Regulation and Secretion of Plasminogen Activators and Their Inhibitors in a Human Leukemic Cell

The secretion of tissue plasminogen activator ft-PA). urokinase (u-PA) and their inhibitors by the human leukemia cell line K562 was examined. K562 cells normally secrete both t -PA and u-PA in a ratio of 3:1 . After addition of 10 or 1 ng/mL phorbol myristate acetate (PMA) to K562 cells. a marked decrease in enzymatic activity is observed in the medium. However. when t-PA antigen rather than activity is measured. an increased amount is found in the medium under these conditions. PMA also induces secretion of the two inhibitors of plasminogen activator: plasminogen activator inhibitor 1 (PAl-i ) and plasminogen activator inhibitor 2 (PAI-2). This accounts for the decrease in total