Figure 3.

Lysates from different cell lines (1 mg/ml) were diluted as indicated, and receptors were captured by the anti-rat p185^neu Ab A11 or the anti-human p185^her2/neu Ab 1E1. The 7.16.4ScFv and pY99 (a monoclonal antiphosphotyrosine) were used to probe the rat p185^neu or the phosphorylated proteins, followed by the detection with the ds-oligo-conjugated anti-polyHis tag Ab or the anti-IgG2b subtype Ab, respectively. Although the p185^her2/neu is constitutively phosphorylated in T6–17 cells, it is transactivated in A431 cells only after EGF stimulation. EGF stimulates heteromer formation of EGFR and p185^her2/neu, which forms an active kinase complex.