Activation of a SOX2-dependent transcriptional regulatory circuit drives glioblastoma.

Overexpression of the transcription factor SRY-related box 2 (SOX2) is characteristic of Glioblastoma (GBM), yet its regulatory network in vivo is poorly understood. Using a human orthotopic tumor model of GBM for ChIP-Seq analysis, we mapped the SOX2 cistrome. Integrative analysis of SOX2 cistrome and GBM transcriptome data identified two transcription factors, oligodendrocyte lineage transcription factor 2 (OLIG2) and zinc finger E-box binding homeobox 1 (ZEB1) as critical SOX2 targets. Their expression is strongly correlated with SOX2 expression in clinical GBM specimens, and all three proteins are frequently co-expressed in primary Glioblastoma cells, even in the setting of EGFR intratumoral heterogeneity. Sox2, Olig2, and Zeb1 expression is activated by the oncogene EGFRvIII in a murine glioma model, and we demonstrate that co-expression of these transcription factors transforms tumor suppressor deficient astrocytes in the absence of an upstream oncogene and that the resulting tumors exhibit the major histopathological features of GBM.