Snail is a multifunctional transcriptional factor that has been described as a repressor in many different contexts. It is also proposed as an activator in a few cases relevant to tumor progression and cell-cycle arrest. This study investigated the detailed mechanisms by which Snail upregulates gene expression of the CDK inhibitor p15 INK4b in HepG2 induced by the tumor promoter tetradecanoyl phorbol acetate (TPA).