Exosome-mediated transfer of circ_0000338 enhances 5-FU resistance in colorectal cancer through regulating miR-217 and miR-485-3p

ABSTRACT

Background: Exosomes are microvesicles secreted by body cells for intercellular communication. Circular RNA circ_0000338 was found to present in extracellular vesicles and improve the chemo-resistance of colorectal cancer (CRC) cells. However, the role of exosomal circ_0000338 in 5-Fluorouracil (5-FU)-resistance in CRC is largely unknown.

Methods: The levels of circ_0000338, microRNA (miR)-217 and miR-485-3p were detected using the qRT-PCR. The IC₅₀ values of cells to 5-FU, cell proliferation and apoptosis were evaluated using CCK-8, colony formation, flow cytometry and western blot assays. The interaction between miR-217 or miR-485-3p and circ_0000338 was confirmed by RIP, dual-luciferase reporter and pull-down assays. Exosomes were isolated by ultracentrifugation, and qualified by transmission electron microscopy (TEM), nanosight tracking analysis (NTA) and western blot. Xenograft models were performed to analyze whether circ_0000338 loaded exosomes could re-resist CRC cells to 5-FU in vivo.

Results: Circ_0000338 was elevated in 5-FU-resistant CRC tissues and cells, and circ_0000338 knockdown sensitized 5-FU-resistant CRC cells to 5-FU through enhancing apoptosis and decreasing proliferation in vitro. Mechanistically, circ_0000338 directly bound to miR-217 and miR-485-3p, and the inhibition of miR-217 or miR-485-3p reversed the effects of circ_0000338 knockdown on cell 5-FU resistance in CRC. Additionally, extracellular circ_0000338 could be incorporated into secreted exosomes and transmitted to 5-FU-sensitive cells. Treatment-sensitive cells with exosomes containing circ_0000338 reduced 5-FU response in CRC both in vitro and in vivo. Besides that, exosomal circ_0000338 was higher in patients exhibiting resistance to 5-FU, and showed well diagnostic efficiency in 5-FU resistant CRC.

Conclusion: The delivery of circ_0000338 via exosomes enhanced 5-FU resistance in CRC through negative regulation of miR-217 and miR-485-3p, indicating a promising diagnostic and therapeutic marker for 5-FU-based chemotherapy in CRC patients.