title: A hypoxia-independent hypoxia-inducible factor-1 activation pathway induced by phosphatidylinositol-3 kinase/Akt in HER2 overexpressing cells.
abstract: HER2 overexpression, a known prognostic factor in many human cancers, can activate phosphatidylinositol-3 kinase (PI-3K)/Akt pathways and plays an important role in mediating cell survival and tumor development. Hypoxia-inducible factors (HIFs) promote angiogenesis and energy metabolism and thereby enhance tumor growth and metastasis. HIFs, composed of alpha and beta subunits, are activated in most human cancers, including those that overexpress HER2. Previous reports have suggested that increased PI-3K/Akt or decreased PTEN activity may activate the HIF pathway in various tumors, but the detailed mechanism is still not completely understood. Here we reported an interaction between the HIF and PI-3K/Akt pathways in HER2-overexpressing cancer cells. Our results indicate that HER2 overexpression, which results in constitutively active Akt, turns on HIF-1alpha independently of hypoxia, and this activation is weaker than that under hypoxic condition. Further investigation showed that Akt is required for the hypoxia-independent HIF activity. The PI-3K/Akt pathway did not affect the HIF-1alpha binding with its E3 ligase von Hippel-Lindau but enhanced the binding affinity between the HIF-1 alpha and beta subunits. Furthermore, we found that Akt interacts with HIF-1beta and regulates HIF activity. Our results indicated that HER2 can induce HIF activation via the activation of Akt suggesting that activation of HER2/Akt pathway may promote angiogenesis independent of hypoxia, which may have important implications for the oncogenic activity of HER2 and Akt.
authors.affiliation: Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Yan M
authors.initials: YM
authors.lastname: Li
authors.forename: Binhua P
authors.initials: BP
authors.lastname: Zhou
authors.forename: Jiong
authors.initials: J
authors.lastname: Deng
authors.forename: Yong
authors.initials: Y
authors.lastname: Pan
authors.forename: Nissim
authors.initials: N
authors.lastname: Hay
authors.forename: Mien-Chie
authors.initials: MC
authors.lastname: Hung
mesh_terms: D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; 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; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D051794:Von Hippel-Lindau Tumor Suppressor Protein
chemical_list: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D004268:DNA-Binding Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; C497396:ARNT protein, human; C497397:Arnt protein, mouse; C497442:HIF1A protein, human; C494918:AKT1 protein, human; C497446:VHL protein, human