A, RNAi-mediated depletion of β-catenin leads to loss of K63-polyubiquitin-modified APC. HEK293 cells were transfected with the indicated siRNAs for 72 h, followed by treatment with 10 μm MG132 together with vehicle (−) or Wnt3a (200 ng/ml) for 4 h. Lysates were immunoprecipitated with K63 polyubiquitin linkage-specific antibodies, and analyzed by immunoblot as indicated. B, HEK293 cells were transfected with siRNA for 72 h as indicated, followed by treatment with 10 μm MG132 for 4 h. Lysates were immunoprecipitated with K63 polyubiquitin linkage-specific antibodies, and analyzed by immunoblot as indicated. C, RNAi-mediated depletion of β-catenin leads to loss of APC-Axin interaction. HEK293 cells were transfected with the indicated siRNAs for 72 h, followed by treatment with 10 μm MG132 for 4 h. Lysates were immunoprecipitated with anti-APC and analyzed by immunoblot as indicated.