title: Cell cycle kinase inhibitor expression and hypoxia-induced cell cycle arrest in human cancer cell lines.
abstract: Flow cytometric analysis of fibroblasts, normal breast epithelial cells and breast or other cancer cell lines identified variation in the abilities of cell lines to undergo cell cycle arrest as a response to hypoxia. Human mammary epithelial cells (HMEC), normal fibroblasts (Hs68 and WI38), HeLa cervical carcinoma and HTB-30 breast carcinoma cells arrest in G(1)/S in response to severe hypoxia. Hep3B hepatocellular carcinoma cells did not exhibit orderly G(1)/S arrest in response to severe hypoxia. We found a general decrease in p16(INK4a) (p16) mRNA levels, with an associated decrease in p16 protein levels in both normal cells and in cancer cells, regardless of their cell cycle response to hypoxia. p27 protein levels did not correlate with the cell line's ability to enter a hypoxic G(1)/S arrest. Furthermore, cell lines that underwent G(1)/S arrest showed decreased expression of hypoxia inducible factor 1 (HIF-1alpha) and at least one member of INK4 or Sdi cell cycle kinase inhibitors families after 12-24 h of hypoxia. Conversely, Hep3B, which did not exhibit orderly hypoxia-associated G(1)/S arrest, also did not show decreased HIF-1alpha, INK4 or Sdi protein levels in hypoxia. Furthermore, Hep3B showed constitutive activating phosphorylation of Akt and inhibitory phosphorylation of GSK3beta, which was the opposite pattern to that exhibited by the cell lines showing the G(1)/S arrest phenotype. Inhibition of GSK3beta by lithium chloride treatment of HeLa cells converted the HIF-1alpha, p16 and p27 loss to levels unchanged by hypoxic exposure. Our results suggest that regulation of the cell cycle during hypoxia in either normal or cancer cells is not simply due to up-regulation of cell cycle kinase inhibitors. Furthermore, decreased protein expression of HIF-1alpha, p16 and p27 was associated with both a hypoxia-induced G(1)/S arrest phenotype and increased GSK3beta activity.
authors.affiliation: Department of Pathology and The University of Calgary and Calgary Laboratory Services, Calgary, Alberta, Canada, T2N 4N1.
authors.forename: Adrian Harold
authors.initials: AH
authors.lastname: Box
authors.forename: Douglas James
authors.initials: DJ
authors.lastname: Demetrick
mesh_terms: D017209:Apoptosis; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D016193:G1 Phase; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006367:HeLa Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016196:S Phase; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C494918:AKT1 protein, human; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3