Article

Catalytic Activity Is Not Required for Secreted PCSK9 to Reduce Low Density Lipoprotein Receptors in HepG2 Cells

Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 08/2007; 282(29):20799-803. DOI: 10.1074/jbc.C700095200
Source: PubMed

ABSTRACT

Proprotein convertase subtilisin/kexin type 9 (PCSK9), a member of the proteinase K subfamily of subtilases, promotes internalization
and degradation of low density lipoprotein receptors (LDLRs) after binding the receptor on the surface of hepatocytes. PCSK9
has autocatalytic activity that releases the prodomain at the N terminus of the protein. The prodomain remains tightly associated
with the catalytic domain as the complex transits the secretory pathway. It is not known whether enzymatic activity is required
for the LDLR-reducing effects of PCSK9. Here we expressed the prodomain together with a catalytically inactive protease domain
in cells and purified the protein from the medium. The ability of the catalytically inactive PCSK9 to bind and degrade LDLRs
when added to culture medium of human hepatoma HepG2 cells at physiological concentrations was similar to that seen using
wild-type protein. Similarly, a catalytic-dead version of a gain-of-function mutant, PCSK9(D374Y), showed no loss of activity
compared with a catalytically active counterpart; both proteins displayed ∼10-fold increased activity in degradation of cell
surface LDLRs compared with wild-type PCSK9. We conclude that the ability of PCSK9 to degrade LDLRs is independent of catalytic
activity and suggest that PCSK9 functions as a chaperone to prevent LDLR recycling and/or to target LDLRs for lysosomal degradation.

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    • "Within the ER, PCSK9 is autocatalytically cleaved (Seidah et al., 2003), resulting in a tightly bound secretable heterodimeric complex (Cunningham et al., 2007). Following binding with PCSK9 (McNutt et al., 2007), LDLR is rerouted from the cell surface recycling pathway toward late endocytic compartments for degradation (Poirier and Mayer, 2013). In a previous study, we have identified annexin A2 as an endogenous PCSK9- binding protein and extrahepatic inhibitor of PCSK9-enhanced LDLR degradation (Mayer et al., 2008; Seidah et al., 2012). "

    Full-text · Article · Nov 2015 · Cell Reports
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    • "Within the ER, PCSK9 is autocatalytically cleaved (Seidah et al., 2003), resulting in a tightly bound secretable heterodimeric complex (Cunningham et al., 2007). Following binding with PCSK9 (McNutt et al., 2007), LDLR is rerouted from the cell surface recycling pathway toward late endocytic compartments for degradation (Poirier and Mayer, 2013). In a previous study, we have identified annexin A2 as an endogenous PCSK9- binding protein and extrahepatic inhibitor of PCSK9-enhanced LDLR degradation (Mayer et al., 2008; Seidah et al., 2012). "

    Full-text · Article · Nov 2015 · Cell Reports
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    • "Secreted PCSK9-promoted degradation of the LDLR requires binding of PCSK9 to the LDLR and internalization of the receptor but does not require the proteolytic activity of PCSK9 [15] [16] [55] . We have shown that PCSK9 interacts with the EGF-A of the LDLR at the cell surface and binds the receptor with a much higher affinity at the acidic environment of the endosome (Fig. 2). "
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    ABSTRACT: Atherosclerotic cardiovascular disease is the main cause of mortality and morbidity in the world. Plasma levels of low density lipoprotein cholesterol (LDL-C) are positively correlated with the risk of atherosclerosis. High plasma LDL concentrations in patients with hypercholesterolemia lead to build-up of LDL in the inner walls of the arteries, which becomes oxidized and promotes the formation of foam cells, consequently initiating atherosclerosis. Plasma LDL is mainly cleared through the LDL receptor (LDLR) pathway. Mutations in the LDLR cause familiar hypercholesterolemia and increase the risk of premature coronary heart disease. The expression of LDLR is regulated at the transcriptional level via the sterol regulatory element binding protein 2 (SREBP-2) and at the posttranslational levels mainly through proprotein convertase subtilisin/kexin-type 9 (PCSK9) and inducible degrader of the LDLR (IDOL). In this review, we summarize the latest advances in the studies of PCSK9.
    Preview · Article · Oct 2015
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