Figure 1.

Overexpressed ErbB2 receptor is activated by heregulin β1 in the cancer cell models used. (A) Total cell lysates were isolated from parental cells (C), ErbB2 overexpressing cells (ErbB-2), and a metastatic cell variant selected in vivo from a lung metastatic nodule induced by MDA231-ErbB2 cells implanted into the mammary fat pad (MDA231-M). Proteins were resolved by SDS–PAGE and immunoblotted with anti-ErbB2 antibody. As an internal control GAPDH was used. (B) Cells were serum-starved for 24 h and then stimulated with 10 ng ml⁻¹ HRG β1 for 10 min. ErbB2 was immunoprecipitated from total cell lysates, resolved by SDS–PAGE, and blots were probed using a phosphotyrosine antibody and reprobed with antibody against ErbB2, as described in Materials and Methods.