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Keywords:

  • human disease;
  • cancer;
  • glioma;
  • oncogene;
  • non-coding RNA;
  • post-transcriptional regulation
  • • 
    miR-21 expression in cancer and other diseases
  • • 
    Mechanisms of miR-21 elevation in cancer: multi-level regulatory control
  • • 
    Transcriptional control
  • • 
    Post-trancriptional regulation
  • • 
    miR-21 functions in cancer
  • • 
    Identification of direct miR-21 targets
  • • 
    miR-21 in gliomas: targeting cell cycle, apoptosis and invasion
  • • 
    miR-21 networking and feedback regulation
  • • 
    miR-21 as a diagnostic and prognostic marker
  • • 
    Potential therapeutic target
  • • 
    Acknowledgements

Abstract

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.