NEDD8 trimers form in WT U2OS cells after treatment with H2O2 and co-immunoprecipitate with endogenous PARP-1 but not with immunoglobulin control (IGG). WT U2OS cells were left untreated of treated with H2O2 (600 μM) for 30 min and were harvested for immunoprecipitation and Western blot analysis 