The role of phosphatidylinositol 3-kinase and the mitogen-activated protein kinases in insulin-like growth factor-I-mediated effects in vascular endothelial cells.
Despite an improved understanding of the molecular mechanisms of insulin-like growth factor-I (IGF-I) signaling and the recognition that IGF-I mediates many effects in endothelial cells, some of which may be important for atherosclerosis, little is known about the signal transduction pathways that mediate the effects of IGF-I in endothelial cells. To that end, we examined the signaling pathways activated by IGF-I in endothelial cells and their contribution to IGF-I-stimulated endothelial cell migration and nuclear factor (NF)-kappaB-dependent transcription. Treatment of bovine pulmonary artery endothelial cells (PAEC) with IGF-I activated the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1/2 and ERK5. In contrast, IGF-I had no effect on either c-Jun amino-terminal kinase or p38 kinase activity. IGF-I also activated phosphatidylinositol (PI) 3-kinase, as reflected by increased phosphorylation of AKT: There was no evidence of cross-talk between the ERK and PI 3-kinase pathways in PAEC. In PAEC transiently transfected with pTK81-NFkappaB-Luc, which contained four copies of the NF-kappaB DNA binding site 5' to a minimal promoter and the luciferase gene, treatment with 50 ng/ml IGF-I increased luciferase activity 1.8-fold. Inhibition of ERK activity using PD98059 and PI 3-kinase activity with LY 294002 abrogated the induction of NF-kappaB-dependent transcription by IGF-I, suggesting that both pathways contribute to the effect of IGF-I on NF-kappaBdependent transcription. In contrast to the effect of tumor necrosis factor-alpha on NF-kappaB activation, Western blot analyses demonstrated that IGF-I had no effect on IkappaB phosphorylation and degradation or nuclear translocation and DNA binding of NF-kappaB. These data suggest a direct of effect of IGF-I on nuclear NF-kappaB. IGF-I also increased endothelial cell migration approximately 2-fold, as demonstrated using a Boyden chamber apparatus. IGF-I-induced endothelial cell migration was inhibited, in part, by LY 294002 but not PD98059. Together, these studies demonstrate that IGF-I activates multiple signaling pathways in endothelial cells with little evidence for cross-talk between the pathways. Moreover, these pathways appear to mediate both overlapping and distinct effects in that activation of both PI 3-kinase and the ERKs contributed to the stimulation of NF-kappaB-dependent transcription by IGF-I, whereas only PI 3-kinase mediated IGF-I-stimulated endothelial cell migration.
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Center for Endocrinology, Robert H. Lurie Cancer Center, Department of Medicine, Northwestern University Medical School and Veterans Affairs Chicago Healthcare System, Lakeside Division, Chicago, Illinois 60611, USA.
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Lowe
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D000818:Animals; D002417:Cattle; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation
D016328:NF-kappa B; D007334:Insulin-Like Growth Factor I; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases