miR-501 overexpression in renal carcinomas

Background: MicroRNAs (miR) are small, noncoding RNAs (20–23 nucleotides) that regulate gene expression. In particular, miRs are involved in many biological processes, including cellular differentiation, proliferation and death. In addition to their physiological functions, miRs are found to be aberrantly expressed in certain carcinomas and to play oncogenic or tumor suppressive roles in neoplastic cells (1). One in 75 people will develop renal cell carcinoma (RCC) during their lifetime being the seventh leading cause of cancer in men and eighth in women in the world. RCC is grouped in different types where the clear cell carcinoma (ccRCC) is the most frequent (2). Since little is known on the role of miRs in renal tumorigenesis, we screened, for some miRs expression, the most common renal carcinomas as clear cell (ccRCC), papillary (pRCC) and chromophobe (chRCC). We investigated miR-501, 196b and 202 that we found overexpressed in Polycystic kidney disease, a hyperproliferative renal disease. In addition, miR-501 was found predominantly expressed in mouse colon, lung and kidney. Methods: We selected and analyzed 41 tumor samples: 24 post-nephrectomy fresh frozen tissues (including 13 ccRCC, 7 pRCC, 1 chRCC, 1 lyposarcoma and 2 oncocytomas) and 17 paraffin-embedded samples (12 ccRCC, 4 pRCC, 1chRCC). Total RNA was extracted with RNeasy Plus Kit (fresh frozen tissues) or the RecoverAll® Total Nucleic Acid Isolation kit (paraffin-embedded tissues). Quantitative Real-time PCR for mature miRs was performed with TaqMan method. Levels of miR expression were calculated as DeltaDeltaCt (DDCt) method by using U6 snRNA as reference, and they were related to those of normal tissue as fold change (2-DDCt). Results: No variations were observed in the expression of miR 196b and 202 in RCC compared to normal tissues. Levels of miR-501 were instead expressed in a different manner in post-nephrectomy fresh-frozen tumors as well as in paraffin-embedded tissues compared to non neoplastic tissues. In four patients miR-501 expression was evaluated in both frozen and paraffin-embedded tissues to look for possible variability due to the different storage. Expression levels found in paraffin-embedded tissues were overlapping with those obtained in frozen tissues. Based on miR-501 expression, renal carcinomas were divided in four groups: 1. lover expression, <0.5 times; 2. like normal, from 0.5 to 2 times; 3. weak over-expression, from 2 to 5 times; and 4. strong over-expression, > 5 times. Overall, miR-501 expression was downregulated (group 1) in 12 patients (3 ccRCC, 7 pRCC, 1 chRCC and 1 oncocytoma); was normal in 10 patients (7 ccRCC, 2 pRCC and 1 lyposarcoma); weakly over-expressed in 7 samples (4 ccRCC, 1 pRCC, 1 oncocytoma and 1 chRCC); strongly over-expressed in 9 ccRCC samples. No correlation between miR-501 expression and tumor grading was observed. Conclusions: Our results demonstrate that in renal carcinomas the miR-501 was mainly over-expressed in ccRCC, while it was mainly unchanged or down-regulated in chRCC and pRCC. The overexpression of miR-501 in ccRCC, therefore, may contribute to features of this cancer playing a role in therapeutic response, metastasis development and survival. References: 1. Di Leva G, Croce CM: Roles of small RNAs in tumor formation. Trends Mol Med. 16(6):257-67, 2010. Review. 2. Brannon AR, Rathmell WK: Renal cell carcinoma: where will the state-of-the-art lead us? Curr Oncol Rep. 12(3):193-201, 2010. Review.