title: VEGF activates protein kinase C-dependent, but Ras-independent Raf-MEK-MAP kinase pathway for DNA synthesis in primary endothelial cells.
abstract: KDR/FIk-1 tyrosine kinase, one of the two VEGF receptors induces mitogenesis and differentiation of vascular endothelial cells. We have previously reported that a major target molecule of KDR/Flk-1 kinase is PLC-gamma, and that VEGF induces activation of MAP kinase, mainly mediated by protein kinase C (PKC) in the NIH3T3 cells overexpressing KDR/FIk-1 (Takahashi and Shibuya, 1997). However, the signal transduction initiated from VEGF in endothelial cells remains to be elucidated. In primary sinusoidal endothelial cells which showed strictly VEGF-dependent growth, we found that VEGF stimulated the activation of Raf-1-MEK-MAP kinase cascade. To our surprise, an important regulator, Ras was not efficiently activated to a significant level in response to VEGF. Consistent with this, dominant-negative Ras did not block the VEGF-induced phosphorylation of MAP kinase. On the other hand, PKC-specific inhibitors severely reduced VEGF-dependent phosphorylation of MEK, activation of MAP kinase and subsequent DNA synthesis. A potent PI3 kinase inhibitor, Wortmannin, could not inhibit either of them. These results suggest that in primary endothelial cells, VEGF-induced activation of Raf-MEK-MAP kinase and DNA synthesis are mainly mediated by PKC-dependent pathway, much more than by Ras-dependent or PI3 kinase-dependent pathway.
mesh_terms: D016475:3T3 Cells / Q000187:drug effects; D000256:Adenoviridae / Q000235:genetics / Q000502:physiology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D002227:Carbazoles / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D004261:DNA Replication / Q000187:drug effects*; D016228:Endothelial Growth Factors / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D011905:Genes, ras; D005822:Genetic Vectors / Q000235:genetics / Q000502:physiology; D007211:Indoles / Q000494:pharmacology; D008222:Lymphokines / Q000494:pharmacology*; D048728:MAP Kinase Kinase Kinase 1; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D017978:Receptors, Growth Factor / Q000502:physiology; D040262:Receptors, Vascular Endothelial Growth Factor; D015398:Signal Transduction / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D000077191:Wortmannin