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.