To understand the role of HIF-1α in APL, we analyzed a number of known HIF-regulated functions: in NB4 cells, HIF-1α down-regulation did not affect proliferation (Supplementary Fig S2B), but impaired basal cell migration (Fig 3D) and in vivo BM homing (Fig 3E), consistently with CXCR4 down-regulation (Fig 3C). This evidence concerns the gene CXCR4 and acute promyelocytic leukemia.