Figure 4.

Antiestrogen induction of EpRE-GstYa-GH reporter gene activity in 231 breast cancer cells is mediated by the ER. 231 cells were transfected with the p41–284GstYa-GH reporter construct along with an expression vector for the wild-type human ER, an expression vector for a DNA binding mutant of the ER (ER_DBDmut, missing amino acids 185–251), an expression vector for a mutant ER that lacks activation function-2 activity (ER_S554fs), or the empty expression vector missing the ER cDNA (pCMV). The cells were also transfected with a β-gal internal control reporter to correct for transfection efficiency. Cells were then treated for 48 hr with varying concentrations of TOT, E₂, or TBHQ as indicated. Media were collected for measurement of GH levels as described. The cells were then harvested for measurement of β-gal activity. Values are the means ± SE from three separate experiments.