Antagonism of CD95 signaling blocks butyrate induction of apoptosis in young adult mouse colonic cells

There is great interest in utilizing butyrate as a chemopreventive agent fo r colon tumorigenesis because of its ability to promote apoptosis in colon tumor cell lines. Because CD95 (APO-1/Fas) transduces signals resulting in apoptosis, we tested the hypothesis that butyrate-dependent colonocyte apop tosis is mediated by this death receptor. Butyrate (1 mM) exposure for 24 h upregulated expression of Fas and its ligand in young adult mouse colon (Y AMC) cells. To delineate the proapoptotic effect of butyrate and to avoid t he confounding effects of detachment from the extracellular matrix, adheren t cell apoptosis was monitored as loss of plasma membrane asymmetry and dis sipation of mitochondrial membrane potential (Delta Psi(mt)) by laser cytom etry. Soluble Fas receptor protein (Fas:Fc chimera) and caspase inhibitors (z-VAD-fmk and z-IETD-fmk) blocked butyrate induction of apoptosis. Treatme nt with Fas agonistic antibody (clone Jo-2) significantly induced cell deat h, indicating that Fas in colonocytes is functional. In addition, butyrate promoted apoptosis by inducing loss of Delta Psi(mt) and phospholipid asymm etry of the plasma membrane after 12 and 24 h of exposure, respectively, be fore cell detachment. Therefore, Fas receptor-dependent signal transduction is involved in butyrate induction of apoptosis in colonocytes.