EGFR/FOXO3a/BIM signaling pathway determines chemosensitivity of BMP4-differentiated glioma stem cells to temozolomide

Accumulating evidence suggests that glioma stem cells (GSCs), which are rare cells characterized by pluripotency and self-renewal ability, are responsible for glioblastoma (GBM) propagation, recurrence and resistance to therapies. Bone morphogenic proteins (BMPs) induce GSC differentiation, which leads to elimination of GSCs and sensitization of glioma to chemotherapeutics. Alterations in the epidermal growth factor receptor (EGFR) gene are detected in more than half of GBMs; however, the role of EGFR in the chemoresistance of GSCs remains unknown. Here, we examined whether EGFR signaling affects BMP4-induced differentiation of GSCs and their response to the alkylating drug temozolomide (TMZ). We show that BMP4 triggers the SMAD signaling cascade in GSCs independent of the EGFR level. BMP4 downregulated the levels of pluripotency markers (SOX2 and OLIG2) with a concomitant induction of an astrocytic marker (GFAP) and a neuronal marker (β-Tubulin III). However, GSCs with different EGFR levels responded differently to treatments. BMP4-induced differentiation did not enhance sensitivity to TMZ in EGFRlow GSCs, in contrast to EGFRhigh GSCs, which underwent apoptosis. We then identified differences in cell cycle regulation. In EGFRlow cells, BMP4-triggered G1 cell cycle arrest which was not detected in EGFRhigh cells. RNA-seq profiles further highlighted transcriptomic alterations and distinct processes characterizing EGFR-dependent responses in the course of BMP4-induced differentiation. We found that the control of BIM (the pro-apoptotic BCL-2 family protein) by the AKT/FOXO3a axis only operated in BMP4-differentiated EGFRhigh cells upon TMZ treatment. The properties of individual glioma stem cells (GSCs) may influence the success of chemotherapy in tackling aggressive brain cancer. GSCs promote tumor growth and chemotherapy resistance in glioblastoma tumors. One potential treatment approach uses bone morphogenetic proteins to induce GSCs to differentiate into less harmful cells. Once the GSC population has dwindled, chemoresistance reduces in many but not all cases. Jakub Mieczkowski, Bozena Kaminska and co-workers at the Nencki Institute of Experimental Biology in Warsaw, Poland, conducted experiments on patient-derived glioblastoma cell cultures. They found that samples with high expression levels of the epidermal growth factor receptor (EGFR) protein in GSCs showed heightened sensitivity to the chemotherapy drug temozolomide after differentiation. Conversely, low levels of EGFR resulted in chemoresistance being maintained after differentiation, which may explain the failure of chemotherapy in some patients.