An analysis of low miR-199a expression in renal cell carcinoma (RCC) and and its association with regulation of GSK-3beta.

Abstract

e15020 Background: Renal cell carcinoma (RCC) is highly resistant to chemotherapy due to a high apoptotic threshold. Recently, we have shown nuclear accumulation of GSK-3β as a new marker of human RCC and identified that GSK-3 positively regulates RCC cell survival and proliferation. It has been reported that GSK-3β is a miR-199a target. Our objectives were to determine the expression level of miR-199a in human RCC and renal cancer cell lines, and to assess the anticancer effect of reintroduction of pre-miR-199a in renal cancer cells in vitro. Methods: TaqMan MicroRNA assay was applied to examine miR-199a expression in 54 human RCCs and normal kidney counterpart as well as in 8 renal cancer cell lines. Immunohistochemical staining was performed to determine the expression pattern of GSK-3β in RCC tissues. Western blotting, quantitative RT-PCR and MTS cell viability assay were used to study the effect of pre-miR-199a reintroduction into renal cancer cells in vitro. Results: We detected low miR-199a expression in 57% (31 of 54) of RCCs. We found that 87% (27 of 31) of low miR-199a tumors were clear cell carcinomas. Downregulation of miR-199a was correlated with higher stage (Chi square for trend 4.605, p=0.0319) and nuclear accumulation of GSK3β (Fisher’s exact test, p=0.0249) in clear cell RCCs. We found high miR-199a expression in two benign renal hamartomas (angiomyolipoma). Reintroduction of pre-miR-199a into renal cancer cells led to decreased GSK-3β, XIAP, Bcl-2 expression and suppression of RCC cells proliferation and survival. Conclusions: We found that miR-199a is downregulated in most RCCs and this tumor phenotype is strongly associated with nuclear accumulation of GSK-3β and malignant potential of clear cell tumors. Our results identify low miR-199a as a novel diagnostic marker in RCC, and suggest reintroduction of pre-miR-199a as a new treatment strategy in RCC.