Figure 2.

Effects of heregulin (HRG) on butylparaben (BP) stimulation of c-Myc protein levels in breast cancer cell lines. (A) BT-474 and (B) MCF-7 breast cancer cells were treated with the indicated concentrations of BP without or with HRG (20 ng/mL) for 2 hr. (C) SKBR3 cells were treated with 10 μM BP in the absence and presence of HRG (20 ng/mL) for 2 hr. The treated cells were then lysed, and the cellular lysates were prepared for Western blots using antibodies against c-Myc as described in “Materials and Methods.” Cells simultaneously treated with 17β-estradiol (E₂) (0.01 μM) were also included for comparison. After exposure to an X-ray film, the membranes were washed and reprobed with an antibody against β-actin as a loading control. This figure is representative of two independent experiments with similar results.