title: Novel loss-of-function PCSK9 variant is associated with low plasma LDL cholesterol in a French-Canadian family and with impaired processing and secretion in cell culture.
abstract: BACKGROUND
  PCSK9 (proprotein convertase subtilisin/kexin type 9) is a polymorphic gene whose protein product regulates plasma LDL cholesterol (LDLC) concentrations by shuttling liver LDL receptors (LDLRs) for degradation. PCSK9 variants that cause a gain or loss of PCSK9 function are associated with hyper- or hypocholesterolemia, which increases or reduces the risk of cardiovascular disease, respectively. We studied the clinical and molecular characteristics of a novel PCSK9 loss-of-function sequence variant in a white French-Canadian family.
  
  
  METHODS
  In vivo plasma and ex vivo secreted PCSK9 concentrations were measured with a commercial ELISA. We sequenced the PCSK9 exons for 15 members of a family, the proband of which exhibited very low plasma PCSK9 and LDLC concentrations. We then conducted a structure/function analysis of the novel PCSK9 variant in cell culture to identify its phenotypic basis.
  
  
  RESULTS
  We identified a PCSK9 sequence variant in the French-Canadian family that produced the PCSK9 Q152H substitution. Family members carrying this variant had mean decreases in circulating PCSK9 and LDLC concentrations of 79% and 48%, respectively, compared with unrelated noncarriers (n=210). In cell culture, the proPCSK9-Q152H variant did not undergo efficient autocatalytic cleavage and was not secreted. Cells transiently transfected with PCSK9-Q152H cDNA had LDLR concentrations that were significantly higher than those of cells overproducing wild-type PCSK9 (PCSK9-WT). Cotransfection of PCSK9-Q152H and PCSK9-WT cDNAs produced a 78% decrease in the secreted PCSK9-WT protein compared with control cells.
  
  
  CONCLUSIONS
  Collectively, our results demonstrate that the PCSK9-Q152H variant markedly lowers plasma PCSK9 and LDLC concentrations in heterozygous carriers via decreased autocatalytic processing and secretion, and hence, inactivity on the LDLR.
authors.affiliation: Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario, Canada. jmayn2@uottawa.ca
authors.forename: Janice
authors.initials: J
authors.lastname: Mayne
authors.forename: Thilina
authors.initials: T
authors.lastname: Dewpura
authors.forename: Angela
authors.initials: A
authors.lastname: Raymond
authors.forename: Lise
authors.initials: L
authors.lastname: Bernier
authors.forename: Marion
authors.initials: M
authors.lastname: Cousins
authors.forename: Teik Chye
authors.initials: TC
authors.lastname: Ooi
authors.forename: Jean
authors.initials: J
authors.lastname: Davignon
authors.forename: Nabil G
authors.initials: NG
authors.lastname: Seidah
authors.forename: Majambu
authors.initials: M
authors.lastname: Mbikay
authors.forename: Michel
authors.initials: M
authors.lastname: Chrétien
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D002478:Cells, Cultured; D008078:Cholesterol, LDL / Q000097:blood*; D005260:Female; D014644:Genetic Variation; D006579:Heterozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010375:Pedigree; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases / Q000097:blood / Q000235:genetics* / Q000378:metabolism; D044465:White People; D055815:Young Adult
chemical_list: D008078:Cholesterol, LDL; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases