Neuropilin-1 is required for endothelial cell adhesion to soluble vascular endothelial growth factor receptor 1

Neuropilin-1 (NRP-1) is a semaphorin receptor involved in neuron guidance, and a co-receptor for selected isoforms of the vascular endothelial growth factor (VEGF) family. NRP-1 binding to several VEGF-A isoforms promotes growth factor interaction with VEGF receptor (VEGFR)-2, increasing receptor phosphorylation. Additionally, NRP-1 directly interacts with VEGFR-1, but this interaction competes with NRP-1 binding to VEGF-A165 and does not enhance VEGFR-1 activation. In this work, we investigated in detail the role of NRP-1 interaction with the soluble isoform of VEGFR-1 (sVEGFR-1) in angiogenesis. sVEGFR-1 acts both as a decoy receptor for VEGFs and as an extracellular matrix protein directly binding to α5β1 integrin on endothelial cells. By combining cell adhesion assays and surface plasmon resonance experiments on purified proteins, we found that sVEGFR-1/NRP-1 interaction is required both for α5β1 integrin binding to sVEGFR-1 and for endothelial cell adhesion to a sVEGFR-1-containing matrix. We also found that a previously reported anti-angiogenic peptide (Flt_2-11 ), which maps in the second VEGFR-1 Ig-like domain, specifically binds NRP-1 and inhibits NRP-1/sVEGFR-1 interaction, a process that likely contributes to its anti-angiogenic activity. In view of potential translational applications, we developed a five-residue-long peptide, derived from Flt_2-11 , which has the same ability as the parent Flt_2-11 peptide to inhibit cell adhesion to, and migration towards, sVEGFR-1. Therefore, the Flt_2-5 peptide represents a potential anti-angiogenic compound per se, as well as an attractive lead for the development of novel angiogenesis inhibitors acting with a different mechanism with respect to currently used therapeutics, which interfere with VEGF-A165 binding.