miR-21: a small multi-faceted RNA

J Cell Mol Med. 2009 Jan;13(1):39-53. doi: 10.1111/j.1582-4934.2008.00556.x.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Apoptosis / physiology
  • Base Sequence
  • Biomarkers, Tumor
  • Cell Cycle / physiology
  • Disease / genetics
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MicroRNAs* / genetics
  • MicroRNAs* / metabolism
  • Molecular Sequence Data
  • Neoplasms / genetics*
  • Neoplasms / pathology
  • Neoplasms / physiopathology*
  • Neoplasms / therapy
  • RNA Processing, Post-Transcriptional
  • Transcription, Genetic


  • Biomarkers, Tumor
  • MIRN21 microRNA, human
  • MicroRNAs