Regulatory Effects of microRNA-92 (miR-92) on VHL Gene Expression and the Hypoxic Activation of miR-210 in Clear Cell Renal Cell Carcinoma

Background & Aims: In order to understand the role of miRNAs in renal tumorigenesis, we undertook a stepwise approach that included a comprehensive differential miRNA expression analysis for the most common histological subtypes of human renal neoplasms appearing in either sporadic or hereditary forms. We also aimed to test the hypothesis that microRNAs can act as an alternative mechanism of VHL gene inactivation and therefore might be correlated with tumorigenesis in ccRCC. Finally, we wanted to explore whether the well-known hypoxic activation of ccRCC is followed by a specific pattern of miRNA expression. Methods: Tumor and normal adjacent kidney parenchyma from patients with RCC were tested for microRNA expression. Twenty cases of different histologies were used for profiling by PCR miRNA arrays. For validation, a separate cohort of samples used to test specifically miR92a expression and its involvement in VHL gene mRNA silencing. Finally, miR210 as a marker of hypoxia was evaluated. Expression values were correlated with important clinicopathologic features from the patients. Results: We identified unique miRNA expression signatures for each histologic subtype of kidney tumors. Expression values for downregulated miRNAs ranged from 0.3-fold (in VHL-clear cell RCC) up to 0.393 fold (in papillary type II (HLRCC) tumors). For the upregulated miRNAs, fold-changes ranged from 2.1 up to 290-fold. Specific patterns together with type-specific profiles were observed. Twenty-three miRNAs were found to be differentially expressed in both sporadic and VHL-dependent ccRCC. Sporadic clear cell tumors showed a unique pattern of 14-miRNA that were absent from the VHL-dependent tumors. These also showed 15 miRNAs specific to the hereditary type. Common miRNAs to both sporadic and hereditary forms included miR-92a and miR-210. For miR-92a, and a striking inverse correlation with VHL mRNA levels was found. For the hypoxia-regulated miR-210, clear cell tumors showed significantly higher expression levels when compared to tumor of non-clear cell histology (9.90-fold vs. 1.36, p<0.001). Conclusions: microRNA expression seems to be involved in every step of RCC pathogenesis: both as an element for tumor development as well as a consequence of or in response to the initial malignant transformation and part of tumor progression. Our data show consistent disregulation of miRNAs in human kidney cancer, some of which are potentially involved in critical gene silencing in RCC and others that are activated as part of the pathophysiological response in these tumors.