Regulation of epidermal growth factor binding in a human keratinocyte cell line by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) decreased the binding of epidermal growth factor (EGF) by the human keratinocyte cell line SCC-12F. This response was concentration dependent (half-maximal effective concentration, EC50 = 1.8 nM) and stereospecific. Scatchard analysis of EGF binding indicated that treatment with TCDD resulted in a loss of high-affinity (Kd = 0.28 nM) binding sites. This loss was accompanied by a concomitant inhibition of EGF-stimulated DNA synthesis. The kinetics for the decrease of EGF binding by TCDD and benzo[a]pyrene (BP) were compared. Inhibition of EGF binding by BP was maximal by 24 hr, with 90% recovery of EGF binding apparent by 48 hr. In contrast, TCDD treatment for 72 hr was required to produce maximal inhibition, and no recovery was evident up to 10 day after removal of TCDD from the growth medium. The data indicate that modulation of EGF binding by TCDD was mediated by the Ah receptor. Subsequent cellular responses, for example, inhibition of EGF-stimulated DNA synthesis, may be important in the expression of altered differentiation patterns observed in human epidermal keratinocytes exposed to TCDD.