FIGURE 7.

Effect of ErbB2 expression on down-regulation of the EGF receptor. Cells constitutively expressing ∼300,000 EGF receptors/cell were stably transfected with wild type ErbB2 (panel A), K732M-ErbB2 (panel B), or Y253D-ErbB2 (panel C) expressed from a tet-inducible promoter. For assay, cells were grown in the absence (open circles) or presence (filled circles) of doxycycline to induce the expression of ErbB2. Cells were treated with 10 nm EGF for the indicated times then washed to remove surface bound EGF. Subsequently, binding of ¹²⁵I-EGF to the cultures was measured as described under “Materials and Methods.”