AlphaII-spectrin participates in the surface expression of cell adhesion molecule L1 and neurite outgrowth

AlphaII-spectrin, a basic component of the spectrin-based scaffold which organizes and stabilizes membrane microdomains in most animal cells, has been recently implicated in cell adherence and actin dynamics. Here we investigated the contribution of all-spectrin to neuritogenesis, a highly complex cellular process which requires continuous actin cytoskeleton remodeling and cross-talk between extracellular cues and their cell surface receptors, including cell adhesion molecules. Using RNA interference-mediated gene silencing to down-regulate alpha II-spectrin expression in human neuroblastoma SH-SY5Y cells, we observed major changes in neurite morphology and cell shape: (1) reduced mean length and a higher number of neurites per cell; occasional long neurites were thinner and displayed abnormal adhesiveness during cell migration resulting in frequent breaks; similar persisting adhesiveness and breaks were also observed in trailing edges of cell bodies; (2) irregular polygonal cell shape in parallel with loss of cortical F-actin from neuronal cell bodies; (3) reduction in protein levels of alpha I- and beta I-spectrins, but not beta II-spectrin (4) decreased global expression of adhesion molecule L1 and spectrin-binding adapter ankyrin-B, which links L1 to the plasma membrane. Remarkably, alpha II-spectrin depletion affected L1 - but not NCAM - cell surface expression, and L1 clustering at growth cones. This study demonstrates that alpha II-spectrin is implicated in normal morphology and adhesive properties of neuron cell bodies and neurites, and in cell surface expression and organization of adhesion molecule L1. (C) 2014 Elsevier Inc. All rights reserved.