Interaction of plasminogen activator inhibitor (PAI-1) with vitronectin.
Immobilized vitronectin was found to bind both purified plasminogen activator inhibitor type 1 (PAI-1) and the PAI-1 in conditioned culture medium of human sarcoma cells. Similarly, immobilized PAI-1 bound both purified vitronectin and vitronectin from normal human serum. These interactions were demonstrated using both enzyme immunoassay and radioiodinated proteins. Solid-phase vitronectin bound PAI-1 with Kd 1.9 x 10(-7) M, and the reverse interaction gave a Kd 5.5 x 10(-8) M. Evidence was also found for a second type of binding with a Kd below 10(-10) M. The molar ratios of the two proteins in the complex at the saturation levels were approximately one molecule of soluble PAI-1 bound per three molecules of immobilized vitronectin and approximately one molecule of soluble vitronectin being bound per one molecule of immobilized PAI-1. Binding of PAI-1 to vitronectin did not lead to an irreversible loss of the ability of PAI-1 to inhibit urokinase (u-PA) and tissue-type plasminogen activator (t-PA). Active u-PA released vitronectin-bound 125I-labeled PAI-1 radioactivity, suggesting that u-PA interacts with the complex. The Mr 50,000 urokinase cleavage product of PAI-1 also bound to vitronectin, but this bound fragment did not inhibit u-PA. Binding of PAI-1 to vitronectin did not interfere with the ability of vitronectin to promote the adhesion and spreading of cells. These results suggest that the interaction between vitronectin and PAI-1 may serve to confine pericellular u-PA activity to focal contact sites where cells use proteolysis in regional detachment.
Salonen
E M
EM
Department of Virology, University of Helsinki, Finland.
Vaheri
A
A
Pöllänen
J
J
Stephens
R
R
Andreasen
P
P
Mayer
M
M
Danø
K
K
Gailit
J
J
Ruoslahti
E
E
D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D008970:Molecular Weight; D015849:Plasminogen Inactivators; D011485:Protein Binding; D011869:Radioligand Assay; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors; D019096:Vitronectin
D006023:Glycoproteins; D015849:Plasminogen Inactivators; D019096:Vitronectin; D014568:Urokinase-Type Plasminogen Activator