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

• Published in: The Journal of biological chemistry 2006-04, Vol.281 (16), p.10883-10889
• Main Authors: Sorrell, Alice M., Shand, John H., Tonner, Elizabeth, Gamberoni, Matteo, Accorsi, Pier A., Beattie, James, Allan, Gordon J., Flint, David J.
• Format: Article
• Language: English
• Subjects: Animals; Biosensing Techniques; Carboxypeptidase B - metabolism; Caspase 3; Caspases - metabolism; Cell Death; Cell Line; Cell-Free System; Chromatography, High Pressure Liquid; Culture Media, Serum-Free - metabolism; Escherichia coli - metabolism; Fibrinolysin - metabolism; Focal Adhesions - metabolism; Glutathione Transferase - metabolism; Heparin - metabolism; Insulin-Like Growth Factor Binding Protein 5 - metabolism; Insulin-Like Growth Factor Binding Protein 5 - physiology; Insulin-Like Growth Factor I - metabolism; Mice; Mice, Transgenic; Mutation; Plasminogen - metabolism; Plasminogen Activator Inhibitor 1 - metabolism; Plasminogen Activators - metabolism; Protein Structure, Tertiary; Recombinant Fusion Proteins - metabolism; Recombinant Proteins - metabolism; Time Factors; Tissue Plasminogen Activator - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M508505200

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.