CXCR4 and neoplasm: Moreover, HIF-2α target genes involved in tumor progression such as metalloproteinase 9 (MMP-9), C-X-C chemokine receptor type 4 (CXCR4, receptor of the chemokine SDF-1), and the more generic target gene erythropoietin (EPO) are up-regulated in H/SB3 cells and decrease by using HIF-2α specific siRNA (Figure 7G).