Exosome-mediated transfer of circ_0063526 enhances cisplatin resistance in gastric cancer cells via regulating miR-449a/SHMT2 axis

Exosomes are critical mediators of intercellular communication. Exosomal circular RNAs (circRNAs) have been reported to play critical roles in the development of chemoresistance in various tumors, including gastric cancer. However, the role of exosomal circ_0063526 in cisplatin (CDDP) resistance of gastric cancer is still unclear. The expression of circ_0063526, microRNA-449a (miR-449a) and serine hydroxymethyltransferase 2 (SHMT2) mRNA was determined by quantitative real-time PCR (qRT-PCR). Cell viability was assessed by the Cell Counting Kit-8 assay. Cell migration and invasion were evaluated by the transwell assay and wound healing assay. Western blot assay was used to measure the protein expression of light Chain 3 (LC3) I/II, p62 and SHMT2. Exosomes were detected using transmission electron microscopy. The size distribution of exosomes was analyzed by nanoparticle tracking analysis. The interaction between miR-449a and circ_0063526 or SHMT2 was confirmed by a dual-luciferase reporter and RNA pull-down assays. Circ_0063526 expression was increased in gastric cancer tissues and cells and CDDP-resistant cells. Extracellular circ_0063526 could be packaged into exosomes and transmitted to sensitive cells, thus disseminating CDDP resistance. Knockdown of exosomal circ_0063526 inhibited CDDP resistance via suppressing migration, invasion and autophagy in gastric cancer cells. Moreover, circ_0063526 was identified as a molecular sponge of miR-449a to upregulate SHMT2 expression. Further, exosomal circ_0063526 regulated SHMT2 expression to enhance CDDP resistance of gastric cancer cells. Additionally, high expression of exosomal circ_0063526 in serum was associated with poor response to CDDP treatment in gastric cancer patients. Exosomal circ_0063526 facilitated CDDP resistance in gastric cancer via regulating the miR-449a/SHMT2 axis.