title: A glycolipid-anchored prion protein is endocytosed via clathrin-coated pits.
abstract: The cellular prion protein (PrPc) is a glycolipid-anchored, cell surface protein of unknown function, a posttranslationally modified isoform of which PrPSc is involved in the pathogenesis of Creutzfeldt-Jakob disease, scrapie, and other spongiform encephalopathies. We have shown previously that chPrP, a chicken homologue of mammalian PrPC, constitutively cycles between the cell surface and an endocytic compartment, with a transit time of approximately 60 min in cultured neuroblastoma cells. We now report that endocytosis of chPrP is mediated by clathrin-coated pits. Immunogold labeling of neuroblastoma cells demonstrates that the concentration of chPrP within 0.05 microns of coated pits is 3-5 times higher than over other areas of the plasma membrane. Moreover, gold particles can be seen within coated vesicles and deeply invaginated coated pits that are in the process of pinching off from the plasma membrane. ChPrP is also localized to coated pits in primary cultures of neurons and glia, and is found in coated vesicles purified from chicken brain. Finally, internalization of chPrP is reduced by 70% after neuroblastoma cells are incubated in hypertonic medium, a treatment that inhibits endocytosis by disrupting clathrin lattices. Caveolae, plasmalemmal invaginations in which several other glycolipid-anchored proteins are concentrated, are not seen in neuroblastoma cells analyzed by thin-section or deep-etch electron microscopy. Moreover, these cells do not express detectable levels of caveolin, a caveolar coat protein. Since chPrP lacks a cytoplasmic domain that could interact directly with the intracellular components of clathrin-coated pits, we propose that the polypeptide chain of chPrP associates with the extracellular domain of a transmembrane protein that contains a coated pit internalization signal.
authors.affiliation: Department of Cell Biology and Physiology, Washington University, School of Medicine, St. Louis, Missouri 63110.
authors.forename: S L
authors.initials: SL
authors.lastname: Shyng
authors.forename: J E
authors.initials: JE
authors.lastname: Heuser
authors.forename: D A
authors.initials: DA
authors.lastname: Harris
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D001923:Brain Chemistry; D051242:Caveolin 1; D022461:Caveolins; D002642:Chick Embryo; D002966:Clathrin / Q000378:metabolism; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D005372:Filipin / Q000494:pharmacology; D006017:Glycolipids / Q000378:metabolism; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000276:immunology / Q000302:isolation & purification; D051379:Mice; D016253:Microscopy, Immunoelectron; D009457:Neuroglia / Q000648:ultrastructure; D009474:Neurons / Q000648:ultrastructure; D009761:Nystatin / Q000494:pharmacology; D009997:Osmotic Pressure; D018620:PrPSc Proteins; D011328:Prions / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000276:immunology / Q000302:isolation & purification; D013347:Subcellular Fractions / Q000648:ultrastructure; D014407:Tumor Cells, Cultured
chemical_list: D000924:Anticholesteremic Agents; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D002966:Clathrin; D006017:Glycolipids; D008565:Membrane Proteins; D018620:PrPSc Proteins; D011328:Prions; D011990:Receptors, Transferrin; D009761:Nystatin; D005372:Filipin