What is the mechanism of microRNA deregulation in carcinogenesis?
MicroRNAs (miRNAs) are endogenous non-protein coding single-stranded RNAs (19–25 nucleotides in length) generated from  cleavage of larger non-coding RNAs by the ribonuclease III enzyme Dicer. They become part of the RNA-induced silencing complex and negatively regulate gene expression by binding to homologous 3'-UTR region of target protein-coding mRNAs as an imperfect match, causing translational repression or degradation. Approximately one-third of the protein-coding genes are susceptible to miRNA regulation. Accumulating evidence indicates that deregulated miRNA expression is associated with the onset and progression of a number of human cancers. Therefore, cancer-associated miRNAs (CA-miRNAs) could regulate target genes by acting either as "oncogenes" or "tumor suppressor miRNA (TS-miRNAs)". In line with this, numerous cancers (e.g. breast, lung, oesophageal, prostate, pancreatic, gastric and colon cancer) have been classified based on their unique miRNA expression profile.