uPA induces up-regulation of XIAP. (A) Up-regulation of different IAP protein mRNAs in HUVECs on treatment with uPA (100 nM) for 6 hours presented as fold expression over unstimulated control. uPA induced a significant increase of IAPs, most prominently the XIAP (*P < .01; n = 4). (B) Dose-dependent effect of uPA (6 hours) on XIAP mRNA expression in HUVECs. Data represent fold increase over control (P < .01, ANOVA; n = 3). (C) Effect of down-regulation of XIAP by siRNA to approximately 35% of control levels on the effect of uPA on the percentage of apoptotic cells. In scrambled siRNA-treated endothelial cells, uPA reduced the percentage of apoptotic cells to approximately half, whereas in specific XIAP siRNA-treated cells, the effect of uPA was significantly smaller (∼ 25%) and not significantly different from control. XIAP down-regulation induced an increase in apoptosis by 2.9-fold compared with scrambled control in untreated endothelial cells (not shown; *P < .01, #P > .05; n = 3).