MiR501-5p stimulating the activity of mToR may result a risk factor for a poor prognosis of clear cell kidney carcinoma

INTRODUCTION & OBJECTIVESS: MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression and are involved in the control of several biological processes such as proliferation differentiation and apoptosis. Abnormal expression and mutation of miRs is implicated in many hereditary and neoplastic diseases including kidney carcinomas. In the last years, is emerging the necessity to use microRNA as biological biomarkers in order to improve diagnosis, prognosis and therapy response in renal carcinomas. Furthermore, miRNAs might be potential targets for novel therapeutic strategies, especially in patients that are resistant to conventional treatments. MATERIAL & METHODS: Analysis of miR501-5p expression was performed by real time RT-PCR. Depletion or enrichment of this miR was conducted by specific antagomiRs and by a plasmid expressing miR501-5p specific sequences, respectively. Analysis of proteins was performed by immunological techniques and cell imaging. Apoptosis and cell cycle were studied by analysis of caspase-3 activity and flow cytometry after DNA staining with propidium iodide, respectively. RESULTS: Follow up data of 25 ccRCC and 5 pRCC patients showed that subjects with low expression of miR501-5p exhibited a good prognosis compared with patients with unchanged or high levels of this microRNA. In order to evaluate the role of miR501-5p in renal cancer, we have depleted it by a specific antagomiR in KJ29 kidney cancer cell line. The transfection of KJ29 cells with antagomiR caused a 50% reduction of miR501-5p expression compared with untransfected cells. Furthermore, the reduction of miR501-5p induced an increase in G0/G1 phase of cell cycle and a decrease of mTOR activity. Consistently, the upregulation of miR501-5p by transfection of KJ29 cells with a plasmid expressing miR501-5p sequences, caused an increase of mTOR activity compared with untransfected cells. The reduction of miR501-5p expression also induced an increased activity of caspase-3, likely in a p53-dependent manner. In fact, miR501-5p depletion enhanced the expression and nuclear translocation of p53 in KJ29 cells. CONCLUSIONS: Our findings suggest that miR501-5p overexpression could induce a resistance to apoptosis and therefore it could be a risk factor for a poor prognosis of renal carcinoma. In fact, lower expression of miR501-5p seems promote a good prognosis in clear cell kidney carcinoma patients. Furthermore, the expression of miR501-5p in combination with mTOR activity could be used as new potential biomarker for the prognosis of renal carcinomas.