Moreover, when we further examined the effect of Bmi-1 on the expression levels of MMP-2 and MMP-7 in A172 and LN229 glioma cells, our result showed that neither overexpressing nor silencing Bmi-1 had any an effect on the mRNA and protein levels of MMP-2 or MMP-7 (Additional file 2: Figure S1), implicating that MMP-9 might be a major mediator for Bmi-1 mediated invasiveness of glioma cells. Here, MMP9 is linked to central nervous system cancer.