Nakano T, Raines E W, Abraham J A, Wenzel F G, Higashiyama S, Klagsbrun M, Ross R
Department of Pathology, University of Washington, Seattle 98195.
J Biol Chem. 1993 Oct 25;268(30):22941-7.
Proliferation of smooth muscle cells (SMCs) in atherosclerosis may be modulated by several growth regulatory molecules. At least two mitogens for SMCs, platelet-derived growth factor (PDGF) A-chain and heparin-binding epidermal growth factor-like growth factor (HB-EGF), can be produced by SMCs themselves and may stimulate smooth muscle proliferation in an autocrine or paracrine fashion. We examined the effects of thrombin, which may be generated at the site of vascular injury during atherogenesis, and the potent anti-inflammatory glucocorticoid, dexamethasone (DEX), on the expression of the genes encoding these two growth factors. Since both PDGF A-chain and HB-EGF have affinity for heparin, we also examined the effect of thrombin and DEX on the release of heparin binding mitogenic activity from SMCs. Treatment of SMCs with thrombin resulted in increases both in the level of the PDGF-A and HB-EGF transcripts in the cells, as well as in released heparin-binding growth factor activity. DEX inhibits the thrombin-stimulated release of mitogenic activity in a dose-dependent manner. An enzyme-linked immunoadsorbent assay showed that DEX inhibits both constitutive and thrombin-stimulated release of PDGF-AA. DEX also decreases both constitutive and thrombin-stimulated mRNA levels for PDGF A-chain and HB-EGF and destabilizes the transcripts for both growth factors. A nuclear run-on assay revealed that DEX acts, in addition, to inhibit constitutive and thrombin-stimulated transcription of the PDGF A-chain and HB-EGF genes. Thus, these findings indicate that expression of PDGF A-chain and HB-EGF may be regulated by thrombin and glucocorticoid at the transcription level. Our results are consistent with the involvement of thrombin-induced growth factor expression in neointimal SMC proliferation and suggest the possibility that intimal proliferation may be attenuated by glucocorticoids.
动脉粥样硬化中平滑肌细胞（SMC）的增殖可能受到多种生长调节分子的调控。至少有两种SMC的促有丝分裂原，即血小板衍生生长因子（PDGF）A链和肝素结合表皮生长因子样生长因子（HB-EGF），可由SMC自身产生，并可能以自分泌或旁分泌方式刺激平滑肌增殖。我们研究了凝血酶（在动脉粥样硬化形成过程中可能在血管损伤部位产生）和强效抗炎糖皮质激素地塞米松（DEX）对编码这两种生长因子的基因表达的影响。由于PDGF A链和HB-EGF都对肝素有亲和力，我们还研究了凝血酶和DEX对SMC释放肝素结合促有丝分裂活性的影响。用凝血酶处理SMC导致细胞内PDGF-A和HB-EGF转录本水平以及释放的肝素结合生长因子活性均增加。DEX以剂量依赖的方式抑制凝血酶刺激的促有丝分裂活性释放。酶联免疫吸附测定表明，DEX抑制PDGF-AA的组成性和凝血酶刺激的释放。DEX还降低了PDGF A链和HB-EGF的组成性和凝血酶刺激的mRNA水平，并使两种生长因子的转录本不稳定。细胞核转录分析表明，DEX还可抑制PDGF A链和HB-EGF基因的组成性和凝血酶刺激的转录。因此，这些发现表明PDGF A链和HB-EGF的表达可能在转录水平受到凝血酶和糖皮质激素的调节。我们的结果与凝血酶诱导的生长因子表达参与新生内膜SMC增殖一致，并提示内膜增殖可能被糖皮质激素减弱的可能性。
