title: Chemotherapy and TRAIL-mediated colon cancer cell death: the roles of p53, TRAIL receptors, and c-FLIP.
abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has recently attracted attention as a potential therapeutic agent in the treatment of cancer. We assessed the roles of p53, TRAIL receptors, and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitory protein (c-FLIP) in regulating the cytotoxic effects of recombinant TRAIL (rTRAIL) alone and in combination with chemotherapy [5-fluorouracil (5-FU), oxaliplatin, and irinotecan] in a panel of colon cancer cell lines. Using clonogenic survival and flow cytometric analyses, we showed that chemotherapy sensitized p53 wild-type, mutant, and null cell lines to TRAIL-mediated apoptosis. Although chemotherapy treatment did not modulate mRNA or cell surface expression of the TRAIL receptors death receptor 4, death receptor 5, decoy receptor 1, or decoy receptor 2, it was found to down-regulate expression of the caspase-8 inhibitor, c-FLIP. Stable overexpression of the long c-FLIP splice form but not the short form was found to inhibit chemotherapy/rTRAIL-induced apoptosis. Furthermore, siRNA-mediated down-regulation of c-FLIP, particularly the long form, was found to sensitize colon cancer cells to rTRAIL-induced apoptosis. In addition, treatment of a 5-FU-resistant cell line with 5-FU down-regulated c-FLIP expression and sensitized the chemotherapy-resistant cell line to rTRAIL. We conclude that TRAIL-targeted therapies may be used to enhance conventional chemotherapy regimens in colon cancer regardless of tumor p53 status. Furthermore, inhibition of c-FLIP may be a vital accessory strategy for the optimal use of TRAIL-targeted therapies.
authors.affiliation: Centre for Cancer Research and Cell Biology, Queen's University Belfast, University Floor, Belfast City Hospital, Lisburn Road, Belfast, United Kingdom BT9 7AB.
authors.forename: Leeona
authors.initials: L
authors.lastname: Galligan
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Longley
authors.forename: Miranda
authors.initials: M
authors.lastname: McEwan
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Wilson
authors.forename: Kirsty
authors.initials: K
authors.lastname: McLaughlin
authors.forename: Patrick G
authors.initials: PG
authors.lastname: Johnston
mesh_terms: D017209:Apoptosis / Q000502:physiology; D001483:Base Sequence; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000503:physiopathology; D017931:DNA Primers; D005434:Flow Cytometry; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D018124:Receptors, Tumor Necrosis Factor; D016159:Tumor Suppressor Protein p53