Effect of MP1 knockdown on cellular signaling pathways. MCF-7 cells were transfected with 30 nM control or MP1 siRNA for 24 or 48 h. (A) Immunoblot of total and phosphor-ERK. The p-ERK/total ERK ratios are expressed relative to the ratio in control samples in a single experiment (24 h) or as the average ± SD of 3 independent experiments (48 h) (p > 0.1). (B) Immunoblot of total and phospho-Akt. Ratios of p-Akt/total Akt are expressed as described for panel A. The ratios for the 48 h time point are the average ± SD of 4 independent experiments (p < 0.05). (C) Immunoblot of ER at 48 h (n = 3 ± SD, p < 0.05). (D) Silencing of MP1 and ER. Cells were transfected with the indicated siRNAs, and extracts were prepared at 48 h. Immunoblots of PARP, ER, MP1, and actin are shown. (E) Quantification of luciferase activity in MCF-7 cells. Cells were co-transfected with ERE-tk 109-luc and pβgal-Basic, then with control or MP1 siRNA and treated with medium containing CSS ± E2. The level of luciferase activity in the presence of CSS was set at 1 in each experiment, and the activity in E2 treated samples was expressed relative to this value. The results shown represent the average ± SD of 4 independent experiments. (*p < 0.05).