Hsa-let-7a And Its Target, Insulin-like Growth Factor 1 Receptor, Are Differentially Expressed In Recurrent Prostate Cancer

Prostate cancer is the most common malignancy in males worldwide.Approximately 30% of those patients who received radical prostatectomy developed clinical recurrence accompanied by elevated serum prostate-specific antigen levels.Recurrence has been the main cause of death of prostate cancer patients who received radical prostatectomy. Presently, prognostic markers, such as the level of prostate-specific antigen, has been used to predict recurrence; However, they do not explain the inter-individual variation in the clinical outcomes among the patients.Therefore, new biomarkers are required to identify the patients who are at a greater risk of developing recurrence following surgery.Knowledge regarding the development of microRNA and cancer stem cells have been significantly improved recent years. MicroRNA, ~22 nucleotides in length, have emerged as one of the key factors of the regulatory network that regulates a wide spectrum of cellular activities, such as proliferation, apoptosis, migration and differentiation Cancer Stem Cells constitute a small part of tumor cells, which are characterized by their ability to seed new tumors. Based on the above-mentioned evidence, a total of 68 patients with histologically confirmed Prostate cancer by radical prostatectomy, including 32 recurrent and 36 non-recurrent cases. 6 candidate microRNAs were selected that have been reported to be differentially expressed in Prostate cancer stem cells based on the microRNA microarray analysis, considering the significant role of Cancer stem cells in the pathogenesis of recurrent Prostate cancer. RT- qPCR was performed to examine the expression levels of the 6 candidate microRNA, and only 1 microRNA, hsa-let-7a, was significantly down-regulated in the recurrent groups. The online microRNA database was searched and IGF1 R was found to be a potential target gene of hsa-let-7a. Luciferase assay was furtherperformed to validate the database search result. m RNA and protein expression patterns in the recurrent and non-recurrent cases were assessed using RT-qPCR and western blotting. The mRNA and protein expression levels of IGF1 R were significantly up-regulated in the recurrent cases. As a downstream effector of IGF1 R,the expression level of inducible nitric oxide synthase was also increased in the recurrent cases, and the concentration of nitric oxide and cGMP were markedly higher in the recurrent compared to non-recurrent groups. To further characterize the role of hsa-let-7a, we transfected hsa-let-7a mimics into LNCaP cells. As expected,exogenous overexpression of hsa-let-7a significantly down-regulated the expression of IGF1 R, as well as its downstream effector, iNOS. The NO and cGMP concentrations were much lower in the cells transfected with hsa-let-7a mimics. Flow cytometry analysis and MTT experiment were used to explore the molecular mechanism underlying the proliferation-regulating effect, and exogenous overexpression of hsa-let-7a significantly introduced apoptosis to the LNCaP cells.In conclusion, the present data demonstrated hsa-let-7a may partly contribute to IGF1 R overexpression in recurrent prostate cancer. And there is a significant role of the hsa-let-7a-IGF1R-iNOS-NO-cGMP in the control of cellular proliferation.Hsa-let-7a may be a novel therapeutic candidate to prevent recurrent PCa given its ability to induce apoptosis and inhibit cell growth.