For transfection of 253-NT cells, 1610 6 cells at 75% confluence were transfected with 7.5 mg of plasmid DNA in Lipofectamine LTX reagent (Invitrogen) following the manufacturer's recommended protocol. After incubation for 24 hours in complete medium, stable transfectants were selected by maintaining cells in complete medium containing geneticin (Invitrogen) at 600 mg/ml with medium changes every 48 hours. For all subsequent experiments, geneticin resistant cells were maintained in complete selection medium.