(A) Comparison of the inhibitory effect of AuNP 4 with the two AuNP controls on arsenic trioxide induced PML degradation. Western blot analysis of PML protein modification and degradation in HeLa-SUMO2 cells treated with C4-AuNP or AuNP 4 or 5 (4 μM) for 1 h, and then were exposed to 1 μM arsenic trioxide for 1 or 24 h. (B) AuNP 4 inhibited protein-protein interactions between SUMOylated PML and RNF4. HeLa-SUMO2 cells were transfected with a plasmid expressing Flag-tagged RNF4, and after 24 h, were treated with C4-AuNP, AuNP 4 or 5 (4 μM) for 24 h followed by exposure to 1 μM arsenic trioxide for 1 h. The Flag-tagged RNF4 protein was immunoprecipitated using an anti-Flag antibody and its association with PML protein was analyzed by Western blot. In both panels A and B, unmodified PML bands and SUMO modified PML bands (labeled with PML-S) are indicated.