SERUM-INDUCED VASCULAR SMOOTH-MUSCLE CELL ELASTOLYTIC ACTIVITY THROUGH TYROSINE KINASE INTRACELLULAR SIGNALING

In previous studies, we related increased elastolytic activity in pulm onary arteries (PA) with endothelial injury to the later development o f PA hypertension in rats. As the mechanism causing the increased PA e lastase was unknown, we hypothesized that serum factors which are acce ssible to vascular smooth muscle cells (SMC) following endothelial inj ury stimulate their elastolytic activity. To test this, we developed a n in vitro assay in which we added [H-3]-elastin to cultured Vascular SMC after 24 h serum starvation and monitored elastolysis following a further 24 h incubation with fetal bovine serum (FBS). We observed tha t serum induced increased elastolytic activity in both PA and aorta-de rived SMC but not in endothelial cells or SMC with low basal levels of elastolytic activity. Maximum stimulation of SMC elastolytic activity occurred with a concentration as low as 1% FBS and despite elastase i nhibitors in serum, suggesting that the activity is confined to the im mediate pericellular region where enzyme concentration is high. Serum- stimulated elastolytic activity was not reproduced by growth factors o r cytokines known to be associated with vascular disease or to induce release of elastases in other cells. The serum inducing elastolytic ac tivity was heat and acid labile. It was associated with increased elas tin adhesion to the 67 kD elastin binding protein on SMC surfaces and was prevented by tyrosine kinase inhibitors but not protein kinase C o r A inhibitors. Our studies therefore suggest a mechanism whereby seru m induction of SMC elastase requires signalling through the elastin bi nding protein and activation of tyrosine kinase. (C) 1994 Wiley-Liss, Inc.