Depletion of death-associated protein-3 induces chemoresistance in gastric cancer cells through the ß-catenin/LGR5/Bcl-2 axis

Previously, we demonstrated that death-associated protein-3 (DAP3) loss drives chemoresistance in gastric cancer cells. In the present study, we aimed to determine the underlying molecular mechanism. The effect of DAP3 silencing on ß-catenin signaling was assessed. The direct mediator of DAP3 silencing-induced chemoresistance was identified. Depletion of DAP3 stimulates nuclear accumulation of ß-catenin and enhances ß-catenin-dependent transcriptional activity in gastric cancer cells. However, the protein kinase B,, extracellular regulated protein kinase and signal transducer and activator of transcription 3 signaling pathways remain unaffected by DAP3 loss. We found that the downstream target gene LGR5 (leucine-rich G-protein coupled receptor 5) is upregulated in DAP3-depleted gastric cancer cells. Moreover, knockdown of LGR5 resensitizes DAP3-depleted gastric cancer cells to 5-fluorouracil (5-FU) and oxaliplatin. We also observed that ectopic expression of LGR5 reduces apoptosis in gastric cancer cells on treatment with 5-FU and oxaliplatin, which is accompanied by prevention of caspase-3 cleavage. The antiapoptotic protein Bcl-2 is identified as a key mediator of LGR5-induced apoptosis resistance in gastric cancer cells. The present findings indicate that DAP3 deficiency-induced chemoresistance in gastric cancer is at least partially mediated through the ß-catenin/LGR5/Bcl-2 axis. Targeting LGR5 may provide a novel strategy to overcome chemoresistance in DAP3-deficient gastric cancer cells.