Autoactivation of avian urokinase-type plasminogen activator (uPA). A novel mode of initiation of the uPA/plasmin cascade.
In contrast to mammalian urokinase-type plasminogen activator (uPA), which is produced and maintained in zymogen form, avian uPA is found in the active two-chain form in cultures of normal and transformed chicken cells in the absence of plasmin, the putative natural activator of pro-uPA. Recombinant chicken uPA (ch-uPAwt) synthesized in two distinct expression systems also presents in the active two-chain form. In addition, conversion to the active uPA in both natural and recombinant expression systems could be prevented by uPA-specific inhibitors including a monoclonal antibody that uniquely inhibits the catalytic activity of ch-uPA. Most significantly, an active site mutant of avian uPA (ch-uPAS353A) that lacks catalytic activity is produced and maintained in single-chain form. Furthermore, the single-chain ch-uPAS353A mutant can be converted to the two-chain form by purified active ch-uPAwt. These results strongly indicate an autocatalytic mechanism of activation of ch-uPA. Autoactivation appears to be an intrinsic property of ch-uPA and may be the initiating molecular event in uPA-mediated proteolytic cascades.
Alexander
D S
DS
Department of Pathology, State University of New York, Stony Brook, New York 11794-8651, USA.
Sipley
J D
JD
Quigley
J P
JP
D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002478:Cells, Cultured; D002642:Chick Embryo; D004789:Enzyme Activation; D005341:Fibrinolysin / Q000378:metabolism; D005347:Fibroblasts / Q000201:enzymology; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics / Q000378:metabolism*
D011994:Recombinant Proteins; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator