FOXD1 promotes chemotherapy resistance by enhancing cell stemness in colorectal cancer through β‑catenin nuclear localization

Forkhead box D1 (FOXD1) serves a critical role in colorectal cancer (CRC). FOXD1 expression is an independent prognostic factor in patients with CRC; however, the molecular mechanism and signaling pathway of FOXD1 that regulates cell stemness and chemoresistance has not been fully characterized. The aim of the present study was to further validate the effect of FOXD1 on the proliferation and migration of CRC cells, and to delve into the possible potential of FOXD1 in the clinical treatment of CRC. The effect of FOXD1 on cell proliferation was assessed using Cell Counting Kit 8 (CCK-8) and colony formation assays. The effect of FOXD1 on cell migration was assessed by wound-healing and Transwell assays. The effect of FOXD1 on cell stemness was assessed by spheroid formation in vitro and limiting dilution assays in vivo. The expression of stemness associated proteins, leucine rich repeat containing G protein-coupled receptor 5 (LGR5), OCT4, Sox2 and Nanog, and epithelial-mesenchymal transition associated proteins, E-cadherin, N-cadherin and vimentin, were detected by western blotting. Proteins interrelationships were assessed by a co-immunoprecipitation assay. Oxaliplatin resistance was assessed using CCK-8 and apoptosis assays in vitro, and using a tumor xenograft model in vivo. By constructing FOXD1 overexpression and knockdown stably transfected strains of colon cancer cells, it was revealed that the overexpression of FOXD1 increased CRC cell stemness and chemoresistance. By contrast, knockdown of FOXD1 produced the opposite effects. These phenomena were caused by the direct interaction between FOXD1 and β-catenin, thus promoting its nuclear translocation and the activation of downstream target genes, such as LGR5 and Sox2. Notably, inhibition of this pathway with a specific β-catenin inhibitor (XAV-939) could impair the effects induced by the overexpression of FOXD1. In summary, these results indicated that FOXD1 may promote cell stemness and the chemoresistance of CRC by binding directly to β-catenin and enhancing β-catenin nuclear localization; therefore, it may be considered a potential clinical target.