Effect of phorbol esters and hormones on rat hepatoma cells producing alpha-fetoprotein

Effect of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on rat AH66 hepatoma cells was studied with a reference to that of insulin and the epidermal growth factor (EGF). In a short term cell incubation, TPA and EGF caused an approximately 2-fold increase in the production of alpha-fetoprotein (AFP) and other acid-precipitable materials, while the same concentration of insulin brought a 3-fold increase. In a long term culture using a low serum medium, TPA as well as insulin and EGF caused remarkable proliferation of AH66 cells, but the increase in cell number was not accompanied by a proportional increase in the levels of AFP of the culture media. These biological effects of TPA, insulin and EGF appeared to resemble each other, and subsequent hormone binding studies showed that TPA inhibited 125I-EGF binding to its membrane receptors without affecting 125I-insulin binding. Scatchard analysis of TPA effect on EGF binding indicated that TPA altered the affinity of the membrane receptors for EGF without changing the total number of available receptors per cell. From these data, it is suggested that some of the biological effects of TPA on AH66 cells may result from alterations in the functions of cell membrane.