Epidermal growth factor (EGF), 2,3,7,8‐tetrachlorodibenzo‐ p ‐dioxin (TCDD) and calcium (Ca 2+ ) induce loss of whole cell [ 125 I]‐EGF binding in a temporally distinct manner

The balance of epidermal proliferation versus differentiation is regulated by EGF Receptor (EGFR) signaling. Previous studies have shown that Ca 2+ ‐ and TCDD‐induced differentiation is associated with loss of EGF binding, but have only examined changes after 24 h of exposure. Varying culture conditions make inter‐study comparison difficult and no single model has addressed early changes in EGF binding nor compared Ca 2+ and TCDD effects on EGFR to that of EGF. Using whole cell [ 125 I]‐EGF binding, we compared the time‐dependent changes in EGF binding following treatment with 100 ng/mL EGF, 10 nM TCDD, 1.8 mM Ca 2+ , or TCDD+Ca 2+ . EGF decreased [ 125 I]‐EGF binding to 10% of basal levels by 4 h and Ca 2+ reduced binding to 60% of basal by 8h; both responses persisted for 5 d. TCDD effects were cyclic, causing decreased EGF binding between 1–12 h, 24–48 h, and >96 h and increased at 20 and 72 h. Interestingly, EGF binding rapidly declined in TCDD+Ca 2+ treated cells with significant decreases within 12 h and a sustained reduction through 5 d. Data show TCDD and Ca 2+ responses separate early and suggest that ligand‐mediated EGFR recycling occurs in TCDD response. [Funding: NIH Grant R01 ES017014]