COMPLEX INTRACELLULAR SIGNAL-TRANSDUCTION REGULATES TISSUE-PLASMINOGEN ACTIVATOR (T-PA) AND PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 (PAI-1) SYNTHESIS IN CULTURED HUMAN UMBILICAL VEIN ENDOTHELIUM

Endothelial cells are central in fibrinolysis because of their high production of both activators (t-PA, uPA) and inhibitors (PAI-1). The t-PA and PAI-1 synthesis could be regulated by signals transduction at several cellular levels. The purpose of this in vitro study, on cultured endothelial cells, was to explore the receptor/second messenger regulation of the t-PA and PAI-1 synthesis. Quiescent confluent human umbilical vein endothelial cells, cultured in passage 1, were exposed to different test substances. Samples from the conditioned medium were collected after 16 and 24 h and analysed for t-PA and PAI-1 antigen. All data presented were related to the data from control dishes (=100%), in the same experiment. The results from the present study (mean +/-95% confidence interval) demonstrated the following. (1) Forskolin, with a documented direct cAMP-inducing effect, decreased the basal PAI-1 production to 61+/-15%, and Na-nitroprusside, with a documented cGMP-inducing effect, increased the basal PAI-1 production to 141+/-38% without affecting the basal t-PA production. The surface receptor agonists isoprenalin or ephedrine, which indirectly affect adenylate cyclase, had no effect on t-PA or PAI-1 production. (2) Phorbolester (PMA), which directly activates proteinkinase C (PKC), increased the basal t-PA and PAI-1 production to 350+/-71%, and 163+/-35% respectively. (3) Thrombin, but not endothelin-1 (ET-1), increased the basal t-PA and PAI-1 production to 195+/-34% and 136+/-18%, respectively, indicating an PKC-mediated thrombin effect. (4) Endotoxin increased both the basal t-PA and PAI-1 production to 130+/-20% and 136+/-30%, respectively. These data indicated that various stimuli involve different pathways e.g. cAMP, cGMP and PKC. Pharmacological interference with the regulation of t-PA and PAI-1 must take this complexity into account.