MicroRNA biogenesis pathways in cancer

The microRNA (miRNA) biogenesis pathway is frequently altered in cancer, leading to global downregulation of miRNA levels in some cancer types. This Review discusses the alterations that affect miRNA biogenesis in cancer. MicroRNAs (miRNAs) are critical regulators of gene expression. Amplification and overexpression of individual 'oncomiRs' or genetic loss of tumour suppressor miRNAs are associated with human cancer and are sufficient to drive tumorigenesis in mouse models. Furthermore, global miRNA depletion caused by genetic and epigenetic alterations in components of the miRNA biogenesis machinery is oncogenic. This, together with the recent identification of novel miRNA regulatory factors and pathways, highlights the importance of miRNA dysregulation in cancer.