Tissue type plasminogen activator, but not urokinase, exerts transformation‐enhancing activity

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Abstract
Previous studies have established that plasma cryoprecipitates of tumor patients, culture media of transformed cells and defined proteolytic fragments of fibronectin enhance the morphological cell transformation (TEF activity) in cultures of chicken embryo fibroblasts infected with temperature‐sensitive mutants of Rous sarcoma virus. We now report that purified human tissue type plasminogen activator (t‐PA), but not urokinase (u‐PA), has a similar TEF activity, at doses as low as 2 ng/ml (30 pM). Specific antibodies effectively neutralized the activity. No significant contamination (≤1%) between the preparations of t‐PA and fibronectin (FN) or its fragments (FNdp) was detected. The results suggest that t‐PA may have a direct role in the process of morphological cell transformation in vitro.