Transcriptional regulation of the platelet-derived growth factor α receptor gene via CCAAT/enhancer-binding protein-δ in vascular smooth muscle cells

Abstract

Inflammatory cytokines stimulate the proliferation of vascular smooth muscle cells (VSMC) and play a pivotal role in the pathogenesis of vascular diseases including atherosclerosis and restenosis. Mitogenic response of interleukin-1β (IL-1β) on VSMC is thought to be mediated by induction of endogenous platelet-derived growth factor (PDGF), especially PDGF-AA. Although the action of PDGF-AA is mediated by its specific receptor, PDGFα- receptor (PDGFαR), very little is known about the regulatory mechanism of PDGFtαR gene expression in VSMC. To understand the mechanism, we studied the transcriptional control of the PDGFαR gene in VSMC after treatment with IL- 1β. IL-1β (10 ng/ml) drastically increased both PDGFαR and CCAAT/enhancer- binding protein δ (C/EBPδ) mRNA levels in a time dependent manner. A rapid induction of C/EBPδ mRNA within 30 min was followed by slower emergence of PDGFαR mRNA, which reached the maximum level in 12 h, whereas C/EBPδ mRNA was detectable at 30 min and reached the maximum level at 3 h. Electromobility shift and supershift assays revealed that IL-1β markedly increased DNA-protein complex, which was mainly composed of C/EBPβ and/or - δ. Both Western blotting and immunohistochemistry demonstrated that either C/EBPβ or -δ expression was induced by IL-1β exclusively in nuclei of VSMC. On the other hand, overexpression of C/EBPδ specifically transactivated the promoter activity of the PDGFαR gene and significantly enhanced VSMC proliferation in PDGF-treated cells. We conclude that induction of PDGFαR expression is mainly mediated by C/EBPδ expression in VSMC, and a high level of C/EBPδ expression may be involved in the pathogenesis of atherosclerosis and restenosis.