2.7. Luciferase reporter assay

Briefly, the cells were seeded in 12 well plates. The next day, the cells were co-transfected with PGL 4.37 [luc2P/ARE/Hygro] reporter (Promega, Madison, WI), as a measure of NRF2 transcription activity, along with renilla as the internal control using polyjet DNA transfecting agent. 24 h after transfection, the cells were treated with a 200 μM mixture of bile salts in pH7 medium or PBS for another 24 h. The cells were harvested and lysed with 1X luciferase passive lysis buffer. Luciferase activity was measured after adding the luciferase reagent and renilla after adding the stop solution using a dual-luciferase reporter assay system (Promega) in a FLUOstar OPTIMA microplate reader (BMG LABTECH, Cary, NC). Luciferase activity was calculated by normalizing the luciferase with the corresponding renilla value and represented as relative luciferase activity.