title: Characterization of a fusion protein consisting of amino acids 1 to 263 of tissue-type plasminogen activator and amino acids 144 to 411 of urokinase-type plasminogen activator.
abstract: A hybrid human cDNA was constructed by splicing of a cDNA fragment of tissue-type plasminogen activator (t-PA), encoding 5'-untranslated, the pre-pro region and amino acids Ser1-Thr263, with a cDNA fragment of urokinase-type plasminogen activator (u-PA), encoding amino acids Leu144-Leu411. The cDNA fragments were obtained from full length t-PA cDNA, cloned from Bowes melanoma poly(A)+ mRNA, and from full length u-PA cDNA, cloned from CALU-3 lung adenocarcinoma poly(A)+ mRNA. The hybrid (t-PA/u-PA) cDNA was expressed in Chinese hamster ovary cells and the translation product purified from the conditioned cell culture media. On SDS-gel electrophoresis under reducing conditions, the protein migrated as a single band with approximate Mr 70,000. On immunoblotting, it reacted both with rabbit antisera raised against human t-PA and against human u-PA. The urokinase-like amidolytic activity of the protein was only 320 IU/mg but increased to 43,000 IU/mg after treatment with plasmin, which resulted in conversion of the single-chain molecule (t-PA/scu-PA) to a two-chain molecule (t-PA/tcu-PA). The specific activity of the protein on fibrin plates was 57,000 IU/mg by comparison with the International Reference Preparation for Urokinase. Both the single-chain hybrid (t-PA/scu-PA) and the two-chain plasmin derivative (t-PA/tcu-PA) bound specifically to fibrin, albeit more weakly than t-PA. The t-PA/tcu-PA hybrid had a higher selectivity for fibrin than tcu-PA, measured in a system composed of a whole human 125I-fibrin-labeled plasma clot immersed in human plasma. Both hybrid proteins activated plasminogen directly with Km = 1.5 microM and k2 = 0.0058 s-1 for t-PA/scu-PA and with Km = 80 microM and k2 = 5.6 s-1 for t-PA/tcu-PA. CNBr-digested fibrinogen stimulated the activation of plasminogen with t-PA/tcu-PA (Km = 0.20 microM and k2 = 1.2 s-1). It is concluded that these t-PA/u-PA hybrid proteins combine, at least to some extent, the fibrin-affinity of t-PA with the enzymatic properties of u-PA (either scu-PA or tcu-PA), which in some assays result in improved fibrin-mediated plasminogen activation.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004247:DNA / Q000235:genetics; D004274:DNA, Recombinant; D004591:Electrophoresis, Polyacrylamide Gel; D005337:Fibrin / Q000378:metabolism; D005341:Fibrinolysin / Q000494:pharmacology; D005342:Fibrinolysis; D006801:Humans; D007700:Kinetics; D010958:Plasminogen / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics*; D010959:Tissue Plasminogen Activator / Q000235:genetics* / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics* / Q000378:metabolism
chemical_list: D004274:DNA, Recombinant; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D005337:Fibrin; D010958:Plasminogen; D004247:DNA; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator