Objective      To investigate the effect of down-regulating sphingosine kinase-1 (Sphk1) on the proliferation

apoptosis and migration in human breast cancer MCF-7 cell line.       Methods      The siRNA against Sphk1 was chemically synthesized and then transfected into MCF-7 cells using Lipofectamine 2000. Transfection efficiency was examined by flow cytometry（FCM）and the expression levels of Sphk1 mRNA and protein were determined by real-time fluorescent quantitative PCR and Western blotting. Cell proliferation and cell apoptosis was assessed by CCK-8 assay and FCM respectively. Cell migration was measured by transwell assay.       Results      The efficiency of siRNA transfection into human MCF-7 cells were 89%. The siRNA against sphk1 gene significantly reduced the mRNA and protein expression of Sphk1 in MCF-7 cells （P0.05）. The siRNA-2 showed most significant effect（P0.01）.The MCF-7 cells transfected with Sphk1 siRNA-2 showed a significant decrease of cell proliferation and migration compared to the control cells. Moreover

significant increase of proportion of apoptotic cells were detected in the transfected cells（P0.05）.       Conclusion      Sphk1 knockdown in breast cancer cells effectively inhibits the proliferation and migration and induces the apoptosis in MCF-7 cells. Sphk1 may become a potential target for gene therapy of breast cancer.