HEPARIN INHIBITS THROMBIN-INDUCED MITOGEN-ACTIVATED PROTEIN-KINASE SIGNALING IN ARTERIAL SMOOTH-MUSCLE CELLS

Purpose: Smooth muscle cell proliferation is a key event in the develo pment of intimal hyperplasia after arterial injury. Heparin can suppre ss smooth muscle cell proliferation in vitro and prevents intimal hype rplasia after arterial injury, but the mechanisms of action are poorly understood. Recently, we observed that heparin inhibited serum-induce d activation of mitogen-activated protein kinase in smooth muscle cell s, but heparin did not inhibit signaling induced by platelet-derived g rowth factor BB and basic fibroblast growth factor, both ligands of ty rosine kinase receptors. Here, we examined the possibility that hepari n inhibits signaling by thrombin and other activators of heterotrimeri c G-proteins. Design of Study: Baboon aortic smooth muscle cells were stimulated with thrombin, angiotensin II, endothelin-l, and lysophosph atidic acid in the presence or absence of heparin. After stimulation, mitogen-activated protein kinase activity was measured with an in-gel phosphorylation assay, mitogen-activated protein kinase kinase-1 was i mmunoprecipitated from the same samples, and activity was measured wit h recombinant mitogen-activated protein kinase as a substrate. DNA syn thesis was measured by H-3-thymidine labeling and scintillation counti ng. Results: Heparin inhibited sustained activity of mitogen-activated protein kinase kinase-1 and mitogen-activated protein kinase and prev ented DNA synthesis induced by thrombin, angiotensin II, endothelin-1, and lysophosphatidic acid. Conclusions: Heparin inhibits growth of ba boon smooth muscle cells by preventing prolonged mitogen-activated pro tein kinase activation elicited by ligands of seven transmembrane doma in receptors and heterotrimeric G-proteins. The results indicate that heparin interferes with a specific pathway in smooth muscle cell growt h, which could be a future target in attempts to inhibit lesion develo pment after vascular surgery.