Lagace, T.A. et al. Secreted PCSK9 decreases the number of LDL receptors in hepatocytes and in livers of parabiotic mice. J. Clin. Invest. 116, 2995-3005

Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Journal of Clinical Investigation (Impact Factor: 13.77). 12/2006; 116(11):2995-3005. DOI: 10.1172/JCI29383
Source: PubMed

ABSTRACT Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a member of the proteinase K subfamily of subtilases that reduces the number of LDL receptors (LDLRs) in liver through an undefined posttranscriptional mechanism. We show that purified PCSK9 added to the medium of HepG2 cells reduces the number of cell-surface LDLRs in a dose- and time-dependent manner. This activity was approximately 10-fold greater for a gain-of-function mutant, PCSK9(D374Y), that causes hypercholesterolemia. Binding and uptake of PCSK9 were largely dependent on the presence of LDLRs. Coimmunoprecipitation and ligand blotting studies indicated that PCSK9 and LDLR directly associate; both proteins colocalized to late endocytic compartments. Purified PCSK9 had no effect on cell-surface LDLRs in hepatocytes lacking autosomal recessive hypercholesterolemia (ARH), an adaptor protein required for endocytosis of the receptor. Transgenic mice overexpressing human PCSK9 in liver secreted large amounts of the protein into plasma, which increased plasma LDL cholesterol concentrations to levels similar to those of LDLR-knockout mice. To determine whether PCSK9 was active in plasma, transgenic PCSK9 mice were parabiosed with wild-type littermates. After parabiosis, secreted PCSK9 was transferred to the circulation of wild-type mice and reduced the number of hepatic LDLRs to nearly undetectable levels. We conclude that secreted PCSK9 associates with the LDLR and reduces hepatic LDLR protein levels.

