Localization of CD9, an Enhancer Protein for Proheparin-Binding Epidermal Growth Factor–Like Growth Factor, in Human Atherosclerotic Plaques

Abstract

Abstract-Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), a member of the EGF family, has a potent mitogenic activity for vascular smooth muscle cells (SMCs). We previously reported that HB-EGF is involved in atherogenesis of human aorta and coronary arteries. ProHB-EGF (the membrane-anchored form of HB-EGF) has also been demonstrated to possess a mitogenic activity, which is Ϸ30-fold increased when coexpressed with CD9 in mouse L cells. Thus, in the process of atherogenesis, CD9 may be involved in the proliferation of SMCs. We immunohistochemically investigated the localization of CD9 and proHB-EGF in the human aorta and coronary arteries. In normal aorta and coronary arteries, CD9 immunostaining was virtually negative, whereas proHB-EGF immunostaining was positive, especially in the arteries of babies. In contrast, in atherosclerotic lesions, some intimal SMCs were strongly positive for CD9 and proHB-EGF immunostaining. The juxtacrine growth activities of human aortic SMCs were inhibited in vitro by adding neutralization antibodies for CD9 or adding the specific inhibitor of HB-EGF. Besides, coexpressed CD9 and proHB-EGF cells markedly incorporated T he proliferation of vascular smooth muscle cells (SMCs) in the intima of arteries is one of the most important events in plaque formation 1 and in coronary restenosis after balloon angioplasty. 2 Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), a member of the EGF family, has been identified as a potent mitogen for SMCs that is comparable to platelet-derived growth factor. 3 Localization and function of HB-EGF have been demonstrated in human hepatocellular carcinoma, 4 gastric mucosa, 5 wound fluid, 6 and balloon-injured rat carotid arteries. 7 Moreover, we have reported that HB-EGF is produced by macrophages and SMCs in the human aorta 8 and coronary arteries. 9 The HB-EGF precursor (proHB-EGF) is expressed on the cell membrane as a membrane-anchored form and can be cleaved to yield a mature biologically active form (soluble HB-EGF). 10 HB-EGF released by SMCs showed mitogenic function in an autocrine and a paracrine fashion. 11 Furthermore, proHB-EGF has also been demonstrated to have a mitogenic activity under the condition of cell-to-cell contact 12 by a so-called juxtacrine mechanism. 13 The juxtacrine growth factor activity of proHB-EGF in mouse L cells is dramatically upregulated Ϸ30-fold when coexpressed with CD9, 12 which was first identified as a cell surface antigen on lymphohematopoietic cells. 14,15 Thus, in the process of atherogenesis, CD9 may be involved in the proliferation of SMCs. In the present study, we investigated the immunohistochemical localization of CD9 and proHB-EGF in human coronary arteries and aorta and examined in vitro the effects of CD9 on the proliferation of human aortic SMCs.

Sunitinib, a Small-Molecule Receptor Tyrosine Kinase Inhibitor, Suppresses Neointimal Hyperplasia in Balloon-Injured Rat Carotid Artery

“…However, using the same assessment, sunitinib did not affect HASMC proliferation induced by HB-EGF, another mitogenic growth factor. 27,28 Moreover, the Boyden chamber assay showed that sunitinib also suppressed HASMC migration induced by PDGFs but not by HB-EGF. These results suggest that sunitinib may significantly and specifically inhibit PDGF-induced VSMC proliferation and migration.…”

Membrane-associated HB-EGF modulates HGF-induced cellular responses in MDCK cells

“…ProHB-EGF may serve a variety of functions depending on its cellular context and has been reported to be mitogenic and cytoprotective in some cells while growth inhibitory and proapoptotic in others (Iwamoto et al, 1999;Nishida et al, 2000;Takemura et al, 1997). ProHB-EGF has also been suggested to promote cell-cell adhesion (Kimber, 2000;Takemura et al, 1997).…”

EGFR Transactivation in the Regulation of SMC Function

“…The functional significance of this elevated expression, however, has not yet been demonstrated. Elevated expression of CD9, an enhancer of pro‐HB‐EGF bioactivity, has also been reported in human atherosclerotic plaques 82. Based on the available data in cultured SMCs showing a requirement of EGFR activation by thrombin and angiotensin II, both regulators of SMC function in vivo , we hypothesize that the EGFR may have an important role in the arterial injury response.…”

“…Elevated expression of CD9, an enhancer of pro-HB-EGF bioactivity, has also been reported in human atherosclerotic plaques. 82 Based on the available data in cultured SMCs showing a requirement of EGFR activation by thrombin and angiotensin II, both regulators of SMC function in vivo, we hypothesize that the EGFR may have an important role in the arterial injury response. It will be an important task to test this hypothesis and to delineate the function of the EGFR in vascular biology.…”