Stanimirovic D B, Ball R, Mealing G, Morley P, Durkin J P
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Canada.
Glia. 1995 Oct;15(2):119-30. doi: 10.1002/glia.440150204.
The increased expression of immunoreactive endothelin-1 (ET-1) in reactive astrocytes and its mitogenic effects on astrocytes and glioma cell lines, have implicated endothelins in the development of reactive gliosis. In this study, an increase in DNA synthesis in rat type I astrocytes was observed after cultures were transiently exposed to ET-1 for 15 min, suggesting that early signal transduction events are essential and sufficient for the propagation of the ET-1-induced mitogenic signal. Prompt increases in inositol triphosphate (IP3) formation and [Ca2+]i were observed upon the addition of ET-1 to these cells. The ET-1-evoked increase in [Ca2+]i consisted of an initial peak which was preserved in Ca(2+)-free medium, and a sustained phase which was abolished in Ca(2+)-free medium and partly attenuated by nifedipine. ET-1 also increased the activity of membrane-associated protein kinase C (PKC) and induced the in vivo phosphorylation of the 85 kD MARCKS protein, an endogenous PKC-specific substrate. The ET-1-evoked increases in DNA synthesis, IP3, [Ca2+]i, membrane PKC, and 85 kD MARCKS protein phosphorylation in rat cortical astrocytes were prevented by either the selective endothelin ETA receptor antagonist, BQ-123, or the phospholipase C (PLC)-specific inhibitor, U-73122. However, the inhibition of PKC activity did not affect ET-1-induced DNA synthesis in rat cortical astrocytes. These results suggest that ET-1-induced IP3 and/or [CA2+]i responses, but not the activation of PKC, are essential for the growth-factor like actions of ET-1 in rat cortical astrocytes.
免疫反应性内皮素-1（ET-1）在反应性星形胶质细胞中的表达增加及其对星形胶质细胞和胶质瘤细胞系的促有丝分裂作用，提示内皮素参与了反应性胶质增生的发展。在本研究中，大鼠I型星形胶质细胞短暂暴露于ET-1 15分钟后，观察到DNA合成增加，这表明早期信号转导事件对于ET-1诱导的促有丝分裂信号的传递至关重要且足够。向这些细胞中添加ET-1后，观察到肌醇三磷酸（IP3）形成和细胞内钙离子浓度（[Ca2+]i）迅速增加。ET-1引起的[Ca2+]i增加包括一个在无钙培养基中保留的初始峰值和一个在无钙培养基中消失且部分被硝苯地平减弱的持续阶段。ET-1还增加了膜相关蛋白激酶C（PKC）的活性，并诱导了内源性PKC特异性底物85 kD MARCKS蛋白的体内磷酸化。选择性内皮素ETA受体拮抗剂BQ-123或磷脂酶C（PLC）特异性抑制剂U-73122均可阻止ET-1引起的大鼠皮质星形胶质细胞中DNA合成、IP3、[Ca2+]i、膜PKC和85 kD MARCKS蛋白磷酸化的增加。然而，PKC活性的抑制并不影响ET-1诱导的大鼠皮质星形胶质细胞中的DNA合成。这些结果表明，ET-1诱导的IP3和/或[Ca2+]i反应，而非PKC的激活，对于ET-1在大鼠皮质星形胶质细胞中的生长因子样作用至关重要。
