Induction of EGFR tyrosine phosphorylation by rDIII. (A) Incubation of MDA-MB-231 cells with 185 nM rDIII for 5 min (lane 4, top) stimulated phosphorylation of EGFR. There is no EGFR stimulation for the 2-min rDIII sample (lane 3), or the 5-min no ligand control (lane 1). To exclude nonspecific effects due to cross-linking, cells were exposed to BS 3 in the absence of ligand (lane 2). To ensure that equal amounts of EGFR protein were loaded, blots were stripped and reprobed with EGFR pAb (bottom). (B) EGFR phosphorylation by 185 nM rDIII (lane 1, top) and 1.7 nM EGF (lane 2) for 5 min in the absence of BS 3 . For control, ligand was omitted (lane 3), and the loading controls are shown in the bottom panel.