Response of a reporter containing the Follistatin promoter to Wnt-3A protein in NCCIT cells . The Follistatin promoter  contains one putative TCF binding site (CTTTGAT). This promoter linked to luciferase was transfected in NCCIT cells, which were then exposed to Wnt-3A CM and CCM for 8 hours. This assay showed a significant increase in activity when cells were stimulated directly with Wnt-3A CM or co-transfected with activated β-catenin (not shown). This effect was abrogated by co-transfection of dominant-negative TCF-4 or axin (not shown). When the TCF site within the Follistatin promoter was mutated into CATCGAT, the Wnt-3A response was abolished.