For promoter activity assay, cells were seeded in triplicate into a 24-well plate and then transfected with 300 ng pGL3 plasmids containing the TERT, GAPBA, or GABPB promoter, together with 12 ng Renilla luciferase (pRL-TK) plasmid (normalizing control) using Lipofectamine 3000 (Invitrogen). At 24 h after the transfection, cells were lysed and luciferase activities were measured using the Dual-Luciferase Reporter Assay System (Promega). Results were presented as relative luciferase activities, which were obtained by dividing firefly luciferase values with Renilla luciferase values for each set of reading.