Binding of αII spectrin to 14-3-3β is involved in NCAM-dependent neurite outgrowth

Members of the 14-3-3 protein family have been implicated in neuronal migration, synaptic plasticity and learning. Using affinity chromatography followed by mass spectrometry analysis, we show here that the cytoskeletal protein αII spectrin is a novel ligand of 14-3-3β. We found that 14-3-3β interacts with αII spectrin via the mode 2 14-3-3 binding motif RLIQS1302HP. Binding required phosphorylation of Ser1302 by casein kinase II and was enhanced in the presence of calmodulin. Co-immunoprecipitation of αII spectrin and 14-3-3β with the neural cell adhesion molecule NCAM suggested that the 14-3-3-spectrin-interaction affects NCAM function. Indeed, disruption of the 14-3-3β/αII spectrin interaction by mutating Ser1302 to Ala enhanced NCAM-dependent neurite outgrowth. Our results indicate that the phosphorylation-dependent interaction between 14-3-3β and αII spectrin acts as a switch between positive and negative regulation of neurite outgrowth stimulated by NCAM, representing a novel and acute mechanism preventing uncontrolled elongation of neuronal processes.