Figure 4.

DPP4 regulates E2F1 activity to enhance binding of E2F1 in the PIN1 promoter in MCF7 cells. (A and B) The E2F1‐luc luciferase promoter‐reporter plasmid and the pRL‐TK vector were cotransfected with His‐DPP4 (A) or siRNA‐DPP4 (B). After 48 h, the firefly luciferase activity was determined in cell lysates and normalized to Renilla luciferase activity. Columns represent the means ± SD of triplicate samples. *P < 0.05, significantly different from control cells. (C) Cells were cotransfected with an E2F1‐luc luciferase promoter‐reporter plasmid and the pRL‐TK vector. At 24 h after transfection, cells were serum starved, treated with 1 mM sitagliptin (SITG) for 24 h and then exposed or not exposed to 1 ng∙mL⁻¹ EGF for 24 h. The firefly luciferase activity was determined in cell lysates, normalized to Renilla luciferase activity and is expressed relative to control cells. Columns represent the means ± SD of triplicate measurements from two experiments. *P < 0.05, significantly different as indicated. (D) Human PIN1 promoter sequence with putative E2F1‐binding site. (E and F) Cell lysates from His‐DPP4 (E) or si‐DPP4 (F) transfected MCF7 cells were subjected to chromatin IP using anti‐E2F1 or IgG antibodies, and the recovered DNA was PCR amplified with primers specific for E2F1‐binding sites in the PIN1 promoter as shown in Figure 2D.