Isono F, Widmer H R, Hefti F, Knüsel B
Andrus Gerontology Center, University of Southern California, Los Angeles 90089.
J Neurochem. 1994 Oct;63(4):1235-45. doi: 10.1046/j.1471-4159.1994.63041235.x.
The protein kinase inhibitors K-252a and K-252b have been shown earlier to block the actions of nerve growth factor and other neurotrophins and, at lower concentrations, to selectively potentiate neurotrophin-3 actions. In the present study we show that K-252a, but not K-252b, enhances epidermal growth factor (EGF)-and basic fibroblast growth factor (BFGF)-induced neurite outgrowth of PC12 cells at higher concentrations than required for neurotrophin inhibition. In parallel, tyrosine phosphorylation of extracellular signal-regulated kinases (Erks) elicited by EGF of bFGF was also increased in the presence of K-252a, and this signal was prolonged for 6 h. EGF- and bFGF-induced phosphorylation of phospholipase C-gamma 1 were not changed. The effect of K-252a on Erks was resistant to chronic treatment with phorbol ester, indicating that protein kinase C is not involved in this potentiation. In partial contrast to the actions of K-252a, the neurotrophin-3-potentiating effect of K-252b was accompanied by an increase in tyrosine phosphorylation of the Erks and of phospholipase C-gamma 1. Finally, although K-252a alone did not induce neurite outgrowth or tyrosine phosphorylation of Erks or phospholipase C-gamma 1, this compound alone stimulated phosphatidylinositol hydrolysis. Our findings identify activities of K-252a besides the direct interaction with neurotrophin receptors and suggest that a K-252a-sensitive protein kinase or phosphatase might be involved in signal transduction of EGF and bFGF. Our results are further compatible with the hypothesis that sustained activation of Erks may be important in PC12 differentiation.
蛋白激酶抑制剂K - 252a和K - 252b先前已被证明可阻断神经生长因子和其他神经营养因子的作用，且在较低浓度时可选择性增强神经营养因子-3的作用。在本研究中，我们发现K - 252a而非K - 252b，在高于抑制神经营养因子所需的浓度下，可增强表皮生长因子（EGF）和碱性成纤维细胞生长因子（BFGF）诱导的PC12细胞神经突生长。同时，在K - 252a存在的情况下，由EGF或bFGF引发的细胞外信号调节激酶（Erks）的酪氨酸磷酸化也增加了，并且该信号延长了6小时。EGF和bFGF诱导的磷脂酶C -γ1的磷酸化没有变化。K - 252a对Erks的作用对佛波酯的长期处理具有抗性，表明蛋白激酶C不参与这种增强作用。与K - 252a的作用部分相反，K - 252b增强神经营养因子-3的作用伴随着Erks和磷脂酶C -γ1的酪氨酸磷酸化增加。最后，尽管单独的K - 252a不会诱导神经突生长或Erks或磷脂酶C -γ1的酪氨酸磷酸化，但该化合物单独刺激磷脂酰肌醇水解。我们的研究结果确定了K - 252a除了与神经营养因子受体直接相互作用之外的活性，并表明一种对K - 252a敏感的蛋白激酶或磷酸酶可能参与EGF和bFGF的信号转导。我们的结果进一步支持了持续激活Erks可能在PC12分化中起重要作用的假说。
