UBR5 and colorectal cancer: We thus expressed an unphosphorylatable mutant of β-catenin (Δ45-β-catenin, found in colorectal cancers; Morin et al., 1997), which is hyperactive in stimulating SuperTOP in WT HEK293T cells, but this activity is much reduced in UBR5 KO cells (Figure 2D).