TCF7L1 regulates colorectal cancer cell migration and invasion by repressing GAS1 expression (RNA-Seq)
Dysregulation of the canonical Wnt/ß-catenin signaling pathway is a hallmark of colorectal cancer (CRC). The T-cell factor/lymphoid enhancer factor (TCF/LEF; hereafter, TCF) family of transcription factors are critical regulators of canonical Wnt/ß-catenin target gene expression. Despite similarity across DNA-binding and protein-binding domains, TCF family members differentially regulate target gene expression in CRC. Of the four TCF family members, TCF7L1 predominantly functions as a transcriptional repressor and it has an oncogenic role in CRC. Despite this role, few target genes regulated by TCF7L1 in CRC have been identified. Through RNA-sequencing of transcripts differentially expressed in control and TCF7L1-overexpressing HCT116 cells, we identified 397 genes that were repressed directly, or indirectly, by TCF7L1. Gene set enrichment analysis found genes associated with epithelial-mesenchymal transition amongst those that are differentially expressed. By silencing and overexpressing TCF7L1 in CRC cell lines, we found that TCF7L1 promoted migration, invasion, and adhesion in vitro. Chromatin immunoprecipitation followed by sequencing (ChIP-sequencing) localized 3661 TCF7L1 binding sites within the CRC genome. Comparison of genes whose expression was downregulated by TCF7L1 and genes with TCF7L1 binding sites revealed 41 novel targets directly regulated by TCF7L1. Among these, we localized a TCF7L1 promoter-proximal binding site within the growth arrest specific 1 (GAS1) gene. We found that ectopic GAS1 expression rescued the TCF7L1-mediated increase in migration and invasion in CRC cells. These findings uncover a novel role for TCF7L1 in repressing GAS1 expression to promote migration and invasion of CRC cells in vitro. Overall design: To investigate the genes regulated directly or indirectly by TCF7L1, we establed stable HCT116 cell lines that expressed Dox-inducible pCW57.1-empty vector, pCW57.1-TCF7L1, pCW57.1-TCF7L1-MUT We utilized lentiviral delivery of shTCF7L1-2 to knockdown endogenous TCF7L1. We treated stable cell lines with Dox to induce expression of an shRNA-resistant TCF7L1 or TCF7L1-MUT Comparison of differentially expressed genes, gene set enrichment analysis, and gene ontology using data obstained from RNA-sequencing