The NFκB pathway as a key mediator of the glioblastoma mesenchymal subtype in glioblastoma stem cells and human tumors.

Abstract

2002 Background: The mesenchymal (MES) subtype of glioblastoma (GBM) is associated with worse prognosis and increased treatment resistance. Several transcription factors driving the MES phenotype have been identified, including STAT3, CEBP-β, and WWTR1/TAZ. However, the key signaling pathways driving this transcriptional program remain unknown. Methods: Expression profiling analyses was performed on multiple GBM stem cell (GSC) lines derived from individual human tumors. Three large GBM tumor gene expression datasets (TCGA, Rembrandt, Erasmus) were also used in the analyses to identify pathways activated in MES tumors and GSCs. Intracranial GSC xenograft models were used for in vivo validation. Results: We found that GSCs with a MES phenotype also demonstrated upregulation of a gene cassette associated with NFκB activation. Analysis of multiple large expression data sets also demonstrated a tight correlation between the MES phenotype and NFκB activation in human tumors. To determine the effect of NFκB activation in GSCs, we stimulated NFκB by addition of the inflammatory cytokine TNFα. This was accompanied by increased expression of the MES transcription factors (STAT3, CEBP-β, TAZ), and MES markers including CD44. Conversely, blockade of NFκB signaling in GSCs by IκB-α was sufficient to prevent TNF-induced MES transition. Investigation of potential source of NFκB activation suggested a role of microglia. Indeed, addition of supernatant from activated microglia was sufficient to activate NFκB and MES transition in GSCs that could be blocked by IκB-α. To test the role of microglia and NFκB activation on treatment resistance in vivo, treatment with minocycline, an inhibitor of microglia activation, led to a reduction of tumor grade and down-regulation of MES markers in intracranial GSC xenografts. Conclusions: NFκB appears to play an important role in induction of the MES phenotype in GBM and GSCs. Furthermore, activation of microglia is a potential source of NFκB activation in these tumors. These data suggest that blockade of NFκB and/or inhibition of microglia activation may be attractive therapeutic approaches for downregulating MES transition and overcoming treatment resistance in GBM.