By comparison with the scrambled non-specific control siRNA (si-NS), transfection with si-HIF-1α at the dose of 100 nM significantly inhibited cell proliferation induced by nicotine (Fig. 3D), indicating that the nicotine-mediated promotion of NPC cells growth might also partially be regulated by activating HIF-1α signaling pathway. This evidence concerns the gene HIF1A and nasopharyngeal carcinoma.