Abstract 1814: Characterization of the MSI2 gene on 17q22-24.2 and its role in Breast Cancer.
Authors: Abdalla Moustafa , Nair Ranju , Kanwar Nisha , Holzapfel Nicholas , Moreno Juan C. , Done Susan J. 
Published: August 2014

Introduction: We have previously found genomic gain on 17q22-24.2 to be a predictor of invasion when detected in duct carcinoma in situ (DCIS), and of nodal metastasis when detected in invasive duct carcinoma (IDC). Within this gene-rich amplicon we have identified a gene, Musashi homolog 2 (MSI2), which appears to play an important role in breast cancer progression. MSI2 is known to have a functional role in neural stem cell maintenance and the regulation of hematopoietic stem cells. More recently, this gene was shown to facilitate progression from the leukemic blast phase to the crisis phase.

Methodology: The mRNA expression profile for MSI2 was determined by qRT-PCR in 9 breast cancer cell lines (MDA-MB-157, MDA-MB-231, MDA-MB-468, BT549, CAMA1, Hs578T, MCF7 and SKBR3) and a non-malignant mammary epithelial cell line (MCF10A). Western blots were used to confirm protein expression. MCF7 mammospheres and MSI2 overexpression clones were assessed for breast stem cell markers. Immunofluorescence was conducted at embryonic stages E10.5 to E15.5 to determine the role of MSI2 in murine mammary bud formation. MDA-MB-231 and MCF7 cells expressing MSI2-GFP and GFP clones were plated on transwells to examine cell migration and invasiveness. Proliferation was analyzed by the MTS assay. To understand the expression of MSI2 in patient tissue, tissue microarrays (TMAs) containing 232 breast cancers were analyzed by immunohistochemistry.

Results: MSI2 was expressed in all breast cell lines tested. Immunohistochemical analyses of MSI2 in normal adult human breast tissue revealed expression in the basal luminal epithelial cells of the terminal duct lobular unit, with little expression in the stroma. In murine mammary line formation, E10.5 to E12.5 showed expression of MSI2 in both the mammary ductal epithelium and the mesenchyme. MSI2 expression diminished in mesenchyme and was restricted to the ductal epithelium by E14.5. MDA-MB-231 and MCF7 cells expressing MSI2-GFP demonstrated a 50% increase in cell migration and 30% more invasion compared to the GFP control. Correspondingly, knockdown clones showed the reverse effect. Increased MSI2 was coupled with an increase in the stem cell markers: CD24, CD44, Aldh1α1, CD133 and ABCG2 receptor. When the study was extended to patient TMAs, high MSI2 expression correlated with higher tumor grade.

Conclusion: These experiments provide strong evidence that MSI2 plays an important role in normal breast development and breast cancer. MSI2 promotes migration and invasion and also appears to increase stem cell related properties which may explain the relationship to higher tumor grade. MSI2 is likely one of the drivers of the 17q22-24.2 amplicon in breast cancer and a better understanding of its role in breast cancer may lead the way to novel therapeutic strategies.

Citation Format: Moustafa Abdalla, Ranju Nair, Nisha Kanwar, Nicholas Holzapfel, Juan C. Moreno, Susan J. Done. Characterization of the MSI2 gene on 17q22-24.2 and its role in Breast Cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1814. doi:10.1158/1538-7445.AM2013-1814