Role of PLCγ and Ca2+ in VEGF- and FGF-induced choroidal endothelial cell proliferation

Although both vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) receptors have been shown to be important in the regulation of vascular endothelial cell growth, the roles of phospholipase C (PLC)gamma and Ca2+ in their downstream signaling cascades are still not clear. We have examined the effects of VEGF and FGF on PLC gamma phosphorylation and on changes in intracellular Ca2+ levels in primary endothelial cells. VEGF stimulation leads to PLC gamma activation and increases in intracellular Ca2+, which are correlated with mitogen-activated protein (MAP) kinase (MAPK) activation and cell growth. Inhibition of Ca2+ increases by the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM resulted in marked inhibition of MAPK activation, which was shown to be linked to regulation of cell growth in these cells. In contrast, FGF stimulation did not lead to PLC gamma activation or to changes in intracellular Ca2+ levels, although MAPK phosphorylation and stimulation of cell proliferation were observed. Neither BAPTA-AM nor the PLC inhibitor U-73122 had an effect on these FGF-stimulated responses. These data demonstrate a direct role for PLC gamma and Ca2+ in VEGF-regulated endothelial cell growth, whereas this signaling pathway is not linked to FGF-mediated effects in primary endothelial cells. Thus endothelial cell-specific factors regulate the ability of VEGF receptors and FGF receptors to couple to this signaling pathway.