Effects of TNF-α and atRA on nuclear levels of NF-κB and RARα. Chondrocytes were 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. (a) Nuclear extracts (30 μg) were resolved on a 7.5% polyacrylamide gel and immunoblotted with antibodies against nuclear factor-κB (NF-κB) p65, retinoic acid receptor (RAR)α, or β-catenin (β-cat). Signal intensities for (b) NF-κB p65 and (c) RARα were quantified by densitometry. Panels (a) and (b): TNF-α induced nuclear localization of NF-κB, which was not significantly reduced by atRA. Panels (a) and (c): RARα nuclear levels were not significantly altered by treatment with TNF-α or atRA. Panel a: The immunoblots shown are representative of three independent experiments. Panels (b) and (c): data are expressed as ratios of intensities of NF-κB or RARα to β-catenin and are means ± standard error. 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).