4-Hydroxy estradiol but not 2-hydroxy estradiol induces expression of hypoxia-inducible factor 1alpha and vascular endothelial growth factor A through phosphatidylinositol 3-kinase/Akt/FRAP pathway in OVCAR-3 and A2780-CP70 human ovarian carcinoma cells

Toxicol Appl Pharmacol. 2004 Apr 1;196(1):124-35. doi: 10.1016/j.taap.2003.12.002.


Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic helix-loop-helix transcription factor composed of HIF-1alpha and HIF-1beta subunits. HIF-1 expression is induced by hypoxia, growth factors, and activation of oncogenes. HIF-1 activates downstream target genes such as vascular endothelial growth factor A (VEGF-A), which plays an important role in tumor progression and angiogenesis. Estrogen exposure is considered to be the major risk factor for ovarian cancer. Estradiol (E2) is usually metabolized by CYP1A1/1A2 and CYP3A4 to the 2-hydroxy estradiol (2-OHE2) and 4-hydroxy estradiol (4-OHE2) in human liver. Many reports have suggested that the formation of 4-OHE2 is important for mammary carcinogenesis. However, the formation of 2-OHE2 may play an important role in exhibiting anticarcinogenic effects. In the present study, we have demonstrated that one of the catechol estrogen metabolites of E2, 4-OHE2, induces HIF-1alpha and VEGF-A expression at protein level in two human ovarian cancer cell lines, OVCAR-3 and A2780-CP70 cells, in dose- and time-dependent manners, whereas the other catechol estrogen metabolite of E2, 2-OHE2, does not alter HIF-1alpha and VEGF-A expression. To explore the mechanism of 4-OHE2-induced HIF-1alpha and VEGF-A expression, we studied whether phosphatidylinositol 3-kinase (PI3K) or mitogen-activated protein kinase (MAPK) signaling pathways are involved in 4-OHE2-induced HIF-1alpha and VEGF-A expression. Our findings indicate that PI3K inhibitors, LY294002 and wortmannin, inhibited HIF-1alpha and VEGF-A expression, whereas MAPK inhibitor, PD98059, did not alter HIF-1alpha and VEGF-A expression induced by 4-OHE2. 4-OHE2, but not 2-OHE2, also induced Akt phosphorylation at Ser473 in dose- and time-dependent manners, and LY294002 and wortmannin inhibited Akt phosphorylation at Ser473 induced by 4-OHE2. Our results also indicated that the mTOR/FRAP inhibitor, rapamycin, inhibited 4-OHE2-induced HIF-1alpha and VEGF-A expression. These results suggest that the PI3K/Akt/FRAP signaling pathway is required for HIF-1alpha and VEGF-A expression induced by 4-OHE2, whereas the MAPK pathway is not required. The finding that induction of HIF-1alpha and VEGF-A expression occurs via the activation of the PI3K/Akt/FRAP signaling pathway could be an important mechanism of 4-OHE2-induced carcinogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Enzyme Inhibitors / pharmacology
  • Estradiol / analogs & derivatives*
  • Estradiol / toxicity*
  • Estrogens, Catechol
  • Female
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • Mitogen-Activated Protein Kinases / metabolism
  • Ovarian Neoplasms / metabolism
  • Ovarian Neoplasms / pathology
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Signal Transduction / drug effects
  • Transcription Factors / biosynthesis*
  • Vascular Endothelial Growth Factor A / biosynthesis*


  • Enzyme Inhibitors
  • Estrogens, Catechol
  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins
  • Transcription Factors
  • Vascular Endothelial Growth Factor A
  • Estradiol
  • 2-hydroxyestradiol
  • 4-hydroxyestradiol
  • AKT1 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases