CHL1 organizes ankyrin-B / ßII spectrin based cytoskeleton in developing neurons (Mus musculus L., 1758)

Abstract

Close homolog of L1 (CHL1) is a member of the L1 family of cell adhesion molecules， which belongs to the immunoglobulin superfamily. In developing brains, CHL1 regulates neuronal migration and axon outgrowth and guidance. The dynamic regulation of cell adhesion through coupling of adhesion receptors with the cytoskeleton is important for these processes. However, the molecular mechanisms by which CHL1 regulates the cytoskeleton remain poorly investigated. Here we report that CHL1 associates with βII spectrin, a membrane-cytoskeleton linker protein which is involved in membrane stabilization as well as vesicle trafficking, independently of its adaptor ankyrin-B. In brains of young CHL1 deficient mice, targeting of βII spectrin to growth cones is reduced, implicating CHL1 as a growth cone-targeting cue for βII spectrin. CHL1 enhances association of βII spectrin with lipid raft micro-domain. Furthermore, we show that CHL1 antibody-treatment induces internalization of CHL1, which is dependent on Ca2+ influx via L-type calcium channels. The association of CHL1 with lipid rafts is required for its internalization and CHL1-dependent detachment of βII spectrin from the plasma membrane. Considering that the polymerization of spectrin meshwork is increased in CHL1 deficient mice, CHL1 may regulate depolymerization of spectrin meshwork through lipid rafts related Ca2+ signaling. For the functional study, we demonstrate that CHL1 antibody-application to live cells in vitro promotes neurite outgrowth, and this effect is abolished either by pharmacological treatments that deplete cellular cholesterol and sphingolipids, or by mutation of CHL1 at the palmitoylation site, suggesting lipid rafts are important for CHL1 dependent neurite outgrowth. Taken together, our data suggest that the dynamic interaction between βII spectrin and CHL1 dependent on lipid rafts plays a role in CHL1-mediated neurite outgrowth.