FIG. 8.

AP-1 is involved in β-catenin/TCF-dependent activation of c-Myc expression in response to mitogens. (A) Diagram of the c-Myc gene (blue) with the 3′ enhancer represented by a black rectangle. The sequence of a 158-bp segment from the enhancer containing two TCF motifs (bold) and an AP-1 motif (underlined) is shown. (B) Real-time PCR analysis of ChIP assays using an anti-c-Jun-specific antibody was conducted in starved (0) HCT116 cells and starved cells cultured in serum-containing medium for 1, 2, 4, or 8 h. Error bars indicate standard errors of the means. (C) Diagram of luciferase constructs where X indicates mutation in the TCF motif, and a black oval indicates a mutation in the AP-1 motif. HCT116 cells were transfected with the indicated luciferase reporters. The next day, cells were starved in serum-deprived medium for 48 h. Serum-containing medium was added to half of the samples for 4 h, and luciferase activities were measured in cell lysates. Data are presented as the relative change in luciferase activity (in relative light units [RLU]) in response to serum and are normalized to levels obtained in cells transfected with pGL3-promoter. Error bars indicate standard deviations. EN, enhancer.