Figure 2.

DPP4 enhances MEK/ERK and JNK/c‐Jun signalling stimulated by EGF in MCF7 cells. (A and B) Cells were transfected with a construct expressing histidine‐tagged DPP4 (His‐DPP4) or mock transfected with empty vector (mock plasmid). At 48 h after transfection, the cells were harvested and lysed. Proteins in whole cell lysates were separated by SDS‐PAGE and immunoblotted. (C and D) Constructs expressing control (siRNA‐control) or DPP4‐specific (siRNA‐DPP4) siRNAs were transfected into MCF7 cells. At 48 h after transfection, the cells were harvested and lysed. Proteins in whole cell lysates were separated by SDS‐PAGE and immunoblotted. (E) Cells were transfected with His‐DPP4 or mock plasmid. At 24 h after transfection, the cells were serum starved, exposed to the indicated concentration of EGF for 30 min, harvested and lysed. Proteins in whole cell lysates were separated by SDS‐PAGE and immunoblotted. (F) siRNA‐control or siRNA‐DPP4 constructs were transfected into MCF7 cells. At 24 h after transfection, the cells were serum starved, exposed to the indicated concentration of EGF for 30 min, harvested and lysed. Proteins in whole cell lysates were separated by SDS‐PAGE and immunoblotted. (G and H) His‐DPP4 or mock plasmid were co‐transfected with the luciferase promoter‐reporter constructs, FOS‐luc (G) or JUN‐luc (F), and the pRL‐TK (Renilla luciferase control reporter) vector into host cells. At 24 h after transfection, the cells were serum starved and then exposed or not exposed to 1 ng∙mL⁻¹ EGF for 24 h. The firefly luciferase activity was determined in cell lysates and normalized to the Renilla luciferase activity. Columns represent the means ± SD of triplicate samples. * P < 0.05, significantly different from control (mock) cells. (I) Cells were co‐transfected with an AP‐1‐responsive luciferase promoter‐reporter plasmid and the pRL‐TK vector. At 24 h after transfection, the cells were serum starved, treated with the indicated concentration of 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 the 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 from cells treated with EGF only.