Notch4-induced inhibition of endothelial sprouting is independent of VEGFR-2 expression. (A) Total protein harvested from each of the Notch mutant cell lines was assayed for expression of VEGFR-2 protein by immunoblotting. Immunoblotting for α-tubulin demonstrates equivalent loading of total protein. Results are representative of 5 separate experiments and quantitation of the 3 experiments was performed by densitometry with VEGFR-2 levels normalized to α-tubulin (B). ^*P < .01 for sample means compared with the empty vector control.