Objective: The function of the endothelial cell (EC)-enriched Rho family guanine nucleotide exchange factor, facio-genital dysplasia-5 (FGD5), is poorly understood. We sought to determine whether FGD5 regulates endothelial cytoskeletal reorganization and angiogenesis.
Methods and results: We observed that FGD5 is expressed in primary human EC isolated from sites across the vasculature. Inhibition of FGD5 expression using RNA interference decreased the protein by ≈70%. In 3-dimensional vascular endothelial growth factor-stimulated angiogenesis in vitro, FGD5-deficient endothelial sprout protrusion was markedly blunted versus nonsilenced controls. FGD5 knockdown impaired adhesion to fibronectin and collagen IV and remodeling of matrix adhesion complexes. Similarly, monolayer electric impedance was decreased, and impedance increased at a slower rate after seeding FGD5-deficient cells versus controls, reflecting decreased EC spreading. Further, FGD5 plays a role in cell survival, because expression of cleaved caspase-3 was increased in FGD5-deficient EC after loss of cell-matrix contacts, and proapoptotic tumor necrosis factor-α stimulation elicited EC with subdiploid DNA content among FGD5-deficient EC. Mechanistically, the phosphatidylinositol 3-kinase/Akt pathway that regulates both adhesive and survival signal transduction pathways requires FGD5. Vascular endothelial growth factor-stimulated Akt phosphorylation and downstream forkhead box protein-O1 inactivation is inhibited by FGD5 loss.
Conclusions: FGD5 regulates endothelial adhesion, survival, and angiogenesis by modulating phosphatidylinositol 3-kinase signaling.