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Background: Chemotherapy can significantly improve the disease‐free survival and overall survival of patients with advanced gastric cancer (GC). 5‐fluorouracil (5‐FU) is frequently applied in the clinic, acting as a first‐line chemotherapy drug of advanced GC, which could be used alone or combining platinum drugs. However, its efficacy is significantly attenuated by chemoresistance, which is associated with patients' poor survival. Recently, there is evidence suggesting that dysregulation of autophagy may contribute to drug resistance in cancer, and circular RNAs (circRNAs) also take part in chemoresistance. However, whether circRNAs participate in 5‐FU chemoresistance through autophagy remains largely unknown. Methods: RNA sequencing technologies and bioinformatics analysis were performed in GC. Sanger sequencing, Actinomycin D assay and RNase R assay confirmed the circular structure of circular CPM (circCPM). Various cell line models and animal models were used to explore related functions in vitro and in vivo. Quantitative Real‐time PCR (qRT‐PCR), fluorescence in situ hybridization, ribonucleic acid; (RNA) pulldown assays, RNA binding protein immunoprecipitation assays and Luciferase reporter assays were applied to explore involved pathways. Results: circCPM was up‐regulated in 5‐FU resistant GC cell lines and tissue. Moreover, high circCPM expression is positively associated with poor survival. Silencing circCPM greatly improved chemosensitivity in vitro and in vivo. Mechanistically, it directly binds to miR‐21‐3p in the cytoplasm and therefore increases the expression of PRKAA2, contributing to the activation of autophagy and chemoresistance. Conclusion: Our results reveal that circCPM has a crucial role in regulating GC autophagy and 5‐FU resistance by targeting PRKAA2. It may function as a new theory basis for assessing the curative effect of GC and reversing 5‐FU chemoresistance. [ABSTRACT FROM AUTHOR]

Gastric cancer (GC) ranks third in mortality among all cancers worldwide. Circular RNAs (circRNAs) play an important role in the occurrence and development of gastric cancer. Forkhead box P2 (FOXP2), as a transcription factor, is closely associated with the development of many types of tumours. However, the regulatory network between FOXP2 and circRNAs remains to be explored. In our study, circST3GAL6 was significantly downregulated in GC and was associated with poor prognosis in GC patients. Overexpression of circST3GAL6 inhibited the malignant behaviours of GC cells, which was mediated by inducing apoptosis and autophagy. In addition, we demonstrated that circST3GAL6 regulated FOXP2 through the mir‐300 sponge. We further found that FOXP2 inhibited MET Proto‐Oncogene (MET), which was the initiating factor that regulated the classic AKT/mTOR pathway of autophagy. In conclusion, our results suggested that circST3GAL6 played a tumour suppressive role in gastric cancer through miR‐300/FOXP2 axis and regulated apoptosis and autophagy through FOXP2‐mediated transcriptional inhibition of the MET axis, which may become a potential target for GC therapy. [ABSTRACT FROM AUTHOR]