Synergistic activation of the P0- pax6b promoter by PBX1a, PREP1 and PDX1 factors. HCT116 cells were transfected with the P0pax6b-gfp/luc reporter plasmid. This reporter plasmid was cotransfected with expression vectors for PBX1a, PREP1 and/or PDX1 as indicated. Luciferase activities were normalized to β-galactosidase activity generated by the internal control plasmid Rous sarcoma virus-β-galactosidase. Normalized Luc activity obtained in the cell transfected without expression vector was arbitrarily set at 1. The data are means ± S.D. of three transfection experiments, each performed in duplicate.