Hypoxia-Inducible Factor-1-Dependent and -Independent Regulation of Insulin-Like Growth Factor-1-Stimulated Vascular Endothelial Growth Factor Secretion
- Department of Cell and Molecular Pharmacology and Experimental Therapeutics (M.G.S., S.A.R.) and Hollings Cancer Center (S.A.R.), Medical University of South Carolina, Charleston, South Carolina
- Address correspondence to:
Dr. Steven A. Rosenzweig, Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, 173 Ashley Ave., Charleston, SC 29425. E-mail: rosenzsa{at}musc.edu
Abstract
Hypoxia-induced stress plays a central role in retinal vascular disease and cancer. Increased hypoxia-inducible factor-1α (Hif-1α) expression leads to HIF-1 formation and the production of vascular endothelial growth factor (VEGF). Cytokines, including insulin-like growth factor-1 (IGF-1), also stimulate VEGF secretion. In this study, we examined the relationship between IGF-1 signaling, HIF-1α protein turnover and VEGF secretion in the ARPE-19 retinal pigment epithelial cell line. Northern analysis revealed that IGF-1 stimulated Hif-1α message expression, whereas the hypoxia-mimetic CoCl2 did not. CoCl2 treatment increased Hif-1α protein accumulation to a greater extent than IGF-1 treatment. However, IGF-1 stimulated a more significant increase in VEGF secretion. IGF-1-stimulated VEGF promoter activity was phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR (mammalian target of rapamycin)-dependent, whereas VEGF secretion was only partially reduced by inhibition of PI3K/Akt/mTOR and HIF-1 activities. Analysis of VEGF promoter truncation mutants indicated that sensitivity to CoCl2 was hypoxia response element (HRE)-dependent with the region upstream of the HRE conferring IGF-1 sensitivity. In conclusion, IGF-1 regulates VEGF expression and secretion via HIF-1-dependent and -independent pathways.
Footnotes
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This work was supported, in part, by Grant CA78887 from the National Institutes of Health, a Department of Defense grant to Hollings Cancer Center, (N6311601MD10004) and a research award from the American Health Assistance Foundation to S.A.R. M.G.S. was funded in part, by an Abney Foundation Research Scholars Award. A portion of this work was presented at the Retinal and Choroidal Angiogenesis Scientific Symposium; 2005 Oct 15-16; Nashville, TN.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.104158.
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ABBREVIATIONS: VEGF, vascular endothelial growth factor; CNV, choroidal neovascularization; RPE, retinal pigment epithelium; IGF, insulin-like growth factor; IGFBP, IGF-binding protein; IGF-1R, IGF-1 receptor; HIF-1, hypoxia-inducible factor-1; HRE, hypoxia response element; PI3, phosphatidylinositol; PI3K, phosphatidylinositol 3-kinase; MAPK, mitogen-activated protein kinase kinase/mitogen-activated protein kinase; LY294002, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; CsA, cyclosporin A; ERK, extracellular signal-regulated kinase; kb, kilobase(s); PBS, phosphate-buffered saline; bp, base pair(s); BCA, bicinchoninic acid; MOPS, 4-morpholinepropanesulfonic acid; mTOR, mammalian target of rapamycin; eIF4E, eukaryotic initiation factor 4E; 4E-BP, eIF4e-binding protein; pVHL, von Hippel-Lindau protein.
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The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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- Received March 7, 2006.
- Accepted May 4, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
