Construction and expression of a hybrid plasminogen activator gene with sequences from non-protease region of tissue-type plasminogen activator (t-PA) and protease region of urokinase (u-PA).

There are two physiological plasminogen activators (PAs), tissue-type PA (t-PA) and urokinase (u-PA) which possess distinct immunological and biochemical characteristics. Using genetic engineering techniques a hybrid t:u-PA cDNA, comprised of amino acid (aa) sequences corresponding to the non-protease region (aa 1-261) of t-PA and the protease region (aa 132-411) of u-PA, was constructed. The t:u-PA gene after insertion into the SV40 expression vector was expressed in monkey Cos-1 cells. The 66-67 kDa t:u-PA was produced in an enzymatically active form. The fibrinolytic activity of the t:u-PA could be quenched by anti-urokinase as well as by anti-t-PA sera. Like urokinase, the t:u-PA showed a high intrinsic plasminogen activation. This activity, as in the case of t-PA, was stimulated by fibrin. The u-PA, on the other hand, stimulated plasminogen activation marginally in the presence of fibrin. Both the t:u-PA and t-PA showed binding affinity for fibrin clot. This study strongly suggests the autonomous nature of the structural domains in PA and also demonstrates the feasibility of shuffling these domains without loss of their functional activities.