L1/HNK-1 carbohydrate- and beta 1 integrin-dependent neural cell adhesion to laminin-1.
We have shown recently that mouse small cerebellar neurons adhere to a short amino acid sequence of the G2 domain of the laminin alpha 1 chain via the cell surface-expressed HNK-1 carbohydrate. Therefore, we were interested in identifying glycoproteins carrying the HNK-1 carbohydrate at the cell surface of these neurons. Adhesion of small cerebellar neurons to laminin is partially dependent on Ca2+, Mn2+, and Mg2+, indicating the involvement of integrins, which were identified as beta 1, alpha 3, and alpha 6. They could be shown to bind to laminin by a beta 1-dependent adhesion mechanism. None of these subunits was found to carry the HNK-1 carbohydrate. HNK-1-immunoreactive glycoproteins were immunoprecipitated and shown to consist of predominantly one molecular species, which was identified as the neural cell recognition molecule L1. L1 was demonstrated to bind in a concentration-dependent and saturating manner to laminin. The binding could be partially inhibited by Fab fragments of monoclonal antibodies against the HNK-1 carbohydrate and against the Ig-like domains of L1. Furthermore, antibodies to the Ig-like domains of L1 and beta 1 integrin inhibited partially cell adhesion to laminin. Determination of the association of L1, beta 1 integrin, and the HNK-1 carbohydrate on the cell surface of live cerebellar neurons by antibody-induced patching and copatching revealed HNK-1 to be linked to L1, but less so to beta 1 integrin. However, only negligible association was found between L1 and beta 1 integrin. Furthermore, it could be shown that adhesion to laminin is mediated by L1/HNK-1- and beta 1 integrin-dependent mechanisms that act at least partially independent of each other.
Hall
H
H
Department of Neurobiology, Swiss Federal Institute of Technology, Zurich, Switzerland.
Carbonetto
S
S
Schachner
M
M
D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D018959:CD57 Antigens / Q000737:chemistry* / Q000378:metabolism; D002241:Carbohydrates / Q000032:analysis; D002413:Cations, Divalent / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000737:chemistry* / Q000378:metabolism; D002531:Cerebellum / Q000737:chemistry / Q000166:cytology; D006023:Glycoproteins / Q000032:analysis / Q000737:chemistry; D019012:Integrin beta1 / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D007797:Laminin / Q000378:metabolism*; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008813:Mice, Inbred ICR; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding / Q000502:physiology
D000954:Antigens, Surface; D018959:CD57 Antigens; D002241:Carbohydrates; D002413:Cations, Divalent; D015816:Cell Adhesion Molecules, Neuronal; D006023:Glycoproteins; D019012:Integrin beta1; D007797:Laminin; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins; D010446:Peptide Fragments