title: The L1 adhesion molecule is a cellular ligand for VLA-5.
abstract: The L1 adhesion molecule is a member of the immunoglobulin superfamily shared by neural and immune cells. In the nervous system L1 can mediate cell binding by a homophilic mechanism. To analyze its function on leukocytes we studied whether L1 could interact with integrins. Here we demonstrate that VLA-5, an RGD-specific fibronectin receptor on a wide variety of cell types, can bind to murine L1. Mouse ESb-MP cells expressing VLA-5 and L1 could be induced to aggregate in the presence of specific mAbs to CD24 (heat-stable antigen), a highly and heterogeneously glycosylated glycophosphatidylinositol-linked differentiation antigen of hematopoietic and neural cells. The aggregation was blocked by both mAbs to L1 and VLA-5, respectively. Aggregation was blocked also by a synthetic RGD-containing peptide derived from the Ig-domain VI of the L1 protein. ESb-MP subclones with low L1 expression could not aggregate. In heterotypic binding assays mouse bone marrow cells could adhere in an L1-dependent fashion to platelets that expressed VLA-5. Also purified L1 coated to polystyrene beads could bind to platelets. The binding of L1-beads was again inhibited by mAbs to L1 and VLA-5, by soluble L1 and the L1-RGD peptide in a dose-dependent manner. Thymocytes or human Nalm-6 tumor cells expressing VLA-5 could adhere to affinity-purified L1 and to the L1-derived RGD-containing peptide coated to glass slides. The adhesion was strongly enhanced in the presence of Mn(2+)-ions and blocked by mAbs to VLA-5. We also demonstrate a direct L1-VLA-5 protein interaction. Our results suggest a novel binding pathway, in which the VLA-5 integrin binds to L1 on adjacent cells. Given its rapid downregulation on lymphocytes after induction of cell proliferation, L1 may be important in integrin-mediated and activation-regulated cell-cell interactions.
authors.affiliation: Tumor Immunology Programme, German Cancer Research Center, Heidelberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ruppert
authors.forename: S
authors.initials: S
authors.lastname: Aigner
authors.forename: M
authors.initials: M
authors.lastname: Hubbe
authors.forename: H
authors.initials: H
authors.lastname: Yagita
authors.forename: P
authors.initials: P
authors.lastname: Altevogt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000935:Antifungal Agents / Q000378:metabolism*; D001792:Blood Platelets / Q000166:cytology; D001854:Bone Marrow Cells; D002448:Cell Adhesion / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D039841:Leukocyte L1 Antigen Complex; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000166:cytology; D019006:Neural Cell Adhesion Molecules / Q000302:isolation & purification / Q000378:metabolism*; D009842:Oligopeptides / Q000302:isolation & purification / Q000378:metabolism; D017469:Receptors, Fibronectin / Q000276:immunology / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000935:Antifungal Agents; D039841:Leukocyte L1 Antigen Complex; D019006:Neural Cell Adhesion Molecules; D009842:Oligopeptides; D017469:Receptors, Fibronectin; C047981:arginyl-glycyl-aspartic acid