Wittmack Ellen K, Rush Anthony M, Hudmon Andy, Waxman Stephen G, Dib-Hajj Sulayman D
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Neurosci. 2005 Jul 13;25(28):6621-30. doi: 10.1523/JNEUROSCI.0541-05.2005.
Nav1.6 is the major sodium channel isoform at nodes of Ranvier in myelinated axons and, additionally, is distributed along unmyelinated C-fibers of sensory neurons. Thus, modulation of the sodium current produced by Nav1.6 might significantly impact axonal conduction. Mitogen-activated protein kinases (MAPKs) are expressed in neurons and are activated after injury, for example, after sciatic nerve transection and hypoxia. Although the role of MAPK in signal transduction and in injury-induced regulation of gene expression is well established, the ability of these kinases to phosphorylate and modulate voltage-gated sodium channels has not been reported. Sequence analysis shows that Nav1.6 contains a putative MAP kinase-recognition module in the cytoplasmic loop (L1), which joins domains 1 and 2. We show in this study that sodium channels and p38 MAP kinase colocalize in rat brain tissue and that activated p38alpha phosphorylates L1 of Nav1.6, specifically at serine 553 (S553), in vitro. None of the other cytoplasmic loops and termini of the channel are phosphorylated by activated p38alpha in these assays. Activation of p38 in the neuronal ND7/23 cell line transfected with Nav1.6 leads to a significant reduction in the peak Nav1.6 current amplitude, without a detectable effect on gating properties. The substitution of S553 with alanine within L1 of the Nav1.6 channel prevents p38-mediated reduction of Nav1.6 current density. This is the first demonstration of MAPK phosphorylation and modulation of a voltage-gated sodium channel, and this modulation may represent an additional role for MAPK in regulating the neuronal response to injury.
Nav1.6是有髓轴突郎飞结处的主要钠通道亚型，此外，还分布于感觉神经元的无髓C纤维上。因此，对Nav1.6产生的钠电流的调节可能会显著影响轴突传导。丝裂原活化蛋白激酶（MAPKs）在神经元中表达，并在损伤后被激活，例如在坐骨神经横断和缺氧后。虽然MAPK在信号转导和损伤诱导的基因表达调节中的作用已得到充分证实，但这些激酶磷酸化和调节电压门控钠通道的能力尚未见报道。序列分析表明，Nav1.6在连接结构域1和2的胞质环（L1）中包含一个假定的MAP激酶识别模块。我们在本研究中表明，钠通道和p38 MAP激酶在大鼠脑组织中共定位，并且在体外，活化的p38α可磷酸化Nav1.6的L1，特别是在丝氨酸553（S553）处。在这些实验中，通道的其他胞质环和末端均未被活化的p38α磷酸化。在转染了Nav1.6的神经元ND7/23细胞系中激活p38会导致Nav1.6电流峰值幅度显著降低，而对门控特性没有可检测到的影响。用丙氨酸替代Nav1.6通道L1中的S553可防止p38介导的Nav1.6电流密度降低。这是MAPK磷酸化和调节电压门控钠通道的首次证明，这种调节可能代表了MAPK在调节神经元对损伤的反应中的另一个作用。
