CDK4 and neoplasm: Our recent study also indicated that Snail, in collaboration with EGR1 and SP1, may directly activate transcription of the inhibitor of cyclin-dependent kinase 4/6 (CDK4/6), p15INK4b, in HepG2 cell stimulated by the phorbol ester tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA)23.