Effect of the novel oncomir MiR-301 on tumor proliferation and invasion in human breast cancer.

Abstract

1076 Background: It is increasingly apparent that micro-RNAs contribute to biological progression in almost all human malignancies. Although several studies have reported the association of dysregulated miRs in human breast cancer, the specific role of miRs in mediating tumor invasion remain to be clarified. We have previously conducted global miR profiling on 74 lymph node negative invasive ductal breast cancer samples, and observed that miR-301 over-expression was strongly associated with either nodal or distant relapse. Hence, the objective of this study is to better understand the function of miR-301 in breast cancer biology, along with identification of its mRNA targets. Methods: MiR-301 expression was evaluated in four breast cancer cell lines. The biological effects of miR-301 knock down were examined in vitro and in vivo using cell viability, clonogenic, cell migration and tumor formation assays. Downstream target genes were also evaluated. Results: MiR-301 was over-expressed in all breast cancer cell lines. AntagomiR caused significant reduction in miR-301 expression, associated with reduced viability, decreased clonogenicity, cell migration and invasion, as well as suppressed tumor growth, demonstrating a strong oncogenic role for miR-301. A tri-pronged approach combining prediction algorithms, experimentally mRNA profiling, along with primary cancer Affymetrix mRNA data identified FOXF2, BBC3, and PTEN as potential targets for miR-301, which could explain the observed phenotypes of reduction. Luciferase reporter assays confirmed that these genes are direct targets of miR-301. In addition, miR- 301 is located within the intron of SKA2, a spindle-kinetochore complex, and these two genes were corroborated to be co-expressed in cancer cell lines as well as primary cancer tissues. Conclusions: We have identified miR-301 as a novel oncomir in human breast cancer, which promotes growth, proliferation, invasion, and metastases, mediated at least by FOXF2, BBC3, and PTEN. Furthermore, the co-expression of miR-301 with SKA2 likely further co-operatively increases genetic instability with failed spindle check-points, thereby accounting for the more aggressive breast cancer clinical behavior. No significant financial relationships to disclose.