Recent investigations by our laboratory have demonstrated that NMI expression is down-regulated in patient breast tumors, especially those displaying invasive/metastatic features. In breast cancer and melanoma cell lines, restored expression of NMI suppresses tumor growth. Furthermore, NMI negatively impacts TGFβ-driven epithelial-mesenchymal-transition (EMT) and alsometastatic invasion of breast cancer. Thus the mechanisms that regulate NMI expression are of potential interest to understand the etiology of breast tumor progression, invasion, metastasis and to identify potentially novel therapeutic targets.

MicroRNAs are critical regulators of gene expression. MicroRNA target prediction searches revealed that the NMI transcript could be targeted by the miR-29 family, a group of miRNAs with multiple roles in diverse cancer types. We hypothesized that miR-29 will negatively regulate NMI expression. Luciferase reporter assays using pMIR-REPORTTM confirmed the projected interaction of miR-29 in the seed region of the 3′ UTR of NMI. Manipulation of miR-29 levels in breast cancer cells by overexpression or silencing showed its inverse relationship with NMI expression. Invasive mesenchymal-like breast cancer cell lines showed elevated endogenous levels of miR-29 relative to tumorigenic/non-metastatic (epithelial like) breast cancer cell lines. Moreover, transient overexpression of miR-29 enhanced breast cancer cell invasion as measured by modified Boyden chamber assay and silencing miR-29 using anti-miRs decreased invasion. Investigations on the impact of miR-29 modulation on EMT revealed that increasing miR-29 levels in epithelial-like breast cancer cell lines caused 3D morphological changes indicative of invasive mesenchymal-like growth, while decreasing miR-29 levels from mesenchymal-like cell types using anti-miRs reversed the phenotype and the growth pattern resembled acinar structures. The significance of our observation was realized when we compared RNA isolated from patient derived breast cancer tumors and compared with RNA from matched adjacent normal breast specimens. Analysis using the McNemar's test showed a strong, inverse relationship between the expression of NMI and the miR-29. We contend that aberrant miR-29 expression may account for reduced NMI in some invasive breast cancers.

Citation Format: Hawley C. Pruitt, Jack W. Rostas III, Brandon J. Metge, Daniel J. Devine, Sarah K. Bailey, Lalita A. Shevde, Rajeev Samant. MicroRNA regulator of NMI: implications for breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4010. doi:10.1158/1538-7445.AM2014-4010