Akt and PP2A Reciprocally Regulate the Guanine Nucleotide Exchange Factor Dock6 to Control Axon Growth of Sensory Neurons

Abstract

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.

AP-1/σ1B-Dependent SV Protein Recycling Is Regulated in Early Endosomes and Is Coupled to AP-2 Endocytosis

“…2) is in line with the increase in Dock6. Akt kinase, activated by PIP 3 , inhibits Dock6 [58]. This supports the data on altered cytoskeleton dynamics.…”

Insights into the biological functions of Dock family guanine nucleotide exchange factors

“…The additional finding that Dock6 is highly expressed in dorsal root ganglion neurons in vivo has prompted studies on its potential role in axon extension (Miyamoto et al 2013). Transgenic mice expressing shRNAs specific to Dock6 show a reduction in the length of peripheral axons at E11, and these mice also fail to form neuronal fiber extension in an injury model in vivo (Table 1; Miyamoto et al 2013). In agreement with in vivo observations, down-regulation of Dock6 expression in explanted dorsal root ganglion neurons impairs axon outgrowth and the extent of side branching.…”

Hypomyelinating leukodystrophy-associated missense mutation in HSPD1 blunts mitochondrial dynamics

“…Cells were scanned every 6 s for a duration of 12 min or 60 min (for movies or statistical data, respectively) using an IX81 microscope with a laser scanning FV1000 system. Values such as mitochondrial fission and fusion frequency and velocity were measured using MetaMorph software (Molecular Devices, Sunnyvale, CA, USA) [11,12]. The values were also confirmed through naked-eye observation of the sequence of photographs that constitutes the AVI file formatted movie.…”

“…The coverslips were mounted onto slides with Vectashield reagent with or without DAPI (Vector Laboratories, Burlingame, CA, USA) for observation using confocal microscopy. The confocal images were collected using an IX81 microscope with a laser-scanning FV500 or FV1000 system (Olympus, Tokyo, Japan) and analyzed using FluoView software (Olympus) [11,12]. For live imaging experiment, cells on CellView glass-bottom dishes (Greiner Bio-One) were cultured in a small CO 2 incubator (Tokai Hit, Shizuoka, Japan) in 5% CO 2 at 37 C and maintained in a culture medium.…”