Identification of β-catenin binding regions in colon cancer cells using ChIP-Seq

Deregulation of the Wnt/beta-catenin signaling pathway is a hallmark of colon cancer. Mutations in the adenomatous polyposis coli (APC) gene occur in the vast majority of colorectal cancers and are an initiating event in cellular transformation. Cells harboring mutant APC contain elevated levels of the beta-catenin transcription coactivator in the nucleus which leads to abnormal expression of genes controlled by beta-catenin/T-cell factor 4 (TCF4) complexes. Here, we use chromatin immunoprecipitation coupled with massively parallel sequencing (ChIP-Seq) to identify beta-catenin binding regions in HCT116 human colon cancer cells. We localized 2168 beta-catenin enriched regions using a concordance approach for integrating the output from multiple peak alignment algorithms. Motif discovery algorithms found a core TCF4 motif (T/A-T/A-C-A-A-A-G), an extended TCF4 motif (A/T/G-C/G-T/A-T/A-C-A-A-A-G) and an AP-1 motif (T-G-A-C/T-T-C-A) to be significantly represented in beta-catenin enriched regions. Furthermore, 417 regions contained both TCF4 and AP-1 motifs. Genes associated with TCF4 and AP-1 motifs bound beta-catenin, TCF4 and c-Jun in vivo and were activated by Wnt signaling and serum growth factors. Our work provides evidence that Wnt/beta-catenin and mitogen signaling pathways intersect directly to regulate a defined set of target genes.