We have pursued the hypothesis, that transforming growth factors alpha and beta are in the Yin and Yang of the autocrine proliferation control of normal tracheo-bronchial epithelium and that disturbances of either one or both of these growth factor systems may be important determinants of the abnormal behavior of transformed cells. Our studies showed that normal rat tracheal epithelial (RTE) cells are dependent on exogenous epidermal growth factor (EGF) for growth ; in contrast transformed RTE cells were EGF-independent. Preneoplastic and neoplastic RTE cell lines were found to secrete TGFA. We examined the function of TGF-alpha/EGF receptors and the growth requirements for TGF-alpha in these cells. The level of immunoprecipitated TGF-alpha/EGF receptor protein in immortalized RTE cells was similar to or less than levels in primary RTE cells. Scatchard analysis of TGF-alpha/EGF receptors in the neoplastic EGV5T cell line revealed the presence of high and low affinity binding sites. A tyrphostin TGF-alpha/EGF receptor tyrosine kinase inhibitor decreased in a dose-dependent manner the proliferation as well as EGF-induced autophosphorylation of the TGF-alpha/EGF receptor. Proliferation of transformed RTE cells was also inhibited when TGF-alpha antisera was added to the media. The data indicate autocrine proliferation control in transformed cells by TGF-alpha. Transformed cells were found to secrete far less TGF-beta-like activity than normal cells and released no detectable amounts of activated TGF-beta. The levels of TGF-beta-1 mRNA expression were similar in normal and transformed cells suggesting a change in post-transcriptional regulation of TGF-beta-1 expression in transformed cells. We also found that many of the transformed cell lines were unresponsive to the growth inhibitory effects of TGF-beta-1. Scatchard and receptor crosslinking analysis indicated that loss of TGF-beta-1 responsiveness of transformed cells was probably not due to changes in receptor number, affinity, or to changes in expression of the three TGF- beta binding protein subtypes. These findings are consistent with the hypothesis that the abnormal growth behavior of transformed RTE cells is in part due to disturbances of the TGF-beta system.
