A tamoxifen-resistant variant (R27) was selected by cloning wild type MCF-7 cells. R27 has the same growth rate as MCF-7 under optimal conditions. But tamoxifen has no effect on the growth rate (growth constant of R27 under control condition, 0.071 +/- 0.007 day-1; tamoxifen-treated cells, 0.073 +/- 0.011 day-1) and minimal effects on thymidine incorporation in R27, whereas tamoxifen has a stro...

Acquired or de novo resistance to the selective estrogen receptor modulators tamoxifen and fulvestrant (ICI) is a major barrier to successful treatment of breast cancer. Gene expression patterns in tamoxifen resistant (TamR-MCF-7) cells were compared to their parental cells (MCF-7L) to identify an aberrantly regulated metabolic pathway. TamR-MCF-7 cells are cross resistant to ICI and doxorubici...

Acquired resistance to tamoxifen (TAM) is a serious therapeutic problem in breast cancer patients. We have shown that Pin1, a peptidyl prolyl isomerase, is consistently overexpressed in TAM-resistant MCF-7 cells (TAMR-MCF-7 cells) and plays a key role in the enhanced angiogenic potential of TAMR-MCF-7 cells. In the present study, we focused on signaling pathways for Pin1 up-regulation in TAMR-M...

The aim of the present study was to establish a tamoxifen-resistant cell line (MCF-7/TAM-R) and to investigate the therapeutic effect of G47Δ on this cell line both in vitro and in vivo. In the present study, the MCF-7/TAM-R monoclonal subline was established after exposing MCF-7 cells to tamoxifen for 21 days. Then, it was compared with a wild-type MCF-7 subline (MCF-7W), which was not treated...

Methotrexate (MTX), as a chemotherapeutic drug, is widely used in the therapy of several cancer types. The efficiency of drug treatment is compromised by the appearance of multidrug resistance (MDR), and the underlying molecular mechanisms remain incompletely understood. We investigated the mechanism of MDR in the MTX-induced breast cancer MCF-7 cells (MCF-7/MTX) using proteomic analysis. MCF-7...

Protein kinase C (PKC) modulates growth, differentiation and apoptosis in a cell-specific fashion. Overexpression of PKC-alpha in MCF-7 breast cancer cells (MCF-7-PKC-alpha cell) leads to expression of a more transformed phenotype. The response of MCF-7 and MCF-7-PKC-alpha cells to phorbol esters (TPA) was examined. TPA-treated MCF-7 cells demonstrated a modest cytostatic response associated wi...

Eukaryotic translation initiation factor 2 alpha (eIF2α), which is a component of the eukaryotic translation initiation complex, functions in cell death and survival under various stress conditions. In this study, we investigated the roles of eIF2α phosphorylation in cell death using the breast cancer cell lines MCF-7 and MCF-7/ADR. MCF-7/ADR cells are MCF-7-driven cells that have acquired resi...

We previously showed that S-adenosylmethionine-mediated hypermethylation of the PTEN promoter was important for the growth of tamoxifen-resistant MCF-7 (TAMR-MCF-7) cancer cells. Here, we found that the basal expression level of methionine adenosyltransferase 2A (MAT2A), a critical enzyme for the biosynthesis of S-adenosylmethionine, was up-regulated in TAMR-MCF-7 cells compared with control MC...