The antiestrogens 4-hydroxytamoxifen and fulvestrant are inhibitors of oncogenic factor Y-box binding protein-1 expression in breast cancer cells

Purpose: The cold-shock protein Y-box binding protein-1 (YB-1) is associated with more frequent relapse and higher aggressiveness in breast cancer and, notably, is a client protein of estrogen receptor α (ERα). Thus, the authors hypothesized that endocrine therapy using the antiestrogens 4-hydroxytamoxifen (4-OHT) and fulvestrant (FUL) may affect YB-1 expression. Materials and Methods: YB-1 localization in the breast cancer cell line MCF-7 was determined by fluorescence microscopy and GST-ERα pull-down assay. Modulation of YB-1 expression in the presence of 4-OHT and FUL was determined by quantitative RT-PCR as well as by Western blot analysis. Results: YB-1 is primary localized in the perinuclear cytoplasm of MCF-7 cells. YB-1 binds directly to recombinant GST-ERα fusion protein as shown by pull-down assay. Incubation experiments with 4-OHT and FUL demonstrated a strong time- and dose-dependent suppression of YB-1 expression by these antiestrogens. Inhibitory effects were assessed on the level of YB-1 mRNA as well as on the level of YB-1 protein. Conclusion: The data presented here suggest that 4-OHT and FUL therapy targets both proliferative ERα as well as pro-oncogenic YB-1. Thus, 4-OHT’s and FUL’s anticancer efficacy may play a more global role in breast cancer progression control than originally thought.

Breast cancer; YB-1; ERα; Antiestrogen; 4-hydroxytamoxifen; Fulvestrant.

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