Oxidative stress regulates lenalidomide-induced up-regulation of DKK1. (A) DKK1 relative expression was evaluated by real-time PCR in 11 samples of myeloma plasma cells cultured in the presence (red bars) or absence (violet bars) of treatment with lenalidomide (100 μM, 24 hours) alone (red bars) or combined with pretreatment with antioxidant agent PBN (2 mM; green bars). (B) In 7 parallel experiments, c-Jun–binding activity was determined. Each sample is expressed as the mean ± SEM of 2 duplicates.