Kinase insert domain receptor (KDR) extracellular immunoglobulin-like domains 4-7 contain structural features that block receptor dimerization and vascular endothelial growth factor-induced signaling.
The vascular endothelial growth factor (VEGF) receptor tyrosine kinase subtype kinase insert domain receptor (KDR) contains seven extracellular Ig-like domains, of which the three most amino-terminal contain the necessary structural features required for VEGF binding. To clarify the functional role of KDR Ig-like domains 4-7, we compared VEGF-induced signaling in human embryonic kidney and porcine aortic endothelial cells expressing native versus mutant receptor proteins in which Ig-like domains 4-7, 4-6, or 7 had been deleted. Western blotting using an anti-receptor antibody indicated equivalent expression levels for each of the recombinant proteins. As expected, VEGF treatment robustly augmented native receptor autophosphorylation. In contrast, receptor autophosphorylation, as well as downstream signaling events, were VEGF-independent for cells expressing mutant receptors. (125)I-VEGF(165) bound with equal or better affinity to mutant versus native receptor, although the number of radioligand binding sites was significantly reduced because a significant percentage of mutant, but not native, receptors were localized to the cell interior. As was the case for native KDR, (125)I-VEGF(165) binding to the mutant receptors was dependent upon cell surface heparan sulfate proteoglycans, and (125)I-VEGF(121) bound with an affinity equal to that of (125)I-VEGF(165) to the native and mutant receptors. It is concluded that KDR Ig-like domains 4-7 contain structural features that inhibit receptor signaling by a mechanism that is independent of neuropilin-1 and heparan sulfate proteoglycans. We speculate that this provides a cellular mechanism for blocking unwanted signaling events in the absence of VEGF.
Tao
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Cardiology Division, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Backer
M V
MV
Backer
J M
JM
Terman
B I
BI
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001011:Aorta; D001665:Binding Sites; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D019281:Dimerization; D016228:Endothelial Growth Factors / Q000378:metabolism / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008222:Lymphokines / Q000378:metabolism / Q000494:pharmacology*; D015513:Oncogene Proteins / Q000378:metabolism; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011869:Radioligand Assay; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry* / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000737:chemistry* / Q000378:metabolism*; D040262:Receptors, Vascular Endothelial Growth Factor; D011994:Recombinant Proteins / Q000378:metabolism; D013552:Swine; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D048868:Adaptor Proteins, Signal Transducing; D016228:Endothelial Growth Factors; D019812:Heparan Sulfate Proteoglycans; D007136:Immunoglobulins; D007527:Isoenzymes; D008222:Lymphokines; C078332:Nck protein; D015513:Oncogene Proteins; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D010738:Type C Phospholipases; D051966:Phospholipase C gamma