title: MicroRNA-221/222 confers tamoxifen resistance in breast cancer by targeting p27Kip1.
abstract: We explored the role of microRNAs (miRNAs) in acquiring resistance to tamoxifen, a drug successfully used to treat women with estrogen receptor-positive breast cancer. miRNA microarray analysis of MCF-7 cell lines that are either sensitive (parental) or resistant (4-hydroxytamoxifen-resistant (OHT(R))) to tamoxifen showed significant (>1.8-fold) up-regulation of eight miRNAs and marked down-regulation (>50%) of seven miRNAs in OHT(R) cells compared with parental MCF-7 cells. Increased expression of three of the most promising up-regulated (miR-221, miR-222, and miR-181) and down-regulated (miR-21, miR-342, and miR-489) miRNAs was validated by real-time reverse transcription-PCR. The expression of miR-221 and miR-222 was also significantly (2-fold) elevated in HER2/neu-positive primary human breast cancer tissues that are known to be resistant to endocrine therapy compared with HER2/neu-negative tissue samples. Ectopic expression of miR-221/222 rendered the parental MCF-7 cells resistant to tamoxifen. The protein level of the cell cycle inhibitor p27(Kip1), a known target of miR-221/222, was reduced by 50% in OHT(R) cells and by 28-50% in miR-221/222-overexpressing MCF-7 cells. Furthermore, overexpression of p27(Kip1) in the resistant OHT(R) cells caused enhanced cell death when exposed to tamoxifen. This is the first study demonstrating a relationship between miR-221/222 expression and HER2/neu overexpression in primary breast tumors that are generally resistant to tamoxifen therapy. This finding also provides the rationale for the application of altered expression of specific miRNAs as a predictive tamoxifen-resistant breast cancer marker.
authors: Department of Molecular and Cellular Biochemistry, College of Medicine, Ohio State University, Columbus, Ohio 43210, USA.
authors: Tyler E
authors: TE
authors: Miller
authors: Kalpana
authors: K
authors: Ghoshal
authors: Bhuvaneswari
authors: B
authors: Ramaswamy
authors: Satavisha
authors: S
authors: Roy
authors: Jharna
authors: J
authors: Datta
authors: Charles L
authors: CL
authors: Shapiro
authors: Samson
authors: S
authors: Jacob
authors: Sarmila
authors: S
authors: Majumder
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D035683:MicroRNAs / Q000378:metabolism*; D008954:Models, Biological; D013629:Tamoxifen / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D050760:Cyclin-Dependent Kinase Inhibitor p27; D035683:MicroRNAs; D013629:Tamoxifen; C525709:MIR221, human; C525710:MIR222, human