The transforming growth factor-betas (TGF-betas) are a group of structurally related peptides that exert multiple effects in various cell types. For example, TGF-beta acting as a multifunctional growth regulatory molecule either stimulates or inhibits the growth of mesenchymal or epithelial cells, respectively. Retinoic acid, like TGF- beta, is a global regulator of gene expression and is known to exert striking effects on cell proliferation and differentiation, to inhibit the growth of some malignant cells and to inhibit the invasiveness of some metastatic cells. Expression of TGF-beta 1,2 and 3 ligands and TGF- beta type I, II and III receptors and retinoic acid receptors-alpha, -beta and -gamma was examined in cultured human lung cancer cells. Specific DNA probes for TGF-betas 1,2 and 3, TGF-beta type I, II and III receptors and retinoic acid receptors-alpha, beta and gamma were used to study expression of these different isoforms in both non-small cell lung cancer cells (NSCLC) and small cell lung cancer cells (SCLC). The relative levels of expression of the TGF-beta mRNAs was TGF- beta1 > TGF-beta2 > TGF-beta3, while that of the TGF-beta receptor mRNAs was type I > type II > type III in both cell types. The level of expression of RAR-alpha, RAR-beta and RAR-gamma mRNAs was approximately equal in most NSCLC cells, while expression of RAR- alpha mRNA was equal to or grater than that of RAR-beta mRNA and significantly higher than that of RAR-gamma mRNA in most SCLC cells. Addition of 13-cis-retinoic acid to SCLC cells cultured using serum-free, hormonally defined medium resulted in a 5-8-fold increase in the level of retinoic acid receptor-beta mRNAs and a 2-fold increase in the level of TGF-beta mRNA. Using an in vitro proliferation assay, addition of 13-cis-retinoic acid resulted in a growth inhibitory effect on the SCLC cells tested using serum-free conditions. These inhibitory effects decreased when the cells were cultured in medium containing serum. Preincubating serum with triglycerides restored the inhibitory effects of 13-cis-retinoic acid demonstrated in serum-free systems. The significance of the project is to increase the expression of one or more of the TGF-beta isoforms in lung cancer cells by treatment with chemopreventitive agents such as retinoic acid. Increased TGF-beta production may be used to slow the proliferation of lung cancer cells. The increase in expression of TGF-beta2 and retinoic acid receptor-beta mRNAs in these cells is influenced by the presence of serum and serum components.
