VEGF inhibits PDGF-stimulated calcium signaling independent of phospholipase C and PKC activation

Abstract

Introduction. Although vascular endothelial growth factor (VEGF) is a potent stimulus for endothelial cell proliferation, little is known about its effect on vascular smooth muscle cells (VSMC), a potent source of VEGF. We have shown that VEGF inhibits platelet derived growth factor (PDGF) induced VSMC proliferation in part by inhibition of ERK MAP kinase and Rb phosphorylation. These experiments examined whether VEGF altered PDGF stimulated intracellular calcium signaling. Methods. Human aortic smooth muscle cells (VSMC), after serum starvation, were stimulated with either PDGF (20 ng/ml) or PDGF (20 ng/ml) with VEGF at 0, 10, 20, 30, 40, and 50 ng/ml. Cell lysates were obtained at 5, 10, 30, and 60 min and Western immunoassay was performed for activated phospholipase C (PLC) and protein kinase C (PKC). Intracellular calcium influx was measured by a Fura2 assay in PDGF and VEGF treated cells. Results. PDGF stimulation resulted in a rapid rise in intracellular calcium which was completely suppressed by the presence of VEGF. PDGF resulted in phosphorylation of PLC by 5 min and peaked at 10 min. VEGF did not activate PLC and reduced PDGF-stimulated PLC activation at 10 min. PKC activation by PDGF was not affected by VEGF. Conclusion. VEGF suppresses PDGF-induced intracellular calcium influx. Although it down regulates PLC activation by PDGF at 10 min, the temporal course of the suppression of intracellular calcium accumulation suggests that the mechanism by which VEGF suppresses PDGF-induced calcium elevation is independent of the PLC pathway.