Lef1 regulates COX-2 transcription in chondrocytes.

Although the involvement of Wnt/beta-catenin signaling pathway in the regulation of COX-2 expression has been suggested, the underlying molecular mechanisms are still unclear. Here, we demonstrate that lymphoid enhancer-binding factor 1 (Lef1) in concert with beta-catenin is associated with the transcriptional regulation of the gene encoding COX-2 in mouse chondrocytes. Our results show that co-overexpression of Lef1 and beta-catenin synergistically upregulates COX-2 expression. Furthermore, decrease of Lef1 expression using Lef1 siRNA results in the downregulation of COX-2 expression. Using bioinformatic analysis, we identified a conserved Lef1-binding site that is mapped at the 3' region of the genomic COX-2 locus. In vivo and in vitro binding of Lef1 at the predicted binding site was proved using chromatin immunoprecipitation assays and electrophoretic mobility shift assays, respectively. Moreover, binding of Lef1 and beta-catenin to the Lef1-binding site transactivates COX-2 promoter activity. Our results indicate a pivotal role of Lef1 in the regulation of COX-2 transcription in arthritic chondrocytes.