title: Identification of cyclooxygenase-2 as a major actor of the transcriptomic adaptation of endothelial and tumor cells to cyclic hypoxia: effect on angiogenesis and metastases.
abstract: OBJECTIVE
  Cyclic hypoxia in tumors originates from heterogeneities in RBC flux and influences not only tumor cells but also endothelial cells lining tumor blood vessels. Whether pO(2) fluctuations, particularly transient reoxygenation periods, alter the well-known hypoxia-inducible factor (HIF)-dependent gene program is largely unknown.
  
  
  METHODS
  We compared the transcriptomic profiles of endothelial and tumor cells exposed to cyclic hypoxia versus continuous hypoxia to uncover a possible differential effect on angiogenesis and metastases.
  
  
  RESULTS
  Microarray analyses identified early genes that were selectively induced by cyclic hypoxia in endothelial cells. Among them, we focused on PTGS2 because the observed increase in mRNA expression led to a significant increase in the expression and activity of cyclooxygenase-2 (COX-2; the protein product of PTGS2). HIF-1alpha was shown to be stabilized by cyclic hypoxia (despite reoxygenation periods) and to favor COX-2 induction as validated by the use of echinomycin and HIF-1alpha targeting small interfering RNA. Using a specific COX-2 inhibitor and a dedicated COX-2 targeting small interfering RNA, we documented that COX-2 accounted for the higher endothelial cell survival and angiogenic potential conferred by cyclic hypoxia. Cyclic hypoxia also led to a preferential COX-2 induction in tumor cells and, contrary to continuous hypoxia, fostered a higher metastatic take of prechallenged tumor cells.
  
  
  CONCLUSIONS
  Our study documents that PTGS2/COX-2 is part of a cyclic hypoxia gene signature and largely accounts for the unique phenotype of endothelial and tumor cells exposed to fluctuations in pO(2), thereby offering new perspectives for the clustering of tumors expressing COX-2 together with other cyclic hypoxia-responsive genes.
authors.affiliation: Université catholique de Louvain, Unit of Pharmacology and Therapeutics (UCL-FATH 5349), Brussels, Belgium.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Daneau
authors.forename: Romain
authors.initials: R
authors.lastname: Boidot
authors.forename: Philippe
authors.initials: P
authors.lastname: Martinive
authors.forename: Olivier
authors.initials: O
authors.lastname: Feron
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics*; D000818:Animals; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology / Q000502:physiology*; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D006801:Humans; D051379:Mice; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D009389:Neovascularization, Pathologic / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D010100:Oxygen / Q000494:pharmacology; D010507:Periodicity; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays
chemical_list: D034741:RNA, Small Interfering; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D010100:Oxygen