title: Role of SGK1 for fatty acid uptake, cell survival and radioresistance of NCI-H460 lung cancer cells exposed to acute or chronic cycling severe hypoxia.
abstract: BACKGROUND
  Unsaturated fatty acids (FA) are required for cancer cell growth. In normoxia cells can generate unsaturated FA from saturated stearic and palmitic acid by desaturation. However, since the desaturation step is oxygen-dependent hypoxic cancer cells display an increased dependence on the uptake of unsaturated FA. Up to now the mechanism of increased FA uptake in hypoxia is largely unknown. Here we aimed to study the role of human serum and glucocorticoid-inducible kinase (SGK1) in the regulation of FA uptake in cancer cells exposed to acute or chronic cycling hypoxia and explore its use as target for the radiosensitization of hypoxic cancer cells.
  
  
  METHODS
  The effect of SGK1-inhibition (GSK650394) on NCI-H460 lung adenocarcinoma cells exposed to normoxia, acute or chronic cycling hypoxia was analyzed under standard and serum-deprived conditions by short-term proliferation, apoptosis and cell death assays. The impact of SGK1-inhibition on radiation sensitivity was determined by standard colony formation assays. The effect of GSK650394 on FA uptake was quantified by measuring intracellular accumulation of fluorescent FA (C1-BODIPY®-C12).
  
  
  RESULTS
  Exposure to acute or chronic cycling hypoxia was associated with up-regulated expression of SGK1 in NCI-H460 cells, increased uptake of FA from the culture medium, and increased sensitivity to serum deprivation. Survival of serum-deprived hypoxic NCI-H460 cells was rescued by the addition of the unsaturated FA, oleic acid, whereas the saturated FA, palmitic acid was highly toxic to the hypoxic cancer cells. Interestingly, SGK1 inhibition abrogated the rescue effect of oleic acid in serum-deprived hypoxic cancer cells and this effect was associated with a reduction in FA uptake particularly in anoxia-tolerant cancer cells exposed to severe hypoxia. Finally, SKG1 inhibition decreased long-term survival and potently sensitized the parental and anoxia-tolerant NCI-H460 cells to the cytotoxic effects of ionizing radiation in normoxia as well as the anoxia-tolerant cancer cells in severe hypoxia.
  
  
  CONCLUSIONS
  Our data suggest that SGK1 plays a role in the regulation of FA uptake that becomes essential under conditions of acute or chronic cycling hypoxia. We assume that SGK1 may represent a promising therapeutic target for the eradication of hypoxic cancer cells.
authors.affiliation: Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital Essen, Virchowstrasse 173, 45122, Essen, Germany.
authors.forename: Johann
authors.initials: J
authors.lastname: Matschke
authors.affiliation: Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital Essen, Virchowstrasse 173, 45122, Essen, Germany.
authors.forename: Elisa
authors.initials: E
authors.lastname: Wiebeck
authors.affiliation: Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital Essen, Virchowstrasse 173, 45122, Essen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hurst
authors.affiliation: Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital Essen, Virchowstrasse 173, 45122, Essen, Germany.
authors.forename: Justine
authors.initials: J
authors.lastname: Rudner
authors.affiliation: Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital Essen, Virchowstrasse 173, 45122, Essen, Germany. verena.jendrossek@uni-due.de.
authors.forename: Verena
authors.initials: V
authors.lastname: Jendrossek
mesh_terms: D000208:Acute Disease; D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects; D015153:Blotting, Western; D049109:Cell Proliferation / Q000502:physiology / Q000528:radiation effects; D002908:Chronic Disease; D005227:Fatty Acids / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011836:Radiation Tolerance; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D005227:Fatty Acids; D017874:Immediate-Early Proteins; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D000099184:Serum-Glucocorticoid Regulated Kinases
keywords: Fatty acid uptake; Hypoxia; Ionizing radiation; Oleic acid; Radioresistance; SCD1; SGK1; Unsaturated fatty acids