Localization of CD9, an enhancer protein for proheparin-binding epidermal growth factor-like growth factor, in human atherosclerotic plaques - Possible involvement of juxtacrine growth mechanism on smooth muscle cell proliferation

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), a member of the ECF family, has a potent mitogenic activity for vascular sm ooth muscle cells (SMCs). We previously reported that HB-EGF is involved in atherogenesis of human aorta and coronary arteries. ProHB-EGF (the membran e-anchored form of HB.EGF) has also been demonstrated to possess a mitogeni c activity, which is approximate to 30-fold increased when coexpressed with CD9 in mouse L cells. Thus, in the process of atherogenesis, CD9 may be in volved in the proliferation of SMCs, We immunohistochemically investigated the localization of CD9 and proHB-EGF in the human aorta and coronary arter ies. In normal aorta and coronary arteries, CD9 immunostaining was virtuall y negative, whereas proHB-EGF immunostaining was positive, especially in th e arteries of babies. In contrast, in atherosclerotic lesions, some intimal SMCs were strongly positive for CD9 and proHB-EGF immunostaining. The juxt acrine growth activities of human aortic SMCs were inhibited in vitro by ad ding neutralization antibodies for CD9 or adding the specific inhibitor of HB-EGF, Besides, coexpressed CD9 and proHB-EGF cells markedly incorporated [H-3]thymidine into the SMCs, CD9 is localized immunohistochemically in the SMCs of the atherosclerotic aorta and coronary arteries, CD9, when coexpre ssed with proHB-EGF, enhances proHB-EGF activities for SMC growth in a so-c alled juxtacrine manner in vitro and may be involved in atherogenesis.