IGF-1-induced VEGF and IGFBP-3 secretion correlates with increased HIF-1 alpha expression and activity in retinal pigment epithelial cell line D407.
OBJECTIVE
To examine insulin-like growth factor (IGF)-1 stimulation of expression of hypoxia inducible factor (HIF)-1 alpha and secretion of vascular endothelial growth factor (VEGF) and IGF binding protein (IGFBP)-3 in human retinal pigment epithelial (RPE) cell line D407.


METHODS
D407 cells cultured in dishes or Transwell inserts were treated with cobalt chloride or varying doses of IGF-1. Whole cell lysates were assayed by immunoblot for HIF-1 alpha expression, whereas conditioned medium was TCA precipitated and assayed by immunoblot for VEGF and ligand blot for IGFBP-3. Cells grown on coverslips were similarly treated and probed with antibodies to HIF-1 alpha, VEGF, and IGFBP-3, and visualized by epifluorescence microscopy. Cells grown on Transwell inserts were probed with antibodies to the Na(+)/K(+)-ATPase alpha-1 subunit and either the alpha or beta subunits of the IGF-1 receptor and visualized in Z-section using confocal microscopy.


RESULTS
Immunoblot analysis of whole cell lysates from IGF-1-treated D407 cells revealed the upregulation of HIF-1 alpha protein. Epifluorescence microscopy demonstrated a positive correlation between HIF-1 alpha expression and nuclear localization, VEGF and IGFBP-3 synthesis and export, and IGF-1 action. Western and ligand blot analyses of RPE cell-conditioned medium indicated that IGF-1 induced increases in VEGF and IGFBP-3 secretion. Cells grown on Transwell inserts exhibited constitutive apical secretion of VEGF and IGFBP-3, which increased on apical or basolateral treatment with IGF-1. Confocal analysis of Transwell-cultured D407 cells confirmed the apical localization of the Na(+)/K(+)-ATPase alpha-1 subunit, characteristic of polarized RPE, with IGF-1 receptor alpha and beta subunits exhibiting a nonpolarized distribution.


CONCLUSIONS
IGF-1 stimulates increased HIF-1 alpha expression as well as VEGF and IGFBP-3 secretion in D407 cells. Similar to their in vivo counterparts, D407 cells maintain reversed epithelial polarity. Apical secretion of VEGF and IGFBP-3 increases in response to either apical or basolateral IGF-1 stimulation consistent with the nonpolarized distribution of IGF-1 receptors.
Department of Cell and Molecular Pharmacology and Experimental Therapeutics and The Hollings Cancer Center, Medical University of South Carolina, Charleston, 29425, USA.
Mark G
MG
Slomiany
Steven A
SA
Rosenzweig
D002460:Cell Line; D016764:Cell Polarity; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D015151:Immunoblotting; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008856:Microscopy, Fluorescence; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D018972:Insulin-Like Growth Factor Binding Protein 3; D014157:Transcription Factors; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I; D000254:Sodium-Potassium-Exchanging ATPase