Modulation of tissue plasminogen activator-catalyzed plasminogen activation by synthetic peptides derived from the amino-terminal heparin binding domain of fibronectin.

Fibronectin is a multidomain adhesive glycoprotein found in plasma, interstitial connective tissue, and basement membrane. Diverse biological activities have been associated with the fibronectin molecule including cell adhesion, cell migration, wound healing, hemostasis, and oncogenic transformation. Binding sites for heparin, fibrin, gelatin/collagen, and cells have been localized to various structural domains of the molecule. In addition, fibronectin also binds both plasminogen and tissue plasminogen activator (t-PA) via a 55-kDa amino-terminal fragment (Moser, T.L., Enghild, J.J., Pizzo, S.V., and Stack, M.S. (1993) J. Biol. Chem. 268, 18917-18923). Although intact fibronectin does not enhance the rate of t-PA-catalyzed plasminogen activation, a mixture of proteolytically degraded fibronectin fragments stimulates the activation reaction, resulting in an 11-fold increase in the kcat/Km. Based on these observations, we have synthesized a variety of peptides derived from the plasminogen/t-PA binding region of fibronectin and determined the effect of these peptides on the initial rate kinetics of plasminogen activation by t-PA as well as on plasmin and t-PA amidolytic activity. Here we report that a specific octapeptide, SRNRCNDQ-NH2, consisting of residues 196-203 of the fibronectin molecule is a potent stimulator of t-PA-catalyzed plasminogen activation, resulting in a 15-fold increase in the kcat/Km of the activation reaction.