MicroRNA‑299‑5p inhibits cell metastasis in breast cancer by directly targeting serine/threonine kinase 39.

Numerous studies have demonstrated that microRNAs (miRNAs) play a key role in human carcinogenesis and metastasis. For example, miR‑299‑5p has previously been revealed to be dysregulated in several human cancers. However, the biological function of miR‑299‑5p in breast cancer remains unclear. The present study demonstrated that miR‑299‑5p was downregulated in breast cancer tissues and cell lines. The restoration of miR‑299‑5p expression suppressed cell migration and invasion, whereas inhibition of miR‑299‑5p promoted cell migration and invasion. In addition, in vivo studies demonstrated that miR‑299‑5p overexpression was able to inhibit tumour metastasis in nude mice. Mechanistically, through bioinformatics analysis and a dual‑luciferase assay, it was confirmed that miR‑299‑5p directly targets serine/threonine kinase 39 (STK39). Silencing STK39 inhibited cell metastasis and suppressed epithelial‑mesenchymal transition markers and matrix metalloproteinase expression, whereas restoration of STK39 expression was able to reverse miR‑299‑5p‑inhibited cell migration and invasion. Collectively, the results of the present study demonstrated that miR‑299‑5p supresses breast cancer cell migration and invasion by targeting STK39. These findings may provide novel insights into miR‑299‑5p and its potential diagnostic and therapeutic benefits in breast cancer.