Abstract 2267: Defining roles of SIN3 isoforms in breast cancer metastasis

Metastasis continues to be the most difficult clinical challenge for breast cancer. These patients have unacceptable survival rates that have not changed in the past 20 years. Therefore, more effective therapeutic options are needed. The purpose of this study is to better understand molecular mechanisms of the SIN3 chromatin complexes that have been functionally associated with breast cancer progression to identify novel targeting strategies. Alteration of the composition of SIN3 complexes regulates the metastatic potential of breast cancer cells; and inhibition of SIN3 complexes induces differentiation and inhibits invasion of breast cancer cells. However, differences in the function of SIN3 isoforms (SIN3A and SIN3B) in breast cancer metastasis have not been characterized. To better define the role of SIN3 isoforms in breast cancer metastasis, we generated stable knockdown of SIN3 isoforms individually and in combination using 3 non-overlapping shRNA in two different metastatic breast cancer cell lines (MDA-MB-231 and -435). No significant change was noted in the proliferation rate of the transduced cells in vitro. Stable knockdown of SIN3B caused a significant decrease in invasion through Matrigel (28 ± 4 invaded cells/field compared to 50 ± 8 for control; p = 0.027) using a modified Boyden chamber that was corroborated by the decreased presence of stellate projections and a more epithelial phenotypic growth in 3D. Surprisingly, stable knockdown of SIN3A significantly increased invasion through Matrigel (98 ± 14 invaded cells/field; p = 0.008) and increased the presence of stellate projections in the 3D growth assay. Dual knockdown of SIN3A and SIN3B caused a significant decrease in invasiveness (19 ± 5 invaded cells/field; p = 0.003) and decreased presence of stellate projections similar to the phenotype noted with individual knockdown of SIN3B. These results were confirmed in vivo with an experimental metastasis assay (lateral tail vein injection in athymic nude mice) in which SIN3B knockdown significantly decreased lung metastasis (70% decrease compared to control; p = 0.009) and SIN3A knockdown increased metastasis (163% increase compared to control; p = 0.096). These results demonstrate key functional differences between SIN3 isoforms in regulating the process of metastasis. Our data suggests metastasis suppressive roles of SIN3A and metastasis promoting roles of SIN3B that will be important in discovering novel therapeutic strategies for metastatic breast cancer patients. Citation Format: Monica J. Lewis, Jianzhong Liu, Douglas R. Hurst. Defining roles of SIN3 isoforms in breast cancer metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2267. doi:10.1158/1538-7445.AM2015-2267