MicroRNA‐99a‐5p suppresses breast cancer progression and cell‐cycle pathway through downregulating CDC25A

In this study, we aimed to explore the association between miR‐99a‐5p and CDC25A in breast cancer and the regulatory mechanisms of miR‐99a‐5p on breast cancer. The expressions of messenger RNA and microRNAs in breast cancer tissues and adjacent tissues were analyzed by the Cancer Genome Atlas microarray analysis. Quantitative real‐time polymerase chain reaction was conducted to find out the expression levels of miR‐99a‐5p and CDC25A. The expression levels of proteins (CDC25A, ki67, cyclin D1, p21, BAX, BCL‐2, BCL‐XL, MMP2, and MMP9) were determined by Western blot analysis. The relationship between miR‐99a‐5p and CDC25A was predicted and verified by bioinformatics analysis and dual luciferase assay. After transfection, cell proliferation, invasion, and apoptosis of breast cancer tissues were, respectively, observed by cell counting kit‐8 assay, transwell assay, and flow cytometry (FCM). Furthermore, the relationship among miR‐99a‐5p, CDC25A, and cell‐cycle progression was determined by FCM assay. The nude mouse transplantation tumor experiment was performed to verify the influence of miR‐99a‐5p on breast cancer cell in vivo. The expression of miR‐99a‐5p in breast cancer tissues and cells was significantly downregulated, whereas CDC25A expression was upregulated. MiR‐99a‐5p targeted CDC25A and suppressed its expression in breast cancer cells. Overexpression of miR‐99a‐5p and decreased expression of CDC25A could suppress breast cancer cell proliferation and invasion and facilitate apoptosis. Cell‐cycle progression was significantly activated by downregulated miR‐99a‐5p and upregulated CDC25A. Moreover, miR‐99a‐5p overexpression repressed the expressions of CDC25A, marker ki67, and Cyclin D1 proteins, whereas it upregulated the expression of p21 protein. MicroRNA‐99a‐5p suppresses breast cancer progression and cell‐cycle pathway through downregulating CDC25A. Overexpression of SIRT1 increases myonuclear density and thus reduces myonuclear domain sizes; conversely, ablation of SIRT1 decreases myonuclear density and thus increases myonuclear domain volumes. Altered satellite cell numbers might explain such a modulation of myonuclear density within muscle fibers.