Banfi C, Mussoni L, Risé P, Cattaneo M G, Vicentini L, Battaini F, Galli C, Tremoli E
Institute of Pharmacological Sciences, University of Milan, Italy.
Circ Res. 1999 Jul 23;85(2):208-17. doi: 10.1161/01.res.85.2.208.
In normal subjects and in patients with cardiovascular disease, plasma triglycerides are positively correlated with plasminogen activator inhibitor type 1 (PAI-1) levels. Moreover, in vitro studies indicate that VLDLs induce PAI-1 synthesis in cultured cells, ie, endothelial and HepG2 cells. However, the signaling pathways involved in the effect of VLDL on PAI-1 synthesis have not yet been investigated. We report that VLDLs induce a signaling cascade that leads to an enhanced secretion of PAI-1 by HepG2 cells. In myo-[(3)H]inositol-labeled HepG2 cells, VLDL (100 microg/mL) caused a time-dependent increase in [(3)H]inositol phosphates, the temporal sequence being tris>bis>monophosphate. VLDL brought about a time-dependent stimulation of membrane-associated protein kinase C (PKC) activity and arachidonate release. Finally, VLDL stimulated mitogen-activated protein (MAP) kinase, and this effect was reduced by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), which suggests that PKC plays a pivotal role in MAP kinase phosphorylation. VLDL-induced PAI-1 secretion was completely prevented by U73122, a specific inhibitor of phosphatidylinositol-specific phospholipase C, by H7 or by PKC downregulation, and by mepacrine (all P<0.01 versus VLDL-treated cells). 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)-octyl ester, which prevents Ca2+ release from intracellular stores, inhibited VLDL-induced PAI-1 secretion by 60% (P<0.05), and the MAP kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor PD98059 completely suppressed both basal and VLDL-induced PAI-1 secretion. These data demonstrate that VLDL-induced PAI-1 biosynthesis results from a principal signaling pathway involving PKC-mediated MAP kinase activation.
在正常受试者和心血管疾病患者中，血浆甘油三酯与1型纤溶酶原激活物抑制剂（PAI-1）水平呈正相关。此外，体外研究表明，极低密度脂蛋白（VLDL）可诱导培养细胞（即内皮细胞和HepG2细胞）合成PAI-1。然而，VLDL对PAI-1合成作用所涉及的信号通路尚未得到研究。我们报告，VLDL可诱导一种信号级联反应，导致HepG2细胞PAI-1分泌增加。在肌醇-[(3)H]标记的HepG2细胞中，VLDL（100μg/mL）使[(3)H]肌醇磷酸酯呈时间依赖性增加，其时间顺序为三磷酸肌醇>二磷酸肌醇>单磷酸肌醇。VLDL引起膜相关蛋白激酶C（PKC）活性和花生四烯酸释放的时间依赖性刺激。最后，VLDL刺激丝裂原活化蛋白（MAP）激酶，1-(5-异喹啉磺酰基)-2-甲基哌嗪（H7）可降低这种作用，这表明PKC在MAP激酶磷酸化中起关键作用。U73122（一种磷脂酰肌醇特异性磷脂酶C的特异性抑制剂）、H7或PKC下调以及米帕林均可完全阻止VLDL诱导的PAI-1分泌（与VLDL处理的细胞相比，所有P<0.01）。3,4,5-三甲氧基苯甲酸8-(二乙氨基)辛酯可阻止Ca2+从细胞内储存释放，抑制VLDL诱导的PAI-1分泌60%（P<0.05），MAP激酶/细胞外信号调节激酶激酶（MEK）抑制剂PD98059可完全抑制基础和VLDL诱导的PAI-1分泌。这些数据表明，VLDL诱导的PAI-1生物合成源于一条主要的信号通路，该通路涉及PKC介导的MAP激酶激活。
