Urokinase-type and tissue-type plasminogen activators have different distributions in cultured bovine capillary endothelial cells.

Abstract

The cell extracts and conditioned medium from cultured bovine capillary endothelial (BCE) cells were examined to determine the types of plasminogen activator (PA) present in each of these two fractions. The fractions were first analyzed by fibrin autography after sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The cell extracts contained two species of PA of Mr 48,000 and 28,000. Multiple forms of PA were detected in the conditioned medium: variable amounts of the Mr 48,000 and 28,000 forms and a broad band of activity with Mr in the range of 67,000-93,000. The major fraction of the Mr 48,000 form was in the cell extract. Treatment of the cells with 12-0-tetradecanoyl phorbol-13-acetate or with a preparation containing angiogenic activity resulted in a proportionate increase in the levels of all forms. The Mr 48,000 form was demonstrated to be a urokinase-like PA, since it was immunoprecipitated with antibodies to urokinase. When conditioned medium or cell extracts from biosynthetically labelled BCE cells were incubated with antiserum to urokinase, the Mr 48,000 form was immunoprecipitated only from the cell extract. The Mr 67,000-93,000 forms were demonstrated to be tissue-type PAs, since they were immunoprecipitated with antibodies to tissue PA. When the same conditioned medium or cell extracts were incubated with antiserum to tissue-type PA, the Mr 67,000-93,000 forms were immunoprecipitated only from the conditioned medium. Therefore, BCE cells are able to produce both tissue-type PA, which is primarily secreted, and urokinase-type PA, which remains primarily cell associated.