Purpose: Diverse circular RNAs (circRNAs) participate in the regulation of drug resistance in human cancers. However, the role of circRNAs in drug resistance in colorectal cancer (CRC) is dismal. In this study, we aimed to explore the effect of circ-PRKDC on 5-fluorouracil (5-FU) resistance in CRC.
Materials and Methods: The levels of circ-PRKDC, microRNA-375 (miR-375) and forkhead box protein M1 (FOXM1) mRNA were determined by quantitative real-time polymerase chain reaction (qRT-PCR). IC₅₀ of 5-FU, cell colony formation ability and invasion were assessed by Cell Counting Kit-8 (CCK-8) assay, colony formation assay and transwell assay, respectively. The protein levels of P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), FOXM1, β-catenin and c-Myc were measured via Western blot assay. The targeting relationship between miR-375 and circ-PRKDC or FOXM1 was investigated by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. The effect of circ-PRKDC in vivo was explored by murine xenograft model assay.
Results: Circ-PRKDC was upregulated in 5-FU-resistant CRC tissues and cells. Circ-PRKDC silencing repressed 5-FU resistance, cell colony formation and invasion in 5-FU-resistant CRC cells in vitro and inhibited 5-FU resistance in vivo. MiR-375 was a target of circ-PRKDC and miR-375 inhibition reversed the effects of circ-PRKDC silencing on 5-FU resistance, cell colony formation and invasion. FOXM1 was a direct target gene of miR-375. MiR-375 suppressed 5-FU resistance by targeting FOXM1. Moreover, circ-PRKDC knockdown decreased FOXM1 expression by targeting miR-375. Additionally, circ-PRKDC knockdown impeded wnt/β-catenin pathway by regulating miR-375 and FOXM1.
Conclusion: Circ-PRKDC enhanced 5-FU resistance in CRC by regulating FOXM1/miR-375 axis and wnt/β-catenin pathway.
Keywords: CRC, 5-FU, circ-PRKDC, miR-375, FOXM1, wnt/β-catenin