Increased expression of MUSASHI1 in epithelial breast cancer cells is due to down regulation of miR-125b.

BACKGROUND: Musashi1 (MSI1) is an oncogenic protein with a crucial role in the proliferation and characteristics of the epithelial cells in breast cancer. The change in expression of MSI1 has a role in solid tumor progression. There are different factors that regulate MSI1 expression in various cancer tissues including microRNAs which are considered as one of the most important of these factors. The aim of our study is identification of the molecular cause of maximal expression of MSI1 in epithelial breast cancer cell lines. RESULTS: Among predicted microRNAs, miR-125b, miR-637 and miR-802 were able to significantly reduce the luciferase activity. In addition, the relative expression of these three miRNAs were measured in the cancerous cell lines that results showed a significant reduction in expression of all microRNAs. On the other hand, only the overexpression of miR-125b caused a change in the expression pattern of MSI1 in breast epithelial cancer cell lines. Accordingly, our results demonstrated that the exogenous expression of miR-125b decreased not only the MSI1 protein but also expression of epithelial markers in breast cancer cells. CONCLUSIONS: The results of luciferase reporter assay showed that MSI1 is a direct target for miR-125b in epithelial breast cancer cells. Moreover, higher amount of MSI1 in those cell lines seems due to the reduced amount of miR-125b, which is responsible for epithelial features of those kinds of cancer cells. Therefore, the modulation of miR-125b may be a potential approach to help to combat against epithelial breast tumors.