Enhancement of neurite outgrowth by the soluble form of human L1 (neural cell adhesion molecule).

L1, a neural cell adhesion molecule, is involved in neurite outgrowth, migration and fasciculation. Although L1 is a membrane glycoprotein expressed on neural cells, the soluble form of L1 is generated in vivo by proteolysis. In the present study, a stable transfectant of Chinese hamster ovary (CHO) cells secreting human L1 without cytoplasmic and membrane spanning domains was generated, and the function of the secreted L1 was examined. Explants from embryonic chick brain stem were cultured on a substrate coated with polyethylenimine (PEI) alone, on substrate-bound L1 or in medium containing soluble L1. The neurites induced by L1, both the substrate-bound form and the soluble form, were 2-3 times longer than those cultured on PEI. The ability of the soluble L1 to induce neurite formation was slightly greater than that of the substrate L1. The present results demonstrated that neurite outgrowth was induced not only by substrate-bound L1 but also by soluble L1. Soluble L1 could be a pharmaceutical candidate for the promotion of nerve regeneration.