Fibrinolytic activity and morphological transformation of hamster embryo cells

Excretion of plasminogen activator from colonies of Syrian hamster embryo cells has been studied after sequential exposure of the cells to benzo[a]pyrene (3 days), and 12-O-tetradecanoyl-phorbol-13-acetate (3 days). The excretion of plasminogen activator was assayed using the fibrin/agarose overlay technique. The frequency of plasminogen activator-positive colonies was about two times higher for morphologically transformed colonies than for colonies with normal morphology growing on the same dish. Thus, 9% of the transformed colonies, compared to 4% of the colonies with normal morphology, gave clear zones of lysis in the fibrin/agarose overlay after 2 h of incubation. The frequency of plasminogen activator-positive colonies on untreated dishes was 2%. The addition of protease inhibitors strongly reduced the formation of clear zones of lysis, while they did not affect the frequency of morphologically transformed colonies. The data show that the expression of plasminogen activator is not an obligatory event in the process of morphological transformation.