TFAP2E methylation promotes 5‑fluorouracil resistance via exosomal miR‑106a‑5p and miR‑421 in gastric cancer MGC‑803 cells

: Hypermethylation of transcription factor activating enhancer‑binding protein 2e (TFAP2E) has been reported to be associated with chemoresistance to 5‑fluorouracil (5‑FU) in gastric cancer (GC). In the present study, the molecular mechanism governing this chemoresistance was investigated. Drug‑resistant human GC MGC‑803/5‑FU cells were established and TFAP2E expression and methylation levels were assessed. Autocrine exosomes from GC culture medium were isolated and characterized. MicroRNA (miRNA) microarray analysis was used to determine the miRNA expression profile of GC cell‑derived exosomes. Exosomes collected from MGC‑803/5‑FU cells were co‑cultured with control cells, and 5‑Aza‑2'‑deoxycytidine (5Aza) was added into MGC‑803/5‑FU cells to investigate the relationship between TFAP2E, exosomes and chemosensitivity. In the present study, it was demonstrated that hypermethylation of TFAP2E resulted in its reduced expression and 5‑FU chemoresistance in GC cells. miRNAs miR‑106a‑5p and miR‑421 were highly expressed and regulated the chemoresistance induced by TFAP2E methylation. Target gene prediction using miRBase, TargetScan and PicTar revealed that E2F1, MTOR and STAT3 may be TFAP2E target genes in GC. Collectively, our data support an important role of exosomes and exosomal miRNAs in TFAP2E methylation‑induced chemoresistance to 5‑FU in GC. These results highlight their potential for miRNA‑based therapeutics.