Abstract: Background and purpose: MicroRNA (miRNA) is closely related to the occurrence and development of tumors. This study aimed to investigate the expression of miR-6775-3p in breast cancer cells and its effect on the biological characteristics of breast cancer cells. Methods: Real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) was used to detect the expression level of miR-6775-3p in four breast cancer cell lines MDA-MB-231, MDA-MB-453, MDA-MB-468 and BT-549. After miR-6775-3p was over-expressed in breast cancer cells with the lowest expression level of miR-6775-3p, the proliferation of cells was detected by cell counting kit-8 (CCK-8) assay, and the migration and invasion ability of cells were detected by transwell migration and invasion assay. To further explore the molecular mechanism of miR-6775-3p in breast cancer, the expressions of cyclin-dependent protein kinase 4 (CDK4), CDK6 and invasion and metastasis markers matrix metalloproteinase 17 (MMP17) and MMP24 in miR-6775-3p overexpressing breast cancer cells were detected by RTFQ-PCR and Western blot. Results: RTFQ-PCR results showed that the expression of miR-6775-3p was the lowest in breast cancer cell line MDA-MB-453, and the expression level of miR-6775-3p was significantly increased after transfection of miR-6775-3p mimics in MDA-MB-453 cells (P<0.001). CCK-8 assay results showed that the cell proliferation activity was significantly decreased after miR-6775-3p was overexpressed in MDA-MB-453 cells (P<0.01). Transwell migration and invasion assay results showed that the cell migration (P<0.001) and invasion abilities (P<0.01) were significantly decreased after miR-6775-3p was over-expressed in MDA-MB-453 cells. RTFQ-PCR and Western blot results showed that the expressions of cyclin-dependent protein kinases CDK4 and CDK6, as well as the mRNA and protein levels of cell invasion and metastasis markers MMP17 and MMP24 were significantly decreased (P<0.01). Conclusion: miR-6775-3p may inhibit the proliferation, migration and invasion of breast cancer cells.

Key words: miR-6775-3p, Breast cancer, Proliferation, Migration, Invasion