title: Plasma Membrane Tetraspanin CD81 Complexes with Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) and Low Density Lipoprotein Receptor (LDLR), and Its Levels Are Reduced by PCSK9.
abstract: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an important factor in plasma cholesterol regulation through modulation of low density lipoprotein receptor (LDLR) levels. Naturally occurring mutations can lead to hyper- or hypocholesterolemia in human. Recently, we reported that PCSK9 was also able to modulate CD81 in Huh7 cells. In the present study, several gain-of-function and loss-of-function mutants as well as engineered mutants of PCSK9 were compared for their ability to modulate the cell surface expression of LDLR and CD81. Although PCSK9 gain-of-function D374Y enhanced the degradation both receptors, D374H and D129N seemed to only reduce LDLR levels. In contrast, mutations in the C-terminal hinge-cysteine-histidine-rich domain segment primarily affected the PCSK9-induced CD81 degradation. Furthermore, when C-terminally fused to an ACE2 transmembrane anchor, the secretory N-terminal catalytic or hinge-cysteine-histidine-rich domain domains of PCSK9 were able to reduce CD81 and LDLR levels. These data confirm that PCSK9 reduces CD81 levels via an intracellular pathway as reported for LDLR. Using immunocytochemistry, a proximity ligation assay, and co-immunoprecipitation, we found that the cell surface level of PCSK9 was enhanced upon overexpression of CD81 and that both PCSK9 and LDLR interact with this tetraspanin protein. Interestingly, using CHO-A7 cells lacking LDLR expression, we revealed that LDLR was not required for the degradation of CD81 by PCSK9, but its presence strengthened the PCSK9 effect.
authors.affiliation: From the Institut National de la Recherche Scientifique-Institut Armand-Frappier, 531 Boulevard des Prairies, Laval, Quebec H7V 1B7, Canada, Department of Malaria, Parasitology and Entomology, Vietnam Military Medical University, 104 Phung Hung Street, Ha Dong District, Hanoi 151000, Vietnam, and.
authors.forename: Quoc-Tuan
authors.initials: QT
authors.lastname: Le
authors.affiliation: From the Institut National de la Recherche Scientifique-Institut Armand-Frappier, 531 Boulevard des Prairies, Laval, Quebec H7V 1B7, Canada.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Blanchet
authors.affiliation: Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, 110 Pine Avenue West, Montreal, Quebec H2W 1R7, Canada.
authors.forename: Nabil G
authors.initials: NG
authors.lastname: Seidah
authors.affiliation: From the Institut National de la Recherche Scientifique-Institut Armand-Frappier, 531 Boulevard des Prairies, Laval, Quebec H7V 1B7, Canada, patrick.labonte@iaf.inrs.ca.
authors.forename: Patrick
authors.initials: P
authors.lastname: Labonté
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D011973:Receptors, LDL / Q000096:biosynthesis* / Q000235:genetics; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D060225:Tetraspanin 28 / Q000235:genetics / Q000378:metabolism*
chemical_list: C554798:CD81 protein, human; C573412:LDLR protein, human; D046912:Multiprotein Complexes; D011973:Receptors, LDL; D060225:Tetraspanin 28; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases
keywords: cell biology; cell surface protein; lipoprotein receptor; proprotein convertase subtilisin/kexin type 9 (PCSK9); protein sorting; protein-protein interaction