VIP21/caveolin, glycosphingolipid clusters and the sorting of glycosylphosphatidylinositol-anchored proteins in epithelial cells.
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.
Zurzolo
C
C
Department of Cell Biology and Anatomy, Cornell University Medical College, New York.
van't Hof
W
W
van Meer
G
G
Rodriguez-Boulan
E
E
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D051242:Caveolin 1; D022461:Caveolins; D002460:Cell Line; D003208:Concanavalin A; D004285:Dogs; D004848:Epithelium / Q000378:metabolism; D006028:Glycosphingolipids / Q000737:chemistry / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D008055:Lipids / Q000032:analysis; D008565:Membrane Proteins / Q000378:metabolism*; D017830:Octoxynol; D051381:Rats; D012995:Solubility; D014162:Transfection
D002352:Carrier Proteins; C495537:Cav1 protein, rat; D051242:Caveolin 1; D022461:Caveolins; D006028:Glycosphingolipids; D017261:Glycosylphosphatidylinositols; D008055:Lipids; D008565:Membrane Proteins; D003208:Concanavalin A; D017830:Octoxynol