Interferon-gamma modulates TRAIL-mediated apoptosis in human colon carcinoma cells.

ABSTRACT

BACKGROUND: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is expressed by immune cells and has been shown to play an important role in tumor surveillance due to its ability to induce apoptosis in various transformed cells. Interferon gamma (IFN-gamma), a multipotent cytokine with broad stimulatory effects on anti-tumoral immune reactions, may exert its cytotoxic activity directly on tumor cells or indirectly via stimulation of effector cells. This study was designed to determine the effect of IFN-gamma on TRAIL-mediated apoptosis in human colon carcinoma cell lines. MATERIALS AND METHODS: Cytotoxicity was assessed by MTT-assay. Expression of death receptors was measured by reverse transcriptase polymerase chain reaction. Apoptosis was assessed by caspase-8 immunoblot, DNA fragmentation and morphological studies. RESULTS: Treatment with TRAIL resulted in detectable cytotoxicity within 5 hours and was enhanced in a dose-dependent manner. When cells were pretreated with IFN-gamma, the cytotoxic effect of TRAIL increased significantly. Treated cells showed a typical apoptotic morphology that was accompanied by internucleosomal cleavage of DNA. Up-regulation of caspase-8 expression and activation were detected as a result of pretreatment with IFN-gamma and subsequent apoptosis mediated by TRAIL. CONCLUSION: Our results demonstrated that IFN-gamma sensitises human colon carcinoma cells to TRAIL-mediated apoptosis, partly by elevated caspase-8 expression.