PT  - JOURNAL ARTICLE
AU  - Lisa Mathiasen
AU  - Daniel M. Dupont
AU  - Anni Christensen
AU  - Grant E. Blouse
AU  - Jan K. Jensen
AU  - Ann Gils
AU  - Paul J. Declerck
AU  - Troels Wind
AU  - Peter A. Andreasen
TI  - A Peptide Accelerating the Conversion of Plasminogen Activator Inhibitor-1 to an Inactive Latent State
AID  - 10.1124/mol.108.046417
DP  - 2008 Sep 01
TA  - Molecular Pharmacology
PG  - 641--653
VI  - 74
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/74/3/641.short
4100  - http://molpharm.aspetjournals.org/content/74/3/641.full
SO  - Mol Pharmacol2008 Sep 01; 74
AB  - The serpin plasminogen activator inhibitor-1 (PAI-1) is a specific inhibitor of plasminogen activators and a potential therapeutic target in cancer and cardiovascular diseases. Accordingly, formation of a basis for development of specific PAI-1-inactivating agents is of great interest. One possible inactivation mode for PAI-1 is conversion to the inactive, so-called latent state. We have now screened a phage-displayed peptide library with PAI-1 as bait and isolated a 31-residue cysteine-rich peptide that will be referred to as paionin-4. A recombinant protein consisting of paionin-4 fused to domains 1 and 2 of the phage coat protein g3p caused a 2- to 3-fold increase in the rate of spontaneous inactivation of PAI-1. Paionin-4-D1D2 bound PAI-1 with a KD in the high nanomolar range. Using several biochemical and biophysical methods, we demonstrate that paionin-4-D1D2-stimulated inactivation consists of an acceleration of conversion to the latent state. As demonstrated by site-directed mutagenesis and competition with other PAI-1 ligands, the binding site for paionin-4 was localized in the loop between α-helix D and β-strand 2A. We also demonstrate that a latency-inducing monoclonal antibody has an overlapping, but not identical binding site, and accelerates latency transition by another mechanism. Our results show that paionin-4 inactivates PAI-1 by a mechanism clearly different from other peptides, small organochemical compounds, or antibodies, whether they cause inactivation by stimulating latency transition or by other mechanisms, and that the loop between α-helix D and β-strand 2A can be a target for PAI-1 inactivation by different types of compounds.