This is achieved in part through the transcriptional activation of genes such as MMP2 and MMP9, which encode matrix metalloproteinases that degrade extracellular matrix barriers (81), as well as CXCR4, a chemokine receptor important in glioma cell migration along stromal cell-derived factor 1 (SDF-1) gradients. The gene discussed is CXCL12; the disease is central nervous system cancer.