FIGURE 9.

Competition binding dose-response curves in CHO cells expressing EGF receptors alone or in the presence of ErbB2. CHO cells were plated in the absence (dashed line) or presence (solid line) of 1 μg/ml doxycycline to induce the expression of ErbB2. Cells were cooled to 4 °C, and ¹²⁵I-EGF was added to each well along with increasing concentrations of EGF (A), TGFα (B), BTC (C), or AREG (D). Plates were processed as described under “Experimental Procedures.” Points represent the mean ± S.D. of triplicate determinations.