MicroRNAs (miRNAs) are a class of naturally occurring small non-coding RNAs that control gene expression at the post-transcriptional level. To date, over 700 human miRNA precursors with over 1,000 mature miRNAs have been reported. miRNAs are related to, but distinct from, short interfering RNAs (siRNAs). A key difference between siRNAs and miRNAs is that siRNAs require almost identical sequences to targets to exert their silencing function, whereas miRNAs usually bind to the 3'-untranslated region (3'-UTR) of target genes through partial sequence homology. Because of this unique feature, a single miRNA has multiple targets and thus, miRNAs could regulate a large fraction of proteincoding genes. This may explain why miRNAs play a fundamental role in regulation of diverse cellular processes such as cell growth, proliferation, differentiation and apoptosis and thus, deregulation of miRNA expression can lead to a variety of disorders including cancer. In this regard, miRNAs can function as either oncogenes or tumor suppressors. For example, miR-21 is an oncogenic miRNA which has been shown to promote tumor growth and metastasis in several types of cancers by targeting multiple tumor suppressors. Therefore, targeting miR-21 may provide a promising strategy for cancer intervention. In this review, we will discuss our current understanding of miR-21-mediated gene silencing, tumor growth and metastasis, and the potential of miR-21 as a cancer biomarker. We will also provide a perspective on targeting miR-21 for cancer therapy.
Current Cancer Therapy Reviews publishes frontier reviews on all the latest advances in clinical oncology, cancer therapy and pharmacology. The journal's aim is to publish the highest quality review articles dedicated to clinical research in the field. The journal is essential reading for all researchers and clinicians in cancer therapy.