title: Self-assembly of HEK cell-secreted ApoE particles resembles ApoE enrichment of lipoproteins as a ligand for the LDL receptor-related protein.
abstract: Recent studies have shown that the lipidation and assembly state of apolipoprotein E (apoE) determine receptor recognition and amyloid-beta peptide (Abeta) binding. We previously demonstrated that apoE secreted by HEK cells stably expressing apoE3 or apoE4 (HEK-apoE) binds Abeta and inhibits Abeta-induced neurotoxicity by an isoform-specific process that requires apoE receptors. Here we characterized the structure of HEK-apoE assemblies and determined their receptor binding specificity. By chromatography, HEK-apoE elutes in high molecular mass fractions and is the size of plasma HDL, consistent with a multiprotein assembly. No lipid was associated with these apoE assemblies. Several methods for analyzing receptor binding indicate that HEK-apoE is a ligand for low-density lipoprotein (LDL) receptor-related protein (LRP) but not the LDL receptor. This suggests that self-assembly of apoE may induce a functional conformation necessary for binding to LRP. Our results indicate that, in addition to lipid content, the assembly state of apoE influences Abeta binding and receptor recognition.
authors.affiliation: Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
authors.forename: Mary Jo
authors.initials: MJ
authors.lastname: LaDu
authors.forename: W Blaine
authors.initials: WB
authors.lastname: Stine
authors.forename: Masaaki
authors.initials: M
authors.lastname: Narita
authors.forename: Godfrey S
authors.initials: GS
authors.lastname: Getz
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Reardon
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
mesh_terms: D000818:Animals; D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D002460:Cell Line; D002850:Chromatography, Gel; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D011973:Receptors, LDL / Q000378:metabolism; D014461:Ultracentrifugation
chemical_list: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D007457:Iodine Radioisotopes; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011973:Receptors, LDL