Role of PLCgamma and Ca(2+) in VEGF- and FGF-induced choroidal endothelial cell proliferation

Although bothvascular endothelial growth factor (VEGF) and fibroblast growth factor(FGF) receptors have been shown to be important in the regulation ofvascular endothelial cell growth, the roles of phospholipase C (PLC)and Ca²⁺ in their downstream signaling cascades are stillnot clear. We have examined the effects of VEGF and FGF on PLCphosphorylation and on changes in intracellular Ca²⁺ levelsin primary endothelial cells. VEGF stimulation leads to PLCactivation and increases in intracellular Ca²⁺, which arecorrelated with mitogen-activated protein (MAP) kinase (MAPK)activation and cell growth. Inhibition of Ca²⁺ increases bythe Ca²⁺ chelator1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid(BAPTA)-AM resulted in marked inhibition of MAPK activation, which wasshown to be linked to regulation of cell growth in these cells. Incontrast, FGF stimulation did not lead to PLC activation or tochanges in intracellular Ca²⁺ levels, although MAPKphosphorylation and stimulation of cell proliferation were observed.Neither BAPTA-AM nor the PLC inhibitor U-73122 had an effect on theseFGF-stimulated responses. These data demonstrate a direct role forPLC and Ca²⁺ in VEGF-regulated endothelial cell growth,whereas this signaling pathway is not linked to FGF-mediated effects inprimary endothelial cells. Thus endothelial cell-specific factorsregulate the ability of VEGF receptors and FGF receptors to couple tothis signaling pathway.