title: Structural requirements for activation of latent platelet-derived growth factor CC by tissue plasminogen activator.
abstract: Platelet-derived growth factor C (PDGF-C) is one of four members in the PDGF family of growth factors, which are known mitogens and survival factors for cells of mesenchymal origin. PDGF-C has a unique two-domain structure consisting of an N-terminal CUB and a conserved C-terminal growth factor domain that are separated by a hinge region. PDGF-C is secreted as a latent dimeric factor (PDGF-CC), which undergoes extracellular removal of the CUB domains to become a PDGF receptor alpha agonist. Recently, the multidomain serine protease tissue plasminogen activator (tPA), a thrombolytic agent used for treatment of acute ischemic stroke, was shown to cleave and activate PDGF-CC. In this study we determine the molecular mechanism of tPA-mediated activation of PDGF-CC. Using various PDGF-CC and tPA mutants, we were able to demonstrate that both the CUB and the growth factor domains of PDGF-C, as well as the kringle-2 domain of tPA, are required for the interaction and cleavage to occur. We also show that Arg231 in PDGF-C is essential for tPA-mediated proteolysis and that the released "free" CUB domain of PDGF-C can act as a competitive inhibitor of the cleavage reaction. Furthermore, we studied how the PDGF-C/tPA axis is regulated in primary fibroblasts and found that PDGF-C expression is down-regulated by hypoxia but induced by transforming growth factor (TGF)-beta1 treatment. Elucidating the regulation and the mechanism of tPA-mediated activation of PDGF-CC will advance our knowledge of the physiological function of PDGF-CC and tPA and may provide new therapeutic opportunities for thrombolytic and cardiovascular therapies.
authors.affiliation: Ludwig Institute for Cancer Research, Stockholm Branch, Box 240, S-171 77 Stockholm, Sweden.
authors.forename: Linda
authors.initials: L
authors.lastname: Fredriksson
authors.forename: Monika
authors.initials: M
authors.lastname: Ehnman
authors.forename: Christina
authors.initials: C
authors.lastname: Fieber
authors.forename: Ulf
authors.initials: U
authors.lastname: Eriksson
mesh_terms: D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics; D025461:Feedback, Physiological; D005347:Fibroblasts; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D018082:Kringles; D008222:Lymphokines / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010982:Platelet-Derived Growth Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D010959:Tissue Plasminogen Activator / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D053773:Transforming Growth Factor beta1
chemical_list: D008222:Lymphokines; D010982:Platelet-Derived Growth Factor; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C411423:platelet-derived growth factor C; D010959:Tissue Plasminogen Activator