Abstract B049: An integrated approach to study miRNA involvement in anti-endocrine resistance in breast cancer

Resistance to endocrine-directed therapy represents a significant problem in the management of breast cancer, with a substantial number of estrogen receptor (ER)-positive patients experiencing relapse post treatment. Recently, microRNAs (miRNAs) have been implicated not only in the initiation and progression of cancer, but also in the development of resistance to therapy. To further investigate the role of miRNAs in anti-endocrine resistance in breast cancer, TaqMan Human MicroRNA Arrays (Applied Biosystems) were used to profile global expression of 667 miRNAs from a cell line series developed from MCF7 cells. This series consisted of parental ER-positive MCF7 cells, estrogen-independent anti-estrogen sensitive LCC1 cells and anti-estrogen resistant LCC9 cells obtained from the stepwise selection of LCC1 cells against increasing concentrations of fulvestrant. Using an in-house developed Java (v6.0) software application, transcriptomic data from these cell lines was integrated with miRNA expression data together with a miRNA-mRNA target site prediction database (compiled from TargetScan) to highlight networks of related genes/miRNAs. Gene Ontology (GO) categories were retrieved from DAVID. Hierarchical clustering produced two distinct clusters of genes which were negatively correlated with two groups of miRNAs differentially expressed >2 fold between the three cell lines. GO analysis revealed that Cluster 1 (2,146 genes negatively correlated with 37 miRNAs) was significantly associated with protein catabolism, chromatin modification and changes in Wnt, TGFβ and Insulin signaling. Cluster 2 (1,289 genes negatively correlated with 7 miRNAs) was associated with neuron differentiation and cell motion as well as changes to the ErbB and mTOR signaling pathways. Both clusters were associated significantly with changes in MAPK signaling. Four miRNAs (miR-20b, -28-5p, -28-3p and -31) were selected for further analysis owing to their increased expression in anti-endocrine resistant LCC9 cells relative to both MCF7 and LCC1 lines. Interestingly, ectopic expression of miR-31, but not miR-20b or -28, conferred resistance to tamoxifen treatment in both MCF7 and LCC1 cells (p