Gene reporter assays to evaluate the functional impact of the most frequent MDM2 basal promoter haplotypes. (A) Schematic representation of constructs tested for luciferase gene reporter assays in pGL3 basic vector. Haplotypes H1A and H1B are identical when excluding the position +309 T > G (see Table 2). (B) Relative luciferase activity of MDM2 promoter haplotypes was measured following transient transfection in HeLa, HepG2 and JEG3 cells. The empty promoterless pGL3 basic vector was used as negative control. Results are expressed in a ratio of Firefly/Renilla activity multiplied by 100. Promoter haplotype H2 was used as reference against which relative expression was compared. Haplotype H1 showed significantly higher expression levels across all three cell lines. The p values are calculated from four replicates with unpaired student's t test. Significant differences are marked with an asterisk (*p < 3 × 10−3; **p < 8 × 10−6).