The murine Lewis lung carcinoma 3LL cells give rise to spontaneous and experimental lung metastasis in C57BL/6 mice. Tumor cells maintained by serial subcutaneous transplantation in mice retain their ability to form lung metastasis, while cells carried in vitro loose metastatic potential with time. In order to obtain the non-metastatic subline, 3LL cells selected for its high lung colonization potential was grown continuously in vitro for 24 weeks. The present study was undertaken to characterize the expression of both urokinase-type plasminogen activator (uPA) and urinary trypsin inhibitor (UTI) in the non-metastatic (3LL(-)) and the metastatic (3LL(+)) cells. Both cells were tested on the Matrigel for invasive ability using a modified Boyden chamber and assayed for expression of uPA and UTI. The 3LL(+) cells secreted 5 times more uPA (6.25 mu g per 10(6) cells per 24 h) than the 3LL(-) cells (1.25 mu g per 10(6) cells per 24 h). The 3LL(+) cells, which expressed 2 times more cell-surface receptor-bound enzymatically active uPA (0.32 +/- 0.06 OD405) than the 3LL(-) cells (0.15 +/- 0.03 OD405), had larger amounts of cell-surface receptor-bound uPA. On the other hands, UTI levels in the conditioned media was decreased 25-fold in the 3LL(+) cells (0.05 mu g/10(6) cells/24 h) compared to the 3LL(-) cells (1.25 mu g/10(6) cells/24 h). The 3LL(-) cells expressed significantly higher levels of cell-associated UTI as indicated by a cell ELISA (3LL(+), 0.30 +/- 0.04 OD450; 3LL(-), 1.30 +/- 0.21 OD450) and by Western blot analysis. Metastatic competence in the 3LL(+) tumor model is associated with increased expression and release of uPA, as well as decreased UTI production, consistent with a more invasive phenotype. These data support our hypothesis that UTI may contribute to the inhibition of uPA expression in tumor cells.

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