NF-κB p65 represses ß-catenin-activated transcription of cyclin D1.

Signaling crosstalk between the ß-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. ß-catenin activated transcription from the cyclin D1 promoter, while co-expression of NF-κB p65 reduced ß-catenin-induced transcription. Chromatin immunoprecipitation revealed lithium chloride-induced binding of ß-catenin on one of the T-cell activating factor binding sites. More interestingly, ß-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 ß-catenin and NF-κB on promoters might contribute to the regulated expression of their target genes.

Intracellular expression of the T-cell factor-1 RNA aptamer as an intramer.

T-cell factor (TCF)-1 protein forms the transcriptional complex with beta-catenin and regulates the expression of diverse target genes during early development and carcinogenesis. We have selected previously an RNA aptamer that binds to the DNA-binding domain of TCF-1 and have shown that it interfered with binding of TCF-1 to its specific DNA recognition sequences in vitro. As an approach to modulate the transcription by TCF/beta-catenin complex in the cells, we have developed the RNA expression vector for stable expression of RNA aptamer inside of the mammalian cells. High level of RNA was expressed as an intramer in the fusion with the stable RNA transcript. The RNA intramer inhibited TCF/beta-catenin transcription activity as shown by luciferase assay. It also modulated the expression of TCF/beta-catenin target genes, such as cyclin D1 and matrix metalloproteinase-7, as predicted to be as an effective inhibitor of the TCF function. In addition, it efficiently reduced the growth rate and tumorigenic potential of HCT116 colon cancer cells. Such RNA intramer could lead to valuable gene therapeutics for TCF/beta-catenin-mediated carcinogenesis.