To test this Tcf4 binding region for enhancer activity, we conducted luciferase reporter assays using the constructs shown in Fig. 1F. The putative Id2-enhancer fragment significantly activated Wnt-signaling dependent transcription from the CMV minimal promoter in two colorectal cancer cell lines (HCT116 and SW480) (Fig. 1G). Here, ID2 is linked to colorectal cancer.