Comparative structure-function analysis of VEGFR-1 and VEGFR-2: What have we learned from chimeric systems?

Activation of vascular endothelial growth factor receptor-1 and -2 (VEGFR-1 and VEGFR-2) plays a critical role in vasculogenesis and angiogenesis. However, the mechanism by which activation of VEGFRs elicits these cellular events is not fully understood. We recently constructed chimeric receptors containing the extracellular domain of human CSF-1R/c-fms fused with the entire transmembrane and cytoplasmic domains of murine VEGFR-1 and VEGFR-2. Selective activation of chimeric VEGFR-2, but not chimeric VEGFR-1, stimulated endothelial cell growth, migration, and differentiation. Stimulation of cells coexpressing chimeric VEGFR-1 and VEGFR-2 suppressed VEGFR-2-mediated endothelial cell growth. Site-directed mutagenesis demonstrated that tyrosines 799 and 1173 are required for VEGFR-2-mediated endothelial cell growth and activation of PI3 kinase. Further site-directed mutagenesis demonstrated that tyrosine 1212, located in the carboxyl tail of VEGFR-2, is required for the ligand-dependent autophosphorylation of the receptor and its ability to activate signaling proteins. Collectively, our results suggest that activation of VEGFR-1 and VEGFR-2 differentially regulates endothelial cell function and angiogenesis. Second, activation of VEGFR-2 is associated with many endothelial cell functions, including cell proliferation, migration, and differentiation. Third, activation of PI3 kinase by VEGFR-2 regulates endothelial cell proliferation.