Renal cell carcinoma(RCC) is one of the most common malignancies in kidney, and usually leads to poor prognosis. Therefore, identifying novel biomarkers for predicting the progression and prognosis of RCC is essential. The purpose of this study is aimed to evaluate the function of miR-221-5p in RCC and the clinical value of miR-221-5p in RCC prognosis after surgery.

In our study, RT-qPCR, wound scratch assay, cell proliferation assay, transwell assay, and flow cytometry assay were performed to explore miR-221-5p expression level and its proliferation, migration and apoptosis in clear cell RCC(ccRCC). Besides, we collected 196 formalin-fixed and paraffin-embedded (FFPE) tissue samples of patients who received partial or radical nephrectomy from May 2006 to October 2016 at Shenzhen Traditional Chinese Medicine Hospital and People's Liberation Army 303 Hospital. The relative levels of miR-221-5p from the FFPE tissue samples was detected by RT-qPCR. The Kaplan-Meier method, Cox regression analyses, and ROC curve analysis were performed to approve the effect of the miR-221-5p expression on patient survival.

In our study, we found that miR-221-5p is significantly upregulated in ccRCC tissues and ccRCC cell lines. Moreover, miR-221-5p promotes cell proliferation, mobility, and inhibits cell apoptosis in 786-O and ACHN cell lines. The Kaplan-Meier analysis indicated that patients with high expression of miR-221-5p had a significantly poor prognosis (P = 0.013). The Cox regression analyses showed that patients with high expression of miR-221-5p remained to have a shorter overall survival (P = 0.025). The ROC curve of miR-221-5p expression combined with tumor stage showed an area under the curve of 0.658 (P < 0.001).

Our results indicated that miR-221-5p might not only be an oncogene in ccRCC cells but also might be an independent prognosis factor of ccRCC.