Biophysical and Biochemical studies on the Mechanism of Crosstalk between Endoglin and the VEGF Pathway
2Department of Medicine and Department of Pharmacology and Cancer Biology, Duke University Medical Center, USA
Endoglin (ENG) is a cell-surface protein expressed mainly in endothelial cells. It has important roles as modulator of various physiological and pathological processes, and is a co-receptor of TGF-ß superfamily. ENG also interacts with vascular endothelial growth factor receptors (VEGFRs). Therefore, complex formation between ENG and VEGFR2 or Neuropilin-1 (NRP1) can modulate the response to VEGF-A. However, studies on complex formation between these full-length receptors in live cells and the consequent effects on signaling and angiogenesis are not fully explored.
We employed a combination of IgG-mediated patching-immobilization of ENG with fluorescence recovery after photobleaching (FRAP) studies on the lateral diffusion of VEGFR2 or NRP1. The effects on downstream signaling and angiogenesis in endothelial cells were assessed following VEGF-A stimulation.
The patch/FRAP studies show that ENG forms stable complexes with VEGFR2 or NRP1, which are enhanced by VEGF-A. Signaling was measured in murine embryonic endothelial cells with and without ENG (MEEC+/+ and MEEC-/-). VEGF-A mediated signaling to VEGFR2 and Erk1/2 was higher in MEEC+/+. MEEC+/+ cells were more efficient in forming vascular sprouts but migrated slower through transwells than MEEC-/-.
ENG forms stable complexes with both VEGFR2 or NRP1, which are enhanced by VEGF-A. ENG is important for VEGF-A mediated signaling and sprouting but inhibits migration. This study thus provides insights into understanding how ENG regulates VEGF signaling and central roles in vascular biology and angiogenesis.