Heparin blockade of thrombin-induced smooth muscle cell migration involvesinhibition of epidermal growth factor (EGF) receptor transactivation by heparin-binding EGF-like growth factor

Agonists of G protein-coupled receptors, such as thrombin, act in part by t ransactivating the epidermal growth factor (EGF) receptor (EGFR). Although at first a ligand-independent mechanism for EGFR transactivation was postul ated, it has recently been shown that this transactivation by various G pro tein-coupled receptor agonists can involve heparin-binding EGF-like growth factor (HB-EGF). Because thrombin stimulation of vascular smooth muscle cel l migration is blocked by heparin and because heparin can displace HB-EGF, we investigated the possibility that thrombin stimulation of smooth muscle cells (SMCs) depends on EGFR activation by HB-EGF. In rat SMCs, EGFR phosph orylation and extracellular signal-regulated kinase (ERK) activation in res ponse to thrombin are inhibited not only by the EGFR inhibitor AG1478 and b y EGFR blocking antibody but also by heparin and by neutralizing HB-EGF ant ibody. HB-EGF-dependent signaling induced by thrombin is inhibited by batim astat, which suggests a requirement for pro-HB-EGF shedding by a metallopro teinase. We further demonstrate that this novel pathway is required for the migration of rat and baboon SMCs in response to thrombin. We conclude from these data that the inhibitory effect of heparin on SMC migration induced by thrombin relies, at least in part, on a blockade of HB-EGF-mediated EGFR transactivation.