USP6 promotes Fzd deubiquitylation. (A) USP6 promotes Fzd5 deubiquitylation in vivo. HEK293T cells were transfected with plasmids encoding Fzd5-V5, Flag-Ub, and the indicated USP6 constructs, and then treated with control or WNT3A CM. (Top) Fzd5 was immunoprecipitated using V5, and its ubiquitylation was detected with anti-Flag antibody. Whole-cell extracts were blotted with anti-V5 (Middle) or anti-USP6 (Bottom) antibodies. (B) In vitro deubiquitylation of Fzds by USP6. HeLa cells were transfected with plasmids encoding Fzd5-V5 and Flag-Ub. Fzd5 was purified using anti-V5 and then incubated with GST-tagged recombinant USP6 or USP6(CS). Fzd5 ubiquitylation was detected by immunoblotting with anti-FLAG. GST and USP2 were used as negative and positive controls, respectively. Data are representative of two independent experiments. IP, immunoprecipitation; WCL, whole cell lysate.