ROLE OF POLYAMINES IN THE REGULATION OF SYNTHESIS AND SECRETION OF PLASMINOGEN ACTIVATOR FROM BOVINE AORTIC ENDOTHELIAL CELLS

Abstract

The effects of three polyamines, putrescine (PUT), spermidine (SPD) and spermine (SPM), were investigated on the synthesis and secretion of plasminogen activator (PA) and antiactivator (PAI) activities in confluent bovine aortic endothelial cells. PA activity was determined bythe fibrin plate method, and individual species with PA and PAI activities were separated and visualized using SDS-PAGE with zymography and reverse fibrin autography. Both control cells and cells treated with polyamines secreted PA activity in a time-dependent fashion. After 24-hour incubation, the three polyamines enhanced PA secretion in a dose-dependent manner (10-6 to 2.5 × 10-3 M), with a potency order of SPM > SPD> PUT, as estimated by the fibrin plate method. The maximum PA releases after PUT (0.5 mM), SPD (2.5 mM) and SPM (0.5 mM) were 1.7, 4.5 and 5.4 times control levels, respectively. Concentrations lower than 1 μM had essentially no effects. The enhancement of PA activity by polyamines was blocked by actino-mycin D and cycloheximide, while it was not affected by inhibitors of polyamine biosynthesis except that the enhancement by PUT (0.5 mM) was reduced by methylglyoxal bis(guanylhydrazone). These data suggest that polyamines directly stimulate PA synthesis and secretion through promotion of gene transcription and translation, and that this effect appears to be related to their position in the biosynthetic pathway of polyamines. The kinetic patterns of activities of ornithine decarboxylase and S-adenosy-methionine decarboxylase in confluent endothelial cells stimulated withfresh culture medium suggest that there is rapid turnover of intracellular polyamines. Multiple forms of secreted PA were observed and both tissue- and urokinase-type PA were enhanced by polyamines, while the PAI activity, as evaluted by reverse fibrin autograpy, was apparently reduced. These experimental results suggest that polyamines may play an important role in the regulation of the synthesis and secretion of plasminogen activators, and that this biological function could be modified by disease states and by agents that are associated with altered polyamine metabolism.