Multiple tandem repeats of PPRE were constructed and cloned upstream the tk promoter. The resulting PPRE-tk constructs were then inserted upstream the luciferase gene and droven the expression of luciferase gene (Figure 1(A)). To test which report constructs were significantly induced by rosiglitazone (a PPARγ agonist), we transiently transfected HepG2 cells with various reporter constructs and treated cells with rosiglitazone. As shown in Figure 1(B), rosiglitazone significantly induced the luciferase activity driven by five, six, seven, or eight tandem repeats of PPRE. The maximal induction was observed in HepG2 cells transfected with five or six tandem repeats of PPRE construct. The β-galactosidase activities were consistent, suggesting that the transfection efficacies were similar in various reporter constructs. Moreover, in vitro imaging showed that bioluminescent signal was significantly induced by rosiglitazone in pGL-PPRE5x-Ptk-transfected HepG2 cells (Figure 1(C)). Ciani et al. constructed the luciferase reporter plasmids containing one, two, three, and five tandem repeats of PPRE, and found that the induced luciferase activity is directly proportional to the number of PPREs present in the promoter region [28]. However, the maximal induction of luciferase
