Dissection of the endogenous cellular pathways of PCSK9-induced low density lipoprotein receptor degradation: evidence for an intracellular route.
Elevated levels of plasma low density lipoprotein (LDL)-cholesterol, leading to familial hypercholesterolemia, are enhanced by mutations in at least three major genes, the LDL receptor (LDLR), its ligand apolipoprotein B, and the proprotein convertase PCSK9. Single point mutations in PCSK9 are associated with either hyper- or hypocholesterolemia. Accordingly, PCSK9 is an attractive target for treatment of dyslipidemia. PCSK9 binds the epidermal growth factor domain A (EGF-A) of the LDLR and directs it to endosomes/lysosomes for destruction. Although the mechanism by which PCSK9 regulates LDLR degradation is not fully resolved, it seems to involve both intracellular and extracellular pathways. Here, we show that clathrin light chain small interfering RNAs that block intracellular trafficking from the trans-Golgi network to lysosomes rapidly increased LDLR levels within HepG2 cells in a PCSK9-dependent fashion without affecting the ability of exogenous PCSK9 to enhance LDLR degradation. In contrast, blocking the extracellular LDLR endocytosis/degradation pathway by a 4-, 6-, or 24-h incubation of cells with Dynasore or an EGF-AB peptide or by knockdown of endogenous autosomal recessive hypercholesterolemia did not significantly affect LDLR levels. The present data from HepG2 cells and mouse primary hepatocytes favor a model whereby depending on the dose and/or incubation period, endogenous PCSK9 enhances the degradation of the LDLR both extra- and intracellularly. Therefore, targeting either pathway, or both, would be an effective method to reduce PCSK9 activity in the treatment of hypercholesterolemia and coronary heart disease.
Poirier
Steve
S
Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montreal, Quebec H2W 1R7, Canada.
Mayer
Gaetan
G
Poupon
Viviane
V
McPherson
Peter S
PS
Desjardins
Roxane
R
Ly
Kevin
K
Asselin
Marie-Claude
MC
Day
Robert
R
Duclos
Franck J
FJ
Witmer
Mark
M
Parker
Rex
R
Prat
Annik
A
Seidah
Nabil G
NG
D000818:Animals; D033941:Clathrin Light Chains / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D006937:Hypercholesterolemia / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D051379:Mice; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D017434:Protein Structure, Tertiary; D011973:Receptors, LDL / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
D033941:Clathrin Light Chains; D011973:Receptors, LDL; C472125:PCSK9 protein, human; C472126:Pcsk9 protein, mouse; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases