[Epidermal growth factor receptor of human liver cancer cells and its modulation by phorbol ester]

Using radioligand binding assay, the presence of epidermal growth factor (EGF) receptors in cells of two human liver cancer cell lines, BEL-7402 and SMMC-7721, was demonstrated. The ligand binding data were analyzed by a computer program. The dissociation constants (KD) of the ligand-receptor binding complex at equilibrium for 7402 and 7721 cells were 1.2 nM and 0.8 nM respectively, and their number of EGF receptors per cell were 6.2 x 10(4) and 2.5 x 10(4) respectively. After the treatment of cells with phorbol 12-myristate 13-acetate (PMA), no change either in the affinity or in the number of EGF receptors was found in 7721 cells. However, in the case of 7402 cells, while the number of receptors, like 7721 cells, remained unchanged, the affinity of EGF receptors displayed a time dependent modulation after PMA treatment. It dropped within the first hour to a KD value of 3.0 nM and then gradually returned to the normal control value at 48 hours or even slightly higher than normal (0.95 nM) at 96 hours of treatment. The modulation or down-regulation of EGF receptors by PMA in 7402 cells was paralleled by the simultaneous inhibition of DNA synthesis in these cells as evidenced from their reduction of 3H-TdR uptake. It is not clear what is the basis for the differences found between 7402 cells and 7721 cells in their number of EGF receptors per cell and their responsiveness to PMA treatment. It might be related to their difference in autocrine secretion of alpha-transforming growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)