Cancer stem cells (CSCs) generate and sustain tumors due to tumor initiating potential, resulting in recurrence or metastasis. We showed previously that knockout of the cell cycle inhibitor, p21CIP1, in the PyMT mammary tumor model, inhibits metastasis; however the exact mechanism remained unknown. Here, we show a pivotal role for p21 in potentiating a cancer stem cell-like phenotype. p21 knockout in PyMT mammary tumor cells suppressed tumorsphere formation, ALDH1 expression, and tumor initiating potential, that were in turn rescued by p21 overexpression. Consistent with these effects, p21 loss caused mesenchymal to epithelial transition that was accompanied by downregulation of Slug, Sox9, basal keratins and upregulation of luminal keratins and Claudin-3. Furthermore, p21 knockout suppressed Wnt/β-catenin signaling which was due to TCF1 downregulation. In turn, TCF1 knockdown in PyMT cells, attenuated Wnt signaling and tumorsphere formation. Interestingly, p21 rescue in p21 knockout cells, caused dramatic upregulation of Cyclin D1, consistent with known inhibition of Cyclin D1 nuclear export by p21. These data suggest that p21 promotes a cancer stem like phenotype via Wnt-TCF1 signaling along with direct upregulation of Cyclin D1 by p21.

Citation Format: Rachel B. Hazan. p21CIP1 promotes mammary cancer initiating cells via activation of Wnt/TCF1/CyclinD1 signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4666.