title: Traffic, polarity, and detergent solubility of a glycosylphosphatidylinositol-anchored protein after LDL-deprivation of MDCK cells.
abstract: Glycosylphosphatidylinositol-anchored proteins, GPI-proteins, are selectively delivered to the apical surfaces of many types of morphologically polarized epithelial cells. It has been proposed that the unit for targeting GPI-proteins to the apical surface is a membrane lipid domain. This sorting domain or molecular cluster has been equated to detergent (Triton X-100)-insoluble membrane fractions that are enriched in enriched in GPI-proteins, glycosphingolipids, and cholesterol. To determine the role of cholesterol in the formation of sorting domains and to examine its importance in the intracellular traffic and membrane polarity of GPI-proteins, we studied the behavior of a model GPI-protein, gD1-DAF, in MDCK cells cultured for 3 or 14 d without their principal source of cholesterol, serum LDL. LDL deprivation affects the intracellular traffic of gD1-DAF. Surface expression of gD1-DAF is reduced in LDL-deprived cells; this reduction is most marked after 3 d of LDL deprivation. We also find a great reduction in the fraction of gD1-DAF that is detergent-insoluble in these cells and a change in its membrane milieu defined by susceptibility to cleavage with PI-specific phospholipase C. Despite these changes, the surface polarity of gD1-DAF is no different in LDL-deprived cells than in control cells.
authors.affiliation: Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Hannan
authors.forename: M
authors.initials: M
authors.lastname: Edidin
mesh_terms: D000818:Animals; D001692:Biological Transport; D002458:Cell Fractionation; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D016764:Cell Polarity; D002784:Cholesterol / Q000096:biosynthesis / Q000378:metabolism; D008078:Cholesterol, LDL / Q000502:physiology*; D003902:Detergents; D004285:Dogs; D004705:Endocytosis; D006031:Glycosylation; D017261:Glycosylphosphatidylinositols; D006596:Hexosaminidases; D007668:Kidney / Q000166:cytology; D008562:Membrane Glycoproteins / Q000032:analysis / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis; D017830:Octoxynol; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010727:Phosphoric Diester Hydrolases; D012995:Solubility
chemical_list: D008078:Cholesterol, LDL; D003902:Detergents; D017261:Glycosylphosphatidylinositols; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D017830:Octoxynol; D002784:Cholesterol; D010727:Phosphoric Diester Hydrolases; D006596:Hexosaminidases; D043265:Phosphatidylinositol Diacylglycerol-Lyase