Exosomal miR-221/222 enhances tamoxifen resistance in recipient ER-positive breast cancer cells

Abstract

Recent studies have demonstrated that specific miRNAs, such as miR-221/222, may be responsible for tamoxifen resistance in breast cancer. Secreted miRNAs enclosed in exosomes can act as intercellular bio-messengers. Our objective is to investigate the role of secreted miR-221/222 in tamoxifen resistance of ER-positive breast cancer cells. Transmission electron microscopy analysis and nanoparticle tracking analysis were performed to determine the exosomes difference between MCF-7(TamR) (tamoxifen resistant) and MCF-7(wt) (tamoxifen sensitive) cells. PKH67 fluorescent labeling assay was used to detect exosomes derived from MCF-7(TamR) cells entering into MCF-7(wt) cells. The potential function of exosomes on tamoxifen resistance transmission was analyzed with cell viability, apoptosis ,and colony formation. MiRNA microarrays and qPCR were used to detect and compare the miRNAs expression levels in the two cells and exosomes. As the targets of miR-221/222, p27 and ERα were analyzed with western blot and qPCR. Compared with the MCF-7(wt) exosomes, there were significant differences in the concentration and size distribution of MCF-7(TamR) exosomes. MCF-7(wt) cells had an increased amount of exosomal RNA and proteins compared with MCF-7(TamR) cells. MCF-7(TamR) exosomes could enter into MCF-7(wt) cells, and then released miR-221/222. And the elevated miR-221/222 effectively reduced the target genes expression of P27 and ERα, which enhanced tamoxifen resistance in recipient cells. Our results are the first to show that secreted miR-221/222 serves as signaling molecules to mediate communication of tamoxifen resistance.

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

“…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 . 51,52 Pichiorri et al 53 found that miR-221/222 expressions were modulated by nucleolin at the post-transcriptional level. Recently, it has been indicated that these miRNAs induce resistance to the selective ER downregulator, and this was caused by the activation of β-catenin and the repression of transforming growth factor-β-mediated growth inhibition.…”

The Role of Exosomes in Breast Cancer

“…In relation to tamoxifen, exosomes from tamoxifen-resistant MCF-7 cells were found to promote proliferation of MCF-7 wild-type cells. Functional assays (cell viability, apoptosis, and colony formation) assessed the involvement of miR-221 and miR-222 in the transfer of this tamoxifen resistance, which was found to be significantly blocked using anti-miR-221/anti-miR-222 (66 ).…”

miR-449a Suppresses Tamoxifen Resistance in Human Breast Cancer Cells by Targeting ADAM22

“…Reports in the recent years have indicated the involvement of miRNAs in tamoxifen resistance as well. Specifically, miR-221/222 enhanced tamoxifen resistance in recipient cells by reducing the target genes expression of P27 and Era [16]. MiR-148a and miR-152 were able to reduce tamoxifen resistance in ER-positive breast cancer via downregulating ALCAM [10].…”