Pivotal Role Of Loss MiR-1254 Expression In Breast Cancer

MicroRNAs (miRNAs) are a class of small non-coding RNAs (about 22 nucleotides) that function in RNA silencing and post-transcriptional regulation of gene expression. A miRNAs usually binds the 3’UTR of mRNA via base pairing with complementary sequence, leading to mRNA destabilization and/or translational inhibition. Hundreds of different mRNA may be regulated by a given miRNA. and multiple miRNAs may target a same mRNA, which give miRNA an important regulatory potential.High frequency of genomic copy number loss on chromosome 10q was identified in breast cancer, suggesting wherein tumor suppressor genes reside. To screen for the potentially deregulated miRNAs at the chromosomal 10q allele in breast cancer, we have screened for the changes in DNA copy numbers of the 45 presently known miRNAs in this location based on the miRbase 18.0 database by use of genomic real-time PCR in 20 archived breast cancer specimens and 4 specimens derived from benign breast diseases, miR-1254 was thus indentified as the most frequently lost miRNA (deleted in 85% cases).We next sought to determine the roles of miR-1254 in ER+breast cancer cells. Three lines of evidence suggested that miR-1254 is a tumour suppressive microRNA in breast cancer. First, miR-1254 suppressed cell growth and promoted apoptosis. Second, miR-1254 suppressed epithelial-mesenchymal transition (EMT) and stem cell-like characteristics in breast cancer cells. Third, xenograft studies showed that miR-1254 antagonism conferred breast cancer cells with enhanced tumour initiating capacity in vivo as well as increased local invasion in primary tumours and pulmonary metastases.EMT and stem-cell like traits have been implicated in the antiestrogen sensitivity of ER+ breast cancer cells. Consistently. miR-1254 antagonism in ER+ breast cancer cells resulted in reduced dependence on estrogen for growth and significant resistance to tamoxifen in vitro and in vivo. Predictably, miR-1254 restoration in TAM-R cells restored sensitivity to tamoxifen. miR-1254 restoration in TAM-R cells also substantially reduced their migratory capacity and the population of stem-cell like cells.To determine the mechanism by which miR-1254 exerts tumor suppressor suppressive properties, we initially employed miRanda and TargetScan to predict the potential mRNA targets of miR-1254. To further narrow down the search of possible downstream effectors of miR-1254. we employed a gene ontology analysis and identified NCOA1, NCOA3, EGFR, ERBB2 and SNAI1 as candidate genes, which are all well-established positive regulators of tamoxifen resistance and/or EMT. Further luciferase reporter assays, western blot as well as IHC staining determined all of the 5 genes are bona fide miR-1254 targets.Collectively, miR-1254 serves as a tumor suppressive miRNA by simultaneously controlling ER/EGFR/HER2 pathway in breast cancer, suggests a broad application prospect in anti-cancer and tamoxifen resistance.