Differential regulation of the expression of transforming growth factor‐βs 1 and 2 by retinoic acid, epidermal growth factor, and dexamethasone in NRK‐49F and A549 cells

Abstract

Although most biological activities of transforming growth factor‐βs 1 and 2 (TGF‐β1 and TGF‐β2) examined in vitro are similar or identical, recent studies suggest that each of these factors may be independently regulated in vivo. In this study we have used highly sensitive and specific sandwich enzyme‐linked immunosorbent assays for TGF‐β1 and TGF‐β2 to examine the effects of a variety of treatments on expression of these two TGF‐β isoforms. We show that epidermal growth factor (EGF) induces secretion of TGF‐β1 and not TGF‐β2, whereas retinoic acid (RA) induces secretion of TGF‐β2 and not TGF‐β1 in NRK‐49F normal rat kidney fibroblasts and A549 human lung carcinoma cells. Moreover, treatment with EGF diminishes the levels of TGF‐β2, while RA decreases the levels of TGF‐β1 in both cell lines. Dexamethasone (Dex), on the other hand, inhibits the secretion of both TGF‐β1 and TGF‐β2 in A549 cells, while selectively inhibiting TGF‐β1 secretion in NRK‐49F cells. The interactive effects of EGF, RA, and Dex on the production of TGF‐β1 and TGF‐β2, which were studied on NRK‐49F cells, demonstrate that EGF blocks the induction of TGF‐β2 mRNA and peptide by RA, while Dex inhibits the induction of TGF‐β1 mRNA and peptide by EGF. These results demonstrate that RA, EGF and Dex are each unique, differential, and interactive regulators of the expression of TGF‐βs1 and 2.