title: Phosphatidylinositol 3-kinase and mek1/2 are necessary for insulin-like growth factor-I-induced vascular endothelial growth factor synthesis in prostate epithelial cells: a role for hypoxia-inducible factor-1?
abstract: Due to the importance of vascular endothelial growth factor (VEGF) in the neovascularization of solid tumors, a clear understanding of how VEGF is regulated in normal and tumor cells is warranted. We investigated insulin-like growth factor (IGF)-I-stimulated signaling pathways that increase the rate of VEGF synthesis in primary cultures of normal prostate epithelial cells (PrEC). IGF-I increased the secretion of VEGF(165) into PrEC growth medium and stimulated transcription of a reporter gene driven by a 1.5-kb region of the VEGF promoter. Inhibition of either phosphatidylinositol 3-kinase (PI3-K) or Mek1/2 signaling pathways completely abrogated the IGF-I-induced increase in VEGF secretion and promoter activity, indicating a dependence on coordinate signaling from both pathways to produce this effect. Levels of the transcription factors hypoxia-inducible factor (HIF)-1 and Fos were elevated in response to IGF-I in a PI3-K-dependent and Mek1/2-dependent manner, respectively. The expression of an activator protein (AP)-1 dominant negative in an immortalized prostate epithelial cell line PZ-HPV-7 suppressed the IGF-I-induced increase in VEGF promoter activity. Mutation of the hypoxia response element (HRE), which mediates hypoxic stimulation of VEGF transcription, did not inhibit the effect of IGF-I on the VEGF promoter, despite the fact that this mutation inhibited PI3-K-stimulated VEGF promoter activity in prostate cancer cells. These data indicate that PI3-K signaling does not increase VEGF transcription through transactivation by HIF-1 at the HRE in normal PrEC. This work also suggests that an additional signal, not stimulated by IGF-I in PrEC, is needed for HIF-1 to stimulate transcription from the VEGF HRE.
authors.affiliation: Hormones and Cancer Group, Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Burroughs
authors.forename: Jennifer
authors.initials: J
authors.lastname: Oh
authors.forename: J Carl
authors.initials: JC
authors.lastname: Barrett
authors.forename: Richard P
authors.initials: RP
authors.lastname: DiAugustine
mesh_terms: D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D009687:Nuclear Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011467:Prostate / Q000166:cytology; D013997:Time Factors; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000187:drug effects; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis*
chemical_list: D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; C065700:myotrophin; D019869:Phosphatidylinositol 3-Kinases