ABSTRACT
Fulvestrant is a selective estrogen receptor downregulator (SERD) and highly effective antagonist to hormone-sensitive breast cancers following failure of previous tamoxifen or aromatase inhibitor therapies. However, after prolonged fulvestrant therapy, acquired resistance eventually occurs in the majority of breast cancer patients, due to poorly understood mechanisms. To examine a possible role(s) of aberrantly expressed microRNAs (miRNAs) in acquired fulvestrant resistance, we compared antiestrogen-resistant and -sensitive breast cancer cells, revealing the overexpression of miR-221/222 in the SERD-resistant cell lines. Fulvestrant treatment of estradiol (E2)- and fulvestrant-sensitive MCF7 cells resulted in increased expression of endogenous miR-221/222. Ectopic upregulation of miR-221/222 in estrogen receptor-α (ERα)-positive cell lines counteracted the effects of E2 depletion or fulvestrant-induced cell death, thus also conferring hormone-independent growth and fulvestrant resistance. In cells with acquired resistance to fulvestrant, miR-221/222 expression was essential for cell growth and cell cycle progression. To identify possible miR-221/222 targets, miR-221- or miR-222- induced alterations in global gene expression profiles and target gene expression at distinct time points were determined, revealing that miR-221/222 overexpression resulted in deregulation of multiple oncogenic signaling pathways previously associated with drug resistance. Activation of ß-catenin by miR-221/222 contributed to estrogen-independent growth and fulvestrant resistance, whereas TGF-ß-mediated growth inhibition was repressed by the two miRNAs. This first in-depth investigation into the role of miR-221/222 in acquired fulvestrant resistance, a clinically important problem, demonstrates that these two 'oncomirs' may represent promising therapeutic targets for treating hormone-independent, SERD-resistant breast cancer.
Subject(s)
Antineoplastic Agents/pharmacology , Breast Neoplasms/genetics , Drug Resistance, Neoplasm , Estradiol/analogs & derivatives , MicroRNAs/genetics , Breast Neoplasms/drug therapy , Breast Neoplasms/metabolism , Cell Line, Tumor , Cell Proliferation , Estradiol/pharmacology , Estrogen Antagonists/pharmacology , Estrogen Receptor alpha/metabolism , Female , Fulvestrant , Gene Expression Regulation, Neoplastic/drug effects , Humans , MicroRNAs/metabolism , Oligonucleotide Array Sequence Analysis , Selective Estrogen Receptor Modulators/pharmacology , Signal Transduction/drug effects , Signal Transduction/genetics , Transforming Growth Factor beta/metabolism , Up-Regulation , beta Catenin/geneticsABSTRACT
To define novel pathways that regulate susceptibility to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in non-small cell lung cancer (NSCLC), we have performed genome-wide expression profiling of microRNAs (miRs). We show that in TRAIL-resistant NSCLC cells, levels of different miRs are increased, and in particular, miR-221 and -222. We demonstrate that these miRs impair TRAIL-dependent apoptosis by inhibiting the expression of key functional proteins. Indeed, transfection with anti-miR-221 and -222 rendered CALU-1-resistant cells sensitive to TRAIL. Conversely, H460-sensitive cells treated with -221 and -222 pre-miRs become resistant to TRAIL. miR-221 and -222 target the 3'-UTR of Kit and p27(kip1) mRNAs, but interfere with TRAIL signaling mainly through p27(kip1). In conclusion, we show that high expression levels of miR-221 and -222 are needed to maintain the TRAIL-resistant phenotype, thus making these miRs as promising therapeutic targets or diagnostic tool for TRAIL resistance in NSCLC.
