title: Overexpression of COX-2 in human osteosarcoma cells decreases proliferation and increases apoptosis.
abstract: Overexpression of cyclooxygenase-2 (COX-2) is generally considered to promote tumorigenesis. To investigate a potential role of COX-2 in osteosarcoma, we overexpressed COX-2 in human osteosarcoma cells. Saos-2 cells deficient in COX-2 expression were retrovirally transduced or stably transfected with murine COX-2 cDNA. Functional expression of COX-2 was confirmed by Northern and Western analyses and prostaglandin production. Overexpression of COX-2 reduced cell numbers by 50% to 70% compared with controls. Decreased proliferation in COX-2-overexpressing cells was associated with cell cycle prolongation in G(2)-M. Apoptosis, measured by both Annexin V binding assay and terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling staining, was increased in cells overexpressing COX-2, and the increase was not reversed by treatment with NS-398, indicating that the effects were not mediated by prostaglandins. Retroviral COX-2 overexpression in two other human osteosarcoma cell lines, U2OS and TE85, also decreased cell viability. However, in the human colon carcinoma HCT-116 cell line, which is deficient in COX-2, retroviral overexpression of COX-2, at similar efficiency as in Saos-2 cells, increased resistance to apoptosis. Reactive oxygen species (ROS), measured by flow cytometry, were increased by COX-2 overexpression in Saos-2 cells but not in HCT-116 cells. Inhibition of peroxidase activity, but not of COX activity, blocked the ROS increase. Antioxidants blocked the increase in ROS and the increase in apoptosis due to COX-2 overexpression in Saos-2 cells. Our results suggest that (a) COX-2 overexpression in osteosarcoma cells may increase resistance to tumorigenesis by increasing ROS to levels that decrease cell viability and (b) the effects of COX-2 overexpression are cell type/tissue dependent.
authors.affiliation: Department of Medicine, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030, USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Xu
authors.forename: Shilpa
authors.initials: S
authors.lastname: Choudhary
authors.forename: Olga
authors.initials: O
authors.lastname: Voznesensky
authors.forename: Meenal
authors.initials: M
authors.lastname: Mehrotra
authors.forename: Monica
authors.initials: M
authors.lastname: Woodard
authors.forename: Marc
authors.initials: M
authors.lastname: Hansen
authors.forename: Harvey
authors.initials: H
authors.lastname: Herschman
authors.forename: Carol
authors.initials: C
authors.lastname: Pilbeam
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology; D001859:Bone Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology*; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000235:genetics; D015232:Dinoprostone / Q000494:pharmacology; D045325:HCT116 Cells; D006801:Humans; D012516:Osteosarcoma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D014161:Transduction, Genetic; D014162:Transfection
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D051546:Cyclooxygenase 2; D015232:Dinoprostone