miR-340 reverses chemotherapy resistance in colon cancer via the PDCD4/WNT/β-catenin signalling pathway

The silencing of miR-340 has been implicated in the progression and migratory capacity of colorectal cancer (CRC); however, its role in modulating oxaliplatin-induced chemotherapy resistance in CRC remains largely unexplored. In this study, we investigated the influence of miR-340 on oxaliplatin resistance in CRC and elucidated the underlying molecular mechanisms. Oxaliplatin-resistant HCT116 (HCT116-OxR) and CT26 (CT26-OxR) cells were induced with 20 ng/mL oxaliplatin for approximately 7 months. The viability of the treated cells was detected by a CCK-8 assay. Apoptosis was determined via flow cytometry. The mRNA and protein expression levels of resistance-related genes were assessed via qRT‒PCR and western blotting (WB), respectively. P-gp expression in HCT116-OxR and HCT116-OxR-miR-506 cells was determined by immunofluorescence (IF) staining. The expression of WNT/β-catenin pathway molecules was determined by qRT‒PCR and WB. The targeted effect of miR-340 on PDCD4 was detected by a Gaussia luciferase secretion assay. miR-340 is downregulated in HCT116-OxR and CT26-OxR cells. Intriguingly, forced expression of miR-340 led to reduced viability in HCT116-OxR and CT26-OxR cells. Furthermore, the upregulation of miR-340 enhanced apoptosis but mitigated the migratory and invasive potential of HCT116-OxR cells. Additionally, miR-340 inhibited the mRNA and protein levels of Bcl-2 while increasing the expression of BAX in HCT116-OxR cells. miR-340 also downregulated the expression of resistance-associated genes and proteins in HCT116-OxR cells. Upon exploring the underlying mechanism further, we discovered that miR-340 also inhibited key components of the WNT/β-catenin signalling pathway, such as WNT5a, WNT5b, β-catenin, c-Myc, and cyclin D1, in HCT116-OxR cells. These findings suggest that miR-340 contributes to overcoming oxaliplatin resistance in CRC, at least partially through downregulation of the WNT/β-catenin pathway. Moreover, miR-340 directly targeted PDCD4 and promoted its transcription. In summary, our findings underscore the potential of miR-340 as a modulator of oxaliplatin resistance in CRC by suppressing the PDCD4/WNT/β-catenin signalling pathway, thereby offering new insights into therapeutic strategies aimed at improving the efficacy of chemotherapy in CRC.