A, MDA-MB-231 cells were stably transfected with pIRES-ERα. Proteins isolated from MCF-7 cells, empty vector MDA-MB-231 transfectants, and ERα transfected MDA-MB-231 single colonies were subjected to immunoblot with an ERα antibody. Two G418-resistant clones (ER19 and ER28) were shown to express high levels of ERα. B, vector control and ERα transfected MDA-MB-231 cells were co-transfected with ERE-tk-luciferase and CMV-β-galactosidase and cultured in medium with 5% charcoal dextran-stripped fetal bovine serum with or without 10 nM E2. The bars represent the means ± S.D. of at least three independent experiments. C, vector control and ERα transfected ER19 cells were treated with oligoamines for 72 h, and ERα expression was determined by Western blot.