Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo 157-8535, Japan.
Sci Signal. 2013 Mar 5;6(265):ra15. doi: 10.1126/scisignal.2003661.
During neuronal development, axons navigate long distances, eventually forming precise connections with such targets as peripheral tissues. Dock6 is a guanine nucleotide exchange factor (GEF) that activates the Rho family guanosine triphosphatases Rac1 and Cdc42 to regulate the actin cytoskeleton. We found that phosphorylation of Ser(1194) in Dock6 inhibited its GEF activity and suppressed axonal growth of embryonic sensory neurons and axon regeneration of postnatal sensory neurons in vitro and in vivo. At early developmental stages, when axons are growing, the protein phosphatase PP2A interacted with and dephosphorylated Dock6, thereby increasing the activity of Dock6. At later developmental stages, the abundance of the kinase Akt increased, resulting in the binding of Akt to Dock6 and the phosphorylation of Dock6 at Ser(1194). In dorsal root ganglion neurons from mice lacking Dock6, reintroduction of Dock6 with a nonphosphorylatable S1194A mutation rescued axon extension but not branch number, whereas reintroduction of Dock6 with a phosphomimetic S1194E mutation resulted in premature branching. Thus, the phosphorylation status of Dock6 at Ser(1194) determines whether it promotes axon extension or branching in sensory neurons, revealing interplay between kinase and phosphatase action on a Rho-GEF during axon growth.
在神经元发育过程中，轴突会进行长距离导航，最终与外周组织等靶标形成精确的连接。Dock6 是一种鸟嘌呤核苷酸交换因子 (GEF)，可激活 Rho 家族鸟苷三磷酸酶 Rac1 和 Cdc42，从而调节肌动蛋白细胞骨架。我们发现 Dock6 丝氨酸 1194 位的磷酸化抑制了其 GEF 活性，从而抑制了胚胎感觉神经元的轴突生长和体外及体内的出生后感觉神经元的轴突再生。在早期发育阶段，当轴突生长时，蛋白磷酸酶 PP2A 与 Dock6 相互作用并使后者去磷酸化，从而增加了 Dock6 的活性。在后期发育阶段，激酶 Akt 的丰度增加，导致 Akt 与 Dock6 结合以及 Dock6 丝氨酸 1194 位的磷酸化。在缺乏 Dock6 的小鼠背根神经节神经元中，引入不能磷酸化的 S1194A 突变 Dock6 可挽救轴突延伸，但不能挽救分支数量，而引入具有磷酸模拟 S1194E 突变的 Dock6 则导致过早分支。因此，Dock6 丝氨酸 1194 位的磷酸化状态决定了其是促进感觉神经元的轴突延伸还是分支，揭示了激酶和磷酸酶在轴突生长过程中对 Rho-GEF 的相互作用。
