microRNAs in Cell Biology and Diseases

The founding members of the miRNA family, lin-4 and let-7, were first identified as fundamental development regulators in Caenorhabditis elegans. The majority of animal miRNAs have been discovered by cloning and by bioinformatic analyses, and their implications in basic cellular functions such as differentiation, proliferation, development, and apoptosis have been clearly documented. Microarray analyses showed that each miRNA downregulates more than 100 mRNAs, impacting many different biologic functions. Among the cell functions regulated by miRNAs are differentiation and maintenance of stemness. The study of the role of miRNAs in a complex disease such as cancer inevitably implies investigating the possible function of the noncoding RNAs in many different fields, from genetic to epigenetic modifications of cancer cells. Many studies have been conducted both in solid tumors and in hematologic malignancies, showing that some miRNAs are expressed at higher levels in cancers, with respect to the normal counterpart, suggesting a possible role as oncogene.