Objective: The present study aims to investigate microRNAs (miRNAs) and messenger RNAs (mRNAs) associated with breast cancer, and to have a better understanding of the mechanism of miRNAs in breast cancer using bioinformatics tools. </p> <p>Methods: Microarray analysis was performed to predict differentially expressed miRNAs related to breast cancer, followed by prediction and verification of target genes. Human breast cancer cells were transfected and divided into Blank group, NC group, miR-21-5p mimic group, miR-21-5p inhibitor group and siRNA-MAPK10 group. RT-qPCR and Western blot analysis were used to detect mRNA and protein expressions of MAPK10 in tissues and transfected cells, MTT assay, scratch test and Transwell assay for detection of the proliferation, migration and invasion, and Annexin-V-R-PE assay for apoptosis of different cell lines.</p> <p>Results: Highly expressed miR-21-5p and lowly expressed MAPK10 were selected for subsequent experiments, according to the microarray analysis. RT-qPCR showed that the expression of MAPK10 in breast cancer tissues was significantly lower than that in adjacent tissues, while it was reciprocal in expression of miR-21. miR-21-5p negatively regulated MAPK10. The expression of MAPK10 reduced in response to miR-21-5p mimic treatment. Compared with the Blank and NC groups, the proliferation, migration, invasion and metastasis of breast cancer cells decreased, and the apoptosis of breast cancer cells increased in the miR-21-5p inhibitor group and siRNA-MAPK10 group, while it was reciprocal in the miR-21-5p mimic group.</p> <p>Conclusion: MiR-21 promotes the proliferation, migration and invasion and inhibits the apoptosis of breast cancer cells by inhibiting MAPK10.

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