Hypoxia-inducible factor-1-dependent and -independent regulation of insulin-like growth factor-1-stimulated vascular endothelial growth factor secretion

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 318; no. 2; p. 666
• Main Authors: Slomiany, Mark G, Rosenzweig, Steven A
• Format: Journal Article
• Language: English
• Published: United States 01-08-2006
• Subjects: Anti-Bacterial Agents - pharmacology; Cell Line; Cobalt - pharmacology; Gene Expression Regulation - drug effects; Humans; Hypoxia - metabolism; Hypoxia-Inducible Factor 1 - biosynthesis; Hypoxia-Inducible Factor 1 - physiology; Immunoblotting; Immunohistochemistry; Insulin-Like Growth Factor I - pharmacology; Ligands; Phosphatidylinositol 3-Kinases - physiology; Promoter Regions, Genetic - genetics; RNA, Messenger - biosynthesis; Signal Transduction - drug effects; Sirolimus - pharmacology; Stimulation, Chemical; Transfection; Vascular Endothelial Growth Factor A - biosynthesis; Vascular Endothelial Growth Factor A - genetics; Vascular Endothelial Growth Factor A - metabolism
• ISSN: 0022-3565
• DOI: 10.1124/jpet.106.104158

Hypoxia-induced stress plays a central role in retinal vascular disease and cancer. Increased hypoxia-inducible factor-1 alpha (Hif-1 alpha) 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-1 alpha protein turnover and VEGF secretion in the ARPE-19 retinal pigment epithelial cell line. Northern analysis revealed that IGF-1 stimulated Hif-1 alpha message expression, whereas the hypoxia-mimetic CoCl2 did not. CoCl2 treatment increased Hif-1 alpha 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.