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.