Biological action of epidermal growth factor and its functional receptors in normal mammary epithelial cells

Abstract

Normal murine mammary epithelial cells possessed the capacity to bind epidermal growth factor (EGF) in a specific and saturable manner. Scatchard plot analysis showed a curvilinear pattern. Assuming that this is not due to negative cooperativity of EGF binding, the data suggest the presence of two classes of receptors with a high and a low affinity: Kd values = 1 x 10(-10)M and 3.6 x 10(-9)M, respectively. The number of high- and low-affinity receptors was estimated to be 800 per cell and 8,600 per cell, respectively. The occupancy of EGF receptors for a half-maximal stimulation of DNA synthesis or inhibition of casein synthesis was about 10% and 6% of total receptors, respectively. A potent tumor promoter, 12-O-tetradecanoylphorbol 13-acetate, acted synergistically with EGF in terms of stimulation of DNA synthesis but not in terms of inhibition of casein synthesis when the two agents were added at a suboptimal concentration. The presence of the tumor promoter increased the amount of EGF bound to mammary cells in culture and also decreased a loss in the amount of EGF in the culture medium. These results indicate that mammary epithelial cells possess functional receptors for EGF, which are modulated by the tumor promoter.