The rat pheochromocytoma cell line, PC12 (Greene and Tischler, 1976), was cultured and transfected as previously described (Liu et al., 1999). Briefly, the transfections were done using a liposome-mediated approach (Lipofectamine, Invitrogen, California, USA). The cells were transfected with pSGB4SH and a luciferase expression construct, pGL-Promoter (Promega Corporation, Wisconsin, USA). The cells were differentiated with 100 ng/ml nerve growth factor (NGF; Upstate Biotechnologies, Inc., New York, USA) for 2 days following transfection and then harvested and assayed for β-gal (Galacto-Star, Applied Biosystems, California, USA) and luciferase (Luciferase Assay System, Promega) activities in a Lumimark microplate luminometer (Bio-Rad, California, USA). To correct for differences in transfection efficiencies between dishes, the β-gal activity in each sample was normalized to the luciferase activity in that same sample.
