title: In vivo evidence that furin from hepatocytes inactivates PCSK9.
abstract: The proprotein convertase PCSK9 plays a key role in cholesterol homeostasis by binding the LDL receptor and targeting it toward degradation. PCSK9 is strongly expressed in the liver and is found in human and mouse plasma as mature (∼ 62 kDa) and inactivated (∼ 55 kDa) forms. Ex vivo data showed that human PCSK9 is inactivated by cleavage at Arg(218)↓ by the overexpressed convertases furin and PC5/6A. Analysis of the plasma of human heterozygotes for R218S and F216L mutations revealed a ∼ 50% reduction in the levels of the ∼ 55-kDa form. To identify the convertase(s) responsible for cleavage at Arg(218) in vivo, we inactivated the genes of furin and/or PC5/6 specifically in hepatocytes. The PCSK9-inactivated form was strongly reduced in mice lacking furin in hepatocytes (Fur-hKO) and only slightly reduced in PC5/6-hKO plasma. In agreement with a key role of furin in regulating PCSK9 activity in vivo, we observed an overall 26% drop in the LDL receptor protein levels of Fur-hKO livers, likely due to the compound effects of a 35% increase in PCSK9 mRNA levels and the loss of PCSK9 cleavage, suggesting a higher activity of PCSK9 in these mice. Overexpression of PCSK9 in primary hepatocytes obtained from these mice revealed that only full-length, membrane-bound, but not soluble, furin is the cognate convertase. We conclude that in hepatocytes furin regulates PCSK9 mRNA levels and is the key in vivo-inactivating protease of circulating PCSK9.
authors.affiliation: Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montreal, Quebec H2W 1R7, Canada.
authors.forename: Rachid
authors.initials: R
authors.lastname: Essalmani
authors.forename: Delia
authors.initials: D
authors.lastname: Susan-Resiga
authors.forename: Ann
authors.initials: A
authors.lastname: Chamberland
authors.forename: Marianne
authors.initials: M
authors.lastname: Abifadel
authors.forename: John W
authors.initials: JW
authors.lastname: Creemers
authors.forename: Catherine
authors.initials: C
authors.lastname: Boileau
authors.forename: Nabil G
authors.initials: NG
authors.lastname: Seidah
authors.forename: Annik
authors.initials: A
authors.lastname: Prat
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D004789:Enzyme Activation / Q000502:physiology; D045683:Furin / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D055785:Gene Knockdown Techniques; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008822:Mice, Transgenic; D020125:Mutation, Missense; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D011973:Receptors, LDL; C472125:PCSK9 protein, human; C472126:Pcsk9 protein, mouse; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C468731:FURIN protein, human; D045683:Furin