MAP kinase pathway is involved in IGF-1-stimulated proliferation of human retinal pigment epithelial cells (hRPE).
OBJECTIVE
To investigate the mitogenic activity of insulin-like growth factor-1 (IGF-1) on the proliferation of human retinal pigment epithelial cells (hRPE) and to elucidate the role of vascular endothelial growth factor (VEGF) and MAP kinase (MAPK) in the IGF-1 signaling cascade.


METHODS
Human RPE specimens were obtained from postmortem non-pathological eyes and cultured in vitro through several passages. Cellular proliferation in the presence of increasing concentrations of IGF-1 and IGF-1 + PD98059 (a known MAPK inhibitor) was measured by [(3)H]thymidine incorporation; trypan blue exclusion studies (T) verified cell viability. Under the same experimental conditions, synthesis of VEGF was measured utilizing [(14)C]methionine immunoprecipitation and immunocytochemical methods as well as Western blot analysis.


RESULTS
IGF-1 stimulated hRPE proliferation, as demonstrated by [(3)H]thymidine incorporation. There was also an IGF-1-induced increase in VEGF synthesis as measured quantitatively by [(14)C]methionine-VEGF immunoprecipitation. This was qualitatively confirmed by immunocytochemistry and Western blotting. PD98059 suppressed both IGF-1-induced cell proliferation as well as IGF-1-stimulated VEGF production.


CONCLUSIONS
These studies suggest that IGF-1 is a mitogen for hRPE cells and also stimulates production of the angiogenic factor, VEGF. Additionally, PD98059 inhibits the production of VEGF, suggesting that the MAP kinase pathway is involved in IGF-1-mediated angiogenesis.
Weng
Christina Y
CY
Department of Ophthalmology and Visual Sciences, WK Kellogg Eye Center, University of Michigan, Ann Arbor, Michigan 48105, USA. wengc@umich.edu
Kothary
Piyush C
PC
Verkade
Angela J
AJ
Reed
David M
DM
Del Monte
Monte A
MA
D018929:Cell Culture Techniques; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D018919:Neovascularization, Physiologic / Q000187:drug effects; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis / Q000235:genetics; D018630:Vitreoretinopathy, Proliferative / Q000378:metabolism
D005419:Flavonoids; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I; D048049:Extracellular Signal-Regulated MAP Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one