Loss of the nuclear Wnt pathway effector TCF7L2 promotes migration and invasion of human colorectal cancer cells

The transcription factor TCF7L2 is indispensable for intestinal tissue homeostasis where it transmits mitogenic Wnt/β-Catenin signals in stem and progenitor cells, from which intestinal tumors arise. Yet, TCF7L2 belongs to the most frequently mutated genes in colorectal cancer (CRC), and growth inhibitory functions of TCF7L2 were proposed. This apparent paradox calls for a clarification of the role of TCF7L2 in colorectal carcinogenesis. Here, we investigated TCF7L2 dependence/independence of CRC cells, and the cellular and molecular consequences of TCF7L2 loss-of-function. By genome editing we readily achieved complete TCF7L2 inactivation in several CRC cell lines without loss of viability, showing that CRC cells have widely lost the strict requirement for TCF7L2. Albeit phenotypic changes manifested in a cell-line-specific fashion, TCF7L2-negative cells exhibited morphological changes, enhanced migration and invasion, and augmented collagen adhesion. Additionally, TCF7L2 deficiency led to reduced proliferation, reminiscent of the physiological role of TCF7L2. To provide a molecular framework for the observed phenotypic changes, we performed global transcriptome profiling. This identified gene-regulatory networks in which TCF7L2 positively regulates the proto-oncogene MYC, while repressing the cell cycle inhibitors CDKN2C/CDKN2D. TCF7L2 also suppresses the pro-metastatic transcription factor RUNX2 and several integrin genes, which is consistent with increased motility and collagen adhesion of TCF7L2-deficient cells. Altogether, we conclude that the proliferation-stimulating activity of TCF7L2 persists in CRC cells. Additionally, TCF7L2 acts as invasion suppressor. Despite its negative impact on cell cycle progression, TCF7L2 loss-of-function may thereby increase malignancy, which could explain why TCF7L2 is mutated in a sizeable fraction of colorectal tumors. TCF7L2 knockout (KO) clones were generated using the CRISPR/Cas9 system targeting exon 6 in HCT116 and HT29 cells. RNA from one wild-type (WT) and one knockout clone was processed and submitted for sequencing for HCT116 cells. For HT29 cells, RNA from one wild-type, one heterozygous (Het), and three knockout clones was processed and submitted for sequencing. In all cases, RNA-seq data from two independent biological replicates were collected.