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. Expression of TGF-beta1, 2 and 3 ligands and TGF-beta type I, II and III receptors was examined in cultured human lung cancer cells. Specific cDNA probes and antibodies for TGF-betas 1, 2 and 3 were used to study expression of these different TGF-beta isoforms in both non-small cell lung cancer cells (NSCLC) and small cell lung cancer cells (SCLC). Expression of TGF-beta1 mRNA was detected in both cell types using Northern blot hybridization, with expression being significantly higher in NSCLC cells. Furthermore, expression of TGF-beta2 and TGF-beta3 mRNAs was also detected in NSCLC and SCLC cells. The relative levels of expression of the TGF-beta mRNAs was TGF-beta1 > TGF-beta2 > TGF-beta3. Expression of TGF-beta type I, II and III receptor mRNAs was also detected in both NSCLC and SCLC cells, with expression of these mRNAs being higher in NSCLC cells than in SCLC cells. The relative level of expression of the TGF-beta receptor mRNAs was type I > type II > type III. TGF-beta1 protein was detected in the conditioned medium of NSCLC and SCLC cells, with the level being higher in several NSCLC cells than in SCLC cells. Addition of TGF-beta resulted in an increase in the level of TGF-beta1 mRNA and a corresponding increase in the amount of TGF-beta1 protein in some NSCLC cells. Our results demonstrate co-expression of the TGF-beta isoforms and their receptors in human NSCLC cells, with expression of TGF-beta1 mRNA and protein more prominent than that of TGF-betas 2 and 3 and TGF-beta type I receptor mRNA more prominent than that of TGF-beta type II and III receptors. Expression of retinoic acid receptor (RAR) and retinoid X receptor (RXR) mRNAs was also detected in both NSCLC and SCLC cells. The level of expression of RAR-alpha, RAR-beta and RAR-~ mRNAs was approximately equal in most NSCLC cells, while expression of RAR-alpha mRNA was equal to or greater than that of RAR-beta mRNA and significantly higher than that of RAR-~ mRNA in most SCLC cells. Expression of RXR-alpha, RXR-beta and RXR-~ mRNAs was approximately equal in both NSCLC and SCLC cells. Retinoic acid increased expression of TGF-beta2 mRNA and decreased expression of TGF- beta3 mRNA in some NSCLC cells; retinoic acid had no effect on TGF-beta mRNAs in SCLC cells. Retinoic acid significantly inhibited colony formation of several NSCLC cells. 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.
