Effects of resveratrol and curcumin treatment on IL-1β-induced IκBα ubiquitination. Serum-starved human chondrocytes were pre-treated with 10 ng/ml IL-1β alone for 4 hours, or 100 μM N-Ac-Leu-Leu-norleucinal (ALLN) for 30 minutes, or pre-treated with 50 μM resveratrol, 50 μM curcumin or 100 μM ALLN alone for 4 hours and then co-treated with IL-1β (10 ng/ml) for 8 hours. Other serum-starved chondrocytes were pre-treated with 50 μM resveratrol or 50 μM curcumin alone for 4 hours and then co-treated with IL-1β (10 ng/ml) for 8 hours. Some cultures were left untreated and evaluated after 12 hours. Cytoplasmic extracts were immunoprecipitated with an antibody against IκBα and subjected to western blot analysis using a monoclonal anti-ubiquitin antibody. Resveratrol (but not curcumin), stabilized IL-1β-induced ubiquitination of IκBα. Data shown are representative of three independent experiments.