Activation of Receptor-bound Single-chain Urokinase-type Plasminogen Activator by Plasmin

Abstract

We investigated the cell surface-focused urokinase-type plasminogen activator (uPA)/plasmin system regulating plasmin prodution. Plasmin cleaves single-chain uPA (pro-uPA) synthesized from cells at amino acid position Lys158-Ile159 bond and the Lys135-Lys136 bond. uPA receptors are occupied by Amino-terminal fragment (ATF) after cleavage at position Lys135-Lys136 bond. Extensive treatment of pro-uPA/uPA with plasmin results in the cleavages of the Lys23-Tyr24 bond and of the Lys35-Lys36 bond in the Growth Factor-like domain (GFD) before binding to the uPA receptor. These polypeptides with the cleavage in the GFD can not bind to the uPA receptors on U937 cells any more. Plasmin, however, does not cleave amino acid sequences within GFD of receptor-bound pro-uPA/uPA on U937 cells, indicating that receptor-bound ATF is resistant to the plasmin action. These provide a feedback mechanism of pro-uPA/uPA binding to the uPA receptor and subsequent plasmin production.