NF-κB p65 represses β-catenin-activated transcription of cyclin D1

► Cyclin D1 transcription is directly activated by β-catenin; however, β-catenin-induced cyclin D1 transcription is reduced by NF-κB p65. ► Protein–protein interaction between NF-κB p65 and β-catenin might be responsible for p65-mediated repression of cyclin D1. ► One of five putative binding sites, located further upstream of other sites, is the major β-catenin binding site in the cyclin D1 promoter. ► NF-κB binding site in cyclin D1 is occupied not only by p65 but also by β-catenin, which is dynamically regulated by the signal. Signaling crosstalk between the β-catenin and NF-κB pathways represents a functional network. To test whether the crosstalk also occurs on their common target genes, the cyclin D1 promoter was used as a model because it contains binding sites for both proteins. β-catenin activated transcription from the cyclin D1 promoter, while co-expression of NF-κB p65 reduced β-catenin-induced transcription. Chromatin immunoprecipitation revealed lithium chloride-induced binding of β-catenin on one of the T-cell activating factor binding sites. More interestingly, β-catenin binding was greatly reduced by NF-κB p65, possibly by the protein–protein interaction between the two proteins. Such a dynamic and complex binding of β-catenin and NF-κB on promoters might contribute to the regulated expression of their target genes.