title: c-FLIP inhibits chemotherapy-induced colorectal cancer cell death.
abstract: c-FLIP inhibits caspase 8 activation and apoptosis mediated by death receptors such as Fas and DR5. We studied the effect of c-FLIP on the apoptotic response to chemotherapies used in colorectal cancer (CRC) (5-fluorouracil, oxaliplatin and irinotecan). Simultaneous downregulation of both c-FLIP splice forms c-FLIP(L) and c-FLIP(S) with siRNA synergistically enhanced chemotherapy-induced apoptosis in p53 wild-type (HCT116p53(+/+), RKO), null (HCT116p53(-/-)) and mutant (H630) CRC cell lines. Furthermore, overexpression of c-FLIP(L), but not c-FLIP(S), potently inhibited apoptosis induced by chemotherapy in HCT116p53(+/+) cells, suggesting that c-FLIP(L) was the more important splice form in mediating chemoresistance. In support of this, siRNA specifically targeted against c-FLIP(L) synergistically enhanced chemotherapy-induced apoptosis in a manner similar to the siRNA targeted against both splice forms. Inhibition of caspase 8 blocked the enhanced apoptosis induced by c-FLIP-targeted (FT) siRNA and chemotherapy. Furthermore, we found that downregulating cell surface DR5, but not Fas, also inhibited apoptosis induced by FT siRNA and chemotherapy. Interestingly, these effects were not dependent on activation of DR5 by its ligand TRAIL. These results indicate that c-FLIP inhibits TRAIL-independent, DR5- and caspase 8-dependent apoptosis in response to chemotherapy in CRC cells. Moreover, targeting c-FLIP in combination with existing chemotherapies may have therapeutic potential for the treatment of CRC.
authors.affiliation: Drug Resistance Group, Centre for Cancer Research and Cell Biology, Queen's University Belfast, University Floor, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, UK. d.longley@qub.ac.uk
authors.forename: D B
authors.initials: DB
authors.lastname: Longley
authors.forename: T R
authors.initials: TR
authors.lastname: Wilson
authors.forename: M
authors.initials: M
authors.lastname: McEwan
authors.forename: W L
authors.initials: WL
authors.lastname: Allen
authors.forename: U
authors.initials: U
authors.lastname: McDermott
authors.forename: L
authors.initials: L
authors.lastname: Galligan
authors.forename: P G
authors.initials: PG
authors.lastname: Johnston
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000378:metabolism; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D015536:Down-Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D019154:Protein Splicing; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D019014:fas Receptor / Q000187:drug effects / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D061945:Caspase Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases