Figure 3

The IGF-1/MEK signaling axis blocks the cytotoxic action of 4-OHT and/or MIF-treatments of ER⁺ breast cancer cells. (a) Graphic representation of Western blot data showing pMAPK1/2 levels in cells treated with hormones in the absence and presence of IGF-1. The pMAPK1/2 level in E2-treated cells were arbitrarily set to a value of 100%; total MAPK levels served as the loading control. (b) Effective and selective blockade of MAPK1/2 phosphorylation by the MEK1 inhibitor PD 98059. Total MAPK1/2 and AKT levels served as loading controls. (c, d) PD 98059 blocked the proliferative effects of IGF-1 and restored the ability of 4-OHT and/or MIF therapy to induce cell detachment and cleavage of PARP (apoptosis) in the MCF-7 cell populations treated with 4-OHT and/or MIF. fold diff., levels of cleaved PARP after correction for differences in protein loading; β-actin levels served as loading controls. (a-d) Cells were treated for the indicated time periods with hormones, as indicated in the absence or presence of IGF-1 at 20 ng/ml and/or PD 98059 at 25 μ;g/ml and harvested for immunoblotting or cell counts, as described in Materials and Methods. Values are expressed as mean ± SD (n = 3). Treatment effects on total cell number were determined to be significant when compared with (a) E2; (b) E2 + IGF-1; (c) E2 + 4-OHT + IGF-1; (d) E2 + MIF + IGF-1; (e) E2 + IGF-1 + PD 98059. *P < 0.001.