Figure 3.

ABCB1 gene promoter activity depends on β-catenin mutation status. (A, C) CAT-ELISA for TOP promoter activity (A) and for ABCB1 promoter activity (C) in HCT116, HAB-18^mut, HAB-68^mut, HAB-85^wt and HAB-92^wt cells. TOP promoter- (A) and ABCB1 promoter- (C) driven reporter gene expressions were strongly enhanced in cells harbouring gain-of-function β-catenin compared with the cell lines where the mut β-catenin allele was ablated. Transfections with the plasmid pFOP-CAT (A) and with the promoter-less plasmid pCAT3-basic (C) as well as transfections without DNA served as controls. The amount of CAT protein was normalised to the protein content of the respective lysate, expressed as pg CAT per mg protein and calculated as percentage of CAT reporter gene expression in HCT116 cells. Values are given as the average of triplicates. (B) Schematic drawing of the ABCB1 promoter, the TCF4-binding sites are marked. Nucleotide sequence and regulatory elements of the 5′-flanking region of the human ABCB1 gene are based on Kohno et al (1990) and Yamada et al (2000). ^*P<0.05.