Abstract 2221: Transforming Growth Factor-beta (TGF-β) directly regulates breast cancer stem cell dynamics in vitro and in vivo
Authors: Tang Binwu , Raviv Asaf , Esposito Dominic , Daniel Catherine , Flanders Kathleen C. , Yang Yu-an , Wakefield Lalage M. 
Published: August 2015

Many tumors consist of a hierarchy of cells with different proliferative and developmental potentials. A small number of cancer stem cells (CSCs) give rise to a larger population of highly proliferative, committed progenitor cells, which may then undergo limited differentiation. Importantly CSCs are uniquely capable of initiating and sustaining tumorigenesis, and they have been implicated in driving disease recurrence after cancer therapy. In order to be able to assess stem cell behavior in real-time at a single cell rather than a population level, we have developed and validated a novel lentiviral-based reporter system for direct visualization, quantitation and isolation of cells with CSC properties. The construct consists of a tandemly-repeated composite SOX2-OCT4 response element (“SORE6”) driving expression of a destabilized green fluorescent protein reporter. Using the human MCF10CA1h breast cancer cell line, we have shown that SORE6-GFP+ cells within the cell population are relatively undifferentiated and enriched for stem cell markers. These cells can self-renew and regenerate SORE6-GFP- cells, show enhanced asymmetric division, and are enriched for tumorigenesis and resistance to chemotherapeutics in vivo. We and others have previously suggested that TGF-β can regulate the CSC population with stimulatory or inhibitory effects depending on model. In the MCF10Ca1h breast cancer model, which retains tumor suppressor responses to TGF-β, we hypothesized that endogenous TGF-β suppresses tumorigenesis by direct effects on the CSCs. Using our reporter, we show TGF-β reduces the size of the CSC population and the frequency of asymmetric self-renewing divisions in the MCF10Ca1h model. Although TGF-β had relatively little effect on invasion and migration of the bulk MCF10Ca1h population, it clearly inhibited migration and invasion of the CSCs, suggesting that biological responses to TGF-β can vary depending on the position of the cell in the differentiation hierarchy. Combining our stem cell reporter with a TGF-β pathway reporter, we show that CSCs have higher endogenous activation of the TGF-β pathway than do the bulk cells, and by time-lapse video microscopy we find that CSCs with active TGF-β signaling are relatively quiescent. Furthermore, neutralization of TGF-β in vivo, leads to an increased representation of CSCs in the MCF10Ca1h tumors. Thus our preliminary results suggest that in breast cancer models where TGF-β acts as a tumor suppressor, TGF-β signaling is preferentially activated in the CSC compartment and may keep a subpopulation of CSCs in a proliferatively quiescent and stationary state.

Citation Format: Binwu Tang, Asaf Raviv, Dominic Esposito, Catherine Daniel, Kathleen C. Flanders, Yu-an Yang, Lalage M. Wakefield. Transforming Growth Factor-beta (TGF-β) directly regulates breast cancer stem cell dynamics in vitro and in vivo. [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 2221. doi:10.1158/1538-7445.AM2015-2221