Induction of urokinase activity and malignant phenotype in bladder carcinoma cells after transfection of the activated Ha-ras oncogene

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Abstract
In order to characterize further the previously observed induction of a highly metastatic phenotype in mouse bladder carcinoma cells by Ha-ras transfection, we studied production of plasminogen activator, in vitro invasiveness, and the potential for lung colonization of these cells. The parent carcinoma cells produced predominantly tissue-type plasminogen activator. Out of 13 clones of ras-transfected cells tested, 8 secreted quantitatively elevated levels of plasminogen activator (up to 3.5-fold) as compared to the control transfectants. The plasminogen activator activity in cell lysates was maximally increased 3-fold, the surface-associated activity increased 2.5-fold. The secreted plasminogen activator of cloned ras-transfected cells was characterized to be predominantly of the urokinase type (71.3% compared to 20.5% with the parental BL cells). Thus, in addition to the quantitative augmentation of plasminogen activator production and secretion in a large fraction of the ras-transfected cell population, a significant qualitative shift from tissue-type to urokinase-type has been observed. In addition, ras-transfection augmented the capacity of the cells for invasion into Matrigel in a double-filter in vitro assay as well as their ability to colonize the lungs of syngeneic animals. These malignant properties of the transfected cells might be responsible for their highly metastatic behaviour induced by ras transfection.