miRNAs in human cancer

Abstract

MicroRNAs (miRNAs) are small (18-25 nucleotides), endogenous, noncoding RNAs that regulate gene expression in a sequence-specific manner via the degradation of target mRNAs or the inhibition of protein translation. miRNAs are predicted to target up to one-third of all human mRNAs. Each miRNA can target hundreds of transcripts and proteins directly or indirectly, and more than one miRNA can converge on a single target transcript; thus, the potential regulatory circuitry afforded by miRNAs is enormous. Increasing evidence is revealing that the expression of miRNAs is deregulated in cancer. High-throughput miRNA quantification technologies provide powerful tools to study global miRNA profiles. It has become progressively more apparent that, although the number of miRNAs (1,000) is much smaller than the number of protein-coding genes (22,000), miRNA expression signatures more accurately reflect the developmental lineage and tissue origin of human cancers. Large-scale studies in human cancer have further demonstrated that miRNA expression signatures are associated not only with specific tumor subtypes but also with clinical outcomes. © 2012 Springer Science+Business Media, LLC.