Cultured human embryonic lung fibroblasts were used as a model to study the effects of transforming growth factor-13 (TGFI3) on the plasminogen activator (PA) activity released by nontumorigenic cells into the culture medium. The cells were exposed to TGFfl under serum-free conditions, and the changes in PA activity and protein metabolism were analyzed by caseinolysis-in-agar assays, zymography, and polypeptide analysis. Treatment of the cells with TGFβ caused a significant decrease in the PA activity of the culture medium as analyzed by the caseinolysis-in-agar assays. The quantitatively most prominent effect of TGFI3 on confluent cultures of ceils was the induction of an Mr 47,000 protein, as detected by metabolic labeling. The Mr 47,000 protein was a PA inhibitor as judged by reverse zymography. It was antigenically related to a PA inhibitor secreted by HT-1080 tumor cells as demonstrated with monoclonal antibodies. The induced Mr 47,000 inhibitor was deposited into the growth substratum of the cells, as detected by metabolic labeling, immunoblotting analysis, and reverse zymography assays of extracellular matrix preparations. TGFI3 also decreased the amounts of urokinase-type and tissue-type PAs accumulated in the conditioned medium, as detected by zymography. Epidermal growth factor antagonized the inhibitory effects of TGFI3 by enhancing the amounts of the PAs. These results indicate that growth factors modulate the proteolytic balance of cultured ceils by altering the amounts of PAs and their inhibitors.
ASJC Scopus subject areas
- Cell Biology