title: Overexpression of cyclooxygenase-2 induces cell cycle arrest. Evidence for a prostaglandin-independent mechanism.
abstract: The immediate-early gene cyclooxygenase 2 (Cox-2) is induced in a variety of hyperplastic pathological conditions, including rheumatoid arthritis and colorectal cancer. Although a causal role for Cox-2 has been proposed, mechanisms by which Cox-2 function contributes to the pathogenesis of hyperplastic disease are not well defined. We constructed a green fluorescent protein-tagged Cox-2 (Cox-2-GFP) to examine its effects on a variety of cell types upon overexpression. Subcellular localization and enzymatic and pharmacological properties of Cox-2-GFP polypeptide were indistinguishable from those of the wild-type Cox-2 polypeptide. Overexpression of the Cox-2-GFP or the Cox-2 polypeptide by transient transfection suppressed the population of cells in the S phase of the cell cycle, with a concomitant increase in G(0)/G(1) population. In contrast, transient overexpression of GFP had no effect on cell cycle distribution, whereas endoplasmic reticulum-retained GFP (GFP-KDEL) overexpression was associated with only a minor decrease of cells in S phase. Interestingly, neither NS-398 (a Cox-2-specific inhibitor) nor indomethacin could reverse the effect of Cox-2-GFP overexpression on cell cycle progression. Furthermore, two mutants of Cox-2, S516Q and S516M, which lack the cyclooxygenase activity, exhibited the same effect as Cox-2-GFP. The cell cycle effect of Cox-2-GFP was observed in ECV-304, NIH 3T3, COS-7, bovine microvascular endothelial cells, and human embryonic kidney 293 cells. These findings suggest that Cox-2 inhibits cell cycle progression in a variety of cell types by a novel mechanism that does not require the synthesis of prostaglandins.
authors.affiliation: Center for Vascular Biology, Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030-3505, USA.
authors.forename: O C
authors.initials: OC
authors.lastname: Trifan
authors.forename: R M
authors.initials: RM
authors.lastname: Smith
authors.forename: B D
authors.initials: BD
authors.lastname: Thompson
authors.forename: T
authors.initials: T
authors.lastname: Hla
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D051546:Cyclooxygenase 2; D016193:G1 Phase / Q000235:genetics / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D049452:Green Fluorescent Proteins; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D008856:Microscopy, Fluorescence; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics* / Q000378:metabolism; D011453:Prostaglandins / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000502:physiology; D014162:Transfection
chemical_list: D007527:Isoenzymes; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011453:Prostaglandins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases