Neural cell adhesion molecule (NCAM) association with PKCβ₂ via βI spectrin is implicated in NCAM-mediated neurite outgrowth

In hippocampal neurons and transfected CHO cells, neural cell adhesion molecule (NCAM) 120, NCAM140, and NCAM180 form Triton X-100–insoluble complexes with βI spectrin. Heteromeric spectrin (αIβI) binds to the intracellular domain of NCAM180, and isolated spectrin subunits bind to both NCAM180 and NCAM140, as does the βI spectrin fragment encompassing second and third spectrin repeats (βI_2–3). In NCAM120-transfected cells, βI spectrin is detectable predominantly in lipid rafts. Treatment of cells with methyl-β-cyclodextrin disrupts the NCAM120–spectrin complex, implicating lipid rafts as a platform linking NCAM120 and spectrin. NCAM140/NCAM180–βI spectrin complexes do not depend on raft integrity and are located both in rafts and raft-free membrane domains. PKCβ₂ forms detergent-insoluble complexes with NCAM140/NCAM180 and spectrin. Activation of NCAM enhances the formation of NCAM140/NCAM180–spectrin–PKCβ₂ complexes and results in their redistribution to lipid rafts. The complex is disrupted by the expression of dominant-negative βI_2–3, which impairs binding of spectrin to NCAM, implicating spectrin as the bridge between PKCβ₂ and NCAM140 or NCAM180. Redistribution of PKCβ₂ to NCAM–spectrin complexes is also blocked by a specific fibroblast growth factor receptor inhibitor. Furthermore, transfection with βI_2–3 inhibits NCAM-induced neurite outgrowth, showing that formation of the NCAM–spectrin–PKCβ₂ complex is necessary for NCAM-mediated neurite outgrowth.