Expression of transforming growth factor-betas (TGF-bs) 1, 2 and 3 was examined in cultured human lung cancer cells. Specific cDNA probes and antibodies for TGF-bs 1, 2 and 3 were used to study expression of these different TGF-b isoforms in both non-small cell lung cancer (NSCLC) cells and small cell lung cancer (SCLC) cells. Expression of TGF-b1 mRNA was detected in both cell types using Northern blot hybridization, with expression being generally higher in NSCLC cells. Furthermore, expression of TGF-b2 and 3 mRNAs was also detected in both NSCLC and SCLC cells, but at levels that were significantly lower than that of TGF-b1 mRNA. Expression of TGF-b type II and type III receptor mRNAs was also detected in both NSCLC and SCLC cells, with expression of both mRNAs being higher in NSCLC cells than in SCLC cells. The level of expression of TGF-b type II receptor mRNA was significantly higher than that of TGF-b type III receptor mRNA. Immunohistochemical staining of cultured NSCLC cells with TGF-b antibodies showed immunoreactive TGF-bs 1, 2 and 3 proteins. Our results demonstrate coordinate expression of the TGF-b isoforms and their receptors in human NSCLC cells, with expression of TGF-b1 mRNA and protein more prominent than that of TGF-bs 2 and 3 and TGF-b type II receptor mRNA more prominent than that of TGF-b type III receptor. 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-a, RAR-b and RAR-g mRNAs was approximately equal in most NSCLC cells, while expression of RAR-a mRNA was equal to or greater than that of RAR-b mRNA and significantly higher than that of RAR-g mRNA in most SCLC cells. Expression of RXR-a, RXR-b and RXR-g mRNAs was approximately equal in both NSCLC and SCLC cells, with the relative abundance being RXR-g greater than RXR-b greater than RXR-a. Retinoic acid increased expression of TGF-b1 and TGF-b2 mRNAs, but not TGF-bA, in some NSCLC cells; retinoic acid had no effect on TGF-b mRNAs in SCLC cells. Immunohistochemical staining of NSCLC cells with antibodies specific for each TFG-b isoform showed increased staining for TGF-b1 and TGF-b2 in NSCLC cells after treatment with retinoic acid. Also 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-b isoforms in lung cancer cells by treatment with chemopreventive agents such as retinoic acid. Increased TGF-b production may be used to slow the proliferation of lung cancer cells.