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Available from: Robert E Hammer, Aug 30, 2015
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    • "First, missense mutations in PCSK9, later determined to confer a gain-of-function, were found to cause a rare form of autosomal dominant hypercholesterolemia [2]; second, loss-of-function PCSK9 mutations identified at relatively high frequencies (2–4%) in certain ethnic populations were associated with lowered plasma LDL-C levels and significant protection from CHD [3,4]. Mechanistic studies determined that PCSK9 binds to the LDL receptor (LDLR) and promotes its lysosomal degradation in cells [5–7]. The molecular mapping of the PCSK9-LDLR binding interface aided the development of therapeutic anti-PCSK9 monoclonal antibodies (mAbs) that effectively block this interaction at the cell surface [8,9]. "
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    ABSTRACT: Purpose of review Proprotein convertase subtilisin/kexin type-9 (PCSK9) binds to LDL receptor (LDLR) and targets it for lysosomal degradation in cells. Decreased hepatic clearance of plasma LDL-cholesterol is the primary gauge of PCSK9 activity in humans; however, PCSK9's evolutionary role may extend to other lipoprotein classes and processes. This review highlights studies that are providing novel insights into physiological regulation of PCSK9 transcription and plasma PCSK9 activity. Recent findings Recent studies indicate that circulating PCSK9 binds to apolipoprotein B100 on LDL particles, which in turn inhibits PCSK9's ability to bind to cell surface LDLRs. Negative feedback of secreted PCSK9 activity by LDL could serve to increase plasma excursion of triglyceride-rich lipoproteins and monitor lipoprotein remodeling. Recent findings have identified hepatocyte nuclear factor-1α as a key transcriptional regulator that cooperates with sterol regulatory element-binding protein-2 to control PCSK9 expression in hepatocytes in response to nutritional and hormonal inputs, as well as acute inflammation. Summary PCSK9 is an established target for cholesterol-lowering therapies. Further study of PCSK9 regulatory mechanisms may identify additional control points for pharmacological inhibition of PCSK9-mediated LDLR degradation. PCSK9 function could reflect ancient roles in the fasting-feeding cycle and in linking lipoprotein metabolism with innate immunity.
    Current Opinion in Lipidology 08/2014; 25(5). DOI:10.1097/MOL.0000000000000114 · 5.80 Impact Factor
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    • "PCSK9 inhibition has the potential to provide a complementary mechanism to other LLTs to significantly reduce LDL-C beyond the efficacy of statins [15, 17–25]. Alirocumab (formerly REGN727/SAR236553; Sanofi-Regeneron) is a fully human, monoclonal antibody targeted to PCSK9 currently in Phase 3 development for the treatment of hypercholesterolemia. "
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    ABSTRACT: Background Individuals with heterozygous familial hypercholesterolemia (heFH) have higher levels of low-density lipoprotein cholesterol (LDL-C) and are predisposed to premature cardiovascular disease. Alirocumab is a fully-human, monoclonal antibody targeted to proprotein convertase subtilisin/kexin type 9 currently in Phase 3 development for the treatment of hypercholesterolemia. Described here are three ODYSSEY Phase 3 trials, FH I (NCT01623115), FH II (NCT01709500) and HIGH FH (patients with heFH and LDL-C levels ≥160 mg/dL) (NCT01617655), in which alirocumab is further evaluated in the heFH population. Methods Multicenter, multinational, randomized, double-blind, placebo-controlled studies have been designed to evaluate efficacy and safety of alirocumab in more than 800 patients with heFH who are not adequately controlled with a maximally-tolerated stable daily dose of statin for ≥4 weeks prior to the screening visit, with or without other lipid-lowering therapy. Patients are randomized (2:1) to receive alirocumab or placebo via a 1-mL subcutaneous auto-injection every 2 weeks (Q2W) for 78 weeks. In studies FH I and II, if their Week 8 LDL-C level is ≥70 mg/dL, patients will undergo a dose uptitration from 75 to 150 mg alirocumab Q2W at Week 12. In HIGH FH, patients will receive alirocumab 150 mg Q2W throughout the entire treatment period. The primary efficacy endpoint in all three studies is the percent change in calculated LDL-C from baseline to Week 24. Conclusions The ODYSSEY FH studies are three Phase 3 studies aiming to further evaluate the efficacy and long-term safety of alirocumab as an effective therapeutic option for patients with heFH.
    Cardiovascular Drugs and Therapy 05/2014; 28(3). DOI:10.1007/s10557-014-6523-z · 2.95 Impact Factor
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    • "sin - like catalytic domain and a C - terminal cysteine / histidine rich domain ( CTD ) ( Figure 1A & B ) ( Henrich et al . , 2005 ) . PCSK9 undergoes autocatalytic cleavage , but the 14 kDa prodomain remains non - covalently attached to the catalytic domain and renders the protease inactive ( Benjannet et al . , 2004 ; Cunningham et al . , 2007 ; Lagace et al . , 2006 ; Seidah et al . , 2003 ) . It is believed that the prodomain acts as a chaperone and assists in folding of the protein ( Kwon et al . , 2008 ) whereas the autocatalytic processing is crucial for the secretion of PCSK9 ( Seidah et al . , 2003 ) . The LDL - R is a multidomain protein comprising an extracellular domain with an N - termina"
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    ABSTRACT: Disrupting the binding interaction between proprotein convertase (PCSK9) and the epidermal growth factor-like domain A (EGF-A domain) in the low-density lipoprotein receptor (LDL-R) is a promising strategy to promote LDL-R recycling and thereby lower circulating cholesterol levels. In this study, truncated 26 amino acid EGF-A analogs were designed and synthesized, and their structures were analyzed in solution and in complex with PCSK9. The most potent peptide had an increased binding affinity for PCSK9 (KD = 0.6 μM) compared with wild-type EGF-A (KD = 1.2 μM), and the ability to increase LDL-R recycling in the presence of PCSK9 in a cell-based assay.
    Chemistry & biology 01/2014; 21(2). DOI:10.1016/j.chembiol.2013.11.014 · 6.59 Impact Factor
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