VEGFR-2 conformational switch in response to ligand binding

VEGFR-2 is the primary regulator of angiogenesis, the development of new blood vessels from pre-existing ones. VEGFR-2 has been hypothesized to be monomeric in the absence of bound ligand, and to undergo dimerization and activation only upon ligand binding. Using quantitative FRET and biochemical analysis, we show that VEGFR-2 forms dimers also in the absence of ligand when expressed at physiological levels, and that these dimers are phosphorylated. Ligand binding leads to a change in the TM domain conformation, resulting in increased kinase domain phosphorylation. Inter-receptor contacts within the extracellular and TM domains are critical for the establishment of the unliganded dimer structure, and for the transition to the ligand-bound active conformation. We further show that the pathogenic C482R VEGFR-2 mutant, linked to infantile hemangioma, promotes ligand-independent signaling by mimicking the structure of the ligand-bound wild-type VEGFR-2 dimer. DOI: http://dx.doi.org/10.7554/eLife.13876.001
eLife digest New blood vessels form by growing out from existing vessels. A signaling molecule called VEGF is crucial for this process and binds to a receptor protein known as VEGFR-2. This binding activates signaling events within the cells that line the blood vessels to promote the growth of new vessels. VEGFR-2 belongs to a family of proteins called receptor tyrosine kinases. The receptor has three main parts: one part extends out of the cell and binds to VEGF, another spans the cell’s membrane, while the third part is found inside the cell. The current model of VEGFR-2 activation is that VEGF binds to individual VEGFR-2 receptor proteins on the membrane, and brings two of them close enough to form a complex called a dimer. The receptor dimer is activated and initiates signaling within the cell. Sarabipour et al. tested this current model and revealed that VEGFR-2 could form a dimer even in the absence of VEGF. This receptor dimer formed through contacts between parts that are inside the cell as well as the regions embedded in the membrane. These VEGFR-2 dimers were active, but only to a low level. However, the activity of the receptor was increased in the presence of VEGF. Sarabipour et al. found that binding of VEGF promoted VEGFR-2 to change its three-dimensional shape, which made it more active. Further work suggested that VEGFR-2 dimers must first correctly assemble in the absence of VEGF so that active VEGFR-2 dimers can form at a later stage. Hence a VEGFR-2 dimer on its own is an important intermediate that is needed for full activation of the receptor. A mutation in the gene that encodes VEGFR-2 causes a disorder called infantile hemangioma that leads to abnormal vessel formation in young children. Sarabipour et al. found that this mutation causes VEGFR-2 to change its shape even when no VEGF is present and thus makes the receptor overly active. Finally, tumors need to form new blood vessels to grow and survive. These new findings suggest that drugs that interact with VEGFR-2 dimers in the absence of VEGF may be able to prevent the receptor from becoming activated and could thus help cut the blood supply to tumors and treat cancers. DOI: http://dx.doi.org/10.7554/eLife.13876.002