Panoramic view of microRNAs in regulating cancer stem cells

Cancer stem cells (CSCs) are a subgroup of tumor cells, possessing the abilities of self-renewal and generation of heterogeneous tumor cell lineages. They are believed to be responsible for tumor initiation, metastasis, as well as chemoresistance in human malignancies. MicroRNAs (miRNAs) are small noncoding RNAs that play essential roles in various cellular activities including CSC initiation and CSC-related properties. Mature miRNAs with ∼22 nucleotides in length are generated from primary miRNAs via its precursors by miRNA-processing machinery. Extensive studies have demonstrated that mature miRNAs modulate CSC initiation and stemness features by regulating multiple pathways and targeting stemness-related factors. Meanwhile, both miRNA precursors and miRNA-processing machinery can also affect CSC properties, unveiling a new insight into miRNA function. The present review summarizes the roles of mature miRNAs, miRNA precursors, and miRNA-processing machinery in regulating CSC properties with a specific focus on the related molecular mechanisms, and also outlines the potential application of miRNAs in cancer diagnosis, predicting prognosis, as well as clinical therapy.