Tumor promotion has been shown to play an important role in the etiology of human cancer. However, there are interspecies and intertissue variations in the response to tumor promoters. The effects of a potent tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA) on human epithelial cells vary depending on culture conditions. TPA induced terminal squamous differentiation and ornithine decarboxylase (ODC) activity on human esophageal epithelial cells cultured in medium 199 containing 10% fetal calf serum and in serum-free LHC media without epidermal growth factor (EGF). These effects were not found in LHC media containing EGF. Therefore, we characterized the binding of [3H]phorbol 12,13-dibutyrate (PDBU) to esophageal cells. Specific binding of [3H]PDBU to cells reached a maximum within 60 minutes and decreased at 120 minutes in medium 199 and LHC-O at 37 degrees C. Furthermore, preincubation of cells in media containing unlabeled PDBU caused reduction in binding (down regulation). By equilibrium analysis, dissociation constant was 24 nM and there were around 2.4 x 10 to the sixth power receptors per cell in medium 199. These characteristics were almost the same in different media. However, binding radioactivity did not decrease after preincubation with unlabeled PDBU in LHC media containing EGF. Results suggest that down regulation may be important for the development of TPA effects on esophageal cells. EGF inhibited down regulation of receptors in serum-free LHC media.
