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MicroRNA-520c-3p negatively regulates EMT by targeting IL-8 to suppress the invasion and migration of breast cancer.

Interleukin-8 (IL-8), which is secreted by cancer cells undergoing epithelial-mesenchymal transition (EMT), can promote EMT in adjacent epithelial-like cells. MicroRNAs (miRNAs/miRs) can affect the expression of target genes via binding to their 3'-untranslated regions (3'-UTRs), which may subsequently affect the biological behaviors of cancer cells. In our previous study, miR-520c-3p was predicted to directly target the 3'-UTR of IL-8. Therefore, the present study was carried out to investigate whether miR-520c-3p can interact with the IL-8 gene and regulate the EMT of breast cancer cells. Web-based prediction algorithms were used to identify miRNAs that potentially target the IL-8 transcript. Luciferase reporter assays were used to confirm the targeting of IL-8 by miR-520c-3p. Reverse transcription-quantitative PCR and western blot analyses were used to examine the levels of IL-8 and EMT-related genes in breast cancer cells. The functional impact of miR-520c-3p on EMT phenotype was evaluated using Transwell and wound-healing assays, and rescue experiments were conducted by overexpressing IL-8 to determine its effect on cell properties. miR-520c-3p was predicted by all three databases, which strongly suggested its interaction with the 3'-UTR of IL-8. The relative Renilla luciferase activity of luciferase reporter construct containing the wild-type 3'-UTR of IL-8 was markedly decreased by miR-520c-3p transfection when compared with scrambled miRNA control transfection (P<0.001). In addition, compared with the scrambled miRNA control transfection, the overexpression of miR-520c-3p significantly reduced the expression of IL-8, and resulted in increased E-cadherin and decreased vimentin and fibronectin levels in MCF-7 and T47D cells (all P<0.001). Introduction of miR-520c-3p inhibited the invasion and migration of MCF-7 and T47D cells (all P<0.001). By contrast, the rescue of IL-8 expression led to the recovery of EMT-related protein expression patterns and cell motility and invasion capabilities. In conclusion, aberrant miR-520c-3p expression may lead to reduced IL-8 expression and promote the mesenchymal phenotype in breast cancer cells, thereby increasing invasive growth.