Inhibition of endothelial sprouting by Notch4 is independent of VE-cadherin expression. (A) Total protein harvested from each of the Notch mutant cell lines was assayed for expression of VE-cadherin protein by immunoblotting. Immunoblotting for α-tubulin demonstrates equivalent loading of total protein. Results are representative of 3 separate experiments, and quantitation of the 3 experiments was performed by densitometry with VE-cadherin levels normalized to α-tubulin (B). ^*P < .001 for sample means compared with the empty vector control.