Knock-down of C-X-C chemokine receptor 7 (CXCR7) upregulates C-X-C motif ligand 12 (CXCL12) expression in acute myeloid leukemia (AML) cells. Using small interfering RNA (siRNA) technology, CXCR4 and CXCR7 were knocked down in U937 cells and then subjected to quantitative reverse transcription polymerase chain reaction (RT-PCR) (A, B) and western blot analysis (C, D). Data are expressed as mean±SD of 3 independent experiments.