Abstract: Objective To examine the role of miR-16-5p in regulating biological behaviors of paclitaxel-resistant breast cancer cells and its molecular mechanism. Methods The expression of miR-16-5p was examined in 13 pairs of breast cancer and adjacent tissues and in parental SKBR-3 cells and paclitaxel-resistant SKBR-3/PR cells using qRT-PCR. The target genes of miR-16-5p were predicted by bioinformatic analysis, and their targeted binding was tested using luciferase assay. The cells were transfected with a miR-16-5p mimics, a miR-16-5p inhibitor, a specific siRNA targeting YWHAQ (si-YWHAQ), or both the miR-16-5p mimics and si-YWHAQ, and the changes in cellular expressions of YWHAQ, Bcl-2 and Bax were detected using Western blot. The changes in proliferation and migration of the cells were evaluated with CCK-8 assay and Transwell assay, and the cell cycle changes and cell apoptosis were analyzed with flow cytometry. Results The expression of miR-16-5p was significantly lower in breast cancer tissues than in paired adjacent tissues (P<0.01). Bioinformatic analysis predicted that YWHAQ was the target gene of miR-16-5p, which was confirmed by luciferase assay. Compared with parental SKBR-3 cells, SKBR-3/PR cells showed a lowered level of miR-16-5p expression and an increased expression of YWHAQ. Transfection with the miR-16-5p mimics significantly inhibited YWHAQ expression (P<0.01), while miR-16-5p inhibitor promoted YWHAQ expression in SKBR-3/PR cells (P<0.01). The miR-16-5p mimics caused cell cycle arrest in G0/G1 phase (P<0.0l), suppressed proliferation and migration, and increased apoptosis rate of SKBR-3/PR cells (P<0.0l). Knocking down YWHAQ also reduced the migration ability of SKBR-3/PR cells and increased cell apoptosis rate. Transfection with either miR-16-5p mimics or si-YWHAQ resulted in increased Bax expression and lowered expressions of YWHAQ and Bcl-2 in the cells. The cells transfected with both miR-16-5p mimics and si-YWHAQ showed obviously suppressed cell migration (P<0.01) and significantly increased apoptosis rate (P<0.01). Conclusion miR-16-5p can modulate the expressions of Bcl- 2 and Bax by targeted regulation of YWHAQ to modify the biological behaviors of paclitaxel-resistant breast cancer cells.

Key words: breast cancer; drug resistance; miR-16-5p; YWHAQ