title: Insulin-like growth factor-binding protein-5 activates plasminogen by interaction with tissue plasminogen activator, independently of its ability to bind to plasminogen activator inhibitor-1, insulin-like growth factor-I, or heparin.
abstract: Transgenic mice expressing IGFBP-5 in the mammary gland exhibit increased cell death and plasmin generation. Because IGFBP-5 has been reported to bind to plasminogen activator inhibitor-1 (PAI-1), we determined the effects of this interaction in HC11 cells. PAI-1 prevented plasmin generation from plasminogen and inhibited cleavage of focal adhesions, expression of caspase 3, and cell death. IGFBP-5 could in turn prevent the effects of PAI-1. IGFBP-5 mutants with reduced affinity for IGF-I (N-term) or deficient in heparin binding (HEP- and C-term E and F) were also effective. This was surprising because IGFBP-5 reportedly interacts with PAI-1 via its heparin-binding domain. Biosensor analysis confirmed that, although wild-type IGFBP-5 and N-term both bound to PAI-1, the C-term E had greatly decreased interaction with PAI-1. This suggests that IGFBP-5 does not antagonize the actions of PAI-1 by a direct molecular interaction. In a cell-free system, using tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) to activate plasminogen, PAI-1 inhibited plasmin generation induced by both activators, whereas IGFBP-5 prevented the effects of PAI-1 on tPA but not uPA. Furthermore, we noted that IGFBP-5 activated plasminogen to a greater extent than could be explained solely by inhibition of PAI-1, suggesting that IGFBP-5 could directly activate tPA. Indeed, IGFBP-5 and the C-term E and F were all able to enhance the activity of tPA but not uPA. These data demonstrate that IGFBP-5 can enhance the activity of tPA and that this can result in cell death induced by cleavage of focal adhesions. Thus IGFBP-5 can induce cell death by both sequestering IGF-I and enhancing plasmin generation.
authors.affiliation: Hannah Research Institute, Ayr KA6 5HL, United Kingdom.
authors.forename: Alice M
authors.initials: AM
authors.lastname: Sorrell
authors.forename: John H
authors.initials: JH
authors.lastname: Shand
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Tonner
authors.forename: Matteo
authors.initials: M
authors.lastname: Gamberoni
authors.forename: Pier A
authors.initials: PA
authors.lastname: Accorsi
authors.forename: James
authors.initials: J
authors.lastname: Beattie
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Allan
authors.forename: David J
authors.initials: DJ
authors.lastname: Flint
mesh_terms: D000818:Animals; D015374:Biosensing Techniques; D043424:Carboxypeptidase B / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D016923:Cell Death; D002460:Cell Line; D002474:Cell-Free System; D002851:Chromatography, High Pressure Liquid; D016895:Culture Media, Serum-Free / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006493:Heparin / Q000378:metabolism*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D010958:Plasminogen / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D010960:Plasminogen Activators / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
chemical_list: D016895:Culture Media, Serum-Free; D018975:Insulin-Like Growth Factor Binding Protein 5; D017395:Plasminogen Activator Inhibitor 1; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D010958:Plasminogen; D006493:Heparin; D005982:Glutathione Transferase; D043424:Carboxypeptidase B; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases