[Retracted] Slug contributes to cancer progression by direct regulation of ERα signaling pathway.

Following the publication of the above paper, it was drawn to the Editor's attention by concerned readers that ß­actin bands shown in Figs. 1, 2 and 4 were strikingly similar, where the experimental conditions reported in Fig. 4 differed from those in Figs. 1 and 2; moreover, the Slug protein bands featured in Figs. 4a and 5a were remarkably similar in spite of the different experimental conditions that were reported in the respective figure legends, and the shape of the vimentin protein bands in Fig. 5e bore a strong similarity to the Slug protein bands that were featured in Fig. 2c, in spite of the bands being of slightly different sizes and arranged in a different orientation.  Although the possibility of publishing a corrigendum was considered, software analysis of the highlighted bands performed independently by the Editorial Office demonstrated that the bands in question were likely to have been matching bands. Therefore, given the number of potential concerns that were identified with the assembly of various of the figures in this paper, the Editor of International Journal of Oncology has decided not to proceed with a corrigendum, and has determined that the paper should instead be retracted from the Journal on account of an overall lack of confidence in the originally presented data. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a satisfactory reply. The Editor apologizes to the readership for any inconvenience caused. [International Journal of Oncology 46: 1461­1472, 2015; DOI: 10.3892/ijo.2015.2878].

Slug contributes to cancer progression by direct regulation of ERα signaling pathway.

Hormone therapy targeting estrogen receptor α (ERα) is the most effective treatment for breast cancer. However, this treatment eventually fails as the tumor develops resistance. Although reduced expression of ER-α is a known contributing factor to endocrine resistance, the mechanism of ER-α downregulation in endocrine resistance is still not fully understood. The present study shows that Slug has an inverse relationship with ERα in breast and prostate cancer patient samples. Also the inhibition of Slug blocks mammary stem cell activity in primary mammary epithelial cells. We hypothesize that Slug may be a key transcription factor in the regulation of ERα expression. To understand the Slug-ERα signaling pathway, we employed resistant cell line MCF-TAMR (ERα relatively negative) derived from its parental MCF-7 (ERα positive) cell line and assessed changes in cell phenotype, activity and response to therapy. Conversely, we performed knockdown of Slug in the high-Slug expressing cell line MDA-MB-231 and assessed reversal of the mesenchymal phenotype. Microarray analysis showed that Slug is overexpressed in high grade breast and prostate cancer tissues. Additionally, Slug overexpression leads to drug resistance. Furthermore, we demonstrated that Slug binds directly to ERα promoter E-boxes and represses ERα expression. This resulted in decrease in epithelial-to-mesenchymal transition in cancer cells. These findings demonstrate that Slug, by regulation of ERα expression, contributes to tumor progression and could serve as an important target for cancer therapy.