MicroRNA-181 serves an oncogenic role in breast cancer via the inhibition of SPRY4

Numerous microRNAs (miRs) have been implicated in breast cancer; however, the molecular mechanism is not fully understood. The present study examined the function and regulatory mechanism of miR-181 in breast cancer. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to examine the RNA and protein expression. MTT assay, wound healing assay and transwell assay were conducted to study cell proliferation, migration and invasion. Luciferase reporter gene assay was used to confirm targeting relationship. The results suggested that the miR-181 expression levels were significantly higher in breast cancer cell lines and clinical tissue samples. The increased expression of miR-181 was markedly associated with higher clinical stage and lymph node metastasis. The patients with high miR-181 expression demonstrated worse prognosis compared with those with a low expression of miR-181. Small interfering RNA-induced miR-181 downregulation significantly inhibited breast cancer cell proliferation, migration and invasion in vitro, and tumor growth in vivo. Protein sprouty homolog 4 (SPRY4), downregulated in breast cancer tissues and cell lines, was observed to be a novel target gene of miR-181. Downregulation of SPRY4 was significantly associated with breast cancer progression in addition to poor prognosis. Knockdown of SPRY4 rescued the inhibitory effects of miR-181 downregulation on the malignant phenotypes of breast cancer cells. Thus, the present study demonstrated that miR-181 serves a promoting role in breast cancer at least in part through the inhibition of SPRY4 expression. The present results expand the understanding of the miR-181/SPRY4 axis' function during for the malignant progression of breast cancer.