Abstract LB-302: Coordinate upregulation of pluripotency factors in a hybrid epithelial/mesenchymal state in anoikis resistant suspended breast epithelial cells

Epithelial cells have an absolute requirement for surface adhesion for survival, and loss of adhesion activates apoptosis, a process named anoikis. During metastasis, cancerous epithelial cells are able to survive anoikis after they have spread from the primary site of the tumor. The mechanisms underlying anoikis survival are not well understood, but include cell lineage switching from epithelial to mesenchymal behavior, implying a role for stem cells. Several studies have shown that the mesenchymal population of tumorigenic breast cells contains stem cells, yet it appears that only a small yet unknown subpopulation of the mesenchymal cells is able to survive the strong selection pressure to survive anoikis in suspension and proliferate to form mammospheres. These studies have been complicated by the fact that heterogeneous cell lines consisting of epithelial and mesenchymal cells were analyzed, obscuring the role of small but possibly relevant subpopulations. Here, we were employing both single cell-derived homogeneous mesenchymal cell clones as well as novel microfluidics-based high throughput qRT-PCR analysis to unravel gene expression in epithelial and/or mesenchymal breast cancer cells during survival of anoikis. We show evidence that during culture of transformed mammary epithelial cells (HMLER) in suspension certain subpopulations disappear and then get repopulated by the surviving, proliferating and differentiating subpopulation in suspension. During this period in suspension critical for repopulation we find coordinate expression of both epithelial and mesenchymal markers, rapid upregulation of pluripotency factors (such as OCT4 and Nanog), as well as of several other genes that have previously been described to indicate poor prognosis for breast cancer survival. Those poor prognosis markers we also found elevated in replated and passaged anoikis-resistant HMLER cells as well as in HMLER-derived mesenchymal clones. By contrast expression of pluripotency factors was only restricted to the suspended state. In conclusion, here we show that in suspended breast epithelial cells there exists an epithelial/mesenchymal hybrid state likely to give rise to differentiated progenies, being able to adapt to the diverse challenging environments such as at secondary metastatic sites in cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-302. doi:1538-7445.AM2012-LB-302