Abstract 2932: HIF-2 alpha is required for the tumor stemness switch of cancer cells during hypoxia/oxidative stress.
Authors: Das Bikul , Bayat-Mokhtari Reza , Tsuchida Rika , Yeger Herman 
Published: August 2014

Abstract
Tumor is characterized by intermittent hypoxia and re-oxygenation that generates oxidative stress. The effect of acute hypoxia microenvironmental stress on the cancer cell behavior is not clearly known. We hypothesized that hypoxia/oxidative stress could re-program cancer cells to a highly aggressive and metastatic state, we termed "tumor stemness state" (1). To test the hypothesis, we have characterized an in vitro model of acute hypoxia/re-oxygenation (2), and identified a highly tumorigenic and metastatic side-population cells (SP) phenotype from a diverse groups of established cancer cell lines including neuroblastoma, rhabdomyosarcoma and small cell lung cancer (3). These post-hypoxia SP cells (henceforth known as SPhox cells) exhibited high metastatic activity, localization in the hypoxic niche, and expressed several stemness associated genes including Nanog, Oct-4 and Bmi-1 (3). In this present study, we report further characterization of the SPhox cells including the expression of stemness associated transcription factors, expression of inflammatory cytokines and receptors, and the putative interaction of SPhox cells with bone marrow (BM) stem cell niche. First, SPhox cells expressed very high level of Nanog, Lin 28, MYC and HIF-2 proteins. Second, SPhox expressed inflammatory Toll-like receptors. Third, SPhox cells increased tolerance to ROS-inducing agents. Fourth, SPhox cells, when co-cultured with mouse BM Sca-1 cells, the CD271+ fraction, enriched in mesenchymal stem cells (4) was expanded. This expanded CD271+/Sca-1+ cells exhibited high expression of Nanog, Lin28, Oct-4, MYC and HIF-2alpha and ABCG2. Furthermore, the conditioned media obtained from the CD271+/Sca-1+/ABCG2+ cells maintained the stemness of the SPhox cells for two weeks. These results indicated the potential interaction between the SPhox and CD271/Sca-1+ cell. However, these characteristics of SPhox cells were transient, reversible, and lasted only for 3-4 weeks, indicating an underlying transient re-programming mechanism behind the SPhox phenotype. Because, recently we discovered a HIF-2alpha dependent transient reprogramming of human ES cells (5), here we investigated the potential role of HIF-2alpha in the re-programming of SP cells to SPhox cells. We found that the specific siRNA gene silencing of HIF-2alpha reduced the SP to SPhox reprogramming by sixteen-fold. Thus, here we have further characterize the tumor stemness state, including the potential role of HIF-2alpha. We suggest that this tumor stemness state could be the part of the cancer cell defense mechanism persist, and reactivate the aggressive/metastatic phenotype of cancer.
1. Das B. PhD thesis, University of Toronto, 2007
2. Das B et al. Cancer Research, 2005
3. Das B et al. Stem Cells, 2008
4. Das B et al. In Press
5. Das B et al. Stem Cells, 2012
Citation Format: Bikul Das, Reza Bayat-Mokhtari, Rika Tsuchida, Herman Yeger. HIF-2 alpha is required for the tumor stemness switch of cancer cells during hypoxia/oxidative stress. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2932. doi:10.1158/1538-7445.AM2013-2932
Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.