Protein bands bound to antibodies were visualized by staining with ECL Plus (Amersham Bioscience, Piscataway, NJ) and data was recorded with a Molecular Dynamics Storm PhosphorImager (Amersham Bioscience, Piscataway, NJ)

Protein bands bound to antibodies were visualized by staining with ECL Plus (Amersham Bioscience, Piscataway, NJ) and data was recorded with a Molecular Dynamics Storm PhosphorImager (Amersham Bioscience, Piscataway, NJ). 2.5. enhanced OHT-induced apoptosis. OHT induced a delayed and prolonged phosphorylation of ERK1/2 that persisted for 80 hours. Addition of PD98059 as late as 24 hours after OHT largely blocked OHT-ER mediated apoptosis. The antagonist, ICI 182,780, blocked both the long-term OHT-mediated phosphorylation of ERK1/2 Lanolin and OHT-induced apoptosis. Our data suggests that the p38 and JNK pathways, which often play a central role in apoptosis, have only a limited role in OHT-ER-mediated cell death. Although quick activation of the ERK1/2 pathway is usually often associated with cell growth, persistent activation of the ERK1/2 pathway is essential for OHT-ER induced cell death. and shrinks some tumors [6; 7; 8; 9; 10]. Long term passaging of breast cancer cells results in resistance to tamoxifen [11]. In cells expressing very high levels of ER, estrogens and other ER ligands induce cell death [12; 13]. Proposed mechanisms for tamoxifen-induced cell death include transcriptional regulation of Bcl-2 family proteins, activation of MAPK and other kinases through nongenomic pathways, and generation of an increase in intracellular Ca++ concentration [7; 14; 15]. In many of these experiments, however, very high, M concentrations of Tam or OHT were used and some of the studies were carried out in cells that lack ER. To analyze these processes in cells that differ only in the presence or absence of ER, we analyzed Tam and OHT-induced cell death in ER-negative HeLa cells stably transfected to express hER (HeLaER6: [16; 17]). We found that OHT induces cell death via two different pathways. When ER unfavorable HeLa cells are managed in medium made up of 10C20 M Tam, OHT, E2 or raloxifene, the cells pass away within 24 hours by a reactive oxygen-based pathway that triggers classical caspase-dependent apoptosis. Low, nM concentrations of OHT and sub-micromolar concentrations of Tam do not kill or damage ER-negative HeLa cells. When ER positive HeLaER6 cells are managed in medium made up of 1C100 nM OHT, they undergo apoptosis over several days. The antagonist: ICI 182,780, the SERM, raloxifene and E2 safeguard the cells against OHT-ER mediated cell death [17]. The mechanism(s) by which OHT-ER induces cell death is largely unknown. Liganded ER can exert its activities through genomic mechanisms and through non-genomic mechanisms based on quick activation of transmission transduction pathways [18; 19; 20]. Rapid activation of the ERK1/2 pathway by E2-ER plays an important role in estrogen activation of cell growth [19; 21; 22; 23]. To analyze the Bcl-X role of transmission transduction pathways in OHT-ER induced cell death, we examined the ability of OHT-ER to activate several signaling pathways. We then evaluated the effect of OHT-ER induced cell death by selectively inhibiting each signaling pathway. Although activation of the JNK and p38 pathways often plays a role in apoptosis, and OHT-ER activated both the JNK and p38 pathways, inhibiting activation of p38 and JNK experienced only a moderate ability to interfere with OHT-ER induced cell death. We found that OHT-ER induces a delayed and prolonged activation of the ERK1/2 signaling pathway. Surprisingly, inhibiting activation of Lanolin the ERK1/2 pathway blocked OHT-ER induced apoptosis. These studies describe a novel long-term OHT-mediated activation of the ERK1/2 pathway and demonstrate that this prolonged activation of the ERK1/2 pathway is critical for OHT-ER induced apoptosis. 2. Experimental Procedures 2.1. Cell lines and cell culture HeLaER6 cells (13, 14) were produced in Phenol Red-free DMEM (Sigma, St. Louis, MO) supplemented with 10% charcoal-dextran-treated fetal bovine serum and 150 g/ml G418 (Invitrogen, Carlsbad, CA). Unless specifically mentioned, HeLaER6 cells were plated in Falcon 12-well plates (Becton Dickinson, Franklin Lakes, NJ) at 100,000 cells/well and produced for 24 h before treatment. 2.2. Assays for cell death and apoptosis OHT was dissolved in Lanolin ethanol and added to cultured cells at 1:1,000 v/v. The same volume of ethanol was added to control cells. Unless otherwise indicated, cells were harvested 72 h after addition of OHT. The adherent cells were harvested by incubating with PBS made up of 1 mM EDTA for 5 min at room temperature. The harvested, formerly adherent, cells were combined with the lifeless cells and late-stage apoptotic cells that were.