Regulatory mechanisms of microRNAs involvement in cancer: the strange case of Dr Jekyll and Mr Hyde

MicroRNAs (miRNAs) are 19 - 24 nucleoticle noncoding RNAs that regulate the translation and degradation of target mRNAs and are extensively involved in human cancers. One unexpected conclusion of the profiling and functional studies in tumourigenesis is that some miRNAs behave in cancer cells in a dual mode, resembling the 'Dr Jekyll and Mr Hyde' story, which centers on a conception of humanity as dual in nature. The authors and others have found that onco-miRNAs and suppressor-miRNAs can represent two different looks of the same gene, behaving as oncogenes or tumour suppressors depending on tissue type and specific targets. In this review, the authors analyse the regulatory mechanisms of the main miRNA genes involved in human tumourigenesis.