Glypican-1 mediates both prion protein lipid raft association and disease isoform formation.
In prion diseases, the cellular form of the prion protein, PrP(C), undergoes a conformational conversion to the infectious isoform, PrP(Sc). PrP(C) associates with lipid rafts through its glycosyl-phosphatidylinositol (GPI) anchor and a region in its N-terminal domain which also binds to heparan sulfate proteoglycans (HSPGs). We show that heparin displaces PrP(C) from rafts and promotes its endocytosis, suggesting that heparin competes with an endogenous raft-resident HSPG for binding to PrP(C). We then utilised a transmembrane-anchored form of PrP (PrP-TM), which is targeted to rafts solely by its N-terminal domain, to show that both heparin and phosphatidylinositol-specific phospholipase C can inhibit its association with detergent-resistant rafts, implying that a GPI-anchored HSPG targets PrP(C) to rafts. Depletion of the major neuronal GPI-anchored HSPG, glypican-1, significantly reduced the raft association of PrP-TM and displaced PrP(C) from rafts, promoting its endocytosis. Glypican-1 and PrP(C) colocalised on the cell surface and both PrP(C) and PrP(Sc) co-immunoprecipitated with glypican-1. Critically, treatment of scrapie-infected N2a cells with glypican-1 siRNA significantly reduced PrP(Sc) formation. In contrast, depletion of glypican-1 did not alter the inhibitory effect of PrP(C) on the beta-secretase cleavage of the Alzheimer's amyloid precursor protein. These data indicate that glypican-1 is a novel cellular cofactor for prion conversion and we propose that it acts as a scaffold facilitating the interaction of PrP(C) and PrP(Sc) in lipid rafts.
Taylor
David R
DR
Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, and Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds, UK.
Whitehouse
Isobel J
IJ
Hooper
Nigel M
NM
D000682:Amyloid / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004195:Disease Models, Animal; D053673:Glypicans / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018621:PrPC Proteins / Q000378:metabolism*; D018620:PrPSc Proteins / Q000378:metabolism*; D017096:Prion Diseases / Q000378:metabolism*; D011328:Prions / Q000378:metabolism*; D020033:Protein Isoforms
D000682:Amyloid; D053673:Glypicans; D018621:PrPC Proteins; D018620:PrPSc Proteins; D011328:Prions; D020033:Protein Isoforms; D006493:Heparin; D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse