Self-Assembly of HEK Cell-Secreted ApoE Particles Resembles ApoE Enrichment of Lipoproteins as a Ligand for the LDL Receptor-Related Protein

• Published in: Biochemistry (Easton) 2006-01, Vol.45 (2), p.381-390
• Main Authors: LaDu, Mary Jo, Stine, W. Blaine, Narita, Masaaki, Getz, Godfrey S, Reardon, Catherine A, Bu, Guojun
• Format: Article
• Language: English
• Subjects: Animals; Apolipoprotein E3; Apolipoprotein E4; Apolipoproteins E - chemistry; Apolipoproteins E - secretion; Apolipoproteins E - ultrastructure; Cell Line; Chromatography, Gel; Fibroblasts - metabolism; Humans; Iodine Radioisotopes; Ligands; Low Density Lipoprotein Receptor-Related Protein-1 - chemistry; Low Density Lipoprotein Receptor-Related Protein-1 - metabolism; Mice; Protein Binding; Receptors, LDL - metabolism; Ultracentrifugation
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi051765s

Recent studies have shown that the lipidation and assembly state of apolipoprotein E (apoE) determine receptor recognition and amyloid-β peptide (Aβ) binding. We previously demonstrated that apoE secreted by HEK cells stably expressing apoE3 or apoE4 (HEK-apoE) binds Aβ and inhibits Aβ-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 Aβ binding and receptor recognition.