MMP9 and glioblastoma: To confirm that EMT activation precedes MES differentiation in GBM progression, we transfected GSC23 cells with siRNAs targeting the most common EMT markers, e.g., ZEB1, ZO-1, and MMP-9, and subsequently examined the protein levels of CD44, a marker of the mesenchymal GSC subtype (Figure 8E–G).