Regulation of mRNAs for type-1 plasminogen activator inhibitor, fibronectin, and type I procollagen by transforming growth factor-beta. Divergent responses in lung fibroblasts and carcinoma cells.

Abstract

Transforming growth factor-beta (TGF beta) is a growth modulator which stimulates the growth of fibroblasts but acts as a strong growth inhibitor for cells of epithelial origin. TGF beta also influences the production of extracellular matrix proteins and of proteases and protease inhibitors by cultured cells. One important protease inhibitor whose production is affected rapidly by TGF beta is the type-1 plasminogen activator inhibitor (PAI-1). To investigate the relationships between PAI-1 and the extracellular matrix, we analyzed the regulation by TGF beta of PAI-1, fibronectin, and type I procollagen in malignant human lung carcinoma cells (A549) and in human lung fibroblasts (WI-38). The expression of the respective genes was examined by polypeptide analyses and by measurements of the steady-state levels of the corresponding mRNAs by Northern hybridization. The mRNA levels for PAI-1 were elevated rapidly by TGF beta in both cell lines. This induction occurred in the presence of cycloheximide and thus was not dependent on protein synthesis. In fact, the effects of TGF beta and cycloheximide on PAI-1 mRNA were additive. In contrast, the induction of fibronectin, beta-actin, and type I procollagen (synthesized only in WI-38 cells) was abrogated by cycloheximide. In general, the effects of TGF beta on the steady-state levels of mRNAs for fibronectin, actin, and type I procollagen mRNA were similar in the two cell types. However, the production of PAI-1 mRNA in response to TGF beta differed in the two cell types, being transient (peak within 5 h) in the carcinoma cells and more persistent in fibroblasts. Thus, the major difference in TGF beta regulation of PAI-1 mRNA between lung fibroblasts and carcinoma cells was the duration of the effect. These results, together with previous data, suggest that PAI-1 and plasminogen activators may be regulated oppositely by TGF beta. We therefore propose a model for TGF beta in the regulation of extracellular proteolytic activity.