Tranque P, Naftolin F, Robbins R
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut 06510.
Endocrinology. 1994 Jun;134(6):2606-13. doi: 10.1210/endo.134.6.8194486.
Rat astrocytes synthesize and secrete two types of plasminogen activators (PAs), tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), whose functions are related to cell proliferation, migration, and differentiation during development. The regulation of PAs produced by brain astrocytes is poorly understood. In a previous report we demonstrated that t-PA and u-PA are each independently regulated by cAMP-dependent protein kinase and protein kinase-C. In the present study we examined the effects of three well characterized astrocyte mitogens, insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), and platelet-derived growth factor (PDGF), on the PA activities produced and secreted by rat astrocytes in vitro. We found that IGF-I and EGF increase cell-associated total PA activity in astrocyte-conditioned medium (CM). The effects of both growth factors were dose and time dependent, and maximal stimulation was achieved after 72 h of treatment with the highest dose tested (100 nM). IGF-I stimulated the cell-associated PA activity more than the CM activity, whereas EGF showed an opposite pattern, suggesting that the secretion of PA is differentially modulated by IGF-I and EGF. PDGF had no effect on astrocyte PA activities at any dose or time point included in the study. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis/zymography showed type-specific changes in CM and cell-associated PA activity after growth factor treatment. IGF-I stimulated only t-PA, whereas EGF induced a marked increase in u-PA activity and a more limited increase in t-PA. PDGF did not modify either t-PA or u-PA activity. In summary, our results show that IGF-I and EGF each had different effects on PA activities, whereas PDGF had no effect. This diversity in the patterns of growth factor regulation of PAs suggests that the production of astrocyte PAs is not simply related to mitogenesis. More likely, astrocyte PAs are involved in a wide range of growth factor-mediated actions in the developing brain.
大鼠星形胶质细胞合成并分泌两种类型的纤溶酶原激活剂（PA），即组织型纤溶酶原激活剂（t-PA）和尿激酶型纤溶酶原激活剂（u-PA），它们的功能与发育过程中的细胞增殖、迁移和分化有关。目前对脑星形胶质细胞产生的PA的调节机制了解甚少。在之前的一份报告中，我们证明t-PA和u-PA各自独立地受cAMP依赖性蛋白激酶和蛋白激酶-C的调节。在本研究中，我们检测了三种特性明确的星形胶质细胞促有丝分裂剂，即胰岛素样生长因子-I（IGF-I）、表皮生长因子（EGF）和血小板衍生生长因子（PDGF），对体外培养的大鼠星形胶质细胞产生和分泌的PA活性的影响。我们发现IGF-I和EGF可增加星形胶质细胞条件培养基（CM）中与细胞相关的总PA活性。两种生长因子的作用均呈剂量和时间依赖性，在用最高测试剂量（100 nM）处理72小时后达到最大刺激效果。IGF-I对与细胞相关的PA活性的刺激作用大于对CM活性的刺激作用，而EGF则呈现相反的模式，这表明IGF-I和EGF对PA分泌的调节存在差异。在本研究涵盖的任何剂量或时间点，PDGF对星形胶质细胞PA活性均无影响。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳/酶谱分析显示，生长因子处理后，CM和与细胞相关的PA活性出现了类型特异性变化。IGF-I仅刺激t-PA，而EGF可显著增加u-PA活性，并使t-PA有更有限的增加。PDGF对t-PA或u-PA活性均无改变。总之，我们的结果表明IGF-I和EGF对PA活性各有不同影响，而PDGF无影响。PA生长因子调节模式的这种多样性表明，星形胶质细胞PA的产生不仅仅与有丝分裂有关。更有可能的是，星形胶质细胞PA参与了发育中大脑广泛的生长因子介导的作用。
