K1146A and K1147A point mutations of the integrin α1 cytoplasmic tail lead to decreased tubulogenesis. Tubulogenesis (A), cell proliferation (B), cell signaling (C), and densitometry analysis (D) were determined as described in Figure 2. Images of cells undergoing tubulogenesis were taken as described in Figure 2A. *Statistically significant differences (P < .05) between the α1KO and the α1 mutant–expressing endothelial cells. Vertical line(s) in panel C have been inserted to indicate a repositioned gel lane.