title: MUC16 mucin (CA125) attenuates TRAIL-induced apoptosis by decreasing TRAIL receptor R2 expression and increasing c-FLIP expression.
abstract: BACKGROUND
  MUC16 (CA125) is a large transmembrane mucin protein (> 200 kDa) aberrantly expressed in approximately 80% of human epithelial ovarian cancers (EOC). MUC16 expression in EOC cells is associated with increased tumorigenesis and inhibiton of genotoxic drug-induced apoptosis. However, the mechanism by which MUC16 mediates these effects is unknown. In the present study, we investigated the mechanisms by which MUC16 attenuates TRAIL-induced apoptosis.
  
  
  METHODS
  MUC16 expression was down-regulated by stably expressing an anti-MUC16 single-chain antibody (scFv) targeted to the endoplasmic reticulum (ER), which prevents cell surface localization of MUC16 in OVCAR3 cells. We also generated a MUC16 C-terminal domain (MUC16CTD) construct that was stably expressed in MUC16 negative SKOV3 cells.
  
  
  RESULTS
  We show that MUC16 attenuates apoptosis, activation of caspase-8 and mitochondria activation in EOC cells in response to TRAIL. MUC16 decreases TRAIL receptor R2 (DR5) expression and inhibits pro-caspase-8 activation at the death-inducing signaling complex (DISC). MUC16CTD expression is sufficient to attenuate the TRAIL signaling cascade. MUC16 knockdown decreases caspase-8 inhibitor cFLIP mRNA levels, increases cFLIP degradation, and consequently increases TRAIL-induced apoptosis. Down-regulation of cFLIP following treatment of MUC16-expressing OVCAR3 cells with cFLIP siRNA also increases TRAIL-induced apoptosis.
  
  
  CONCLUSIONS
  These findings indicate that MUC16 protects EOC cells against TRAIL-induced apoptosis through multiple mechanisms including the blockade of TRAIL R2 expression and the regulation of cFLIP expression at both the transcriptional and the protein level.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Matte
authors.forename: Denis
authors.initials: D
authors.lastname: Lane
authors.forename: Marianne
authors.initials: M
authors.lastname: Boivin
authors.forename: Claudine
authors.initials: C
authors.lastname: Rancourt
authors.affiliation: Département de Microbiologie et Infectiologie, Faculté de Médecine et des sciences de la santé, Université de Sherbrooke, 3001, 12ième Avenue Nord, Sherbrooke, Québec J1H 5N4, Canada. alain.piche@usherbrooke.ca.
authors.forename: Alain
authors.initials: A
authors.lastname: Piché
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D018394:CA-125 Antigen / Q000235:genetics* / Q000378:metabolism; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000096:biosynthesis*; D063646:Carcinogenesis / Q000235:genetics; D000077216:Carcinoma, Ovarian Epithelial; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009375:Neoplasms, Glandular and Epithelial / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D059748:Proteolysis; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000096:biosynthesis* / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000096:biosynthesis* / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D018394:CA-125 Antigen; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C451759:MUC16 protein, human; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D053181:Caspase 8