Chae K-S, Dryer S E
Department of Biology and Biochemistry, University of Houston, Houston, TX 77205-5001, USA.
Neuroscience. 2005;135(4):1013-6. doi: 10.1016/j.neuroscience.2005.06.060. Epub 2005 Sep 13.
Endogenous beta-neuregulin-1 is required for the plasma membrane expression of large-conductance (BK-type) Ca2+-activated K+ channels in developing chick ciliary neurons of the chick ciliary ganglion. During normal development, beta-neuregulin-1 acts in concert with transforming growth factor-beta1 to stimulate movement of large-conductance Ca2+-activated K+ channels from intracellular stores into the plasma membrane, although these two growth factors preferentially act on different intracellular pools. We have previously shown that actions of transforming growth factor-beta1 on ciliary neurons require activation of phosphoinositol 3-kinase and Akt, as well as a parallel cascade composed of the small GTPase Ras and a mitogen-activated protein kinase (extracellular signal-regulated kinase). In addition, we have shown that the actions of beta-neuregulin-1 require activation of phosphoinositol 3-kinase and the protein kinase Akt. Here we examine whether beta-neuregulin-1-evoked mobilization of large-conductance Ca2+-activated K+ channels also requires activation of a Ras-extracellular signal-regulated kinase signaling cascade. We observed that application of beta-neuregulin-1 caused a robust and MEK1/2-dependent increase in extracellular signal-regulated kinase diphosphorylation that indicates activation of this signaling cascade in ciliary ganglion neurons, similar to what we have previously observed for transforming growth factor-beta1. However, activation of this cascade is not necessary for beta-neuregulin-1-evoked mobilization because stimulation of macroscopic large-conductance Ca2+-activated K+ channels persisted in cells treated with the MEK1/2 inhibitors PD98059 or U0126, in cells over-expressing dominant-negative forms of extracellular signal-regulated kinase, and in cells treated with the Ras inhibitor FTI-277. These results indicate that the mechanisms that underlie beta-neuregulin-1 and transforming growth factor-beta1 mobilization of large-conductance Ca2+-activated K+ channels are only partly overlapping, possibly because they cause recruitment of spatially distinct signaling complexes.
内源性β-神经调节蛋白-1是雏鸡睫状神经节发育中的睫状神经元大电导（BK型）Ca2+激活K+通道质膜表达所必需的。在正常发育过程中，β-神经调节蛋白-1与转化生长因子-β1协同作用，刺激大电导Ca2+激活K+通道从细胞内储存库转运到质膜，尽管这两种生长因子优先作用于不同的细胞内池。我们之前已经表明，转化生长因子-β1对睫状神经元的作用需要磷酸肌醇3激酶和Akt的激活，以及由小GTP酶Ras和丝裂原活化蛋白激酶（细胞外信号调节激酶）组成的平行级联反应。此外，我们还表明，β-神经调节蛋白-1的作用需要磷酸肌醇3激酶和蛋白激酶Akt的激活。在这里，我们研究β-神经调节蛋白-1诱发的大电导Ca2+激活K+通道的动员是否也需要Ras-细胞外信号调节激酶信号级联反应来激活。我们观察到，应用β-神经调节蛋白-1会导致细胞外信号调节激酶双磷酸化的强烈且MEK1/2依赖性增加，这表明该信号级联反应在睫状神经节神经元中被激活，这与我们之前对转化生长因子-β1的观察结果相似。然而，该级联反应的激活对于β-神经调节蛋白-1诱发的动员并非必需，因为在用MEK1/2抑制剂PD98059或U0126处理的细胞中、在过表达细胞外信号调节激酶显性负性形式的细胞中以及在用Ras抑制剂FTI-277处理的细胞中，宏观大电导Ca2+激活K+通道的刺激仍然持续存在。这些结果表明，β-神经调节蛋白-1和转化生长因子-β1动员大电导Ca2+激活K+通道的潜在机制只是部分重叠，可能是因为它们导致了空间上不同的信号复合物的募集。
