Expression of a soluble isoform of cell adhesion molecule 1 in the brain and its involvement in directional neurite outgrowth.
Cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, is expressed on superior cervical ganglion neurites and mediates cell-cell adhesion by trans-homophilic binding. In addition to the membrane-bound form, we have previously shown that a soluble form (sCADM1) generated by alternative splicing possesses a stop codon immediately downstream of the immunoglobulin-like domain. Here, we demonstrate the presence of sCADM1 in vivo and its possible role in neurite extension. sCADM1 appears to be a stromal protein because extracellular-restricted, but not intracellular-restricted, anti-CADM1 antibody stained stromal protein-rich extract from mouse brains. Murine plasmacytoma cells, P3U1, were modified to secrete sCADM1 fused with either immunoglobulin (Ig)G Fc portion (sCADM1-Fc) or its deletion form that lacks the immunoglobulin-like domain (DeltasCADM1-Fc). When P3U1 derivatives expressing sCADM1-Fc or DeltasCADM1-Fc were implanted into collagen gels, Fc-fused proteins were present more abundantly around the cells. Superior cervical ganglion neurons, parental P3U1, and either derivative were implanted into collagen gels separately, and co-cultured for 4 days. Bodian staining of the gel sections revealed that most superior cervical ganglion neurites turned toward the source of sCADM1-Fc, but not DeltasCADM1-Fc. Furthermore, immunofluorescence signals for sCADM1-Fc and membrane-bound CADM1 were co-localized on the neurite surface. These results show that sCADM1 appears to be involved in directional neurite extension by serving as an anchor to which membrane-bound CADM1 on the neurites can bind.
Hagiyama
Man
M
Division of Molecular Pathology, Department of Cancer Biology, Institute of Medical Science, The University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Ichiyanagi
Naoki
N
Kimura
Keiko B
KB
Murakami
Yoshinori
Y
Ito
Akihiko
A
D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism*; D018920:Coculture Techniques; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D020287:In Situ Nick-End Labeling; D018799:Intercellular Adhesion Molecule-1 / Q000096:biosynthesis*; D051379:Mice; D008810:Mice, Inbred C57BL; D016501:Neurites / Q000378:metabolism*; D020033:Protein Isoforms / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction
D020033:Protein Isoforms; D018799:Intercellular Adhesion Molecule-1