Activation of the rat PF4 promoter by USF1 and USF2 through the E-box motifs. (A) Activation of the rat PF4 promoter by USF1 and USF2. A transient transfection assay was performed with PF4luc and USF expression vectors. PF4luc contains 1.1 kb of PF4 promoter in front of the luciferase gene. pcDNA3 vectors (0.5 μg), expressing either USF1 or USF2 or a mix of both vectors, were cotransfected with PF4luc into HepG2 cells. Relative luciferase activities were measured. The columns and vertical bars represent mean ± SE of 6 replicates. *A significant difference (P < .05) between control and USF1, USF2, and USF1 + USF2. #A significant difference (P < .05) between USF1 and USF2 and USF1 + USF2. (B) Activation of the rat PF4 promoter through E-box motifs. PF4luc or PF4mut, both of which constructed by mutating the E-box motifs in the rat PF4 promoter, was transfected into HEL cells. After the transfection, cells were incubated with medium containing 10 nM PMA, and luciferase activities were measured. The columns and vertical bars represent mean ± SE of 6 replicates. *A significant difference (P < .05).