title: Cyclooxygenase-2 overexpression reduces apoptotic susceptibility by inhibiting the cytochrome c-dependent apoptotic pathway in human colon cancer cells.
abstract: The cyclooxygenase-2 (COX-2) gene encodes an inducible enzyme that converts arachidonic acid to prostaglandins and is up-regulated in colorectal neoplasms. Evidence indicates that COX-2 may regulate apoptosis and can influence the malignant phenotype. Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit COX enzymes and induce apoptosis in colorectal cancer cell lines, which may contribute to their antitumor effects. To determine whether forced COX-2 expression modulates susceptibility to drug-induced apoptosis, HCT-15 colon carcinoma cells were stably transfected with the COX-2 cDNA, and two clones overexpressing COX-2 were isolated. Selective COX-2 (NS398) and nonselective (sulindac sulfide) COX inhibitors, as well as 5-fluorouracil (5-FU), induced apoptosis (terminal deoxynucleotidyl transferase-mediated nick end labeling in a dosage-dependent manner. Forced COX-2 expression significantly attenuated induction of apoptosis by all three of the drugs compared with parental HCT-15 cells. NSAIDs and 5-FU induced the mitochondrial release of cytochrome c as well as caspase-3 and -9 activation, and to a much lesser extent, caspase-8. COX-2-overexpressing cells showed reduced cytochrome c and caspase activation, relative to parental cells. A specific inhibitor of caspase-3 restored cell survival after drug treatment. COX-2 transfectants were found to overexpress the antiapoptotic Bcl-2 mRNA and protein relative to parental cells. In conclusion, forced COX-2 expression significantly attenuates apoptosis induction by NSAIDs and 5-FU through predominant inhibition of the cytochrome c-dependent apoptotic pathway. COX-2-mediated up-regulation of Bcl-2 suggests a potential mechanism for reduced apoptotic susceptibility.
authors.affiliation: Department of Gastrointestinal Medicine and Nutrition, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: Yunjie
authors.initials: Y
authors.lastname: Sun
authors.forename: Xi Ming
authors.initials: XM
authors.lastname: Tang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Half
authors.forename: M Tien
authors.initials: MT
authors.lastname: Kuo
authors.forename: Frank A
authors.initials: FA
authors.lastname: Sinicrope
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D003110:Colonic Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology*; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000037:antagonists & inhibitors* / Q000502:physiology; D015232:Dinoprostone / Q000096:biosynthesis; D004789:Enzyme Activation; D005472:Fluorouracil / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008565:Membrane Proteins; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D009578:Nitrobenzenes / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D061945:Caspase Inhibitors; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D003574:Cytochrome c Group; D007527:Isoenzymes; D008565:Membrane Proteins; D009578:Nitrobenzenes; D019384:Nucleic Acid Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D020169:Caspases; D015232:Dinoprostone; D005472:Fluorouracil