title: Effects of rs6234/rs6235 and rs6232/rs6234/rs6235 PCSK1 single-nucleotide polymorphism clusters on proprotein convertase 1/3 biosynthesis and activity.
abstract: BACKGROUND
  Proprotein convertase 1/3 (PC1/3) is one of the endoproteases initiating the proteolytic activation of prohormones and proneuropeptides in the secretory pathway. It is produced as a zymogen that is subsequently modified by activity-determining cleavages at the amino and the carboxyl termini. In human, it is encoded by the PCSK1 locus on chromosome 5. Spontaneous inactivating mutations in its gene have been linked to obesity. Minor alleles of the common non-synonymous single-nucleotide polymorphisms (SNPs) rs6232 (T>C, N221D), rs6234 (G>C, Q665E) and rs6235 (C>G, S690T) have been associated with increased risk of obesity. We have shown that the variations associated with these SNPs are linked on minor PCSK1 alleles.
  
  
  OBJECTIVE
  In this study, we examined the impact of amino acid substitutions specified by the minor PCSK1 alleles on PC1/3 biosynthesis and prohormone processing activity in cultured cells.
  
  
  METHODS
  The common and variant isoforms of PC1/3 were expressed in transfected rat pituitary GH4C1 cells with or without proopiomelanocortin (POMC) as a substrate. Secreted PC1/3- or POMC-related proteins and peptides were analyzed by immunoblotting and immunoprecipitation.
  
  
  RESULTS
  When expressed in GH4C1 cells, the triple-variant PC1/3 underwent significantly more proteolytic processing at the amino and carboxyl termini than the common and double-variant isoforms. However, there was no detectable difference among these isoforms in their ability to process POMC in the transfected cells.
  
  
  CONCLUSIONS
  Since truncation of PC1/3 in its C-terminal region reportedly renders the enzyme unstable, we speculate that the accentuated processing of the triple variant in this region may, in vivo, create a subtle deficit of PC1/3 enzymatic activity in endocrine and neuroendocrine cells, causing impaired processing of prohormones and proneuropeptides to their bioactive forms.
authors: Chronic Disease Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada. mmbikay@ohri.ca
authors: Majambu
authors: M
authors: Mbikay
authors: Francine
authors: F
authors: Sirois
authors: Kabwe K
authors: KK
authors: Nkongolo
authors: Ajoy
authors: A
authors: Basak
authors: Michel
authors: M
authors: Chrétien
mesh_terms: D000483:Alleles; D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D000818:Animals; D015870:Gene Expression; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D008958:Models, Molecular; D020641:Polymorphism, Single Nucleotide; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D045664:Proprotein Convertase 1 / Q000096:biosynthesis* / Q000235:genetics*; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D011333:Pro-Opiomelanocortin; D045664:Proprotein Convertase 1