Structural requirements for the stimulation of neurite outgrowth by two variants of laminin and their inhibition by antibodies.
Laminin derived from the Engelbreth-Holm-Swarm (EHS) tumor and a lamininlike molecule synthesized by RN22 Schwannoma cells both stimulate rapid neurite outgrowth, consistent with a common neurite-promoting site. However, antilaminin antisera can only inhibit the activity of the EHS laminin. The blocking antibodies in such sera are directed against the terminal heparin-binding domain of the laminin long arm (Edgar, D., R. Timpl, and H. Thoenen. 1984. EMBO [Eur. Mol. Biol. Organ.] J. 3: 1463-1468). These epitopes are demonstrated by immunoblotting to be part of the A chain and to be absent in RN22 laminin, showing (through metabolic labeling) that the cells synthesized little if any 440-kD A chain. This indicates that the antibody inhibition was probably due to steric hindrance, a common neurite-promoting site, apparently not being antigenic in native molecules. Antibodies raised against a 25-kD proteolytic fragment derived from the long arm of laminin were then used as probes to identify other potential neurite-promoting structures. Although these antibodies do not cross-react with native laminin, they recognized the B chains of denatured EHS and RN22 molecules on immunoblots. The antibodies also bound to the large proteolytic fragment, derived from the long arm of laminin that contains the neurite-promoting site, thus inhibiting its activity. Taken together, these results point to the localization of normally nonantigenic, defined, B chain sequences within or close to the neurite-promoting site of laminin.
D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001369:Axons / Q000502:physiology*; D001667:Binding, Competitive; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000276:immunology; D007118:Immunoassay; D007797:Laminin / Q000276:immunology / Q000502:physiology*; D009442:Neurilemmoma / Q000378:metabolism*; D012513:Sarcoma, Experimental / Q000378:metabolism*; D013724:Teratoma; D014407:Tumor Cells, Cultured
D000906:Antibodies; D000939:Epitopes; D007797:Laminin