title: The paranodal complex of F3/contactin and caspr/paranodin traffics to the cell surface via a non-conventional pathway.
abstract: During myelination, membrane-specialized domains are generated by complex interactions between axon and glial cells. The cell adhesion molecules caspr/paranodin and F3/contactin play a crucial role in the generation of functional septate-like junctions at paranodes. We have previously demonstrated that association with the glycosylphosphatidylinositol-linked F3/contactin is required for the recruitment of caspr/paranodin into the lipid rafts and its targeting to the cell surface. When transfected alone in neuroblastoma N2a cells, caspr/paranodin is retained in the endoplasmic reticulum (ER). Using chimerical constructs, we show that the cytoplasmic region does not contain any ER retention signal, whereas the ectodomain plays a crucial role in caspr/paranodin trafficking. A series of truncations encompassing the extracellular region of caspr/paranodin was unable to abolish ER retention. We show that N-glycosylation and quality control by the lectin-chaperone calnexin are required for the cell surface delivery of caspr/paranodin. Cell surface transport of F3/contactin and caspr/paranodin is insensitive to brefeldin A and the two glycoproteins are endoglycosidase H-sensitive when associated in complex, recruited into the lipid rafts, and expressed on the cell surface. Our results indicate a Golgi-independent pathway for the paranodal cell adhesion complex that may be implicated in the segregation of axonal subdomains.
authors.affiliation: Neurobiologie des Interactions Cellulaires et Neuropathologie, FRE 2533 CNRS, Institut Jean-Roche, 13916 Marseille, France.
authors.forename: Carine
authors.initials: C
authors.lastname: Bonnon
authors.forename: Laurence
authors.initials: L
authors.lastname: Goutebroze
authors.forename: Natasha
authors.initials: N
authors.lastname: Denisenko-Nehrbass
authors.forename: Jean-Antoine
authors.initials: JA
authors.lastname: Girault
authors.forename: Catherine
authors.initials: C
authors.lastname: Faivre-Sarrailh
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D019921:Biotinylation; D001921:Brain / Q000378:metabolism; D020126:Brefeldin A / Q000494:pharmacology; D015704:CD4 Antigens / Q000096:biosynthesis; D016466:CHO Cells; D019556:COS Cells; D002448:Cell Adhesion; D015816:Cell Adhesion Molecules, Neuronal / Q000737:chemistry* / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D003001:Cloning, Molecular; D058966:Contactins; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D037102:Lectins / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D021962:Membrane Microdomains; D051379:Mice; D008856:Microscopy, Fluorescence; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D051381:Rats; D013997:Time Factors; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D015704:CD4 Antigens; D015816:Cell Adhesion Molecules, Neuronal; C491322:Cntnap1 protein, mouse; C105177:Cntnap1 protein, rat; D058966:Contactins; D037102:Lectins; D008164:Luminescent Proteins; D011500:Protein Synthesis Inhibitors; D014415:Tunicamycin; D049452:Green Fluorescent Proteins; D020126:Brefeldin A