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Reexamination of the Role of Plasminogen Activator Production for Growth in Semisolid Agar of Neoplastic Hamster Cells

Environmental Carcinogenesis Group, Laboratory of Pulmonary Function and Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, N.C. 27709 [J.C.B., S.S.], and Cell Genetic Section, Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, Maryland 20205 [K.O., T.K.]

Enhanced plasminogen activator production has been proposed by others as the basis for growth ability in semisolid agar of transformed cells. Four types of experiments have supported this hypothesis: correlative studies; experiments with plasminogen-depleted serum; experiments with sera which contain elevated levels of plasminogen; and studies with temperature sensitive mutants. In the present report; this relationship was reexamined with chemically transformed hamster cell lines which display a qualitative and quantitative correlation between tumorigenicity and growth in semisolid agar, but with 4 approaches cited above there was no evidence to support a role of plasminogen activator production for growth in semisolid agar of these cells. Cell lines isolated on the basis of varying levels of fibrinolytic activity did not display a correlation between the level of fibrinolytic activity and cloning efficiency in semisolid agar. Plasminogen depletion of serum by lysine-Sepharose affinity chromatography reduced the ability of the serum to support growth of the cells in agar. Part of this reduction was ascribed to a general decrease in the ability of plasminogen-depleted serum to support anchorage-dependent cell growth in liquid media. The ability of plasminogen-depleted serum to support anchorage-dependent and -independent cell growth could not be restored by exogeneous plasminogen, suggesting that the process of plasminogen depletion removes factors other than plasminogen which are responsible for the reduction in growth support by this depleted serum. Addition of plasminogen to fetal bovine serum did not enhance the ability of cells to grow in agar. Mutants of hamster cells that were temperature sensitive for growth in agar were not temperature sensitive for production of plasminogen activator. Thus, the results with hamster cells do not support a direct role of plasminogen activator production for growth in semisolid media of these cells.

¹ To whom requests for reprints should be addressed.

Received 6/11/79. Accepted 1/23/80.