cells were quantitated in LPMC from five Crohn's disease patients treated with cA2. In all four patients who demonstrated clinical and endoscopic improvement, decreased numbers of LPMC producing IFN-gamma and TNF-alpha following CD2/CD28 activation paralleled improvement in disease activity over 8 wk. In one patient who did not improve, increased numbers of TNF-alpha- and IFN-gamma-secreting LPMC were observed. In three of four responding patients, CD2/CD28-activated PBMC demonstrated increased IFN-gamma production over 8 wk. These observations suggest that TNF-alpha may be a cofactor for mucosal Th1 responses, and improvement in clinical parameters and intestinal inflammation induced by cA2 in Crohn's disease may be mediated by down-regulation of mucosal Th1 cytokines.