Introduction: MicroRNA (miRNA) was discovered by the 2006 Nobel Laureates, Mello and Fire, and is now known to be responsible for regulation of gene and protein expression. MicroRNAs (miRNAs) are a class of naturally occurring small noncoding RNAs that regulate protein expression by targeting the mRNA of protein coding genes for either translation repression or RNA degradation. Initially expressed in the nucleus as part of a long primary transcript (>1kb), miRNAs are processed by RNase III Dicer into 18-25 nucleotide mature miRNAs. In animals, these single-stranded mature miRNAs bind through partial sequence homology to the 3’ untranslated region (3’UTR) of targeted mRNAs to prevent translation. This regulatory role of miRNAs in gene expression has been implicated in cellular development, growth, differentiation, and apoptosis. miRNA is much shorter than traditional message RNA and is more resistant to degradation and can be extracted successfully from many types of fixed tissues.Increasing evidence indicates that dysregulation of certain miRNAs is associated with cancer. Examination of miRNA expression patterns in lung carcinoma, breast cancer, and acute lymphocytic leukemia show different miRNA expression profile when compared to normal tissue. Recognition of miRNAs that are differentially expressed between normal and tumor samples may help to identify those that are involved in human cancer and establish the basis to unravel their pathogenic role. Here we examine the expression profile of 95 miRNA in clear cell renal-cell carcinoma (RCC) and normal kidney tissue, demonstrating the existence of a unique RCC miRNA signature.
Method: IRB approval was obtained for the current work. Eight high-grade RCC clear cell tumor specimens, along with patient-matched normal kidney tissue, were obtained at Boston Medical Center after partial or radical nephrectomy and isolated for total RNA. 95 primers pairs, individually designed to detect a miRNA species that are found in the literature to be associated with cancers, were used in a real-time PCR assay to quantify expression (SBI, Mountain View, CA). Statistical analysis was performed to evaluate expression pattern in RCC and normal kidney samples (ABI, CA).
Results: Our analysis of eight high-grade RCC and their patient-matched normal tissue reveal a dysregulation of several miRNAs in the tumor. These miRNAs are known to regulate pathways controlled by classic tumor suppressors and oncogenes including MYC, RAS, Wnt, and p53. In addition, some of these miRNAs have been implicated in the classical kidney cancer pathways such as angiogenic factors in the VHL and HIF-1 pathways. Most of the miRNA species that were differentially expressed were in lower levels in the tumor when compared to the normal matched tissue.
Conclusion: Given that cancer develops through the continuous accumulation of genetic and epigenetic alterations, miRNAs may open a new avenue for better understanding of the pathogenesis of RCC. This is important because miRNAs can serve not only as diagnostic markers, they may also potential targets for therapy, as knocking down over expressed miRNAs or expressing silenced miRNAs in cancer cells might contribute to a therapeutic effect.