STAT3 and glioblastoma: In addition, we also observed a strong increase (15.2-fold) in 6× STAT3 RE luciferase activity in GBM-R2I2 cells without STAT3 overexpression, and observed a similar increase (13.4-fold) in the GBM-R2I2 cells with STAT3 overexpression, implying that GBM-R2I2 cells have sufficient STAT3 to stimulate transcription.