Abstract
Gene expression in normal cells is highly regulated by complex gene regulatory networks. Disruption of these networks may lead to cancer. Recent studies have revealed the existence of an abundant class of small nonprotein‐coding regulatory RNAs, known as microRNAs (miRNAs). MiRNAs may regulate diverse biological processes including development, cell proliferation, differentiation and apoptosis, through suppressing the expression of their target genes. Posttranscriptional silencing of target genes by miRNAs occurs either by cleavage of homologous target messenger RNAs (mRNAs), or by inhibition of target protein synthesis. Computational predictions indicate that 1 miRNA may target on hundreds of genes, and suggest that over 50% of human protein‐coding genes might be regulated by miRNAs. MiRNAs are receiving increased attention in cancer genomic research. We are beginning to understand that miRNAs may act as oncogenes and/or tumor suppressor genes within the molecular architecture of gene regulatory networks, thereby contributing to the development of cancer. MiRNAs may provide useful diagnostic and prognostic markers for cancer diagnosis and treatment, as well as serving as potential therapeutic targets or tools. © 2006 Wiley‐Liss, Inc.