Abstract 347: The role of the epithelial-mesenchymal transition in the maintenance of stemness in neural and glioma stem cells

Abstract

Abstract Despite advances in treatment, Glioblastoma multiforme (GBM) continues to carry a horrible prognosis with an average overall survival of only 14 months [Stupp et al, 2005]. GBMs are heterogeneous tumors that contain a subpopulation of stem-cell like cells called glioblastoma stem cells (GSCs). GSCs appear to be chemotherapy- and radiation-resistant and are thought to be responsible for GBM progression [Kang et al, 2007; Bao et al, 2006]. More effective GBM therapies must target GSCs, underscoring the importance of understanding GSC biology. Our study examines the epithelial-mesenchymal transition (EMT) and its converse, the mesenchymal-epithelial transition (MET), in the context of GSCs and neural stem cells (NSCs). We hypothesize that the zinc-finger enhancer binding transcription factor (ZEB)/miR-200 feedback loop is relevant in the context of GSCs and is modulated by TGF-β and BMP. We have found that ZEB1 and miR-200 define divergent glioma cell populations: qRT-PCR shows differential expression of ZEB1 and miR-200 in mature human astrocytes, human fetal NSC, and human GSCs (GliNS1). In GSCs, BMP antagonism (noggin) or TGF-β stimulation results in increased ZEB1 expression. Conversely, BMP4 stimulation increases miR-200b/c, while noggin or TGF-β treatment decrease miR-200b/c expression. BrdU proliferation studies show increased proliferation with TGF-β stimulation and decreased proliferation with BMP treatment in three GSC lines. TGF-β signaling also confers an invasive phenotype in GSCs while BMP4 treatment decreases invasion, suggesting a role for TGF-β and BMP parallel to that seen in EMT and MET. Western blot analysis reveals that treatment of GSCs with TGF-β induces phosphorylation of Stat3, which has been shown to be a driver of EMT [Carro MS, 2010]. Interestingly, BMP and TGF-β treatment does not change Sox2 protein expression, suggesting that the GliNS1 GSCs retain their stem cell identity. However, Bmi1 increases with BMP stimulation and decreases with TGF-β treatment, while ID1 increases with BMP treatment, suggesting that the stem-ness in GSCs is modulated by these cytokines. In conclusion, BMP and TGF-β control the ZEB1/miR-200 feedback loop in GSCs and affect cell proliferation and invasive capability. We are continuing studies to determine the relevance of TGF-β and BMP signaling to patients with GBM. 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 347. doi:1538-7445.AM2012-347