title: Role of hypoxia-inducible factor (HIF)-1alpha versus HIF-2alpha in the regulation of HIF target genes in response to hypoxia, insulin-like growth factor-I, or loss of von Hippel-Lindau function: implications for targeting the HIF pathway.
abstract: Overexpression of hypoxia-inducible factors (HIF), HIF-1alpha and HIF-2alpha, leads to the up-regulation of genes involved in proliferation, angiogenesis, and glucose metabolism and is associated with tumor progression in several cancers. However, the contribution of HIF-1alpha versus HIF-2alpha to vascular endothelial growth factor (VEGF) expression and other HIF-regulated target genes under different conditions is unclear. To address this, we used small interfering RNA (siRNA) techniques to knockdown HIF-1alpha and/or HIF-2alpha expression in response to hypoxia, insulin-like growth factor (IGF)-I, or renal carcinoma cells expressing constitutively high basal levels of HIF-1alpha and/or HIF-2alpha due to loss of von Hippel-Lindau (VHL) function. We found that HIF-1alpha primarily regulates transcriptional activation of VEGF in response to hypoxia and IGF-I compared with HIF-2alpha in MCF-7 cells. We also observed a reciprocal relationship between HIF-1alpha and HIF-2alpha expression in hypoxia in these cells: HIF-2alpha siRNA enhanced HIF-1alpha-mediated VEGF expression in MCF-7 cells in response to hypoxia, which could be completely blocked by cotransfection with HIF-1alpha siRNA. In contrast, in renal carcinoma cells that constitutively express HIF-1alpha and HIF-2alpha due to loss of VHL function, we found that high basal VEGF, glucose transporter-1, urokinase-type plasminogen activator receptor, and plasminogen activator inhibitor-1 expression was predominantly dependent on HIF-2alpha. Finally, we showed that a newly identified small-molecule inhibitor of HIF-1, NSC-134754, is also able to significantly decrease HIF-2alpha protein expression and HIF-2alpha-regulated VEGF levels in renal carcinoma cells. Our data have important implications for how we target the HIF pathway therapeutically.
authors.affiliation: Cell Growth Regulation and Angiogenesis Laboratory, Cancer Research UK Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, United Kingdom.
authors.forename: Veronica A
authors.initials: VA
authors.lastname: Carroll
authors.forename: Margaret
authors.initials: M
authors.lastname: Ashcroft
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism; D002292:Carcinoma, Renal Cell / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D018390:Gene Targeting; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D007680:Kidney Neoplasms / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis / Q000235:genetics; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007334:Insulin-Like Growth Factor I; D007546:Isoquinolines; D034741:RNA, Small Interfering; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C502338:NSC-134754; C497446:VHL protein, human