Abstract TMEM-039: THE ROLE OF SNAIL IN CELL DIFFERENTIATION STATUS: EPITHELIAL-MESENCHYMAL TRANSITION AND CANCER STEM CELLS

Abstract

Abstract PURPOSE: The epithelial-mesenchymal transition (EMT) is a process by which epithelial cells lose their cell polarity and cell-cell adhesion, and become mesenchymal cells with migratory and invasive properties. EMT is essential for numerous developmental processes such as gastrulation, and is involved in the initiation of metastasis for cancer progression. Cancer cells that undergo EMT are enabled to metastasize to form secondary tumors. One characteristic of advanced tumors is a low expression level of let-7, a miRNA known to be vital in both maintenances of cellular differentiation and tumor suppression. There is a gap in the literature concerning the mechanism of let-7 downregulation. Our purpose in this study is to present data that shows Snail, an EMT inducer, directly represses let-7, hence inducing cancer stem cells. EXPERIMENTAL PROCEDURES: Ovarian, pancreatic and breast cancer cell lines treated with TGFβ or EGF, inducers of EMT, were studied in our experiments. Expression of several markers at protein level was visualized with immunofluorescence and quantified with flow cytometry. Gene expression of mesenchymal, epithelial and pluripotency factors and miRNAs was detected by q-RT-PCR. Chromatin immunoprecipitation of Snail was performed in ovarian cancer lines. Let-7i promoter luciferase with and without Snail were co-transfected into OVSAHO and 293T cell lines and followed by luciferase assays for detection of bioluminescence. Snail was knocked down by lentiviral small hairpin RNA. Snail was overexpressed by estrogen receptor fusion protein. Orthotopic xenografts of patient-derived ovarian cancer cells were used to test the effect of Snail knockdown on tumor burden. RESULTS: In selected ovarian cancer lines, levels of Snail expression correlated directly with Nanog, and indirectly with let-7 expression. Snail bound promoters of let-7 in cell lines tested. Luciferase assays demonstrated direct repression of let-7 transcription by Snail. Metastatic burden was significantly reduced in cell line xenografts in which Snail was knocked down. CONCLUSIONS: Let-7 is confirmed to be negatively related to Snail. Our preliminary data also shows Snail directly represses let-7, therefore induces properties of stemness in cancer cells. Cell line and patient-derived data support the relationship between Snail expression, let-7 downregulation, and the induction of cancer stem cells. Snail knockdown appears to disrupt the cancer stem cell state and reduces disease progression. Citation Format: Hanmin Wang, Alyse Huisken-Hill, Evgeny Chirshev, Juli Unternaehrer-Hamm. THE ROLE OF SNAIL IN CELL DIFFERENTIATION STATUS: EPITHELIAL-MESENCHYMAL TRANSITION AND CANCER STEM CELLS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-039.