Activation of ALK1 and ALK5 signaling has different effects on VEGF expression, cell proliferation, and tube formation in vitro. HAECs were transfected with scrambled control siRNA (SCR) or siRNA to the indicated receptors and SMADs. The following day, the cells were treated with control medium, TGFβ1 (1 ng/mL), or BMP-9 (10 ng/mL) for 24 hours. VEGF expression was determined by real-time PCR (A), and VEGF in the media was determined by immunoblotting (B). Stimulation of cell proliferation was determined by 3H-thymidine incorporation (C), and the effect on tube formation of media collected from the transfected and treated cells was determined on Matrigel (D); images were obtained 6 hours after plating. Asterisks indicate statistically significant differences compared with control (scrambled siRNA, control treatment). **P < .01; ***P < .001; Tukey test.
