Paris S, Chambard J C, Pouysségur J
Centre de Biochimie, Université de Nice, Faculté des Sciences, Parc Valrose, France.
J Biol Chem. 1988 Sep 15;263(26):12893-900.
Basic fibroblast growth factor (FGF) and alpha-thrombin can stimulate DNA synthesis in Chinese hamster fibroblasts (CCL39) by two separate signaling pathways (Chambard, J.C., Paris, S., L'Allemain, G., and Pouysségur, J. (1987) Nature 326, 800-803) but can also act synergistically. We have examined whether this synergism might depend upon changes in inositol lipid metabolism. Indeed, FGF, which has no effect on its own on phosphoinositide hydrolysis, potentiates (by up to 2-fold) thrombin-induced formation of inositol phosphates. This enhancing effect is also observed upon direct activation by AIF4- of the GTP-binding protein coupled to phospholipase C, and is best revealed when phospholipase C is weakly stimulated. With low thrombin concentrations or with AIF4-, the formation of inositol phosphates is immediately increased with a marked reduction of the initial lag, whereas at high thrombin concentrations, the stimulation by FGF becomes pronounced only after desensitization of phospholipase C to thrombin. FGF-induced potentiation is not mimicked by calcium ionophores, but is likewise elicited by epidermal growth factor, platelet-derived growth factor, and to a lesser extent by insulin, other growth factors known to activate receptor tyrosine kinases. We therefore propose that the tyrosine kinase-activating growth factors enhance the coupling between GTP-binding protein and phospholipase C, presumably through the phosphorylation of one of these two proteins. Treatment of cells with pertussis toxin attenuates thrombin-induced phospholipase C activity but does not impede the potentiation by FGF. Comparison of the potentiating effects of FGF on inositol phosphate formation and on DNA synthesis suggests than an increased production of second messengers by the inositol lipid pathway in the first hours of stimulation might be, at least in part, responsible for the synergistic actions of FGF and thrombin on DNA synthesis.
碱性成纤维细胞生长因子（FGF）和α-凝血酶可通过两条独立的信号通路刺激中国仓鼠成纤维细胞（CCL39）中的DNA合成（尚巴尔，J.C.，帕里斯，S.，拉勒曼，G.，和普伊斯瑟古尔，J.（1987年）《自然》326卷，800 - 803页），但它们也能协同发挥作用。我们研究了这种协同作用是否可能取决于肌醇脂质代谢的变化。实际上，FGF自身对磷酸肌醇水解没有影响，但能增强（高达2倍）凝血酶诱导的肌醇磷酸形成。在通过AIF4 - 直接激活与磷脂酶C偶联的GTP结合蛋白时也观察到这种增强作用，并且当磷脂酶C受到微弱刺激时最为明显。在低凝血酶浓度或使用AIF4 - 时，肌醇磷酸的形成立即增加，初始延迟明显缩短，而在高凝血酶浓度下，FGF的刺激仅在磷脂酶C对凝血酶脱敏后才变得明显。FGF诱导的增强作用不能被钙离子载体模拟，但表皮生长因子、血小板衍生生长因子以及程度较轻的胰岛素（已知能激活受体酪氨酸激酶的其他生长因子）也能引发这种作用。因此，我们提出激活酪氨酸激酶的生长因子增强了GTP结合蛋白与磷脂酶C之间的偶联，大概是通过这两种蛋白之一的磷酸化实现的。用百日咳毒素处理细胞会减弱凝血酶诱导的磷脂酶C活性，但不会阻碍FGF的增强作用。FGF对肌醇磷酸形成和DNA合成的增强作用比较表明，在刺激的最初几个小时内，肌醇脂质途径中第二信使产量的增加可能至少部分地是FGF和凝血酶对DNA合成协同作用的原因。
