uPA promotes endothelial cell survival. (A) HUMECs recovered after 24 hours from cultures seeded subconfluently on vitronectin (5000) under control conditions (2820 ± 45) or in the presence of uPA (100 nM; 4090 ± 345) or of VEGF₁₆₅ (1.25 nM; 4210 ± 130). A reduction in cell number was found under serum reduced conditions that was prevented by uPA or VEGF₁₆₅ (*P < .01 vs control; n = 3). (B) Percentage of apoptotic HUMECs seeded on vitronectin for 24 hours under control conditions or in the presence of uPA (100 nM) or VEGF₁₆₅ (1.25 nM). Both uPA and VEGF₁₆₅ significantly reduced the percentage of apoptotic cells (*P < .01; n = 4). (C) Time course of recovered endothelial cells seeded on vitronectin in the absence or presence of uPA (100 nM) or VEGF₁₆₅ (1.25 nM). A significant increase was seen only in the presence of VEGF₁₆₅ (*P < .01, ANOVA; n = 3). (D) Dose dependency of the effects of uPA or VEGF₁₆₅ on the number of endothelial cells recovered 96 hours after seeding on different matrices in percentage of attached cells (2 hours after seeding). The effects of both uPA and VEGF₁₆₅ were dependent on the presence of an adhesive matrix (*P < .01, ANOVA; n = 3).