Effects of proteasome inhibitors on Btk expression in heterologous cells and in chicken B-cell lines. (A) 293T and COS-7 cells were transiently transfected with Btk-GFP. Cells were cultured in the presence or absence of 10 μM MG132 for 16 hours, and total cell lysates were subjected to Western blot analysis. (B) B41-13 (Btk-defective chicken B cells reconstituted with human Btk under the control of the chicken β-actin promoter) and DT40 cells were treated with MG132 as indicated, and cell extracts were subjected to immunoblotting analysis (the blot from B41-13 cell extracts was decorated with polyclonal antihuman Btk antibody, whereas polyclonal antichicken Btk antibody was used in the blot of the DT40 lysates).