Analysis showed that miRNAs are dysregulated in clear cell renal cell carcinoma and may contribute to kidney cancer pathogenesis by targeting more than 1 key molecule. We identified mechanisms that may contribute to miRNA dysregulation in clear cell renal cell carcinoma. Dysregulated miRNAs represent potential biomarkers for kidney cancer.

Metastasis results in most of the cancer deaths in clear cell renal cell carcinoma (ccRCC). MicroRNAs (miRNAs) regulate many important cell functions and play important roles in tumor development, metastasis and progression. In our previous study, we identified a miRNA signature for metastatic RCC. In this study, we validated the top differentially expressed miRNAs on matched primary and metastatic ccRCC pairs by quantitative polymerase chain reaction. We performed bioinformatics analyses including target prediction and combinatorial analysis of previously reported miRNAs involved in tumour progression and metastasis. We also examined the co-expression of the miRNAs clusters and compared expression of intronic miRNAs and their host genes. We observed significant dysregulation between primary and metastatic tumours from the same patient. This indicates that, at least in part, the metastatic signature develops gradually during tumour progression. We identified metastasis-dysregulated miRNAs that can target a number of genes previously found to be involved in metastasis of kidney cancer as well as other malignancies. In addition, we found a negative correlation of expression of miR-126 and its target vascular endothelial growth factor (VEGF)-A. Cluster analysis showed that members of the same miRNA cluster follow the same expression pattern, suggesting the presence of a locus control regulation. We also observed a positive correlation of expression between intronic miRNAs and their host genes, thus revealing another potential control mechanism for miRNAs. Many of the significantly dysregulated miRNAs in metastatic ccRCC are highly conserved among species. Our analysis suggests that miRNAs are involved in ccRCC metastasis and may represent potential biomarkers.

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428 Background: The von Hippel-Lindau (VHL) gene is lost in 70% of clear cell Renal Cell Carcinomas (ccRCC); however, additional mechanisms are proposed to regulate VHL expression, including suppression by microRNAs (miRNAs). miRNAs are a class of naturally occurring, small non-coding RNA molecules that downregulate gene expression of target mRNAs. We demonstrate that ccRCC-dysregulated miRNAs can target multiple members of the ccRCC-related signaling pathways. Methods: miR-17 and miR-224 mimics and inhibitors were transfected into ccRCC cell lines using siPORT (Ambion). PicTar and TargetScan were used for target prediction. Target expression and miRNA expression was analyzed by qRT-PCR (Ambion). Western blot antibodies were purchased from Millipore or Cell Signaling. Cell lines were purchased from ATCC. All methods followed the manufacturer’s protocol. Results: According to our preliminary results, the miRNAs that are dysregulated in ccRCC specimens are predicted to target multiple members of the hypoxia-related pathways. To confirm the in silico analysis, miR-17 and miR-224 were selected for experimental target validation, as they were among the most up-regulated miRNAs in ccRCC. We experimentally validated VHL and HIF1α as likely direct targets of miR-17 and miR-224. Luciferase reporter assay confirmed that miR-17 directly downregulates VHL. Moreover, VHL protein level decreased upon miR-17 and miR-224 transfection. We also established a negative correlation between the expression of miR-17 and two predicted targets VEGF-A, EGLN3 in RCC specimens, and miR-224 and its predicted targets SMAD4 and SMAD5. This suggests that downstream signaling pathways are also modulated by miR-17 and miR-224. These results confirm the most important findings of the bioinformatics analysis: miR-17 targets different molecules along the same signaling pathway and that multiple ccRCC-dysregulated miRNAs can synergistically suppress a single target, which functions in the pathogenesis. Conclusions: Our results indicate that miRNAs possibly regulate hypoxia-related pathways at multiple points. This is of special interest as miRNAs may serve as potential therapeutic targets.