Lipocortin V may function as a signaling protein for vascular endothelial growth factor receptor-2/Flk-1

Binding of vascular endothelial growth factor (VEGF) to its receptor, VEGFR -2 (Flk-1/KDR), induces dimerization and activation of the tyrosine kinase domain of the receptor, resulting in autophosphorylation of cytoplasmic tyr osine residues used as docking sites for signaling proteins that relay the signals for cell proliferation, migration, and permeability enhancement. We explored the VEGF/ receptor signaling pathway by performing a two-hybrid s creen of a rat lung cDNA library in yeast using the intracellular domain of rat VEGFR-2 as bait. Two clones encoding lipocortin V were isolated. Subse quent studies with the yeast two-hybrid assay showed that the complete intr acellular domain of VEGFR-2 was required for the interaction. Coimmunopreci pitation of translated proteins confirmed the interaction between the VEGF receptor and lipocortin V, VEGF induced a rapid tyrosine phosphorylation of lipocortin V in human umbilical vein endothelial cells (HUVEC). Pretreatme nt of HUVEC with antisense oligodeoxyribonucleotide (ODN) for lipocortin V significantly inhibited VEGF-induced cell proliferation, which was accompan ied by a decrease in protein synthesis and tyrosine phosphorylation of lipo cortin V, Our results indicate that lipocortin V may function as a signalin g protein for VEGFR-2 by directly interacting with the intracellular domain of the receptor and appears to be involved in regulation of vascular endot helial cell proliferation mediated by VEGFR-2. (C) 1999 Academic Press.