tor inhibitor type 1 expression in vascular endothelial cells. Am J

gen activator inhibitor type 1 (PAI-1) regulates fibrinolytic activity and mediates vascular atherothrombotic disease. Endothelial cells (ECs) synthesize and secrete PAI-1, but the intracellular signaling pathways that regulate PAI-1 expression are not entirely known. We hypothesize that the phosphatidylinositol 3-kinase (PI3K)/protein ki-nase Akt pathway, which regulates endothelial function, could mod-ulate PAI-1 expression in ECs. Cultured bovine aortic and human saphenous vein ECs were stimulated with TNF-, ANG II, insulin, or serum, and PAI-1 expression was determined by Northern and West-ern analyses. Inhibition of PI3K with wortmannin or LY-294002 enhanced PAI-1 expression induced by these extracellular stimuli. Similarly, overexpression of a dominant-negative mutant of PI3K or Akt increased TNF-- and insulin-induced PAI-1 expression. The increase in PAI-1 was due to transcriptional and posttranscriptional mechanisms as PI3K inhibitors increased PAI-1 promoter activity an