Plasminogen activator synthesis accompanying chemical carcinogen-inducedin vitro transformation of syrian hamster and guinea-pig fetal cells

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Abstract
The production of the extracellular protease, plas-minogen activator, in relationship to growth in semi-solid medium and tumorigenicity has been studied in Syrian hamster embryo and strain 2 guinea-pig embryo cell culture models of chemical carcinogenesis. Whereas normal hamster and guinea-pig embryo cells had negligible levels of plasminogen activator, neoplastically transformed cells derived from cultures exposed to chemical carcinogens had high levels of plasminogen activator and grew as progressively enlarging colonies in soft agar. The development of plasminogen activator secretion in relation to neoplastic transformation was further studied in the guinea-pig cells where the latent period between carcinogen exposure and neoplastic transformation ranged from 4 months to more than one year. The production of plasminogen activator in this system also exhibited a long latent period, and acquisition of extracellular plasminogen activator correlated temporally with growth in agar and tumorigenicity. Plasminogen activator and growth in semi-solid agar in concert are useful markers for identification of neoplastic cells transformed in culture following exposure to a chemical carcinogen.