A SPEN Complex Serves as a Scaffold to Coordinate Multiple Epigenetic Regulatory Mechanisms in Breast Cancer Stem Cells

There is substantial evidence that many cancers, including human breast cancer are hierarchically organized and driven by a cellular population that displays stem cell properties. These stem-like cells (CSC’s) mediate tumor metastasis and by virtue of their relative therapeutic resistance mediate tumor recurrence. Both normal and malignant stem cells are regulated through epigenetic mechanisms which involve DNA and histone modifications as well as noncoding RNAs. However, the mechanisms responsible for coordinating these multiple levels of epigenetic regulation in CSC’s remain elusive. Here, we identify a SPEN-Xist complex in breast CSC’s cells which, by virtue of inclusion of multiple epigenetic regulatory proteins, provides a scaffold for coordinating multiple levels of epigenetic regulation in these cells. Genetic knockdown of SPEN or XIST significantly reduces the CSC population as accessed by ALDH expression, sphere formation or tumor initiating capacity in xerograph models. Gene expression analysts suggests that the SPEN- XIST complex modulates multiple CSC regulatory pathways via the coordination of epigenetic modulatory proteins. This work has fundamental implications for understanding the epigenetic regulation of cancer stem cells as well as for developing strategies to target these cells Two control samples compared to two SHARP knockdown samples

大量确凿证据表明，包括人类乳腺癌在内的多种癌症均呈层级化组织结构，其发生发展由一类具备干细胞特性的细胞群体驱动。这类干细胞样细胞（癌症干细胞，Cancer Stem Cell，CSC）可介导肿瘤转移，且因其相对的治疗抵抗性而促成肿瘤复发。正常干细胞与恶性干细胞均通过表观遗传机制调控，此类机制涵盖DNA与组蛋白修饰以及非编码RNA调控。然而，在CSC中协调多维度表观遗传调控的具体分子机制仍不明晰。本研究在乳腺癌CSC中鉴定出一种SPEN-XIST复合物，该复合物因包含多种表观遗传调控蛋白，可作为分子支架协调这类细胞内的多维度表观遗传调控过程。通过基因敲低SPEN或XIST的表达，可显著降低CSC群体的丰度，该效应可通过乙醛脱氢酶（Aldehyde Dehydrogenase，ALDH）表达检测、成球实验以及异种移植瘤模型中的肿瘤起始能力进行评估。基因表达分析结果显示，SPEN-XIST复合物可通过协同表观遗传调控蛋白，调控多条CSC相关的核心调控通路。本研究对于解析癌症干细胞的表观遗传调控机制，以及开发靶向这类细胞的治疗策略均具有重要的基础研究价值。本研究设置了两份对照样本与两份SHARP基因敲低样本进行对比。