Figure 4.

Introduction of E2F binding sites into the p15^INK4B promoter suppresses its induction by TGF-β. (A) E2F binding sites from the hamster DHFR promoter were introduced into the minimal inducible p15^INK4B promoter construct, p15P113-luc (14), to create p15+1×E2F-luc. The mutant E2F binding sites were inserted into the same position to create p15+1×mE2F-luc. Two copies of the same wild-type or mutant E2F binding sites were similarly introduced to create p15+2×E2F-luc and p15+2×mE2F-luc. Nucleotide sequences for the wild-type and mutant E2F binding sites are underlined. (B) Constructs shown in A were transiently transfected into HaCaT cells, and their relative light units were measured after cells were treated with or without 100 pM human TGF-β1 for 24 hr. Induction folds by TGF-β are shown. Error bars = SD of duplicates.