Effect of atRA on NF-κB and RAR activity. Chondrocytes were transfected with (a) a κB reporter or (b) a retinoic acid response element (RARE) reporter and treated with or without tumour necrosis factor (TNF)-α (30 ng/ml) and/or all-trans retinoic acid (atRA; 1, 10, or 100 nmol/l) for 24 hours. Panel a: TNF-α-induced nuclear factor-κB (NF-κB) activity was reduced by atRA in a concentration-dependent manner. Panel b: TNF-α had no effect on the concentration-dependent increases in RAR activity. Data are ratios of NF-κB- or retinoic acid receptor (RAR)-regulated firefly luciferase units to constitutive SV40-regulated renilla luciferase units, and are means ± standard error (based on at least three replicates) from a single experiment, representative of three independent experiments. Data were evaluated by one-way analysis of variance and Tukey's multiple comparisons tests. Unlabelled bars or bars labelled with the same lower case letters are not significantly different (P > 0.05). RLU, relative luciferase units.