FIGURE 1:

APC and Axin have regions with potentially redundant functions, and Axin has two domains/motifs essential for βcat destruction. (A) Drosophila APC2. Top, regions that may have redundant functions. Bottom, unique functions of APC2. (B) Drosophila Axin. Top, regions that may have redundant functions. Bottom, regions with unique functions. (C) Comparison of human APC1 and fly APC2, indicating truncated protein present in SW480 cells. (D) Schematic representation of Axin mutants. (E) Wild-type Axin can reduce βcat levels. Axin-RFP expressed in SW480 cells and stained for βcat via antibody. Arrows, transfected cells. (F, G) AxinΔβcat-RFP (F) and AxinΔDIX-RFP (G) cannot facilitate βcat destruction. (H) Deleting either the βcat-binding site or DIX domain of Axin impairs its ability to reduce βcat levels. Quantification of βcat relative to untransfected cells in 10 cells each measured in three independent experiments. (I) Wnt-regulated transcription remains high in cells expressing Axin mutants that delete the βcat-binding or DIX domain. Quantification of TOP/FOPflash reporter gene assay of indicated constructs in SW480 cells. Triplicates were measured in three independent experiments. Student’s t test was used. (J) Immunoblot of indicated constructs to compare expression levels. aPKCγ is a loading control.