Objective  To investigate the mechanisms of microRNA-31-5p (miR-31-5p) and special AT-rich sequence-binding protein 2 (SATB2) expression in breast cancer, and their effects on breast cancer cell proliferation and migration.

  Methods  The clinicopathological data of 80 patients with breast cancer who underwent surgical resection in General Hospital of Tianjin Medical University from March 2017 to December 2020 were retrieved. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to detect the expression of miR-31-5p and SATB2 transcripts in breast cancer tissues and cell lines. The dual luciferase assay was employed to determine the interaction between miR-31-5p and SATB2 mRNA. For the in vitro studies, the breast cancer cells were transfected with either miR-31-5p-agomir-NC, miRNA-31-5p-agomir, or miRNA-31-5p-agomir in combination with pcDNA3.1-SATB2 constructs. Cells with no intervention constituted the normal group. The EDU staining and Transwell chamber migration assays were performed to detect in vitro proliferation and metastasis activity in each group of cells. The in vitro findings were further validated in vivo by subcutaneous implantation of breast cancer cells in nude mice, to detect the growth and metastasis potential of the breast cancer cells in vivo. Western blot was used to detect the expression of SATB2, E-cadherin, and Vimentin.

  Results  The expression of miRNA-31-5p was decreased, whereas, the expression of SATB2 was increased in breast cancer tissues and breast cancer cells compared with that in adjacent tissues and normal breast cells. The dual luciferase assays revealed that miRNA-31-5p can target the expression of SATB2. Furthermore, the cell proliferation and migration potential as well as the expression of SATB2 and Vimentin in miR-31-5p-agomir-transfected breast cancer cells were significantly decreased compared with those of normal breast cancer cells both in vitro as well as in vivo. However, the expression of E-cadherin was increased in the miRNA-31-5p-agomir-transfected breast cancer cells compared with that in normal breast cancer cells. Interestingly, these effects were partially reversed in the pcDNA3.1-SATB2- transfected breast cancer cells and the differences were statistically significant (all P < 0.05).

  Conclusions  The expression of miR-31-5p was decreased while that of SATB2 was increased in breast cancer. Furthermore, overexpression of miRNA-31-5p can significantly inhibit the proliferation and migration of MDA-MB-231 cells in vitro, and their growth and metastasis in vivo. However, transfection of these cells with pcDNA3.1-SATB2 can partially reverse this inhibitory effect.