Low Density Lipoprotein Binds to Proprotein Convertase Subtilisin/Kexin Type-9 (PCSK9) in Human Plasma and Inhibits PCSK9-mediated Low Density Lipoprotein Receptor Degradation

• Published in: The Journal of biological chemistry Vol. 288; no. 12; pp. 8279 - 8288
• Main Authors: Kosenko, Tanja, Golder, Mia, Leblond, Geoffrey, Weng, Willy, Lagace, Thomas A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 22.03.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Binding, Competitive; Cell Line, Tumor; Cholesterol Regulation; HEK293 Cells; Humans; Lipid Metabolism; Lipids; Lipoprotein Receptor; Lipoproteins, HDL - blood; Lipoproteins, LDL - blood; Lipoproteins, LDL - chemistry; Lipoproteins, VLDL - blood; Low Density Lipoprotein (LDL); Proprotein Convertase 9; Proprotein Convertases - blood; Proprotein Convertases - chemistry; Protein Binding; Protein Interaction Domains and Motifs; Protein-Protein Interactions; Proteolysis; Receptors, LDL - chemistry; Receptors, LDL - metabolism; Serine Endopeptidases - blood; Serine Endopeptidases - chemistry; Lipid Metabolism; Low Density Lipoprotein (LDL); Lipoprotein Receptor; Cholesterol Regulation; Protein-Protein Interactions
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.M112.421370

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a secreted protein that binds to the epidermal growth factor-like-A domain of the low density lipoprotein receptor (LDLR) and mediates LDLR degradation in liver. Gain-of-function mutations in PCSK9 are associated with autosomal dominant hypercholesterolemia in humans. Size-exclusion chromatography of human plasma has shown PCSK9 to be partly associated with undefined high molecular weight complexes within the LDL size range. We used density gradient centrifugation to isolate LDL in plasma pooled from 5 normolipidemic subjects and report that >40% of total PCSK9 was associated with LDL. Binding of fluorophore-labeled recombinant PCSK9 to isolated LDL in vitro was saturable with a KD ∼ 325 nm. This interaction was competed >95% by excess unlabeled PCSK9, and competition binding curves were consistent with a one-site binding model. An N-terminal region of the PCSK9 prodomain (amino acids 31–52) was required for binding to LDL in vitro. LDL dose-dependently inhibited binding and degradation of cell surface LDLRs by exogenous PCSK9 in HuH7 cells. LDL also inhibited PCSK9 binding to mutant LDLRs defective at binding LDL. These data suggest that association of PCSK9 with LDL particles in plasma lowers the ability of PCSK9 to bind to cell surface LDLRs, thereby blunting PCSK9-mediated LDLR degradation. Background: Secreted PCSK9 regulates LDL levels in plasma by mediating degradation of hepatic LDL receptors. Results: LDL binds to PCSK9 in human plasma and in vitro and inhibits PCSK9 binding to cell surface LDL receptors. Conclusion: A large proportion of circulating PCSK9 is bound to LDL in humans. Significance: Regulatory mechanisms that affect activity of secreted PCSK9 represent novel targets for cholesterol-lowering therapies.