Abstract
The malignant primary brain tumor glioblastoma (GBM) has a dismal prognosis and current treatment options are insufficient to cure patients. The stem cell transcription factor SOX2 has been indicated as vital for GBM stem cell maintenance in vitro and GBM tumor formation in vivo, rendering it a putative therapeutic target for GBM. However, a few studies, including previous work from our lab, suggest a dichotomy in SOX2 dependence between different patients. To elucidate whether SOX2 independent GBMs exist and if so, how they are distinguished, we have investigated how altered SOX2 expression affects a panel of primary human GBM lines cultured under stem cell conditions. We found that elevated SOX2 expression inhibited proliferation in a dose-dependent manner in three out of four GBM cell lines. Global gene expression analysis showed that cells representing proliferation-inhibited and refractory cell lines end up on different ends of the developmental- to injury response GBM stem cell axis, were resistance to SOX2 overexpression was connected to an injury response expression profile. CRISPR/Cas9 mediated SOX2 knockout revealed a SOX2 independence in the refractory cell line, where cells lacking SOX2 could be propagated both in vitro and in vivo, implicating SOX2 as a non-essential gene for injury response-driven GBM stem cells. In current work, SOX2-dependent cell lines are engineered to express inducible exogenous SOX2 with concomitant endogenous SOX2 knockout, providing a system where SOX2 can be turned off at any time point. This system will be used in further studies elucidating the nature of SOX2 dependence and independence in GBM stem cells.