Human hepatocellular carcinoma HepG2 cells, which were purchased from Bioresource Collection and Research Center (Hsinchu, Taiwan), were maintained in Dulbecco's modified Eagle's medium (Life Technologies, Gaithersburg, MD, USA) supplemented with 10% fetal bovine serum at 37°C. Cells were transfected with PPRE reporter constructs and pcDNA3.1/lacZ DNA (Invitrogen, Carlsbad, CA, USA) by SuperFect® transfection reagent (Qiagen, Valencia, CA, USA). Twenty-four hours later, transfected cells were treated with 0.5 µM rosiglitazone maleate (Alexis, San Diego, CA, USA). Luciferase assay and β-galactosidase assay were performed as described previously [24], [25]. Induction fold was calculated by dividing the relative luciferase unit (RLU) of rosiglitazone-treated cells by the RLU of untreated cells.
