Abstract 3385: Sox2 is necessary for glioblastoma cell plasticity

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background and Objective: The HMG-box transcription factor Sox2 is essential for the maintenance of stem cells from early development to adult tissues. Sox2 activates and represses the expression of different gene sets in various tissues during development through HMG-box domain-mediated DNA binding. Sox2 can reprogram differentiated cells into pluripotent cells in concert with other factors, and is overexpressed in various cancers, including glioblastoma (GBM). Employing a GBM patient-derived cancer stem cell (CSC) and isogenic serum differentiated cell (SDC) model we show that Sox2 regulates distinct gene sets in glioblastoma stem and differentiated cells. Experimental Approaches: Differentially expressed genes (DEGs) between Sox2-positive and Sox2-negative cells in SDCs and isogenic CSCs were compiled from genome-wide transcriptome data (Illumina HT12v4.0). Metacore (Thomson Reuters) and IPA (Ingenuity Systems) software applications were used to further analyze the datasets. Gene Expression data obtained from the TCGA Data Portal (https://tcga-data.nci.nih.gov/tcga/, July 2, 2012) for 517 GBM cases was used to study genes correlated with Sox2 expression. Results: Sox2 knockdown in GBM SDCs abolished the dedifferentiation and acquisition of CSC phenotype in vitro. Sox2 knockdown affected the expression of 736 genes in SDCs, 453 downregulated and 283 upregulated, and 799 genes in CSCs, 341 downregulated and 458 upregulated. The expression of genes associated with stem cells and malignancy were commonly downregulated in Sox2-deficient CSCs and SDCs. Upon Sox2 knockdown, proneural (PN) and classical (CL) signature genes are downregulated in SDC and modestly in CSC, while mesenchymal (MES) signature genes are upregulated in both groups. Genes previously shown to be associated with pluripontency and CSCs were specifically affected in the CSC state, while ESC self-renewal genes and cytokine signaling were downregulated and the Wnt pathway was activated in differentiated Sox2-deficient cells. Overlap with Sox2 binding to cis-regulatory sequences was observed for 25.1% and 15.1% of DEGs in SDC and CSC, respectively. Significantly, 28.6% of genes positively correlating with Sox2 expression in the TCGA dataset overlapped with the DEGs in HF2303: 3 genes in both CSC and SDC states, 1 in CSCs, and the remaining 12 in the SDC state suggesting that genes correlated with Sox2 expression in the tumors are better represented in SDCs than in CSCs. Conclusions: Our results indicate that Sox2 regulates the expression of key genes and pathways involved in GBM malignancy, in both cancer stem-like and differentiated cells, and maintains plasticity leading to bidirectional conversion between the two states. These findings have significant clinical implications. Citation Format: Artem D. Berezovsky, Laila M. Poisson, Xin Hong, Tom Mikkelsen, Ana C. deCarvalho. Sox2 is necessary for glioblastoma cell plasticity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3385. doi:10.1158/1538-7445.AM2014-3385