title: Activators of protein kinase C selectively mediate cellular cytotoxicity to hypoxic cells and not aerobic cells.
abstract: OBJECTIVE
  By understanding the signal transduction pathways through which a cell responds to changes in environmental oxygen levels, we may be able to therapeutically exploit this response by manipulating these pathways.
  
  
  METHODS
  The human adenocarcinoma cell line A549 was exposed to varying durations of hypoxia alone and then plated for survival, or treated with PKC activating agents for 1 h before plating for survival. Western blots were used to determine the kinetics of PKC epsilon and phospholipase C induction.
  
  
  RESULTS
  The level of hypoxic killing was directly related to the time of exposure and inversely related to the level of oxygen in the environment. Exposure of the cells to protein kinase C (PKC) activators for 1 h after chronic hypoxic exposure increased cell killing by at least an additional three logs beyond that found for hypoxia alone. Treatment of cells with an inactive phorbol ester 4 alpha-phorbol-12,13-didecanoate (PDA) resulted in no increase in hypoxic cell killing, even at the highest concentrations of PDA which produced no detectable toxicity under normal aerobic conditions. Using inhibitors of phospholipases A2 and C, we were able to completely inhibit the additional hypoxic cell killing induced by TPA, but not the uninduced hypoxic cell killing.
  
  
  CONCLUSIONS
  These studies suggest that accumulation of phospholipid breakdown products may be responsible for TPA induced cell killing, and that hypoxic cells differ from aerobic cells in their ability to tolerate these products.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, CA 94305-5468.
authors.forename: A C
authors.initials: AC
authors.lastname: Koong
authors.forename: E Y
authors.initials: EY
authors.lastname: Chen
authors.forename: C Y
authors.initials: CY
authors.lastname: Kim
authors.forename: A J
authors.initials: AJ
authors.lastname: Giaccia
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D015687:Cell Hypoxia; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation; D006801:Humans; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D010703:Phorbol Esters; C008876:phorbol-12,13-didecanoate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate