RNA-binding protein Musashi1 (MSI1) shows an increased expression level in several cancers and has been introduced as a prognostic marker in some malignancies. It is expected that if any miRNA is encoded by this gene, it might have a role in cancer development or could be considered as a prognostic biomarker. Accordingly, in this study, we aimed to find novel miRNA(s) inside the intronic regions of the MSI1 gene. Here, we report two novel miRNAs within intron 4 of MSI1 gene, named MSM2 and MSM3, which were selected among several miRNA precursors predicted by bioinformatic studies. For experimental analysis, corresponding precursor miRNAs were transfected into HEK293T cells and exogenous expression of the mature miRNAs were detected. Two mature miRNAs, MSM3-3p and MSM3-5p were generated by MSM3 precursor and one, MSM2-5p was derived from MSM2. Besides, endogenous expression of MSM2-5p and MSM3-3p was detected in MCF-7 and SH-SY5Y cell lines. Expression of both mature miRNAs was also detected in clinical samples of breast cancer. Additionally, the interaction between the MSM3-3p and 3'UTR region of PDE11A was confirmed by dual luciferase assay. Overall, our data demonstrated that MSI1 gene encodes two novel miRNAs in breast cancer cells.
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