THE EXTRACELLULAR-MATRIX PROTEINS LAMININ AND FIBRONECTIN CONTAIN BINDING DOMAINS FOR HUMAN PLASMINOGEN AND TISSUE-PLASMINOGEN ACTIVATOR

This study describes the binding of plasminogen and tissue-type plasmi nogen activator (t-PA) to the extracellular matrix proteins fibronecti n and laminin. Plasminogen bound specifically and saturably to both fi bronectin and laminin immobilized on microtiter wells, with K(d(app)) values of 115 and 18 nM, respectively. Limited proteolysis by endoprot einase V8 coupled with ligand blotting analysis showed that both plasm inogen and t-PA preferentially bind to a 55-kDa fibronectin fragment a nd a 38-kDa laminin fragment. Amino acid sequence analysis demonstrate d that the 55-kDa fragment originates with the fibronectin amino termi nus whereas the laminin fragment was derived from the carboxyl-termina l globular domain of the laminin A chain. Ligand blotting experiments using isolated plasminogen domains were also used to identify distinct regions of the plasminogen molecule involved in fibronectin and lamin in binding. Solution phase fibronectin binding to immobilized plasmino gen was mediated primarily via lysine binding site-dependent interacti ons with plasminogen kringles 1-4. Lysine binding site-dependent bindi ng of soluble laminin to immobilized plasminogen kringles 1-5 as well as an additional lysine binding site-independent interaction between m ini-plasminogen and the 38-kDa laminin A chain fragment were also obse rved. These studies demonstrate binding of plasminogen and tissue-type plasminogen activator to specific regions of the extracellular matrix glycoproteins laminin and fibronectin and provide further insight int o the mechanism of regulation of plasminogen activation by components of the extracellular matrix.