The paranodal complex of F3/contactin and caspr/paranodin traffics to the cell surface via a non-conventional pathway

J Biol Chem. 2003 Nov 28;278(48):48339-47. doi: 10.1074/jbc.M309120200. Epub 2003 Sep 12.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Axons / metabolism
  • Biotinylation
  • Brain / metabolism
  • Brefeldin A / pharmacology
  • CD4 Antigens / biosynthesis
  • CHO Cells
  • COS Cells
  • Cell Adhesion
  • Cell Adhesion Molecules, Neuronal / chemistry*
  • Cell Adhesion Molecules, Neuronal / metabolism
  • Cell Line, Tumor
  • Cell Membrane / metabolism*
  • Cloning, Molecular
  • Contactins
  • Cricetinae
  • Cytoplasm / metabolism
  • Endoplasmic Reticulum / metabolism
  • Glycosylation
  • Golgi Apparatus / metabolism
  • Green Fluorescent Proteins
  • Lectins / metabolism
  • Luminescent Proteins / metabolism
  • Membrane Microdomains
  • Mice
  • Microscopy, Fluorescence
  • Precipitin Tests
  • Protein Binding
  • Protein Structure, Tertiary
  • Protein Synthesis Inhibitors / pharmacology
  • Protein Transport
  • Rats
  • Time Factors
  • Tunicamycin / pharmacology

Substances

  • CD4 Antigens
  • Cell Adhesion Molecules, Neuronal
  • Cntnap1 protein, mouse
  • Cntnap1 protein, rat
  • Contactins
  • Lectins
  • Luminescent Proteins
  • Protein Synthesis Inhibitors
  • Tunicamycin
  • Green Fluorescent Proteins
  • Brefeldin A