title: Growth factor-mediated induction of HDM2 positively regulates hypoxia-inducible factor 1alpha expression.
abstract: The hypoxia-inducible factor 1 (HIF-1) transcriptional complex is regulated by cellular oxygen levels and growth factors. The phosphoinosotide 3-kinase (PI-3K)-Akt/protein kinase B (PKB) pathway has been shown to regulate HIF-1 activity in response to oncogenic signals and growth factors. We assessed whether the HDM2 oncoprotein, a direct target of Akt/PKB, could regulate HIF-1alpha expression and HIF-1 activity under normoxic conditions. We found that growth factor stimulation, overexpression of Akt/PKB, or loss of PTEN resulted in enhanced expression of both HIF-1alpha and HDM2. Growth factor-mediated induction of HIF-1alpha was ablated by transient expression of a dominant negative form of Akt/PKB or by treatment with LY294002. Transient expression of HDM2 led to increased expression of HIF-1alpha. Pulse-chase and cycloheximide experiments revealed that HDM2 did not significantly affect the half-life of HIF-1alpha. Growth factor-induced HIF-1alpha and HDM2 proteins were localized to the nucleus, and induction of both proteins was observed in both p53(+/+) and p53(-/-) HCT116 cells to comparable levels. Importantly, insulin-like growth factor 1-induced HIF-1alpha expression was observed in p53-null mouse embryo fibroblasts (MEFs) but was significantly impaired in p53 Mdm2 double-null MEFs, indicating a requirement for Mdm2 in this process. Finally, we showed that phosphorylation at Ser166 in HDM2 contributed in part to growth factor-mediated induction of HIF-1alpha. Our study has important implications for the role of the PI-3K-Akt/PKB-HDM2 pathway in tumor progression and angiogenesis.
authors.affiliation: Cell Growth Regulation and Angiogenesis Laboratory, Cancer Research UK Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, Surrey SM2 5NG, United Kingdom.
authors.forename: Julia I
authors.initials: JI
authors.lastname: Bárdos
authors.forename: Noan-Minh
authors.initials: NM
authors.lastname: Chau
authors.forename: Margaret
authors.initials: M
authors.lastname: Ashcroft
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002867:Chromones / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006133:Growth Substances / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D009025:Morpholines / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051736:Proto-Oncogene Proteins c-mdm2; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D002867:Chromones; D004791:Enzyme Inhibitors; D006133:Growth Substances; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009025:Morpholines; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051736:Proto-Oncogene Proteins c-mdm2; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C497442:HIF1A protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; C494918:AKT1 protein, human