title: Cis-activation of L1-mediated ankyrin recruitment by TAG-1 homophilic cell adhesion.
abstract: Neural cell adhesion molecules (CAMs) of the immunoglobulin (Ig) superfamily mediate not only cell aggregation but also growth cone guidance and neurite outgrowth. In this study we demonstrate that two neural CAMs, L1-CAM and TAG-1, induce the homophilic aggregation of Drosophila S2 cells but are unable to interact with each other when expressed on different cells (trans-interaction). However, immunoprecipitations from cells co-expressing L1-CAM and TAG-1 showed a strong cis-interaction between the two molecules in the plane of the plasma membrane. TAG-1 is linked to the membrane by a glycosylphosphatidylinositol (GPI) anchor and therefore is unable to directly interact with cytoplasmic proteins. In contrast, L1-CAM-mediated homophilic cell adhesion induces the selective recruitment of the membrane skeleton protein ankyrin to areas of cell contact. Immunolabeling experiments in which S2 cells expressing TAG-1 were mixed with cells co-expressing L1-CAM and TAG-1 demonstrated that the homophilic interaction between TAG-1 molecules results in the cis-activation of L1-CAM to bind ankyrin. This TAG-1-dependent recruitment of the membrane skeleton provides an example of how GPI-anchored CAMs are able to transduce signals to the cytoplasm. Furthermore, such interactions might ultimately result in the recruitment and the activation of other signaling molecules at sites of cell contacts.
authors.affiliation: Department of Anatomy and Cell Biology, University of Michigan, Ann Arbor, Michigan 48109-0616, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Malhotra
authors.forename: P
authors.initials: P
authors.lastname: Tsiotra
authors.forename: D
authors.initials: D
authors.lastname: Karagogeos
authors.forename: M
authors.initials: M
authors.lastname: Hortsch
mesh_terms: D000818:Animals; D017487:Ankyrins / Q000378:metabolism*; D002448:Cell Adhesion; D015816:Cell Adhesion Molecules, Neuronal; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D058969:Contactin 2; D004330:Drosophila / Q000235:genetics; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism*
chemical_list: D017487:Ankyrins; D015816:Cell Adhesion Molecules, Neuronal; D058969:Contactin 2; D039841:Leukocyte L1 Antigen Complex; D008562:Membrane Glycoproteins; D019006:Neural Cell Adhesion Molecules