Pro-inflammatory cytokine such as interleukin (IL)-1beta causes inflammation of articular cartilage via induction of cyclooxygenase (COX)-2 expression. We investigated in this study the role of beta-catenin in the IL-1beta regulation of COX-2 expression in articular chondrocytes. IL-1beta increased expression of COX-2 and induced accumulation and nuclear translocation of transcriptionally competent beta-catenin. Inhibition of beta-catenin degradation by the treatment of cells with LiCl or proteasome inhibitor stimulated expression of COX-2, indicating that transcriptionally active beta-catenin is sufficient to induce COX-2 expression. This was demonstrated further by the observation that ectopic expression of transcriptionally competent beta-catenin stimulated expression of COX-2. Levels of beta-catenin and COX-2 protein were increased in osteoarthritic and rheumatoid arthritic cartilage, suggesting that beta-catenin may play a role in the inflammatory responses of arthritic cartilage. Taken together, our data suggest that accumulation of transcriptionally active beta-catenin contributes to the expression of COX-2 in articular chondrocytes.