VWF-deficient cells display enhanced angiogenesis in vitro. VWF-specific (20nM; siVWF, closed bars), or control siRNA (20nM; siCTL, open bars) was transfected into HUVECs for 24 or 48 hours. VWF expression was measured in these cells by (A) RT-PCR, (B) Western blotting (representative blot shown), or (C) VWF ELISA. (D) HUVECs treated with control or VWF-specific siRNA for 24 hours were seeded onto Matrigel. Capillary network formation was observed in the presence (right panels) or absence (left panels) of 10 μg/mL VWF after 24 hours and quantified in panel E by measuring total tube length in micrometers. (Bar = 200 μm). Data for siVWF in panels A and C have been normalized to siCTL. siCTL, nonspecific siRNA-treated cells; siVWF, VWF siRNA-treated cells; UT, untreated cells (n = 3). Error bars = mean ± SEM. *P < .05; **P < .01; ***P < .001 (Student t test).