Bmi-1 activates MMP-9 in glioma cells. A, Real-time PCR quantification of MMP-9 mRNA expression levels in vector-control cells and Bmi-1-overexpressing cells (Bmi-1). MMP-9 expression levels are presented as the fold changes relative to that in vector-control cells and normalized to GAPDH. B, ELISA for secreted MMP-9 protein in cell supernatants. C, Gelatin zymography assay of MMP-9 gelatinase activity in cell supernatants. Vector: pMSCV-vector. Error bars represent the mean ± SD of three independent experiments; ** P < 0.01.