Finding New Partnerships: The Function of Individual Extracellular Receptor Domains in Angiogenic Signalling by VEGF Receptors

Vascular endothelial growth factors (VEGFs) constitute a family of polypeptides regulating blood and lymphatic vessel development. VEGFs bind to type V receptor tyrosine kinases (RTKs), VEGFR-1, VEGFR-2, and VEGFR-3, but also bind directly to neuropilins and heparan sulphate glycosaminoglycans (HSPG), or indirectly to co-receptors such integrins and semaphorins. VEGFR activation results from ligand-induced dimerisation, which is mediated by the extracellular receptor domain (ECD). Recent studies established that dimerisation is necessary, but not sufficient, for receptor activation, since it was shown that only distinct orientations of receptor monomers give rise to active receptor dimers that are capable to instigate transmembrane signalling. Additional complexity in VEGFR signalling arises from association with specific co-receptors, which is determined by ligand- and ECD-specific interaction domains. In the following, the role of the different extracellular subdomains in VEGFR activation and signalling is discussed. We give an overview of the mechanistic concepts arising from recent structural studies that led to the development of novel allosteric receptor inhibitors and discuss their possible application in therapies aimed at pathological angiogenesis