Vascular Endothelial Growth Factor Receptor-2 and Neuropilin-1 Form a Receptor Complex that is Responsible for the Differential Signaling Potency of VEGF165 and VEGF121

Abstract

The two most abundant secreted isoforms of vascular endothelial growth factor A (VEGF165 and VEGF12l) are formed as a result of differential splicing of the VEGF-A gene. VEGF165 and VEGF 121 share similar affinities at the isolated VEGF receptor (VEGFR)-2 but have been previously demonstrated to have differential ability to activate VEGFR-2-mediated effects on endothelial cells. Herein we investigate whether the recently described VEGF165 isoform-specific receptor neuropilin-1 (Npn-1) is responsible for the difference in potency observed for these ligands. We demonstrate that although VEGFR VIEGFR-2 and Npn-1 form a complex, this complex does not result in an increase in VEGF165 binding affinity. Therefore, the differential activity of VEGF165 and VEGF121 cannot be explained by a differential binding affinity for the complex. Using an antagonist that competes for VEGF165 binding at the VEGFR-2·Npn complex, we observe specific antagonism of VEGF165-meditated phosphorylation of VEGFR-2 without affecting the VEGF121, response. These data indicate that the formation of the complex is responsible for the increased potency of VEGF165 versus VEGF12l. Taken together, these data suggest a receptor-clustering role for Npn-1, as opposed to Npn-1 behaving as an affinity-converting subunit.