VIP21/caveolin, glycosphingolipid clusters and the sorting of glycosylphosphatidylinositol-anchored proteins in epithelial cells

EMBO J. 1994 Jan 1;13(1):42-53.

Abstract

We studied the role of the association between glycosylphosphatidylinositol (GPI)-anchored proteins and glycosphingolipid (GSL) clusters in apical targeting using gD1-DAF, a GPI-anchored protein that is differentially sorted by three epithelial cell lines. Differently from MDCK cells, where both gD1-DAF and glucosylceramide (GlcCer) are sorted to the apical membrane, in MDCK Concanavalin A-resistant cells (MDCK-ConAr) gD1-DAF was mis-sorted to both surfaces, but GlcCer was still targeted to the apical surface. In both MDCK and MDCK-ConAr cells, gD1-DAF became associated with TX-100-insoluble GSL clusters during transport to the cell surface. In dramatic contrast with MDCK cells, the Fischer rat thyroid (FRT) cell line targeted both gD1-DAF and GlcCer basolaterally. The targeting differences for GSLs in FRT and MDCK cells cannot be accounted for by a differential ability to form clusters because, in spite of major differences in the GSL composition, both cell lines assembled GSLs into TX-100-insoluble complexes with identical isopycnic densities. Surprisingly, in FRT cells, gD1-DAF did not form clusters with GSLs and, therefore, remained completely soluble. This clustering defect in FRT cells correlated with the lack of expression of VIP21/caveolin, a protein localized to both the plasma membrane caveolae and the trans Golgi network. This suggests that VIP21/caveolin may have an important role in recruiting GPI-anchored proteins into GSL complexes necessary for their apical sorting. However, since MDCK-ConAr cells expressed caveolin and clustered GPI-anchored proteins normally, yet mis-sorted them, our results also indicate that clustering and caveolin are not sufficient for apical targeting, and that additional factors are required for the accurate apical sorting of GPI-anchored proteins.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carrier Proteins / metabolism*
  • Caveolin 1
  • Caveolins*
  • Cell Line
  • Concanavalin A
  • Dogs
  • Epithelium / metabolism
  • Glycosphingolipids / chemistry
  • Glycosphingolipids / metabolism*
  • Glycosylphosphatidylinositols / chemistry
  • Glycosylphosphatidylinositols / metabolism*
  • Lipids / analysis
  • Membrane Proteins / metabolism*
  • Octoxynol
  • Rats
  • Solubility
  • Transfection

Substances

  • Carrier Proteins
  • Cav1 protein, rat
  • Caveolin 1
  • Caveolins
  • Glycosphingolipids
  • Glycosylphosphatidylinositols
  • Lipids
  • Membrane Proteins
  • Concanavalin A
  • Octoxynol