Fig. 2.
HER3 associates with MTK1 in both T-47D and MCF-7 cells. Cells were stimulated as described in Fig. 1. Cell lysates were incubated with antibody directed against phosphotyrosine (pTyr), MTK1, or normal rabbit IgG. Proteins were resolved by SDS-PAGE and immunoblotted with anti-phosphotyrosine antibody (A, top panel) or antibody specific for phosphotyrosine 1289 of HER3 (B, top panel). The membranes were re-probed for MTK1 (bottom panels). MCF-7 cell lysates were prepared as described above and a fraction of the immunoprecipitate (15%) was immunoblotted using anti-phosphotyrosine antibody (Panel C, lanes a & b), while the remaining immunoprecipitation was silver stained (lanes c & d). HER3 peptides were identified in the HRG stimulated sample (arrows) by LC–MS/MS with 99.9% confidence (D).