Abstract: Objective To investigate the regulatory effect of miR-4324 on ankyrin 2 (Talin2) expression and biological behaviors of breast cancer cells and the clinical implications of changes in miR-4324 and Talin2 expressions in breast cancer. Methods In breast cancer and adjacent tissues, the expressions of Talin2 and miR-4324 were examined with immunohistochemistry and qRT-PCR, respectively and the association of Talin2 expression levels with the prognosis and clinicopathological features of breast cancer patients was analyzed. The human breast cancer cell line SKBR-3 was transfected with miR-4324 mimic, miR-4324 inhibitor, si-Talin2, or both miR-4324 inhibitor and si-Talin2, and the changes in biological behaviors of the cells were examined; the cellular expression of Talin2at the mRNA and protein levels were detected with qRT-PCR and Western blotting. Dual luciferase reporter gene assay was used to verify the targeting relationship between miR-4324 and Talin2. The effect of miR-4324-mediated regulation of Talin2 on SKBR-3 cell migration was assessed using Transwell assays. Results Talin2 expression was significantly higher in breast cancer tissues than in the adjacent tissues, and its expression level was correlated with lymph node metastasis and high HER-2 expression in breast cancer (P<0.05) but not with the patient's age, clinical stage, histological grade or expressions of estrogen and progesterone receptors (P>0.05). The expression of miR-4324 was significantly reduced in breast cancer tissues as compared with the adjacent tissues (P<0.01). In SKBR-3 cells, transfection with miR-4324 mimics significantly inhibited proliferation, migration and invasion (P<0.05) and promoted apoptosis (P<0.01) of the cells. Dual luciferase reporter gene assay confirmed that cotransfection with miR-4324 mimics significantly reduced luciferase activity of Talin2-3'-UTR WT reporter plasmid (P<0.05). Transfection of the cells with miR-4324 mimics significantly reduced mRNA and protein expressions of Talin2 (P<0.05). Transwell migration assay showed that the migration ability of SKBR-3 cells was significantly enhanced after transfection with miR- 4324 inhibitor (P<0.01), lowered after transfection with si-Talin2 (P<0.01), and maintained at the intermediate level after co-transfection with miR-4324 inhibitor + si-Talin2 group (P<0.05). Conclusions High expression of Talin2 is associated with lymph node metastasis and HER-2 overexpression in breast cancer patients. Down-regulation of miR-4324 inhibits the proliferation, invasion and migration and induces apoptosis of breast cancer cells, and the inhibitory effect of miR-4324 knockdown on breast cancer cell migration is mediated probably by targeted inhibition of Talin2 expression.

Key words: breast cancer; miR-4324; Talin2