Cancer stem cells (CSCs) are unique subpopulation of tumor cells that possess self-renewal and differentiation capacity, and can give rise to the entire heterogeneous population of the tumor tissue. The self-renewal and differentiation properties of CSCs are regulated and maintained by the CSC niche. However, the mechanism of this maintenance, especially the contribution of differentiated cancer cells, remains to be fully elucidated. It has been shown that vascular endothelial cells can activate the Notch signaling pathway in glioblastoma (GMB) stem-like cells, and that was required for self-renewal of GBM stem-like cells. Given the fact that GBM stem-like cells differentiate into vascular endothelial cells, it raises the possibility that these differentiated cells that arise from CSCs might generate a CSC niche. In this study, we addressed this hypothesis using a model of CSCs, miPS-LLCcm, derived from mouse induced pluripotent stem cells (miPSCs) we have established recently.
We found in vitro cultured miPS-LLCcm cells were autonomously balanced with stem-like cells and differentiated cells. The analysis of VEGFR2 and VE-cadherin expression, and in vitro tube formation assay indicated the differentiation capacity of miPS-LLCcm into vascular endothelial cells. In the presence of the conditioned medium from bulk population of miPS-LLCcm cells, self-renewal capacity of CSC population of miPS-LLCcm, which was evaluated by spheroid formation in suspension culture, was enhanced, partly in Notch depending manner. In addition, we found that the ligands for Notch activation were secreted from the differentiated tumor cells including vascular endothelial cells. In addition, the secreted factor(s) from differentiated cells appeared to regulate the differentiation lineage of CSCs, since miPS-LLCcm could not differentiate into vascular endothelial lineages after cultivation of only stem cell population.
Our results indicate that the differentiated progenies of CSCs containing vascular endothelium play important roles for regulating the CSC's properties. Therefore, miPS-LLCcm cells create their own in vitro niche to maintain themselves in the hierarchy of differentiating CSCs.
Citation Format: Akifumi Mizutani, Shuichi Matsuda, Ting Yan, Marta Prieto-Vila, Ling Chen, Ayano Satoh, Tomonari Kasai, Junko Masuda, Takyuki Kudoh, Hiroshi Murakami, Li Fu, David S. Salomon, Masaharu Seno. Cancer stem cells maintain a hierarchy of differentiation by creating their niche. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3026. doi:10.1158/1538-7445.AM2014-3026