Figure 3 . Axin is the target protein of HCJA121 and HCJA404. (a) A cartoon representation of HCJA121 (sapphire sticks) and HCJA404 (purple sticks) docked onto the crystal structure of the DAX domain of axin (PDB 1WSP). The related two protomers of DAX are in blue and green, respectively. b) K781A or L784A mutations within the DAX domain showed decreased acceleration of melanogenesis following treatment with compounds HCJA121 and HCJA404 compared to their effects in wild-type (WT) B16 cells. (c) Stimulation of melanin content and tyrosinase activity by HCJA121 and HCJA404 (20 μ M) in K781A or L784A mutated B16 cells was significantly decreased relative to that in the control cells. The results represent the means ± S.E.M from five independent experiments (N=5). Data were analysed by ANOVA, significantly different as indicated. (d) Co-IP of axin and LRP6 from B16 cells implies that the compounds could enhance the interaction between axin and LRP6. The protein was first precipitated using an axin antibody and subsequently with an LRP6 antibody. The amount of each sample assessed by WB was 50μ g. Data shown are means ± S.E.M; n = 5 per group. significantly different as indicated (*P < 0.05, **P< 0.01, ***P < 0.001, and ****P< 0.0001).