Tumor Invasion and Metastasis Initiated by mir-106b in Breast Cancer by Targeting BRMS1 and RB.

Abstract

Abstract Background: MicroRNAs (miRNAs) are noncoding RNAs that have recently been demonstrated to have an important role in tumor metastasis. Mir-106b family is reported to promote the proliferation of cancer as an oncogene. However, whether mir-106b has roles in breast cancer metastasis and EMT remains unknown. Therefore, functional characterization of mir-106b in breast cancer cells would potentially facilitate our understanding of the development of breast cancer.Methods: Mir-106b expression and location in primary breast cancer samples from patients with metastasis were compared to the samples without metastasis by in situ hybridization analysis. Differentially expressed miRNAs in MDA-MB-231 breast cancer cell line were quantified by qRT-PCR and Northern Blot followed by scratch assays, migration assay, Boyen chamber assay and invasion assay to determine the significance of mir-106b in metastasis. Lentivirus-mediated miRNA transduction was used to determine the significance of mir-106b function. Target scan and luciferase reporter assay were used to identify the targets of mir-106b. Mir-106b targets' gene expression (BRMS1 and RB) was determined by qRT-PCR and western blot. The expression of E-cadherent by immunofluorescence and Western Blot were used to determine the regulation of mir-106b on the effect of TGF- β induced EMT.Results: Mir-106b was dramatically increased in primary breast cancer samples from patients with metastasis compared to the samples without metastasis, which is negatively correlated with patients' prognosis. MDA-MB-231 cells transfected with lentivirus-mir106b had a higher ability of invasion and migration. Conversely, transfecting mir-106b ASO into MDA-MB-231 cells decreased the invasion and migration ability in vitro. Silencing BRMS1 (breast cancer metastasis suppressor 1) and RB (retinoblastoma), which were proved to be new targets of mir-106b by luciferase assay, showed the similar results with mir-106b over-expressing. Furthermore, the expression of mir-106b in MCF10A cells was increased during TGF-βinduced EMT, while TGF-β-induced EMT was inhibited in MCF10A cells transfected with mir-106b ASO. Furthermore, we found that mir106b-expressing MDA-MB-231 cells gave rise to more tumors and metastasized more frequently in vivo.Conclusion: mir-106b can promote breast cancer invasion and metastasis by targeting BRMS1 and RB. Mir-106b mediates TGF-β-induced EMT, which is an early process of tumor metastasis. Therefore, mir-106b may be an effective maker to predict prognosis of breast cancer patients, and a new targets to treat breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6157.