miRNAs are small non-coding RNAs (ncRNAs) (21–23 nt long) that regulate gene expression at the post-transcriptional level by binding to messenger RNAs (mRNAs) and inhibiting their translation into proteins or by binding to other ncRNAs.
First discovered in 1993 in Caenorhabditis elegans, miRNAs had tremendous impact on the study of gene expression regulation and regulatory networks. Since their discovery as post-transcriptional regulators, specific links have been discovered between miRNA and human pathologies, and further studies indicate the utility of some miRNAs as biomarkers for cancer and other diseases. Some miRNA-targeted therapeutics have been tested in clinical trials, including a miRNA mimic of the tumor suppressor miR-34, which reached phase I clinical trials for treating cancer, and antimiRs for miR-122, which reached phase II trials for treating hepatitis.
Recently, miRNAs were shown to be present in human body fluids, resulting in the potential use of these small RNAs as non-invasive biomarkers . The great potential of extracellular miRNAs as biomarkers is their high stability in plasma, serum, saliva, urine and many other fluids. This stability is due to the formation of complexes of extracellular miRNAs in membrane-bound vesicles such as exosomes, which offers them protection from RNAses. Moreover, miRNAs can be found complexed with the Argonaute2 (Ago2) protein, part of the RNA-induced silencing complex (RISC) responsible of the RNA silencing mediated by miRNAs. miRNAs also complex with high density lipoprotein (HDL), which provides the mechanism for a new pathway for intercellular communication. In fact, miRNAs transported by HDL can be delivered to recipient cells, where they can alter the expression of their targets .
Given the rising interest in miRNAs and more generally other ncRNAs as potential biomarkers, University of Copenhagen researchers present an updated version of the miRandola database, with extensive addition of curated publications, new visualizations and additional functionality in the web interface.
Circos plot of the most representative tumor types in the database. The plot shows how many RNAs are shared by different tumors
Availability – miRandola is available at http://mirandola.iit.cnr.it/.