Alpha6-Integrin Regulates FGFR1 Expression through the ZEB1/YAP1 Transcription Complex in Glioblastoma Stem Cells Resulting in Enhanced Proliferation and Stemness

Glioblastoma (GBM) is the most lethal primary brain tumor in adults and is known to be particularly aggressive and resistant to anti-cancer therapies, mainly due to the presence of GBM stem cells (GBMSC). By in vitro approaches supported by analysis from patients' databases, we determined how alpha 6-integrin and Fibroblast Growth Factor Receptor 1 (FGFR1) work in concert to regulate proliferation and sternness of GBMSC. We showed that alpha 6-integrin regulates the expression of FGFR1 and its target gene Fokhead Box M1 (FOXM1) via the ZEB1/YAP1 transcription complex. These results were in accordance with the positive correlation observed in GBM between alpha 6-integrin expression and its target genes ZEB1/YAP1, FGFR1, and FOXM1 in the databases, TCGA and Rembrandt. In addition, the clinical data demonstrate that GBM patients with high levels of the five genes signature, including alpha 6-integrin, ZEB1/YAP1, FGFR1 and FOXM1, have a significantly shorter overall survival. In vitro, we observed a similar decrease in the expression of sternness-related factors, neurospheres forming capacity, as well as spheroids growth when alpha 6-integrin or FGFR1 was blocked individually with specific siRNA, whereas the combination of both siRNA led to a significantly higher inhibition of spheres formation. These data suggest that co-administration of anti-FGFR1 and anti-alpha 6-integrin could provide an improved therapeutic response in GBMSC.