Department of Breast Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Cancer Med. 2018 Feb;7(2):454-462. doi: 10.1002/cam4.1296. Epub 2018 Jan 22.
Understanding the mechanism by which cancer cells enhance stemness facilitates cancer therapies. Here, we revealed that a stem cell transcription factor, SALL4, functions to enhance stemness in basal-like breast cancer cells. We used shRNA-mediated knockdown and gene overexpression systems to analyze gene functions. To evaluate stemness, we performed a sphere formation assay. In SALL4 knockdown cells, the sphere formation ability was reduced, indicating that SALL4 enhances stemness. CD44 is a membrane protein and is known as a stemness factor in cancer. CD44 splicing variants are involved in cancer stemness. We discovered that SALL4 modulates CD44 alternative splicing through the upregulation of KHDRBS3, a splicing factor for CD44. We cloned the KHDRBS3-regulated CD44 splicing isoform (CD44v), which lacks exons 8 and 9. CD44v overexpression prevented a reduction in the sphere formation ability by KHDRBS3 knockdown, indicating that CD44v is positively involved in cancer stemness. In addition, CD44v enhanced anoikis resistance under the control of the SALL4 - KHDRBS3 network. Basal-like breast cancer is an aggressive subtype among breast cancers, and there is no effective therapy so far. Our findings provide molecular targets for basal-like breast cancer therapy. In the future, this study may contribute to the establishment of drugs targeting cancer stemness.
了解癌细胞增强干性的机制有助于癌症治疗。在这里，我们揭示了一种干细胞转录因子 SALL4，它在基底样乳腺癌细胞中增强干性。我们使用 shRNA 介导的敲低和基因过表达系统来分析基因功能。为了评估干性，我们进行了球体形成实验。在 SALL4 敲低细胞中，球体形成能力降低，表明 SALL4 增强了干性。CD44 是一种膜蛋白，被认为是癌症中的干性因子。CD44 的剪接变体参与了癌症干性。我们发现 SALL4 通过上调 CD44 的剪接因子 KHDRBS3 来调节 CD44 的选择性剪接。我们克隆了 KHDRBS3 调节的 CD44 剪接异构体（CD44v），它缺失了外显子 8 和 9。CD44v 的过表达阻止了 KHDRBS3 敲低导致的球体形成能力下降，表明 CD44v 正向参与癌症干性。此外，CD44v 在 SALL4-KHDRBS3 网络的控制下增强了无锚定抵抗。基底样乳腺癌是乳腺癌中侵袭性较强的亚型，目前尚无有效的治疗方法。我们的研究结果为基底样乳腺癌的治疗提供了分子靶点。在未来，这项研究可能有助于开发针对癌症干性的药物。
