Western blot analysis was performed as previously described (Park et al., 2012 (link)). Proteins were isolated from cells or mouse tissues by homogenization in RIPA buffer with complete mini protease inhibitor cocktail (Roche). Protein concentrations were determined by the Pierce BCA protein assay kit (Thermo Fisher Scientific). Anti-IKKβ, anti-IKKα, anti-Smurf2, and anti-Histone H3 antibodies were purchased from Cell Signaling Technology; anti–β-catenin, anti–β-actin, and anti-GAPDH antibodies were purchased from Sigma-Aldrich; and antiubiquitin monoclonal antibody was purchased from Santa Cruz Biotechnology. For immunoprecipitation experiments, control or shIKKβ 3T3-L1 cells, or adipose SV cells were incubated with 100 nM of PS-341 for 4 h. The whole-cell lysates were isolated, incubated with anti–β-catenin antibody overnight at 4°C, and then incubated with Protein A Agarose beads (Roche) for another 5 h. The samples were washed and analyzed by Western blot using antiubiquitin monoclonal antibodies.