Our findings suggest that Akt signaling regulates neurite outgrowth by stabilizing radixin interactions with F-actin, thus facilitating local F-actin dynamics. Introduction Ezrin, radixin, and moesin, collectively known as ERM proteins, coordinate membraneCcytoskeletal interactions for various forms of cell motility including neuron morphogenesis. and growth cone formation. Our findings suggest that Akt signaling regulates neurite outgrowth by stabilizing radixin interactions with F-actin, thus facilitating local F-actin dynamics. Introduction Ezrin, radixin, Rabbit Polyclonal to TAF1A and moesin, collectively known as ERM proteins, coordinate membraneCcytoskeletal interactions for various forms of cell motility including neuron morphogenesis. ERM proteins share a C-terminal actin-binding domain name and an N-terminal FERM domain name that binds to membrane proteins such as CD44 and the axon adhesion molecule L11,2, thereby linking filamentous actin (F-actin) and the membrane to regulate growth cone dynamics3. ERM proteins also act as scaffolds for adaptor and signaling NBI-74330 molecules that regulate cytoskeletal dynamics. The activity of each ERM protein is usually regulated by the phosphorylation of a conserved threonine residue in the actin-binding domain (T567 in ezrin, T564 in radixin, and T558 in moesin) that blocks the intramolecular association of the N- and C-terminal regions and allows ERM proteins to bind to F-actin and other proteins4C7. However, it is not known whether additional phosphorylation on C-terminus of ERM is related to its functions. In developing neurons, ERM proteins are expressed in growth cones and among ERM proteins, radixin is usually predominant at the leading edge of dorsal root ganglion (DRG) growth cones8,9. In sympathetic neurons, nerve growth factor (NGF) deprivation-induced growth cone collapse is usually accompanied by a local decrease in radixin levels. The suppressed expression of radixin and moesin, but not of ezrin, NBI-74330 impairs growth cone morphology, cytoskeletal organization, and growth cone motility in cortical and hippocampal neurons10,11. In addition, the suppression of ERM phosphorylation by inhibiting phosphoinositide 3-kinase (PI-3K) in the growth cones of DRG axons results in growth cone collapse. The PI-3K pathway regulates diverse neuronal activities, mainly through the downstream molecule Akt/protein kinase B. In addition to a critical role in neuronal survival12C15, PI3K/Akt signaling has been implicated in dendritic morphogenesis16, neuronal polarity and growth17, synaptogenesis and spinogenesis18, plasticity19, axon establishment, and axon elongation during development by phosphorylating glycogen synthase kinase (GSK)-3, which leads to GSK3 inactivation20C23. While Akt is usually localized at the axon tip, phosphorylated (inactive) GSK3 is restricted to the tip of growing axons in cultured hippocampal neurons and regulates neuronal polarity. Moreover, Akt links a host of upstream signaling molecules to axon development, axon growth, and dendrite NBI-74330 elongation in the central nervous system (CNS) by activating mTORC1 and S6 kinase, which regulate cap-dependent protein translation, and by inhibiting TSC1/224C27. However, evidence suggests that an mTORC1-impartial pathway regulates axon regrowth in phosphatase and tensin homolog-deficient neurons28,29, causing the aberrant activation of Akt signaling. Moreover, our recent study showed that Akt1 regulates the formation of NBI-74330 growth cones and functions through the phosphorylation of S14 on inhibitor of DNA binding 2 (Id2), which is a unfavorable regulator of basic helixCloopChelix transcription factors30. Akt-phosphorylated Id2 accumulates at the tip of growing axons where radixin is usually enriched, and the association with radixin contributes to axon growth and proper growth cone function. Thus, Akt may regulate growth cone dynamics through alternative signaling pathways including the phosphorylation of ERM proteins. Phosphorylation can promote or inhibit protein ubiquitination in several ways. First, phosphorylation positively or negatively regulates E3 ligase activity through direct phosphorylation on it. For instance, Akt increased E3 ligase activity of Mdm2 by phosphorylation by preventing its autoubiquitination, thereby promotes UPS dependent degradation of p53, which is well known target of Mdm2. In contrast, Mdm2 activity is usually inhibited by c-Abl phosphorylation of Y394. Second, phosphorylation promotes recognition by an E3 ligase by creating a phosphodegron, short motif that mediate phosphorylation dependent recognition by E3 ligase. The majority of phosphorylation dependent ubiquitination targets are recognized by SCF (Skp1/cullin/ F-box protein).