Abstract LB-207: ΔNp63α regulates quiescence, stem or progenitor activity of normal and malignant breast cells in a cell type-specific manner
Authors: Amin Md. Ruhul , Morita-Fujimura Yuiko , Ikawa Shuntaro 
Published: August 2015

[Introduction]

Despite apparent resection of tumors, breast cancer patients often suffer relapse years after due to remnant dormant tumor cells. Nevertheless, the molecular mechanism regulating dormancy of breast cancer cell is still unclear. On the other hand, relapsed tumor is generally believed to be derived from cancer stem cells retaining normal stem cell property, which can undergo quiescence. ΔNp63α, an N-terminally truncated isoform of p51/p63 protein was shown to play crucial roles in the maintenance of stem cells within mammary epithelium. Furthermore, both tumor suppressive and oncogenic roles of ΔNp63α have been reported in mammary carcinogenesis. Thus, we investigated the role of ΔNp63α in the regulation of normal and malignant breast cells.

[Method]

MCF10A, normal human mammary epithelial cells and breast cancer cell lines of different subtypes were introduced with doxycycline-inducible constructs of ΔNp63α. These cells were subjected to cell cycle analysis, western blot, BrdU-Ki-67 immunostaining. Stemness was determined by mammosphere formation assay combined with flow cytometry analysis of cell surface markers. Drug response was studied using MTT assay. Also luminal breast cancer cell line, MCF7, was subjected to combined mRNA-miRNA microarray analysis.

[Result]

The induction of ΔNp63α in MCF7 luminal breast cancer cell line led the cells to acquire phenotype typical to quiescent luminal progenitor-like cells. Furthermore, the BMP and Wnt signaling pathways emerged as regulators of ΔNp63α-induced quiescence by microarray analysis. Interestingly, these quiescent cells exhibited down-regulation of BRCA1-dependent DNA repair pathways making them more sensitive to DNA damaging drug, Doxorubicin, but more resistant to anti-mitotic drug, Paclitaxel. Conversely, induction of ΔNp63α in MCF10A normal basal cells resulted in increased cell proliferation and expansion of mammary stem-like cells. ΔNp63α expression also led to the increase of cells expressing breast cancer stem cell markers in both MCF7 and MCF10A cells. However, induction of ΔNp63α affected neither cell proliferation nor the increase of mammary stem- or luminal progenitor-like cells in more aggressive luminal (T47D) and basal (MDA-MB-231) breast cancer cells containing mutant p53. This result interestingly suggested a cell type-specific function of ΔNp63α. We also identified a microRNA network that might regulate quiescence in ΔNp63α-expressing breast cancer cells which will be presented at the meeting in detail.

[Conclusion]

Our results suggest that the role of ΔNp63α in regulating quiescence, stem or progenitor activity in normal and breast cancer cells is cell type-specific. Given the heterogeneity in the cellular origin of breast cancer subtypes, ΔNp63α-directed chemotherapeutic strategy might be instructive to target therapeutically resistant breast cancer cells.

Citation Format: Md. Ruhul Amin, Yuiko Morita-Fujimura, Shuntaro Ikawa. ΔNp63α regulates quiescence, stem or progenitor activity of normal and malignant breast cells in a cell type-specific manner. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-207. doi:10.1158/1538-7445.AM2015-LB-207