Downregulation of miR-221/222 enhances sensitivity of breast cancer cells to tamoxifen through upregulation of TIMP3

Abstract

Aberrantly expressed microRNAs (miRNAs) are involved in breast tumorigenesis. It is still unclear if and how miRNAs-221/222 are implicated in breast cancer and the resistance to estrogen receptor modulator tamoxifen. We investigated the roles and mechanisms of miR-221/222 in breast cancer cells, particularly in modulating response to tamoxifen therapy. MCF-7 and MDA-MB-231 breast cancer cells were transfected with antisense oligonucleotides AS-miR-221 and AS-miR-222 and their expression of miR-221 and miR-222 was assessed. The correlation of miR-221/222 with tissue inhibitor of metalloproteinase-3 (TIMP3) expression was investigated by fluorescence quantitative PCR and western blotting analysis. The therapeutic sensitivity of these cells, transfected and untransfected, to tamoxifen was determined. Transfection of AS-miR-221 and AS-miR-222 dramatically inhibited expression of miR-221 and miR-222, respectively, in both MCF-7 and MDA-MB-231 cells (P<0.05-0.01). Downregulation of miR-221/222 significantly increased the expression of TIMP3 compared with controls (P<0.05-0.01). The viability of estrogen receptor (ER)-positive MCF-7 cells transfected with AS-miR-221 or/and AS-miR-222 was significantly reduced by tamoxifen (P<0.05-0.01). We have demonstrated for the first time that suppression of miRNA-221/222 increases the sensitivity of ER-positive MCF-7 breast cancer cells to tamoxifen. This effect is mediated through upregulation of TIMP3. These findings suggest that upregulation of TIMP3 via inhibition of miRNA-221/222 could be a promising therapeutic approach for breast cancer.

Mesenchymal Stem Cell–Derived Exosomes Stimulate Cycling Quiescence and Early Breast Cancer Dormancy in Bone Marrow

“…The function of the transferred anti-miRNA was assessed in drug sensitivity analyses (29,33). Primed MSCs were transfected with Cy5-anti-miR-222 or Cy5-control anti-miR.…”

Recent trends in microRNA research into breast cancer with particular focus on the associations between microRNAs and intrinsic subtypes

“…42 However, the miR-221/222 cluster is associated with tamoxifen resistance in breast cancer cells. 43,44 Miller et al 45 reported that miR-221/222 expressions were upregulated in endocrine therapy-resistant luminaltype breast cancer cells. MiR-221/222 are negative regulators of p27 kip1 , a cell cycle inhibitor and tumor suppressor, [46][47][48][49][50] and upregulated expressions of these miRNAs and significant reductions in p27 kip1 levels have been reported in tamoxifen-resistant breast cancer cells; therefore, miR-221/222 might regulate tamoxifen sensitivity via the direct targeting of p27 kip1 .…”

MicroRNAs regulate the epithelial–mesenchymal transition and influence breast cancer invasion and metastasis

“…76 Transfection of ASOs AS-miR-221 and AS-miR-222 into breast cancer cells dramatically inhibited the expression of miR-221 and miR-222, respectively, and the suppression of miRNA-221/222 increased the sensitivity of ER-positive MCF-7 breast cancer cells to tamoxifen. 77 A recent study reported a tumor treatment strategy that simultaneously disturbs the function of multiple oncogenic miRNAs. The strategy uses a viral vector to mediate the expression of an artificially designed interfering long non-coding RNA (lncRNA).…”