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Mol Cell Biol. 2004 Oct;24(19):8541-55.

Direct repression of FLIP expression by c-myc is a major determinant of TRAIL sensitivity.

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  • 1Laboratory of Molecular Oncology and Cell Cycle Regulation, Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, 415 Curie Blvd., CRB 437A, Philadelphia, PA 19104, USA.


Tumor necrosis factor alpha (TNF-alpha)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF-alpha family of death receptor ligands and holds great therapeutic potential as a tumor cell-specific cytotoxic agent. Using a panel of established tumor cell lines and normal cells, we found a significant difference between the number of TRAIL-sensitive cells expressing high levels of c-myc and TRAIL-resistant cells expressing low levels of c-myc (P < 0.05, n = 19). We also found a direct linear correlation between c-myc levels and TRAIL sensitivity in TRAIL-sensitive cell lines (r = 0.94, n = 6). Overexpression of c-myc or activation of a myc-estrogen receptor (ER) fusion sensitized TRAIL-resistant cells to TRAIL. Conversely, small interfering RNA (siRNA)-mediated knockdown of c-myc significantly reduced both c-myc expression and TRAIL-induced apoptosis. The gene encoding the inhibitor of caspase activation, FLICE inhibitory protein (FLIP), appears to be a direct target of c-myc-mediated transcriptional repression. Overexpression of c-myc or activation of myc-estrogen receptor (ER) decreased FLIP levels both in cell culture and in mouse models of c-myc-induced tumorigenesis, while knocking down c-myc using siRNA increased FLIP expression. Chromatin immunoprecipitation and luciferase reporter analyses showed that c-myc binds and represses the human FLIP promoter. c-myc expression enhanced TRAIL-induced caspase 8 cleavage and FLIP cleavage at the death-inducing signaling complex. Combined siRNA-mediated knockdown of FLIP and c-myc resensitized cells to TRAIL. Therefore, c-myc down-regulation of FLIP expression provides a universal mechanism to explain the ability of c-myc to sensitize cells to death receptor stimuli. In addition, identification of c-myc as a major determinant of TRAIL sensitivity provides a potentially important screening tool for identification of TRAIL-sensitive tumors.

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