Abstract 4768: A SHARP /Xist complex regulates breast cancer stem cells

Abstract

Abstract Many cancers including breast cancer display hieratical organization and are driven by a cellular sub-population that displays stem cell properties. These cancer stem cells (CSC’s) mediate metastasis and contribute to treatment resistance highlighting the importance of elucidating CSC regulatory pathways. Nuclear proteins and lncRNAs involved in the maintenance of chromatin structure have been shown to play roles in CSC regulation. Among them the polycomb proteins bmi-1 and EZH2 are involved in epigenetic regulation of CSC’s in breast and other cancers. SHARP/SPEN, an RNA binding protein, has been previously been found to bind the lncRNA Xist which, by recruiting the PRC2 polycomb complex mediates transcriptional repression of the X chromosome. We utilized breast cancer cell lines and xenograft models to examine the role of the SHARP/Xist complex in the regulation of breast CSC’s. In a series of breast cancer cell lines including MCF7 (luminal )and SUM 159 (basal/claudin low) cells, SHARP mRNA and protein as well as the lncRNA Xist were more highly expressed in cells expressing aldehyde dehydrogenase as accessed by the Aldefluor assay than in ALDH -cells . Conditional knockdown of SHARP or Xist in SUM159 significantly decreased the ALDH+ CSC population without affecting cell growth in vitro. Furthermore, SHARP or Xist knockdown significantly reduced tumor initiating capacity and growth of SUM 159 cells in NOD/SCID mice. To determine the mechanism of breast CSC regulation by the SHARP complex we compared mRNA expression patterns of control and SHARP knockdown SUM 159 cells using RNAseq. There was significant overlap between the genes regulated by SHARP with genes regulated by the PCR1 and PRC2 polycomb complexes in addition to many histone genes. These studies suggest that the SHARP/Xist complex my regulate breast CSC’s through epigenetic regulatory histone and polycomb genes. Since SHARP expression is elevated in a number of cancers including breast cancer this pathway may represent a novel therapeutic target. Citation Format: Yongyou Zhu, Li Shang, Justin Colacino, Michael Brooks, Ramdane Harouaka, Chang-Ching Lin, Ming Luo, Max S. Wicha. A SHARP /Xist complex regulates breast cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4768. doi:10.1158/1538-7445.AM2017-4768