Krichevsky, AnnaGabriely, Galina2015-05-042009Krichevsky, Anna M., and Galina Gabriely. 2009. “miR-21: a small multi-faceted RNA.” Journal of Cellular and Molecular Medicine 13 (1): 39-53. doi:10.1111/j.1582-4934.2008.00556.x. http://dx.doi.org/10.1111/j.1582-4934.2008.00556.x.1582-1838http://nrs.harvard.edu/urn-3:HUL.InstRepos:15035028Abstract More than 1000 microRNAs (miRNAs) are expressed in human cells, some tissue or cell type specific, others considered as house-keeping molecules. Functions and direct mRNA targets for some miRNAs have been relatively well studied over the last years. Every miRNA potentially regulates the expression of numerous protein-coding genes (tens to hundreds), but it has become increasingly clear that not all miRNAs are equally important; diverse high-throughput screenings of various systems have identified a limited number of key functional miRNAs over and over again. Particular miRNAs emerge as principal regulators that control major cell functions in various physiological and pathophysiological settings. Since its identification 3 years ago as the miRNA most commonly and strongly up-regulated in human brain tumour glioblastoma [1], miR-21 has attracted the attention of researchers in various fields, such as development, oncology, stem cell biology and aging, becoming one of the most studied miRNAs, along with let-7, miR-17–92 cluster (‘oncomir-1’), miR-155 and a few others. However, an miR-21 knockout mouse has not yet been generated, and the data about miR-21 functions in normal cells are still very limited. In this review, we summarise the current knowledge of miR-21 functions in human disease, with an emphasis on its regulation, oncogenic role, targets in human cancers, potential as a disease biomarker and novel therapeutic target in oncology.en-UShuman diseasecancergliomaoncogenenon-coding RNApost-transcriptional regulationJournal Article2015-05-0410.1111/j.1582-4934.2008.00556.x