The Developmental Transcription Factor TBX3 Physically Engages with the Wnt/β-catenin Transcriptional Complex in Human Colorectal Cancer Cells to Regulate Metastasis Genes

Wnt signaling orchestrates gene expression in a plethora of processes during development and adult cell homeostasis via the action of nuclear β-catenin. Furthermore, neoplasia of the colorectal epithelium begins with aberrant Wnt/β-catenin signaling. Yet, little is known about how β-catenin generates context-specific transcriptional outcomes. We have previously identified the developmental transcription factor TBX3 as a tissue-specific component of the Wnt/β-catenin nuclear complex during mouse forelimb development. In this study, we show that TBX3 is present and functionally active in human colorectal cancers. TBX3 genomic binding pattern suggests a regulatory role that broadly coincides with that of Wnt/β-catenin. Moreover, proteomics proximity labelling indicated that, during Wnt pathway activation, TBX3 is vicinal to several protein partners, including the transcription factors TCF/LEF and chromatin remodeling complexes which are usually found at Wnt responsive elements. Sequence and structure analysis revealed that TBX3 possesses an exposed Asp-Pro-Phe (NPF) motif predicted by AlphaFold2 Multimer to mediate direct interactions with several Wnt-activated TBX3 partners. Deletion of NPF abrogates TBX3 proximity to these partners and its ability to modulate Wnt-dependent transcription. TBX3 emerges as a key modulator of the oncogenic activity of Wnt/β-catenin in colorectal cancer, and its mechanism of action exposes a novel druggable protein interaction surface. ### Competing Interest Statement The authors have declared no competing interest.