FZD6 promotes 5-fluorouracil resistance through inhibiting pyroptosis in colorectal cancer

Resistance to 5-fluorouracil (5-FU) causes treatment failure in most colorectal cancer (CRC) cases. Pyroptosis is associated with chemotherapy resistance, although its role in 5-FU resistance in CRC is not well understood. To investigate this, we performed proteomic sequencing and bioinformatics analysis on wild-type and 5-FU-resistant CRC cell lines. Subsequently, Frizzled receptor 6 (FZD6) knockdown and overexpression cell lines were established using a lentiviral system. CCK-8, colony formation, and EdU assays were performed to assess the viability and proliferative potential of 5-FU-treated cells. The morphological changes associated with pyroptosis were examined by microscopic imaging and electron microscopy. The nuclear expression of β-catenin was examined by immunofluorescence and western blotting. These findings indicated that FZD6 protein was upregulated in the 5-FU-resistant CRC cells compared with the corresponding wild-type cell lines, an observation further validated through immunohistochemical analysis of clinical samples. Additionally, 5-FU treatment induced NLRP3/caspase-1/GSDMD-mediated classical pyroptosis in the wild-type CRC cells and decreased their viability, while the pyroptosis inhibitor Ac-FITD-CMK enhanced drug resistance. Furthermore, overexpression of FZD6 promoted nuclear translocation of β-catenin, reduced pyroptosis, and increased 5-FU resistance. In contrast, 5-FU treatment did not induce significant pyroptosis in drug-resistant cells, while pyroptosis inducers (nigericin or LPS + ATP) significantly reduced cell viability regardless of 5-FU. Moreover, knockdown of FZD6 decreased nuclear translocation of β-catenin, enhanced pyroptosis, and reduced 5-FU resistance. Finally, β-catenin knockdown enhanced pyroptosis and decreased 5-FU resistance. Thus, FZD6 promotes 5-FU resistance in CRC cells by inhibiting pyroptosis through increased nuclear translocation of β-catenin.