title: Stanniocalcin-1 Potently Inhibits the Proteolytic Activity of the Metalloproteinase Pregnancy-associated Plasma Protein-A.
abstract: Stanniocalcin-1 (STC1) is a disulfide-bound homodimeric glycoprotein, first identified as a hypocalcemic hormone important for maintaining calcium homeostasis in teleost fish. STC1 was later found to be widely expressed in mammals, although it is not believed to function in systemic calcium regulation in these species. Several physiological functions of STC1 have been reported, although many molecular details are still lacking. We here demonstrate that STC1 is an inhibitor of the metzincin metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A), which modulates insulin-like growth factor (IGF) signaling through proteolytic cleavage of IGF-binding proteins (IGFBPs). STC1 potently (Ki = 68 pm) inhibits PAPP-A cleavage of IGFBP-4, and we show in a cell-based assay that STC1 effectively antagonizes PAPP-A-mediated type 1 IGF receptor (IGF1R) phosphorylation. It has recently been found that the homologous STC2 inhibits PAPP-A proteolytic activity, and that this depends on the formation of a covalent complex between the inhibitor and the proteinase, mediated by Cys-120 of STC2. We find that STC1 is unable to bind covalently to PAPP-A, in agreement with the absence of a corresponding cysteine residue. It rather binds to PAPP-A with high affinity (KD = 75 pm). We further demonstrate that both STC1 and STC2 show inhibitory activity toward PAPP-A2, but not selected serine proteinases and metalloproteinases. We therefore conclude that the STCs are proteinase inhibitors, probably restricted in specificity to the pappalysin family of metzincin metalloproteinases. Our data are the first to identify STC1 as a proteinase inhibitor, suggesting a previously unrecognized function of STC1 in the IGF system.
authors.affiliation: From the Department of Molecular Biology and Genetics and.
authors.forename: Søren
authors.initials: S
authors.lastname: Kløverpris
authors.affiliation: From the Department of Molecular Biology and Genetics and.
authors.forename: Jakob H
authors.initials: JH
authors.lastname: Mikkelsen
authors.affiliation: From the Department of Molecular Biology and Genetics and.
authors.forename: Josefine H
authors.initials: JH
authors.lastname: Pedersen
authors.affiliation: From the Department of Molecular Biology and Genetics and.
authors.forename: Malene R
authors.initials: MR
authors.lastname: Jepsen
authors.affiliation: From the Department of Molecular Biology and Genetics and.
authors.forename: Lisbeth S
authors.initials: LS
authors.lastname: Laursen
authors.affiliation: the Department of Biomedicine, Aarhus University, DK-8000 Aarhus, Denmark.
authors.forename: Steen V
authors.initials: SV
authors.lastname: Petersen
authors.affiliation: From the Department of Molecular Biology and Genetics and co@mbg.au.dk.
authors.forename: Claus
authors.initials: C
authors.lastname: Oxvig
mesh_terms: D015153:Blotting, Western; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011266:Pregnancy-Associated Plasma Protein-A / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D017526:Receptor, IGF Type 1; D017451:Receptors, Somatomedin / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D006023:Glycoproteins; C000597236:IGF1R protein, human; D018974:Insulin-Like Growth Factor Binding Protein 4; D036341:Intercellular Signaling Peptides and Proteins; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; C114997:STC2 protein, human; C051795:teleocalcin; D017526:Receptor, IGF Type 1; C430889:PAPPA2 protein, human; D011266:Pregnancy-Associated Plasma Protein-A
keywords: IGF-binding protein; disulfide; insulin-like growth factor (IGF); metalloprotease; metzincin; pappalysin; protease inhibitor; proteolysis; stanniocalcin