Figure 1.

Transgene constructs and experimental time line. A, Two transgene constructs were generated by inserting three tandem GC-rich sequences with a TATA box or minimal TK promoter into the pGL3 basic luciferase vector. B, Transgene constructs are expressed and induced by E2 in breast cancer cells. ZR-75 cells were transfected with different reporter genes and increasing amount of ERα. (GC)₃-TATA-Luc (PXP2), which has been extensively used in in vitro studies, was included as a control. Cells were treated with DMSO or 10 nm E2 and luciferase activity determined as described in Materials and Methods. *, Significant (P < 0.05) induction. C, Experimental time line. The 21-d-old animals were injected with different compounds sc for 3 d consecutively and killed 24 h after the last injection. Tissues were separated and homogenized, and luciferase activity was measured as outlined in Materials and Methods.