KLF4 and SOX9 transcription factors antagonize ß-catenin and inhibit TCF-activity in cancer cells.

The transcriptional activator ß-catenin is a key mediator of the canonical Wnt signaling pathway. ß-catenin itself does not bind DNA but functions via interaction with T-cell factor (TCF)/lymphoid-enhancing factor (LEF) transcription factors. Thus, in the case of active Wnt signaling, ß-catenin, in cooperation with TCF/LEF proteins family, activates the expression of a wide variety of genes. To date, the list of established ß-catenin interacting targets is far from complete. In this study, we aimed to establish the interaction between ß-catenin and transcription factors that might affect TCF activity. We took advantage of EMSA, using TCF as a probe, to screen oligonucleotides known to bind specific transcription factors that might dislodge or antagonize ß-catenin/TCF binding. We found that Sox9 and KLF4 antagonize ß-catenin/TCF binding in HEK293, A549, SW480, and T47D cells. This inhibition of TCF binding was concentration-dependent and correlated to the in vitro TCF-luciferase functional assays. Overexpression of Sox9 and KLF4 transcription factors in cancer cells shows a concentration-dependent reduction of TCF-luciferase as well as the TCF-binding activities. In addition, we demonstrated that both Sox9 and KLF4 interact with ß-catenin in an immunoprecipitation assay and reduce its binding to TCF4. Together, these results demonstrate that Sox9 and KLF4 transcription factors antagonize ß-catenin/TCF in cancer cells.