Abstract 4189: Tumor suppressive microRNA-218 regulates oncogenes of focal adhesion pathways in renal cell carcinoma.
Authors: Enokida Hideki , Yamasaki Takeshi , Yoshino Hirofumi , Hidaka Hideo , Itesako Toshihiko , Nakagawa Masayuki , Seki Naohiko 
Published: August 2014

INTRODUCTION&OBJECTIVES: Our recent microRNA (miRNA) expression signature of renal cell carcinoma (RCC) revealed downregulation of miR-218 in RCC, suggesting that it might be a tumor suppressor. The aim of this study is to investigate the functional significance of miR-218 and to identifymiR-218-mediated cancer pathways in RCC.

METHODS: We evaluated miR-218 expression in 33 RCC clinical specimens and adjacent normal kidney tissues by stem-loop RT-PCR. We performed gain-of-function studies (cell migration and cell invasion assays) by using miR-218 transfectants (TFs). Oligo-microarray analyses of the miR-218 TFs and the RCC specimens were carried out to identify molecular targets of miR-218. According to GENECODIS software, we focused on the “focal adhesion”pathway, in which caveolin-2 (CAV2) was a candidate target gene. A luciferase reporter assay was performed to determine miR-218binding sites with CAV2 3’UTR. Loss-of-function assays using si-CAV2 were performed to investigate the functional significance of CAV2. The expression of CAV2 mRNA and protein was evaluated by qRT-PCR and immunohistochemistry. Furthermore, to investigate signaling pathways regulated by CAV2, we performed gene expression analysis of si-CAV2TFs.

RESULTS: The expression of miR-218 was significantly reduced in the RCC specimens. Significant inhibitions of cell migration and invasion were observed in the miR-218 TFs. Gene expression analysis showed that 615 genes were downregulated in the miR-218 TFs. The GENECODIS software revealed that miR-218 appeared to regulate 25 pathways (P&lt;0.0001). In these pathways, we focused on ten genes in “focal adhesion” and seven genes in “tight junction”. CAV2 was the most upregulated gene among the genes related to these pathways by using available data sets (GSE36895 and GSE22541) in gene expression omnibus (GEO). Luciferase reporter assay showed that CAV2 was directly regulated by miR-218. Silencing study of CAV2 demonstrated significant inhibition of cell migration and invasion. The mRNA and protein expression of CAV2 were significantly up-regulated in RCC specimens. Gene expression analysis of si-CAV2 TFs revealed that CAV2 might control 15 pathways including “tight junction” pathway, containing pro-metastatic genes such as claudin-1, AKT3 and R-Ras2.

CONCLUSION: Tumor suppressive miR-218contributes to inhibition of cell migration and invasion through regulating focal adhesion pathway, especially CAV2 in RCC. This is the first report that CAV2 contributes to metastatic processes in RCC.

Citation Format: Hideki Enokida, Takeshi Yamasaki, Hirofumi Yoshino, Hideo Hidaka, Toshihiko Itesako, Masayuki Nakagawa, Naohiko Seki. Tumor suppressive microRNA-218 regulates oncogenes of focal adhesion pathways in renal cell carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4189. doi:10.1158/1538-7445.AM2013-4189